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MEH A > Session 6 Lecture 2 > Flashcards

Session 6 Lecture 2 Flashcards

1
Q

What is the aim of homeostasis mechanisms?

A

Act to counteract changes in the internal environment

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2
Q

Define homeostasis?

A

The regulation of variables so that internal conditions remain stable and relatively constant.

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3
Q

What does failure in homeostasis lead to?

A

Disease

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4
Q

Is homeostasis a steady state?

A

No - it is a dynamic equilibrium

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5
Q

Where are the homeostasis mechanisms found in the body?

A

Exist at all levels - cells, tissues, organs and organism.

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6
Q

What are the main communication pathways of the body?

A

Nervous system and endocrine system

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7
Q

What is the role of the control centre?

A
  • Determines set point
  • Analyses afferent pathway
  • Determines appropriate response
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8
Q

What is an effector?

A

Agents that cause change.

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9
Q

What is feedback?

A

The output (effect) has an effect on the control centre.

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10
Q

What is a biological rhythm?

A

Rather than a set point being a fixed steady value, it can vary over time, giving rise to biological rhythm.

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11
Q

What is circadian rhythm?

A

Often referred to as ‘body clock’. It is any biological process that displays an endogenous, entrainable oscillation of about 24 hours.

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12
Q

Define zeitgebers

A

These are at external/environmental cue that keeps us on a 24hour cycle.

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13
Q

Give some examples of cues from the environment that keep us on a 24hour body clock (zeitgebers)

A

Light, temperature, social interaction, exercise, eating and drinking pattern.

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14
Q

What is responsible for controlling circadian rhythm?

A

The suprachiasmatic nucleus (tiny region of the brain in the nucleus)

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15
Q

What causes ‘jet lag’?

A

Long haul flights, crossing time zones can result in a mismatch between environmental cues and the body clock.

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16
Q

What hormone is involved in setting the body clock?

A

Melatonin - released from the pineal gland

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17
Q

What is negative feedback?

A

Response in a way to reverse the direction of change

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18
Q

What is positive feedback?

A

Response in a way so as to change the variable even more in the direction of change

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19
Q

When is positive feedback used?

A

When rapid change is desirable

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20
Q

Give an example of positive feedback

A

Blood clotting
Ovulation
Ferguson reflex

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21
Q

What is the ferguson reflex?

A
  • Example of positive feedback
  • Neuroendocrine reflex comprising the self-sustaining cycle of uterine contractions initiated by pressure at the cervix or vaginal walls.
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22
Q

What is the total body water as a % of lean body mass of a male?

A

50-60%

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23
Q

What is the total body water as a % of lean body mass of a female?

A

45-50%

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24
Q

What is the total body water in litres for a 70kg male?

A

42l

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25
Q

What monitors the osmotic pressure of blood plasma?

A

Osmoreceptors in hypothalamus

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26
Q

What is osmolarity?

A

The number of osmoles per litre of solution (related to VOLUME)

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27
Q

What is osmolality?

A

The number of osmoles per kg of solution (related to MASS)

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28
Q

Define osmole

A

The amount of substance that dissociates in solution to form one mole of osmotically active particles.

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29
Q

What is the osmolarity of 1mM of NaCl?

A

2mOsmol/L (1 each from Na and Cl)

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30
Q

When is serum osmolality useful?

A

When investigating hyponatraemia.

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31
Q

How many atom/molecules/ions in 1 mol?

A

6.02 x 10^23

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32
Q

What does a 1 molar (1M) solution contain?

A

1 mole substance in 1 litre

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33
Q

What happens immediately when you have high blood osmolality?

A

Detected by osmorecpetors in hypothalamus
Feel thirsty
Drinking reduces osmolality

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34
Q

What happens (more long term) when you have high blood osmolality?

A

Posterior pituitary releases more ADH which increases H2O absorption form ruin into blood

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35
Q

What is meant by high blood osmolality?

A

Body needs to conserve water

36
Q

What is meant by low blood osmolality?

A

Body needs to excrete water

37
Q

What happens when you have low blood osmolality?

