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Endocrine > Intro to endocrine system > Flashcards

Intro to endocrine system Flashcards

1
Q

what is the definition of the endocrine system?

A

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

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2
Q

in what way may response differ?

A

response may be fast (within seconds) or slow (over days)

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3
Q

What are the 3 types of signalling which should not be confused with endocrine?

A
  • paracrine
  • autocrine
  • exocrine
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4
Q

what is paracrine signalling?

A

act local to the site of synthesis, do not travel to distant sites e.g. histamine

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5
Q

what is autocrine signalling?

A

act on/in the same cell that synthesises the hormone e.g. cytokines

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6
Q

what is exocrine signalling?

A

released from exocrine glands via ducts to the external environment e.g. saliva

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7
Q

with what system does the endocrine system communicate and control all body functions?

A

nervous system

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8
Q

what are 3 different types of communication?

A
  • endocrine
  • neural
  • neuroendocrine
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9
Q

what does endocrine communication involve?

A
  • Hormones travel in the blood to their target organs/tissues, distal to where it is produced
  • tissues detect hormones through the presence of specific receptors for that chemical on/in the cells.

No receptor = no response

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10
Q

what does neural communication involve?

A

Neurotransmitters released from presynaptic neurons travel across the synaptic cleft to the postsynaptic cell to influence its activity. Neurotransmitter acts locally within synaptic cleft

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11
Q

what does neuroendocrine communication involve?

A

this is when nervous and endocrine systems combine -nerves release hormones into blood. After entering blood, they travel to their target cells

-are called neurohormones and released by neuroendocrine cells

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12
Q

Why is the response to any one hormone highly specific?

A

because only target cells have receptors for the hormone; however the same hormone can have different effects in different target cells

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13
Q

endocrine function is embedded in a number of physiological systems as well as…

A

being a diffuse system of glands in its own right

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14
Q

what are the sites of principle endocrine glands?

A

hypothalamus, pituitary, thyroid, parathyroid, adrenal glands (both cortex and medulla) as well as kidneys themselves.

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15
Q

what are the 6 features of an endocrine hormone?

A
  1. Produced by a cell or group of cells
  2. Secreted from those cells into the blood 3.Transported via the blood to distant targets
  3. Exert their effects at very low concentrations
  4. Act by binding to receptors on target tissues
  5. Have their action terminated, often via negative feedback loops
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16
Q

what is the classification of endocrine hormones?

A
  • peptide hormones
  • steroid hormones
  • amine hormones
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17
Q

what are peptide hormones composed of?

A

chains of amino acids, ranging from long to small

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18
Q

what are steroid hormones derived from?

A

cholesterol

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19
Q

what are amine hormones derived from?

A

all derived from one or two amino acids- tryptophan or tyrosine

20
Q

outline the way peptide hormones are synthesised

A
  • synthesised in advance of need, then stored in vesicles until required
  • initial protein produced by ribosomes is large and inactive –> preprohormone
  • Preprohormones contain one or more copies of the active hormone in their amino acid sequence
  • preprohormones then cleaved into smaller units in the RER to leave smaller but still inactive proteins called pro hormones
  • Prohormones are packaged into vesicles in the golgi apparatus, along with proteolytic enzymes which break the prohormone down into active hormone + other fragments
  • Hormones and fragments are stored in vesicles in the endocrine cells until release is triggered then all vesicle contents are released into plasma i.e. will have both hormone and fragments in plasma
  • Measuring inactive fragments in plasma can be useful clinically e.g. C-peptide in diabetes
21
Q

what is C-peptide?

A

is the inactive fragment cleaved from the insulin prohormone. Levels of C-peptide in plasma or urine are often measured to indicate endogenous insulin production from the pancreas

22
Q

Why do we measure C-peptide and not insulin directly, in diabetics?

A

Because if they’re injecting themselves with insulin, they’re going to have different levels of insulin in their body to what they are actually endogenously producing, so C-peptide gives a more realistic result.

23
Q

are peptide hormones hydrophilic or hydrophobic?

A

hydrophilic

24
Q

what is the mechanism of action of peptide hormones?

