2/3/99

Physiology II

 

Endocrine System

·         Communication system of the body is hormones and nervous system

2 ways to classify hormones

1.        chemical—3 groups of hormones

a)       peptide/protein hormones—growth hormone, insulin, hypothalamic releasing hormones

b)       steroids—derived from cholesterol w/ minor variations—testosterone, estrogen, Aldosterone

c)       amino acid derivatives—tyrosine which leads epinephrine, dopamine, & thyroxin—tryptophane which leads to serotonin & MSH

2.         functionally—2 types

a)       Second messenger—does not enter the cell, affects receptor on outside of the cell, and activate proteins inside the cell  (cAMP, phospholipase c, calmodulin—cascade event)—all hypothalamus to pituitary to affect (peptide hormones)—insulin (protein)—pituitary to  ??

b)       steroidal hormones—their job is to affect transcription and translation of  specific segments of the genome—receptor is inside the cell anywhere—many different ways to get inside the cell—ex:  thyroxin is a chromosomal receptor

 

·         feedback mechanism

·         negative—end product controls its production—ex:  estrogen, testosterone

·         positive—ex:  oxytonin (uterine contractions)—presence of end product enhances its own production

·         growth hormone doesn’t have a feedback

·         control mechanism

 

·         as of 1973 it was difficult to detect the presence hormones

·         radio-immuno assay—tool of measuring extremely small amounts of hormones

·         first used for insulin, good b/c protein and is antigenic

·         use ab and it will cross link and precipitate out

·         use iodine (I-25, gives out a strong signal) to link and label

·         known amount of ab and known amount of label, precipitate

·         higher [ ]in plasma, the less stuff left in suspension

·         sensitive detection for hormone which is in small amounts

 

Minimal requirements for a hormonal reaction

            1.  is the hormone there and how much—RIA only looks at this part

       2.  look for the receptors—type II diabetes

3.        is the cell capable of responding

 

·         released by glandular structures

·         hypothalmus—center of the limbic system—reward and punishment area

·         pituitary—small structure, above optic chiasm—small amount of tissue, plays an important role in homeostasis

·         anterior—epithelial tissue from the mouth – Rathke’s pouch, own blood supply, gets info from blood

·         posterior—nervous tissue from the  hypothalmus

·         controls many vegetative functions

 

·         nuclei from hypothalmus release peptide hormones

·         affects anterior pituitary

1.  acidophiles—most dominant—somatropes—growth hormone (GH)—growth hormone releasing factor—no specific target—peptide hormone that acts by steroidal means

2. 20%-basophilic—corticotropes—ACTH—corticotropic releasing factor—adrenal cortex
3. basophilic—thyrotropes—TSH--thyroid
4. basophilic—gonadotropes –FSH & LH--gonades
5. usually suppresssed—lactotropes—Prolactin—breast hormone

 

·         hypothalmus stimulates the production of 1-4

·         hypothalmus inhibits 5, only not inhibited during very high levels of estrogen

 

Growth Hormone

·         somatotropic hormone or somatotropin

·         191 aa

·         single chain

·         22,005 MW

·         increase mitosis and differentiation and protein synthesis

·         lack hormone will be short in stature

·         main thrust is deposition of protein

·         intake of aa into the cell

·         in extreme cases of GH

·         leaving behind glucose by acting on insulin

·         person has high blood glucose level

·         stimulates islets of pancreas

·         pituitary diabetes—very painful

·         acromegaly—excessive GH later in life, bones get thick, and starts later in life