Fig 025 Pituitary Hormones

Pituitary

The pituitary gland (hypophysis) is often called the "master gland" of the body because it produces hormones that regulate other endocrine glands. It has two major parts: anterior pituitary and posterior pituitary.

Negative Feedback Loops

The anterior pituitary maintains homeostasis by using negative feedback to regulate hormone secretion.

• The hypothalamus signals the pituitary gland to release more of a pituitary hormone (e.g., ACTH).
• The pituitary hormone acts on another endocrine gland (e.g., adrenal cortex) to release additional hormones (e.g., cortisol) that produce physiologic actions.
• These hormones also act on the hypothalamus and/or anterior pituitary to inhibit the release of the pituitary hormone (e.g., ACTH).

Overall, a negative feedback loop means that when the level of a pituitary hormone is high, further secretion of the hormone is inhibited. When the level of the hormone is low, the secretion of the hormone is stimulated.

Anterior Pituitary

The anterior pituitary (adenohypophysis) secretes six hormones. Each hormone is secreted by a different cell type, except for FSH and LH which are secreted by the same cell type.

• Adrenocorticotropic hormone (ACTH) - stimulates the adrenal cortex to produce steroids
  • Mineralocorticoids (e.g., aldosterone) - act on the kidney to regulate ion balance and increase blood pressure
  • Glucocorticoids (e.g., cortisol) - stimulate gluconeogenesis, suppresses immune responses, and modulates CNS function
• Thyroid-stimulating hormone/ (TSH) - stimulates the thyroid to produce thyroxine (T₄) and triiodothyronine (T₃ which influence the basal metabolic rate and protein synthesis
• Follicle-stimulating hormone (FSH)
  • Testis - stimulates spermatogenesis and inhibin production
  • Ovary - stimulates development of ovarian follicles and estrogen production
• Luteinizing hormone (LH)
  • Testis - stimulates secretion of testosterone
  • Ovary - stimulates ovulation and progesterone production
• Prolactin - stimulates milk production in mammary glands
• Growth hormone (GH) - effects by direct action of GH and indirect actions through GH-induced production of insulin-like growth factor-1 (IGF-1) by the liver; major promoter of body growth

Posterior Pituitary

Posterior pituitary (neurohypophysis) only secretes two hormones. Each hormone is synthesized in cell bodies of neurons in the hypothalamus and released from axon terminals in the posterior pituitary.

• Antidiuretic hormone (ADH; vasopressin) - increases water reabsorption in the kidney
• Oxytocin
  • Stimulates contraction of smooth muscle in the uterus during childbirth
  • Stimulates ejection of milk by the mammary gland