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Solved Examples on Chemical Coordination and Integration

Question1: Which one of the following is not a second messenger in hormone action? [CBSE PMT’2006]

(a) Calcium

(b) Sodium

(c) cAMP

(d) cGMP

Answer: b

Solution:

In heart cells AMP acts as secondary messenger which is made in the response of adrenaline and it stimulates Ca2+ ions to come out from the sarcoplasmic reticulum of muscle fibres which causes muscle contraction. cGMP which acts as secondary messenger works on the action of acetylcholine, increase in flow of Ca2+into muscle fibres and hence causes muscle relaxation. There is no role of sodium in hormonal action.

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Question2: Feeling the tremors of an earthquake a scared resident of seventh floor of a multistoried building starts climbing down the stairs rapidly. Which hormone initiated this action? [CBSE PMT’2007]

(a) Adrenaline

(b) Glucagon

(c) Gastrin

(d) Thyroxine

Answer: b

Solution:

It is commonly called as ‘emergency hormone’ or 3F-hormone (for fear, fight and flight). Its secretion is regulated by SNS, and not by pituitary as in case of adrenal cortex. It stimulates sweating, heart beat and breathing rate. It causes the dilation of coronary artery (supplying blood to the heart muscles), bronchioles (for increasing inspiratory volume) and pupil (for better vision).

Question3: The blood calcium level is lowered by the deficiency of [CBSE PMT’2008]

(a) Parathormone

(b) Thyroxine

(c) Both calcitonin and parathormone

(d) Calcitonin

Answer: a

Solution:

A peptide hormone secreted by the parathyroid gland in response to low levels of calcium in the blood. It acts to maintain normal blood levels of calcium by increasing the number of osteoclasts, which break down the bone matrix and release calcium into the blood. It also increases the reabsorption of calcium and magnesium ion in the kidney tubules so that their concentration is maintained in the blood.

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