NEET Previous Year Questions (2016-2025): Body Fluids & Circulation

Ans: (c)

• A. Nodal tissue: The heart has specialized nodal tissues, such as the sinoatrial (SA) node and atrioventricular (AV) node, which generate and conduct electrical impulses. The SA node is known as the natural pacemaker of the heart, initiating rhythmic contractions. This is a critical intrinsic mechanism for regulating heart activity.
• B. A special neural center in the medulla oblongata: The medulla oblongata in the brainstem contains the cardiovascular center that regulates heart rate and blood pressure. This center has two components: the cardiac accelerator center (sympathetic stimulation increases heart rate) and the cardiac inhibitory center (parasympathetic stimulation decreases heart rate). This represents the extrinsic neural regulation of the heart.
• C. Adrenal medullary hormones: Hormones such as adrenaline and noradrenaline secreted by the adrenal medulla play a vital role in increasing heart rate and the force of cardiac contractions during stress or emergencies, part of the "fight or flight" response.

• D. Adrenal cortical hormones: These hormones, such as cortisol and aldosterone, are involved in long-term stress responses and electrolyte balance, but they do not play a direct role in the immediate regulation of cardiac activities. Therefore, this option is incorrect.

Ans: (a)
The electrical pathway for the conduction of an action potential through the heart is a precisely coordinated process, essential for maintaining the heart's rhythmic beating. To understand this conduction pathway, it's important to know the roles of the specific components involved:

SA node (Sinoatrial node): Often referred to as the pacemaker of the heart. It initiates the electrical impulse, causing the atria to contract.
AV node (Atrioventricular node): Receives the impulse from the SA node and provides a slight delay, allowing the ventricles time to fill with blood before they contract.
AV bundle (Bundle of His): Transfers the electrical impulse from the AV node to the bundle branches.
Bundle branches: Conducts the impulses through the interventricular septum.
Purkinje fibers: Distribute the electrical impulse throughout the ventricles, stimulating them to contract uniformly and powerfully.

The correct sequence for the pathway of an action potential through the heart follows a route designed to efficiently coordinate the heartbeat starting from the initiation of the action potential to the consequential contraction of the heart muscles. The sequence is:

SA node (E): The pacemaker where the electrical activity originates.
AV node (C): Where the impulse is delayed slightly.
AV bundle (A): Conducts the impulse from the AV node to the bundle branches.
Bundle branches (D): Leads the impulse to the Purkinje fibers.
Purkinje fibers (B): Distributes the impulse throughout the ventricles.

Ans: (a)

• P wave represents depolarisation of atria.

• QRS complex represents depolarisation of ventricles.

• T wave represents repolarisation of ventricles.

• T-P gap represents the time when heart muscles are electrically silent.

Ans: (a)
The P-wave in the ECG represents the electrical activity associated with depolarisation of the atria.

Ans: (d)

• Tricuspid valves guard the opening between right atrium and right ventricle.

• Sino-atrial node is the cardiac musculature in the right upper corner of the right atrium.

• Mitral valves guard the opening between the left atrium and left ventricle.

• Semilunar valves guard the opening of the ventricles into the pulmonary artery and aorta.

Ans: (d)
The 'Lub' sound occurs due to the closure of the tricuspid and bicuspid (mitral) valves during the start of systole, preventing backflow of blood into the atria.

Ans: (a)

• P-wave: Depolarisation of atria
• Q-wave: Beginning of systole
• QRS complex: Depolarisation of ventricles
• T-wave: Repolarisation of ventricles

Ans: (c)
The correct answer is Option C : B and C only.

• Statement A is incorrect. Basophils are actually the least abundant cells of the total white blood cells (WBCs), not the most abundant.
• Statement B is correct. Basophils do secrete histamine, serotonin, and heparin. Histamine and serotonin are involved in inflammatory response, while heparin is an anticoagulant.
• Statement C is also correct. Basophils are involved in the inflammatory response. They release chemicals such as histamine and serotonin that dilate blood vessels and attract other white blood cells to the site of inflammation.
• Statement D is incorrect. Basophils do not have a kidney-shaped nucleus. That description is more appropriate for monocytes, another type of white blood cell.
• Statement E is incorrect. Basophils are not agranulocytes. They are granulocytes, a category of white blood cells characterized by the presence of granules in their cytoplasm. Agranulocytes, which lack visible cytoplasmic granules, include lymphocytes and monocytes.

Ans: (c) 

Neutrophils are the most abundant, around 60-65%.

Monocytes make up about 6-8%.

Lymphocytes make up about 20-25%.

Eosinophils make up about 2-3%.

Ans: (c)

• Option (c) is the correct answer because coagulum or clot is formed mainly of a network of threads called fibrins. Hence, Statement I is incorrect.
• RBCs are destroyed in the spleen so spleen is known as the graveyard of erythrocytes. Hence, Statement II is correct.

Ans: (b)

• Option (a) is incorrect because bicuspid and tricuspid valves open due to pressure exerted by blood present in atria and decrease in pressure in ventricles during ventricular diastole.
• Option (b) is the correct answer because during joint diastole, blood moves freely from atrium to ventricle as atrioventricular valve remain open during joint diastole.
• Option (c) is incorrect because decrease in ventricular pressure, during ventricular diastole closes semilunar valves to produce 'dub' heart sound.
• Option (d) is incorrect because SA node generates action potential to stimulate atrial contraction.

