Endocrine Overview Flashcards
glands
types of cells in them
types of glands and examples
synthesize, concentrate, or alter a product for the ultimate process of secretion
histology: cuboical or columnar epithelial cells on a basement membrane, surrounded by blood vessel plexus
- endocrine: secrete directly into bloodstream - usually affect distant tissues
- exocrine: secrete into ducts
ex. salivary, sweat, mammary glands. exocrine pancreas
autocrine vs. paracrine
autocrine action : when secretory products affect the secreting cells directly
paracrine action : when secretory products affect adjacent cells
four classes of endocrine product
cells can be generally classified by product
- glycoproteins (FSH, LH)
- proteins and peptides: (POMC proopiomelanoctin, calcitonin, PTH)
- steroids (gonads: testosterone/estrogen. adrenal cortex: corticosterone, aldosterone)
- amino acid derivatives (adrenalin - adrenal medulla, melatonin - pineal )
explain the role of post-translational modification in peptide hormone synthesis
most peptide hormones are synthesized from larger precursors containing multiple hormones (need ppost-trans proteolysis and/or mod to regulate fx)
explain the difference between the way protein/peptide hormones signal and lipid-soluble hormones signal
protein/peptide hormones
- bind to cell surface receptors to activate second messenter systems
lipid soluble hormones
- diffuse through pl membrane, maybe nuclear membrane and bind to receptors to regulate gene transcription
negative feedback
regulatory mechanism in which initiation of a response to an endocrine signal produces a signal that reduced or stop further signaling
pituitary gland
parts and embryonic origin
two distinct embryonic origins:
- oral ectoderm - invagination of roof of mouth - Rathke’s pouch
- anterior pit (pars distalis)
- intermediate pit (pars intermedia)
- tuberal pit regions
- ALL THREE TOGETHER = adenohyposhysis
- neural ectoderm - brain tissue - infundibulum
- posterior pit (pars nervosa) (neurohypophysis)
pituitary gland
blood supply to the pituitary
blood supply is designed to allow hypothalamus (base of brain) to regulate secretion from adenohypophysis
key: endrocrine = need blood supply through which to be distributed through body
how this happens
- primary plexus (at median eminence of hypothalamus) collects hypothal products and shunts into portal veins
- portal veins connect to secondary plexus (in ant pituitary) which bathes cells of adenohypophysis
portal circ provides neurovascular link between hypothalamus and anterior pituitar
three types of cells in adenohypophysis
- acidophilic: GH or PRL (neither are glycosylated)
- basophilic: glycoprotein hormones containing sialic acid, ex. FSH, LH, POMC derivatives like ACTH
- chromophobic: dont stain bc of lack of secretory granules
FSH
- secreted from
- type of hormone
- hypothalmic regulation via…
- fx
follicle stimulating hormone
- anterior lobe of adenohypophysis
- glycoprotein
- GnRH +, inhibin -
- follicle devpt. spermatogenesis
LH
- secreted from
- type of hormone
- hypothalmic regulation via…
- fx
leutenizing hormone
- anterior lobe of adenohypophysis
- glycoprotein
- GnRH +
- follicle maturation. progesterone/androgen release
TSH
- secreted from
- type of hormone
- hypothalmic regulation via…
- fx
thyroid stimulating hormone
- anterior lobe of adenohypophysis
- glycoprotein
- TRH +
- stimulates TH synthesis/storage/release
MSH
- secreted from
- type of hormone
- hypothalmic regulation via…
- fx
melanophore stimulating hormone
- intermediate lobe of adenohypophysis
- 13 aa peptide
- CRF +
- pigmentation
ACTH
- secreted from
- type of hormone
- hypothalmic regulation via…
- fx
adrenocorticotropic hormone
- anterior lobe of adenohypophysis
- 39 aa peptide
- CRF +
- stimulates adrenal cortex secretion
GH
- secreted from
- type of hormone
- hypothalmic regulation via…
- fx
growth hormone/somatotropin
- anterior lobe of adenohypophysis
- protein
- somatotropin releasing factor (GHRH, SRF) +. somatostatin -.
- acts on long bones via somatomedin intermediates (IGFs)
PRL
- secreted from
- type of hormone
- hypothalmic regulation via…
- fx
prolactin
- anterior lobe of adenohypophysis
- protein
- PRH +. dopamine -.
