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1. Which of the following is an example of primary active transport?
a. Na+ – H+ exchanges
b. Na+ – Ca2+ exchange
c. The Na+/K+ ATPase
d. Cl—HCO3- exchange
e. None of the above
Correct Answer: The Na+/K+ ATPase
The Na+/ K+ ATPase is the sodium pump and exchanges 3 intracellular Na+ for 2 extracellular K+ each molecule of ATP hydrolyzed
Na+-H+ exchange and Na+-Ca2+ exchange are examples of secondary active transport
Cl–HCO3- exchange is passive and is driven by the prevailing electrochemical gradients
2. During the process of excitation-contraction coupling:
a. Release of Ca2+ causes the binding sites on the thin filaments to be uncovered
b. Acetylcholine binds to muscarinic receptors
c. The transverse tubules release Ca2+ in response to depolarization of the cell through an unknown mechanism
d. Cross-bridges form when ATP binds to myosin
Correct answer: (a.) Release of Ca2+ causes the binding sites on the thin filaments to be uncovered
– Ca2+ binds to troponin, inducing a conformational change that is transmitted to tropomyosin. Tropomyosin shifts and exposes the myosin binding sites, so that cross-bridge cycling can occur
– Acetylcholine binds to nicotinic receptors at the motor end plate
– Located in the T-tubule membrane, closely associated with the foot of the SR Ca2+ channel, is the T-tubule voltage sensor. The voltage sensor changes conformation in response to the depolarization of the action potential. This conformational change is transmitted to the foot of the SR Ca2+ channel, causing it to open and allowing Ca2+ Note that this direct mechanical interaction between the T-tubule voltage sensor and the SR Ca2+ channel is specific for excitation-contraction coupling in skeletal muscle. There are different mechanisms and different sources of Ca2+ used in smooth muscle excitation-contraction coupling. Thus, the mechanism of Ca2+ release is known.
– Cross-bridges form between the actin filaments and the myosin head
A. Have membranes similar to the cell membrane.
B. Are the chief site for protein synthesis.
C. Are the chief sites for generation of ATP.
D. Are more numerous in brown than in white fat cells.
E. Are absent near the membranes of actively secreting cells.
A. True – Both membranes have the same lipid bilayer structure.
B. False – This applies to the ribosomes.
C. True – ATP is formed by oxidative phosphorylation.
D. True – Brown fat cells can generate energy, and hence heat, more rapidly.
E. False – They are concentrated where most energy is required.
4. The elastic recoil of muscles and tendons in the legs
A. Increases jumping height when someone jumps from a height immediately before take off.
B. Improves performance during sprinting.
C. Contributes more to performance when sprinting on a cinder track than on a concrete surface.
D. Can be improved by training.
E. Is greater in weight lifters than in skiers.
A. True – The elastic tissue in extensor muscles is stretched by the initial downward jump.
B. True – Elastic recoil aids the activity independently of muscular contractions.
C. False – The concrete surface ‘reflects’ more of the energy stored during landing the foot on the surface.
D. True – Training which stretches the muscles achieves this.
E. False – Compared with skiers, weight lifters produce little muscle stretch and rebound during training.
5. Normal blood clotting requires
A. Inactivation of heparin.
B. Inactivation of plasmin (fibrinolysin).
C. Calcium ions.
D. An adequate intake of vitamin K.
E. An adequate intake of vitamin C.
A. False – The anticoagulant effects of heparin are overwhelmed.
B. False – Blood clots in spite of the fibrinolytic system.
C. True – Removal of calcium ions prevents clotting.
D. True – Vitamin K is needed by the liver for synthesis of prothrombin and other factor
E. False – The spontaneous bleeding from the gums etc. seen in scurvy is due to capillary abnormality, not a clotting defect.
6. QRS complex in the ECG:
a) Has a normal duration of 0.3 second
b) Has a normal shape in cases of bundle branch block
c) Is due to ventricular depolarization
d) Is due to ventricular systole
e) Represents atrial repolarization
Correct answer: (c) QRS complex occurs due to ventricular depolarization
A. False: QRS complex has a normal duration of 0.1 to 0.12 second
C. True: QRS complex occurs due to ventricular depolarization
E. P wave represents atrial depolarization
7. Adrenaline secretion from the adrenal glands increases the
A. Blood glucose level
B. Blood free fatty acid level.
C. Blood flow to skeletal muscle.
D. Blood flow to the splanchnic area.
E. Release of renin in the kidneys
A. True – By promoting glycogenolysis in the liver
B. True – By promoting lipolysis in the fat stores
C. True – By its predominant effect on beta-receptors in the smooth muscle of skeletal muscle arterioles
D. False – Splanchnic flow falls since alpha-receptors predominate in splanchnic arterioles.
E. True – Juxtaglomerular cells respond to beta-receptor stimulation by releasing renin.
8. Secretion of gastric juice
A. Increases when food stimulates mucosal cells in the pyloric region.
B. Is associated with a decrease in the pH of venous blood draining the stomach.
C. In response to food is reduced after vagotomy.
D. Is essential for protein digestion.
E. Is essential for absorption of vitamin B12
A. True – Cells in the pylorus release gastrin when food enters the stomach.
B. False – Venous blood pH rises as bicarbonate enters the circulation in the ‘alkaline tide’.
C. True – Vagal activity plays an important role in gastric juice secretion.
D. False – Pancreatic trypsin and chymotrypsin can digest proteins.
E. True – Without gastric ‘intrinsic factor’, Vitamin B12 is not absorbed from the gut.
9. When a patient’s mean arterial blood pressure falls by 50 per cent
a. Renal blood flow falls by less than 10 per cent.
b. Glomerular filtration falls by about 50 per cent.
c. There is an increase in the circulating aldosterone level.
d. Renal vasoconstriction occurs.
e. Urinary output ceases
A. False – Autoregulation cannot compensate for such large falls.
B. False – It falls to about zero when glomerular capillary pressure falls below the sum of intra-capsular pressure plus plasma oncotic pressure – around 30–40 mmHg.
C. True – Due to release of renin and angiotensin formation, aldosterone is secreted.
D. True – Reflex sympathetic vasoconstriction due to greatly decreased baroreceptor stimulation.
E. True – When glomerular filtration stops, urinary output stops.
10. Blockade of parasympathetic activity causes a reduction in
A. Sweat production.
B. Resting heart rate.
C. The strength of skeletal muscle contraction.
E. Intestinal motility.
A. False – Sweat glands are innervated by sympathetic cholinergic nerves.
B. False – Resting heart rate rises due to blockade of vagal tone.
C. False – Parasympathetic nerves are not involved in skeletal muscle activity.
D. True – Dryness of the mouth results from blockade of salivary secretion.
E. True – Parasympathetic nerves are motor to intestinal smooth muscle.