Sunday, January 13, 2008

1 - physiology mcqs - 1 to 10

1. Parathyroid hormone (PTH)

(a) Is a 184 amino acid peptide hormone
(b) Acts on a cell surface receptor that increases intracellular cyclic AMP
(c) Increases calcium release from bone
(d) Increases production of 1,25 dihydroxy-vitamin D3 in the kidney
(e) Reduces calcium absorption from the gastrointestinal tract


b , c , d are true . PTH increases serum calcium by releasing calcium from bone and increasing gastrointestinal absorption. It increases the renal hydroxylation of Vitamin D3. It is an 84 amino acid peptide hormone with a half-life of several minutes.


2. Anti-diuretic diuretic hormone (ADH)

(a) Is produced by the anterior lobe of the pituitary gland
(b) Is released by neurosecretion
(c) Serum levels are increased by a low plasma osmolality
(d) Secretion is increased in the early post-operative period
(e) Acts by increasing the permeability of the distal convoluted tubule


only b and d are true . ADH is released by neurosecretion from the posterior pituitary gland. The cell bodies of the neurosecretory cells are found in the supraoptic and paraventricular nuclei of the hypothalamus. ADH is release in response to an increase in plasma osmolality. It acts by increasing water reabsorption by the renal collecting ducts. Increased ADH is part of the stress response seen in the early post-operative period.


3. Regarding the sensory dermatomes

(a) C3 and C4 supply the tip of the shoulder
(b) L1 supplies the umbilicus
(c) L4 and L5 supply the sole of the foot
(d) Sacral nerves supply the perianal skin
(e) The facial nerve supplies the face


a , c , d are right . C3 and C4 supply both the shoulder tip and the diaphragm. Hence referral to the shoulder tip from diaphragmatic irritation. The umbilicus is supplied by T10 nerve roots. L1 supplies the inguinal region via the ileo-inguinal nerve. The S2-S4 supplies the perianal skin. The facial nerve supplies the nerves of facial expression. The sensory supply to the face is via the trigeminal nerve.


4. The sympathetic nervous system

(a) Produces pupillary dilatation
(b) Reduces gastrointestinal motility
(c) Constricts bronchiole smooth muscle
(d) Constricts skin and mucous membrane blood vessels
(e) Contracts the bladder detrusor muscle


a , b , d are true . The sympathetic nervous system produces the ' flight or fight' response. It dilates the pupil, reduces gastrointestinal motility and produces bronchodilatation. It diverts blood away from the skin by constricting blood vessels and relaxes the detrusor muscle of the bladder.


5. Cerebrospinal fluid

(a) Has a composition almost identical to that of the brain extracellular fluid
(b) Is produced by the choroid plexus
(c) Circulates from the subarachnoid space into the cerebral ventricles
(d) Is absorbed through the arachnoid villi
(e) Absorption is independent of intraventricular pressure


only c is wrong . Cerebrospinal fluid is produced by the choroid plexuses of the lateral and third ventricles. It circulates from the cerebral ventricles, throught the foramina of Magendie and Luschka of the fourth ventricle into the subarachnoid space. Absorption occurs by bulk flow, a pressure-dependant process, via the arachnoid villi into the venous sinuses.


6. Smooth muscle cells

(a) Microscopically have a striated appearance
(b) Do not possess actin and myosin
(c) Show spontaneous muscle contraction
(d) Adjacent cells are electrically coupled
(e) Are controlled by the autonomic nervous system


c , d , e are true . Unlike skeletal and cardiac muscle, smooth muscle cells do not have striated appearnce. They do however still contain both actin and myosin. Smooth muscle cells have intrinsic contractile properties the activity of which is controlled by the autonomic nervous system. Smooth muscle and cardiac muscle cells are electrically coupled.


7. Regarding pain sensation

(a) It arises by stimulation of free nerve endings
(b) Is transmitted to the central nervous system by myelinated A fibres
(c) Central transmission occurs via the spinothalamic tracts
(d) The thalamus is important in the perception of pain
(e) Can be reduced by local anaesthetics that reduce potassium influx into nerve fibres


b and e are false . The majority of pain sensation arises from the stimulation of free nerve endings. Pain sensation is transmitted to the CNS in small unmyelinated C fibres. It is then transmitted to the thalamus in the spinothalamic tracts. Local anaesthetics work by blocking sodium channels in nerve fibres.


8. Following a total gastrectomy

(a) Anaemia can occur due to iron deficiency
(b) Anaemia can occur due to B12 deficiency
(c) Protein digestion is significantly impaired
(d) Diarrhoea is a frequent complaint
(e) Fainting and collapse may occur after a meal


except c all are true . After total gastrectomy anaemia can occur due to both iron and B12 deficiency. Gastric acid is required for normal iron absorption. Intrinsic factor is required for B12 absorption. All patients should receive B12 injections every three months. Post gastrectomy diarrhoea is a common complaint. Dumping syndrome is the result of rapid transit of a hyperosmolar meal into the small intsetine. The osmotic load can produce hypovolaemia. Rapid glucose absorption and result in preciptoud insulin release and a reactive hypoglycaemia.


9. Haemorrhage in man

(a) Produces venoconstriction
(b) Produces widespread arteriolar dilatation
(c) Produces a fall in cardiac output
(d) Causes splenic contraction
(e) Increases aldosterone secretion


b and d are false . Haemorrhage produces both venous and arteriolar contraction. Cardiac output is intially reduced. Hypovolaemia increase aldosterone secretion. Renal reabsorption of sodium is increased and volume homeostasis is eventually achieved. Unlike carnivores, the human spleen does not act as a significant resevoir of red blood cells and does not contract in response to blood loss.


10. The prothrombin time

(a) Assesses the intrinsic pathway of the blood coagulation system
(b) Can be prolonged in jaundiced patients
(c) Is increased by warfarin
(d) Is increased by heparin
(e) Can be restored to normal by the administration of protamine


only b and c are true . The prothrombin time assess the extrinsic pathway of the blood coagulation cascade. In jaundiced patients the absorption of fat-soluble vitamins, including Vitamin K, is reduced. Vitamin K is necessary for the synthesis of clotting factors II, VII, IX and XI. Warfarin is a vitamin K antagonits. Heparin potentiates the activity of antithrombin III and has no effect on the external pathway or prothrombin time. Protamine neutralises the activity of heparin.


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