Endocrine Flashcards
neurosecretory cells
above the pituitary
secrete hormones that control the anterior pituitary
hypothalamic/hypophyseal portal circulation
hypothalamic hormones released to special capillaries that feed the anterior pituitary inferiorly
anterior pituitary
derived from epithelial lining from mouth
3/4 of adult pituitary size
doubles during pregnancy –> pituitary infarctions
thyrotrophs
stimulated by TRH
secrete thyrotropin (TSH)
gonadotrophs
stimulated by GnRH
secrete gonadotropins (LH, FSH)
corticotrophs
stimulated by CRH
secrete ACTH
somatotrophs
stimulated by GHRH; inhibited by somatostatin
secrete GH
what are hormones released from the hypothalamus?
releasing hormones - can be stimulating or inhibitory
small peptides with pulsatile secretion & short half-lives
travel to the anterior pituitary for regulation
what are hormones released from the anterior pituitary?
tropic hormones
pulsatile secretion
critical for hypothalamic releasing hormone function
constant stimulation can shut down the response (ex. constant secretion of GnRH can shut down release of LH & FSH
circadian rhythm
regulation of hypothalamic releasing hormones
Corticotropin releasing hormone (CRH)
stimulates ACTH release
production of glucocorticoids by and androgens by adrenal cortex
Thyrotropin releasing hormone (TRH)
stimulates TSH release and prolactin (PRL)
production of thyroid hormones (T3,T4)
Growth hormone releasing hormone (GHRH)
stimulates GH release
postnatal body growth
Luteinizing hormone releasing hormone (LHRH) aka GnRH
stimulates FSH and LH release
ovulation, progesterone & estrogen production, testosterone production
Somatostatin, somatotropin release inhibiting factor (SRIF)
inhibits GH (&GHRH) and TSH release
Prolactin (PRL)
milk production by mammary glands
inhibited by dopamine; stimulated by TRH
Dopamine
inhibits prolactin secretion
can have leaking milk from breasts with antagonists
lactotrophs
stimulated by TRH; inhibited by dopamine
release prolactin (PRL)
What hormone is released in direct response to hypothalamic TRH?
prolactin
role of ACTH
increases synthesis of glucocorticoids and androgens in adrenal cortex
proliferation, maintenance of adrenal cortex
cAMP as 2nd messenger
synthesized from POMC (alpha-MSH & CLIP) in corticotrophs
released in response to stress
What is a negative feedback of ACTH and CRH release?
cortisol
excessive glucocorticoids over time - shut down ACTH and CRH –> adrenal cortex will atrophy
What happens if you have too much ACTH?
hyperpigmentation - stimulating melanocyte synthesis from alpha-MSH in the POMC
Addison’s disease
What is the enzyme used to cleave POMC?
pro hormone convertase I –> cleaves to ACTH and beta-lipoprotein
role of ADH (AVP) in ACTH release
stimulates production of ACTH by thirst response stress
increases BP indirectly by the production of cortisol
role of CRH
comes from the paraventricular nucleus in the hypothalamus - stimulate release of ACTH in anterior pituitary
binds to receptors on corticotrophs –> increase cAMP –> activate PKA –> POMC production/cleavage
role of glucocorticoids
negative feedback on ACTH and CRH
excessive ACTH w/o cortisol
dexamethasone suppression of ACTH
congenital adrenal hyperplasia
elevated ACTH due to lack of glucocorticoid synthesis –> adrenal hypertrophy and hyperplasia
what is the response to stress?
increased CRH secretion - stress signals override
-released during starvation
chronic stress - increases threshold for negative feedback…brain does not respond to cortisol & keeps making ACTH
TSH aka thyrotropin
share the same alpha chain with LH & FSH
regulates T3, T4 production and proliferation of thyroid follicular cells
stimulated by TRH; inhibited by thyroid hormones & somatostatin
what leads to an enlarged thyroid (goiter)?
no production of thyroid hormone to produce the negative feedback –> release too much TSH
prevented by iodine supplements
growth hormone (GH) aka somatotropin
most abundant in anterior pituitary
stimulated by GHRH; inhibited by somatostatin
filtered & eradicated quickly - short half life
JAK/STAT signaling
pulsatility higher at night & in adolescence
also acts on IGF (somatomiden)
somatostatin
inhibits GH and GHRH
What stimulates the release of GH?
- GHRH
- starvation, low glucose
- gherlin
- exercise & stress
- thyroid hormones
- high levels of amino acids
increases glucose levels, shuts down insulin, releases energy
what are the direct actions of growth hormones?
breaks fats (lipolysis) & glycogen –> liberates energy
oxidation of FA
ketogenic
prevents sugar uptake
inhibits insulin - diabetes
increase thyroid secretion
does not break proteins - increases synthesis & transport
Anabolic actions of growth hormone
mediated through IGF-1 (somatomedin)
increases muscle mass (protein synthesis), growth, & bone density
somatomedin C
longer half life than GH - more accurate measurement when testing to see if someone is deficient
-last longer in blood
bone and cartilage growth when stimulated by GH
Gigantism
overproduction of GH before the epiphyseal plates close
Acromegaly
overproduction of GH after the epiphyseal plates have closed –> thicker bones
Laron syndrome
GH deficiency
- pituitary dwarfism
- IGF deficiency
- GH receptor mutation
will have low sugar, obesity, low muscle mass, high LDL and cholesterol, premature aging
role of Prolactin
made in lactotrophs
- JAK/STAT signaling
- stimulated by TRH; inhibited by dopamine
- increase breast development & milk production
- decrease release of LH and FSH - suppress pulses
- absence or excess can cause infertility or cancer (breast or prostate)
- suppress kisspeptin
- regulation of steroid genesis
- immune - associated w/ autoimmune diseases
Kisspeptin
peptide in hypothalamus that produces GnRH
inhibited by prolactin
treatment for excess prolactin secretion?
