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Endocrine > Introduction to Endocrine > Flashcards

Introduction to Endocrine Flashcards

1
Q

Give an example of a fast response caused by the endocrine system

A

Increased heart rate in response to adrenaline

The response may be slow (over a few days) such as increased protein synthesis as a response to growth hormone

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2
Q

What is the definition of paracrine chemicals, autocrine chemicals and exocrine chemicals

ALL ARE NOT TO BE CONFUSED WITH THE ENDOCRINE SYSTEM

A

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

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

Exorine - released from the exocrine glands via ducts to the external environment including the GI tract (saliva, sweat, bile)

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3
Q

No receptor for endocrine hormone?

A

No response

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4
Q

What does the endocrine system cooperate intimately with?

A

Cooperates intimately with the nervous system to provide further control, particularly for long term phenomena such as growth

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5
Q

Where does a neurotransmitter act?

A

In the synaptic cleft

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6
Q

Give an example of where neurones produce a hormone that enters the blood?

A

hypothalamic – posterior pituitary axis.

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7
Q

Although hormones are highly specific how can a hormone exhibit different properties in different portions of the body?

A

Hormones can have different effects in different target cells

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8
Q

What is the fucntion of hormones?

A

To bring about an increase or a decrease in a particular activity in the target cells and tissues

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9
Q

What hormones does the thyroid produce?

A

Thyroxin and triiodothyronine (target tissue is many organs, responsible for metabolism, growth and development)

Calcitonin, primary target is in bone, meant to regulate plasma calcium levels, however the effects are minimal in humans

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10
Q

What hormone does the parathyroid produce?

A

Parathyroid hormone

Site of action - bones and the kidney

Regulates plasma calcium and phosphate levels

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11
Q

What hormones are produced by the adrenal cortex?

A

Aldosterone - Kidney is the primary target - responsible for sodium and potassium homeostasis

Cortisol - primary target is many tissues - main effect is the stress response

Androgens - primary target is many tissues - main effect is sex drive in females

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12
Q

What hormones are produced by the adrenal medulla?

A

Epinephrine

Norepinephrine

Target cell is many tissues

Main effect is the fight or flight response

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13
Q

What hormones are produced by the kidney?

A

1,25 Dihydroxy vitamin D3 - (target cell is the intestine, increases calcium absorption)

Erythropoetin (target tissue is the bone marrow - red blood cell production)

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14
Q

What are the concentrations of endocrine hormones?

A

Very low concentrations (10 to the power of minus 9/12 Moles)

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15
Q

What are the three classifications of endocrine hormones?

A

Peptide - chains of amino acids

Steroid - derived from cholesterol

Amine hormones - tryptophan or tyrosine

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16
Q

When is the peptide hormone synthesised?

A

In advance of when it is needed - it is then stored in vesicles until it is required

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17
Q

What is a prehormone?

A

It is an inactive initial protein produced by the ribosome which contains one or more copies of the active hormone in their amino acid sequence

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18
Q

How are prehormones converted into prohormones?

A

Prehormones - Cleaved into smaller units in the RER to leave smaller but still inactive proteins

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19
Q

What happens to prohormones?

A

They are packaged into vesicles in the golgi apparatus, along with proteolytic enzymes which break the prohormone down into active hormone and other fragments

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20
Q

What is meant by co-secretion?

A

When release of the vesicle is triggered, the hormone and other fragments are expelled

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21
Q

Give examples of peptide hormones

A

Thyrotropin releasing hormone

Follicle stimulating hormone

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22
Q
A

In summary - the Prehormone is made by ribosomes and is cleaved to form the prohormone in the RER. The prohormone is packaged in a vesicle with proteolytic enzymes in the golgi apparatus. Exocytosis follows (co-secretion)

23
Q

What is C-peptide?

A

C-peptide 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 (produced in equal amounts). However, because insulin is metabolised faster, levels of C-peptide are typically about 5x higher than endogenous insulin.

C-peptide levels are a direct measure of endogenous insulin - insulin medication for those who are diabetic will not contain these C-peptides

24
Q

How are peptide hormones transported in the blood and how do they enter a cell?

A

Transported in the plasma because they are water soluble

Cannot cross cell membrane so bind to membrane bound receptors on target cell.

25
Q

What is the response time for peptide hormone receptors?

A

Create relatively fast biological responses (seconds to minutes)

26
Q

What pathways are often involved in peptide hormone receptors?

A

G protein coupled receptor or tyrosine kinase linked signalling pathways. These pathways phosphorylate existing proteins in the cells and modify their function e.g. open or close ion channels, activate or inactivate enzymes

27
Q

How does a GPCR result in modification of existing proteins?

