Hormone Produced by Different Glands and its Function-2

Posterior Lobes of Pituitary Gland (Neurohypohysis)

When the cells in the nerve tracts (hypothalamo-hypophyseal tract) linking the posterior pituitary and the hypothalamus are electrically stimulated, the posterior pituitary, also known as the neuro-hypophysis, releases hormones. The posterior pituitary is where this tract ends after starting in the hypothalamus. Oxytocin and antidiuretic hormone are produced by the hypothalamic nerve cells and are kept in the posterior pituitary gland. The posterior pituitary gland secretes oxytocin and vasopressin, sometimes referred to as ADH or antidiuretic hormone. Despite not producing hormones itself, the posterior lobe does store and release two hormones produced by the hypothalamus.

• Antdiuretic Hormone (ADH)
  • The hypothalamus produces the antidiuretic hormone (ADH), also known as "vasopressin," which is then stored in and released from the posterior lobe in response to a number of stimuli such increased plasma osmolality and decreased extracellular fluid (ECF). Alcohol, elevated ECF volume, and decreased plasma osmolality all prevent ADH secretion. It influences the kidneys to increase water reabsorption and reduce urine production. The hypothalamic supraoptic nucleus secretes it mostly.
  • Functions of the ADH:
  • By regulating the ultimate volume and concentration of urine, ADH's main function is to control the volume of extracellular fluid.
  • Reabsorbing water from the renal tubules is made easier by ADH.
  • The pressor (hypertensive) impact of ADH is due to the hormone's direct constrictor action on vascular smooth muscle.
• Oxytocin
  • At the conclusion of pregnancy, oxytocin causes the uterus to contract and the mammary glands to release milk. The paraventricular nucleus of the hypothalamus is the primary site of secretion.
  • Functions of the Oxytocin
  • Milk ejection (Galactokinetic action): A neuroendocrine reaction causes a lactating memory gland to release milk. Sucking typically sets off this reaction because it activates breast areola receptors. The hypothalamus receives the nerve impulses and releases the oxytocin. To cause the milk to be expelled, the myoepithelial cells surrounding the alveoli and lactiferous ducts contract in response to oxytocin (let down reflex).
  • Uterine contraction: The myometrium contracts strongly and rhythmically as a result of oxytocin's direct action on the uterine smooth muscle. Oxytocin sensitivity in the uterus varies depending on its physiologic state and hormonal balance.

The Intermediate Lobe of Pituitary Gland

The pars intermedia, or intermediate lobe, of the pituitary gland atrophies after birth and develops into a distinct lobe in adulthood. Melanocytes stimulating hormone (MSH), which promotes the growth and development of the melanocytes that give skin its color, is secreted by this gland.

Thyroid Gland

Just below the pharynx, on the front and sides of the trachea, is where the thyroid gland is found. It is situated between the vertebrae C5, C6, C7, and T1. It weighs roughly 25 grams and is a very vascular gland. It has an isthmus, which is the center portion that connects its two lobes. The lobes measure around 5 cm long and 3 cm wide, and they are essentially cone-shaped. Thyroxine (T4) and triiodothyronine are produced by follicular cells, which make up the thyroid gland (T3). The hormone calcitonin, which helps to control calcium hemeostasis, is secreted by parafollicular (C) cells that are located between the follicles. During the dormant stage, thyroid follicle cells contain a substance called colloid that is thick, sticky, and semifluid. The hormones of the thyroid gland exert a wide range of metabolic and physiologic actions that affect nearly every tissue in the body.

Thyroid Hormones:

Thyroxine (T4), also known as tetraiodothyronine because it contains four atoms of iodine, and triiodothyronine (T3), which contains three atoms of iodine, are secreted by the follicular cells of the thyroid gland. T3 is created at the target tissues, while T4 is mostly produced by thyroid follicle cells. The majority of peripheral tissues have an enzyme that changes T4 into T3 by removing one iodine atom. The hypothalamopituitary axis controls how much of these hormones are present in the blood plasma. Thyroid stimulating hormone (THS), which is produced by the anterior pituitary, promotes the release of T3 and T4 into the blood. T3 is only 10% of total testosterone and T4 is 90%, but T3 is more powerful.

