Tag: control and coordination in living organisms

MSH stimulates secretion of melanin from pigment cells in the skin and thereby causes skin darkening as required for camouflage in some lower vertebrates. Depending on the amount of melanin and carotene, the colour of skin is determined from pale yellow to dark. Thus, the correct answer is option A.

Rickets is a disorder caused by a lack of vitamin D, calcium, or phosphate. It leads to softening and weakening of the bones. Vitamin D helps the body control calcium and phosphate levels. If the blood levels of these minerals become too low, the body may produce hormones that cause calcium and phosphate to be released from the bones. This leads to weak and soft bones.

A fall in the concentration of calcium in the bloodstream is detected by the parathyroid glands, which then produce parathyroid hormone. 

Hormones of the adrenal cortex and pineal body are under control of tropic hormones of the anterior pituitary gland. The hormonal secretion of anterior pituitary is under control of regulatory hormones of the hypothalamus. The hormones of posterior pituitary are stored in axon ending and are secreted under nervous control. Thus, the correct answer is C.

Aldosterone of the adrenal cortex is life-saving hormone because it serves to retain sodium and water to maintain a sufficient blood volume for circulation. So, it maintains the osmolarity and volume of ECF. The pituitary gland regulates secretion of other endocrine glands. Pineal gland secretes melatonin that regulates body’s daily rhythms. Thyroid hormones regulate the basic metabolic rate. Thus, the correct answer is C.

The third ventricle (ventriculus tertius) is one of four connected fluid-filled cavities comprising the ventricular system within the rabbit's brain. The third ventricle is a narrow vertical cleft between the 2 lateral ventricles.

The main hormone secreted by the testes is testosterone, an androgenic hormone. The placenta is an endocrine gland, that is only present during pregnancy. It secretes human chorionic gonadotrophin hormone (hCG), which is present only during pregnancy.

The thymus gland is an integral part of immune system. It helps in the maturation of lymphocytes. The thymus serves a vital role in the training and development of T-lymphocytes or T-cells, an extremely important type of white blood cell. So, the correct answer is option B.

The adrenal medulla secretes 2 hormones - adrenalin and noradrenalin. 

The hypothalamus is a mass of grey matter present at the base of the cerebrum. The centre for thirst and drinking regulation is present in lateral hypothalamus while that for hunger and satiety is present in the arcuate nucleus, ventral nucleus and lateral hypothalamic area. The anterior hypothalamic region regulates body temperature.