dopamine agonist - natural inhibitor of prolactin
posterior pituitary
- neuroendocrine system
- does not produce hormones
- stores & releases oxytocin & ADH
oxytocin role
uterine contraction, milk ejection
- levels and receptors increased during pregnancy
- stop postpartum hemorrhage
- linked to limbic system (emotions)
- similar structure to ADH - water retention, [] urine, decrease urine output, increase Na+ loss
ADH (vasopressin) role
conserve water, concentrate urine
where are the neuron bodies located?
paraventricular and supraoptic nucleus in hypothalamus - secrete oxytocin & ADH - stored in posterior pituitary
mechanism of oxytocin
activates G coupled receptor –> activate PI3K
PKC and PLC increase intracellular contraction causing contraction
other functions of oxytocin
- limbic system - maternal and social bonding
- methylation in receptor - autism
- role in cardiomyocytes & neural development
- anti-depressants
- inhibit fear
- decreases cortisol levels
release of oxytocin
- sucking on nipple
- site & sound of infant
- downward movement of fetus through birth canal
ADH role
- water, salt, urea retention –> prevent dehydration
- constriction of blood vessels
- increase ACTH secretion
- increase urine osmolarity
- upregulate AQPA2 through cAMP/PKA signaling
- increase Na+/K+ pump, NKCC, ROMK, NCC, ENaC, UTA-1,3
release of ADH
- increased plasma osmolality
- drop in blood volume
- angiotensin II
- thirst reflex
diabetes insipidus
- lack of functioning ADH receptors or AQP2
- chronic lithium ingestion
- amyloid degeneration, polycystic kidney disease
effects: thirsty, dilute urine, hyperosmolarity blood, excess urine, hypokalemia
central vs. nephrogenic diabetes insipidus
central - no production of ADH; giving ADH helps the functioning
nephrogenic - receptors are hindered; giving more ADH does not help
SIADH
excess ADH secretion –> hyponatremia, [] urine
- ectopic expression of ADH from tumor
- not much change in volume due to ANP effects
why do you not give salt to SIADH patients?
will demyelinate neurons & destroy CNS
Another name for Anterior Pituitary
adenohypophysis
another name for Posterior Pituitary
neurohypophysis
anterior pituitary parts
- pars tuberalis - wraps around infundibulum
- pars intermedia - divides anterior/posterior; adjacent to pars nervosa
- pars distalis - largest; anterior lobe
posterior pituitary parts
- pars nervosa - largest
2. pars infundibulum - connecting stalk to hypothalamus
hormones released from posterior pituitary
oxytocin, ADH
hormones released from anterior pituitary
LH, FSH, ACTH, TSH
Hypophyseal (rathke) pouch
formed from oral ectoderm
forms the anterior pituitary
Neurohyphyseal pouch/bud
formed from neuroectoderm
forms the posterior pituitary
Hypothalamic-Hypophyseal Tract
- communication b/w hypothalamus & posterior pituitary (nerves)
- supraoptic nuclei –> synthesize ADH
- paraventricular nuclei –> synthesize oxytocin
Hypothalamic-Hypophyseal Portal System
- communication b/w hypothalamus & anterior pituitary (blood vessels)
- superior hypophyseal arteries –> hypophyseal portal veins
- 2 plexuses
what does the superior hypophyseal artery supply?
infundibulum & median eminence
what does the inferior hypophyseal artery supply?
posterior hypothalamus
Pars Distalis
- chromophils –> acidophils (acidic), basophils (basic)
2. chromophobes - no stain; little cytoplasm
acidophils - pars distalis
- somatotrophs (most) - secrete GH (somatostatin)
- mammotrophs (lactotrophs) - secrete PRL
polypeptide hormones
basophils - pars distalis
- gonadotrophs - secrete FSH, LH, & ICSH (in males)
- thyrotrophs - secrete TSH
- corticotrophs - secrete ACTH & LPH
glycoprotein hormones
Pars Tuberalis
mostly gonadotrophs (FSH, LH)
Pars Intermedius
mostly corticotrophs (ACTH) & chromophores cleave POTC (MSH) colloid filled cysts (remnants of rathke) infiltration of basophils into pars nervosa
Pars nervosa
no synthesis of hormones
PVN & SON –> neurosecretory bodies (NB)
Pituicytes - supporting glial cells for neurons
Pituitary Adenomas
- growth in pituitary - overproduction of certain cell types (acidophils or basophils)
- release hormone in high amounts
- hormone producing (PRL, ACTH, GH)
- nonfunctioning - can compress on hypothalamus & optic chiasm
Thyroid
- produces T3,T4, & calcitonin
- hormone stored outside of cells (lumen of follicle) & can be held for a long time
- follicular (thyroytes) & parafollicular (C cells)
Follicular Cells aka thyrocytes
- squamous or columnar - depending on activity
- produce thyroglobulin stored in colloid lumen
- rich in RER for protein synthesis
Parafollicular (C) cells
- larger, lighter staining
- produce calcitonin
- upregulated Golgi apparatus for calcitonin synthesis
Parathyroid gland
- PTH release - Ca++ regulation
- supplied by inferior thyroid arteries
- Principle cells - secrete PTH; replaced w/ adipocytes during aging
- Oxyphil cells - nonfunctional; less PTH synthesis; more cytoplasm staining
Adrenal Glands
- supplied by superior, middle, inferior suprarenal arteries
- drained by suprarenal vein
- cortex and medulla