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*Diabetes & Endocrinology > Intro to Endocrine > Flashcards

Intro to Endocrine Flashcards

1
Q

Define the endocrine system

A

A system that integrates + controls organ function via secretion of hormones from cells/tissues/glands which are then carried in blood to target organs, distal from site of synthesis, where they influence activity of target organ

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2
Q

Give an example of a fast response in the endocrine system

A

Increased heart rate in response to adrenaline - within seconds

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3
Q

Give an example of a slow response in the endocrine system

A

Increased protein synthesis in response to growth hormone - over days

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4
Q

What other chemicals should endocrine hormones not be confused with?

A

Paracrine
Autocrine
Exocrine

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5
Q

Describe the action of paracrine chemicals

A

Act local to site of synthesis e.g. histamine

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6
Q

Describe the action of autocrine chemicals

A

Acton on/in the same cell that synthesises the hormone e.g. cytokine

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7
Q

Describe the action of exocrine chemicals

A

Released from exocrine glands via ducts to external environment e.g. saliva, sweat, bile

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8
Q

What other system does the endocrine system communicate with to control all body functions?

A

Nervous system

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9
Q

How do target tissues detect endocrine hormones?

A

Specific receptors for the chemical are on/in cells

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10
Q

How do neurotransmitters travel to target sites?

A

Neurotransmitters released from presynaptic neurons travel across synaptic cleft to postsynaptic cell to influence its activity

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11
Q

Do neurotransmitters work locally or distally?

A

Locally within synaptic cleft

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12
Q

What occurs when endocrine and nervous systems combine (‘neuroendocrine’)?

A

Nerves release hormones which enter blood and travel to target cells

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13
Q

Why is response to any one hormone highly specific?

A

Because only target cells have receptors for the hormone e.g. adrenal medulla

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14
Q

While response of target cell is specific, same hormone can have different effects in diff target cells, give an example

A

INSULIN
In skeletal muscle/adipose tissue - increase glucose uptake
In liver - increased glycogenesis/decreased gluconeogenesis

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15
Q

Give examples of endocrine function embedded in a physiological system

A

Reproductive, renal, gastrointestinal

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16
Q

Endocrine system is also a diffuse system of glands in its own right - name the 4 main ones

A 
Thyroid gland
Parathyroid glands
Adrenal gland
Pituitary gland
(and hypothalamus from nervous system)
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17
Q

At what concentrations do endocrine hormones exert their effects?

A

Very low concentrations (10-9 -10-12 M) - only need tiny amount for physiological response

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18
Q

How are endocrine hormones actions generally terminated?

A

Negative feedback loops

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19
Q

What are the 3 classifications of endocrine hormones?

A

Peptide (most common)
Amine
Steroid

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20
Q

What are peptide/protein hormones composed of?

A

Short or long chains of amino acids

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21
Q

What are amine hormones derived from?

A

One of two amino acids (tyrptophan or tyrosine) - in reality all are derived from tyrosine other than melatonin

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22
Q

What are steroid hormones all derived from?

A

Cholesterol

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23
Q

What are peptide hormones initially synthesised as?

A

Preprohormone

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24
Q

What does the large, inactive preprohormone contain?

A

One or more copies of the active hormone in their amino acid sequence

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25
Q

What are preprohormones cleaved into?

A

Prohormones (smaller, still inactive units)

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26
Q

Where in the cell are preprohormones cleaved?

A

Endoplasmic reticulum

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27
Q

Where are prohormones packaged into vesicles?

A

Golgi apparatus in endocrine cells

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28
Q

What are prohormones packed into vesicles alongside? And what is their function?

A

Proteolytic enzymes

Break down prohormone into active hormone + other fragments

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29
Q

What happens when release of vesicles is triggered?

A

All vesicle contents are released into plasma (co-secretion)

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30
Q

Give an example of inactive fragments being useful in clinical practice

A

In diabetes - C-peptide in plasma can be measured

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31
Q

What is a c-peptide?

A

Inactive fragment cleaved from insulin prohormone

32
Q

What do levels of c-peptide in plasma/urine indicate?

A

Endogenous insulin production from the pancreas (although levels are usually about 5x higher than that of inendogenous insulin)

33
Q

Why is it useful to measure C-peptide and not insulin directly?

A

Diabetic would be taking insulin - difficult to differentiate between that and what their pancreas is actually producing

34
Q

Why do peptide hormones transport easily via the blood?

A

They are water soluble (lipophobic/hydrophillic)

35
Q

Why is the hydrophillic property of peptide hormones a bad thing?

A

They cannot cross the cell membrane and so have to bind to membrane receptors on target cell

36
Q

How quick are the responses once receptors are bound to peptide hormones?

A

Relatively fast (seconds to minutes)

37
Q

How do most peptide hormones work?

A

Via modulating either the GPCR or tyrosine kinase linked signalling pathways

38
Q

What do the GPCR or tyrosine kinase linked signalling pathways do?

A

Phosphorylate existing proteins in the cell and modify their function e.g. open/close ion channels, activate or inactivate enzymes

39
Q

What are the 2 types of cell surface receptors peptide hormones will bind to?

