introduction - hormones

Question 1

3 classes of hormone

Answer 1

protein/polypeptide
steroid
miscellaneous

Question 2

describe protein hormones with an example

Answer 2

produced as precursors
pre-pro-hormone - longer - cleaved to make active hormone
pro-hormone = pro-opiomelanocortin (POMC) hormone = ACTH

Question 3

describe steroid hormones

Answer 3

precursor is cholesterol
eg cortisol
ACTH stimulates production of cholesterol

Question 4

describe protein hormone synthesis

Answer 4

anterior pituitary - corticotroph cell
AA building block
Enter through AA transporter
signal in nucleus cause gene to be transcribed
translation of prohormone mRNA to RER - protein translation occurs
Golgi
Vesicles - enzymes that cleave bits – liberate active hormone
Not lipid soluble
near to cell surface
Leave by exocytosis when signal into capillaries (blood stream)

Question 5

how long are protein hormones in the blood

Answer 5

short lived action

metabolised and broken down

Question 6

describe steroid hormone synthesis

Answer 6

adrenal cortical cell
LDL rich in cholesterol – LDL receptors in vesicles, endocytosis
cholesterol split from lipoproteins, esterified and in cytoplasmic vesicles
esterase liberate
StAR (steroidogenic Acute Regulatory protein) - get enzyme cholesterol into mt where enzymes are - rate limiting - if can’t get into mt can’t produce hormone
series of enzyme pathways that make final enzyme – depend where in body as to which enzyme sequence [precursor steps]
lipid soluble - diffuse into bloodstream - not stored in cells

Question 7

describe protein hormone transport

Answer 7

secreted into blood
half life few minutes
diffuse into adrenal gland but short lived - ACTH broken down

Question 8

describe steroid hormone transport

Answer 8

in blood bind to albumin (high conc - weakly bind to most hormones) and cortisol binding globulin (CBG) - specific to hormone
stay in blood
small pool of free hormone - active - can get in and out of cell

Question 9

describe the dynamic equilibrium of steroid hormone transport

Answer 9

free hormone + plasma protein [dynamic equilibrium] protein bound hormone
decrease free hormone in blood = change in eq so amount in blood is constant = endocrine cell increase hormone synthesis and release
increase plasma protein = change in eq to increase plasma bound hormone = increase in hormone synthesis and release - free hormone is mopped up so gland makes more eg in pregnancy CBG is increased

Question 10

describe protein hormone signalling

Answer 10

ACTH bind to G protein receptor 
activates G protein 
activates adenylate cyclase - ATP-cAMP 
activate PKA (protein kinase A) 
activate esterase and StAR protein 
kick start steroid synth pathway

Question 11

what is StAR protein

Answer 11

steroidogenic acute regulatory protein

Question 12

describe steroid hormone signalling

Answer 12

free cortisol enters cell by passive diffusion
bind to intracellular glucocorticoid receptor (GR - specific receptor for cortisol) in cytoplasm - steroid receptor complex translates to nucleus
up and down regulate transcription and translation
slow process
v powerful - dramatically affect cell’s function

Question 13

describe hormone homeostasis

Answer 13

stress causes anterior pituitary gland - ACTH
secrete to adrenal gland make cortisol
cortisol diffuse into corticotroph - inhibit ACTH production
-ve feedback (closed look feedback)
make sure don’t have long exposure to cortisol - v powerful