Detailed Notes on Anterior Pituitary Hormones and Related Endocrine Functions - March 26

Anterior Pituitary Hormones

• General Functions:
  • Anterior pituitary synthesizes and secretes hormones, regulating various body functions.
  • Hormones include TSH, ACTH, FSH, LH, growth hormone, prolactin, and endorphins.
  • Each hormone has specific roles and is regulated by hypothalamic releasing hormones.

Key Hormones Secreted by Anterior Pituitary

• Thyroid Stimulating Hormone (TSH):
  • Stimulates the thyroid gland to release thyroid hormones.
• Adrenocorticotropic Hormone (ACTH):
  • Stimulates the adrenal cortex to produce cortisol.
  • Component of the body's chronic stress response.
• Follicle Stimulating Hormone (FSH):
  • Involved in reproductive processes.
• Luteinizing Hormone (LH):
  • Involved in reproductive functions alongside FSH.
• Growth Hormone (GH):
  • Major role in growth and metabolism, stimulates muscle and bone growth, promotes protein synthesis, and fat breakdown.
• Prolactin:
  • Stimulates lactation in females; aids sperm production and testosterone regulation in males.
  • Exhibits varying functions across species (e.g., osmoregulation in fish).
• Endorphins:
  • Act as natural pain relievers; released in response to pain or pleasurable activities.

Regulation of Anterior Pituitary Hormones

• Hormonal release is regulated by hypothalamic hormones:
  • Each anterior pituitary hormone has a corresponding releasing hormone (e.g., Thyrotropin-Releasing Hormone for TSH).
  • Additional inhibitory hormones can also regulate synthesis and secretion (e.g., growth hormone inhibitory hormone).

Growth Hormone

• Functions:

  • Stimulates tissue growth, especially muscle and bone. Promotes protein synthesis and fat breakdown for energy.
  • Plays a vital role in overall metabolic functions.

• Regulation of Growth Hormone Release:

  • Involves hypothalamic releasing hormone (GHRH) and inhibitory hormone (somatostatin).
  • Growth hormone release occurs in pulses, approximately 8 to 10 times in a 24-hour cycle.

• Disorders Related to Growth Hormone:

  • Overproduction may lead to gigantism; underproduction can result in dwarfism.

• Growth Hormone Mechanism:

  • GH acts on the liver to induce production of Insulin-like Growth Factor 1 (IGF-1).
  • IGF-1 mediates effects of GH on muscle and bone, promotes fat breakdown.

Thyroid Hormones

• Functions:

  • Regulates metabolism, body temperature, heart rate, and growth.
  • Involved in blood pressure regulation and digestive function.

• Thyroid Hormone Forms:

  • T3 (triiodothyronine) and T4 (thyroxine) play critical roles in metabolic processes.

• Regulation of Thyroid Hormones:

  • Controlled via the hypothalamus-pituitary-thyroid axis.
  • Low iodine levels can lead to hypothyroidism and goiter due to the inability to synthesize T3 and T4.

Calcium Homeostasis

• Calcitonin:

  • Secreted by the thyroid gland to lower blood calcium levels by promoting calcium deposition in bones and reducing kidney reabsorption.

• Parathyroid Hormone:

  • Opposes calcitonin by raising blood calcium levels through bone resorption and kidney absorption.

Stress Response Regulation

• Stress response is divided into two phases: acute and chronic.

  • Acute Response:

  • Triggered by the sympathetic nervous system, leading to release of epinephrine and norepinephrine from the adrenal medulla.

  • Prepares the body for ‘fight or flight’ response.

  • Chronic Response:

  • Involves the hypothalamic-pituitary-adrenal (HPA) axis and secretion of glucocorticoids (especially cortisol) from the adrenal cortex.

  • Increases blood glucose and mobilizes energy for prolonged stress handling.

• Key Hormones in Stress Response:

  • Epinephrine/Norepinephrine: Mobilize energy, increase heart rate, and redirect blood flow during acute stress.
  • Cortisol: A glucocorticoid that promotes glucose production and energy mobilization during chronic stress.

Coordination of Nervous and Endocrine Systems

• The nervous system and endocrine system work synergistically for bodily functions.

• Gastric Hormones:

  • Hormones such as gastrin, secretin, and cholecystokinin (CCK) are secreted in response to food intake, aiding digestion and absorption.

• GIP (Gastric Inhibitory Polypeptide):

  • Stimulates glucose absorption while inhibiting gastric secretion, illustrating coordinated control.

• The effective interaction between nervous and endocrine systems ensures homeostasis and metabolic balance in the body.