BIOL40C Ch. 18 Endocrine System

• endocrine: hormones delivered by blood
• nervous: NTs released locally 

• endocrine: usually far from site of release; binds to receptors on/in target cells
• nervous: at synapse (close to site of release); binds to receptors in postsynaptic membrane 

• endocrine: cells throughout body
• nervous: muscle, gland cells, other neurons 

• endocrine: seconds to hours to days
• nervous: milliseconds 

• endocrine: seconds to days
• nervous: milliseconds 

glands that secrete their hormones into the interstitial fluid surrounding the secretory cells, rather than into ducts

nervous and endocrine systems act as a highly coordinated system

cell with a receptor for a hormone

number of target cell receptors decreases in response to the presence of excess hormone

number of receptors increases in response to hormone deficiency 

• 1) steroid
• 2) thyroid
• 3) gas 

• 1) aldosterone
• 2) cortisol
• 3) androgens
• 4) calcitriol
• 5) estrogen
• 6) progesterone
• 7) testosterone

ACACEPT 

• 1) T3 (triiodothyronine)
• 2) T4 (thyroxine)  

nitric oxide

• 1) amines
• 2) peptides/proteins
• 3) eicosanoids 

• 1) serotonin
• 2) histamine
• 3) melatonin
• 4) epinephrine
• 5) norepinephrine

SHMEN

• 1) prostaglandins
• 2) leukotrienes 

within the cytosol or nucleus

target cell's plasma membrane

transport proteins

• 1) make lipid-soluble proteins temporarily water-soluble (thereby increasing solubility in blood)
• 2) retard passage of small hormone molecules through kidney filtering
• 3) provide a ready reserve of hormone 

• water-soluble H binds to membrane receptor
• receptor activates G-protein
• G-protein activates adenylate cyclase
• adenylate cyclase converts ATP into cAMP
• cAMP activates protein kinases 
• protein kinases phosphorylate enzymes which catalyze reactions that produce physiological response 

1 bound H activates many G-proteins, which activates many molecules of adenylate cyclase to convert several ATPs into cAMP

massive watery diarrhea

• toxin causes G protein to lock in activated state in intestinal epithelium 
• cAMP causes intestinal cells to actively transport Cl- (Na+ & H2O follow) into lumen 

2nd H strengthens effects of first

ex: thyroid & epi 

2 H's act together for greater effect

ex: estrogen & LH

2 H's with opposite effects 

ex: insulin vs. glucagon

chemical that binds to a receptor and mimics the action of a naturally occurring substance

chemical that binds to a receptor and blocks or dampens agonist-mediated responses

in the sella turcica of the sphenoid bone

infundibulum

pituitary gland

anterior pituitary

posterior pituitary

hypothalamus

• 1) lactotrophs
• 2) gonadotrophs
• 3) somatotrophs
• 4) thyrotrophs
• 5) corticotriphs

"lagstick" 

prolactin

PFL H TAM

• FSH
• LH

PFL H TAM 

hGH

PFL H TAM

thyroid stimulating hormone

PFL H TAM 

• 1) ACTH (adrenocorticotrophic H)
• 2) MSH (melanocyte-stimulating H) 

• 1) hypothalamic regulating hormones
• 2) negative feedback  

• 1) superior hypophyseal arteries
• 2) hypophyseal portal system 

carry releasing factors from hypothalamus directly to pars distalis of anterior pit.

• 1) vasopressin (ADH)
• 2) oxytocin 

cells in paraventricular & supraoptic nuclei that secrete oxytocin & ADH into the posterior pituitary

• 1) stimulates contraction of uterine smooth muscle cells during childbirth
• 2) stimulates contraction of myoepithelial cells in mammary glands to cause milk ejection 

• 1) decrease urine volume (conserve body water)
• 2) perspiration (decrease water loss)
• 3) raise BP by constricting arterioles 

• 1) hyposecretion of ADH
• 2) nonfunctional ADH receptors 

inability to synthesize/secrete ADH

failure of kidney to respond to ADH

• IGF's
• produced by liver when stimulated by hGH
• stimulates growth (cartilage proliferation) in childhood 

