Endocrinology Quiz: Pituitary Hormones

Endocrine System

• The endocrine system is critical for adapting the human organism to internal and external environmental changes.
• A hormone is a substance produced by one cell type, transported by the bloodstream, and triggers a response in distant target cells.

Pituitary Hormones

• The pituitary gland, also called the "master gland", is a small gland at the base of the brain.
• The pituitary is controlled by the hypothalamus and feedback mechanisms from target glands.
• It is composed of two lobes:
  • The anterior lobe (adenohypophysis) secretes ACTH, GH, FSH, LH, TSH, and prolactin.
  • The posterior lobe (neurohypophysis) secretes vasopressin and oxytocin.
• Pituitary hormone secretion is regulated by releasing hormones (RH) and inhibitory hormones (IH) from the hypothalamus, transported via the hypothalamic-hypophyseal portal circulation. An example of a releasing hormone is TSHRH from the hypothalamus.

Growth Hormone

• Growth hormone promotes growth in childhood and maintains muscle and bone mass in adults.
• Growth is facilitated by anabolic action.
• Regulation involves releasing hormones (GH-RH) and inhibitory hormones (GH-RIH, or somatostatin) from the hypothalamus.
• Dysfunction of the growth hormone can lead to conditions like dwarfism (before puberty) or acromegaly (after puberty) depending on the age of onset.

Prolactin

• Prolactin stimulates milk production in women.
• In men, low prolactin levels may be associated with sexual problems; however, most men don't utilize prolactin.

Disorders of Prolactin Secretion

• Hyperprolactinemia is characterized by the hypersecretion of prolactin.
• Causes can be physiological (like pregnancy or breastfeeding) or pathological (like prolactinoma).

Symptoms of Hyperprolactinemia

• In women: Infertility, galactorrhea (abnormal lactation), irregular menstrual cycles, amenorrhea (absence of ovulation), and breast pain.
• In men: Impotence, gynecomastia (breast tissue development).
• Treatment typically involves dopaminergic agonists like bromocriptine.

Adrenocorticotropic Hormone (ACTH)

• ACTH promotes cortisol production, which helps manage stress and maintain blood pressure.
• The adrenal glands, located above the kidneys, comprise an outer cortex and inner medulla.
• The adrenal cortex produces steroid hormones (mineralocorticoids like aldosterone and glucocorticoids like cortisol and cortisone).
• The adrenal medulla produces catecholamines.

Thyroid-Stimulating Hormone (TSH)

• TSH regulates the thyroid gland, promoting metabolism.
• TSH release is controlled by hypothalamic thyrotropin-releasing hormone (TRH).

Luteinizing Hormone (LH)

• In women, LH maintains estrogen levels, regulates progesterone, and facilitates ovulation.
• In men, LH regulates testosterone production.

Follicle-Stimulating Hormone (FSH)

• FSH stimulates estrogen release in women and sperm production in men.

Placental Hormone (HCG)

• HCG, a placental hormone, is essential in human pregnancy.

Posterior Pituitary Hormones

• The posterior pituitary gland produces oxytocin and antidiuretic hormone (ADH).
• Oxytocin is involved in uterine contractions and milk ejection after childbirth.
• ADH regulates water balance in the body.

ADH Regulation and Deficiency

• ADH's release is regulated by osmoreceptors in the hypothalamus and baroreceptors in the cardiovascular system.
• ADH deficiency results in diabetes insipidus.
• Desmopressin is a synthetic ADH used in treating diabetes insipidus.