CH3 Anterior Pituitary Gland Flashcards
What are the components of the anterior pituitary (adenohypophysis)?
pars anterior and pars intermedia
Name both the hypophysiotropic hormone and the tropic hormone paired with Lactotrophs.
Dopamine –> Prolactin
Name both the hypophysiotropic hormone and the tropic hormone paired with Corticotrophs.
Corticotropic-Releasing Hormone –> Proopiomelanocortin PMOC (ACTH, beta-lipotropin LPH, alpha-melanocyte-stimulating hormone MSH, beta-endorphin)
Name both the hypophysiotropic hormone and the tropic hormone paired with Thyrotrophs.
Thyrotropin-releasing hormone –> Thyroid-stimulating hormone
Name both the hypophysiotropic hormone and the tropic hormone paired with Gonadotrophs.
LHRH –> LH & FSH
Name both the hypophysiotropic hormone and the tropic hormone paired with Somatotrophs.
GHRH –> Growth Hormone
What does LH & FSH do?
stimulate gonadal production of sex steroids. Mediates reproductive function and behavior.
What does ACTH do?
stimulates adrenal glands to produce steroid hormones. Regulate water and sodium balance, inflammation, and metabolism
What does GH do?
exerts directly effects on tissue growth and differentiation – indirect effects through stimulation of Insulin-like Growth Factor 1 (mediates some growth and differentiation effects of GH)
What governs the pattern hormone release? Where is it located?
Cyclic pattern of hormone release is governed by the nervous system – the hypothalamic Suprachiasmatic Nucleus “the internal biological clock/circadian clock”, which is synchronized/entrained by external signals (e.g. light and dark)
What are the 3 families of anterior pituitary hormones? Which hormones constitute each family?
Glycoproteins (TSH, FSH, LH), Pro-opiomelanocortin POMC (ACTH, beta-LPH, alpha-MSH, beta-endorphin), Growth Hormone & Prolactin (GH & Prolactin)
What stimulates ACTH release?
psychologic stress and physical stress
What receptor does ACTH bind to? What are its effects?
Melanocortin Receptor 2 - MC2R (adrenal cortex); stimulation and release of glucocorticoids (cortisol) & mineralocorticoids (aldosterone)
What is the feedback mechanism for ACTH release?
Cortisol on anterior pituitary and hypothalamus (inhibit CRH release) (negative feedback)
What factors inhibit GH release?
somatostain, IGF-1, glucose, nonesterified free fatty acids
How is GH found in serum? What purpose does this serve?
GH is found bound to GH-binding protein (by proteolytic cleavage of the GH membrane receptor). This serves as a reservoir for GH & prolongs its half life.
When and how is GH released? Over time?
nocturnally, in a pulsatile manner; increase during childhood, peak during puberty, fall with aging
What does GH stimulate?
IGF-1, lipolysis, amino acid transport into cells, protein synthesis
How does GH affect hepatocytes (the liver)?
stimulates hepatic IGF-1 (insulin-like growth factor 1) and hepatic glucose production
How does GH compare to insulin?
GH counteracts the action of insulin on lipid and glucose metabolism: decrease skeletal muscle glucose utilization, increase lipoylysis, stimulate hepatic glucose production
What are the physiologic effects of IGF-1?
act as mitogens (stimulate DNA, RNA, & protein synthesis) and parallel effects to GH (stimulates bone formation, protein synthesis, glucose uptake in muscle, neuronal survival, myelin synthesis, collagen synthesis, decreases collagen degradation, inhibit protein degradation in muscle)
How do IGF receptors work?
IGF-1 binds to receptor and activates autophosphorylating tyrosine kinase domain. This causes a cascade via phosphorylation of substrate proteins.
How do IGF-RECEPTORS compare to insulin-RECEPTORS?
receptors have similar structure and function (receptor tyrosine kinase), but insulin receptor is involved in metabolic functions and IGF-1 receptors mediate growth and differentiation. (recall: IGF-1 parallels GH, which counteracts insulin)
What stimulates production of prolactin? How?
stimulated by elevated estrogen levels (proliferation of lactrotrophs), stimulated by sucking (decreases dopamine release & relieves tonic inhibition); also stimulated by LHRH, serotoninergic & opiodergic pathways
How is sucking of the breast an example of a stimulus-secretion (neuroendocrine) reflex?
Sucking causes the hypothalamus to decrease the amount of dopamine released (tonic inhibition), therefore relieving the lactotroph of tonic inhibition, allowing for more prolactin to be released.
How is prolactin regulated?
Prolactin is tonically inhibited by production of dopamine, somatostatin, and gamma-aminobutyric acid (GABA)
How does dopamine inhibit the lactotroph?
Dopamine binds to Dopaminergic (D2) Gi-protein-coupled receptors. It inhibits adenylate cyclase, activates K+ channels (hyperpolarization), inhibits Ca++ channels (hyperpolarization)
What is the feedback mechanism of Prolactin?
Prolactin binds to receptors on Dopaminergic Neurons, increasing dopaminergic tone (increasing dopamine synthesis & inhibiting prolactin release from lactrotrophs)
What are Adenomas? Which one is the most common?
Adenoma is a small tumor that causes excess production of pituitary tropic hormones. Prolactinomas are most common.
What kind of adenoma presents with elevated milk secretion (galactorrhea) and reproductive dysfunction (infertility).
Prolactinoma (hyperprolactinemia)
What kind of adenoma presents with acromegaly (abnormal growth of hands/feet/face), bone overgrowth, & soft tissue overgrowth in adults / gigantism in children?
Growth Hormone-secreting adenoma
What kind of adenoma presents with Cushing Syndrome (central obesity, proximal myopathy, hypertension, mood chanes, dorsocervical fat pads, & hyperglycemia)?
Cortotropin-releasing adenoma (excess cortisol)
What kind of adenoma presents with insufficient hormone production?
Gonadotroph pituitary adenoma
What is Sheehan Syndrome?
damage to pituitary gland due to ischemia (because of excessive blood loss during childbirth)
What is Laron Syndrome? How does it present?
GH insensitivity syndrome (failure to generate IGF-1 & IGFBP-3 due to mutations or deletions in GH receptor gene) - presents as dwarfism
What are the paired measurements of anterior pituitary hormones?
ACTH-cortisol, GH-IGF1, LH-estradiol, FSH-progesterone, TSH-thyroxine
