Human Endocrine System

Fall in levels of estrogen and progesterone stimulates the secretion of FSH and LH.

Progesterone level rises rapidly from 15^th day onwards for 7 days and then, declines at very low level.

The pineal hormone melatonin is involved in controlling biological rhythms and photoperiodism.

Leydig cells in the testis secrete male sex hormone testosterone.

Endocrine glands secrete hormones directly into the bloodstream to regulate body functions. Plasma cells produce antibodies, salivary glands produce saliva (exocrine), and prostate glands produce fluid for semen (exocrine). Only endocrine glands are primarily defined by hormone secretion.

Abscisic acid (ABA) is sometimes called the stress hormone because it initiates and maintains seed and bud dormancy and brings about the closure of stomata.

Hormones are non-antigenic. They are secreted into blod prior to use and may be amino acids, amino acid derivatives, steroid, polypeptide or proteins, amines or glycoprotein.  

The testes of the male begin to produce testosterone at puberty in response to LH. Progesterone is released by ovary in response to high blood levels of LH.

When two hormones work together these are known as synergesic hormone. Ex. – FSH and LH.

Thymosin controls growth in childhood.

Testosterone is a steroid hormone from the androgen group and is found in humans and other vertebrates.

Androgens are steroid hormones that regulate male characteristics and reproduction, including testosterone. They are produced primarily in the gonads (testes in males, ovaries in females) and adrenal glands. Option A correctly identifies androgen as a hormone class.

The pancreas is an endocrine gland secreting insulin (from beta cells) and glucagon (from alpha cells). These are opposing hormones regulating blood glucose - insulin lowers it, glucagon raises it. Options B and C list pituitary/gonadal hormones. Option A is correct.

Adrenaline (epinephrine) binds to beta-1 adrenergic receptors in the heart, increasing heart rate, force of contraction, and cardiac output. This is part of the sympathetic 'fight or flight' response. Gastrin stimulates gastric acid secretion, glucagon raises blood glucose, and thyroxine regulates basal metabolism but does not directly stimulate cardiac function like adrenaline does.

Somatotropic hormone (growth hormone, GH) is synthesized and secreted by somatotroph cells in the anterior pituitary gland. It stimulates growth, cell reproduction, and regeneration. The pancreas secretes insulin and glucagon, the adrenal secretes catecholamines and corticosteroids, and the thyroid secretes thyroid hormones - none of which are somatotropic hormone.