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The Exocrine system Cheat Sheet by

Year 1, CTS module, .

Lipid-­soluble hormones

Steroid hormones
aldost­erone, cortisol, testos­terone, oestrogen
Tyroid hormones
T3 & T4
Gases
nitric oxide (hormone & neurot­ran­smiter)
1. lipid-­soluble hormone diffuses into cell
2. activated recept­or-­hormone complex alters gene expression
3. newly formed mRNA directs synthesis of specific proteins on ribosomes

- increase solubility in blood
- slow rate of hormone loss in urine
- provide a ready reserve of hormone

Hypoth­alamus & pituitary gland

the hypoth­alamus is the major link between nervous & endocrine systems, & it regulatesthe pituitary gland.

the pituitary gland is pea-shaped & secretes 7 hormones, it had two anatom­ica­lly­/fu­nct­ionally distinct portions, the anterior pituitary is stimulated by releasing hormones from hypoth­alamus & is suppressed by inhibiting them.

Pineal gland

small endocrine gland attached to roof of third ventricle, secretes melatonin which contri­butes to mainta­ining biological clock & more is secreted in darkness - gland is very developed in nocturnal animals.

Parath­yroid glands

Hormone + source
control
Action
PTH from chief cells
low blood Ca2+ levels stimulate secretion (& vice versa)
increases blood Ca2+ & Mg2+ levels & decreases blood HPO42- level, increases bone resorption by osteoc­lasts, increases Ca2+ reabso­rption * HPO42- excretion by kidneys, promotes formation of calcitriol (vit D active form) which increases rate of dietary Ca2+ & Mg2+ absorp­tion.
two [airs of small, round masses of tissue attached to posterior surface of lateral lobes of thyroid gland

Adrenal glands

Hormone + source
control
Action
a) cortex hormones
1. minera­loc­ort­icoids from zona glomer­ulosa cells
increased blood K+ level & angiot­ensin II stimulate secretion
increase blood levels of Na+ & water, decrease blood level of K+
2. glucoc­ort­icoids from zona fasiculata cells
ACTH stimulates release; cortic­otr­opi­n-r­ele­asing hormone promotes ACTH secretion in response to stress & low blood levels of glucoc­ort­icoids
increase protein breakdown (except in liver), stimulate glucon­eog­enesis & lipolysis, provide resistance to stress, dampen inflam­mation, depress immune responses
3. androgens from zona reticu­laris cells
ACTH stimulates secretion
assist in early growth of axillary & pubic hair in both sexes, in females - contribute to libido & are source of oestrogen after menopause
b) medulla hormones
1. adrena­lin­e/n­ora­dre­naline from chromaffin cells
sympat­hetic pregan­glionic neurons release ACh which stimulates secretion
enhances effects of sympat­hetic division of autonomic nervous system during stress
two (one superior to each kidney - suprarenal glands) with two struct­ura­lly­/fu­nct­ionally distinct regions - medulla & cortex.
  

Water-­soluble hormones

Amine hormones
adrena­line, noradr­ena­line, dopamine
(tyrosine)
 
histamine
(histi­dine)
 
serotonin & melatonin
(trypt­ophan)
Peptid­e/P­rotein hormones
amino acid polymers 3-49aa­/50­-200aa
 
(peptide) oxytocin, ADH
 
(protein) human growth, insulin
eicosanoid hormones
derived from arachi­donic acid/m­embrane lipids. Prosta­gla­ndins & leukot­rienes. Local hormones secreted by all cells (except RBCs).
1. hormone binding to receptor activates G protein, activating adenylate cyclase
2. activated adenylate cyclase converts ATP --> cAMP
3. cAMP activates protein kinases
4. activated protein kinases phosph­orylate cellular proteins
5. millions of phosph­ory­lated proteins cause reactions that produce physio­logical responses

Anterior pituitary

Hormone
Target tissues
Action
hGH
liver
stimulates liver, muscle, cartilage & bone to synthesise & secrete insuli­n-like growth factos (IGFs) which promote growth of body cells, protein synthesis, tissue repair, lipolysis & elevates blood [glucose].
TSH
thyroid gland
stimulates synthesis & secretion of thyroid hormones
FSH
ovaries & testes
initiates develo­pment of oocytes & induces ovarian secretion of estrogens/ stimulates testes to produce sperm
LH
ovaries & testes
stimulates secretion of oestrogen & proges­terone, ovulation & formation of corpus luteum/ stimulates testes to produce testos­terone
prolactin (PRL)
mammary glands
promotes milk production
ACTH
adrenal cortex
stimulates secretion of glucoc­ort­icoids
MSH
brain
exact role unknown, may influence brain activity, excess can cause skin darkening

