Human Physiology I — Digestion, Respiration and Circulation — Practice

Question 1

The dental formula of an adult human is:
(a) 2123/2123 (b) 2122/2122 (c) 2033/2033 (d) 1123/1123

Accepted Answer

(a) 2123/2123.

Each half of each jaw has 2 incisors, 1 canine, 2 premolars and 3 molars, giving 2123/2123 and 32 teeth in total. Human teeth are thecodont, diphyodont and heterodont.

Question 2

Protein digestion begins in the stomach through the action of:
(a) pepsin (b) trypsin (c) salivary amylase (d) pancreatic lipase

Accepted Answer

(a) pepsin.

Pepsin, secreted as inactive pepsinogen and activated by the HCl of gastric juice, begins protein digestion in the stomach, breaking proteins into peptides.

Question 3

Bile aids digestion of fats by:
(a) emulsifying them without any enzyme (b) hydrolysing them to fatty acids (c) converting them to glucose (d) supplying lipase

Accepted Answer

(a) emulsifying them without any enzyme.

Bile contains no digestive enzyme. It emulsifies large fat globules into small droplets, greatly increasing the surface area on which pancreatic lipase can act.

Question 4

The products of fat digestion are absorbed mainly into the:
(a) lacteals (lymph) (b) blood capillaries (c) hepatic portal vein (d) stomach wall

Accepted Answer

(a) lacteals (lymph).

Fatty acids and glycerol re-form into fats inside the intestinal cells, are packaged as chylomicrons, and enter the lacteals (lymphatic vessels of the villi) — unlike glucose and amino acids, which enter the blood directly.

Question 5

The main site of digestion and absorption of food is the:
(a) small intestine (b) stomach (c) large intestine (d) mouth

Accepted Answer

(a) small intestine.

Most enzymatic digestion is completed and nearly all absorption occurs in the small intestine, whose villi and microvilli enormously increase the absorptive surface area.

Question 6

The volume of air inspired or expired during a normal breath is called the:
(a) tidal volume (b) vital capacity (c) residual volume (d) inspiratory reserve volume

Accepted Answer

(a) tidal volume.

Tidal volume (~500 mL) is the air moved in or out in a single normal breath. Reserve volumes are the extra air moved during forced breathing.

Question 7

Vital capacity is equal to:
(a) TV + IRV + ERV (b) TV + IRV + RV (c) IRV + ERV + RV (d) TV + ERV + RV

Accepted Answer

(a) TV + IRV + ERV.

Vital capacity is the maximum air expelled after a maximum inspiration — the sum of tidal volume, inspiratory reserve and expiratory reserve. Residual volume is excluded (adding it gives total lung capacity).

Question 8

About 97% of the oxygen carried in blood is transported as:
(a) oxyhaemoglobin (b) dissolved in plasma (c) bicarbonate (d) carbamino-haemoglobin

Accepted Answer

(a) oxyhaemoglobin.

Roughly 97% of O₂ binds haemoglobin as oxyhaemoglobin; only about 3% is carried dissolved in plasma.

Question 9

The largest fraction of carbon dioxide is transported in blood as:
(a) bicarbonate ions (b) carbamino-haemoglobin (c) dissolved CO₂ (d) carbonic acid

Accepted Answer

(a) bicarbonate ions.

About 70% of CO₂ travels as bicarbonate (HCO₃⁻) in plasma, formed via carbonic anhydrase in the RBCs; ~20–25% is carbamino-haemoglobin and ~7% is dissolved.

Question 10

The respiratory centre that regulates breathing is located in the ______ and responds chiefly to ______.
(a) medulla oblongata; CO₂/H⁺ (b) cerebellum; O₂ (c) hypothalamus; O₂ (d) pons; glucose

Accepted Answer

(a) medulla oblongata; CO₂/H⁺.

The respiratory centre in the medulla oblongata (moderated by the pons) controls breathing rate mainly in response to the CO₂ and H⁺ concentration of the blood, not primarily to oxygen.

Question 11

The blood group regarded as the universal donor is:
(a) O (b) AB (c) A (d) B

Accepted Answer

(a) O.

Group O red cells carry neither A nor B antigen, so they are not attacked by anti-A or anti-B antibodies in a recipient's plasma. Group AB, having no plasma antibodies, is the universal recipient.

Question 12

Erythroblastosis foetalis may occur when:
(a) an Rh⁻ mother carries an Rh⁺ foetus (b) an Rh⁺ mother carries an Rh⁻ foetus (c) both parents are Rh⁻ (d) the mother is blood group O

Accepted Answer

(a) an Rh⁻ mother carries an Rh⁺ foetus.

If an Rh⁻ mother is sensitised to Rh⁺ foetal blood, her anti-Rh antibodies can cross the placenta in a later Rh⁺ pregnancy and destroy the foetal RBCs — erythroblastosis foetalis.

Question 13

The pacemaker of the human heart is the:
(a) SA node (b) AV node (c) bundle of His (d) Purkinje fibres

Accepted Answer

(a) SA node.

The sino-atrial (SA) node in the right atrium initiates each heartbeat and sets the rhythm; the impulse then passes to the AV node, bundle of His and Purkinje fibres. The heart is myogenic.

Question 14

The first heart sound 'lub' is produced by the closure of the:
(a) atrioventricular valves (b) semilunar valves (c) tricuspid valve only (d) bicuspid valve only

Accepted Answer

(a) atrioventricular valves.

The 'lub' (first sound) is the closure of the atrioventricular (tricuspid and bicuspid) valves at the start of ventricular systole; the 'dub' (second sound) is the closure of the semilunar valves.

Question 15

If the stroke volume is 70 mL and the heart rate is 72 beats per minute, the cardiac output is approximately:
(a) 5 L/min (b) 0.5 L/min (c) 50 L/min (d) 1 L/min

Accepted Answer

(a) 5 L/min.

Cardiac output = stroke volume × heart rate = 70 mL × 72 = 5040 mL/min ≈ 5 L/min — the volume of blood each ventricle pumps per minute.

Practice — Human Physiology I — Digestion, Respiration and Circulation

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