Functions of Thyroid Hormones (T3 T4):

• Almost all metabolically active tissue is consumed by O2.
• They energize lipolysis (Fat metabolism).
• They encourage the breakdown of proteins in tissue.
• They improve intestinal glucose absorption, raising blood glucose levels.
• By combining the effects of the thyroid and catecholamines on the heart, they boost cardiac output. The cerebral cortex and basal ganglia must mature in order to produce thyroid hormone. They influence cholesterol metabolism and lower blood cholesterol levels.
• By enhancing GH secretion, they improve healthy growth.

Regulation of thyroid hormone secretion:

The thyrotropin releasing hormone (TRH) produced by the hypothalamus stimulates TSH secretion. The plasma levels of T3 and T4 affect how much TSH is secreted. TSH secretion decreases as T3 and T4 levels rise and vice versa through a negative feedback mechanism.

Calcitonin:

The thyroid gland's parafollicular or C cells secrete the hormone calcitonin. To lower the blood calcium level, it works on the kidneys and bone cells. By inhibiting calcium reabsorption by the renal tubules and reducing calcium release from its reservoir source, the bone matrix, calcitonin promotes the secretion of calcium through the urine. The outcomes differ from those of parathyroid hormone.

Regulation of Blood Calcium Level:

• The thyroid gland releases calcitonin when the blood calcium level is elevated. Since calcium is better absorbed by the bones thanks to calcitonin, the blood calcium level stabilizes.
• The parathyroid glands release parathyroid hormone when the blood level is low (PTH). The bones release calcium as a result of PTH. Additionally, it activates vitamin D and causes the kidneys to reabsorb calcium, which is then absorbed by the intestines. The blood calcium level subsequently returns to normal.

Blood Supply of the Thyroid Gland:

• The superior thyroid artery and inferior thyroid artery both supply the thyroid gland. The superior, inferior, and intermediate thyroid veins are used to drain venous blood.

Supply of Nerves to the Thyroid Gland

• The superior, middle, and inferior sympathetic ganglia all contribute to the nerves that supply the thyroid gland.

Parathyroid Glands

Four parathyroid glands are located behind the thyroid gland. Compared to the thyroid gland, they are much smaller. Each gland measures between 40 and 50 milligrams. To release parathyroid hormone (PTH), also known as parathormone, is the main duty. Cells and oxyphil cells make up each parathyroid gland. This hormone is secreted by the parathyroid glands' principal cells. The oxyphil cells' purpose is unknown.

Parathyroid Hormone (PTH):

• Three body-wide mineral concentrations are regulated by this hormone: calcium, phosphorus, and magnesium.

Functions of the Parathyroid Hormone:

• The major function of parathyroid hormone is to increase the blood calcium level when it is low. This is achieved by:
  • Bone calcium being released (bone resorption)
  • Using calcitriol to increase the amount of calcium that is absorbed (taken up into the blood) from the intestine.
  • Lowering calcium excretion via the kidneys
  • To keep the level of phosphate in the blood stable, it causes the kidneys to eliminate phosphate in the urine.
  • It increases magnesium excretion to control blood levels.

Blood Supply of the Parathyroid Gland (PTH):

• It receives blood flow from the internal thoracic and inferior thyroid arteries' branches. The internal thoracic, left bracheocephalic, and inferior thyroid veins receive the venous blood drainage. Parathyroid lymphatic arteries empty into deep cervical lymph nodes.

Supply of Nerves to the Parathyroid Gland (PTH):

• The parathyroid gland is innervated by both sympathetic and parasympathetic fibers.