Biology

Circulation

❤️ Chapter 11 · MDCAT Biology
📅 Updated Jan 2026 ⏱️ 30 min read 🎯 High-yield

Circulation — Complete MDCAT Notes & MCQs

Full MDCAT Biology Chapter 11 on circulation: heart anatomy, cardiac cycle, heart sounds, ECG, conduction system, blood vessels, cardiac output, lymphatic system, fetal shunts, and edema. Includes 199 solved MCQs with explanations and year-wise past papers.

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⚡Quick Answers to Common Searches

Direct, snippet-optimized answers to the top questions students search about Circulation.

What is circulation?

Circulation is the continuous movement of blood through the heart and blood vessels, delivering O₂ and nutrients and removing CO₂ and waste. The lymphatic system returns excess fluid.

What are the 4 chambers of the heart?

Right atrium (receives deoxygenated blood), right ventricle (to lungs), left atrium (receives oxygenated), left ventricle (thickest wall, to body).

What is the cardiac cycle?

One complete heartbeat (~0.8 s): atrial systole (0.1 s), ventricular systole (0.3 s), joint diastole (0.4 s).

S1 vs S2 heart sounds?

S1 "Lubb" = closure of AV valves (start of ventricular systole). S2 "Dubb" = closure of semilunar valves (start of diastole).

What do ECG waves mean?

P-wave: atrial depolarization. QRS: ventricular depolarization. T-wave: ventricular repolarization.

What is the pacemaker?

The SA (sinoatrial) node in the right atrium. It fires ~70 bpm and sets the heart rhythm.

Arteries vs veins?

Arteries carry blood away, thick muscular walls, high pressure, no valves. Veins carry blood to heart, thin walls, low pressure, valves.

Where does gas exchange occur?

In capillaries — one-cell-thick vessels with slowest flow and largest total cross-sectional area.

What is cardiac output?

CO = SV × HR. Average at rest ~5 L/min (70 mL stroke volume × 72 bpm).

Frank-Starling Law?

More stretch → stronger contraction. ↑EDV → ↑stroke volume. The heart pumps what it receives.

Functions of lymphatic system?

Returns interstitial fluid to blood, transports dietary fats (lacteals), immune defense (nodes, spleen, thymus).

Primary vs secondary lymphoid organs?

Primary: bone marrow, thymus (maturation). Secondary: lymph nodes, spleen, tonsils, Peyer's patches (immune response).

What is the thoracic duct?

Largest lymphatic vessel. Drains most of the body's lymph into the left subclavian vein.

What causes edema?

↑capillary hydrostatic pressure, ↓plasma proteins (↓osmotic pressure), ↑capillary permeability, or lymphatic blockage.

How many MCQs from Circulation?

Circulation typically contributes 4–6 MCQs out of 81 Biology MCQs in MDCAT.

❓People Also Ask — Circulation

Questions students most frequently search about this chapter. Answers are direct and exam-focused.

QWhat is the difference between pulmonary and systemic circulation?
Pulmonary circulation carries blood between heart and lungs (right ventricle → lungs → left atrium). Systemic circulation carries blood between heart and body (left ventricle → body → right atrium).
QWhat is the function of the pericardium?
The pericardium is a double-layered fibro-serous sac that protects the heart, anchors it in the mediastinum, and reduces friction during contractions.
QWhy is the left ventricle wall the thickest?
The left ventricle pumps blood through the entire systemic circuit (whole body), requiring much higher pressure than the right ventricle, which only pumps to lungs.
QWhat do chordae tendineae do?
Chordae tendineae are string-like cords that anchor AV valves to papillary muscles, preventing valve prolapse into the atria during ventricular systole.
QWhat is the significance of the AV nodal delay?
The 0.1-second delay at the AV node ensures the atria finish contracting and fully fill the ventricles before ventricular systole begins.
QWhat causes the plateau phase in cardiac muscle?
The plateau phase is caused by Ca²⁺ influx through L-type channels, balancing K⁺ efflux. This prolongs the action potential and prevents tetanic contractions.
QWhat is the difference between stroke volume and cardiac output?
Stroke volume = blood pumped per beat (~70 mL). Cardiac output = stroke volume × heart rate (~5 L/min).
QWhich vessel has the highest blood pressure?
The aorta has the highest blood pressure (~120/80 mmHg). Pressure decreases as blood moves through arteries → arterioles → capillaries → veins.
QWhy do veins have valves?
Veins have low pressure and blood must move against gravity. Valves prevent backflow and ensure unidirectional flow toward the heart.
QWhat is a portal vein?
A portal vein carries blood between two capillary beds. The hepatic portal vein carries nutrient-rich blood from the gut to the liver.
QWhat is the function of lymph nodes?
Lymph nodes filter lymph, trap foreign particles (bacteria, cancer cells), and house lymphocytes that mount immune responses.
QWhat is the function of the spleen?
The spleen filters blood, removes old RBCs (red pulp), stores blood, and mounts immune responses (white pulp).
QWhat are lacteals?
Lacteals are specialized lymph capillaries in the small intestine villi that absorb dietary fats (chylomicrons) and transport them to the thoracic duct.
QWhat are fetal shunts?
Foramen ovale (RA→LA, bypasses lungs), ductus arteriosus (pulmonary artery→aorta), ductus venosus (umbilical vein→IVC, bypasses liver).
QWhat is the coronary sinus?
The coronary sinus collects deoxygenated blood from cardiac veins and empties into the right atrium. It delivers the heart's own used blood back to circulation.
QWhy is blood flow slowest in capillaries?
Continuity equation (V = Q/A). Capillaries collectively have the largest total cross-sectional area, so velocity drops, allowing time for exchange.
QWhat is the difference between pulmonary artery and pulmonary vein?
Pulmonary artery carries deoxygenated blood from right ventricle to lungs. Pulmonary vein carries oxygenated blood from lungs to left atrium. (Reversed from usual pattern.)
QWhat is the normal resting heart rate?
Normal resting heart rate is 60–100 beats per minute, with an average of ~72 bpm in adults. Below 60 = bradycardia; above 100 = tachycardia.
QWhat is blood pressure?
Blood pressure is the force exerted by circulating blood on vessel walls. Normal is ~120/80 mmHg (systolic/diastolic). Systolic during contraction; diastolic during relaxation.
QWhat is the difference between semilunar and AV valves?
AV valves (tricuspid, bicuspid) separate atria from ventricles. Semilunar valves (pulmonary, aortic) separate ventricles from great arteries. Both prevent backflow.

📋Syllabus & Learning Outcomes

According to PMDC/PMC MDCAT syllabus, Circulation covers:

📝Full Notes — Circulation

❤️ Circulation – Cardiovascular & Lymphatic Systems

🫀 Heart Anatomy & Conduction

  • Pericardium: double‑layered sac (fibrous + serous) – protection & reduced friction.
  • Chambers: RA, RV, LA, LV. Left ventricle thickest wall (pumps to systemic circuit).
  • Valves:
    • AV valves: tricuspid (right), bicuspid/mitral (left) – attached to chordae tendineae & papillary muscles (prevent prolapse).
    • Semilunar valves: pulmonary & aortic – prevent backflow into ventricles.
  • Conduction: SA node (pacemaker, ~70 bpm) → AV node (delay 0.1 s) → Bundle of His → right & left bundle branches → Purkinje fibers.
  • Cardiac Cycle (0.8 s): Atrial systole (0.1 s) → Ventricular systole (0.3 s) → Joint diastole (0.4 s).

📈 Heart Sounds & ECG

  • S1 ("Lubb") – closure of AV valves (onset of ventricular systole).
  • S2 ("Dubb") – closure of semilunar valves (end of systole).
  • ECG waves:
    • P wave: atrial depolarization.
    • QRS complex: ventricular depolarization (atrial repolarization hidden).
    • T wave: ventricular repolarization.
    • P‑R interval – AV nodal delay (normal 0.12–0.2 s).
  • ⚠️ Trap: QRS is not ventricular contraction – it's depolarization preceding contraction.

🩸 Blood Vessels

VesselStructureFunction
ArteriesThick wall (elastic + muscle)Conduct blood away; aorta = pressure reservoir
ArteriolesSmooth muscle dominantResistance vessels – regulate BP & flow
CapillariesEndothelium only (single layer)Exchange of gases/nutrients; slowest velocity, largest area
VeinsThin wall, wide lumen, valvesCapacitance vessels (volume reservoir); return blood
  • Coronary arteries: arise from aorta; coronary sinus drains into RA.
  • Hepatic portal vein: carries nutrient‑rich blood from gut to liver (no direct return to heart).

📊 Cardiac Output (CO) & Regulation

  • CO = Stroke Volume × Heart Rate (≈5 L/min at rest).
  • Frank‑Starling Law: ↑ venous return → ↑ end‑diastolic volume (EDV) → stronger contraction → ↑ stroke volume.
  • Plateau phase of action potential: due to Ca²⁺ influx (L‑type channels) → prolonged contraction prevents tetany.

💧 Lymphatic System

  • Returns excess interstitial fluid (lymph) to blood; transports dietary fats (lacteals in small intestine).
  • Primary lymphoid organs: bone marrow (B‑cell production), thymus (T‑cell maturation, Hassall's corpuscles).
  • Secondary: lymph nodes, spleen (white pulp immune, red pulp filters RBCs), tonsils, Peyer's patches.
  • Thoracic duct: drains most of body's lymph into left subclavian vein.
  • Right lymphatic duct: drains upper right quadrant into right subclavian vein.

🩺 Fetal Shunts & Edema

  • Foramen ovale: RA → LA (bypasses lungs).
  • Ductus arteriosus: pulmonary artery → aorta.
  • Ductus venosus: umbilical vein → IVC (bypasses liver).
  • Edema: ↑ capillary permeability, ↓ plasma proteins (e.g., liver disease), or lymphatic blockage.

🔑 High‑Yield MCQs & Traps

  • S1 – closure of AV valves; S2 – closure of semilunar valves.
  • SA node = pacemaker; AV node delay allows ventricular filling.
  • QRS complex = ventricular depolarization (contraction follows).
  • Thickest myocardium: left ventricle.
  • Capillaries – slowest flow, largest total cross‑sectional area (not aorta).
  • Veins are capacitance vessels; arteries are pressure reservoirs.
  • Hepatic portal vein carries nutrient‑rich blood to liver (not oxygenated).
  • CO = SV × HR; Frank‑Starling: ↑ EDV → ↑ contraction force.
  • Thoracic duct drains into left subclavian vein.
  • Fetal shunts: foramen ovale, ductus arteriosus, ductus venosus (bypass lungs/liver).
  • Lymph nodes filter lymph; spleen filters blood.

