Endocrinology Flashcards
Most common ectopic thyroid tissue site
tongue (lingual thyroid). removal may result in hypothyroidism if it is the only thyroid tissue present.
branchial cleft cyst origin
persistent cervical sinus
Thyroid tissue origin
endoderm
parafollicular cell origin
neural crest
adrenal cortex and medulla origin
cortex from mesoderm, medulla from neural crest
chromaffin cell regulatory control
preganglionic sympathetic fibers
Melanotropin (MSH) origin
Intermediate lobe of pituitary.
Anterior pituitary other name
adenohypophysis
Anterior pituitary origin
oral ectodrm (Rathke pouch)
Hormones that share alpha subunit
TSH, LH, FSH, and hCG. Beta subunit determines specificity.
proopiomelanocortin (POMC(
ACTH and MSH are derivates of proopiomelanocortin (POMC)
hormones of anterior pituitary
FLAT Pig: FSH, LH, ACTH, TSH, PRL, GH.
Basophils
B-FLAT: basophils-FSH, LH, ACTH, TSH
Acidophils
GH, PRL
posterior pituitary other name
neurohypophysis
Origin of ADH and oxytocin
supraoptic and paraventricular nuclei
ADH and oxytocin transport
carrier proteins called neurophysins.
posterior pituitary embryo origin
neuroectoderm
Islets of langerhans
collections of alpha, beta, and gamma endocrine cells in the pancreas.
Islets of langerhans origins
Arise from pancreatic buds.
Islets of langerhans organizations
alpha cells peripherally, beta cells centrally, delta cells interspersed
alpha cells secrete
glucagon
delta cells secrete
somatostatin
Insulin synthesis
preproinsulin synthesized in RER –> cleavage of “presignal” –> proinsulin (stored in secretory granules) –> cleavage of proinsulin –> exocytosis of insulin and C-peptide equally.
C-peptide significance
increased in insulinoma and sulfonylurea use, whereas exogenous insulin lacks C-peptide
Insulin receptors
tyrosine kinase
insulin MOA
activates gene transcription
anabolic effects of insulin
1) Increases glucose transport in skeletal muscle and adipose tissue.
2) increases glycogen synthesis and storage
3) increases TG synthesis
4) increases Na+ retention
5) increases protein synthesis
6) increases cellular uptake of K+ and amino acids
7) decreases glucagon release
8) decreases lipolysis in adipose tissue
insulin and placenta
doesn’t cross it, unlike glucose
GLUT-4 expression
adipose tissue + striated muscle. exercise can also increase GLUT-4 expression
GLUT-1
RBCs, brain, cornea, placenta
GLUT-2
beta-islet cells, liver, kidney, small intestine
GLUT-3
brain, placenta
GLUT-5
fructose, spermatocytes, GI tract
insulin-independent glucose uptake pneumonic
BRICK L, brain, RBCs, intestine, cornea, kidney, liver
Major regulator of insulin release
glucose
Why is there increased insulin sensitivity with oral vs. IV glucose?
Incretins such as glucagon-like peptide 1 (GLP-1), which are released after meals + increased beta cell sensitivity to glucose.
Insulin growth pathway
insulin binds to receptor –> tyrosine phosphorylation –> RAS/MAP kinase pathway –> cell growth, DNA synthesis
Insulin glucose uptake pathway
insulin binds to receptor –> tyrosine phosphorylation –> Phosphoinositide-3 kianse pathway –> vesicles containing GLUT-4 translocate to membrane –> glucose enters via GLUT-4 carriers
Insulin release pathway
Glucose enters beta cells through GLUT-2 transporters –> undergoes glycolysis –> increased ATP/ADP ratio–> ATP-sensitive K+ channels close –> membrane depolarized –> voltage-gated Ca2+ channels open –> Ca2+ influx –> exocytosis of insulin vesicles.
glucagon effects
1) glycogenolysis, gluconeogenesis
2) lipolysis, ketone production
glucagon inhibitors
insulin
hyperglycemia
*somatostain
CRH function
increases ACTH, MSH, beta-endorphin
CRH and steroids
chronic exogenous steroids decrease CRH
dopamine effects
decrease prolactin, decrease TSH
tesamorelin
GHRH analog used to treat HIV-associated lipodystrophy
prolactin endocrine effects
decreases GnRH (which explains amenorrhea/hypogonadism in pituitary prolactinoma)
somatostatin endocrine efects
decreases GH, TSH
TRH affects
increases TSH + *prolactin
prolactin structure
homologous to GH
Prolactin regulation
1) tonically inhibited by dopamine from hypothalamus. 2) Prolactin in turn inhibits its own secretion by increasing dopamine synthesis and secretion from hypothalamus. 3) TRH increases prolactin secretion.