Ans: (c)

• Option (c) is the correct answer because hepatic portal system is a unique vascular connection between digestive tract and liver.
• Option (a) is not correct because hepato-cystic system is part of biliary pathway where common hepatic duct joins cystic duct of gall bladder.
• Option (b) is incorrect because hepato-pancreatic system is a part of biliary pathway where common bile duct fuses with pancreatic duct.
• Option (d) is incorrect because renal portal system is a unique vascular connection between lower parts of the body and kidney.

Ans: (b)
Option (b) is the correct answer as a healthy adult man has, on an average, 5 millions to 5.5 millions of RBCs (erythrocytes) mm^-3 of blood.
Blood normally contains 1,50,000 - 3,50,000 platelets mm^-3.
Neutrophils form 60-65 percent of the total WBCs, monocytes form 6-8 percent of the total WBCs and eosinophils form 2-3 percent of the total WBCs. The total WBCs are approximately 6000-8000 mm^-3 of blood.
Thus, the formed elements in the decreasing order of their abundance in blood in humans: -
Erythrocytes - Platelets - Neutrophils - Monocytes - Eosinophils

Ans: (b)
Individuals with the AB blood group have both A and B antigens on the surface of their red blood cells (RBCs). Since they do not have anti-A and anti-B antibodies in their plasma, they can receive blood from any blood group (A, B, AB, or O) without experiencing an immune reaction. Hence, they are referred to as "universal recipients.

Ans: (c)

• During coagulation of blood, an enzyme complex thrombokinase helps in the conversion of prothrombin (present in plasma) into thrombin.
• Thrombin further helps in the conversion of inactive fibrinogens into fibrins which form network of threads.
• Renin is secreted by JG cells in response to fall in glomerular blood flow, which converts angiotensinogen in blood to angiotensin-I
• Epinephrine or adrenaline is secreted by adrenal medulla in response to stress of any kind and during emergency.

Ans: (a)
The QRS complex represents the depolarisation of the ventricles, which initiates the ventricular contraction. The contraction starts shortly after Q and marks the beginning of the systole.

Ans: (c)
Eosinophils are associated with allergic reactions and release histaminase, Basophils secrete histamine, serotonin, heparin etc. and are involved in inflammatory reactions, Neutrophils are phagocytic cells; Both B and T lymphocytes are responsible for immune responses of the body.

Ans: (b)
P wave represent atrial depolarization.
QRS complex '' ventricular ''.
T - wave '' repolarisation of ventricles.
Reduction in the size of T-wave indicates coronary ischemia.

Ans: (d)
Cardiac output = Stroke volume ×  Heart rate
Where stroke volume = End diastolic volume - End systolic volume
= 100 ml - 50 ml
= 50 ml
∴  5000 mL = 50 mL × Heart rate
⇒  Heart rate = 5000 / 50  = 100 beats per minute.

Ans: (a)
The opening between the right atrium and the right ventricle is guarded by a valve formed of three muscular flaps or cusps, the tricuspid valve, whereas a bicuspid or mitral valve guards the opening between the left atrium and the left ventricle.

Ans. (d)

• Fibrinogen is a protein present in the plasma of the blood. It plays an essential role in blood clotting.
• Antibodies are derived from γ-Globulin fraction of plasma proteins which means globulins are involved in defence mechanisms.
• Albumin is a plasma protein mainly responsible for Blood Colloidal Osmotic Pressure (BCOP).

Ans: (d)
Red blood cells of adult humans do not have cell organelles including nucleus, Golgi bodies, mitochondria, ribosomes, etc. It increases the surface area of RBCs and enables them to contain more haemoglobin (the oxygen carrying pigment).

Ans: (c)
In hepatic portal system, hepatic portal vein drains blood to liver from intestine.

Ans: (d)
Thrombocytes are called blood platelets. They are minute disc-shaped cell fragments in mammalian blood. They are formed as fragments of larger cells found in red bone marrow; they have no nucleus. They play an important role in blood clotting and release thromboxane A2 , serotonin and other chemicals, which cause a chain of events leading to the formation of a plug at the site of the damage, thus preventing further blood loss. A reduction in their number can lead to clotting factors which will lead to excessive loss of blood from the body.

Ans: (c)
Serum is the fluid that separates from blood plasma on centrifugation. Serum is essentially similar in composition to plasma but lacks fibrinogen and other substances that are used in the coagulation process.

Ans: (a)
Hepatic Vein, because the liver produces urea and other waste materials and then it pours it all in the right atrium of the heart for oxygenation. The heart distributes the blood to various parts of the body from here. So the impure blood brought by the Hepatic Vein and other blood vessels get distributed through the aorta. This will automatically imply that the Renal Artery will contain lesser impure blood than the Hepatic Vein.

Ans: (c) 
Arteries have higher blood pressure than vein because blood is forced inside them from heart and also their lumen is narrow.

Ans: (c)

• Blood is a connective tissue that is composed of plasma, red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). Plasma is the liquid component of blood that makes up about 55% of the total blood volume. It is composed of water, proteins, salts, hormones, and other substances. Red blood cells carry oxygen to the tissues and remove carbon dioxide, while white blood cells are responsible for immune responses and fighting infections.
• Serum is the liquid component of blood that remains after the blood has clotted and the clotting factors (including fibrinogen) have been removed. Hence, option (a) is incorrect.
• Lymph is a fluid that is similar in composition to plasma but contains a lower concentration of proteins. It is formed from the interstitial fluid that bathes the body tissues and returns to the bloodstream through lymphatic vessels. Hence, option (b) is incorrect.
• Option (d) is also incorrect as plasma cannot be obtained from the subtraction of lymphocytes from blood.