💡 MDCAT focus: valve timing, conduction pathway, vessel functions, and lymphatic drainage.

✅Practice MCQs — Test 1

🧪 Basic Concepts

50 MCQs
1The double-layered membranous sac that encloses the human heart and reduces friction during contractions is known as the:
  • A. Pleura
  • B. Pericardium
  • C. Peritoneum
  • D. Endocardium
Answer: B. Pericardium
The pericardium is a fibro-serous sac that protects the heart and anchors it in the mediastinum.
2Which chamber of the heart possesses the thickest muscular walls to facilitate high-pressure blood ejection?
  • A. Right Atrium
  • B. Right Ventricle
  • C. Left Atrium
  • D. Left Ventricle
Answer: D. Left Ventricle
The left ventricle must generate enough pressure to drive blood through the entire systemic circuit (the whole body).
3The bicuspid (mitral) valve is located between which two structures?
  • A. Right atrium and Right ventricle
  • B. Left atrium and Left ventricle
  • C. Left ventricle and Aorta
  • D. Right ventricle and Pulmonary artery
Answer: B
The bicuspid valve ensures one-way flow from the left atrium to the left ventricle.
4What is the primary function of the chordae tendineae during ventricular contraction?
  • A. To open the AV valves
  • B. To close the semilunar valves
  • C. To prevent AV valves from eversion into atria
  • D. To initiate the heartbeat
Answer: C
They anchor the valve flaps to papillary muscles to prevent backflow (prolapse) under high pressure.
5In a normal cardiac cycle of 0.8 s, the duration of ventricular systole is approximately:
  • A. 0.1 s
  • B. 0.3 s
  • C. 0.4 s
  • D. 0.8 s
Answer: B. 0.3 s
Ventricular contraction lasts for about 0.3 seconds of the total cycle.
6The 'Lubb' sound of the heart is primarily caused by the:
  • A. Opening of semilunar valves
  • B. Closure of atrioventricular valves
  • C. Closure of semilunar valves
  • D. Blood entering the atria
Answer: B
The first heart sound occurs at the start of ventricular systole when AV valves (tricuspid and mitral) snap shut.
7Which component of the cardiac conduction system is known as the 'Pacemaker'?
  • A. AV Node
  • B. Bundle of His
  • C. SA Node
  • D. Purkinje fibers
Answer: C. SA Node
The Sinoatrial (SA) node spontaneously generates electrical impulses that set the heart's rhythm.
8Which type of blood vessel contains valves to prevent the backward flow of blood?
  • A. Arteries
  • B. Arterioles
  • C. Capillaries
  • D. Veins
Answer: D. Veins
Due to low pressure, veins require valves to ensure blood moves toward the heart against gravity.
9The exchange of nutrients, gases, and wastes between blood and tissue cells occurs exclusively in the:
  • A. Venules
  • B. Arterioles
  • C. Capillaries
  • D. Lymphatic vessels
Answer: C. Capillaries
Capillary walls are only one cell thick, allowing for efficient diffusion.
10Which structural layer is significantly thicker in arteries compared to veins?
  • A. Tunica intima
  • B. Tunica media
  • C. Tunica externa
  • D. Endothelium
Answer: B. Tunica media
Arteries have a much thicker layer of smooth muscle and elastic fibers to handle high blood pressure.
11What is the primary function of the lymphatic system regarding fluid balance?
  • A. Pumping blood to the tissues
  • B. Returning excess interstitial fluid to the blood
  • C. Oxygenating the tissues
  • D. Producing red blood cells
Answer: B
It recovers fluid that leaks out of capillaries and returns it to the venous circulation.
12Which of the following is considered a primary lymphatic organ?
  • A. Spleen
  • B. Lymph node
  • C. Thymus
  • D. Tonsils
Answer: C. Thymus
The thymus and bone marrow are primary organs where lymphocytes (T and B cells) mature.
13Lymph is most similar in composition to which of the following?
  • A. Whole blood
  • B. Interstitial fluid
  • C. Intracellular fluid
  • D. Plasma minus proteins
Answer: B. Interstitial fluid
Lymph is essentially interstitial fluid once it enters the lymphatic vessels.
14The right lymphatic duct drains lymph from which part of the body?
  • A. The entire lower body
  • B. The upper left quadrant
  • C. The upper right quadrant
  • D. The entire body
Answer: C
It drains the right side of the head, neck, chest, and the right arm.
15Which of these is a major function of the spleen?
  • A. Pumping lymph through vessels
  • B. Filtering blood and removing old RBCs
  • C. Secreting digestive enzymes
  • D. Absorbing dietary fats
Answer: B
The spleen acts as a blood filter and a 'graveyard' for old or damaged red blood cells.
16The systemic circulation begins in the _______ and ends in the _______.
  • A. Left ventricle; Right atrium
  • B. Right ventricle; Left atrium
  • C. Left atrium; Right ventricle
  • D. Right atrium; Left ventricle
Answer: A
Oxygenated blood leaves the left ventricle to the body and returns deoxygenated to the right atrium.
17During the atrial systole phase of the cardiac cycle, what happens to the ventricles?
  • A. They are in systole
  • B. They are in diastole
  • C. They are pumping blood to the aorta
  • D. Their semilunar valves are open
Answer: B
Ventricles must be relaxed (diastole) to receive the blood being pumped by the atria.
18The hepatic portal vein is unique because it carries blood from the:
  • A. Liver to the heart
  • B. Digestive tract to the liver
  • C. Kidneys to the liver
  • D. Aorta to the liver
Answer: B
It transports nutrient-rich blood to the liver for processing before it enters general circulation.
19Which factor is most responsible for the movement of lymph through lymphatic vessels?
  • A. Pressure from the heart
  • B. Skeletal muscle contractions
  • C. Suction from the lungs
  • D. Active transport by endothelial cells
Answer: B
Lymph vessels rely on nearby muscle activity and internal valves to move fluid.
20In the human heart, the coronary sinus empties deoxygenated blood directly into the:
  • A. Left atrium
  • B. Right atrium
  • C. Superior vena cava
  • D. Right ventricle
Answer: B. Right atrium
The right atrium receives all systemic deoxygenated blood, including that from the heart muscle via the coronary sinus.
21What happens to the pressure in the ventricles during the 'isovolumetric contraction' phase?
  • A. It decreases rapidly
  • B. It increases rapidly
  • C. It remains constant
  • D. It equals atmospheric pressure
Answer: B
Pressure rises as the ventricle contracts while all valves (AV and Semilunar) are closed.
22The term 'End-Diastolic Volume' (EDV) refers to the volume of blood in the:
  • A. Atria at the end of their contraction
  • B. Ventricles at the end of their filling phase
  • C. Aorta after ventricular ejection
  • D. Ventricles after they have finished contracting
Answer: B
It is the maximum volume of blood a ventricle holds just before it contracts.
23Which of these blood vessels acts as a 'pressure reservoir' to maintain blood flow during diastole?
  • A. Capillaries
  • B. Large elastic arteries
  • C. Large veins
  • D. Venules
Answer: B
Elastic arteries like the aorta stretch during systole and recoil during diastole to keep blood moving.
24The total cross-sectional area is highest in which part of the circulatory system?
  • A. Aorta
  • B. Arteries
  • C. Capillaries
  • D. Vena cava
Answer: C. Capillaries
Billions of capillaries together provide a massive surface area, causing blood to flow slowly for exchange.
25Oedema (tissue swelling) can be caused by a significant decrease in:
  • A. Blood hydrostatic pressure
  • B. Plasma protein concentration
  • C. Capillary permeability
  • D. Lymphatic vessel diameter
Answer: B
Low proteins mean lower osmotic pressure, failing to pull fluid back into the blood from tissues.
26The delay of approximately 0.1 s at the AV node is essential because it:
  • A. Allows the SA node to reset
  • B. Allows the atria to finish contracting and fill the ventricles
  • C. Slows down the heart rate
  • D. Increases the force of contraction
Answer: B
It ensures the ventricles are fully filled before they begin to contract.
27Which structure prevents the mixing of oxygenated and deoxygenated blood in the human heart?
  • A. Pericardium
  • B. Atrioventricular valves
  • C. Interventricular septum
  • D. Coronary arteries
Answer: C. Interventricular septum
This muscular wall separates the right (deoxygenated) and left (oxygenated) ventricles.
28'Lacteals' are specialized lymph capillaries found in the:
  • A. Alveoli
  • B. Villi of the small intestine
  • C. Glomerulus of the kidney
  • D. Dermis of the skin
Answer: B
Lacteals are specifically designed to absorb dietary fats in the digestive tract.
29The semilunar valves close when the:
  • A. Ventricular pressure exceeds arterial pressure
  • B. Atrial pressure exceeds ventricular pressure
  • C. Ventricular pressure falls below arterial pressure
  • D. SA node fires
Answer: C
As ventricles relax, back-pressure from the arteries snaps the semilunar valves shut (the 'Dubb' sound).
30Compared to arteries, veins are generally:
  • A. Narrower and thicker-walled
  • B. Wider-lumened and thinner-walled
  • C. Under higher internal pressure
  • D. Devoid of any tunica externa
Answer: B
Veins have a larger internal diameter (lumen) and thinner walls, acting as blood reservoirs.
31The 'Dubb' sound marks the beginning of:
  • A. Ventricular systole
  • B. Atrial systole
  • C. Ventricular diastole
  • D. Isovolumetric contraction
Answer: C. Ventricular diastole
The second heart sound occurs as the semilunar valves close at the start of ventricular relaxation.
32Which of these is NOT a function of the lymphatic system?
  • A. Transport of dietary lipids
  • B. Production of antibodies
  • C. Thermoregulation via sweat
  • D. Filtering of foreign particles
Answer: C. Thermoregulation via sweat
Thermoregulation is a function of the skin and nervous system, not the lymphatic system.
33Which chamber receives blood through the Superior and Inferior Vena Cava?
  • A. Right atrium
  • B. Left atrium
  • C. Right ventricle
  • D. Left ventricle
Answer: A. Right atrium
These major veins return deoxygenated blood from the body to the right atrium.
34What happens to the atrioventricular valves when the pressure in the ventricles exceeds the pressure in the atria?
  • A. They open to allow filling
  • B. They close to prevent backflow
  • C. They remain open for atrial contraction
  • D. They evert into the atria
Answer: B
Rising pressure in the ventricles forces the AV valves shut to prevent blood from leaking back into the atria.
35The 'P-wave' of an ECG (Electrocardiogram) represents:
  • A. Ventricular depolarization
  • B. Atrial depolarization
  • C. Ventricular repolarization
  • D. Atrial repolarization
Answer: B. Atrial depolarization
The P-wave is the electrical signal for atrial contraction.
36Capillary walls consist of a single layer of:
  • A. Smooth muscle cells
  • B. Elastic connective tissue
  • C. Endothelial cells
  • D. Ciliated columnar cells
Answer: C. Endothelial cells
This single layer of simple squamous epithelium (endothelium) is ideal for diffusion.
37The pulmonary vein is an exception among veins because it carries:
  • A. Blood at high pressure
  • B. Deoxygenated blood
  • C. Oxygenated blood
  • D. Blood to the lungs
Answer: C. Oxygenated blood
It returns oxygen-rich blood from the lungs to the left atrium.
38Pre-capillary sphincters are rings of smooth muscle that regulate blood flow into:
  • A. Arteries
  • B. Arterioles
  • C. Capillary beds
  • D. Venules
Answer: C. Capillary beds
These sphincters control which tissues receive blood based on metabolic need.
39What is the typical average cardiac output for an adult at rest?
  • A. 2 L/min
  • B. 5 L/min
  • C. 10 L/min
  • D. 25 L/min
Answer: B. 5 L/min
Average stroke volume (70 mL) × Heart rate (72 bpm) ≈ 5 Liters per minute.
40Which of these is a primary lymphatic organ located behind the sternum that shrinks after puberty?
  • A. Spleen
  • B. Tonsils
  • C. Thymus
  • D. Lymph node
Answer: C. Thymus
The thymus is where T-lymphocytes mature; it undergoes involution (shrinking) as we age.
41The pulmonary semilunar valve prevents blood from flowing back into the:
  • A. Right atrium
  • B. Right ventricle
  • C. Left ventricle
  • D. Pulmonary vein
Answer: B. Right ventricle
It stops blood in the pulmonary artery from returning to the right ventricle.
42During the joint diastole of 0.4 s, what is happening in the heart?
  • A. Only the atria are relaxed
  • B. Only the ventricles are relaxed
  • C. All chambers are relaxed and filling with blood
  • D. The heart is actively pumping blood to the lungs
Answer: C
This resting phase allows passive filling of both the atria and ventricles.
43The heart sounds can be best heard using which medical instrument?
  • A. Sphygmomanometer
  • B. Stethoscope
  • C. Electrocardiograph
  • D. Thermometer
Answer: B. Stethoscope
A stethoscope is used to auscultate (listen to) heart and lung sounds.
44Intercalated discs are specialized cell junctions found in:
  • A. Skeletal muscle
  • B. Smooth muscle
  • C. Cardiac muscle
  • D. Nerve tissue
Answer: C. Cardiac muscle
These junctions allow the heart muscle cells to contract in a synchronized, wave-like fashion.
45The average pulse rate of a healthy adult at rest is approximately:
  • A. 40-50 bpm
  • B. 70-80 bpm
  • C. 100-120 bpm
  • D. 140-160 bpm
Answer: B. 70-80 bpm
72 bpm is the classical average for a resting adult.
46Which of these substances is NOT typically found in lymph?
  • A. Water
  • B. Leukocytes
  • C. Erythrocytes
  • D. Proteins
Answer: C. Erythrocytes
Red blood cells (erythrocytes) stay within the blood vessels and do not enter the lymph.
47The thoracic duct empties into the venous system at the junction of the:
  • A. Right subclavian vein
  • B. Left subclavian vein
  • C. Superior vena cava
  • D. Hepatic portal vein
Answer: B. Left subclavian vein
The left subclavian vein receives lymph from the majority of the body via the thoracic duct.
48An individual with an extremely low concentration of plasma albumin is likely to experience:
  • A. High blood pressure
  • B. Excessive tissue fluid accumulation
  • C. Increased oxygen carrying capacity
  • D. Faster blood clotting
Answer: B
Low albumin reduces osmotic pressure, leading to fluid leaking into tissues (oedema).
49Which chamber of the heart is the first to depolarize during a normal heartbeat?
  • A. Left atrium
  • B. Right atrium
  • C. Right ventricle
  • D. Left ventricle
Answer: B. Right atrium
Depolarization begins at the SA node, which is located in the wall of the right atrium.
50The coronary arteries branch off from which major vessel?
  • A. Superior Vena Cava
  • B. Pulmonary Artery
  • C. Aorta
  • D. Pulmonary Vein
Answer: C. Aorta
The heart muscle receives its own oxygenated blood supply through arteries branching from the base of the aorta.