Pancreas

Hormone + source
control
Action
glucagon from alpha cells of pancreatic islets
decreased blood level of glucose, exercise, & mainly protein meals stimulate secretion, somato­statin (growth hormone) & insulin inhibits.
raises blood glucose by accele­rating glycogen breakdown into glucose in liver (glyco­gen­oly­sis), converting other nutrients into glucose in liver (gluco­neo­gen­esis) & releasing glucose in blood
insulin from beta cells of pancreatic islets
increased blood level of glucose, ACh, arginine & leucine, glucagon GIP, hGH, & ACTH stimulate, somato­statin inhibits
lowers blood glucose by accele­rating transport of glucose into cells, converting glucose into glycogen & decreasing glycog­eno­lysis & glucon­eog­enesis, increases lipoge­nesis & stimulates protein synthesis
somato­statin from delta cells of pancreatic islets
pancreatic polype­ptide inhibits
inhibits secretion of insulin & glucagon, slows absorption of nutrients from GI tract
pancreatic polype­ptide from F cells of pancreatic islets
meals with protein, fasting, exercise & acute hypogl­ycemia stimulate, somato­statin & elevated blood glucose inhibit
inhibits somato­statin secretion, gallbl­adder contra­ction & secretion of pancreatic digestive enzymes
located posterior & inferior to stomach, both endocrine & exocrine gland.
  

Hormone intera­ctions

permissive effect
requires recent­/si­mul­taneous exposure to 2nd hormone
synerg­istic effect
two hormones have greater impact than indivi­dually
antago­nistic effect
two hormones have opposing actions
cell target respon­siv­eness is dependent on the [hormone] in blood, number of receptors on target cell, & the influences of other hormones.

Thyroid gland

Hormone + source
control
Action
T3 & T4 from follicular cells
secretion increased by TRH which stimulates release of TSH in response to low thyroid hormone levels, low metabolic rate, cold, pregnancy & high altitudes. TRH/TSH secretions inhibited by high thyroid hormone levels & high iodine level
increase basal metabolic rate, stimulate protein synthesis, increase glucose & fatty acid use for ATP produc­tion, increase lipolysis, enhance choles­terol excretion, accelerate body growth, contribute to nervous system develo­pment
calcitonin (CT) from parafo­lli­cular cells
high blood Ca2+ levels stimulate secretion (& vice versa)
lowers blood levels of Ca2+ & HPO42- by inhibiting bone resorption by osteoc­lasts & by accele­rating calciu­m/p­hos­phate uptake into bone extrac­ellular matrix
butter­fly­-sh­aped, located inferior to larynx & anterior to trachea. together with hGH & insulin, thyroid hormones accelerate growth (parti­cularly in nervou­s/s­keletal systems)

Thymus

- located superiorly to heart
- secretes thymosin
- promotes prolif­eration & maturation of T cells (lymph­ocyte that destroys microo­rga­nisms & foreign substa­nces)

Testes

testos­terone
stimulates descent of testes before birth, regulates sperma­tog­enesis, promotes develo­pment & mainte­nance of male secondary sex charac­ter­istics
inhibin
inhibits secretion of FSH from anterior pituitary
- oval glands in scrotum
- main hormone produced & secreted is testos­terone

Posterior pituitary

Hormone
Target tissues
control
action
oxytocin
uterus, mammary glands
neuros­ecr­etory cells of hypoth­alamus secrete OT in response to uterine distention & stimul­ation of nipples
stimulates contra­ction of smooth muscle cells of uterus during childb­irth; stimulates contra­ction of myoepi­thelial cells in mammary glands to cause milk ejection
ADH
kidneys, arteri­oles, sudori­ferous (sweat) glands
neuros­ecr­etory cells of hypoth­alamus secrete ADH in response to elevated blood osmotic pressure, dehydr­ation, loss of blood volume, pain or stress; inhibitors of ADH are low blood osmotic pressure, high blood volume & alcohol
conserves water by decreasing urine volume, decreases water loss through perspi­ration, raises BP by constr­icting arterioles
does not synthesise hormones, stores & releases oxytocin & ADH

Ovaries

Hormone
action
estrogens & proges­terone
together with gonado­tropic hormones of anterior pituitary, regulate female reprod­uctive cycle & oogenesis, maintain pregnancy, prepare mammary glands for lactation & promote develo­pment & mainte­nance of female secondary sex charac­ter­istics
relaxin
increases flexib­ility of pubic symphysis during pregnancy, helps dilate uterine cervix during labour & delivery.
inhibin
inhibits secretion of FSH from anterior pituitary
- paired oval bodies in the female pelvic cavity
- produce several steroid hormones

Other

skin
vit D - mineral homeos­tasis
liver
angiot­ens­inogen - increases BP
small intestine
secretin - increases pancreatic juice secretion
heart
ANP - decreases bp
stomach
gastrin - increases stomach motility
kidney
EPO - increases RBC production
       
 

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  • Published: 17th May, 2023
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