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Related Subjects: |Adrenal Physiology |Addisons Disease |Phaeochromocytoma |Adrenal Adenomas |Adrenal Cancer |Cushing's Syndrome |Cushing's Disease |Congenital Adrenal hyperplasia |Primary hyperaldosteronism (Conn's syndrome) |ACTH |McCune Albright syndrome |Male Infertility |Prolactin |Prolactinoma |Sheehan's syndrome

Overview of Pituitary Anatomy and Physiology

The pituitary gland, often referred to as the "master gland," plays a crucial role in regulating various physiological processes through the secretion of hormones. It is located at the base of the brain and is divided into two main parts: the anterior and posterior pituitary.

Key Concepts

• Anatomy of the Pituitary Gland:
  • Located in the sella turcica, a bony cavity at the base of the skull.
  • Connected to the hypothalamus by the pituitary stalk (infundibulum).
  • Divided into two main lobes:
    • Anterior Pituitary (Adenohypophysis): Larger, glandular portion.
    • Posterior Pituitary (Neurohypophysis): Smaller, neural portion.

Embryology

• Adenohypophysis - Anterior pituitary descends from Rathke's pouch
• Neurohypophysis - Posterior pituitary is a direct extension from the hypothalamus, connected to it via the infundibular stalk, which is also considered part of the neurohypophysis
• The lobes are separated by a pars Intermedia.

Anterior Pituitary (Adenohypophysis)

• Produces and secretes hormones in response to hypothalamic releasing and inhibiting hormones.
• Main Hormones:
  • Growth Hormone (GH):
    • Stimulates growth, cell reproduction, and regeneration.
    • Increases protein synthesis and fat metabolism.
  • Prolactin (PRL):
    • Stimulates milk production in the mammary glands.
  • Adrenocorticotropic Hormone (ACTH):
    • Stimulates the adrenal cortex to produce cortisol.
  • Thyroid-Stimulating Hormone (TSH):
    • Stimulates the thyroid gland to produce thyroid hormones (T3 and T4).
  • Follicle-Stimulating Hormone (FSH):
    • Stimulates gamete production (sperm in males, ova in females).
  • Luteinizing Hormone (LH):
    • Triggers ovulation and stimulates the production of sex hormones (estrogen and progesterone in females, testosterone in males).

Posterior Pituitary (Neurohypophysis)

• Stores and releases hormones produced by the hypothalamus.
• Main Hormones:
  • Antidiuretic Hormone (ADH, Vasopressin):
    • Regulates water balance by increasing water reabsorption in the kidneys.
    • Constricts blood vessels, raising blood pressure.
  • Oxytocin:
    • Stimulates uterine contractions during labour.
    • Promotes milk ejection during breastfeeding.
    • Involved in social bonding and sexual reproduction.

Regulation of Pituitary Hormone Secretion

• Hypothalamic Control:
  • Releasing and inhibiting hormones from the hypothalamus regulate the secretion of anterior pituitary hormones.
  • Examples:
    • Thyrotropin-releasing hormone (TRH) stimulates TSH release.
    • Corticotropin-releasing hormone (CRH) stimulates ACTH release.
    • Gonadotropin-releasing hormone (GnRH) stimulates FSH and LH release.
    • Growth hormone-releasing hormone (GHRH) stimulates GH release.
    • Somatostatin inhibits GH release.
    • Dopamine inhibits prolactin release.
• Feedback Mechanisms:
  • Negative feedback loops help maintain hormone levels within a narrow range.
  • Example: High levels of cortisol inhibit CRH and ACTH secretion.

Clinical Relevance

• Pituitary Disorders:
  • Hypopituitarism:
    • Underproduction of pituitary hormones.
    • Causes: Tumours, trauma, infections.
    • Symptoms: Fatigue, weakness, growth retardation, infertility.
  • Hyperpituitarism:
    • Overproduction of pituitary hormones.
    • Causes: Pituitary adenomas.
    • Symptoms: Depend on the hormone involved (e.g., acromegaly from excess GH, Cushing's disease from excess ACTH).
  • Diabetes Insipidus:
    • Deficiency of ADH.
    • Symptoms: Excessive thirst and urination.
    • Causes: Damage to the hypothalamus or pituitary gland.
  • Syndrome of Inappropriate ADH Secretion (SIADH):
    • Excessive release of ADH.
    • Symptoms: Water retention, hyponatremia.
    • Causes: Tumours, medications, central nervous system disorders.

Summary

The pituitary gland plays a central role in regulating various physiological processes through the secretion of hormones. The anterior pituitary produces hormones that influence growth, metabolism, and reproduction, while the posterior pituitary releases hormones that regulate water balance and uterine contractions. Understanding the anatomy and physiology of the pituitary gland is essential for diagnosing and treating endocrine disorders.