✅Practice MCQs — Test 2

🧪 Advanced Concepts

50 MCQs
1During the 'isovolumetric contraction' phase of the cardiac cycle, which of the following remains constant?
  • A. Ventricular pressure
  • B. Ventricular volume
  • C. Atrial pressure
  • D. Aortic pressure
Answer: B
'Isovolumetric' means 'same volume.' The ventricles are contracting, but since both the AV and semilunar valves are closed, the volume cannot change while pressure skyrockets.
2If the SA node fails to fire, the heart's rhythm is typically taken over by the AV node. This resulting rhythm is known as:
  • A. Ectopic focus
  • B. Nodal rhythm
  • C. Ventricular escape
  • D. Sinus arrhythmia
Answer: B. Nodal rhythm
The AV node acts as the secondary pacemaker (40–60 bpm). If both fail, the Purkinje fibers take over at a 'ventricular escape' rate (15–40 bpm).
3The 'dicrotic notch' observed in an aortic pressure curve is caused by:
  • A. The opening of the aortic valve
  • B. The rapid ejection of blood
  • C. The closure of the aortic semilunar valve
  • D. The start of atrial systole
Answer: C
As the aortic valve snaps shut at the start of diastole, a brief rebound of blood against the closed valve causes a momentary increase in aortic pressure.
4Which factor would cause a decrease in the Net Filtration Pressure (NFP) at the arterial end of a capillary?
  • A. Increased blood hydrostatic pressure
  • B. Decreased plasma colloid osmotic pressure
  • C. Increased interstitial fluid hydrostatic pressure
  • D. Increased capillary permeability to proteins
Answer: C
NFP = (BHP + IFOP) - (IFHP + BCOP). Increasing the pressure of the fluid outside the vessel (IFHP) pushes back against the blood, reducing filtration.
5The first heart sound (S1) occurs at the beginning of ______ and corresponds to the ______ on an ECG.
  • A. Ventricular diastole; T-wave
  • B. Ventricular systole; QRS complex
  • C. Atrial systole; P-wave
  • D. Isovolumetric relaxation; P-R interval
Answer: B
S1 marks the closure of AV valves, which happens immediately after ventricular depolarization (QRS).
6According to Poiseuille's Law, if the radius of an arteriole is reduced by half (vasoconstriction), the resistance to blood flow increases by:
  • A. 2 times
  • B. 4 times
  • C. 8 times
  • D. 16 times
Answer: D. 16 times
Resistance is inversely proportional to the fourth power of the radius (r⁴). 2⁴ = 16.
7Which of the following describes the 'Cisterna Chyli'?
  • A. A lymph node in the neck
  • B. The sac-like origin of the thoracic duct in the abdomen
  • C. The valve preventing backflow in the right lymphatic duct
  • D. A specialized macrophage in the spleen
Answer: B
The Cisterna Chyli is the dilated sac at the level of L2 that receives lymph from the lower limbs and intestines.
8The absolute refractory period of cardiac muscle is significantly longer than that of skeletal muscle. This prevents:
  • A. Fatigue
  • B. Tetanic contractions
  • C. Atrial fibrillation
  • D. Rapid heart rates
Answer: B. Tetanic contractions
The long plateau phase (calcium influx) ensures the heart relaxes and fills before it can contract again, preventing a sustained (tetanic) contraction which would stop the pump.
9In a patient with severe Vitamin B12 deficiency, the blood flow velocity might increase due to:
  • A. Increased blood viscosity
  • B. Decreased blood viscosity
  • C. Increased peripheral resistance
  • D. Decreased cardiac output
Answer: B
Fewer RBCs (anemia) lead to 'thinner' blood. Lower viscosity reduces resistance, increasing velocity and potentially causing a 'hemic murmur.'
10During the 'Reduced Ejection' phase of the cardiac cycle:
  • A. Aortic pressure starts to fall
  • B. Ventricular pressure is at its absolute peak
  • C. The AV valves are open
  • D. The T-wave begins on the ECG
Answer: D
The T-wave represents repolarization, which begins while the ventricles are still finishing their ejection of blood at a slower rate.
11Which statement regarding the lymphatic system is anatomically INCORRECT?
  • A. Lymphatic capillaries are more permeable than blood capillaries.
  • B. The thoracic duct enters the junction of the left internal jugular and left subclavian veins.
  • C. Lymph flows from the convex side of a lymph node to the concave hilum.
  • D. Lymphatic vessels contain more valves than veins.
Answer: C
Actually, lymph enters through multiple afferent vessels on the convex side and exits through a single efferent vessel at the hilum.
12A drug that blocks the effects of Acetylcholine on the heart would result in:
  • A. Decreased heart rate (Bradycardia)
  • B. Increased heart rate (Tachycardia)
  • C. Decreased force of contraction
  • D. Shortened P-R interval
Answer: B
Acetylcholine (Parasympathetic) slows the heart. Blocking it (e.g., Atropine) allows the Sympathetic system to dominate, increasing the rate.
13Which layer of the heart is histologically identical to the endothelium of blood vessels?
  • A. Epicardium
  • B. Myocardium
  • C. Endocardium
  • D. Pericardium
Answer: C. Endocardium
The endocardium is the simple squamous epithelial lining that is continuous with the tunica intima of the great vessels.
14The 'Frank-Starling Law' of the heart primarily relates:
  • A. Heart rate to blood pressure
  • B. Stroke volume to end-diastolic volume
  • C. Oxygen consumption to heart size
  • D. Arterial resistance to venous return
Answer: B
It states that the more the heart is stretched (higher EDV), the more forcefully it contracts (higher Stroke Volume), within physiological limits.
15Which of these is a 'Multipennate' characteristic of the heart's pumping mechanism?
  • A. The spiraling arrangement of ventricular muscle fibers
  • B. The rapid conduction of Purkinje fibers
  • C. The delay at the AV node
  • D. The closure of the foramen ovale
Answer: A
The cardiac muscle fibers are arranged in a spiral or 'wringing' fashion, which allows the ventricles to squeeze blood upward toward the outflow tracts.
16Which of the following has the most significant effect on blood flow through a capillary bed?
  • A. Mean arterial pressure
  • B. Local metabolic factors (e.g., CO₂, H⁺)
  • C. Sympathetic innervation of capillaries
  • D. Atmospheric pressure
Answer: B
Capillaries themselves are not innervated. Flow is controlled by arterioles and pre-capillary sphincters responding to local 'autoregulation' needs.
17The 'P-R Interval' longer than 0.20 s usually indicates:
  • A. Rapid SA node firing
  • B. A delay or block in conduction through the AV node
  • C. Hypertrophy of the left ventricle
  • D. Failure of the Purkinje fibers
Answer: B
The P-R interval measures the time from the start of atrial depolarization to the start of ventricular depolarization. A long interval signifies a 'First-degree heart block.'
18Which ion's rapid influx is responsible for the depolarization phase (Phase 0) of a ventricular action potential?
  • A. Ca²⁺
  • B. K⁺
  • C. Na⁺
  • D. Mg²⁺
Answer: C. Na⁺
Fast voltage-gated sodium channels open, leading to a rapid spike in membrane potential.
19In the fetal heart, the 'Ductus Arteriosus' connects the:
  • A. Two atria
  • B. Right ventricle and Left ventricle
  • C. Pulmonary artery and Aorta
  • D. Pulmonary vein and Left atrium
Answer: C
It allows blood to bypass the non-functional fetal lungs by shunting it directly into the systemic circulation.
20Edema is a common side effect of right-sided heart failure because:
  • A. Systemic venous pressure increases
  • B. Pulmonary capillary pressure increases
  • C. Plasma protein synthesis stops
  • D. Blood volume decreases
Answer: A
When the right heart fails, blood 'backs up' into the systemic veins, increasing hydrostatic pressure and forcing fluid into tissues (e.g., swollen ankles).
21Which specific protein in the heart acts as a 'calcium sensor' to initiate contraction?
  • A. Myosin
  • B. Tropomyosin
  • C. Troponin C
  • D. Actin
Answer: C. Troponin C
Calcium binds to Troponin C, causing a conformational change in tropomyosin that exposes myosin-binding sites on actin.
22The velocity of blood flow is slowest in the capillaries primarily because:
  • A. Capillary pressure is the lowest
  • B. Capillaries are the furthest from the heart
  • C. The total cross-sectional area of all capillaries is the largest
  • D. Capillary walls are very thin
Answer: C
Continuity equation (V = Q/A). As total area (A) increases, velocity (V) must decrease to maintain the same flow rate (Q).
23Which lymphatic organ contains both 'Red Pulp' and 'White Pulp'?
  • A. Thymus
  • B. Spleen
  • C. Tonsils
  • D. Peyer's Patches
Answer: B. Spleen
White pulp is involved in immune functions (lymphocytes), while red pulp filters the blood (removes old RBCs).
24A 'positive inotropic' agent is one that:
  • A. Increases the heart rate
  • B. Decreases the heart rate
  • C. Increases the force of contraction
  • D. Decreases the force of contraction
Answer: C
