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Endocrinology > Introduction to the Endocrine System > Flashcards

Introduction to the Endocrine System Flashcards

1
Q

What is the endocrine sytem?

A

System that integrates and controls organ function via the secretion of chemicals from cells, tissues or glands where they can be carried in the blood to target organs distal from the site of hormone synthesis, where they influence the activity of that organ

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2
Q

What should endocrine hormones not be confused with?

A

Paracrine chemicals
Autocrine chemicals
Exocrine chemicals

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3
Q

What are paracrine chemicals?

A

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

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4
Q

What are autocrine chemicals?

A

Chemicals that act on/in the same cells that it is synthesised

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5
Q

What are exocrine chemicals?

A

Chemicals that are released from exocrine glands via ducts to the external environment

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6
Q

Which system does the endocrine system communicate with?

A

Nervous system

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7
Q

Where do hormones travel?

A

In the blood

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8
Q

What site do hormones reach?

A

Site distal to that where the chemical is made

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9
Q

How do tissues detects specific hormones?

A

Through the presence of specific receptors for that hormones

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10
Q

What if there is no receptor for the hormone on that cell?

A

There will be no response

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11
Q

Where are neurotransmitters release from?

A

Pre-synaptic neurons

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12
Q

Where do neurotransmitters travel?

A

Across the synaptic cleft to the post synaptic neuron

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13
Q

What is the difference between hormones and neurotransmitters?

A

They act locally in the synaptic cleft whereas hormones travel to distal sites

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14
Q

When the endocrine and nervous system combine what do nerves release?

A

Hormones which enter the blood and travel to their target tissue

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15
Q

Why is the response to one hormone highly specific even though hormones travel throughout the body in blood?

A

Because only target cells have specific receptors for that hormone

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16
Q

Is the effect of one hormone the same on all cells with the receptor?

A

The same hormone can have different effects in different target cells

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17
Q

How do hormones generally change activity in a cell?

A

Switch enzymes on or off

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18
Q

What are the sits of primary endocrine glands?

A 
Hypothalamus 
Pituitary 
Thyroid 
Parathyroid 
Adrenal glands 
Kidneys 
Medulla 
Cortex
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19
Q

What are the 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
  4. Exert their effects at very low concentrations (act in the range 10-9 -10-12 M)
  5. Act by binding to receptors on target tissues
  6. Have their action terminated, often via negative feedback loops.
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20
Q

What are the classifications of endocrine hormones?

A

Peptide or protein
Steroid hormones
Amine hormones

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21
Q

What are peptide hormones composed from?

A

Amino acid chains

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22
Q

What are steroid hormones derived from?

A

Cholesterol

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23
Q

What are amine hormones derived from?

A

Two amino acids

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24
Q

Where are peptide hormones synthesised?

A

In advance and stored in vesicles

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25
Q

What are preprohormones?

A

Initial protein produced by ribosomes

Contain one or more copies of the active hormones in their amino acid sequence

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26
Q

Where are preprohormones cleaved?

A

On the RER

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27
Q

What are preprohormones cleaved into?

A

Prohormones

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28
Q

Where are prohormones packaged into vesicles?

A

In the golgi apparatus

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29
Q

What are prohormones packaged with?

A

Proteolytic enzymes

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30
Q

What do the proteolytic enzymes do to the prohormones?

A

Break down the prohormone into active hormone and other fragments

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31
Q

Where are vesicle contents of peptide hormones released?

A

Into the plasma

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32
Q

What is C-peptide?

A

Inactive fragment that is cleaved from insulin prohormone

33
Q

Why are C-peptide levels measured?

A

Levels of C-peptide in plasma or urine are often measured to indicate endogenous insulin production from the pancreas (produced in equal amounts).

34
Q

Why can peptide hormones not easily cross the cell membrane?

A

Because they are lipophobic

35
Q

What is a benefit to peptide hormones being hydrophillic?

A

Then can transport in the blood easily

36
Q

How do most peptide hormones work?

A

Via modulating either the GPCR or tyrosine kinase linked signalling pathways. These pathways phosphorylate existing proteins in the cell and modify their function e.g. open or close ion channels, activate or inactivate enzymes.

