M32: Endocrine System - Pituitary & Hypothalamus Flashcards
Which structure connects the hypothalamus to the pituitary gland?
infundibulum
(hypothalamus superior to pituitary)
general role of hypothalamus
- receives input from cortex, thalamus & internal organs
- regulates homeostasis via ANS - temp, thirst, hunger, sex, fight/flight
how many different hormones does the hypothalamus produce?
9 total
- 7 control anterior pituitary gland secretions (5 releasing and 2 inhibitory)
- 2 are shuttled to posterior pituitary for storage
how many different hormones does the pituitary gland produce?
- produces 7
- secretes 9 (2 are stored in posterior pituitary)
sella turcica
indentation in spehenoid bone that provides extra protection for pituitary gland
2 lobes of pituitary gland
ANTERIOR (aka adenohypophysis)
- 75% of pituitary weight
- releases 7 hormones
POSTERIOR (aka neurohypophysis)
- partially made of nervous tissue
- releases 2 hormones from hypothalamus
name the cells that make hormones in hypothalamus and pituitary glands
neurosecretatory cells
how do hormones secreted from hypothalamus reach the anterior pituitary?
HYPOPHYSEAL PORTAL SYSTEM
- neurosecretatory cells in hyporthalamus make the hormones and package into vessicles
- axonal transport
- hormones released into PRIMARY PLEXUS (first capillary bed of portal system, in infundibulum)
- hormones travel through HYPOPHYSEAL PORTAL VEIN to SECONDARY PLEXUS (more capillary beds!) in anterior pituitary
- hormones leave pituitary via HYPOPHYSEAL VEIN
does every hormone produced in the hypothalamus trigger release of pituitary hormones?
NO
- only 7/9 are releasing/inhibiting hormones that affect the pituitary
- other 2 are stored in pituitary
“three hormone system”
-> hormone produced by gland
-> hormone reaches target tissue
-> target tissue releases hormone that effects first hormone
cycle produces negative or positive feedback
tropic hormones
hormones that work on other endocrine glands or target tissues in the body that can secrete their own hormones
- hormones from pituitary gland are tropic hormones
Cells of anterior pituitary and hormones they secrete
SOMATOTROPHS: secrete human growth hormone (hGH)
THYROTROPHS: secrete thyroid stimulating hormone (TSH)
GONADOTROPHS: secrete follice stimulating hormone (FSH) and lutenizing hormone (LH)
LACTOTROPHS: secrete prolactin
CORTICOTROPHS: secrete adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone (MSH)
hGH functions
Human growth hormone
- released in bursts every few hours (especially during sleep) by somatotrophs
- most plentiful hormone in AP
Direct Actions: changes to metabolism
- stimulates lipolysis
- slows glucose uptake into cells
- slows glucose use in ATP production when blood glucose levels drop
Indirect Actions: tissue growth
- increases synthesis of INSULIN-LIKE GROWTH FACTORS (IGF) -> increases cell growth and repair
- common target cells are liver, skeletal muscle, cartilage and bone
TSH
thyroid stimulating hormone
FSH and LH
follicle stimulating hormone and luteinizing hormone
ACTH
adrenocorticotropic hormone
MSH
melanocyte-stimulating hormone
- don’t really know what it does
- in excess, can cause darkening of the skin
lipolysis
breakdown of triglycerides into free fatty acids as fuel for body
Function of Insulin-like growth factors (IGF)
Increases cell growth and repair
e.g. increase pr- synthesis, stimulation of osteoblasts
What side effects result from takign hGH as a muscle building suppliment?