Inotropy refers to contractility. Adrenaline is a positive inotrope; Beta-blockers are negative inotropes.
25The 'Anulus Fibrosus' of the heart serves to:
  • A. Protect the coronary arteries
  • B. Electrically insulate the atria from the ventricles
  • C. Secrete pericardial fluid
  • D. Attach the heart to the diaphragm
Answer: B
This fibrous skeleton prevents electrical impulses from passing directly from atria to ventricles, forcing the signal through the AV node.
26During the 'c' wave of the atrial pressure curve:
  • A. The atrium is contracting
  • B. The AV valve bulges into the atrium during ventricular contraction
  • C. The atrium is filling with blood from the veins
  • D. The semilunar valves are closing
Answer: B
The 'a' wave is atrial systole, the 'c' wave is ventricular systole causing the AV valve to bulge, and the 'v' wave is venous filling.
27Which vessel has the highest 'Compliance' (stretchability)?
  • A. Aorta
  • B. Arterioles
  • C. Capillaries
  • D. Veins
Answer: D. Veins
Veins are roughly 24 times more compliant than arteries, allowing them to act as volume reservoirs.
28The primary force moving fluid back into the capillary at the venous end is:
  • A. Blood Hydrostatic Pressure (15 mmHg)
  • B. Blood Colloid Osmotic Pressure (25 mmHg)
  • C. Interstitial Fluid Pressure (0 mmHg)
  • D. Gravity
Answer: B
Because plasma proteins (albumin) cannot leave the capillary, they create a 'pull' (osmotic pressure) that exceeds the 'push' of hydrostatic pressure at the venous end.
29'Lymphedema' following a mastectomy (breast removal) is usually caused by:
  • A. Overproduction of lymph
  • B. Removal of axillary lymph nodes
  • C. Infection of the heart
  • D. Low protein diet
Answer: B
If the 'drains' (lymph nodes) are removed, the fluid from the arm has no path to return to the blood, causing massive swelling.
30The 'Lubb' sound is lower in pitch and longer in duration than the 'Dubb' sound because:
  • A. The AV valves are smaller than semilunar valves
  • B. Ventricular contraction is slower than relaxation
  • C. The vibration of the heavy ventricular walls and blood
  • D. The aorta is more elastic than the pulmonary artery
Answer: C
S1 (Lubb) is muffled by the thick muscle of the contracting ventricles, whereas S2 (Dubb) is a sharper snap of the valves alone.
31In an ECG, the 'Q' wave is specifically caused by:
  • A. Depolarization of the main ventricular mass
  • B. Depolarization of the interventricular septum
  • C. Atrial repolarization
  • D. The closing of the mitral valve
Answer: B
The first part of the ventricles to depolarize is the septum (from left to right), creating the small downward Q wave.
32Which condition would lead to 'Secondary Polycythemia' and increased blood viscosity?
  • A. Living at high altitudes
  • B. Chronic hemorrhaging
  • C. Overhydration
  • D. Iron deficiency
Answer: A
Low oxygen at high altitudes triggers Erythropoietin (EPO) release, increasing RBC count and making the blood thicker/more viscous.
33The total duration of one cardiac cycle is inversely proportional to:
  • A. Stroke Volume
  • B. Heart Rate
  • C. Blood Pressure
  • D. Body Temperature
Answer: B. Heart Rate
If Heart Rate increases, the time for each cycle must decrease. Specifically, the diastole phase shortens more than the systole phase.
34Which of the following structures is NOT involved in the 'Pulmonary Circuit'?
  • A. Right Ventricle
  • B. Pulmonary Semilunar Valve
  • C. Left Atrium
  • D. Left Ventricle
Answer: D. Left Ventricle
The pulmonary circuit ends when oxygenated blood reaches the left atrium. The left ventricle begins the systemic circuit.
35'Active Hyperemia' refers to:
  • A. Redness of skin due to cold
  • B. Increased blood flow to a tissue due to increased metabolic activity
  • C. Blood pooling in the veins
  • D. A decrease in blood pressure
Answer: B
When a muscle works, it produces CO₂ and Adenosine, which dilate local arterioles to bring in more blood.
36Which hormone is a potent vasoconstrictor and also stimulates the release of Aldosterone?
  • A. ANP (Atrial Natriuretic Peptide)
  • B. Angiotensin II
  • C. Adrenaline
  • D. Thyroxine
Answer: B. Angiotensin II
Part of the RAAS system, Angiotensin II raises blood pressure by tightening vessels and retaining salt/water.
37Lymphatic capillaries are absent in which of the following tissues?
  • A. Skeletal muscle
  • B. Central Nervous System (CNS)
  • C. Dermis of the skin
  • D. Digestive tract
Answer: B. CNS
The brain and spinal cord lack traditional lymphatic vessels. Bone marrow and teeth also lack them.
38The 'vagal tone' on the heart primarily affects the:
  • A. Purkinje fibers
  • B. Myocardium of the left ventricle
  • C. SA and AV nodes
  • D. Aortic arch
Answer: C
The Vagus nerve (Parasympathetic) innervates the nodes to keep the resting heart rate (~70 bpm) lower than the SA node's intrinsic rate (~100 bpm).
39During exercise, the 'End-Systolic Volume' (ESV) usually:
  • A. Increases
  • B. Decreases
  • C. Stays the same
  • D. Becomes zero
Answer: B. Decreases
Increased sympathetic stimulation makes the heart contract more forcefully, leaving less blood behind in the ventricle after each beat.
40A patient with 'Mitral Stenosis' (narrowing of the bicuspid valve) would likely show:
  • A. Left Atrial Hypertrophy
  • B. Right Ventricular atrophy
  • C. Low Pulmonary blood pressure
  • D. Increased Aortic pressure
Answer: A
The left atrium has to work much harder to push blood through a narrow opening into the ventricle, causing the atrial muscle to thicken.
41The 'Mean Arterial Pressure' (MAP) is closer to the diastolic pressure than the systolic pressure because:
  • A. The heart spends more time in diastole than in systole
  • B. Systolic pressure is harder to measure
  • C. Diastolic pressure is always 80 mmHg
  • D. The aorta is very elastic
Answer: A
In a 0.8 s cycle, diastole is 0.5 s and systole is 0.3 s. Formula: MAP = DBP + 1/3(SBP - DBP).
42Which of these describes the 'Bainbridge Reflex'?
  • A. Increased heart rate due to increased venous return (atrial stretch)
  • B. Decreased heart rate due to high blood pressure
  • C. Fainting due to seeing blood
  • D. Increased breathing rate during exercise
Answer: A
When the right atrium is stretched by extra blood, it triggers a reflex to speed up the heart to 'clear out' the volume.
43The 'Fenestrated' capillaries are commonly found in the:
  • A. Blood-brain barrier
  • B. Kidneys and small intestine
  • C. Liver and Spleen
  • D. Lungs
Answer: B
'Fenestra' means windows. These allow for high rates of filtration (kidneys) or absorption (intestines).
44'Stenosis' of the pulmonary semilunar valve would first lead to hypertrophy of the:
  • A. Left Atrium
  • B. Left Ventricle
  • C. Right Atrium
  • D. Right Ventricle
Answer: D. Right Ventricle
The right ventricle must generate more pressure to overcome the narrowed valve to get blood to the lungs.
45If the P-R interval is 0.15 s and the QRS complex is 0.08 s, the total time for ventricular filling is roughly:
  • A. 0.23 s
  • B. 0.50 s
  • C. 0.80 s
  • D. 0.10 s
Answer: B. 0.50 s
Ventricular filling occurs during diastole, which is roughly 0.5 s in a normal 75 bpm heart.
46Which part of the brain contains the 'Cardiovascular Center'?
  • A. Cerebrum
  • B. Medulla Oblongata
  • C. Cerebellum
  • D. Hypothalamus
Answer: B. Medulla Oblongata
The medulla controls autonomic functions like heart rate (Cardioacceleratory/inhibitory centers) and blood vessel tone (Vasomotor center).
47The 'S-T segment' of an ECG is electrically neutral because:
  • A. The heart is at rest
  • B. The ventricles are completely depolarized (plateau phase)
  • C. The atria are repolarizing
  • D. The AV node is delaying the signal
Answer: B
During this time, the entire ventricular myocardium is depolarized, so there is no difference in potential to create a wave.
48Which factor would NOT increase the 'Stroke Volume'?
  • A. Increased Preload (EDV)
  • B. Increased Afterload (Back pressure)
  • C. Increased Contractility
  • D. Decreased Heart Rate (allowing more filling time)
Answer: B
Afterload is the resistance the heart must pump against. Higher afterload (like hypertension) makes it harder to eject blood, reducing stroke volume.
49The 'Thoracic Pump' helps venous return by:
  • A. Increasing abdominal pressure during inhalation
  • B. Decreasing thoracic pressure during inhalation
  • C. Both A and B
  • D. Contracting the walls of the Vena Cava
Answer: C. Both A and B
Inhalation creates a 'vacuum' in the chest and 'squeezes' the abdomen, pushing blood toward the heart.
50Which valve is under the highest physical stress in the human heart?
  • A. Tricuspid
  • B. Pulmonary
  • C. Mitral (Bicuspid)
  • D. Aortic
Answer: C. Mitral (Bicuspid)
The Mitral valve must withstand the massive pressure of the left ventricle contracting to prevent backflow into the atrium. It is the most common valve to fail or require replacement.

