Endocrinology- Embriology, anatomy, Physiology Flashcards
(43 cards)
Thyroid development
Thyroid diverticulum arises from floor of primitive pharynx and descends into neck. Connected to tongue by thyroglossal duct. Foramen cecum is normal remnant of thyroglossal duct.
Thyroid follicular cells are derived from endoderm; parafollicular cells (aka, C cells, produce Calcitonin) are derived from neural crest.
Thyroid development
Pathology
Thyroglossal duct cyst presents as an anterior midline neck mass that moves with swallowing or protrusion of the tongue (vs persistent cervical sinus leading to branchial cleft cyst in lateral neck).
Most common ectopic thyroid tissue site is the tongue (lingual thyroid). Removal may result in hypothyroidism if it is the only thyroid tissue.
Adrenal cortex and medulla
- Derived from
Adrenal cortex (derived from mesoderm) and medulla (derived from neural crest).
GFR: Glomerular, fascicular, Reticular
Anterior pituitary (adenohypophysis)
- Derived from
- Hormones it produce
Secretes FSH, LH, ACTH, TSH, prolactin, GH, and β-endorphin. Melanotropin (MSH) secreted from intermediate lobe of pituitary.
*Derived from oral ectoderm (Rathke pouch)
α subunit—hormone subunit common to TSH, LH, FSH, and hCG.
B-FLAT: Basophils—FSH, LH, ACTH, TSH.
Acidophils: GH, PRL.
Posterior pituitary (neurohypophysis
- Derived from
- Hormones it produce
Stores and releases vasopressin and oxytocin, both
made in the hypothalamus (supraoptic and paraventricular nuclei) and transported to posterior pituitary via neurophysins (carrier proteins).
Derived from neuroectoderm.
Endocrine pancreas cell types
α = glucagon (peripheral)
β = insulin (central)
δ = somatostatin (interspersed)
Insulin synthesis
Preproinsulin cleavage of “presignal” proinsulin (stored in secretory granules) cleavage of proinsulin exocytosis of insulin and C-peptide equally.
Insulin and C-peptide are increased in insulinoma and sulfonylurea use, whereas exogenous insulin lacks C-peptide.
Anabolic effects of insulin:
Increase glucose transport in skeletal muscle and
adipose tissue
Increase glycogen synthesis and storage
Increase triglyceride synthesis
Increase Na+ retention (kidneys)
Increase protein synthesis (muscles)
Increase cellular uptake of K+ and amino acids
Decrease glucagon release
Decrease lipolysis in adipose tissue
insulin-independent glucose uptake (organs)
Insulin-dependent glucose transporters
BRICK LIPS: Brain, RBCs, Intestine, Cornea,Kidney, Liver, Islet (β) cells, Placenta, Spermatocytes
GLUT4: adipose tissue, striated muscle
**insulin does not cross placenta.
Insulin Regulation
incretins ([GLP-1], [GIP])
Release decrease by α2, increase by β2 (2 = regulates insulin)
Glucose enters β cells ATP generated from glucose metabolism closes K+ channels and depolarizes β cell membrane . Voltage-gated Ca2+ channels open
Ca2+ influx and stimulation of insulin exocytosis
Glucagon Function and Regulation
Promotes glycogenolysis, gluconeogenesis, lipolysis, and ketone production.
Secreted in response to hypoglycemia. Inhibited by insulin, hyperglycemia, and somatostatin.
Hypothalamic-pituitary hormones
- ADH
- GHRH
water permeability of distal convoluted tubule and collecting duct cells in kidney (AQP2). Stimulus for secretion is Higher plasma osmolality.
Increase GH. Analog (tesamorelin) used to treat HIV‑associated lipodystrophy.
Hypothalamic-pituitary hormones
- CRH
- Dopamine
Increase ACTH, MSH, β-endorphin. Decrease in chornic steroid use.
Decrease prolactin, TSH. antipsychotics (antagonist) can cause galactorrhea.
Hypothalamic-pituitary hormones
- GnRH
- MSH
Increase FSH, LH. Suppressed by hyperprolactinemia.
Tonic GnRH suppresses HPG axis. Pulsatile GnRH leads to puberty, fertility.
Increase melanogenesis by melanocytes. Causes hyperpigmentation in Cushing disease
Hypothalamic-pituitary hormones
- Oxytocin
- Prolactin
Causes uterine contractions during labor. Responsible for milk letdown reflex in response to suckling.
Decrease GnRH Pituitary. prolactinoma cause amenorrhea, osteoporosis, hypogonadism, galactorrhea.
Hypothalamic-pituitary hormones
- Somatostatin
- TRH
Decrease GH, TSH. Analogs used to treat acromegaly.
Increase TSH, prolactin. Increase TRH (eg, in 1°/2° hypothyroidism) may increase prolactin secretion causing galactorrhea.
Prolactin
- Function
- Regulation
Stimulates milk production in breast; inhibits ovulation in and spermatogenesis by inhibiting GnRH.
is tonically inhibited by dopamine from tuberoinfundibular pathway of hypothalamus. Prolactin in turn inhibits its own secretion by increasing dopamine synthesis. TRH increase prolactin secretion.
Dopamine agonists (eg, bromocriptine) can be used in treatment of prolactinoma.
Dopamine antagonists (eg, most antipsychotics) and estrogens (eg, OCPs, pregnancy) stimulate prolactin secretion.
Growth hormone (somatotropin)
- Function
- Regulation
Stimulates linear growth and muscle mass through IGF-1 (somatomedin C) secretion by liver. Increase insulin resistance (diabetogenic).
Secretion increase during exercise, deep sleep, puberty, hypoglycemia. Secretion inhibited by glucose and somatostatin release via negative feedback by somatomedin.
Appetite regulation
- Ghrelin
Stimulates hunger (orexigenic effect) and GH release (via GH secretagogue receptor).
Sleep deprivation or Prader-Willi syndrome increase ghrelin production.
Acts via lateral area of hypothalamus to increase appetite (hunger center).
Appetite regulation
- Leptin
Satiety hormone. Produced by adipose tissue.
Mutation of leptin gene congenital obesity. Sleep deprivation or starvation decrease leptin production.
Acts via ventromedial area of hypothalamus to decrease appetite (satiety center)
Appetite regulation
- Endocannabinoids
Act at cannabinoid receptors in hypothalamus and nucleus accumbens, increase appetite.
*exogenos endocannabinoids cause the munchies
Antidiuretic hormone (vasopressin)
Regulates serum osmolality (V2-receptors) and blood pressure (V1-receptors).
ADH level is decreased in central diabetes insipidus (DI), normal or increased in nephrogenic DI.
Desmopressin (ADH analog) is a treatment forcentral DI and nocturnal enuresis.
Aromatase inhibitors
Anastrozole, exemestane
Adrenal steroids
Pag. 326
