What is the main organ of the circulatory system?
A) Brain
B) Heart ✅
C) Kidney
D) Lung Explanation: The heart is the central organ that pumps blood throughout the body.
Which blood vessels carry blood away from the heart?
A) Veins
B) Capillaries
C) Arteries ✅
D) Venules Explanation: Arteries carry oxygen-rich blood away from the heart to the body.
Which component of blood helps in oxygen transport?
A) Platelets
B) White blood cells
C) Red blood cells ✅
D) Plasma Explanation: Red blood cells contain hemoglobin, which binds to oxygen for transport.
How many chambers does the human heart have?
A) 2
B) 3
C) 4 ✅
D) 5 Explanation: The heart has four chambers—two atria and two ventricles.
Which side of the heart pumps deoxygenated blood to the lungs?
A) Left
B) Right ✅
C) Top
D) Bottom Explanation: The right side of the heart pumps blood to the lungs for oxygenation.
What type of blood do pulmonary arteries carry?
A) Oxygenated
B) Deoxygenated ✅
C) Mixed
D) Nutrient-rich Explanation: Pulmonary arteries carry deoxygenated blood to the lungs.
The fluid part of blood is called:
A) Platelet
B) Plasma ✅
C) Serum
D) Lymph Explanation: Plasma is the liquid portion of blood that carries cells and nutrients.
Which blood cells fight infection?
A) Red blood cells
B) White blood cells ✅
C) Platelets
D) Plasma Explanation: White blood cells (leukocytes) defend the body against infections.
What valve prevents backflow between the left atrium and left ventricle?
A) Tricuspid
B) Pulmonary
C) Mitral (Bicuspid) ✅
D) Aortic Explanation: The mitral valve allows blood to flow from the left atrium to the left ventricle.
Which part of the heart receives oxygen-poor blood?
A) Left atrium
B) Right atrium ✅
C) Left ventricle
D) Right ventricle Explanation: The right atrium receives deoxygenated blood from the body.
What does a red blood cell lack?
A) Nucleus ✅
B) Cytoplasm
C) Cell membrane
D) Hemoglobin Explanation: Mature red blood cells lack a nucleus to maximize space for hemoglobin.
What is the function of platelets?
A) Fight infections
B) Carry oxygen
C) Aid in blood clotting ✅
D) Maintain blood pressure Explanation: Platelets are involved in clot formation to prevent bleeding.
What is the normal human blood pressure reading?
A) 90/60 mmHg
B) 120/80 mmHg ✅
C) 140/90 mmHg
D) 160/100 mmHg Explanation: A typical healthy adult blood pressure is 120/80 mmHg.
Where is the human heart located?
A) Right chest
B) Center of the chest
C) Slightly left of center ✅
D) Abdomen Explanation: The heart is located slightly to the left of the midline in the chest.
Which blood vessel returns blood to the heart from the body?
A) Pulmonary artery
B) Aorta
C) Vena cava ✅
D) Coronary artery Explanation: The superior and inferior vena cava bring deoxygenated blood to the heart.
Which part of the blood is responsible for nutrient transport?
A) Plasma ✅
B) Platelets
C) Red blood cells
D) White blood cells Explanation: Plasma transports nutrients, hormones, and waste products.
Which circuit carries blood between the heart and lungs?
A) Coronary
B) Systemic
C) Pulmonary ✅
D) Renal Explanation: The pulmonary circuit carries blood from the heart to the lungs and back.
What is the thickest part of the heart wall?
A) Endocardium
B) Epicardium
C) Myocardium ✅
D) Pericardium Explanation: The myocardium is the muscular layer responsible for heart contractions.
Which artery supplies the heart muscle with blood?
A) Pulmonary artery
B) Aorta
C) Coronary artery ✅
D) Carotid artery Explanation: Coronary arteries supply blood to the heart muscle.
Which chamber pumps oxygen-rich blood to the body?
A) Right atrium
B) Right ventricle
C) Left ventricle ✅
D) Left atrium Explanation: The left ventricle pumps oxygenated blood into the aorta for systemic circulation.
🟡 Moderate Level (Questions 21–40)
What structure separates the left and right sides of the heart?
A) Valve
B) Septum ✅
C) Atrium
D) Ventricles Explanation: The septum is a wall that divides the left and right sides of the heart.
What is the largest artery in the human body?
A) Carotid
B) Aorta ✅
C) Pulmonary
D) Femoral Explanation: The aorta is the main artery that distributes oxygenated blood to the body.
What triggers the heartbeat?
A) AV node
B) SA node ✅
C) Bundle of His
D) Purkinje fibers Explanation: The SA node acts as the pacemaker, initiating each heartbeat.
Which blood group is known as the universal donor?
A) A
B) B
C) AB
D) O negative ✅ Explanation: O negative blood can be given to any other blood group.
Which vessel has valves to prevent backflow of blood?
A) Arteries
B) Veins ✅
C) Capillaries
D) Arterioles Explanation: Veins have valves to keep blood flowing toward the heart.
The lymphatic system drains into which circulatory vessel?
