hypothalamic and pituitary part 1 Flashcards
what is the pituitary gland composed of?
anterior pituitary
posterior pituitary
what is the neural portion of the pituitary?
neurohypophysis (posterior)
what is the epithelial portion of the pituitary?
adenohypophysis (Anterior)
what connects hypothalamus and pituitary gland?
hypophyseal stalk
where do tumors of the pituitary put their pressure, what symptoms do these cause?
on optic nerves
visual issues, dizziness
where is posterior pituitary derived from?
neural tissue
cell bodies of axons and nerves whose cell bodies
are in hypothalamus
what are the nuclei of posterior pituitary? what do they secrete?
Supraoptic nucleus (ADH)
paraventricular nucleus (Oxytocin)
what are the connections between the hypothalamus and anterior pituitary?
neural and hormonal
what is the anterior pituitary derived of?
endocrine cells from primitive foregut
what does anterior pituitary secrete?
ACTH TSH LH FSH GH Prolactin
How is anterior pituitary connected to hypothalmus?
Hypothalamic-hypophysial portal blood vessels
How does the hypothalamic-hypophysial portal system work? what occur?
releasing or release inhibiting hormones delivered directly
from hypothalamus to anterior pituitary in high
concentrations
do hormones from hypothalamic-hypophysial portal system appear in systemic circulation?
not in high concentrations
what are the hormone families of the anterior pituitary?
ACTH Fam
TSH, FSH, LH Fam
GH, Prolactin fam
what secretes ACTH
Corticotrophs
what secretes TSH
thyotrophs
what secretes FSH and LH
gonadotrophs
what secretes GH
somatotrophs
what secretes Prolactin
lactotrophs
describe how TSH is secreted?
what are the steps from the hypothalamus to anterior pituitary?
TRH from hypothalamus
target thyrotrophs in anterior pituitary
describe how ACTH is secreted?
what are the steps from the hypothalamus to anterior pituitary?
CRF from hypothalamus
target corticotrophs in anterior pituitary
describe how LH, FSH is secreted?
what are the steps from the hypothalamus to anterior pituitary?
GnRH from hypothalamus
target gonadotrophs in anterior pituitary
describe how Prolactin is secreted?
what are the steps from the hypothalamus to anterior pituitary?
Increase in TRH and decrease in PIF from hypothalamus
target lactotrophs in anterior pituitary
How are endocrine axes maintained?
around a set point via negative feedback inhibition
what is one of the most common ways that hypothalamic hormones are secretes?
in a pulsatile manner through circadian rhythms
what is a primary endocrine disorder?
defect in peripheral endocrine gland causes hormone imbalance
what is a secondary endocrine disorder?
defect in pituitary gland causes hormone imbalance
what is a tertiary endocrine disorder?
defect in hypothalamus causes hormone imbalance
name the major anterior pituitary gland axes
hypothalamus- pituitary- gonad
hypothalamus- pituitary- liver
hypothalamus- pituitary- prolactin
hypothalamus- pituitary- thyroid
hypothalamus- pituitary- adrenal
where are FSH and LH released from?
how are they regulated
from anterior pituitary gonadotropes
they are regulated by hypothalamic GnRH (pulsatile release)
why is FSH and LH important?
estrogen and progesterone in females
(normal menstrual cycle depends on it especially!)
testosterone in males
what can inhibit GnRh production?
extreme energy deficits, extreme exercise, depression
What is acromegaly caused by? symptoms?
excessive secretion of growth hormone in adulthood
too much growth of soft tissue, cartilage, bone in face hands and feet
shows gradually
What is growth hormone produced by and what does it target?
what inhibits it?
somatotropes in anterior pituitary
targets liver and bone
Somatostatin and IGF1 as part of negative feedback
what type of signalling is GH receptor linked to?
JAK-STAT signalling
what stimulated GH?
FASTING/HUNGER/STARVATION
HYPOGLYCEMIA
GHRELIN CAN STIMULATE IT!
puberty
exercise
sleep
stress
what are the three direct actions of GH?
- Growth
- hypertrophy - cell reproduction
- hyperplasia - metabolism
- increase protein synthesis
- increase glycogen and fat breakdown
what are the indirect actions of GH and how is it relevant?
most growth is indirect
tells liver cells to make IGF1, targetting almost every cell in body
stimulates hypertrophy and hyperplasia
What two cells are produced by the hypothalamus that affect anterior pituitary GH?
how do they do it?