A
  • Water soluble so dissolve easily in plasma
  • Water soluble however means cannot cross cell membrane so bind to membrane bound receptors on target cell
  • Once bound, receptors create fast biological responses
  • Most peptide hormones work via modulating either the G-protein coupled receptor or tyrosine kinase linked receptor
  • These pathways phosphorylate existing proteins in the cell and modify their function e.g. open or close ion channels, activate or inactivate enzymes
25
Q

how does modulation of a G-protein linked receptor work?

A

activates 2nd messenger and/or ion channels - rapid response

26
Q

how does modulation of a tyrosine-kinase linked receptor work?

A

alters gene expression- longer lasting activity

27
Q

outline how steroid hormones are synthesised

A
  • Steroid hormones are synthesized directly as needed, rather than being stored and released
  • This is because they are highly lipophilic (lipid soluble-so diffuse through cell membrane) so cannot be retained within lipid membranes
  • Once synthesized, they diffuse across the membrane into the ISF and the blood
  • Being poorly soluble in water they are transported bound to carrier proteins such as albumin
  • This stabilises their transport through the plasma and protects them from enzymatic degradation, phenomenally increasing their half life
28
Q

what organs produce steroid hormones and what hormones are they?

A
  • gonads–> sex steroids
  • placenta–> HCG
  • kidney –> vitamin D3
  • adrenal cortex –> corticosteroids
29
Q

what is the mechanism of action of steroid hormones?

A
  • Lipophilic- cross plasma membrane easily both into and out of cells
  • Hence receptors are located inside cells
  • Receptors trigger 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
  • Relatively slow process so there is a lag time between hormone release and biological effect
  • Some evidence suggests steroids may occasionally bind to cell surface receptors = rapid response
30
Q

what are the 2 branches of tyrosine hormones?

A

catecholamines and thyroid hormones

31
Q

what are most amine hormones derived from ?

A

tyrosine

32
Q

what is the only amine not derived from tyrosine?

A

melatonin

33
Q

catecholamines work in the same way as what type of hormone?

A

peptide hormone

34
Q

thyroid hormones work in the same way as what type of hormone?

A

steroid hormone

35
Q

what part of lipophilic hormone circulating in plasma is the physiologically important part?

A

the small amount of unbound, as only free hormone can diffuse across capillary walls to target cells

36
Q

identify a ratio that takes into account the binding ratio of free hormone

A

Free hormone: hormone-protein complex, much in favour of bound hormone, but ratio must be maintained

37
Q

what happens as free hormone leaves the plasma to be taken up by cells?

A

more hormone is released

38
Q

what does total plasma hormone consist of?

A

free hormone + complexed hormone

39
Q

what is a cause of the fact that peptide and catecholamines are water soluble?

A
  • they are vulnerable to degradation before they reach their target
  • have a short half-life in the plasma
40
Q

how does removal of hormone occur?

A

by excretion or metabolic transformation and mainly occurs in the liver and kidneys

41
Q

what is the control of hormone secretion through?

A

1) Negative feedback control
2) neural feedback loops eg adrenaline, aka neurons stimulate the release of hormones
3) some hormones can be subject to multiple control mechanisms e.g. Plasma [glucose], autonomic nerve activity, presence of food in the gut, plus additional hormones such as glucagon all influence [insulin]plasma

42
Q

what is up-regulation and when does it happen?

A
  • happens after prolonged exposure to low hormone in plasma
  • is an increase in number of hormone receptors on target tissues (increases tissue sensitivity to hormone).
43
Q

what is down-regulation and when does it happen?

A
  • happens after prolonged exposure to high hormone in plasma
  • is a decrease in receptor number on target tissues (decreases tissue sensitivity to hormone).
44
Q

what may up/down regulation also affect?

A

May affect not only the hormone’s own receptors but also receptors for other hormones (permissive or antagonistic effects)

45
Q

what is a permissive effect?

A

the presence of one hormone enhances the effect of another eg epinephrine causes only modest lipolysis in adipose tissue, but when thyroid hormones are also present, greatly increased lipolysis occurs.

46
Q

why is it clinical relevance that single values of hormone may be misleading?

A

because most hormones are released in short bursts so hormone levels in plasma vary widely

Endocrine (6 decks)

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