Human Endocrine System

In women, relaxin is secreted into the circulation by the corpus luteum in the ovary. During pregnancy it is also released from the placenta, the membranes, which surround the foetus, and the lining of the uterus. During pregnancy, relaxin levels are at their highest in the first trimester. At this time it is believed to promote implantation of the developing foetus into the wall of the uterus and the growth of the placenta. Towards the end of pregnancy, relaxin promotes rupture of the membranes surrounding the foetus and the growth, opening and softening of the cervix and vagina to aid the process of childbirth. Relaxin can relax the ligaments at the front of the cervix to ease delivery of the baby. 

Gonadotropins are secreted from the anterior pituitary gland and act on the gonads (i.e., the ovaries or testes). Gonadotrophs secrete two primary gonadotropins: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). 

Estrogen promotes the development of the ductal system, while progesterone promotes the development of the lobulo-alveolar system in the breasts during pregnancy.

Androgens include the male hormones testosterone and androsterone and promote development of male sex characteristics. The androgens promote the secondary sex characteristics of muscle growth, lowered voice range, the Adam's apple, and increased body hair.

Follicle-stimulating hormone (FSH) is synthesized and secreted under the influence of GnRH on the anterior pituitary. It regulates the development, growth, maturation of ovarian follicle, pubertal maturation and reproductive processes of the body. FSH and luteinizing hormone (LH) act synergistically in reproduction. Under the influence of FSH ovary secretes estrogen. Thus the correct answer is option C.

The major sex hormone in men is testosterone, which is produced mainly in the testes. They are crucial for male sexual and reproductive function. They are also responsible for the development of secondary sexual characteristics in men, including facial and body hair growth, and bone and muscle development. 

Progesterone is a natural female hormone. It is called as the pregnancy hormone, it is essential before and during pregnancy. After ovulation occurs, the ovaries start to produce progesterone needed by the uterus. Progesterone causes the uterine lining or endometrium to thicken. This helps prepare a supportive environment in the uterus for a fertilized egg. After 8 to 10 weeks of pregnancy, the placenta takes over progesterone production from the ovaries and substantially increases progesterone production.

The secretion of pituitary gonadotrophic hormones is stimulated by gonadotropin hormone-releasing hormone (GnRH) from the hypothalamus and modulated by testicular hormones. At the onset of puberty, the pituitary gland secretes GnRH, or gonadotropin-releasing hormone. In response, the hypothalamus release follicle stimulating hormone (FSH) and luteinizing hormone (LH) into the male system. LH enters the testes, stimulating the Leydig cells to release testosterone. Testosterone hormone is responsible for the secondary sexual characteristics like deepening of the voice, the growth of facial, axillary, and pubic hair, and the beginnings of the sex drive.

Insulin and glucagon work synergistically to keep blood glucose concentrations normal. An elevated blood glucose concentration results in the secretion of insulin which leads to glucose transportation into body cells. Glucagon is secreted by the alpha cells of the pancreas when blood glucose is low. Glucagon's function is to cause the liver to release stored glucose from its cells into the blood. Corticoids are also responsible for the regulation of glucose metabolism. 

Alpha cells are endocrine cells in the islets of Langerhans of the pancreas. Thy are responsible for synthesizing and secreting the peptide hormone glucagon, which elevates the glucose levels in the blood.

The posterior pituitary is the part of the brain that extends down from hypothalamus; the posterior pituitary and infundibulum are together termed as neurohypophysis. Pars nervosa is the posterior lobe of pituitary associated with neurohypophysis while pars distalis is anterior lobe of the adenohypophysis. Supraoptic and paraventricular nuclei of hypothalamus secrete oxytocin and vasopressin which are then stored and released into blood stream via neurohypophysis. Thus, the correct answer is option C.

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 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 synthesis and secretion of estrogen is stimulated by follicle-stimulating hormone (FSH), which is, in turn, controlled by the hypothalamic gonadotropin releasing hormone (GnRH).