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BS - Gastrointestinal System pt.1 > Metabolic Rate, Growth & Disease > Flashcards

Metabolic Rate, Growth & Disease Flashcards

1
Q

How is acute regulation of plasma glucose maintained?

A

Through the action of insulin and glucagon

There are some modifications by adrenaline

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2
Q

What is the role of growth hormone in children?

A

It promotes growth

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3
Q

What does deficiency and excess growth hormone in children lead to?

A

Deficiency leads to dwarfism after birth

Excess leads to gigantism

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4
Q

Why does growth deficiency only lead to dwarfism after birth?

A

Before birth, there are hormones related to growth hormone that produce the same growth response

Maternal insulin is also important

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5
Q

Why does growth hormone not have the same effect in adults?

A

The epiphyses of the long bones are closed, so there is no change in stature

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6
Q

What does an excess of growth hormone cause in adults?

A

Acromegaly

Bones become excessively thickened, soft tissues and other tissues overgrow

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7
Q

How does someone with acromegaly often die?

A

Through heart failure

This is due to the extra strain on the cardiovascular system from tissue overgrowth

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8
Q

What does growth hormone deficiency cause in adults?

How does this change when growth hormone is administered?

A

Deficiency gives no obvious disease

When GH is administered:

  1. increase in lean body mass
  2. decrease in fat
  3. increase in vigour and wellbeing
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9
Q

What is the role of the hypothalamus in GH regulation?

A

It integrates signals that are driving or suppressing expression of GH

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10
Q

What are the 2 nuclei of the hypothalamus involved in GH regulation?

How do they affect each other?

A
  1. paraventricular nucleus secretes somatostatin
  2. arcuate nucleus secretes GRH

They inhibit each other, leading to an episodic cyclic response

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11
Q

How will the paraventricular and arcuate nuclei influence GH production?

A

Somatostatin from the paraventricular nucleus suppresses anterior pituitary GH

GHR from the arcuate nucleus increases anterior pituitary GH

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12
Q

What factors will increase growth hormone secretion?

A
  1. low glucose
  2. amino acids
  3. TRH
  4. Ghrelin
  5. androgens/oestrogens
  6. sleep, exercise and stress
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13
Q

How does Thyroid hormone (T3) influence GH production?

A

It increases growth hormone production

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14
Q

What is the main result of growth hormone secretion?

A

It will increase metabolic activity and produce IGFs (insulin-like growth factors)

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15
Q

What is the role of IGFs?

A

They provide feedback inhibition and longer-term growth

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16
Q

How does growth hormone release change during the day?

A

There are lots of rapid pulses of release

More is released at night

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17
Q

What is the mechanism behind growth hormone secretion?

A
  1. GRH binds to the receptor
  2. This causes activation of adenylate cyclase
  3. adenylate cyclase activates protein kinase a
  4. this causes a enzymatic cascade leading to Ca2+ influx
  5. Growth hormone is released by exocytosis
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18
Q

What is the effect of somatostatin on growth hormone release?

A

It will inhibit adenylate cyclase

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19
Q

What are the 2 variants of growth hormone?

A

22 kDa form predominates

20 kDa form

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20
Q

What happens to growth factor after it is released into the circulation?

A

About 40% of the molecule binds to a carrier protein in the plasma

This protein is made by cleaving its receptor

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21
Q

What is the half-life of growth hormone?

How does binding to a carrier protein in the plasma affect this?

A

25 minutes

Binding to a carrier protein increases half-life as GH is protected from cleavage by proteases

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22
Q

What receptor does growth hormone bind to?

A

It acts via a tyrosine kinase associated receptor

This leads to protein phosphorylation

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23
Q

Why is growth hormone said to have “diabetogenic effects”?

A

It antagonises the effect of insulin to increase blood glucose concentration

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24
Q

How fast are the effects of growth hormone?

How are longer-term effects mediated?

A

Rapid effects in minutes to hours

Longer term effects on growth are mediated via insulin-like growth factor 1 (somatomedin)

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25
Q

How does growth hormone affect:

i. liver
ii. fat
iii. muscle
iv. insulin?

A

i. increased gluconeogenesis
ii. increased lipolysis
iii. decreased glucose uptake
iv. creates insulin-resistance

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26
Q

Why does growth hormone antagonise the effects of insulin receptors?

A

If muscles take up less glucose, this can be used for the RBCs and the brain

The muscles can use the fatty acids produced from lipolysis

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27
Q

When is somatomedin released?

What must be present?

A

It is released from many tissues in response to GH

It requires insulin to be present as well

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28
Q

What are the 2 IGFs (somatomedins)?

A
  1. IGF1 is the main active IGF that is stimulated by GH

2. IGF2 is not stimulated by GH

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29
Q

What is significant about IGF1 having a strong homology to insulin?

A

The receptors are similar and work in the same way

IGF1 will work okay on the insulin receptor and vice versa

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30
Q

What is the role of IGF1?

What happens if it is present in excess?

