Intro to Endocrine

Question 1

define endocrine glands

Answer 1

produce hormones and secrete them into circulation to (usually) act at a specific and distant target cell/tissue/organ

Question 2

what are the general types of hormone effects? (6)

Answer 2

1. metabolism
2. cardiovascular dynamics
3. stress responses
4. immune regulation
5. growth and development: cell, tissue, organ, and organism levels
6. reproduction

Question 3

describe endocrine axes (4)

Answer 3

1. regulate many hormones
2. have several levels of control via regulatory, trophic, and effector hormones
   -sensor releases regulatory hormones (usually end in RH)
   -amplifier releases trophic hormone (end in TH or SH)
   -effector releases effector hormone, which goes to periphery and acts on target cells
3. negative feedback
   -hormones released from various levels of the axis (esp effector hormone) regulates secretion of the entire axis
4. lots crosstalk and redundancy between axes:
   -regulatory hormone from one can act on amplifier of another!
   -trophic hormone from one can act on effector of another!

Question 4

describe mechanisms for hormone release (2)

Answer 4

1. most hormones:
   -made ahead of time
   -stored in vesicles
   -released when triggered via physiologic status, regulatory/trophic hormone binding, etc.
2. some important hormones:
   -NOT stored: made on demand
   -ex. cortisol

Question 5

describe hormone secretion rhythms (4)

Answer 5

1. pulsatile/ultradian:
   -prevents receptor down-regulation
   -maintains homeostasis via negative feedback
   - <24 hours cycle
2. daily/circadian:
   -cortisol, growth hormone
3. monthly/seasonal:
   -reproductive cycles
4. developmental:
   -puberty/menopause

Question 6

describe regulation of circulating hormone levels (2)

Answer 6

determined by:

1. rate of hormone release:
   -negative or positive feedback
   -presence of initial trigger at sensor (low blood pressure, high glucose, etc.)
2. rate of hormone metabolism/clearance:
   -peripheral: liver or kidney
   -in the target tissue/cell: after the hormone does its cellular job

Question 7

what are the 3 major types of hormones?

Answer 7

1. protein/peptide:
   -protein: >20 amino acids
   -peptide: <20 amino acids
2. steroid
   -lipophilic
3. tyrosine-derived
   -lipophilic

lipophilic: not water-soluble in the bloodstream, transported bound to plasma proteins (esp albumin)

Question 8

how do hormones interact with target cells?

Answer 8

1. requires target cell to express a specific receptor
2. hormone receptor binds a specific hormone (ligand)
   -once bound to hormone, receptor undergoes a conformational change that allows the receptor to transduce a signal (catalyze a biochemical reaction or alter the activity of adjacent molceules)
3. this leads to a cellular response
4. receptor can be:
   -on cell membrane: hydrophilic hormones most commonly
   -in cytoplasm: hydrophobic
   -in nucleus: hydrophobic

Question 9

what are the types of cell surface receptors?

Answer 9

1. ion channel linked
   -FAST action
2. enzyme linked
3. G protein coupled

Question 10

describe the action of intracellular receptors

Answer 10

1. hormone-receptor binding
   -steroid and thyroid hormones
2. receptor dimerization and binding to DNA
3. alteration of gene transcription
   -takes a long time to effect but effect is long lasting and may need to wean off if induced via drugs

Question 11

describe the levels of hormone action

Answer 11

1. whole body level
2. molecular level
3. cellular level

the same hormone can promote different cellular responses in different target tissues

Question 12

describe the general mechanisms of endocrine disorders (4)

Answer 12

1. hormone excess/hyperfunction:
   -hyperplasia/hyperfunction of a gland
   -functional (hormone-producing) tumors in a gland
   -excessive stimulation of a gland (something acting like a trophic hormone)
2. hormone deficiency/hypofunction:
   -congenital defects of an endocrine gland
   -destruction of an endocrine gland: autoimmune, ischemic, inflammatory, neoplastic (non-functional)
   -destruction of active hormones
3. decreased response to hormones at target tissue
   -less receptor expression at the target cell
   -altered receptor structure/function/signaling (ex. type 2 diabetes)
4. increased response to hormone at target tissue
   -lack of receptor down-regulation

Question 13

describe the 2 general diagnostic approaches for endocrine disease

Answer 13

physical exam and imaging really don’t help!

1. measure basal (resting) hormone levels
   -too much=hyper
   -too little = hypo
   -pros: technically easy and cheap
   -cons: stress, illness, or other factors confound!
2. dynamic testing: ask the endocrine organ to respond to stimuli
   -suppression test: do/give something that should suppress the organ and see if it lowers hormone levels
   -stimulation test: do/give something that should stimulate the endocrine organ and see if it increases hormone levels
   -pros: more accurate
   -cons: time consuming!