- stimulates milk secretion
cell types in neurohypophysis
- axonal processes of unmyelinated nerve fibers originating in paraventricular nucleus (oxytocin cells) and supraoptic nucleus (AVP cells) of hypothalamus
- pituicytes, glial-like support cells for axons
- endothelial cells, make up fenestrated blood vessels of gland
hypothalmic-neurohypophyseal signalling
paraventricular/supraoptic nuclei axons from hypothalamus converge at median eminence to form hypothatamy-hypophyseal tract which enters posterior lobe
- axons end near cap plexus of neurohypophysis (NOT on other neurons/effector cells)
- can affect fx of cells in adenohypophysis via portal circ
- can also be transported to effectors
hormones of posterior pituitary and how they reach the bloodstream/target organs
- terminal parts of the axons contain stored hormone - Herring bodies
- hormones are transported in granules through axon as:
- prepro-oxyphysin: oxytocin + neurophysin I
- prepro-vasopressophysin: vasopressin + neurophysin II
- stimulation of hypothal leads to release of hormones from post pit into bloodstream to targets
- oxytocin –> uterus and mammary glands
- AVP –> kidney
thyroid gland
- embryology
- histological features
embryology
derived from endoderm which evaginates from floor of mouth and contains tubules from fifth pharyngeal pouch that contain NC-derived “C cells”/parafollicular/clear cells
- C cells secrete calcitonin (drops Ca levels, opposes PTH fx)
histology
single layer of cuboidal epithelium surrounding extracellular colloid (contains thyroglobulin) secreted by follicular cells)
- thyroglobulin = TH precursor
thyroid hormone
- basics
- synthesis
- release
- negative feedback role
basics:
synthesized from thyroglobulin + iodide
T3 (7% v active), T4 (35% not v active)
synthesis
- TG is a 2-subunit glycoprotein synthesized by follicular cells and secreted into colloidal space
- follicular cells pick up and concentrate iodide (20:1 or more over pl concentration), before…
three step I incorporation/TH synthesis process
- oxidation: peroxidase take iodide to iodine
- I + TG Tyr linkage
- coupling of T1 or T2/liberation of Ala side chain = T3, T4
release
- initiated by TSH, which stimulates follicular cell endocytosis of colloid
- colloid delivered to lysosomes; proteolysis leads to release of TH and ultimate secretion of T3 and T4
- T4>T3, but T4 can be converted to T3 in peripheral tissues
negative feedback
- T3, T4 inhibit TRH secretion from hypothal
- T3 T4 inhibit TSH secretion from ant pituitary
physiological effects of thyroid fx
metabolic effects
growth effects: need both TH and GH for normal growth; TH- individuals are cretins (short stature, cog deficits from abnormal neural development)
explain the role of I uptake/transport in terms of causes of thyroid disease, prevention of thyroid disease, and treatment of thyroid disease
- low dietary intake of I
- can lead to low TH and goiter (also due to high TSH signalling)
- use of iodized salt can help treat I-deficiency goiters
- thiocyanate, perchlorate, periodate all inhibit I uptake
- can be used to treat hyperthyroidism
- propylthiouracil and sulfonamide block iodination of Tyr in TG
- can be used to treat hyperthyroidism
- genetic disorders causing failure of I trap: conversion of I to I2 or I-Tyr coupling can lead to hypothyroidism
Grave’s disease
hyperthyroid condition in which antibodies constitutively activate thyroid receptor
- thyrotoxicosis
- exopthalmia (bulging eyes)
Hashimoto’s disease
autoimmune disease against thyroglobulin or other thyroid components with resultant hypothyroidism
importance of maintaining calcium homeostasis
sources of Ca for maintaining homeostasis
3 major calcitropic hormones
Ca is used in neuromuscular transmission, controlling enzyme activity, maintaining bone strength
sources of Ca:
- BONE: hydroxyapatite (reason for PO4 levels altered by bone resorption/mineralization)
- INTESTINE: abs
- KIDNEY: reabs
major calcitropic hormones
- PTH
- calcitriol (1,25 dihidroxy vit D)
- calcitonin
parathyroid gland structure and cell types
parathyroid gland encapsulated and septated by connective tissue
- principal/chief cells: abundant, pale/slightly acidophilic cytoplasm with lots of granules and lipid droplets. secrete PTH - increases pl Ca
- oxyphilic cells: larger cells with smaller, heterochromatic nuclei with acidophilic cytoplasm and no secretory granules. unknown fx
clear/C/parafollicular cells
round cells with clear cytoplasm located outside of throid follicles
secrete calcitonin
- 32 aa peptide hormone
- lowers pl Ca and PO4 by inhibiting bone resorption
- directly inhibits osteoclast activity
- increases Ca excretion in urine
adrenal gland structure
located in extraperiotoneal space superior to kidney
2 major parts:
- cortex: outer zone with 3 layers
- medulla: center of gland, composed of chromaffin cells (derived from NC cells). 10% of gland. secretes epi/norepi.