Because hGH stimulates growth and repair -> cancer growth
Becasue hGH slows glucose intake into cells -> diabetes
regulation of hGH
- Controlled by growth hormone releasing hormone (GHRH) and growth hormone-inhibiting hormone (GHIH)
- released during deep sleep, SNS arousal, when blood fatty acids low or amino acids high
- decreases with aging and obesity
GHRH
- stimulates hGH secretion
- hGH stimulates glycogen breakdown
- blood-glucose rises to normal
- hyperglycaemia inhibits GHRH release
GHIH
- inhibits hGH secretion
- decreased glycogen breakdown
- blood-glucose falls to normal
- hypoglycaemia inhibits GHIH release
gigantism and acromegaly
gigantism: presence of excess human growth hormone throughout childhood into adulthood (andre the giant)
acromegaly: larger features of hands and feet because growth plates fuse later due to excess hGH
somatotrophs secrete…
hGH
Thyrotrophs secrete…
TSH
gonadotrophs secrete…
FSH and LH
lactotrophs secrete…
prolactin
corticotrophs secrete…
ACTH MSH
TSH functions
- produced by thyrotroph cells in AP (when stimulated by TRH from hypothalamus)
- stimulates synthesis and release of T3 and T4 from thyroid
- blood concentrations of T3 and T4 control TRH release (negative feedback)
- thyroid regulates basal metabolic rate
What stimulates FSH and LH release?
- release stimulated via gonadotropin
releasing hormone (GnRH) from hypothalamus
FSH function and regulation
Function:
- formation of follicles in ovary
- stimulates follicles to secrete estrogen
- stimulates sperm production in testes
Regulation:
- release stimulated via gonadotropin releasing hormone (GnRH) from hypothalamus
- released by gonadotrophs in AP
- inhibited by estrogen in females and testosterone in males
LH function and regulation
In females it stimulates:
- ovulation of 2nd oocyte from ovary
- formation of corpus luteum
- secretion of estrogen and progesterone
In males it stimulates:
- interstitial cells to secrete testosterone
Regulation:
- release stimulated via gonadotropin releasing hormone (GnRH) from hypothalamus
- released by gonadotrophs in AP
- inhibited by estrogen in females and testosterone in males
PRL function and regulation
Regulation
- Prolactin inhibiting hormones (PIH) and prolactin releasing hormones (PRH) from hypothalamus regulate lactotrophs
- PIH released most of the time
- prgenancy increases PRH and suckling reduces PIH
Functions:
- females: under right condition, causes milk production
PRL only a mild stimulant for milk production, there are a lot of other factors involved
- males: too much may cause erectile dysfunction
ACTH (adrenocorticotropic hormone) function and regulation
Functions:
- targets adrenal cortex
- produces/secretes cortisol and other glucocorticoids
Regulation:
- corticotropin-releasing hormone (CRH) from hypothalamus stimulates corticotrophs in AP to release ACTH
- glucocorticoids inhibit CRH and ACTH (negative feedback)
Posterior pituitary gland function
does not synthesize hormones!
- stores/releases OXYTOCIN and ANTIDIURETIC HORMONE (ADH)
hypothalamus to posterior pituitary gland pipeline
- oxytocin and ADH produced in hypothalamus neurosecretatory cells
- travel through axons in HYPOTHALAMIC-HYPOPHYSEAL TRACT in infundibulum
- released at PP in CAPILLARY PLEXUS OF INFUNDIBULAR PROCESS
- supplied by INFERIOR HYPOPHYSEAL ARTERY, exits via POSTERIOR HYPOPHYSEAL VEIN
Oxytocin function and regulation
affects uterus and mammary glands
During delivery:
- stretching of cervix stimulates release
- stimulates smooth muscle contraction in uterus
- positive feedback loop
After delivery:
- released during suckling & hearing baby’s cry - stimulates milk ejection
3 functions of ADH (antidiuretic hormone)
aka VASOPRESSIN
- increase water reabsorbtion in kidneys
- sudoriferous (sweat) glands - decrease sweating
- increase blood pressure-vasoconstriction
ADH regulation
2 pathways
ADH released:
- dehydration (high blood osmotic pressure) stimulates hypothalamic osmoreceptors
- osmoreceptors activate neurosecretatory cells that synthesize ADH
- ADH liberated from PP axon terminal, goes into bloodstream
- Effects: kidneys retain water, sweat glands decreases water loss, vasoconstriction
ADH inhibited
- overhydration (low osmotic pressure) inhibits hypothalamic osmoreceptors
- inhibition of osmoreceptors reduces or stops ADH secretion
How does alcohol consumption effect ADH
inhibits ADH secretion
- lose too many fluid because not able to reabsorb water
- causes a hangover/thirst next day
what vessel provides blood supply to the primary plexus?
superior hypophyseal artery
