Lecture 6

Question 1

Give 2 specific examples of an endocrine reflex loop

Answer 1

1. Parathyroid gland senses low plasma calcium (homeostatically regulated) —-> parathyroid hormone activates PTH, PTH acts off bone and kidney to liberate minimal calcium
   Results: higher plasma calcium which shuts off system
2. Eat a meal—> stretch receptors will send a signal to CNS (AP), efferent neuron will signal to the pancreas and beta cells will release insulin
   Results: low glucose in blood

Question 2

Up regulation

Answer 2

• Try to maintain response despite low [hormone]
• increase number of receptor in response to decrease in [hormone]

Question 3

Down-regulation

Answer 3

• decrease in the number of receptor in response to high hormone
• usually involved endocytosis of membrane receptors

Question 4

Up/down regulation are long term affects that take __________

Answer 4

Time
- time required for endo/exocytosis and protein synthesis (days to weeks)
- faster to adjust sensitivity of receptors that are already there
(Sensitization and desensitization)

Question 5

Any hormone that controls the release of another hormone is called

Answer 5

Tropic hormone

Question 6

Example of a tropic hormone (pathway)

Answer 6

Hypothalamic releasing hormones —-> thyrotropin releasing hormone (TRH) goes into the portal system and acts on specialized cells in the anterior pituitary that will then release TSH. Then TSH causes release of thyroid hormones from thyroid

Question 7

Give an example of a tropic hormone not from the hypothalamus

Answer 7

Thyrotropin stimulating hormone from anterior pituitary

Question 8

Synergism

Answer 8

Cell/tissue are under influence of multiple hormones with functional overlap

Question 9

Permissiveness

Answer 9

If hormone A can’t produce its full effect without the presence of hormone B, hormone B is permissive for A

Reproductive hormone+thyroid hormone = normal reproductive development

Question 10

Functional antagonism

Answer 10

Hormones with opposite actions
For example: insulin (decrease glucose in blood) and glucagon and growth hormone (increase glucose in blood)
- they don’t need to share receptors or signalling pathways

Question 11

Agonist vs antagonist

Answer 11

Agonist: a ligand binds to a receptor and enhances its activity (serotonin for serotonin receptor)
Antagonist: a ligand binds to a receptor and inhibits it’s activity (clozapine is serotonin antagonist)

agonists may have opposite effects in different tissues
- for example: adrenaline dilates blood vessels in skeletal muscle and constricts blood vessels in intestine

Question 12

Specificity

Answer 12

Receptors may show preference to a particular ligand or type of ligand
Very specific—-> binds few ligands
non specific—> able to bind to many ligands (not all at the same time)
Ligands can also show specificity to receptors (important in drug development)

Question 13

Competition

Answer 13

Multiple ligands can compete for the same receptor active site, but usually one ligand binds better because it has higher affinity

Question 14

Competitive antagonists

Answer 14

Same binding site on receptor as agonist, but can be overcome with higher concentration of agonist

Question 15

Non-competitive antagonist

Answer 15

• Different binding site on receptor (allosteric site) than agonist
• Or bind to same active site but cannot unbind (irreversible antagonist)
• cannot be overcome by agonist

Question 16

EC50

Answer 16

Concentration of agonist producing 50% of maximal response

Question 17

EC50 when there is a competitive antagonist

Answer 17

Increase in agonist to flush it out therefore same maximal response but there will be a higher EC50

Question 18

EC50 with a non-competitive antagonist

Answer 18

antagonist effect cannot be be over come by an increase in agonist therefore maximal possible response decreases with increasing antagonist