Mammalia: Endocrine Glands | Zoology Optional Notes for UPSC PDF Download

Endocrine Glands in Mammals

Pituitary Gland: The Master Regulator

• The pituitary gland, also known as the hypophysis cerebri, is a small structure attached to the ventral side of the brain.
• It consists of two main parts: the larger adenohypophysis (pars buccalis) and the smaller neurohypophysis (pars nervosa).
• The adenohypophysis and neurohypophysis are ectodermal derivatives, originating from distinct sources during embryonic development.

Function:

• The pituitary gland plays a crucial role in hormone regulation, with the adenohypophysis secreting various hormones such as adrenocorticotropic hormone and somatotropic hormone.
• The neurohypophysis releases neuropeptides like oxytocin and vasopressin.
• Hormone secretion is intricately regulated by neurosecretion from the hypothalamus.

Blood Supply:

• The anterior pituitary is supplied by both the internal carotid artery and the hypophysial portal vein.
• The posterior pituitary is supplied with the inferior hypophysial artery.

Thyroid Gland: Metabolic Control Center

• The thyroid gland, usually located in the neck region, consists of two lobes connected by an isthmus.
• It originates from endoderm and arises as a median evagination of the pharynx floor during embryonic development.

Function:

• The thyroid gland produces thyroxine, a derivative of the amino acid tyrosine.
• Iodine ions, absorbed from the blood, are converted into iodine molecules and incorporated into thyroxine molecules.

Parathyroid Glands: Calcium Regulators

• Usually found in two pairs in mammals, the parathyroid glands are endodermal derivatives from the third and fourth pharyngeal pouches during embryonic development.

Cell Types:

• Parathyroid glands consist of large granular eosinophil cells and non-granular chromophobe cells.
• They secrete parathormone and calcitonin, which play antagonistic roles in calcium metabolism.

Pancreas: Dual Functional Organ

• The pancreas has both exocrine and endocrine elements.
• The acinar tissue produces pancreatic juice for digestive functions, while the islet tissue, known as islets of Langerhans, releases hormones into the blood.

Cell Types:

• The islet tissue contains alpha and beta cells, each producing specific hormones.

Adrenal Glands: Cortex and Medulla Dynamics

• Derived from mesodermal inter-renal tissues, the adrenal cortex secretes glucocorticoids and mineralocorticoids.
• Glucocorticoids, like cortisol, play a significant role in carbohydrate and protein metabolism.

Adrenal Medulla:

• The adrenal medulla, derived from neural crest cells, releases catecholamines, including adrenaline and noradrenaline.
• Catecholamines affect blood pressure, vessel constriction, and various metabolic processes.

Gastrointestinal Hormones: Gut Regulators

• Gastrin, secretin, and cholecystokinin are gastrointestinal hormones regulating stomach activity.
• Gastrin stimulates HCl secretion, while secretin and cholecystokinin control enzyme-rich pancreatic juice release.

Gonadal Hormones: Regulators of Reproduction

Testis:

• Testosterone and androsterone, androgens produced by the testis, regulate male reproduction.
• Androgens play a role in spermatogenesis and influence gonadotropin release.

Ovary:

• Ovaries produce estrogens, progesterone, and relaxin.
• Estrogens regulate reproductive system development, while progesterone prepares the uterine wall for implantation.
• Relaxin relaxes the pubic symphysis during parturition.

Conclusion:

Endocrine glands in mammals intricately regulate physiological processes, influencing metabolism, calcium balance, reproductive functions, and more. Understanding their structure and functions is crucial for comprehending the complexity of hormonal control in vertebrates, particularly mammals.