Write a brief note about the secretary glands of brain

Secretory glands of the brain, also known as neuroendocrine glands, are specialized structures that secrete hormones directly into the bloodstream. These hormones affect various organs and tissues throughout the body and play a vital role in maintaining homeostasis. They help regulate important physiological functions such as growth, metabolism, sleep, reproduction and response to stress. The primary secretory glands of the brain are the pituitary gland and the pineal gland. These glands are located within the central nervous system but also act as endocrine organs. They are directly or indirectly controlled by the hypothalamus and are involved in the production and secretion of hormones that regulate body functions like stress response, reproductive cycles, circadian rhythms and metabolic activity.

1. Pituitary Gland (Hypophysis)

The pituitary gland is a small pea-shaped endocrine gland located at the base of the brain in a bony cavity called the sella turcica of the sphenoid bone. It is connected to the hypothalamus by a stalk called the infundibulum. It is often referred to as the "master gland" because it controls the function of many other endocrine glands by releasing stimulating hormones.

There are two major parts of the pituitary gland:

A. Anterior Pituitary (Adenohypophysis)

The anterior pituitary is made up of glandular epithelial tissue and develops from Rathke's pouch (oral ectoderm origin). It is the largest part of the pituitary and is richly supplied with blood via the hypophyseal portal system, which carries hormones from the hypothalamus. These hypothalamic hormones stimulate or inhibit the secretion of anterior pituitary hormones.

The anterior pituitary synthesizes and secretes six major peptide hormones, which regulate various physiological processes in the body.
  • Growth Hormone (GH): Promotes growth of bones and muscles and regulates metabolism.
  • Thyroid Stimulating Hormone (TSH): Stimulates the thyroid gland to produce T3 and T4 hormones.
  • Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal cortex to secrete cortisol and other glucocorticoids.
  • Follicle Stimulating Hormone (FSH): Controls the development of follicles in ovaries and spermatogenesis in testes.
  • Luteinizing Hormone (LH): Triggers ovulation in females and testosterone production in males.
  • Prolactin (PRL): Promotes milk production in lactating females.

B. Posterior Pituitary (Neurohypophysis)

The posterior pituitary is made up of neural tissue and does not produce hormones itself. It is formed from an outgrowth of the hypothalamus and consists mainly of axon terminals of hypothalamic neurons. It stores and releases hormones that are synthesized in the hypothalamus.

It acts as a storage and release site for two important hormones which are produced in the hypothalamus and transported through axons.
  • Oxytocin: Causes uterine contractions during childbirth and helps in milk ejection from mammary glands.
  • Antidiuretic Hormone (ADH) or Vasopressin: Regulates water balance by increasing water reabsorption in kidneys.

2. Pineal Gland

The pineal gland is a small, pine cone-shaped structure located near the center of the brain between the two cerebral hemispheres in a groove where the two halves of the thalamus join. It is part of the epithalamus and has both neural and endocrine features.

The pineal gland is responsible for the secretion of the hormone melatonin, which regulates sleep-wake cycles (also called circadian rhythms). Its activity is influenced by the light-dark cycle sensed through the retina.
  • Melatonin
    • This hormone is secreted during darkness and inhibited by light. It helps regulate sleep patterns and biological timing such as seasonal reproduction in animals.
    • Melatonin secretion is controlled by a pathway that involves the retina, suprachiasmatic nucleus (SCN) of the hypothalamus, and sympathetic nerves. Thus, light and dark cycles affect the pineal gland directly, allowing it to synchronise internal body functions with the environment.




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