NEET Practice Questions (MCQs) with Answers & Solutions

NCERT page number 327

21.6.2 Mechanism of Hearing

Neural Control And Coordination

NCERT page number 327

21.6.2 Mechanism of Hearing

Neural Control And Coordination

NCERT page number 327

21.6.2 Mechanism of Hearing

Neural Control And Coordination

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.

(b) Achondroplasia is a disorder inherited a dominant characteristic in which bones of arms and legs fail to grow to normal size due to defect in both cartilage and bone. It results in a type of dwarfism characterised by short limbs, a normal sized head and body and normal intelligence.

Refer NCERT, Heading22.2.1 Para 1 page 331