A

It enhances protein synthesis and growth

In excess, it can cause hypoglycaemia

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31
Q

Other than growth hormone, what other 3 factors affect growth?

A
  1. insulin - especially in utero
  2. steroids
  3. thyroid hormones
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32
Q

How do sex steroids and glucocorticoids affect growth?

A

Sex steroids accelerate growth but hasten maturity

(this is bc they increase rate of growth as well as fusion of the epiphyses)

Glucocorticoids slow growth

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33
Q

Why are thyroid hormones involved in growth?

A

They are essential for normal growth and response to GH

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34
Q

What are the 2 forms of thyroid hormones?

A

T3 - triiodothyronine

T4 - thyroxine

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35
Q

What is strange about the mechanism of action of thyroid hormones?

A

They are peptide hormones but have intracellular receptors

They will enter the nucleus to affect transcription

(they act like steroids)

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36
Q

How is T4 carried in the blood?

A

It is tightly bound to carrier proteins

These are thyroid binding globulin and transthyretin

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37
Q

How does being bound to proteins affect the activity and half-life of T4?

A

It has a low free concentration in the circulation

It is also very stable and the half-life is prolonged

Half life = 8 days

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38
Q

What is the half-life of T3?

Why is it different to T4?

A

1 day

T3 is less bound to protein and less stable

It is the active form that enters cells to produce effects

39
Q

What will stimulate production and release of thyroid hormones?

A

Thyrotropin from the anterior pituitary gland

this is TSH

40
Q

What are the roles of thyroid hormones?

A
  1. increase metabolic rate
  2. increase heat generation
  3. essential for normal growth and development
41
Q

What is the structure of the thyroid gland like?

A

It is anchored to thyroid cartilage and moves on swallowing

It contains follicles which contain thyroglobulin

42
Q

What are C cells?

A

Clear cells

They secrete calcitonin, which is involved in calcium handling

43
Q

What is the role of TSH on the basolateral membrane of the thyroid follicular cell?

A

It increases the activity of the Na/I cotransporter (NIS)

This enhances the uptake of iodine by the follicular cell so that the ratio of follicular cell iodine:plasma iodine increases

44
Q

What happens to iodide after it has entered the follicular cell?

What happens at the same time?

A

It is transported into the follicular lumen

The follicular cell also secretes thyroglobulin

45
Q

What happens during iodination?

What stimulates this process?

A

TSH stimulates iodination of thyroglobulin in the follicular lumen

46
Q

What happens after iodination is completed?

A

CONJUGATION

TSH stimulates the conjugation of iodinated tyrosines to form T4 and T3 linked to thyroglobulin

47
Q

What happens after conjugation is completed?

A

TSH stimulates endocytosis of iodinated thyroglobulin into the follicular cells

48
Q

What happens after endocytosis is completed?

A

PROTEOLYSIS

TSH stimulates the proteolysis of the iodinated thyroglobulin, forming T3 and T4

49
Q

What happens after proteolysis is completed?

A

TSH stimulates secretion of T4 and T3 into the circulation

50
Q

What other type of thyroid hormone is produced?

A

rT3 which is inactive

51
Q

What is meant by TSH having a trophic effect on cells?

A

The thyroid gland becomes enlarged (hyperplasia) if TSH levels are high

52
Q

What are the 2 enzymes that will deiodiniate T4 into T3?

Where are they found?

A
  1. Type I

found in liver, kidney and thyroid

  1. Type II

found in pituitary, CNS and placenta

53
Q

What is the role of the Type III enzyme?

A

It cleaves T4 to rT3

54
Q

What will inhibit Type I and Type II?

A

Type I is inhibited by stress and caloric restriction

Type II is constitutive (active all the time)

55
Q

What happens to T3 once it has entered a cell?

A

It migrates to the nucleus, where it binds to the thyroid hormone receptor

This then binds to the response element of the relevant gene to activate or suppress transcription

56
Q

How does T3 affect the Na+/K+ pump and the beta adrenergic receptors?

A
  1. increases activity of Na+/K+ pump

2. activates beta-adrenergic receptors which increases sympathetic stimulation

57
Q

How does thyroid hormone acutely increase metabolic rate and heat production?

A
  1. increases metabolic rate via “futile cycles” that do not actually achieve anything
  2. mitochondrial decoupling only generates heat, and no ATP is produced
58
Q

How does thyroid hormone affect activities in the liver?

A

Increases gluconeogenesis (glucose production)

Increases glycogenolysis (glycogen breakdown)

59
Q

What is an example of a futile cycle involving fats?

A

Thyroid hormone causes both lipolysis and lipogenesis

Lipolysis provides free glycerol for gluconeogenesis

60
Q

What is an example of a futile cycle involving proteins?

What is the overall effect of this?

A

Thyroid hormone increases proteolysis, but also protein synthesis

Proteolysis provides amino acids for gluconeogenesis

Net effect is muscle wasting

61
Q

How does thyroid hormone affect the Na+/K+ pump?