arterial supply to adrenal gland
3 arteries that distribute blood in 2 ways
- superior, middle, inferior suprarenal aa. form a plexus on the outside of the adrenal gland
distribution of blood from plexus
- blood distributed to ZG (fenestrated caps), through ZF (sinusoids), to ZR (capillaries) and on into medulla (same caps cont’d)
- medullary arterioes proceed straight from plexus to medulla
why? gives medulla dual arterial supply of blood with cortex secretions and blood with good oxygen/nutrient supply
venous drainage of adrenal gland
whole adrenal gland drained by single central vein
L - into renal vein
R - into superior vena cava
nerve supply to adrenal gland
myelinated (pregang) sympathetic fibers: end on medullary cells - regulate secretion of catecholamines
unmyelinated (postgang) sympathetic fibers: associated with cortical blood vessels
adrenal medulla
- cell types and functions
- control of adrenal medullary cell secretion
- composed of chromaffin cells of two types
- granules with dense cores : contain norepi
- less densely staining, more homogenous : contains epi
- epi production dependent on adrenal cortex stimulation
catecholamine (norepi/epi) release stimulated by sympathetic nerve activation
effects of catecholamines
- stimulate glycogenolysis in liver and sk muscle (glycogen –> glucose)
- mobilize FFA from adipose tissue
- increase basal metabolic rate via fright/fight/flight syndrome
adrenal cortex layers and general features
cells of adrenal cortex have lots of SER (indicator of steroidogenesis)
- zona glomerulosa 15%
- zona fasciculata 78%
- zona reticularis 7%
ZG general features
- rounded clusters of cells with intesely staining nuclei, little cytoplasm, lots of SER
- mitochondria that are elongated and cristae that are broad/flat
- secretes mineralocorticoids: maintain electrolyte balance (ex. aldosterone)
aldosterone function
- secreted from ZG
- regulated by RAS
- triggered by low bp
effect: Na reabsorption in kidneys
ZF general features
- large polyhedral cells in columns or cords 1-2 cells thick, separated by sinusoids
- light staining spherical nuclei
- acidophilic nucleus
- lots of SER, developed Golgi complex, many mitochondria (rounded, tubular cristae) and lipid droplets with precursors of steroids
- secrete glucocorticoids
glucocorticoids
- released in response to ACTH (adrenocorticotropic hormone) from hypothalamohypophyseal system
- KEY HORMONE: cortisol
- high glucocorticoid levels can decrease lymphocyte/plasma cell numbers –> immunosuppressive
ZR general features
- cells (smaller than those in ZF) in rows or colums
- deep staining nuclei
- some lipid droplets
- secrete gonadocorticoids (androgens) in sm amounts
control of cortical secretion
- ZG - mineralocorticoid secretion
- indep of hypothalamohypophysial axis
- mostly controlled by RAS
- ZF/ZR - glucocorticoid/gonadocorticoid secretion
- controlled by hypothalamohypophyseal axis for basal and stress-induced secretion
- hypothalamus - corticotropin releasing factor (CRF)
- ant pituitary - ACTH (response to CRF)
- adrenal cortex - glucocorticoids/some androgens
- negative feedback on ACTH!!!
- controlled by hypothalamohypophyseal axis for basal and stress-induced secretion
CRF-ACTH-glucocorts/androgens
list some examples of post-translational modification that are used to process peptide hormones
- di-basic cleavage
- C terminal trimming of basic residues
- amidation of C terminal glycines
ex. PTH needs to be amidated to bind to PTH-R
