31 Years NEET Previous Year Questions: Body Fluids & Circulation - 1 Free

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.

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.

• 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.

The P-wave in the ECG represents the electrical activity associated with depolarisation of the atria.

• 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.

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.

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

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.

Correct option: C

Neutrophils are the most abundant type of white blood cells and constitute about 60-65% of total leukocytes.

Monocytes account for approximately 6-8% of the leukocyte population.

Lymphocytes make up about 20-25% of total white blood cells.

Eosinophils are present in smaller numbers, roughly 2-3%.

Thus the correct matching is A-II, B-III, C-IV, D-I, which corresponds to option 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.

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

• 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.

• 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.

Fibrins are formed by the conversion of inactive fibrinogens in the plasma by the enzyme thrombin.

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.

Stroke volume = End diastolic volume - End systolic volume
= 100 - 50 = 50 mL
Cardiac output = Heart beat x stroke volume
∴ Heart beat = Cardiac output/Stroke volume = 5000 / 50 = 100 beats per minute

Arter y is blood vessel which receives blood from heart, has elastic thick wall shows jerky movements due to pumping activity of heart. Vein is a blood vessel which carries blood towards the heart, has wider lumen with internal valves where blood flows smoothly and slowly. Blood capillary is a very fine blood vessel which has a single layered wall. Pulmonary veins are the only veins which carry oxygenated blood. (_PO₂ = 95 mmHg, _PCO₂ = 40 mmHg)

B-lymphocytes cells are involved in antibody production.

The P-wave represents the electrical excitation (or depolarisation) of the atria, which leads to the contraction of both the atria. 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.

Spleen is an organ of the lymphatic system located in the left side of the abdominal cavity under the diaphragm, the muscular partition between the abdomen and the chest. It is called graveyard of RBC because fragment of red blood cells, old and dead cells are constantly being removed from the blood streams by it.

70% to 75% CO₂ is transported as primary buffer of the blood. Bicarbonate ion (HCO₃) in blood plasma. When CO₂ diffuses from tissues into blood then it is acted upon by the enzyme carbonic anhydrase.

P wave is formed when the atria (the two upper chambers of the heart) contract to pump blood into the ventricles. 

QRS Complex is formed when the ventricles (the two lower chambers of the heart) are contracting to pump out blood. It is one complete pulse.

ST segment measures the end of the contraction of the ventricles to the beginning of the rest period before the ventricles begin to contract for the next beat.

T wave measures the resting period of the ventricles.

So, the correct answer is option C.

Hypertension is the term for blood pressure that is higher than normal (120/80). In this measurement, 120 mm Hg (millimeter of mercury pressure) is the systolic, or pumping, pressure and 80 mm Hg is the diastolic, or resting pressure. If repeated checks of blood pressure 190/100 mm Hg) of an individual is 140/90 (140 over 90) or higher, it shows hypertension. High blood pressure (190/100 mm Hg) leads to heart diseases and also affects vital organs like brain and kidney. 

Arteries are best defined as the vessels which break up into capillaries which reunite to form a vein.
Arteries are the blood vessels which carry oxygenated blood from the heart to the organs. It breaks up into several branches of capillaries before entering the organs. These capillaries again reunite to form venules and ultimately veins which carry the deoxygenated blood towards the heart. 

Fibrinogen, the protein of blood plasma is converted to insoluble protein fibrin during the clotting process. The fibrinogen free fluid obtained after removal of the clot, called blood serum is plasma minus fibrinogen.

‘Bundle of His’ are a typical cardiac muscle fibres, connecting the atria with ventricle.

Blood transports oxygen from respiratory organs to the tissue cells and also transports carbon dioxide from the tissue cells to the respiratory membrane. About 97% of oxygen is transported by RBCs in the blood while the remaining three percent of oxygen is carried in a dissolved state through plasma. Nearly 20-25% of carbon dioxide is transported by RBCs whereas 70% is carried as bicarbonate. About 7% of CO₂ is carried in dissolved state through plasma.

Tricuspid valve is the valve in the heart between the right atrium and right ventricle. The valve opens to allow blood to flow from atrium into the ventricle. Thus if tricuspid valve is partially nonfunctional, then the flow of blood into the pulmonary artery will be reduced

The three calle/es in ABO blood groups in humans can produce six different genotypes and four different phenotypes

In a standard ECG, the P-wave is a small upward wave that indicates the depolarisation of the atria. This is caused by the activation of SA node.