A

it causes a sodium leak

this increases Na+/K+ ATPase activity which wastes energy

62
Q

Why is there usually no hyperglycaemia under the action of thyroid hormones?

A

Insulin control is normal

Thyroid hormones enhance the insulin response as everything is just running a bit faster than normal, and more heat is generated

63
Q

What organ depends on thyroid hormone for development?

What does deficiency in infancy lead to?

A

The brain depends on thyroid hormone for development and growth

deficiency leads to cretinism and dwarfism

64
Q

What is cretinism?

A

A marked impairment of brain function

65
Q

What does deficiency of thyroid hormone cause in later childhood?

A

Severe impairment of growth

Catch-up growth is possible if the thyroid hormone is replaced

66
Q

What is a goitre and what is it caused by?

A

It is a lump in the neck

It is caused by low thyroid hormone leves, as this means more TSH is produced

This causes the thyroid gland to enlarge

67
Q

What usually causes a goitre?

A

it is common in areas with low environmental iodine

68
Q

How does autoimmunity affect the thyroid gland?

A

It can cause both hyperthyroidism or hypothyroidism

69
Q

How can autoimmunity cause hyperthyroidism?

What condition is this?

A

Antibodies against the TSH receptor may activate it, driving excess TH production and cause hyperthyroidism

This is Graves disease

70
Q

What are the symptoms of Graves disease?

A
  1. weight loss
  2. tremor
  3. sweating
  4. tachycardia
  5. dislike of hot weather
71
Q

Why do people with Graves disease have double vision?

A

Graves disease is a consequence of excess tissue growth

Exophthalmos develops - eyeballs project out of the front of the face

72
Q

What is pretibial myxoedema in Graves disease?

A

Excess hypertrophy of tissue down the front of the shins

73
Q

What is the difference between pretibial myxoedema and myxoedema?

A

Myxoedema is thickening of the tissue, which occurs in hypothyroidism

74
Q

How can autoimmunity cause hypothyroidism?

What condition is this?

A

Antibodies that destroy TSH receptors or other thyroid targets cause hypothyroidism

This is Hashimoto’s thyroiditis

75
Q

What are the symptoms of Hashimoto’s thyroiditis?

A
  1. weight gain
  2. hypothermia
  3. tiredness
  4. constipation
  5. skin thickening and oedema
  6. bradycardia
  7. dislike of cold weather
76
Q

What is secondary anovulation in Hashimoto’s thyroiditis?

A

Ovulation terminates - it is amenorrhea

77
Q

What is the main glucocorticoid in humans?

A

Cortisol

78
Q

What causes the hypothalamus to release CRH?

A

It will integrate stress factors and diurnal rhythm to release CRH

79
Q

What is the action of CRH?

A

It induces ACTH release from the anterior pituitary gland

80
Q

What is the role of ACTH?

A

It stimulates adrenal cortex hypertrophy and cortisol production

81
Q

What is the effect of iatrogenic steroids on cortisol production?

A

They will feedback into the pituitary and the hypothalamus to suppress ACTH (and glucocorticoid) production

They cause adrenal atrophy

82
Q

What happens if someone takes steroids for too long?

A

The body is not in a position to replace the steroids after they have stopped being taken

This is due to atrophy

83
Q

What are the key drivers for glucocorticoid production?

A

Physical, emotional and biochemical stress

84
Q

What is the mechanism of action of glucocorticoids?

How rapid is their effect?

A

They act via a nuclear receptor to induce gene transcription

They take hours/days to exert an effect

85
Q

What is the main effect of glucocorticoids?

A

They inhibit insulin responses and enhance SNS responses

This targets glucose to the brain, whilst other tissues use fatty acids

86
Q

How do glucocorticoids affect the liver?

A

They promote gluconeogenesis and glucose release

87
Q

How do glucocorticoids affect fat and muscle?

A

In fat, they stimulate lipolysis

This gives glycerol for gluconeogenesis andfree fatty acids for energy

In muscle they stimulate protein breakdown to release amino acids for gluconeogenesis

88
Q

What type of effect do glucocorticoids have and why?

A

Diabetogenic effect

They act against insulin to increase glucose availability

89
Q

What are the main 2 beneficial chronic effects of glucocorticoids?

A
  1. immunosuppression

2. reduction in inflammation and cytokine production

90
Q

How do glucocorticoids affect the CNS and blood cell production?

A
  1. they have complex CNS effects ranging from euphoria (smaller doses) to psychosis (increased doses)
  2. they stimulate haematopoiesis and GI tract mucosa
91
Q

How do glucocorticoids affect the skin and fat distribution?

A

They cause truncal obesity - fat is distributed from peripheral to central

They cause skin thinning, muscle wasting and osteoporosis

92
Q

What does excess glucocorticoids cause?

A

Cushing’s disease

93
Q

What does adrenocortical insufficiency cause?

A

Addison’s disease

This leads to a high ACTH which gives a slate grey pigmentation

BS - Gastrointestinal System pt.1 (22 decks)

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