Describe in detail about the structural organization of mammalian pituitary gland with emphasis on its hormones and their functions. (IFS 2019/15 Marks)

Introduction:

The pituitary gland, also known as the hypophysis, is a small, pea-sized gland located at the base of the brain. It is divided into two main parts: the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis). 

Structural Organization of the Mammalian Pituitary Gland

1. Overview

• The pituitary gland, also known as the hypophysis, is a small, pea-shaped gland located at the base of the brain, housed in the sella turcica of the sphenoid bone.
• It is often referred to as the "master gland" because it regulates various endocrine glands.

2. Division of the Pituitary Gland

• Anterior Pituitary (Adenohypophysis).
• Posterior Pituitary (Neurohypophysis).
• Intermediate Lobe (rudimentary in humans).

Anterior Pituitary (Adenohypophysis)

• Derived from ectodermal tissue of the oral cavity (Rathke’s pouch).
• Comprises three regions:
  
  • Pars Distalis: Major secretory region.
  • Pars Tuberalis: Surrounds the infundibulum.
  • Pars Intermedia: Present in some mammals; almost absent in humans.

Hormones Secreted:

• Growth Hormone (GH):
  
  • Stimulates growth of bones, muscles, and tissues.
  • Regulates metabolism of proteins, fats, and carbohydrates.
• Prolactin (PRL): Promotes milk production in mammary glands.
• Thyroid-Stimulating Hormone (TSH): Stimulates thyroid gland to release thyroxine (T4) and triiodothyronine (T3).
• Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal cortex to produce cortisol.
• Follicle-Stimulating Hormone (FSH): Regulates gamete production in ovaries and testes.
• Luteinizing Hormone (LH): Induces ovulation in females and testosterone production in males.

Posterior Pituitary (Neurohypophysis)

• Derived from neuroectoderm of the diencephalon.
• Composed of:
  
  • Pars Nervosa: Main storage site.
  • Infundibulum: Connects the pituitary to the hypothalamus.
• Does not produce hormones but stores and releases them.

Hormones Released:

• Antidiuretic Hormone (ADH) (Vasopressin): Regulates water balance by increasing water reabsorption in kidneys.
• Oxytocin:
  
  • Stimulates uterine contractions during childbirth.
  • Promotes milk ejection from mammary glands.

Intermediate Lobe

• Present prominently in lower vertebrates; reduced in humans.
• Produces Melanocyte-Stimulating Hormone (MSH):
  
  • Influences pigmentation by acting on melanocytes.

Functional Integration with the Hypothalamus

• The hypothalamus regulates the pituitary gland through:
  
  • Releasing Hormones (e.g., GnRH, TRH, CRH).
  • Inhibitory Hormones (e.g., Somatostatin, Dopamine).
• Hypothalamo-hypophyseal portal system facilitates direct transport of hormones.

Conclusion:

The pituitary gland plays a crucial role in regulating various bodily functions through the production and release of hormones from its anterior and posterior parts. The hormones produced by the pituitary gland have diverse functions in growth, reproduction, stress response, and water balance.