37
Q

What is the drawback to peptide hormones being hydrophilic?

A

They cannot diffuse across the cell membrane

38
Q

Why do peptide hormones bind to a cell surface receptor?

A

Because they are lipophobic and cannot readily cross the cell membrane

39
Q

What 2 types of receptors will peptide hormones typically bind to?

A

Tyrosine kinase linked

G protein coupled receptors

40
Q

What do G protein coupled receptors typically do?

A

Activate a 2nd messenger system

41
Q

What do tyrosine kinase linked receptors typically do?

A

Alter gene expression

42
Q

Where are steroid hormones derived from ?

A

Cholesterol

43
Q

When are steroid hormones synthesised?

A

As they are needed

44
Q

Are steroid hormones typically stored?

A

No

45
Q

Why are steroid hormones not pre made then stored?

A

Because they are highly lipophilic and would just diffuse out of the cell membrane

46
Q

Once synthesised where do steroid h. travel?

A

Diffuse out of the membrane into the ISF then into the blood

47
Q

Why are steroid h. bound to plasma proteins?

A

Because they are hydrophobic

48
Q

What is the effect of binding steroid h. to plasma proteins?

A

Stabilises their transport through the blood and protects them from enzymatic degradation

49
Q

Why is there a longer 1/2 life of steroid hormones?

A

Because they are bound to proteins protecting them

50
Q

Which organs produce steroid hormones?

A

Gonads
Kidneys
Adrenal cortex
Placenta

51
Q

What determines which steroid is produced in which cell?

A

Different types of enzymes synthesising different types of cholesterol

52
Q

Where are steroid hormone receptors located?

A

Inside cells (cytoplasmic or nuclear receptors)

53
Q

What effect do steroid hormones have on the cell?

A

Either trigger or repress gene function within the nucleus

Consequently the either upregulate or downregulate protein synthesis

54
Q

What do genes ultimately control?

A

The synthesis of protein

55
Q

Do steroid hormones exert a fast response?

A

No long

56
Q

Which is the only amine hormone not derives from tyrosine?

A

Melatonin

57
Q

From which amino acid are most amine hormones derived from?

A

Tyrosine

58
Q

Which amino acid is melatonin derived from?

A

Tryptophan

59
Q

What does melatonin regulate?

A

Circadian rhythm

60
Q

Where is dopamine released?

A

From the brain

61
Q

Where is noriepinepherine released?

A

From neurons

62
Q

Where is epinephrine released from?

A

Adrenal medulla

63
Q

Name 3 amine hormones?

A

Dopamine
Noriepinepherine
Epinephrine

64
Q

Which form of steroid hormone is active?

A

The unbound fraction

65
Q

What does the law of mass dictate abut steroid hormones?

A

That as free hormone is taken up by the cell

More hormone is released from the carriers

66
Q

What does free hormone + complexed hormone =

A

Total plasma (hormone)

67
Q

Is a lot of steroid hormone unbound?

A

No only a small ratio

68
Q

Are peptide hormones easily degraded?

A

Yes they are very vulnerable to degradation

69
Q

How is prolonged action achieved with peptide hormones?

A

Continued secretion

70
Q

What does the concentration of hormone in the blood depend on?

A

The rate of secretion and the rate of removal

71
Q

Where does hormones removal usually occur?

A

In the liver or kidneys

72
Q

How are most endocrine pathways controlled?

A

Through negative feedback

73
Q

When levels are high what happens in negative feedback?

A

Negative feedback switches off production

74
Q

What do some endocrine pathways respond to?

A

Neural feedback

75
Q

How can hormones influence the ability of the target cell to respond?

A

Regulate the number of hormone receptors

76
Q

What is often seen after prolonged exposure to low concentration hormone?

A

Upregulation in the number of hormone receptors on the target cell

77
Q

What is often seen after prolonged exposure to high concentration hormone?

A

Down regulation in the number of hormone receptors on the target cell

78
Q

What is meant by permissive effects?

A

When the presence of one hormone enhances the effect of another

79
Q

Give an example of permissive effects

A

Epinephrine in the presence of thyroid hormones creates greatly increased lipolysis

Endocrinology (19 decks)

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