ch. 9 | the endocrine system

• endocrine system: system of glands & hormones secreting cells that regulate body functions through chemical messages (hormones)
• endocrine glands: secrete a chemical signal directly into the bloodstream
• exocrine glands: secrete a chemical signal through ducts or tubes

• 2 types of hormones:

   1. steroid: dissolves in fats or lipids; go directly into the target cell

   2. nonsteroid: dissolves in water; bind to receptors on target cell membrane 

glands:

• pituitary gland: influenced by the hypothalamus

• anterior pituitary

-shares blood supply w hypothalamus

-hormones:

thyroid-stimulating hormone (TSH)- controls metabolism
follicle-stimulating hormone (FSH)- promotes egg & sperm development
luteinizing hormone (LH)- controls ovulation & production of estrogen/testosterone
adrenocorticotropic hormone (ACTH)- breaks down proteins/fats, forms glucose

-disorders from too little/too much secretion of human growth hormone (hGH):

pituitary dwarfism: too little hGH prior to puberty,  does not grow to normal height

gigantism: too much hGH prior to puberty, taller-than-normal height

acromegaly: excess secretion of hGH after puberty, condition in which long bones can no longer grow but bones in hands/feet/face/jaw thicken & grow longer 

• posterior pituitary

-"extension of the brain"

-axons & terminals of specialized nerve cells from hypothalamus

-hormones:

oxytocin: stimulates contraction of uterus during birth, stimulates lactation
antidiuretic hormone (ADH): acts to conserve body water & increases blood pressure 

• thyroid gland: regulates metabolism

-calcitonin: hormone secreted by cells of thyroid gland that inhibit osteoclast activity & lowers blood calcium levels

• parathyroid gland: regulate calcium levels, embedded in posterior of thyroid gland 

-secrete PTH which acts on osteoclasts to release calcium & reduce calcium excretion & to release calcitriol (increases blood calcium levels)

• pancreas: regulate blood sugar levels 

-alpha cells: secrete glucagon
-beta cells: secrete insulin
-secretions of glucagon & insulin are coordinated to prevent blood glucose levels from rising too much after a meal & falling too much btwn meals
-hypoglycemia: blood glucose levels are below normal
-hyperglycemia: blood glucose levels are above normal
-diabetes mellitus: elevated blood glucose levels & impairs glucose tolerance
  type I: lack of insulin; immune sys. destroyed by beta cells; develops early in life (juvenile diabetes)
  type II: decreased sensitivity of target cells to insulin; develops later in life (lifestyle diabetes)

• adrenal glands: sit on top of each of the kidneys 

-types of steroid hormones secreted:
mineralocorticoids: outer zone of adrenal cortex; regulate mineral composition of the blood
glucocorticoids: middle layer of adrenal cortex; regulate energy balance
androgens: inner zone of adrenal cortex; influence sexual characteristics & behaviors
epinephrine & norepinephrine: adrenal medulla; regulate body's response to stress & exercise

• pineal gland: sets daily sleep/wake cycles

-secretes melatonin (hormones that helps set timing of body's biological clock)