✅Practice MCQs — Test 3

🧪 Exam-Level Questions

50 MCQs
1The 'Thebesian veins' (Venae Cordis Minimae) represent a unique shunt in coronary circulation because they:
  • A. Carry oxygenated blood to the right atrium
  • B. Drain deoxygenated blood directly into the chambers of the heart, primarily the left side
  • C. Supply the SA node exclusively
  • D. Prevent myocardial infarction during coronary occlusion
Answer: B
While most coronary blood returns via the coronary sinus to the right atrium, Thebesian veins drain directly into the heart chambers. When they drain into the left atrium/ventricle, they contribute to a 'physiological shunt,' mixing deoxygenated blood with oxygenated blood.
2According to the Law of Laplace (T = P × r / w), why is the left ventricle more prone to failure in cases of chronic dilation than the right ventricle?
  • A. Increased radius (r) requires higher wall tension (T) to generate the same systolic pressure (P)
  • B. The left ventricle has fewer intercalated discs
  • C. The wall thickness (w) decreases as the heart dilates, reducing efficiency
  • D. Both A and C are correct
Answer: D
Laplace's Law states that wall tension (T) is proportional to pressure (P) and radius (r), and inversely proportional to wall thickness (w). Dilation increases r and decreases w, requiring the muscle to generate much higher tension to maintain blood pressure, eventually leading to failure.
3During which phase of the cardiac cycle is coronary blood flow to the left ventricular myocardium at its absolute MINIMUM?
  • A. Atrial Systole
  • B. Isovolumetric Contraction
  • C. Isovolumetric Relaxation
  • D. Ventricular Diastole
Answer: B
During isovolumetric contraction, the high intramyocardial pressure squeezes the coronary arteries shut. Because the aortic pressure hasn't yet risen to open the valves and the heart is contracting most forcefully, flow to the left ventricle is restricted.
4In the 'v' wave of a Jugular Venous Pulse (JVP) tracing, the rise in pressure is caused by:
  • A. Atrial contraction
  • B. Bulging of the tricuspid valve into the atrium
  • C. Venous return filling the atrium against a closed tricuspid valve
  • D. Rapid ventricular filling
Answer: C
The 'a' wave is atrial contraction; the 'c' wave is the tricuspid bulge during systole; the 'v' wave represents the passive filling of the atrium while the tricuspid valve is still closed.
5Which physiological change occurs when moving from a standing to a supine (lying down) position?
  • A. Decreased venous return
  • B. Increased Stroke Volume via the Frank-Starling mechanism
  • C. Increased heart rate due to baroreceptor reflex
  • D. Decreased end-diastolic volume
Answer: B
Lying down removes the effect of gravity on the lower limbs, increasing venous return (Preload). This increases End-Diastolic Volume, which, by Frank-Starling's Law, increases Stroke Volume.
6A patient has a Heart Rate of 75 bpm, an End-Diastolic Volume of 140 mL, and an End-Systolic Volume of 70 mL. What is their Ejection Fraction (EF)?
  • A. 40%
  • B. 50%
  • C. 60%
  • D. 70%
Answer: B. 50%
Stroke Volume (SV) = EDV - ESV = 140 - 70 = 70 mL. EF = (SV / EDV) × 100 = (70 / 140) × 100 = 50%.
7The 'Secondary Pacemaker' of the heart (AV node) has a slower conduction velocity (0.01 to 0.05 m/s) compared to Purkinje fibers (2 to 4 m/s). This is primarily due to:
  • A. Larger cell diameters in the AV node
  • B. Fewer gap junctions between AV nodal cells
  • C. Increased number of sodium channels in the AV node
  • D. Presence of the Anulus Fibrosus
Answer: B
The 'AV nodal delay' is caused by small fiber diameters and a lower density of gap junctions, which increases resistance to electrical flow, ensuring the atria finish contracting before the ventricles start.
8What is the primary hemodynamic consequence of 'Mitral Regurgitation' during ventricular systole?
  • A. Increased Aortic pressure
  • B. Decreased Left Atrial pressure
  • C. Presence of a systolic murmur and pulmonary edema
  • D. Increased End-Systolic Volume only
Answer: C
In mitral regurgitation, blood flows backward into the left atrium during systole. This raises atrial pressure (leading to pulmonary edema) and creates a 'whooshing' murmur.
9The plateau phase (Phase 2) of the ventricular action potential is maintained by the balance between:
  • A. Inward Na⁺ and outward K⁺
  • B. Inward Ca²⁺ (L-type channels) and outward K⁺
  • C. Inward K⁺ and outward Ca²⁺
  • D. Inward Cl⁻ and outward Na⁺
Answer: B
The plateau is unique to cardiac muscle. It is caused by slow calcium channels opening (inward flow) while potassium slowly leaks out (outward flow), delaying repolarization.
10In the context of Starling's Forces, 'Myxedema' (hypothyroidism) causes non-pitting edema primarily through:
  • A. Increased Blood Hydrostatic Pressure
  • B. Decreased Plasma Oncotic Pressure
  • C. Accumulation of glycosaminoglycans in the interstitial space, increasing Interstitial Oncotic Pressure
  • D. Lymphatic obstruction
Answer: C
Hypothyroidism causes proteins/sugars to build up in the tissues, which 'pulls' water out of the capillaries via osmosis.
11Which of the following would shift the Oxygen-Hemoglobin dissociation curve to the RIGHT (Bohr Effect) in systemic capillaries?
  • A. Decreased PCO₂
  • B. Increased pH (Alkalosis)
  • C. Increased temperature and 2,3-DPG
  • D. Decreased temperature
Answer: C
A right shift means hemoglobin has a lower affinity for oxygen (unloads it easier). This is caused by high CO₂, high H⁺ (acidity), high temperature, and high 2,3-DPG—all conditions of active tissues.
12The 'Functional Syncytium' of the heart is interrupted only by:
  • A. The Interventricular Septum
  • B. The Fibrous Skeleton (Anulus Fibrosus)
  • C. The Chordae Tendineae
  • D. The Papillary Muscles
Answer: B
The fibrous skeleton is non-conductive tissue. Without it, the impulse would spread everywhere at once. It forces the impulse to 'funnel' through the AV bundle.
13During intense exercise, the 'Total Peripheral Resistance' (TPR) actually decreases. Why?
  • A. The heart pumps less blood to the skin
  • B. Massive vasodilation in skeletal muscles outweighs vasoconstriction in the viscera
  • C. Blood viscosity decreases due to sweating
  • D. Parasympathetic activity increases
Answer: B
While the sympathetic system constricts vessels in the gut and kidneys, the local metabolic products in working muscles cause massive dilation, lowering the overall resistance the heart faces.
14A 'Positive Lusitropic' effect refers to:
  • A. Faster heart rate
  • B. Increased contraction force
  • C. Faster rate of myocardial relaxation
  • D. Increased conduction velocity
Answer: C
Lusitropy is relaxation. Adrenaline has a positive lusitropic effect because it speeds up the calcium pump (SERCA), allowing the heart to relax faster and fill more during high heart rates.
15The 'Incisura' (Dicrotic Notch) on an arterial pressure tracing is NOT seen in the:
  • A. Aortic arch
  • B. Radial artery
  • C. Pulmonary artery
  • D. Left Ventricular pressure curve
Answer: D
The notch is a feature of arterial pressure caused by the backflow of blood closing the semilunar valves. The ventricle's pressure simply drops toward zero during diastole; it doesn't show a dicrotic notch.
16Which component of the lymphatic system is the ONLY one to contain 'Hassall's Corpuscles'?
  • A. Spleen
  • B. Tonsils
  • C. Thymus Medulla
  • D. Lymph node Cortex
Answer: C
Hassall's corpuscles are epithelial whorls found in the medulla of the thymus. They are a key histological marker for the thymus.
17If the 'Reflection Coefficient' (σ) of a capillary wall for proteins is 0, it means:
  • A. The capillary is impermeable to proteins
  • B. The capillary is completely permeable to proteins (e.g., Sinusoids)
  • C. No filtration can occur
  • D. The osmotic pressure gradient is maximized
Answer: B
A coefficient of 1 means 100% reflection (impermeable). A coefficient of 0 means the protein crosses as easily as water, meaning the protein cannot exert an osmotic 'pull' (observed in liver sinusoids).
18What would be the effect of a 'Beta-1 Adrenergic Antagonist' (Beta-blocker) on the Cardiac Function Curve?
  • A. Shift upward and to the left
  • B. Shift downward and to the right
  • C. No change in Stroke Volume
  • D. Increase in End-Diastolic Volume for the same Stroke Volume
Answer: B
Beta-blockers decrease contractility (negative inotropy). To pump the same amount of blood, the heart must stretch more (higher EDV/preload), shifting the curve down and right.
19Which vessel has the highest 'Wall-to-Lumen' ratio?
  • A. Aorta
  • B. Arterioles
  • C. Capillaries
  • D. Vena Cava
Answer: B. Arterioles
Arterioles have the thickest muscle layer relative to their small internal diameter, which is why they are the primary site of blood pressure regulation.
20'Critical Closing Pressure' is the arterial pressure at which:
  • A. The heart stops beating
  • B. Blood flow stops because the small vessels collapse
  • C. The valves of the heart fail to open
  • D. Oxygen can no longer diffuse
Answer: B
In very small vessels, if the blood pressure drops below a certain point, the surface tension and tissue pressure overcome the internal pressure, and the vessel collapses shut.
21'Interleukin-7' (IL-7) is a cytokine primarily produced by stromal cells in the ______ to support B-cell development.
  • A. Spleen
  • B. Bone Marrow
  • C. Thymus
  • D. Lymph nodes
Answer: B. Bone Marrow
While B-cells are part of the lymphatic system's immune response, their primary maturation site (the Bone Marrow) uses IL-7 as a growth factor.
22In a 'Type I Second-Degree AV Block' (Wenckebach), the ECG shows:
  • A. A constant, prolonged P-R interval
  • B. Progressively lengthening P-R intervals until a QRS is dropped