A) Aorta
B) Subclavian vein ✅
C) Pulmonary vein
D) Jugular artery Explanation: The lymphatic system empties into the subclavian veins near the heart.
Which vitamin is essential for blood clotting?
A) Vitamin A
B) Vitamin B12
C) Vitamin C
D) Vitamin K ✅ Explanation: Vitamin K is needed to synthesize clotting factors in the liver.
Which component makes up most of the blood volume?
A) RBCs
B) WBCs
C) Plasma ✅
D) Platelets Explanation: Plasma makes up about 55% of total blood volume.
What causes the “lub-dub” sound of the heart?
A) Muscle contractions
B) Valve closure ✅
C) Blood flow
D) Electrical impulses Explanation: The “lub” is caused by AV valve closure; the “dub” is semilunar valve closure.
Which organ produces most plasma proteins?
A) Heart
B) Kidney
C) Liver ✅
D) Spleen Explanation: The liver synthesizes proteins like albumin and fibrinogen.
What condition is characterized by narrowed coronary arteries?
A) Anemia
B) Atherosclerosis ✅
C) Hypertension
D) Myocarditis Explanation: Atherosclerosis involves plaque buildup that narrows coronary arteries.
What does ECG stand for?
A) Electrocardiogram ✅
B) Electrocardiograph
C) Electromyogram
D) Echocardiogram Explanation: ECG records the electrical activity of the heart.
Which blood cell is most numerous in the human body?
A) White blood cell
B) Platelets
C) Red blood cells ✅
D) Lymphocytes Explanation: RBCs are the most abundant cells in the blood.
Which artery supplies blood to the brain?
A) Carotid ✅
B) Brachial
C) Renal
D) Femoral Explanation: Carotid arteries carry oxygenated blood to the brain.
What is anemia primarily caused by?
A) Low WBCs
B) Low RBCs or hemoglobin ✅
C) Clotting deficiency
D) Infection Explanation: Anemia results from reduced oxygen-carrying capacity due to low hemoglobin or RBC count.
Which part of the ECG represents ventricular contraction?
A) P wave
B) T wave
C) QRS complex ✅
D) U wave Explanation: The QRS complex shows ventricular depolarization (contraction).
Which heart valve opens into the aorta?
A) Tricuspid
B) Mitral
C) Pulmonary
D) Aortic ✅ Explanation: The aortic valve opens from the left ventricle into the aorta.
Which ion is essential for muscle contraction in the heart?
A) Sodium
B) Calcium ✅
C) Potassium
D) Chloride Explanation: Calcium ions facilitate contraction of cardiac muscle fibers.
Which layer lines the inner surface of blood vessels?
A) Tunica media
B) Tunica adventitia
C) Tunica intima ✅
D) Endothelium Explanation: The tunica intima (endothelium) lines the blood vessels’ inner surface.
What hormone increases heart rate?
A) Insulin
B) Cortisol
C) Adrenaline (Epinephrine) ✅
D) Thyroxine Explanation: Adrenaline stimulates the heart to beat faster during stress or exertion.
🔴 Hard Level (Questions 41–50)
What is the function of the Purkinje fibers?
A) Pump blood
B) Transmit nerve signals
C) Conduct electrical impulses in ventricles ✅
D) Carry oxygen Explanation: Purkinje fibers rapidly conduct impulses to ensure synchronized ventricular contraction.
Which protein in RBCs binds oxygen?
A) Globulin
B) Myoglobin
C) Albumin
D) Hemoglobin ✅ Explanation: Hemoglobin is the oxygen-carrying molecule in red blood cells.
What is the lifespan of a red blood cell?
A) 10 days
B) 60 days
C) 120 days ✅
D) 180 days Explanation: RBCs circulate for about 120 days before being broken down.
Which heart structure prevents overfilling?
A) AV node
B) Pericardium ✅
C) Pulmonary valve
D) Septum Explanation: The pericardium is a protective sac that limits overexpansion.
Which condition is caused by abnormal heart rhythm?
A) Tachycardia
B) Arrhythmia ✅
C) Stroke
D) Embolism Explanation: Arrhythmia refers to irregular or abnormal heart rhythms.
Which cell fragments help in clot formation?
A) Leukocytes
B) Platelets (Thrombocytes) ✅
C) Erythrocytes
D) Lymphocytes Explanation: Platelets play a critical role in blood clotting.
The Frank-Starling law relates to:
A) Nerve conduction
B) Cardiac output and stretch ✅
C) Valve function
D) Clotting Explanation: The law describes how increased venous return stretches heart muscle, increasing force of contraction.
Which cardiac enzyme is a marker of heart attack?
A) Lipase
B) Troponin ✅
C) Amylase
D) Pepsin Explanation: Elevated troponin levels indicate damage to heart muscle cells.
Which part of the ECG shows atrial contraction?
A) QRS complex
B) T wave
C) P wave ✅
D) ST segment Explanation: The P wave represents depolarization (contraction) of the atria.
Which condition is caused by fluid accumulation around the heart?
A) Pericarditis
B) Cardiac tamponade ✅
C) Myocardial infarction
D) Cardiomyopathy Explanation: Cardiac tamponade is a life-threatening condition where fluid compresses the heart.