Anatomy and Physiology 2 Chapter 18 - Endocrine System Target Cell Receptors

4 things about extracellular receptors

1. used by water soluble hormones

2. produce indirect effects via secondary messengers

3. secondary messengers always change rate of metabolic reactions

4. secondary messengers can…

   1. activate

   2. inhibit

   3. act as cofactors

primary messenger

hormones binds to extracellular receptor

secondary messenger

intermediary molecule that appears due to a hormone; leads to change in cellular function

G-protein coupled receptor

activated by the primary messenger, it is the enzyme complex coupled to a membrane receptor that links between primary and secondary messenger

amplification

a few hormones bind and lead to thousands of secondary messengers; magnifies effect of hormone on target cell

down-regulation

hormone prescence decreases cell # of receptors; when hormone levels are high = cells less sensitive which is usually when hormones are in the bloodstream for a long time

*includes insulin and type II diabetes

up-regulation

abscence of hormone triggers more receptors; when levels of a hormone are low = cells become more sensitive due to the hormone not being present often

*uterine oxytocin receptors close to birth

4 things about intracellular receptors

1. used by lipid soluble hormones

2. hormones diffuse across the membrane

3. hormones produce direct effects by binding to intercellular receptors

4. gene activity altered:

   1. affect transcription and therefore translation

   2. affects metabolic activity and structure

4 steps for how steroids work as intracellular receptors starting at arrival of target cell

1. diffuse through plasma membrane

2. bind to receptor in cytoplasm or nucleus

3. gene activiation (on or off)

4. transcription and translation = response

4 steps for how thyroid hormones work as intracellular receptors starting at arrival of target cell

1. gets into the membrane via carrier-mediated processes

2. bind to mitochondria or nucleus

3. gene activation (on or off)

4. transcription and translation = response

3 things that degree of target cell activation depends on

1. level of hormone in the blood

2. # of receptors on/inside target cells

3. how strongly the hormone and receptor interact

endocrine reflexes

hormone secretion is most often controlled by negative feedback; stimulus causes the production of a thing that reduces the stimulus

3 categories of endocrine reflexes

1. humoral vs. neural vs. hormonal

2. simple vs. complex reflex

3. neuroendocrine reflexes

humoral reflex

hormone release caused by altered levels of certain critical ions or nutrients; ex. parathyroid gland releasing PTH due to low Ca2+

neural reflexes

hormone release caused by neural input; ex. neuron sends response to medulla in the adrenal gland to secrete E and NE

hormonal reflexes

hormone release caused by another hormone (a tropic hormone); ex. hypothalamus releases hormone to anterior pituitary gland to release other hormones, final hormone released causes hypothalamus to stop

simple reflex

involves 1 hormone; controls hormone secretion by the heart, pancreas, parathyroid gland, and digestive tract; often humoral

complex reflex

involves 1+ intermediary steps, 2+ hormones, and the hypothalamus; often hormonal

neuroendocrine reflexes

pathways include both neural and endocrine components; issued by changing amount of hormone secreted and pattern of hormone released (hypothalamic and pituitary hormones released in sudden bursts and frequency changes response of target cells)

3 types of interactions of hormones at target cells

1. permissiveness: 1 hormone can’t exert its effect without another hormone being present

2. synergism: 1+ hormone produces some effects on target cell leading to amplification

3. antagonism: 1+ hormone oppose(s) action of another hormone