4) renal failure increases prolactin release via reduced prolactin elimination
5) pregnancy –> estrogen –> increased prolactin
TRH and hypothyroidism and amenorrhea
TRH increases prolactin secretion in hypothyroidism –> hyperprolactinemia inhibits GnRH
cry of baby and prolactine mechanism
cry of baby activates higher cortical centers –> inhibit hypothalamus from secreting dopamine
somatotropin
GH
somatomedin C
IGF-1
GH actions
1) stimulates linear growth and muscle mass through IGF-1 secretion
2) increased insulin resistance
GH regulation and secretion
- released in pulses in response to GHRH.
- secretion increases during exercise, deep sleep, puberty, hypoglycemia.
- secretion inhibited by glucose and somatostatin release via negative feedback by somatomedin.
orexigenic
means stimulates hunger
positive ghrelin regulation
sleep deprivation + Prader-Willi
Ghrelin effects
stimulates hunger + GH release
leptin source
adipose tissue
endocannabinoids and munchies mechanism
act at cannabinoid receptors in hypothalamus and nucleus accumbens, two key brain areas for the homeostatic and hedonic control of food intake, thus increasing appetite.
source of ADH
supraoptic nuclei
V1 vs. V2 ADH receptors
V2 regulate serum osmolarity, V1 regulate BP
ADH level in Central and nephrogenic DI
down in central, normal or increased in nephrogenic
nephrogenic DI etiology
mutation in V2 receptor
desmopressin acetate 1) MOA, 2) clinical use
ADH analog
central DI + nocturnal enuresis
ADH regulation
osmoreceptors in hypothalamus; hypovolemia
17alpha-hydroxylase lab profile
1) mineralocorticoids
2) cortisol
3) sex hormones
4) BP
5) potassium
6) other
1) increased
2) decreased
3) decreased
4) increased
5) decreased
6) decreased andostenedione
21-hydroxylase lab profile
1) mineralocorticoids
2) cortisol
3) sex hormones
4) BP
5) potassium
6) other
1) down
2) down
3) up
4) down
5) up
6) increased renin activity + increased 17-hydroxy-progesterone
11beta-hydroxylase lab profile
1) mineralocorticoids
2) cortisol
3) sex hormones
4) BP
5) potassium
6) other
1) decreased aldosterone, but increased 11-deoxycorticosterone so increased Bp
2) down
3) up
4) up
5) down
6) decreased renin
Cortisol carrier protein
corticosteroid-binding globulin (CBG)
cortisol and immunology caveat
exogenous corticosteroids can cause reactivation of TB and candidiasis by blocking IL-2 production
cortisol and BP mechanism
1) Upregulates alpha1-receptors on arterioles, increasing sensitivity to NE and E.
2) At high concentrations, can bind to mineralocorticoid (aldosterone) receptors.
cortisol actions
BIG FIB.
Increases BP
Increases Insulin resistance
Increases Gluconeogenesis, lipolysis, and proteolysis
Decreases Fibroblast activity (causes striae)
Decreases Inflammatory and Immune responses
Decreases Bone formation (by decreasing osteoblast activity)
Cortisol and immune modification mechanism
1) inhibits production of leukotrienes and PGs
2) inhibits WBC adhesions –> neutrophilia
3) blocks histamine release from mast cells.
4) reduces eosinophils
5) blocks IL-2 production
cortisol regulation
CRH –> ACTH –> cortisol production. Excess cortisol deceases CRh, ACTH, etc.
Plasma calcium forms
1) ionized (45%)
2) bound to albumin (40%)
3) bound to anions (15%)
calcium and pH mechanism
increased pH increases affinity (negative charge) of albumin for Ca –> hypocalcemia (cramps, pain, paresthesias, carpopedal spasm).
D3 sources
sun, fish, plants
D2 sources
Ingestion of plants, fungi, yeasts
Vitamin D negative regulation
1,25-(OH)2 feedback inhibits its own production
PTH and urine cAMP
PTH increases urine cAMP
RANK-L
- receptor activator of NH-kB ligand.
- secreted by osteoblasts and osteocytes.
- Binds RANK (receptor) on osteoclasts and their precursors to stimulate osteoclasts and increase calcium, leading to bone resportion.
other regulator of PTH
decreased serum Mg increases PTH, but severely decreased Mg decreases PTH secretion.
Common causes of hypomagnesemia
diarrhea, aminoglycosides, diuretics, alcohol abuse.
PTH and vitamin D mechanism
positive regulator of 1alpha-hydroxylase
calcitonin source
parafollicular cells (C cells) of thyroid
Source of T3/T4
Follicles of thyroid. Most T3 formed in target tissues.
