Introduction to Endocrine (incomplete)

Question 1

autocrine

Answer 1

hormone that has an effect on the cell by which it is secreted

Question 2

paracrine

Answer 2

hormone that has an effect on cells in its vicinity

Question 3

endocrine

Answer 3

hormone with secretions into surrounding medium eg blood

Question 4

what is special about the action of the peptide somatostatin

Answer 4

paracrine action in the pancreas but endocrine fashion in the brain

Question 5

amines

Answer 5

pre-synthesised and stored in vesicles, and are released in response to stimuli by Ca²⁺ ion dependent exocytosis

hydrophilic and are transported mainly free in the plasma

Question 6

what are all steroid synthesised from

Answer 6

cholesterol - they are secreted on demand

Question 7

secretion of steroids

Answer 7

are lipophilic so once they are syntehsised they are immediately capable of moving out the cell (this is why they are secreted on demand)

are hydrophobic and transported bound to plasma proteins

only the biologically active ones are free

Question 8

what is the rate limiting step for the production of steroid hormones

Answer 8

conversion of cholesterol to pregnenolone

Question 9

what is the purpose of carrier proteins

Answer 9

steroids, T3 and T4 are lipophilic, so travel bound to plasma proteins

these provide a reservoir of hormone in the blood and extend the half-life of the hormone in the circulation, contributing to a longer duration of action

thus maintain a relatively constant concentration of free lipophilic hormone in the blood

Question 10

what does albumin bind

Answer 10

steroids and thyroxine

Question 11

g protein coupled receptors

Answer 11

bind hormone on their extra cellular domain and activate the membrane G protein complex with their intracellular domain

activated complex then activates a number of regulatory signalling cascades:

• stimualtes cAMP by generation of AC
• activates PLC leading to generation of IP₃ and release of intracellular calcium

Question 12

tyrosine kinase

Answer 12

an enzyme that can transfer a Pi group from ATP to a protien in a cell

functions as an ‘on’ ‘off’ switch in many cellular functions

Question 13

insulin receptor

Answer 13

tyrosine kinase receptor

• insulin binds to the a subunits, casuing the ß subunits to dimerise and autophosphorylate thus activating the catalytic activity of the receptor

Question 14

nuclear receptors

Answer 14

found within cells

lipid soluble molecules pass through the cell membrane and typically bind with their nuclear receptors in the cell cytoplasm

then the activated hormone is translocated to the nucleus where it binds to nuclear DNA

causes changes in gene transcription

Question 15

class 1 NR

Answer 15

activated by many steroid hormones

in the absence of an activating ligand they are found in the cytoplasm bound to a heat shock protein

moved to the nucleus when they are activated

Question 16

class 2 NR

Answer 16

activated by most lipids

Constitutively present int he nucleus

Question 17

glucocorticoid receptors

Answer 17

corticosteroids enter the cell and bind to the GR in the cytoplasm, and translocate to the nucleus where the transcription of target genes is initiated