GhRh stimulates GH production in anterior pituitary
GHIH(somatostatin) inhibits GH
greater production of GH has what feedback effect?
decreases GHRH from hypothalamus
increases IGF1 from liver
greater production of IGF1 from liver has what feedback effect?
decreases GH
increases GHIH
what two hormones affect GH production? from where and how
ghrelin from stomach
GHRH from hypothalamus
two different receptors
what is a secondary deficiency in production of GH?
not enough GH from anterior pituitary
what is a tertiary deficiency in production of GH?
not enough ghrelin and GHRH
what can be used to treat defective release of GHRH?
semorelin
what can be used as replacement of GHRH?
somatropin
somatrem
what can be used due to failure of IGF1 release from GH, GH deficiency or patients with GH antibody?
mecasermin
what causes gigantism?
in youth, before closure of bone epiphyses due to IGF1 stimulation!!
what factors cause liver to produce IGF1?
what will this cause the liver to do?
what is this called?
increased carb uptake which allows for insulin availability
increased protein uptake, amino acids are available
causes mitogenesis, lypolysis, differentiation
FAVORABLE GROWTH PROMOTING FACTORS
describe unfavorable conditions that will stop GH and the liver will not make IGF1
what will happen?
enough carbs to have insulin
not enough protein to have amino acids
lipogenesis and carb storage will occur
WEIGHT GAIN!
what will cause a fasted state?
what will happen to GH levels and IGF1?
what will this cause?
decreased carbs and little insulin
increased protein for amino acids
gh levels will go up, so will IGF1
lipolysis, ketogenic metabolism and diabetogenic
how is GH related to insulin insensitivity?
raises blood glucose by decreasing peropheral glucose intake,
stimulate hepatic gluconeogenesis
what is a sensitive test for acromegaly
patient has :
high GH and IGF1
doesnt suppress GH production in response to oral glucose
ALSO PITUITARY ENLARGEMENT ON MRI!
what are the main metabolic functions of GH?
diabetogenic effect
increased protein synthesis and growth factor
increased linear growth
how does GH cause a diabetogenic effect?
decreases glucose uptake by target tissues
increase lipolysi in fat
incraes blood insulin levels
how does GH cause an increase in protein synthesis?
what is the main mediator
increases uptake of amino acids
stimulates DNA, RNA and protein
is mediated by IGF1
how does GH cause an increase in linear growth?
what is the main mediator
stimulates DNA, RNA and protein synthesis
increase in metabolism in cartilage forming cells and chondrocytes
mediated by IGF1
when is GH level highest during the day?
during life?
sleep, exercise
puberty, lowest during adulthood
what can disturb GH secretion?
sleep disturbances, fluctuates throughout day
what causes GH deficiency, why is it bad?
decreases GHRH causes it (hypothalamus issue)
can’t make IGF1 (somatomedins)
What causes GH excess? why is it bad?
pituitary adenoma
Gigantism and acromegaly!
what does prolactin do?
primarily makes lactation happen
also suppresses GnRH, stopping LH and FSH
decreases sexual drive and reproduction
what makes prolactin and when
what stops it?
lactotropes, 5th week of pregnancy, pulsatile
inhibited by hypothalamic dopamine, feedback by prolactin causes dopamine to be made
what stimulates prolactin secretion?
pregnancy breast feeding sleep stress TRH
what inhibits prolactin secretion?
dopamine/ agonists
somatostatin
prolactin itself
what are pituitary adenomas, what do they cause?
adenomas release active hormone into blood excessively
usually prolactinoma!
what causes hypopituitarism?
brain damage such as a stroke or injury
tumors
non pituitary tumors such as craniopharyngioma (most common tumor affecting HP axis in kids)
infections
infarction such as sheehan syndrome
autoimmune
pituitary hypoplasia
genetic disorders
describe steps in oxytosin secretion?
preprooxyphysin
to prooxyphysin in hypothalamus
to hypothalamic-hypophyseal tract( neurophysins cleaved)
to posterior lobe of pituitary as oxytocin
to breast
what does oxytocin do?
milk letdown
- contraction of cells lining milk ducts
- caused by sucking, sight of infant
uterine contraction
- caused by dilation of cervix
- causes uterine contractions
- induces labor