A

By activation of a 2nd messenger system and/or ion channels

28
Q

How fast is the GPCR response?

A

Rapid

29
Q

What is the intracellular effect of tyrosine kinase inhibitors?

A

Alter gene expression

Slower but longer lasting activity

30
Q

Are steroid hormones stored?

A

No, they are synthesized directly as needed

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

31
Q

How are steroid hormones transported in the blood?

A

They are bound to carrier proteins such as albumin - this stabilizes their transport through the plasma and protects them from enzymatic degradation, increases their half life (60-90 minutes vs 2 minutes for amine hormones)

32
Q

What are steroid hormones produced by?

A
  1. Gonads (testes and ovary) – sex steroids
  2. Placenta - hCG, sex steroids
  3. Kidney - Vitamin D3
  4. Adrenal cortex - corticosteriods
33
Q

What determines which specific steroid hormone is produced?

A

Different cells produce different enzymes which synthesise different derivatives of cholesterol

34
Q

Where are the receptors for steroid hormones?

A

Located inside cells (cytoplasmic or nuclear receptors) trigger either activation or repression of gene function within the nucleus

Known as the genomic effect

35
Q

What is the effect of genes being the receptors for steroid hormones?

A

Either increase or decrease protein synthesis

36
Q

What is the time delay between a steroid hormone being released and the biological effect?

A

This is a relatively slow process so there is a lag time between hormone release and biological effect (hours to days) but effect persists for around the same time. Some evidences suggests steroids may occasionally bind to cell surface receptors → rapid response.

37
Q
A

In summary

Steroid hormone is bound to carrier protein

Must be unbound to enter the cell

Receptor is within the cytoplasm or nucleus

Receptor-hormone complex activates or inhibits one or more gene

Corresponding mRNA transcription takes place

Translation results in new proteins

38
Q

What are most amine hormones derivatives of?

A

Tyrosine

Only amine hormone not derived from tyrosine is melatonin which is derived from tryptophan. Melatonin regulates circadian rhythm.

39
Q

Which amine hormones are said to act in a similar mechanism to peptide hormones?

A

Catecholamines

(Dopamine, norepinephrine, epinephrine)

40
Q

What amine hormones are said to be of a similar mechanism of action to steroid hormones?

A

Thyroid hormones:

Thyroxine

Triiodothyronine

41
Q

Describe the ratio between the free hormone : hormone-protein complex

A

Ratio is much in the favour of bound (complexed) hormone

42
Q

What is significant about the levels of free hormone in health?

A

They remain constant

The Law of Mass Action dictates that as free hormone leaves the plasma (taken up by cells) more hormone is released from the carriers. Typically only minute quantities of hormone are required for physiological functions.

Free hormone + complexed hormone = Total plasma [hormone]

43
Q

What two benefits are conferred by the hormone carrier protein?

A

Increases solubility

Protects form degradation

44
Q

Why do peptide and catecholamine hormones have a short half life?

A

Vulnerable to degradation before they reach their target organ

There is short action so requires continues secretion

45
Q

How long does the effect of a steroid hormone / thyroid hormone last?

A

Usually hours to days

46
Q

What determines the concentration of hormone in the blood?

A

The rate of secretion and the rate of removal

47
Q

How is removal of hormones achieved?

A

Excretion

Metabollic transformation

Mainly occurs in the liver and kidneys

48
Q

Which hormones are secreted easily?

A

Catecholamine and peptide hormones

Steroids and thyroid hormones take hours and days to excrete or metabolise, because protein-bound.

49
Q

What are the control mechanisms of hormone secretion?

A

Negative feedback such as parathyroid hormone (increase in plasma calcium inhibits the parathyroid cell)

Neural feedback (fight or flight response)

Plasma molecules

Autonomic nerve activity

Food in the gut

Other hormones

50
Q

Give an example of a neural feedback loop

A

Adrenaline

Sympathetic discharge results in release of adrenaline from the adrenal medulla to the blood stream

51
Q

When would we see an increase in the number of hormone receptors on target tissues?

A

After prolonged exposure to low hormone concentrations in the plasma

This increases the tissue sensitivity to the hormone

Conversely, often after prolonged exposure to high [hormone] plasma we see down-regulation = decrease in receptor number on target tissues (decreases tissue sensitivity to hormone).

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

52
Q

Give an example of a permissive effect of a hormone

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.

TH increases synthesis of receptors for epinephrine on adipocytes. TH itself has no effect on lipolysis but is permissive to epinephrine.

53
Q

Why must 24 hour monitoring may be required to give the true picture of hormone levels?

A

Most hormones are released in short bursts so [hormone] varies widely. Clinical relevance is that single values of [hormone] may be misleading

Endocrine (25 decks)

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