Chemical Coordination and Control MCQs for NEET — Zoology Questions with Answers

Thyroxine, the principal hormone, of thyroid gland, is required for tissue differentiation and metamorphosis (the rapid tranformation from the larval to adult form) in amphibians. Thyroxine triggers a response from the hypothalamus, (probably by a genetic mechanism) followed by the production and release of TSH (Thyroid stimulating hormone), thus metamorphosis begins and tadpoles metamorphose into frogs. Thiourea is an organic compound of carbon, nitrogen, sulphur and hydrogen, with the formula CSN₂H₄ OR (NH₂)₂CS. It is similar to urea. except that oxygen atom is replaced by a sulphur atom.

(b) Secretin is a polypeptide hormone secreted by the mucosa of duodenum and jejunum.

It perform two functions:

(a) It stimulates sodium bicarbonate from the pancreas which neutralises the acid in the chyme so that it will not damage the wall of the small intestine.

(b) It increases the rate of bile secretion in the liver.

(C) Secretin and cholecystokinin (CCK) are two main gastrointestinal (GI) hormones secreted in duodenum of alimentary canal. CCK stimulates gall bladder contraction and thus increases the flow of bile salts into the intestine. Secretin stimulates the release of an alkaline pancreatic fluid that neutralises stomach acid as it enters the intestine.

Ovary is the primary female sex organ that produces the female gamete (ovum) and several steroid hormones (ovarian hormones). The two steroid hormones produced by ovary are oestrogen and progesterone. Oestrogens produce wide ranging actions such as stimulation of growth and activities of female secondary sex organs, development of growing ovarian follicles, appearance of female secondary sex characters (e.g., high pitch of voice, etc.) mammary gland development. Oestrogens also regulate female sexual behaviour.
The pars distalis region of pituitary, commonly called produced anterior pituitary, Growth Hormone (GH), prolactin (PRL), Thyroid stimulating Hormone (ACTH), Luteinizing hormone (LH) and follicle stimulating hormone(FSH). Over secretion of GH stimulates abnormal growth of the body lead to gigantism and low secretion of GH results in stunted growth resulting in pituitary dwarfism.
Alpha cells of islets of Langerhans of the endocrine pancreas secrete a hormone called glucagon. It is a peptide hormone and plays an important role in maintaining the normal blood glucose levels. It acts mainly on the liver cells (hepatocytes) and stimulates glycogenolysis resulting in an increased blood sugar (hyperglycemia). In addition, this hormone stimulates the process of gluconeogenesis which also contributes to hyperglycemia. Glucagon reduces the cellular glucose uptake and utilization. Thus. glucagon is a hyperglycemic hormone.

(a): Gonadotropin releasing hormone (GnRH), stimulates the anterior lobe of the pitutary gland to secrete two gonadotropic hormones, follicle stimulating hormone (FSH) and luteinizing hormone(LH). In male LH activates the Leydig's (interstitial) cells of the testis to secrete androgens.

(b) Parathyroid hormone (PTH) stimulates the reabsorption of ${\mathrm{Ca}}^{2+}$ by renal tubules and increases ${\mathrm{Ca}}^{2+}$ absorption from digested food. It means PTH increases the blood ${\mathrm{Ca}}^{2+}$ level. Old aged persons have weak immunity because thymus is degenerated in old individuals resulting in a decreased production of thymosin. Osteoporosis in women occurs due to decreased level of estrogen.

(b): Hypothalamus is connected to the anterior lobe of pitutary gland by hypophyseal portal veins. The latter carry blood containing neurohormones (releasing factors) from the hypothalamus to the anterior lobe of the pituitary.

(b) Insulin decreases the level of glucose in the blood. It acts by stimulating liver cells and muscle cells to take up glucose from the blood and convert it into glycogen. When the blood sugar level drops, the secretion of insulin is suppressed. When the blood sugar level increases, the secretion of insulin is stimulated.