Lec 19 - Endocrine Flashcards
endocrine system; collectively regulate what, common feature, what else can it exist as
- several organs located throughout the body, sometimes embedded in other structures
- collectively regulate most aspects of growth, maturation and physiology
- common feature of releasing signaling molecules (hormones) into the circulation
- can also exist as single cells e.g. in mucosa of GI and respiratory tract: diffuse neuroendocrine system
hormones; three main classes and what they do / how they are synthesized
- cells signal each other via molecules know as hormones
- three main classes:
1) Proteins & Polypeptides - produced via standard protein synthesis
- stored in cytoplasmic vesicles until released
2) Steroids
- synthesized by sER
- generate from cholesterol or fatty acids stored in lipid droplets
- hormone itself is not stored in cell
3) Amino Acid Derivatives
- modified by biochemical pathways in cell
- most, but not all, can be stored
- some stain with chromium or silver
- some of these are also neuro-transmitters
hormone signalling; types and how it works, how does it affect other cells
Endocrine
* hormone released by cell into blood
* travels to distant site(s) to affect other cells
Paracrine
* hormone released by cell into extracellular space
* affect other cells locally
Neuroendocrine
* hormone released by neuron into blood
* travels to distant site(s) to affect other cells
microcirculation; synthesizing, release, recovery, entering blood
- typically, endocrine cell synthesizes hormone & stores it in cytoplasmic vesicles
- hormone released into basal
extracellular space; enters blood via fenestrations in endothelial cells - endocrine cell can also recover
hormone from storage depot and
transport it through cell to basal space - hormone enters blood via
fenestrations in endothelial cells
endocrine vs exocrine glands, what doesnt apply to endocrine glands, what are they made of
- epithelial cells of mature endocrine glands can be arranged in clusters, cords/sheets, or hollow spheres
- endocrine glands loose their duct
(and connection to epithelium of
origin) during development
~both types are generally made of epithelial cells specialized for secretion
- terms like simple vs compound; acinar vs tubular; serous vs mucous, etc. do not apply to endocrine glands
pituitary glands/hypophysis; parts and whats included
-anterior pituitary; pars tuberalis, pars inermedia, pars distalis
posterior pituitary; infundibular stalk, pars nervosa
neurohypophysis; what comes from it, axons surrounded by what, hormone storage, hormone secretion, reduced release
- unmyelinated axons from neurons in supraoptic & paraventricular nuclei extend into pars nervosa
*axons surrounded by modified glial cells: pituicytes (P) - peptide hormones stored at swollen
axon terminals: neurosecretory bodies (NB) (also called Herring bodies) - hormones released by neural activity; taken up by capillaries (C)
Reduced release of ADH (tumour; trauma) leads to diabetes insipidus
adenohypophysis; cells, waht does staining reveal (3), specialized stains reveal what, hormones released where, benign tumors
- cells of adenohypophysis produce variety of hormones
- routine H & E staining reveals:
Acidophils (A): eosinophilic granules containing growth hormone; prolactin
Basophils (B): basophilic granules
containing FSH, ACTH, TSH, LH
Chromophobes (C): inactive/stem
cells?
- specialized stains or IHC reveal
specific cell types - hormones released into sinusoidal capillaries of pituitary portal system;
distributed to cells of body and/or other endocrine glands - hormones released also feed back on hypophysis to influence activity
Benign tumours: cause effects due to production or compression
hypothalamic regulation; neurons release what, carried by what, where do neurons project, names and where they come from
- neurons (green) release regulating hormones into stalk region of pituitary
- carried by portal bv & regulate
release of hormones from adenohypophysis - neurons (yellow) directly project into pars nervosa; release hormones stored in their Herring bodies
basophil - TSH, FSH, LH, ACTH
acidophil - GH, prolactin
pars nervosa; ADH, oxytocin
adrenal gland; size, composed of what, how vascular
- paired glands located on cranial end of kidneys
- largest endocrine mass in body
- composed of two main regions:
~cortex (3 layers) derived from mesoderm
~medulla derived from neural crest - very vascular with large sinuses in medulla
adrenal cortex; layers and what is involved, functions
Zona Glomerulosa (Z. Arcuata)
* electrolyte balance via mineralcorticoids: e.g. aldosterone
* regulation of Na+ and K+ levels
Zona Fasciculata
* energy metabolism via glucocorticoids: cortisol, corticosterone
* regulation of carbohydrate, lipid &
protein metabolism; immune system
(sex hormones)
Zona Reticularis
* sexual development via sex hormones: estrogens, androgens,
progesterone (glucocorticoids)
adrenal cortex; arrangement, species, overall appearance
zona glomerulosa
* cells arranged in clusters
* usually not a wide zone
* ruminants & humans
zona fasciculata
* radially arranged cords; 1 or 2 cells thick
* cells usually contain lipid droplets that get extracted during processing
zona arcuata
* cells arranged in arcs
* most veterinary species
zona reticularis
* irregular network of cords of cells
* often a thin region
Overall, appearance of cells in cortex varies with gland activity, histological processing & species
adrenal medulla; cell type, preganglionic fibers, epi and norepi, clusters make what
- Chromaffin cells (pheochromocytes) of adrenal medulla are modified neurons, derived from neural crest
- preganglionic fibres of sympathetic nervous system synapse with
chromaffin cells; also some parasympathetic neurons/ganglia - autonomic NS induces release of catecholamine hormones epinephrine & norepinephrine into blood
- clusters of cells make only one type of hormone
adrenal dysfunction; cushings, addisons disease, pheochromocytomas
Hyperadrenocorticism (Cushing Syndrome)
- excessive secretion of hormones, especially cortisol
- most commonly due to neoplasia (tumours); often ‘benign’ tumor in adenohypophysis (most common), or adrenal cortical tumour (rare)
- similar symptoms can arise with chronic corticosteroid therapy, or
with production of excessive adrenal sex hormones
Hypoadrenocorticism (Addison Disease)
- adrenal insufficiency; poorly understood- often autoimmune
- usually bilateral with all regions of cortex affected
Pheochromocytomas
- neoplasia of chromaffin cells of adrenal medulla
- often incidental finding with imaging- symptoms vague/intermittent
- can be locally invasive
thyroid gland; shape, covered by what, vascular, what does it produce, involved in what
- large butterfly shaped structure on
ventral surface of neck - covered by thin CT capsule; trabeculae project into gland dividing it into lobules
- very well vascularized with
extensive sinusoids/capillaries - produces and stores thyroid
hormones:
thyroxine (T4)
triiodothyronine (T3) - involved in cellular metabolism,
heat regulation, regulation of growth & development, etc
