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YR2 endocrine and diabetes > introduction to endocrine > Flashcards

introduction to endocrine Flashcards

1
Q

what is the endocrine system

A

integrates and controls organ function via the secretion of hormones from cells, tissues or glands which are then carried in the blood to target organs, distal to the site of hormone synthesis where they influence the activity of that target organ

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2
Q

what is the response time for the endocrine system

A

can be fast or slow e.g. adrenaline vs growth hormone

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3
Q

how do hormones travel in the body

A

in the blood to their target organs/tissues

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4
Q

how do hormones carry out their actions

A

tissues detect hormones through the presence of specific receptors for that chemical on/in the cells

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5
Q

how do hormones carry out effects on only certain cells

A

only particular cells express the specific receptor for the hormone

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6
Q

describe neural communication

A

NT released from presynaptic neuron
travels across the synaptic cleft
influences activity of postsynaptic neuron
NT acts locally within the synaptic cleft

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7
Q

what does neuroendocrine refer to

A

endocrine and nervous systems combined

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8
Q

what is a neuroendocrine hormone

A

hormone released by a nerve which enters the blood and travels to a target cell (distal site of action)

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9
Q

define endocrine

A

ductless glands and secretions (hormones)

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10
Q

define exocrine

A

ducted glands and secretions
glands deliver secretions to the external environment including GI tract
bile, saliva, sweat

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11
Q

define autocrine secretion

A

cells secrete chemicals that bind to receptors on the same cell
e.g. cytokines

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12
Q

define paracrine secretion

A

chemicals diffuse in ECF to affect neighbouring cells
e.g. histamine
NOT THE SAME AS ENDOCRINE HORMONES

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13
Q

what is the function of a hormone

A

to bring about changes in the activity of their target cells and tissues

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14
Q

7 features of endocrine hormones

A
  1. produced by cell/cells
  2. secreted into the blood
  3. transported via the blood to distal targets
  4. exert effects at very low concentrations
  5. act by binding to receptors on target tissues
  6. action is terminated (often via -ve feedback loops)
  7. released in short bursts, 24hr monitoring is clinically required
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15
Q

what concentrations do hormones act at in the body

A

10^19 - 10^-12 M

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16
Q

3 classes of hormones

A

protein/peptide hormones
amine hormones
steroid hormones

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17
Q

what is the most common type of hormone

A

peptide hormone

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18
Q

what are protein hormones made from

A

amino acid chains

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19
Q

examples of protein hormones

A

TRH
FSH
insulin

20
Q

synthesis of protein hormones

A

synthesised as preprohormones in advance of need

cleaved into prohormone and stored in vesicles in the endocrine cell until required

21
Q

sequence of protein hromone synthesis

A
  1. large and inactive preprohormone synthesised by ribosomes
  2. prohormone formed in ER by cleaving off signal sequence
  3. prohormones packaged into vesicles in GA along with proteolytic enzymes
  4. hormones and fragments are stored in vesicles until release is triggered into the plasma (co-secretion)
22
Q

clinical use of inactive protein hormone fragments in the plasma

A

e.g. C peptide in diabetes (inactive fragment from insulin prohormone)
levels of C peptide in the plasma indicate endogenous insulin production from the pancreas
C peptide and insulin are produced in equal amounts but insulin is metabolised faster (C peptide levels 5x higher than insulin)
type 1 diabetics inject exogenous insulin so their insulin levels aren’t representative of their pancreatic funciton

23
Q

mechanism of action of protein hormones

A

water soluble - easily dissolve in plasma
bind to membrane bound receptors on target cell (GPCR or tyrosine kinase linked receptors)
short 1/2 life in plasma
fast response

24
Q

why are protein hormones vulnerale to degradation

A

they are water soluble

25
Q

why do protein hormones require continued secretion for prolonged action

A

they have a short 1/2 life in the plasma

26
Q

how to the receptors for protein hormones produce a response

A

phosphorylate existing proteins in the cell and modify their function

27
Q

how do G protein coupled receptors work

A

activates 2nd messenger system +/- ion channels
modification of existing proteins
rapid response

28
Q

how to tyrosine kinase receptors work

A

alter gene expression
2nd messengers may also alter gene expression
slower
longer lasting activity

29
Q

what are amine hormones derived from

A

tryptophan or tyrosine (amino acids)

in reality all are derived from tyrosine except melatonin

30
Q

2 classes of amine hormones

A

catecholamines

thyroid hormones

31
Q

examples of catecholamines

A

dopamine
norepinephrine
epinephrine
similar mechanism of action of peptide hormones

32
Q

solubility of catecholamines

A

hydrophilic
transported in solution in the plasma
vulnerable to degradation before reaching their target

33
Q

half life of catecholamines

A

2 mins

prolonged action requires continued secretion

34
Q

examples of thyroid hormones

A

thyroxine (tetraiodothyronine, T4)
triiodothyronine (T3)
similar mechanism of action to steroid hormones

35
Q

solubility of thyroid hormones

A

lipophilic
diffuse across cell membrane into the blood
circulate in plasma bound to specific transport plasma proteins

36
Q

half life of thyroid hormones and length of action

A

hrs-days
alter protein synthesis via modifying gene expression
effect persists for hrs-days

37
Q

derivation of steroid hormones

A

all are lipids derived from cholesterol

38
Q

when are steroid hormones synthesised and why

A

directly as needed
they are highly lipophilic so cannot be maintained within lipid membranes
once synthesised they diffuse across membrane into ISF and blood

39
Q

how are steroid hormones transported

A

poorly soluble in water
bind to carrier proteins e.g. albumin
increased stability in plasma and protected from enzymatic degradation

40
Q

half life of steroid hormones and length of action

A

60-90mins

slow onset of action but action persists longer than amine/protein hormones

41
Q

4 locations of production of steroid hormones

A
  1. gonads - sex steroids
  2. placenta - hCG, sex steroids
  3. kidney - vitamin D3
  4. adrenal cortex - corticosteroids
42
Q

why do the actions of steroid hormones differ

A

which specific steroid hormone is produced is determined by the different enzymes present in cells that synthesise different derivatives of cholesterol

43
Q

mechanism of action of steroid hormones

A

readily cross the plasma membrane in/out of cells
receptors are located inside cells
genomic effect - intracellular receptors lead to a change in gene expression
increase/decrease in protein synthesis within the cell
slow process but effect persists for hrs-days

44
Q

physiological activity of lipophilic hormones

A

small amount of unbound free steroid in the plasma (physiologically important fraction)
only free hormone can diffuse to target cells

in health levels of free hormone remain constant

as free hormone leaves the plasma more hormone is released from the carriers

45
Q

total plasma [hormone]

A

= free hormone + complexed hormone

free hormone: bound hormone is in favour of bound hormone

46
Q

how is the plasma [hormone] determined

A

by the balance between secretion and degradation

47
Q

what determines hormone secretion

A

in most endocrine pathways secretion is responsive to -ve feedback reflexes e.g. PTH

neuroendocrine pathways respond to neural feedback loops e.g. adrenaline

some hormones are subject to multiple mechanisms e.g. insulin

YR2 endocrine and diabetes (4 decks)

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