1b. Overview continued + Steroid & Amine hormones

Question 1

What are steroid hormones derived from

Answer 1

cholesterol

Question 2

When are steroid hormones synthesised and why is this

Answer 2

synthesised directly as needed as they are highly lipophilic (lipid soluble) so cannot be retained within lipid membranes

Question 3

What happens to steroid hormones once they are synthesised

Answer 3

they diffuse across the membrane into the ISF and the blood

Question 4

how are steroid hormones transported through the body

Answer 4

as they are poorly water soluble they are transported bound to carrier proteins e.g. ALBUMIN

Question 5

Why are steroid hormones bound to carrier proteins

Answer 5

to stabilise transport throughout the body and protect them from enzymatic degradation (phenomenally increases their half life to around 60-90 mins instead of 2mins)

Question 6

where in the body are steroid hormones produced and give examples at each location

Answer 6

1. gonads (testes/ovaries) - sex steroids
2. placenta - hCG, sex steroids
3. Kidneys - Vitamin D3
4. Adrenal cortex - corticosteroids

Question 7

what determines which specific steroid hormone is ultimately produced from cholesterol

Answer 7

different cells having different enzymes synthesising different derivatives of cholesterol - this common ancestry explains why there are cross effects of excess steroids (e.g. see body builders)

Question 8

where are steroid hormone receptors located on the cell and why

Answer 8

receptors are located inside the cell (cytoplasmic or nuclear receptors) because they are lipophilic so can cross the plasma membrane easily

Question 9

what do steroid hormones trigger when they bind to receptors

Answer 9

either activation or inhibition of gene function within the nucleus = GENOMIC EFFECT

genes control the synthesis of protein so these hormones either increase or decrease protein synthesis

Question 10

why is there a lag time between steroid hormone release and biological affect (hours to days)

Answer 10

because protein synthesis is a relatively slow process - the effects however will persist for around the same time though

Question 11

how would a steroid hormone produce a rapid response

Answer 11

by occasionally binding to cell surface receptors and using 2nd messenger systems

Question 12

What are amine hormones derived from

Answer 12

one of two amino acids

1. Tyrosine
2. Tryptophan

Question 13

What is the only amine hormone derived from tryptophan and what is its role

Answer 13

melatonin - regulates circadian rhythm

Question 14

amine hormones derived rom tyrosine can be split into what two groups

Answer 14

1. catecholamines

2. thyroid hormones

Question 15

name three catecholamines and where they are secreted from

Answer 15

1. dopamine - brain
2. norepinephrine - neurons
3. epinephrine - adrenal medulla

Question 16

what is the mechanism of action for catecholamines

Answer 16

similar mechanism to peptide hormones (hydrophilic)

Question 17

name 2 thyroid hormones

Answer 17

1. Triiodothyronine (T3)

2. Thyroxine (T4)

Question 18

What is the mechanism of action for thyroid hormones

Answer 18

similar mechanism to steroid hormones (lipophilic)

Question 19

what are “free hormones”

Answer 19

the small amount of lipophilic (steroid/thyroid) hormones that are unbound within the plasma (i.e. should have a carrier but do not)

Question 20

what is the free hormone: hormone-protein complex ratio and what is it in favour of

Answer 20

the ratio between the number of free hormones to complexed (protein bound) hormones in the plasma

the ratio is much in favour of bound hormones

Question 21

what can free hormones do that bound hormones can’t

Answer 21

diffuse across capillary walls to target cells

Question 22

what does the law of mass action dictate in terms of free hormones

Answer 22

as free hormones leave the plasma and are taken up by cells, more hormones are released from their carriers to maintain the ratio - allows for a reservoir of hormones to be ready for action

Question 23

What does hormone concentration in the blood depend on

Answer 23

rate of secretion and rate of removal

Question 24

how does removal of hormones occur

Answer 24

excretion or metabolic transformation - mainly in the liver and kidneys

Question 25

why are catecholamine and peptide hormones excreted quickly/easily

Answer 25

they have a short half life in plasma (mins to hours) as they are unbound so are metabolised or excreted very quickly

Question 26

why does it take longer for steroid and thyroid hormones to be excreted

Answer 26

they have a long half life (hours to days) as they are protein bound so take much longer to be metabolised or excreted

Question 27

what are the two main main control mechanisms endocrine pathways will respond to

Answer 27

1. negative feedback reflexes - e.g. parathyroid hormone

2. neural feedback loops e.g. adrenaline

Question 28

How do neural feedback loops work using adrenaline as an example

Answer 28

1. fright/flight/fight response elicited
2. generalised sympathetic discharge including activation of sympathetic fibres to adrenal medulla occurs
3. specialised cells in adrenal medulla release adrenaline into the blood stream

Question 29

give an example of a hormone whose secretion can be subject to multiple control mechanisms

Answer 29

insulin - plasma glucose concentration, autonomic nerve activity, presence of food in gut, presence of additional hormones in the plasma

Question 30

What is up-regulation and when does it occur

Answer 30

the increase in the number of hormone receptors on target tissues to increase the tissue sensitivity to the hormone -occurs after prolonged exposure to low hormone concentration in the plasma

Question 31

what is down regulation and when does it occur

Answer 31

the decrease in the number of hormone receptors on target tissues to decrease the tissue sensitivity to the hormone - occurs after prolonged exposure to high hormone concentration in the plasma

Question 32

what is a permissive effect

Answer 32

when the presence of one hormone enhances the effect of another e.g. the presence of thyroid hormone (TH) increases synthesis of receptors for epinephrine on adipocytes greatly increasing epinephrines ability to release fatty acids

Question 33

what is the clinical relevance to be aware of for hormone levels in the body

Answer 33

may be misleading as hormone release occurs in short bursts so concentration in plasma be may not prove accurate - 24hr monitoring is required to give a true depiction of hormone levels