CSIR-NET Life Sciences Unit 7 PYQs: Animal Physiology Questions with Solutions

The SA and AV nodes carry M₂ muscarinic receptors. Vagal acetylcholine acts through G_i: the βγ subunits open GIRK (K_ACh) channels and cAMP falls, which slows the pacemaker potential and the heart rate. N_M receptors are at the skeletal neuromuscular junction.

Each synaptic vesicle releases one quantum of acetylcholine, which produces a small depolarisation of about 0.5 mV at the end plate: the miniature end-plate potential (Fatt and Katz). A nerve impulse releases hundreds of quanta at once, and these add up to the full end-plate potential, which reaches threshold.

Answer: (2) Factor V

Vitamin K is the cofactor for γ-glutamyl carboxylase, which adds the Ca²⁺-binding Gla residues to factors II, VII, IX and X (and to proteins C and S). Factor V is a non-enzymatic cofactor with no Gla domain, so it does not depend on vitamin K. That is why warfarin does not lower factor V.

Answer: (3) Chenodeoxycholic acid

The liver makes the primary bile acids, cholic and chenodeoxycholic acid. Gut bacteria 7α-dehydroxylate them to the secondary bile acids, deoxycholic and lithocholic acid. Ursodeoxycholic acid is also formed by bacteria, by epimerising chenodeoxycholic acid, so it is counted as secondary in humans.

Answer: (3) Renalase

Renalase is a flavoprotein secreted by the kidney into the blood. It breaks down circulating catecholamines and helps regulate blood pressure and heart rate, so it is a renal hormone. Megalin and cubilin are endocytic receptors in the proximal tubule. Uroguanylin is made in the intestine and acts on the kidney.

Answer: (2) 29 pg

Mean corpuscular haemoglobin (MCH) in a healthy adult is about 27–32 picograms per red cell, so about 29 pg. It equals haemoglobin concentration divided by red cell count, for example 15 g/dL ÷ 5 × 10⁶/µL ≈ 30 pg. Values below 27 pg mean hypochromic cells, as in iron deficiency.

Answer: (3) 18-hydroxylase

Only zona glomerulosa cells express aldosterone synthase (CYP11B2). It carries out the final 11β- and 18-hydroxylation and the 18-oxidation that turn corticosterone into aldosterone. The zona fasciculata has 11β-hydroxylase (CYP11B1) and 17α-hydroxylase, so it makes cortisol instead.

Answer: (1) Calcitonin

Calcitonin receptors are G_s-coupled GPCRs. In osteoclasts they raise cAMP, which shuts down bone resorption. Oxytocin acts through G_q (IP₃ and Ca²⁺). Prolactin and leptin bind cytokine-type receptors that signal through JAK–STAT.

Answer: (4) 0.5% NaCl

Plasma is isotonic with about 0.9% NaCl. In a hypotonic solution water enters red cells by osmosis. They first swell, and lysis starts at about 0.45–0.5% NaCl, so 0.5% NaCl causes haemolysis. The 1.0%, 1.5% and 2.0% solutions are isotonic or hypertonic, so cells keep their shape or shrink.

Answer: (2) Increased blood pressure in the afferent arterioles leading to glomerulus.

The juxtaglomerular cells act as a baroreceptor. Higher pressure in the afferent arteriole stretches them and suppresses renin release. Renin is stimulated by sympathetic nerves and circulating catecholamines (β₁ receptors), by prostaglandins (PGE₂, PGI₂), and by low NaCl reaching the macula densa.

Answer: (1) Prostacyclin

Prostacyclin (PGI₂) is made by endothelium. It raises cAMP in vascular smooth muscle and platelets, so it dilates vessels and stops platelets aggregating. It is the physiological opposite of thromboxane A₂ from platelets. Thromboxane A₂, angiotensin II and endothelin-1 are all vasoconstrictors.

Answer: (2) Small, round shaped and dense core

In electron micrographs, acetylcholine and amino-acid transmitters sit in small clear vesicles. Noradrenaline and other catecholamines are stored in small (40–60 nm) dense-core vesicles, whose dark core is the amine. Large dense-core vesicles (about 100 nm) mainly hold neuropeptides. Flattened clear vesicles are typical of inhibitory (GABA and glycine) synapses.

Answer: (3) Oxidized Iodine

Thyroid peroxidase uses H₂O₂ to oxidise iodide (I⁻) to a reactive iodine species at the apical membrane. The same enzyme then attaches it to tyrosine residues of thyroglobulin, forming MIT and DIT (organification), and couples them to T₃ and T₄. Iodide in its reduced form cannot iodinate tyrosine.

Answer: (3) Opening of Na⁺ channels in the outer segment of photoreceptors

In darkness, cGMP is high and holds cGMP-gated Na⁺/Ca²⁺ channels in the outer segment open. Cations flow in, and K⁺ leaves from the inner segment. This standing inward current (the dark current) keeps the rod depolarised at about −40 mV. Light activates PDE, cGMP falls, the channels close and the cell hyperpolarises.

Answer: (2) 2- monoacylglycerols

Pancreatic lipase, anchored by colipase, attacks the ester bonds at positions 1 and 3 of a triacylglycerol. The products are two free fatty acids and 2-monoacylglycerol, which are taken up from micelles and re-esterified to triacylglycerol in the enterocyte.

Answer: (3) Fructose

GLUT5, on the brush border of enterocytes, is a facilitative transporter specific for fructose. Glucose and galactose enter instead by the Na⁺-coupled SGLT1. All three monosaccharides leave across the basolateral membrane through GLUT2. Lactose must first be split by lactase.