Pituitary Gland- Hypophysis- Master Gland

The pituitary gland, often referred to as the master gland, plays a crucial role in the endocrine system by secreting hormones that facilitate communication throughout the body via the bloodstream. It exerts control over various hormone-producing glands, such as the thyroid, adrenal glands, ovaries, and testes. This control allows the pituitary gland to regulate the production and release of hormones from these glands, thereby influencing a wide range of bodily functions. Due to its central role in coordinating and controlling the activities of multiple glands, the pituitary gland is commonly described as the master gland.

What does the pituitary gland do? 

The pituitary gland, which is often referred to as the "master gland," secretes hormones from both the anterior (front) and posterior (back) parts of the gland. These hormones play vital roles in regulating various processes and functions throughout the body.

The anterior pituitary gland produces and releases several hormones, including:

1.     Growth hormone (GH): Stimulates growth and development in tissues and organs.

2.     Prolactin (PRL): Stimulates milk production in lactating individuals.

3.     Adrenocorticotropic hormone (ACTH): Stimulates the adrenal glands to produce cortisol and other steroid hormones.

4.     Thyroid-stimulating hormone (TSH): Stimulates the thyroid gland to produce thyroid hormones.

5.     Follicle-stimulating hormone (FSH): Stimulates the growth of ovarian follicles in females and sperm production in males.

6.     Luteinizing hormone (LH): Triggers ovulation in females and stimulates testosterone production in males.

• If hormones are being over-produced, then this can cause problems depending on the hormone creating concern. 
• The pituitary gland, commonly referred to as the hypophysis, is positioned beneath the hypothalamus.
• The pituitary gland, also known as the hypophysis, measures approximately 1 cm in length, 1-1.5 cm in width, and 0.5 cm in thickness.
• The pituitary gland, known as the hypophysis, is positioned adjacent to the optic chiasma within the concavity of the sphenoid bone.
• The pituitary gland consists of two main lobes: the anterior lobe and the posterior lobe. Between these two lobes, there is a smaller region known as the pars intermedia or intermediate lobe. 

Anterior lobe (Adenohypophysis):

• The glandular, anterior lobe of the pituitary gland is known as the anterior pituitary or adenohypophysis. It is one of the two major parts of the pituitary gland, with the other part being the posterior pituitary or neurohypophysis. 
• The anterior pituitary is responsible for the synthesis and secretion of several important hormones that regulate various physiological processes throughout the body.

Hormones of adenohypophysis: 

      1: Growth hormone (Somatotropin)

• The hormone primarily associated with growth and the growth rate of the body is growth hormone (GH), also known as somatotropin. GH is secreted by the anterior pituitary gland and plays a crucial role in regulating growth and development during childhood and adolescence. GH promotes growth by stimulating the production of insulin-like growth factors (IGFs) in the liver and other tissues. These IGFs, particularly IGF-1, exert their effects on bone, cartilage, and muscle cells, promoting cellular growth and division.
• Secretion of GH is controlled by two hormone produced by hypothalamus- Growth hormone releasing hormone (GHRH) and Growth hormone inhibiting hormone(GHIH)
• The pituitary gland, often referred to as the master gland, plays a crucial role in the endocrine system by secreting hormones that facilitate communication throughout the body via the bloodstream. It exerts control over various hormone-producing glands, such as the thyroid, adrenal glands, ovaries, and testes. This control allows the pituitary gland to regulate the production and release of hormones from these glands, thereby influencing a wide range of bodily functions. Due to its central role in coordinating and controlling the activities of multiple glands, the pituitary gland is commonly described as the master gland.

A table summarizing the hormones of the pituitary gland and their functions.

• • Secretion of GH is controlled by two hormone produced by hypothalamus- Growth hormone releasing hormone (GHRH) and Growth hormone inhibiting hormone(GHIH)

     2: Prolactin

  •  In female; stimulate growth of mammary gland and milk production
  • The secretion of prolactin from the anterior lobe of the pituitary gland is predominantly inhibited by a hormone called Prolactin Inhibiting Hormone (PIH), which is produced by the hypothalamus.