A

G protein couple receptor

Tyrosine kinase linked receptor

40
Q

Describe the mechanism of a G protein coupled receptor

A

Activates 2nd messenger system (which alters gene expression) and/or ion channels leading to modification of existing proteins

41
Q

Does the G protein coupled receptor cause a faster or slower response?

A

Faster (rapid response)

42
Q

Describe the mechanism of a tyrosine kinase linked receptor

A

Alters gene expression

43
Q

Does the tyrosine kinase linked receptor produce a faster or slower response?

A

Slower, longer lasting activity

44
Q

From which amino acid are most amine hormones derived from?

A

Tyrosine

45
Q

What are the 3 catecholamine hormones?

A

Dopamine, norepinephrine, epinephrine (hydrophillic - similar mechanism of action to peptide hormones)

46
Q

What are the 2 thyroid amine hormones?

A

Thyroxine, triiodothyronine (lipophillic - similar mechanism of action to steroid hormones)

47
Q

What is the only amine hormones not derived from tyrosine and what is its function?

A

Melatonin, derived from tryptophan

Melatonin regulates circadian rhythm

48
Q

What makes steroid hormones different to other types of hormones?

A

Steroid hormones are synthesised directly as needed, rather than stored and released

49
Q

Why are steroid hormones synthesised directly as needed?

A

They are highly lipophilic so cannot be retained within lipid membranes; once synthesised they diffuse across membrane into ISF and the blood

50
Q

Due to being poorly soluble in water, how are steroid hormones transported?

A

Bound to carrier proteins e.g. albumin

51
Q

How do carrier proteins aid the transport of steroid hormones through plasma?

A

They stabilise transport and protect them from enzymatic degradation, phenomenally increasing their half life

52
Q

What is the half life of steroid hormones compared to amine hormones?

A

60-90 mins for steroid; 2 mins for amine

53
Q

What 4 places in the body produce steroid hormones, and what specific hormones do they produce?

A

GONADS - sex steroids
PLACENTA - hCG, sex steroids
KIDNEY - vitamin D3
ADRENAL CORTEX - corticosteroids

54
Q

As prev said, all steroid hormones are derived from cholesterol, but how is it decided which specific hormone is ultimately produced?

A

Determined by diff cells having diff enzymes synthesising diff derivatives of cholesterol

55
Q

Where are steroid hormone receptors located?

A

Inside cells (cytoplasmic or nuclear receptors)

56
Q

What effect do steroid hormones have on the cell?

A

Either trigger activation or repression of gene function within nucleus = genomic effect (then have a knock on effect on protein synthesis)

57
Q

Is the process of steroid hormone effect fast or slow?

A

Relatively slow process

lag time between hormone release an biological effect (hours to days) but effect persists for around the same time

58
Q

Is there any unbound free steroid/thyroid hormone in plasma?

A

Yes, a small amount; this is the physiologically important fraction

59
Q

What can be done ONLY by a free hormone?

A

Diffusion across capillary walls to target cells

60
Q

What does the Law of Mass Action dictate?

A

As free hormone leaves the plasma, more hormone is released from carriers; allows for a reservoir of hormone ready for action

61
Q

Free hormone + complexed hormone =

A

Total plasma (hormone)

62
Q

What determines {Hormone}plasma ?

A

The balance between secretion and degradation/excretion

63
Q

In most endocrine pathways, what is secretion a response to?

A

Negative feedback reflexes

64
Q

Give an example of a hormone which operates via negative feedback reflex

A

Parathyroid hormone (causes increased bone resorption, increased kidney reabsorption of Ca, production of calcitrol = increased plasma Ca which triggers inhibition of parathyroid hormone)

65
Q

Give a hormone which responds to a neural feedback loop

A

Adrenaline

66
Q

Name a hormone who’s secretion is subject to multiple control mechanisms

A

Insulin

67
Q

What affects insulin secretion?

A
  • plasma glucose
  • autonomic nerve activity
  • presence of food in gut
  • additional hormones such as glucagon
68
Q

When normal plasma hormone concentration is disrupted, what type of responses are initiated?

A

Homeostatic

69
Q

Prolonged exposure to low {hormone}plasma often leads to…

A

up-regulation of receptor number

70
Q

Prolonged exposure to high {hormone]plasma often leads to…

A

down-regulation of receptor number

71
Q

Homeostatic responses affect the hormones own receptors, but also…

A

receptors for other hormones (permissive or antagonistic effects)

72
Q

What is a ‘permissive effect’?

A

Presence of one hormone enhances effect of another

73
Q

Give an example of hormones working in a permissive effect

A

Epinephrine only modest lipolysis but with thyroid hormones greatly increased lipolysis occurs (increased synthesis of epinephrine receptors on adipocytes)

74
Q

What is an ‘antagonistic effect’?

A

Presence of one hormone reduces the effect of another

75
Q

Give an example of hormones working in an antagonistic effect

A

Growth hormone impairs the response to insulin by decreasing number of insulin receptors on tissues

76
Q

In clinical practice, what is required to give a true picture of hormone levels?

A

24 hour monitoring (most hormones are released in short bursts)

*Diabetes & Endocrinology (24 decks)

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