  • C. No relationship between P waves and QRS complexes
  • D. A shortened P-R interval
Answer: B
This is a classic advanced medical concept often referenced in higher-tier physiology sections.
23The 'T-wave' in an ECG represents ventricular repolarization. Why is it usually a positive (upward) deflection if repolarization is the opposite of depolarization?
  • A. The atria repolarize at the same time
  • B. Repolarization occurs from the epicardium to the endocardium (reverse direction)
  • C. The electrodes are placed incorrectly
  • D. It represents the closing of the semilunar valves
Answer: B
Depolarization goes from endocardium to epicardium. Because the last cells to depolarize are the first to repolarize, the 'electrical vector' for repolarization points in the same direction as depolarization.
24'Chylomicrons' enter the blood circulation at the:
  • A. Hepatic portal vein
  • B. Left subclavian vein
  • C. Mesenteric artery
  • D. Inferior Vena Cava
Answer: B. Left subclavian vein
Fats are absorbed into lacteals, travel through the thoracic duct, and enter the blood at the left subclavian vein, bypassing the liver initially.
25The 'Windkessel Effect' refers to:
  • A. The pumping action of the skeletal muscles
  • B. The elastic recoil of the aorta maintaining flow during diastole
  • C. The suction created by the atria
  • D. The filtering of lymph in the nodes
Answer: B
This term describes how elastic arteries convert pulsatile flow into continuous flow.
26Which of these would result from an 'Arteriovenous (A-V) Fistula'?
  • A. Decreased Cardiac Output
  • B. Increased Total Peripheral Resistance
  • C. Increased Venous Return and High-Output Heart Failure
  • D. Decreased Pulse Pressure
Answer: C
An A-V fistula is a direct 'short circuit' from an artery to a vein. Blood skips the resistance of capillaries, rushing back to the heart, which increases venous return and forces the heart to pump excessively.
27'Peyer's Patches' are specialized lymphatic tissues found in the:
  • A. Duodenum
  • B. Ileum
  • C. Ascending colon
  • D. Stomach
Answer: B. Ileum
These are part of GALT (Gut-Associated Lymphoid Tissue) and are specifically concentrated in the ileum of the small intestine.
28The 'Anabolic Phase' of the cardiac action potential (Phase 4) in SA nodal cells is characterized by:
  • A. A stable resting membrane potential
  • B. A slow 'Funny Current' (I_f) primarily due to Na⁺ influx
  • C. Rapid K⁺ efflux
  • D. Ca²⁺ efflux
Answer: B
The SA node never 'rests.' Its Phase 4 is a slow upward drift caused by 'funny channels' that open when the cell is hyperpolarized, leading to the next beat.
29During a 'Valsalva Maneuver' (forced expiration against a closed glottis), what happens to venous return initially?
  • A. It increases due to abdominal pressure
  • B. It decreases due to increased intrathoracic pressure compressing the Vena Cava
  • C. It stays the same
  • D. It bypasses the right atrium
Answer: B
The high pressure in the chest prevents blood from entering, which eventually leads to a drop in blood pressure and a reflex increase in heart rate.
30The most abundant type of protein in the 'White Pulp' of the spleen involved in identifying pathogens is:
  • A. Hemoglobin
  • B. Complement proteins
  • C. Immunoglobulins (Antibodies)
  • D. Fibrinogen
Answer: C
The white pulp is essentially a large lymph node for the blood, filled with B and T lymphocytes producing antibodies.
31'Isovolumetric Relaxation' begins immediately after:
  • A. The 'Dubb' sound
  • B. The 'Lubb' sound
  • C. The P-wave
  • D. The opening of the Mitral valve
Answer: A
The closure of the semilunar valves (S2/Dubb) marks the end of ejection and the start of the period where the ventricle relaxes without changing volume.
32Which heart chamber has the lowest oxygen saturation in its blood supply?
  • A. Right Atrium
  • B. Right Ventricle
  • C. Coronary Sinus
  • D. Pulmonary Artery
Answer: C. Coronary Sinus
The heart muscle extracts more oxygen (~75%) than any other tissue. Therefore, the blood leaving the heart muscle via the coronary sinus has the lowest O₂ levels in the entire body.
33A 'Bruit' is a sound heard over an artery that usually indicates:
  • A. Normal laminar flow
  • B. Turbulent flow due to narrowing (stenosis)
  • C. Complete blockage
  • D. Low blood pressure
Answer: B
When an artery is partially blocked, the Reynolds number increases, flow becomes turbulent, and it creates a sound called a bruit.
34The 'Blood-Thymus Barrier' exists to:
  • A. Keep T-cells from entering the blood
  • B. Prevent immature T-cells from being exposed to 'self' antigens in the blood
  • C. Stop bacteria from entering the thymus
  • D. Regulate the temperature of the thymus
Answer: B
This barrier ensures that T-cells 'graduate' only after they have been properly screened against self-reactivity in a controlled environment.
35'Reynolds Number' (Re) is used to predict:
  • A. The force of a heartbeat
  • B. Whether blood flow is laminar or turbulent
  • C. The oxygen content of blood
  • D. The rate of lymph formation
Answer: B
Re = (Density × Velocity × Diameter) / Viscosity. If Re > 2000, flow usually becomes turbulent.
36Which of the following is a 'Negative Chronotropic' factor?
  • A. Adrenaline
  • B. Thyroxine
  • C. Increased K⁺ concentration (Hyperkalemia)
  • D. Sympathetic stimulation
Answer: C
High potassium outside cells makes it harder for them to repolarize and fire again, slowing or even stopping the heart.
37In the fetal circulation, the 'Ductus Venosus' allows blood to bypass the:
  • A. Lungs
  • B. Heart
  • C. Liver
  • D. Kidneys
Answer: C. Liver
Oxygenated blood from the umbilical vein shunts through the ductus venosus directly into the Inferior Vena Cava, bypassing the fetal liver.
38'Opsonization,' a key function of the lymphatic immune response, refers to:
  • A. The bursting of a cell
  • B. Coating a pathogen with antibodies to make it easier for phagocytes to eat
  • C. The migration of WBCs through vessel walls
  • D. The production of memory cells
Answer: B
Antibodies act as 'handles' for macrophages.
39The 'C-reactive protein' (CRP) is a marker of inflammation produced by the:
  • A. Heart
  • B. Spleen
  • C. Liver
  • D. Lymph nodes
Answer: C. Liver
CRP is an acute-phase reactant synthesized by the liver in response to cytokines from the immune system.
40Which of these has the HIGHEST velocity of blood flow?
  • A. Aorta during systole
  • B. Arterioles
  • C. Capillaries
  • D. Vena Cava
Answer: A. Aorta during systole
Velocity is highest where total cross-sectional area is lowest (the Aorta).
41The 'J-point' on an ECG is the junction between:
  • A. The P-wave and Q-wave
  • B. The QRS complex and the S-T segment
  • C. The T-wave and U-wave
  • D. The R-wave and S-wave
Answer: B
The J-point is often used in clinical settings to detect 'ST-elevation' during heart attacks.
42'Cardiac Tamponade' is a life-threatening condition where:
  • A. The heart muscle turns to fat
  • B. Fluid builds up in the pericardial sac, preventing the heart from filling
  • C. The valves become calcified
  • D. The SA node stops working
Answer: B
Because the pericardium is fibrous and doesn't stretch, fluid buildup (blood or pus) squeezes the heart, dropping cardiac output to near zero.
43Which of these is a 'Secondary' lymphoid tissue?
  • A. Bone Marrow
  • B. Thymus
  • C. Tonsils
  • D. All are primary
Answer: C. Tonsils
Tonsils, Spleen, and Lymph nodes are secondary (where the 'battle' happens). Bone marrow and Thymus are primary (where 'soldiers' are made).
44'Pulse Pressure' is defined as:
  • A. SBP + DBP
  • B. (SBP + 2DBP) / 3
  • C. SBP - DBP
  • D. DBP + 1/3(SBP)
Answer: C. SBP - DBP
For 120/80, the pulse pressure is 40 mmHg. It reflects the stroke volume and arterial compliance.
45The 'Starling's Law of the Capillary' states that fluid movement is governed by:
  • A. Hydrostatic pressure only
  • B. Osmotic pressure only
  • C. The balance between Hydrostatic and Osmotic pressures
  • D. The concentration of glucose
Answer: C
Fluid leaves at the arterial end (Hydrostatic > Osmotic) and returns at the venous end (Osmotic > Hydrostatic).
46'Ejection Fraction' is a clinical measure of:
  • A. Heart Rate
  • B. Blood Pressure
  • C. Ventricular Efficiency/Contractility
  • D. Lung Capacity
Answer: C
It measures what percentage of the blood in the ventricle is actually pumped out. Normal is >55%.
47The 'Foramen Ovale' in the fetus allows blood to flow from:
  • A. Right Atrium to Left Atrium
  • B. Left Atrium to Right Atrium
  • C. Right Ventricle to Pulmonary Artery
  • D. Aorta to Pulmonary Artery
Answer: A
This allows oxygenated blood from the placenta to bypass the lungs and go straight to the left heart for systemic distribution.
48'Hemangioblasts' are the precursor cells for:
  • A. Only Red Blood Cells
  • B. Only White Blood Cells
  • C. Both Blood Cells and Blood Vessels
  • D. Lymphatic nodes
Answer: C
These are embryonic cells that differentiate into both hematopoietic stem cells and endothelial cells.
49Which layer of the artery is most involved in 'Atherosclerosis'?
  • A. Tunica Media
  • B. Tunica Externa
  • C. Tunica Intima
  • D. Vasa Vasorum
Answer: C. Tunica Intima
Cholesterol plaques build up under the endothelium (tunica intima), eventually narrowing the lumen.
50A 'Third Heart Sound' (S3) is sometimes heard in athletes or heart failure patients. It is caused by:
  • A. Atrial contraction
  • B. Closure of the AV valves
  • C. Rapid, turbulent filling of the ventricles during early diastole
  • D. A leak in the aortic valve
Answer: C
S3 is the 'ventricular gallop,' occurring just after S2 when the blood rushes into a very compliant or very dilated ventricle.

