Hypothalamus/Pituitary II

Vocabulary flashcards covering pituitary anatomy, GnRH signaling, gonadotropins, receptors, regulatory hormones, and related concepts from the lecture notes.

Anterior Pituitary (adenohypophysis)

Glandular lobe forming from Rathke's pouch; secretes FSH, LH, TSH, ACTH, prolactin, and other hormones.

Posterior Pituitary (neurohypophysis)

Neural lobe derived from brain; stores and releases vasopressin (ADH) and oxytocin; connected to hypothalamus.

Sella Turcica

Saddle-shaped depression in the sphenoid bone that encases and protects the pituitary.

Median Eminence

Hypothalamic region where GnRH is released into the hypophyseal portal system; a circumventricular organ.

Circumventricular Organ

Brain regions with leaky capillaries (blood-brain barrier is not tight) allowing hormone exchange.

Hypophyseal Portal System

Two capillary beds in series linking hypothalamus to anterior pituitary; enables small amounts of hypothalamic hormones to regulate pituitary.

GnRH (Gonadotropin-Releasing Hormone)

Hormone produced in the hypothalamus (POA and ARC) that stimulates LH and FSH release from gonadotropes in pulsatile fashion.

Gonadotropes

Anterior pituitary cells that secrete FSH and LH in response to GnRH signaling.

Luteinizing Hormone (LH)

Glycoprotein with alpha and beta subunits; beta subunit is LH-specific; stimulates ovarian hormone production and ovulation; half-life ~60 minutes.

Follicle Stimulating Hormone (FSH)

Glycoprotein with alpha and beta subunits; beta subunit is FSH-specific; stimulates follicle growth and estradiol production; half-life ~240 minutes.

Alpha Subunit

Shared subunit present in LH, FSH, TSH, and hCG.

LH Beta Subunit

Beta subunit unique to LH, conferring receptor specificity.

FSH Beta Subunit

Beta subunit unique to FSH, conferring receptor specificity.

Activin

TGF-β family member produced by many tissues; promotes FSH production via SMAD signaling.

Inhibin

TGF-β family protein produced mainly by the ovary; inhibits activin signaling and reduces FSH production.

TGF-β Superfamily

Family of proteins (including activin and inhibin) that regulate many physiological processes.

FSH Receptor

Receptor on granulosa cells activated by FSH; promotes follicle growth and estradiol production.

LH Receptor

Receptor on theca cells activated by LH; drives steroid production and ovulation; also activated by hCG and eCG.

hCG (human Chorionic Gonadotropin)

Placental hormone that activates LH receptors to maintain progesterone production during pregnancy.

eCG (Equine Chorionic Gonadotropin)

Produced by equine placental tissue; activates LH and FSH receptors in horses; used for superovulation in other species; longer half-life.

Rathke's Pouch

Embryonic diverticulum of the stomodeum that forms the anterior pituitary.

Infundibulum

Diverticulum of the brain floor that connects hypothalamus to the pituitary; forms the pituitary stalk.

GnRH Pulses

Pulsatile GnRH release driving LH and FSH pulses; used as a proxy measurement when portal blood is inaccessible.

LH Pulse Regulation

GnRH pulse frequency is the primary regulator of LH pulses; one GnRH pulse yields one LH pulse; LH has a short half-life.

FSH Regulation

FSH secretion is driven by GnRH and modulated by activin and inhibin; FSH has a longer half-life and basal secretion.

Activin's Role in FSH

Promotes FSH production via signaling in gonadotropes.

Inhibin's Role

Inhibits activin signaling, reducing FSH production; part of the ovarian regulatory loop.

Estradiol and Inhibin Feedback

Estradiol and inhibin suppress FSH during the follicular phase; GnRH triggers LH and FSH surge.

Gonadotropin-TGF-β Pathways

Activin/Inhibin are part of the TGF-β superfamily that regulate gonadotropin secretion.

Gonadotropin Receptors in Ovary

FSH receptor on granulosa cells stimulates follicle growth and estradiol production.

Gonadotropin Receptors in Ovary (LH)

LH receptor on theca cells stimulates steroid production and ovulation; activated by LH, hCG, and eCG.

PKC Signaling in Gonadotropes

GnRH binding activates Protein Kinase C, stimulating subunit production of FSH and LH.

Measurement of GnRH Pulses

GnRH is hard to measure in systemic blood; portal blood is difficult to collect; pulses are inferred by LH/FSH patterns.