801. What is the clearance of a substance when its concentration in plasma is 1 mg/ml, its concentration in urine is 10 mg/ml and the urine flow is 2 mLimin
A. 2 mLimin
B. 10 mLimin
D. 200 mLimin
E. Clearance cannot be determined from the information given

802. Regarding the proximal tubule, the following statements are true except
A. Na is cotransported out of the tubule with glucose
B. Na is actively transported into the intercellular spaces by NaIK ATPase
C. The cells are characterised by a brush border and tight junctions
D. Vasopressin increases the permeability to water by causing the rapid insertion of water channels into the luminal membrane
E. Water moves passively out of the tubule along osmotic gradients

803. With regard to the effect of hormones on renal tubules, which is correct
A. Aldosterone increases K reabsorption from the distal tubule
B. Angiotensin II increases H+ secretion from the proximal tubules
C. ADH increases water reabsorption in the proximal tubule
D. Atrial natriuretic peptide decreases N a reabsorption from the proximal tubules
E. Parathyroid hormone increases phosphate reabsorption

804. The thin ascending loop of Henle is
A. Relatively permeable to water
B. Relatively impermeable to Na
C. Permeable to both water and Na
D. Relatively impermeable to water
E. Relatively impermeable to both water and Na

805. Action potential initiation in the sinoatrial and atrioventricular nodes results from
A. N a influx
B. K influx
C. Ca influx
D. Na and Ca influx
E. Increased K conductance

806. As a percentage of total blood volume, which of the following values are correct
A. 40% is in the pulmonary circulation
B. 13% is in the systemic arteries
C. 20% is in the systemic arterioles and capillaries
D. 30% is in the veins
E. none of the above are correct

807. Which is not correct about reflex mechanisms acting on the circulation
A. The baroreceptors in the carotid bodies are stimulated when blood pressure increases
B. The Bainbridge reflex causes increase in heart rate
C. The Cushing reflex is a special central nervous system ischaemic response resulting from increased intracranial pressure
D. The maximum firing per change in pressure of the carotid baroreceptors occurs at a mean arterial pressure of 90 mmHg
E. The glossopharyngeal nerve is involved in baroreceptor reflex system

808. When the cholinergic vagal fibres to nodal tissues are stimulated
A. The membrane becomes hyperpolarised
B. The slope of the prepotential is decreased
C. Acetylcholine decreases conductance to Ca via muscarinic receptors
D. Acetylcholine increases the permeability of nodal tissues to potassium via muscarinic receptors
E. All of the above are true

809. Heart rate is accelerated by
A. Decreased activity of baroreceptors in the left ventricle
B. Increased activity ofbaroreceptors in the pulmonary circulation
C. Increased intracranial pressure
D. Expiration
E. Increased activity of baroreceptors in the arteries

810. Regarding coronary blood flow
A. Systolic blood flow in subendocardial arteries is greater than in the epicardial
B. Less than 50% of oxygen is removed during passage when in the resting state
C. The coronary circulation is well supplied by parasympathetic vasodilatory fibres
D. Sympathetic vasoconstrictoryfibres predominate in epicardial vessels
E. None of the above

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