T3 functions
4 B’s –> Brain maturation, Bone growth (synergistic with GH), Beta-adrenergic affects (increases beta1 receptor expression in heart), increases Basal metabolic rate.
*also increases glycogenolysis, gluconeogenesis, lipolysis.
How does T3 increase basal metabolic rate?
via increased Na+/K+-ATPase activity, leading to increased O2 consumption, RR, body temperature
TSI
thyroid-stimulating immunoglobulin. Graves disease.
Wolff-Chaikoff effect
Excess iodine temporarily inhibits thyroid peroxidase, leading to decreased iodine organification, and decreased T3/T4 production.
When is TBG (thyroxine-binding globuline) increased and decreased?
Decreased –> hepatic failure, steroids.
Increased –> pregnancy (via estrogen), OCP use.
what converts T4 to T3?
5’-deiodinase
T3 vs. T4 potency
T3 binds nuclear receptor with greater affinity
Thyroid peroxidase functions
1) oxidation and organification of iodide
2) coupling of monoiodotyrosine (MIT) and di-iodotyrosine (DIT).
T4 structure
DIT + DIT
T3 structure
DIT + MIT
propylthiouracil and methimazole and thyroxine actions
Propylthiouracil inhibits both thyroid peroxidase and 5’deiodinase. Methimazole inhibits thyroid peroxidase only.
T3/T4 synthesis
Thyroglobulin secreted into follicular lumen –> organification of I2 by thyroid peroxidase –> T4 endocytoses back into epithelial cell –> coupling reaction, T4, T3 to circulation
thyroglobulin derived from
tyrosine
Iodine uptake mechanism
cotransport with Na
hormones that act through cAMP pathway
FLAT ChAMP –> FSH, LH, ACTH, TSH, CRH, hCG, ADH (V2), MSH, PTH.
ALSO –> calcitonin, GHRH, glucagon.
hormones that act through cGMP
Think vasodilators. BNP, ANP, EDRF (NO)
other name for NO
EDRF, endothelium-derived relaxation factor.
Hormones that act through IP3 pathway
GOAT HAG.
GnRH, Oxytocin, ADH (V1), TRH, Histamine (H1-receptor), Angiotensin II, Gastrin
hormones that act through an intracellular receptor
Progesterone, estrogen, testosterone, cortisol, aldosterone, T3/T4, vitamin D
hormones that act through receptor tyrosine kinase (MAP kinase pathway)
Insulin, IGF-1, FGF, PDGF, EGF
hormones that act through nonreceptor tyrosine kinase (JAK/STAT)
Prolactin, immunomodulators (eg, IL-2, IL-6, IFN), GH, G-CSF, Epo, thrombopoietin.
steroid transport
lipophilic. thus must be bound to specific binding globulins to increase their solubility
affect of SHBG in men
Sex hormone binding globulin. Lowers free testosterone causing gynecomastia.
Cause of hirsutism in women
Decreased SHBG raises free testosterone.
SHBG increased with…
OCPs, pregnancy
steroid signaling pathway
Hormone binds to receptor in nucleus or cytoplasm –> transformation of receptor to expose DNA-binding domain –> bidns to enhancer-like element in DNA –> activates gene transcription.
Most common cause of cushings
exogenous corticosteroids (resulting in decreased ACTH and bilateral adrenal atrophy)
Causes of cushings
1) exogenous corticosteroids
2) primary adrenal adenoma, hyperplasia, or carcinoma – result in decreased ACTH, atrophy of uninvolved adrenal gland. Can also present with pseudohyperaldosteronism.
3) ACTH-secreting pituitary adenoma (Cushing disease).
4) paraneoplastic ACTH secretion
what causes most endogenous Cushings?
ACTH-secreting pituitary adenoma.
Cushing disease
ACTH-secreting pituitary adenoma
Cushing’s presentation
HTN, weight gain, moon facies, abdominal striae, truncal obesity, buffalo hump, skin changes, osteoporosis, hyperglycemia (insulin resistance), ammenorrhea, immunosuppression
Cushing’s screening tests
1) increased free cortisol on 24-hr urinalysis
2) increased midnight salivary cortisol
3) NO suppression with overnight low-dose dexamethasone test.
4) measure serum ACTH
What is the use of a high-dose dexamethasone suppression test?
Suppression = Cushing disease
No suppression = ectopic ACTH secretion
What is the use of a CRH stimulation test?
Increased ACTH, cortisol = Cushing disease
No increased ACTH, cortisol = ectopic ACTH secretion
Lab findings for exogenous glucocorticoids or adrenal tumor
ACTH will be LOW