Hypothalamus and Pituitary Physiology Flashcards
What are the hormones of the hypothalamus? What is the major function of each?
- TRH: stimulates secretion of TSH (and PRL) by AP
- CRH: stimulates secretion of ACTH by AP
- GnRH: stimulates secretion of LH and FSH by AP
- GHRH: stimulates secretion of GH by AP
- SRIF: inhibits secretion of GH (SRIF is actually somatostatin)
- PIF: inhibits secretion of PRL by AP (PIF is actually dopamine)
What are the hormones of the anterior pituitary? What is the major function of each?
- FSH: stimulates spermatogenesis in testes; stimulates follicular development and estrogen synthesis in ovaries
- LH: stimulates testosterone synthesis in testes; stimulates ovulation, formation of corpus luteum, estrogen and progesterone synthesis in ovaries
- ACTH: stimulates synthesis and secretion of adrenocortical hormones (aldosterone, cortisol, androgens)
- TSH: stimulates synthesis and secretion of T3/T4 by thyroid
- PRL: stimulates breast milk production and assists in its secretion
- GH: stimulates protein synthesis, IGF-1 synthesis in liver, and overall growth
- “FLAT PiG”
- (MSH: stimulates melanin synthesis in melanocytes)
What are the hormones of the posterior pituitary? What is the major function of each?
- ADH/vasopressin: stimulates water reabsorption in kidneys and arterial vasoconstriction
- oxytocin: stimulates milk ejection from breasts, stimulates uterine contractions
What does the hypothalamic-pituitary unit regulate?
- regulates the thyroid, adrenal, and reproductive glands
- controls milk production and ejection, growth, osmoregulation
What is another name for the pituitary gland? What about for it’s anterior and posterior lobes? Where is each lobe derived from? How is the pituitary connected to the hypothalamus?
- pituitary is AKA the hypophysis
- anterior lobe (AKA adenohypophysis) derived from the primitive foregut (the oral cavity, specifically; called Rathke’s pouch)
- posterior lobe (AKA neurohypophysis) derived from neural tissue
- both lobes connect to the hypothalamus via the infundibulum (a neural connection); the anterior lobe also connects via the hypothalamic-hypophysial portal vessels (a blood connection, allowing for a hormonal connection)
What is unique about the posterior pituitary and its hormones?
- the posterior pituitary is technically a direct extension of the hypothalamus, and is made up of the terminal axons of the hypothalamic neural tissue; they release the hormones/neuropeptides into fenestrated capillaries
- the cell bodies of these axons are located in the hypothalamus (NOT in the posterior pituitary)
- this means the hormones secreted by the posterior pituitary (ADH and oxytocin) are really synthesized by the hypothalamus; they are therefore called neuropeptides
Where is ADH synthesized? Oxytocin?
- these are the hormones of the posterior pituitary; they are technically neuropeptides since they are made in the hypothalamus
- ADH is mainly synthesized in the supraoptic nuclei of the hypothalamus
- oxytocin is mainly synthesized in the paraventricular nuclei of the hypothalamus
Why aren’t large amounts of hypothalamic hormones found in the systemic circulation?
- because of the unique vascular connection between the hypothalamus and anterior pituitary
- the hypothalamic-hypophysial portal vessels are a unique network of vessels that connect the two structures; as a result, any releasing or inhibiting hormones released by the hypothalamus really only go to the anterior pituitary (they won’t make it into the systemic circulation)
What percentage of tissue in the anterior pituitary is responsible for synthesizing/secreting each of its six hormones? Which cell type is involved in each? Which cell type is acidophilic? Basophilic?
- GH: somatotrophs, 20% of anterior pituitary tissue
- ACTH: corticotrophs, 15%
- PRL: lactotrophs, 15%
- FSH and LH: gonadotrophs, 15% (total)
- TSH: thyrotrophs, 5%
- acidophils: somatotrophs (GH) and lactotrophs (PRL)
- basophils: corticotrophs (ACTH), gonadotrophs (FSH, LH), thyrotrophs (TSH)
What is GH? What stimulates GH secretion by the anterior pituitary? What inhibits it?
- growth hormone AKA somatotropin (an AP hormone)
- the most important hormone for normal growth throughout life
- stimulated by hypothalamus’ GHRH (GH releasing hormone), hypoglycemia, starvation, stress, exercise, puberty
- inhibited by hypothalamus’ somatostatin/SRIF (somatotropin release inhibiting factor), hyperglycemia, obesity, senescence, pregnancy
What are the major effects of GH? What are somatomedins?
- diabetogenic effects: increases insulin resistance to decrease glucose uptake, results in increased insulin secretion
- increases protein synthesis and organ growth*
- increases linear growth*
- *these are largely mediated by somatomedins (AKA insulin-like growth factors or IGFs), which are upregulated in the liver by GH; they use a tyrosine kinase mechanism of action, similar to insulin; the most important is somatomedin C (AKA IGF-1)
What will result from GH deficiency? GH excess?
- GH deficiency (mainly only an issue during childhood and puberty): short stature, mild obesity, delayed puberty
- GH excess: gigantism if pre-puberty, acromegaly if post-puberty
What is PRL? What stimulated PRL secretion by the anterior pituitary? What inhibits it? What is unique in its regulation compared to other anterior pituitary hormones?
- prolactin (an AP hormone)
- responsible for milk production and breast development
- stimulated by hypothalamus’ TRH (thyrotropin releasing hormone, which also stimulates TSH release)
- inhibited by dopamine (AKA PIF) unlike other AP hormones that are largely stimulated for regulation, prolactin is actually largely inhibited; the major factors that inhibit this dopamine-induced inhibition are pregnancy and breast suckling
What are the major effects of PRL?
- prolactin stimulates breast development during puberty and pregnancy, and stimulates lactogenesis
- it also inhibits hypothalamic GnRH (gonadotropin releasing hormone), resulting in anti-fertility effects (for example, it inhibits ovulation in females, which is why fertility decreases during breastfeeding)
What will result from PRL deficiency? PRL excess?
- PRL deficiency: failure to lactate
- PRL excess: galactorrhea, infertility
