U01.08.04 Hypothalamic-Pituitary Hormones

The hypothalamus and pituitary gland work together to regulate various body functions through the secretion of hormones. Understanding these hormones, their functions, and their clinical implications is crucial for medical students, especially when preparing for exams like the USMLE.

Hormones and Their Functions

Hormone	Function	Clinical Notes
ADH	Increases water permeability of distal convoluted tubule and collecting duct	Stimulated by increased plasma osmolality. In SIADH, ADH is elevated despite low plasma osmolality.
CRH	Increases ACTH, MSH, and β-endorphin levels	Decreased in chronic exogenous steroid use.
Dopamine	Decreases prolactin and TSH secretion	Dopamine antagonists (e.g., antipsychotics) can cause galactorrhea due to hyperprolactinemia.
GHRH	Increases GH secretion	Increases in FSH and LH secretion
GnRH	Stimulates lactogenesis. Pituitary prolactinoma can cause amenorrhea, osteoporosis, hypogonadism, and galactorrhea. Breastfeeding increases prolactin, which delays postpartum ovulation (natural contraception).	Suppressed by hyperprolactinemia. Tonic GnRH analog (e.g., leuprolide) suppresses HPG axis. Pulsatile GnRH promotes puberty and fertility.
MSH	Increases melanogenesis by melanocytes	Causes hyperpigmentation in Cushing disease as MSH and ACTH share the same precursor molecule, POMC.
Oxytocin	Causes uterine contractions during labor; responsible for milk letdown	Modulates fear, anxiety, social bonding, mood, and depression.
Prolactin	Decreases GnRH secretion	Also known as growth hormone inhibiting hormone (GHIH). Analogs are used to treat acromegaly.
Somatostatin	Decreases GH and TSH secretion	Also known as growth hormone inhibiting hormone (GHIH). Analogs used to treat acromegaly.
TRH	Increases TSH and prolactin secretion	Increased TRH (e.g., in primary/secondary hypothyroidism) may increase prolactin secretion, leading to galactorrhea.

Hormones and Their Functions

Key Points to Remember

ADH (Antidiuretic Hormone): Regulates water balance by increasing water reabsorption in the kidneys. In SIADH (Syndrome of Inappropriate ADH Secretion), ADH is inappropriately elevated, leading to water retention and hyponatremia.
CRH (Corticotropin-Releasing Hormone): Stimulates the secretion of ACTH, which in turn stimulates cortisol production. Chronic steroid use suppresses CRH levels.
Dopamine: Acts as a prolactin-inhibiting factor. Dopamine antagonists, such as antipsychotics, can disrupt this balance, leading to hyperprolactinemia and symptoms like galactorrhea.
GHRH (Growth Hormone-Releasing Hormone): Promotes the release of growth hormone (GH). Tesamorelin, a GHRH analog, is used in treating HIV-associated lipodystrophy.
GnRH (Gonadotropin-Releasing Hormone): Controls the release of FSH and LH, essential for reproductive function. Hyperprolactinemia can suppress GnRH, leading to reproductive issues.
MSH (Melanocyte-Stimulating Hormone): Increases melanin production in the skin, leading to hyperpigmentation. This is particularly noted in Cushing’s disease due to the shared precursor with ACTH.
Oxytocin: Known for its role in labor and breastfeeding, oxytocin also influences emotional responses, including bonding and anxiety.
Prolactin: Primarily responsible for milk production after childbirth. Elevated prolactin levels, often due to pituitary adenomas, can cause menstrual irregularities and other reproductive issues.
Somatostatin: Inhibits the release of GH and TSH. It is utilized in the treatment of conditions like acromegaly through the use of somatostatin analogs.
TRH (Thyrotropin-Releasing Hormone): Stimulates the release of TSH and prolactin. Increased TRH, particularly in hypothyroidism, can lead to elevated prolactin levels and associated symptoms like galactorrhea.

This structured format should help in quickly understanding and reviewing the key concepts related to hypothalamic-pituitary hormones, which are vital for clinical practice and exam preparation.

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USMLE Step 1 Review Series

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U01.08.04 Hypothalamic-Pituitary Hormones

Hormones and Their Functions

Key Points to Remember

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