• hGH excess in children
• before growth plates close 

• hGH excess in adults
• after growth plates close

hunchback

hGH deficiency

dwarfism as a result of thyroid H deficiency

• GHRH released to stimulate hGH by somatotrophs
• hGH & IGFs speed up breakdown of glycogen into glucose, which enters the blood faster
• blood glucose rises 

• GHIH released to inhibit secretion of hGH
• low hGH & IGFs decreases rate of glycogen breakdown
• blood glucose level falls 

corticotrophs

lagstiCk & pfl h taM 

below larynx

center of colloid surrounded by follicular cells

• 1) principal/follicular cells
• 2) C/parafollicular cells 

thyroglobulin

calcitonin

• 1) T3 (triiodothyronine)
• 2) T4 (thyroxine) 

• 1) iodide trapping
• 2) TGB synthesis
• 3) oxidation of iodide & iodination of tyrosine
• 4) T1 & T2 coupling
• 5) pinocytosis & digestion of colloid
• 6) secretion of thyroid Hs, & transport in blood 

thyrotropin releasing H

• released in response to low T3/T4
• stimulates release of TSH by thyrotrophs 

• 1) increase basal metabolic rate
• 2) stimulate synthesis of Na/K pumps
• 3) stimulate protein synthesis
• 4) increase body temp
• 5) increase use of glucose & FAs for ATP synthesis
• 6) stimulate lipolysis
• 7) enhance some actions of catecholamines via  receptors to increase force/rate of heart contraction
• 8) promote growth with GH & insulin 

agitated, hyperactive

lethargic, mentally dull

Hashimoto's disease 

Ab's produced mimic TSH, causing excess thyroid H secretion

enlargement of the thyroid

inadequate dietary iodine

leads to low levels of thyroid, causing stimulation of TSH 

embedded on posterior surfaces of lateral lobes of thyroid

• 1) increase blood Ca & Mg, decreases HPO4
• 2) increase bone resorption by osteoclasts
• 3) increase Ca reabsorption & HPO4 excretion by kidneys
• 4) promotes formation of calcitriol (active vit. D) -> increases rate of dietary Ca/Mg absorption

blood calcium level

negative feedback loop not involving pituitary 

superior to kidneys

• 1) zona glomerulosa
• 2) zona fasciculata
• 3) zona reticularis

mineralocorticoids (aldosterone) 

glucocorticoids (cortisol)

androgens (DHEA)

renin-angiotensin pathway

angiotensin II, high plasma [K+] 

• increase blood levels of Na+ & H2O
• decrease blood level of K+ 

• increase protein breakdown
• stimulate stimulate gluconeogenesis & lipolysis
• depress immune responses (anti-inflammatory)

corticotropin-releasing H

• neurosecretory cell release stimulated by low cortisol blood levels
• promotes release of ACTH

negative feedback system 

• hypersecretion of cortisol
• breakdown of muscle protein, redistribution of fat, poor wound healing

• may be due to
• 1) tumor in adrenal gland secreting cortisol, or
• 2) tumor in pituitary gland secreting ACTH

• autoimmune disease where adrenal cortex is destroyed
• reduced cortisol & aldosterone secretion (hyposecretion)
• life-threatening due to dehydration 

• males: insignificant
• females: sex drive; converted to estrogen in postmenopausal females

posterior/inferior to stomach

• 1) alpha cells (glucagon)
• 2) beta cells (insulin)
• 3) delta cells (somatostatin)
• 4) F cells (pancreatic polypeptide) 

• low blood glucose: glucagon release
• high blood glucose: insulin secretion

negative feedback loop 

inability to produce/use insulin

• polyuria
• polydipsia
• polyphagia 

• Type I: insulin dependent; absolute insulin deficiency
• Type II: insulin-INdependent; down-reg of insulin receptors 

• 1) insulin
• 2) glucagon
• 3) cortisol
• 4) catecholamines
• 5) GH 

attached to 3rd ventricle of brain

melatonin

• setting biological clock
• involved in jetlag/SAD