📄Past Paper MCQs

📅 Actual MDCAT / NUMS Questions

49 MCQs
1The delay in the conduction of the impulse at the AV node is approximately 0.1 seconds. This delay is functionally significant because it:
MDCAT 2023 (PMDC)
  • A. Allows the ventricles to depolarize completely
  • B. Allows the atria to empty their blood into the ventricles
  • C. Protects the ventricles from high atrial rates
  • D. Ensures the semilunar valves stay closed
Answer: B
The delay ensures the atria finish contracting and fully fill the ventricles before ventricular systole begins.
2During the isovolumetric contraction phase of the cardiac cycle:
NUMS 2022
  • A. All four heart valves are closed
  • B. The AV valves are open, and semilunar valves are closed
  • C. Aortic pressure is at its maximum
  • D. Ventricular volume is decreasing rapidly
Answer: A
Isovolumetric contraction means all valves are closed; volume is constant while pressure rises.
3Which of the following ECG components represents the time taken for the impulse to travel from the SA node to the ventricular muscle?
MDCAT 2021 (National)
  • A. QRS complex
  • B. P-R interval
  • C. S-T segment
  • D. T-wave
Answer: B. P-R interval
The P-R interval includes atrial depolarization and the AV delay, representing SA node to ventricular muscle conduction.
4The 'Lubb' sound of the heart is produced during the beginning of:
UHS MDCAT 2017
  • A. Atrial Systole
  • B. Ventricular Systole
  • C. Ventricular Diastole
  • D. Joint Diastole
Answer: B. Ventricular Systole
S1 (Lubb) occurs at the start of ventricular systole when AV valves close.
5In which of the following vessels is the velocity of blood flow the lowest?
NUMS 2023
  • A. Aorta
  • B. Arterioles
  • C. Capillaries
  • D. Venules
Answer: C. Capillaries
Velocity is lowest in capillaries due to largest total cross-sectional area.
6Edema (accumulation of fluid in interstitial spaces) is most likely to occur when there is:
MDCAT 2020 (SZABMU)
  • A. Increased plasma albumin concentration
  • B. Decreased capillary hydrostatic pressure
  • C. Increased capillary permeability
  • D. Increased lymphatic drainage
Answer: C
Increased capillary permeability allows proteins to leak, increasing interstitial osmotic pressure and causing edema.
7The correct sequence of the cardiac conduction system is:
MDCAT 2019 (UHS)
  • A. SA node → Bundle of His → AV node → Purkinje fibers
  • B. SA node → AV node → Bundle of His → Purkinje fibers
  • C. AV node → SA node → Purkinje fibers → Bundle of His
  • D. Purkinje fibers → Bundle of His → AV node → SA node
Answer: B
SA node → AV node → Bundle of His → Purkinje fibers is the correct pathway.
8The volume of blood pumped by each ventricle per minute is called:
NUMS 2021
  • A. Stroke volume
  • B. Cardiac output
  • C. End-systolic volume
  • D. Tidal volume
Answer: B. Cardiac output
Cardiac output = Stroke volume × Heart rate, measured in L/min.
9Which of the following is a primary lymphoid organ in humans?
MDCAT 2022 (PMDC)
  • A. Spleen
  • B. Tonsils
  • C. Thymus
  • D. Lymph node
Answer: C. Thymus
Thymus and bone marrow are primary lymphoid organs where lymphocytes mature.
10The blood vessel that carries deoxygenated blood from the heart muscle to the right atrium is the:
UHS MDCAT 2018
  • A. Superior Vena Cava
  • B. Coronary Sinus
  • C. Pulmonary Artery
  • D. Left Coronary Artery
Answer: B. Coronary Sinus
The coronary sinus collects deoxygenated blood from cardiac veins and empties into the right atrium.
11During ventricular diastole, the semilunar valves close to prevent the backflow of blood from the:
MDCAT 2023
  • A. Atria into the ventricles
  • B. Ventricles into the atria
  • C. Aorta and pulmonary artery into the ventricles
  • D. Vena cava into the atria
Answer: C
Semilunar valves close when ventricular pressure drops below arterial pressure, preventing backflow into ventricles.
12If the heart rate is 75 beats per minute, the duration of one cardiac cycle is:
NUMS 2020
  • A. 0.1 s
  • B. 0.3 s
  • C. 0.8 s
  • D. 1.0 s
Answer: C. 0.8 s
Cardiac cycle duration = 60 / HR = 60/75 = 0.8 seconds.
13Which wave of the ECG represents ventricular repolarization?
MDCAT 2016 (UHS)
  • A. P-wave
  • B. QRS complex
  • C. T-wave
  • D. U-wave
Answer: C. T-wave
The T-wave corresponds to ventricular repolarization.
14Lymph capillaries in the villi of the small intestine that absorb fats are known as:
NUMS 2019
  • A. Venules
  • B. Sinusoids
  • C. Lacteals
  • D. Arterioles
Answer: C. Lacteals
Lacteals are specialized lymphatic capillaries that absorb dietary fats (chylomicrons).
15What is the main factor that maintains the osmotic pressure of the blood?
MDCAT 2021
  • A. Glucose
  • B. Hemoglobin
  • C. Plasma proteins (mainly albumin)
  • D. Sodium ions
Answer: C
Plasma proteins, especially albumin, generate colloid osmotic pressure that retains water in blood vessels.
16The 'Frank-Starling Law' of the heart relates the stroke volume to:
NUMS 2023 (Advanced Tier)
  • A. Heart rate
  • B. Arterial blood pressure
  • C. End-diastolic volume (degree of stretch)
  • D. Total peripheral resistance
Answer: C
Frank-Starling: increased venous return stretches the heart, leading to stronger contraction and increased stroke volume.
17Chordae tendineae are found in:
MDCAT 2015 (UHS)
  • A. Atria of the heart
  • B. Ventricles of the heart
  • C. Only the right atrium
  • D. Aorta and Pulmonary trunk
Answer: B
Chordae tendineae anchor AV valve cusps to papillary muscles within the ventricles.
18The thickest layer of the wall of an artery is the:
NUMS 2018
  • A. Tunica intima
  • B. Tunica media
  • C. Tunica externa
  • D. Endothelium
Answer: B. Tunica media
Arteries have a thick tunica media of smooth muscle and elastic fibers to withstand pressure.
19Which chamber of the heart receives oxygenated blood from the lungs via the pulmonary veins?
MDCAT 2022
  • A. Right Atrium
  • B. Right Ventricle
  • C. Left Atrium
  • D. Left Ventricle
Answer: C. Left Atrium
Pulmonary veins carry oxygenated blood to the left atrium.
20The 'P-wave' of an ECG is caused by:
NUMS 2021
  • A. Atrial depolarization
  • B. Ventricular depolarization
  • C. Atrial repolarization
  • D. Ventricular repolarization
Answer: A. Atrial depolarization
P-wave represents atrial depolarization and contraction.
21In the human heart, the tricuspid valve is situated between the:
MDCAT 2017 (UHS)
  • A. Left atrium and left ventricle
  • B. Right atrium and right ventricle
  • C. Left ventricle and aorta
  • D. Right ventricle and pulmonary artery
Answer: B
The tricuspid valve separates the right atrium and right ventricle.
22Which of the following is NOT a component of the lymphatic system?
NUMS 2020
  • A. Spleen
  • B. Pancreas
  • C. Thymus
  • D. Tonsils
Answer: B. Pancreas
Pancreas is an exocrine/endocrine gland, not part of the lymphatic system.
23The hepatic portal vein carries blood from the ______ to the ______.
MDCAT 2023
  • A. Liver; Heart
  • B. Kidney; Liver
  • C. Intestine; Liver
  • D. Liver; Intestine
Answer: C
Hepatic portal vein transports nutrient-rich blood from digestive tract to the liver.
24The coronary arteries arise from the base of the:
NUMS 2022
  • A. Pulmonary artery
  • B. Aorta
  • C. Superior vena cava
  • D. Left ventricle
Answer: B. Aorta
Coronary arteries branch from the ascending aorta just above the aortic valve.
25Ventricular repolarization is represented on an ECG by the:
MDCAT 2020
  • A. P-wave
  • B. QRS complex
  • C. T-wave
  • D. PR segment
Answer: C. T-wave
The T-wave corresponds to ventricular repolarization.
26The percentage of the total blood volume occupied by erythrocytes is called:
NUMS 2017
  • A. Blood count
  • B. Hematocrit
  • C. Hemoglobin concentration
  • D. Plasma volume
Answer: B. Hematocrit
Hematocrit is the proportion of blood volume made up of red blood cells.
27Which of the following has the highest pressure?
MDCAT 2018 (UHS)
  • A. Aorta
  • B. Arterioles
  • C. Capillaries
  • D. Venules
Answer: A. Aorta
Aortic pressure is highest (around 120/80 mmHg).
28The duration of the atrial systole in a normal cardiac cycle is:
NUMS 2019
  • A. 0.1 s
  • B. 0.3 s
  • C. 0.4 s
  • D. 0.5 s
Answer: A. 0.1 s
Atrial systole lasts about 0.1 seconds.
29Intercalated discs are a feature of:
MDCAT 2022
  • A. Skeletal muscle
  • B. Smooth muscle
  • C. Cardiac muscle
  • D. Nerve tissue
Answer: C. Cardiac muscle
Intercalated discs connect cardiac muscle cells, allowing synchronized contraction.
30The bicuspid valve is also known as the:
NUMS 2021
  • A. Tricuspid valve
  • B. Mitral valve
  • C. Semilunar valve
  • D. Pulmonary valve
Answer: B. Mitral valve
Bicuspid valve = mitral valve (left atrioventricular valve).
31Heart sounds are produced by the:
MDCAT 2019
  • A. Contraction of the heart muscles
  • B. Flow of blood into the chambers
  • C. Closure of the heart valves
  • D. Firing of the SA node
Answer: C. Closure of the heart valves
Heart sounds are caused by turbulence from valve closure.
32Which organ acts as a 'filter' for the blood, removing old RBCs?
NUMS 2023
  • A. Liver
  • B. Spleen
  • C. Kidney
  • D. Thymus
Answer: B. Spleen
The spleen filters blood and removes aged red blood cells.
33Total peripheral resistance is primarily regulated by:
MDCAT 2023 (PMDC)
  • A. Large arteries
  • B. Arterioles
  • C. Capillaries
  • D. Veins
Answer: B. Arterioles
Arterioles are the main site of resistance regulation due to their muscular walls.
34During the 'Joint Diastole' phase of the cardiac cycle:
NUMS 2018
  • A. Both atria and ventricles are relaxed
  • B. Only the atria are relaxed
  • C. Only the ventricles are relaxed
  • D. The whole heart is contracting
Answer: A
Joint diastole is when all four chambers are relaxed and filling passively.
35In an ECG, the QRS complex occurs during:
MDCAT 2021
  • A. Atrial contraction
  • B. Ventricular contraction
  • C. Ventricular filling
  • D. Atrial filling
Answer: B. Ventricular contraction
QRS complex represents ventricular depolarization, leading to contraction.
36The layer of the heart wall that contains the cardiac muscle fibers is the:
NUMS 2020
  • A. Epicardium
  • B. Myocardium
  • C. Endocardium
  • D. Pericardium
Answer: B. Myocardium
Myocardium is the muscular layer of the heart.
37Which of the following is NOT a function of lymph?
MDCAT 2022
  • A. Transport of oxygen to the brain
  • B. Transport of dietary fats
  • C. Returning proteins to the blood
  • D. Immune defense
Answer: A
Oxygen is transported by blood, not lymph.
38The SA node is located in the wall of the:
NUMS 2022
  • A. Left atrium
  • B. Right atrium
  • C. Left ventricle
  • D. Right ventricle
Answer: B. Right atrium
Sinoatrial node is in the right atrium near the opening of the superior vena cava.
39The pressure in the aorta is highest during:
MDCAT 2017
  • A. Atrial systole
  • B. Ventricular systole
  • C. Ventricular diastole
  • D. Joint diastole
Answer: B. Ventricular systole
Aortic pressure peaks during ventricular systole when blood is ejected.
40White pulp of the spleen is primarily involved in:
NUMS 2023
  • A. RBC destruction
  • B. Blood storage
  • C. Immune response
  • D. Bile production
Answer: C. Immune response
White pulp contains lymphocytes and is involved in immune functions.
41The amount of blood remaining in the ventricle after contraction is the:
MDCAT 2023
  • A. End-diastolic volume
  • B. Stroke volume
  • C. End-systolic volume
  • D. Cardiac output
Answer: C. End-systolic volume
End-systolic volume (ESV) is the blood left after ejection.
42Which part of the brain controls the heart rate?
NUMS 2019
  • A. Cerebrum
  • B. Medulla Oblongata
  • C. Hypothalamus
  • D. Cerebellum
Answer: B. Medulla Oblongata
The medulla oblongata houses the cardiovascular center regulating heart rate.
43The pulmonary artery carries blood from the:
MDCAT 2016
  • A. Left ventricle to the lungs
  • B. Right ventricle to the lungs
  • C. Left atrium to the lungs
  • D. Right atrium to the lungs
Answer: B. Right ventricle to the lungs
Pulmonary artery carries deoxygenated blood from right ventricle to lungs.
44The internal lining of the heart and blood vessels is composed of:
NUMS 2021
  • A. Cuboidal epithelium
  • B. Columnar epithelium
  • C. Simple squamous epithelium (Endothelium)
  • D. Stratified epithelium
Answer: C. Simple squamous epithelium (Endothelium)
Endothelium is simple squamous epithelium lining the cardiovascular system.
45A person with blood group AB has:
MDCAT 2022
  • A. Anti-A and Anti-B antibodies
  • B. No antibodies in plasma
  • C. No antigens on RBCs
  • D. Only A antigens
Answer: B. No antibodies in plasma
Blood group AB has both A and B antigens on RBCs and no antibodies in plasma.
46Which valve prevents the backflow of blood into the left ventricle?
NUMS 2020
  • A. Mitral valve
  • B. Tricuspid valve
  • C. Aortic semilunar valve
  • D. Pulmonary semilunar valve
Answer: C. Aortic semilunar valve
Aortic semilunar valve prevents backflow from aorta into left ventricle.
47The condition where the heart rate is higher than 100 bpm is called:
MDCAT 2020
  • A. Bradycardia
  • B. Tachycardia
  • C. Myocardial Infarction
  • D. Hypertension
Answer: B. Tachycardia
Tachycardia is a resting heart rate above 100 bpm.
48Lymph from the majority of the body is returned to the blood via the:
NUMS 2022
  • A. Right lymphatic duct
  • B. Thoracic duct
  • C. Superior vena cava
  • D. Hepatic vein
Answer: B. Thoracic duct
The thoracic duct drains lymph from the entire body except the right upper quadrant.
49The 'Plateau Phase' in a cardiac muscle action potential is due to the influx of:
MDCAT 2023 (PMDC)
  • A. Na⁺ ions
  • B. K⁺ ions
  • C. Ca²⁺ ions
  • D. Mg²⁺ ions
Answer: C. Ca²⁺ ions
Calcium influx through L-type channels maintains the plateau phase.

