W1: Intro to Endocrinology

Question 1

what are the 2 major control systems of the body?

Answer 1

endocrine system
nervous system

Question 2

why do we need control systems in the body?

Answer 2

Monitor & coordinate internal env & make appropriate adaptive changes (HOMEOSTASIS)
Reg growth, dev, reprod, senescence
Enable animal to respond & adapt to changes in external env

Question 3

what is the main diff btwn NS & ES?

Answer 3

NS uses ‘hard-wired’ connections to communicate
ES much more diffuse (no direct connection btwn sending & receiving cell)
Messages sent via ‘non-wired’ pathway (e.g. body fluids)

Question 4

what are 3 similarities of NS & ES?

Answer 4

BOTH send chemical signals
BOTH affect specific target organs or tissues
BOTH work to maintain homeostasis

Question 5

nervous vs endocrine (5)

Answer 5

v rapid action vs slower response
point to point vs more diffuse
short duration vs longer duration
abrupt end to signal vs effect/signal activity tails off
each signal identical in strength (freq changes) vs stimulus intensity reflected by amount hormone secreted

Question 6

a hormone is a chemical substance which…

Answer 6

Is synthesised & secreted by a specific endocrine cell type
Is transported thru circulation at v low concs
Elicits a specific response in a distant target tissue
Reaches all tissues, but only acts in specific areas (those w/ correct receptors)

Question 7

Many ‘hormones’ & other regulatory molecules also…

Answer 7

Engage in local PARACRINE & AUTOCRINE signalling (not bloodstream)
Have inhibitory rather than excitatory actions

Question 8

hormone definition

Answer 8

chemical messenger prod & secreted by a specialised endocrine gland that’s transported in the bloodstream to a distant target organ/cell where it elicits a physical response

Question 9

4 diff modes of cell-cell communication

Answer 9

endocrine
paracrine & autocrine (helps cell sense its own activity - form of reg)
neuroendocrine (e.g. hypo-pit system)
neurotransmitter

Question 10

why can the same hormone have diff effects on diff tissues?

Answer 10

bc depends on type of receptor expressed on target tissue

Question 11

what is a gland?

Answer 11

collection of specialised secretory cells

Question 12

role of an endocrine gland?

Answer 12

secretes a hormone into bloodstream

Question 13

what is an exocrine gland?

Answer 13

secretes substances into system of ducts

Question 14

what are extracellular signalling molecules a collective term for?

Answer 14

hormones, NTs, neuromodulators, growth factors, cytokines

Question 15

what are the 3 classes of hormone?

Answer 15

Proteins/Peptides (hydrophilic) - growth hormone
Cholesterol Derivatives (hydrophobic) – steroids, vitamin D
Modified AAs – adrenaline (hydrophilic), thyroid hormones (hydrophobic)

Question 16

steroid hormone synthesis

Answer 16

Cholesterol taken up by cell
Stored in esterified form in lipid droplets (can be de-esterified when needed)
Cholesterol transported to mit, where cytochrome P450 side-chain cleavage enzyme (P450scc) removes a side chain from cholesterol converting it into pregnenolone (intermediate)
Pregnenolone undergoes further enzyme-catalysed changes to yield:
Progesterone, androgens, oestrogens, glucocorticoids, mineralocorticoids

Question 17

peptide/protein hormone synthesis

Answer 17

Translated from specific mRNA in RER
Initially synthesised as inactive PRE-PROHORMONES
Signal peptide (‘PRE-‘) removed by endopeptidase to give PROHORMONE
PROHORMONE sent via Golgi to secretory granule
Further processing of prohormone (at any stage) to generate active HORMONE e.g.
Glycosylation, disulfide bond formation, subunit assembly, endopeptidase cleavage to gen multiple fragments

Question 18

diffs btwn organelles of peptide & steroid hormone-secreting cells

Answer 18

peptide - lots RER, well-developed golgi

steroid - lots lipid droplets, lots SER, not so well-developed golgi

Question 19

transport of protein/peptide hormones

Answer 19

Await secretion
Soluble in blood plasma
Short half-life in blood
Inactivated by peptidases/proteases

Question 20

transport of steroid hormones

Answer 20

Synthesised on demand
Poor solubility in blood plasma
Bind to plasma ‘carrier proteins’ (large water soluble proteins) (e.g. albumen)
Only ‘free’ (unbound) steroid is bio-available
Longer half-life in blood (~hours)
Duration of action: hours-days
Inactivated by excretion &/or liver metabolism

Question 21

how are hormones regulated?

Answer 21

often -ve feedback
to maintain homeostasis

Question 22

circulating hormone levels are influence by…

Answer 22

Rate of secretion – by endocrine gland
Rate of metabolism – by target tissue, blood, liver, kidney
Serum binding proteins – transport in blood

Question 23

what are the diff patterns of hormone release?

Answer 23

hourly pulses
24h cycle
monthly cycle

Question 24

time-frame of response for diff hormone types

Answer 24

NTs – milliseconds
Peptide hormones – secs-mins
Protein hormones – mins-hrs
Steroid hormones – hrs-days

Question 25

target cell recognition: specific receptors…

Answer 25

Are proteins on or w/in target cell
Have high affinity for hormone (Ka 10-8 to 10-10 M)
Binding starts chain of events that —> biological response
Receptor number is dynamic