    3:Thyroid stimulating hormone (TSH):

  • Stimulate thyroid gland to produce thyroxine.
  • The secretion of TSH (thyroid-stimulating hormone) is primarily regulated by thyrotropin-releasing hormone (TRH) from the hypothalamus. TRH acts on the anterior pituitary gland to stimulate the release of TSH.  
  • Thyroid-stimulating hormone (TSH), also known as thyrotropin, is secreted by the anterior pituitary gland and stimulates the thyroid gland to produce and release thyroid hormones, including thyroxine (T4) and triiodothyronine (T3).
  • When TSH binds to specific receptors on the surface of thyroid cells, it triggers a cascade of events that lead to the synthesis and secretion of thyroid hormones. The thyroid gland is responsible for producing and releasing T4 and T3, which are iodine-containing hormones.
  • The levels of thyroid hormones in the bloodstream provide negative feedback to the hypothalamus and the anterior pituitary, inhibiting the release of TRH and TSH. This feedback loop helps maintain a balance in the production and secretion of thyroid hormones. It's worth noting that there is no widely recognized hormone called thyrotropin-inhibiting hormone (TIH) involved in the regulation of TSH secretion.

     4:Adrenocorticotropic hormone (ACTH):

  •  Stimulate adrenal cortex to secrete glucocorticoids
  •  Regulated by corticotropic releasing hormone (CRH) and corticotropic inhibiting hormone (CIH) from hypothalamus

     5:Luteinizing hormone (LH):

  • Stimulate corpus luteum to secrete progesterone and estrogen
  •  Luteinizing hormone (LH) is indeed a hormone that plays a significant role in the reproductive system, particularly in women
  •  LH is produced and released by the anterior pituitary gland, and its levels fluctuate throughout the menstrual cycle. One of the primary functions of LH is to trigger ovulation, which is the release of a mature egg from the ovary.
  •  LH is produced and released by the anterior pituitary gland, and its levels fluctuate throughout the menstrual cycle. One of the primary functions of LH is to trigger ovulation, which is the release of a mature egg from the ovary.
  • During the menstrual cycle, LH levels rise dramatically around the middle of the cycle, known as the LH surge. This surge of LH stimulates the final maturation of the ovarian follicle and prompts the release of the mature egg from the ovary. This egg is then available for fertilization by sperm.

     6:Follicle stimulating hormone (FSH):

  • Follicle-stimulating hormone (FSH) plays a significant role in controlling the menstrual cycle and stimulating the growth and development of eggs in the ovaries.
  •  FSH is a hormone produced and released by the anterior pituitary gland. Its primary function is to promote the growth and maturation of ovarian follicles, which are small fluid-filled sacs within the ovaries that contain developing eggs or oocytes.

     7:Melanocytes stimulating hormone (MSH):

  • Stimulate melanocyte formation
  •  Melanocyte-stimulating hormone (MSH) is a group of peptide hormones that are produced by various sources, including the skin, pituitary gland, and hypothalamus. MSH plays a crucial role in producing pigmentation found in the skin, hair, and eyes.
  • The production of MSH is enhanced in response to ultraviolet (UV) radiation. When the skin is exposed to UV radiation, such as from sunlight, it triggers an increase in MSH production. This increase in MSH stimulates specialized skin cells called melanocytes to produce a pigment called melanin. 

   Hormones of Neuro-hypophysis:

  • It doesnot synthesize hormone, rather it stores the hormones produced by hypothalamus

        Vasopressin (Anti-diuretic hormone)

  • -help in osmoregulation
  • – increase permeability of PCT, and stimulate reabsorption of water
  • – Inhibit by alcohol
  •  Vasopressin, also known as antidiuretic hormone (ADH) or arginine vasopressin (AVP), is a nonapeptide that is synthesized in the hypothalamus and plays vital roles in various physiological functions. Its primary function is to regulate the body's osmotic balance, blood pressure, sodium homeostasis, and kidney functioning.
  •  One of the key effects of ADH is its influence on the kidney's ability to reabsorb water. When ADH is present, it stimulates the expression of water transport proteins, such as aquaporin-2, in the late distal tubule and collecting duct of the kidney. This increased expression of water channels facilitates water reabsorption from the urine back into the bloodstream, thereby conserving water and concentrating the urine.

        Oxytocin

  • Stimulus uterus contraction during child birth, milk ejection
  • Oxytocin is a natural hormone that plays important roles in childbirth, lactation, and various aspects of human behavior and reproductive systems.
  •  During childbirth, oxytocin is released by the pituitary gland in response to the stretching of the cervix and uterus. It stimulates contractions of the uterine muscles, promoting labor and facilitating the delivery of the baby. Oxytocin also plays a role in the bonding between the mother and her newborn baby, contributing to the formation of maternal behavior and nurturing instincts.