🔍Direct Search Queries — Circulation

Exact search terms students use on Google for this chapter. Click any to jump to the relevant section:

circulation MDCAT notes human heart anatomy and function cardiac cycle phases heart sounds S1 S2 ECG waves explained SA node pacemaker function AV node delay significance arteries vs veins vs capillaries cardiac output calculation Frank-Starling law of heart lymphatic system organs primary vs secondary lymphoid organs thoracic duct drainage hepatic portal vein function coronary sinus anatomy fetal circulation shunts foramen ovale ductus arteriosus causes of edema what is circulation in biology difference between systole and diastole what is stroke volume what is ejection fraction function of pericardium what are intercalated discs circulation MCQs with answers circulation MCQs pdf heart MCQs MDCAT past papers circulation UHS MDCAT biology MCQs NUMS biology past papers circulation chapter 11 class 11 notes heart structure class 11 biology lymphatic system class 11 notes

❔Frequently Asked Questions

What is circulation in biology?
Circulation is the continuous movement of blood through the heart and blood vessels, delivering oxygen, nutrients, and hormones to tissues and removing carbon dioxide and waste products. The lymphatic system returns excess interstitial fluid to blood.
What are the 4 chambers of the human heart?
Right atrium (receives deoxygenated blood), right ventricle (pumps to lungs), left atrium (receives oxygenated blood), and left ventricle (pumps to body; thickest wall).
What is the cardiac cycle?
The cardiac cycle is one complete heartbeat lasting ~0.8 seconds: atrial systole (0.1 s), ventricular systole (0.3 s), and joint diastole (0.4 s).
What is the difference between S1 and S2 heart sounds?
S1 ('Lubb') is caused by closure of AV valves at the start of ventricular systole. S2 ('Dubb') is caused by closure of semilunar valves at the start of ventricular diastole.
What do the ECG waves represent?
P-wave: atrial depolarization. QRS complex: ventricular depolarization (atrial repolarization hidden). T-wave: ventricular repolarization.
Which node is the pacemaker of the heart?
The SA (sinoatrial) node is the pacemaker, generating impulses at ~70 bpm. It is located in the right atrium wall.
What is the difference between arteries and veins?
Arteries carry blood away from the heart, have thick muscular walls, high pressure, no valves. Veins carry blood toward the heart, have thin walls, low pressure, and valves.
Where does gas exchange occur?
In capillaries — one cell-thick vessels with the slowest blood flow and largest total cross-sectional area, allowing diffusion.
What is cardiac output?
Cardiac output = Stroke Volume × Heart Rate. Average at rest is ~5 L/min (70 mL × 72 bpm).
What is the Frank-Starling Law?
Increased venous return stretches the heart (↑EDV), causing stronger contraction (↑stroke volume). The heart pumps what it receives.
What are the functions of the lymphatic system?
Returns excess interstitial fluid to blood, transports dietary fats (lacteals), and provides immune defense (lymph nodes, spleen, thymus).
What is the difference between primary and secondary lymphoid organs?
Primary (bone marrow, thymus): where lymphocytes mature. Secondary (lymph nodes, spleen, tonsils, Peyer's patches): where immune responses occur.
Which duct drains most of the body's lymph?
The thoracic duct drains the entire body except the right upper quadrant and empties into the left subclavian vein.
What is the hepatic portal vein?
A vein carrying nutrient-rich blood from the digestive tract to the liver for processing before it enters general circulation. It does not carry oxygenated blood.
What are fetal shunts?
Foramen ovale (RA→LA, bypasses lungs), ductus arteriosus (pulmonary artery→aorta), ductus venosus (umbilical vein→IVC, bypasses liver).
How many MCQs come from Circulation in MDCAT?
Circulation typically contributes 4–6 MCQs out of 81 Biology MCQs in MDCAT.
Which topics from Circulation are most frequently asked in MDCAT?
Cardiac cycle phases, S1/S2 heart sounds, ECG waves, SA node, valve locations, arteries vs veins, capillary function, cardiac output, thoracic duct, fetal shunts, and edema causes.
What causes edema?
Edema is caused by increased capillary hydrostatic pressure, decreased plasma proteins (lowering osmotic pressure), increased capillary permeability, or lymphatic blockage.
What is the coronary sinus?
It is a collection of veins that drain deoxygenated blood from the heart muscle into the right atrium.
What is blood pressure?
Blood pressure is the force exerted by circulating blood on vessel walls. Normal is ~120/80 mmHg (systolic/diastolic). Systolic is during ventricular contraction; diastolic is during relaxation.

📚Other Biology Chapters

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Biodiversity
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Bioenergetics
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4
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5
Coordination & Control
6
Enzymes
11
Homeostasis
15
Immunity

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