A
  • Detected by osmoreceptors
  • Posterior pituitary secretes less ADH
  • Decreased reabsorption of H2O from urine into blood
38
Q

What releases insulin?

A

Beta cells of the pancreas

39
Q

What is the endocrine system?

A

Collection of glands locates throughout the body

40
Q

What are hormones?

A

Chemical signals produced in endocrine glands or tissues that travel in the bloodstream to cause an effect to other tissues.

41
Q

Apart from endocrine glands, with other organs and tissues release important hormones?

A
  • Heart (ANP & BNP)
  • Liver (IGF1)
  • Stomach (gastric, ghrelin)
  • Adipose (leptin)
42
Q

What hormones does the placenta produce?

A

Inhibin, placental lactogen

43
Q

What hormones does the kidney produce?

A

Erythropoietin, renin, calcitriol

44
Q

Define autocrine

A

Hormone signal acts back on the cell of origin

45
Q

Define paracrine

A

Hormone signal carried to adjacent cells over a short distance via interstitial fluid

46
Q

Define endocrine

A

Hormone signal released into bloodstream and carried to distant target cells

47
Q

Define neurocrine

A

Hormone originates in neurone and after transport down axon released into bloodstream and carries to distant target cells

48
Q

What similarities do neurones and endocrine cells have?

A

Both can secrete and both can be depolarised

49
Q

At what sort of concentration are hormones present in the blood?

A
  • Very low concentrations

- Pico molar range

50
Q

How can hormones be classified?

A
  • By chemical type

- Water solubility

51
Q

What are the different types of hormones based on their chemical structure?

A
  • Peptide/polypeptide
  • Amino acid derivatives (amines)
  • Glycoproteins
  • Steroids
52
Q

Peptide/polypeptide hormone characteristics

A
  • Largest group
  • Short chains of amino acids
  • Water soluble
  • eg insulin, glucagon, growth hormone
53
Q

Amino acid derivative (amine) hormone characteristics?

A
  • Synthesised from aromatic amino acids
  • Adrenal medulla hormones water soluble
  • Thyroid hormones lipid soluble
  • eg adrenaline, noradrenaline, melatonin
54
Q

Glycoprotein hormones characteristics?

A
  • Large protein molecules
  • Often made up of subunits
  • Carbohydrate side chain
  • All water soluble
  • eg LH, FSH and TSH
55
Q

Steroid hormones characteristics?

A
  • All derived from cholesterol
  • Steroidogenic tissues convert cholesterol to different hormones
  • All lipid soluble
  • eg cortisol, aldosterone, testosterone
56
Q

What is the significance of a hormone being lipid soluble?

A

Passes through the plasma membrane therefore the receptor is INISDE the cell

57
Q

What are the two main ways hormones are transported in the body?

A
  • travel in simple solution

- bind to protein

58
Q

What type of hormone is biologically active?

A

Only free form hormone

59
Q

What are the roles of carrier proteins?

A
  • Increase solubility of hormone in plasma
  • Increase half life
  • Readily accessible reserve
60
Q

Name two hormones that don’t require a binding protein

A

Peptides and adrenaline

61
Q

What factors determine hormone levels in the blood?

A
  • Rate of production
  • Rate of delivery
  • Rate of degradation
62
Q

Rate of production

A

Synthesis & secretion, the most highly regulated aspect of hormonal control

63
Q

Rate of delivery

A

Higher blood flow to a particular organ will deliver more hormone

64
Q

Rate of degradation

A

Hormones are metabolised and excreted from the body

65
Q

How do hormones exert their effects?

A

By binding to specific receptors

66
Q

What do water soluble hormones bind to?

A

Cell surface receptors

67
Q

What do lipid soluble hormones bind to?

A

Intracellular receptors

68
Q

What is obesity a result of?

A

Chronic imbalance between energy intake and energy expenditure BMI > 30Kg/m-2

69
Q

Where is the appetite control centre?

A

Ar hate nucleus in the hypothalamus

70
Q

What do the primary neurones in the accurate nuclear process?

A

Neuronal, nutrient and hormonal signals

71
Q

What are the different types of primary neurone?

A
  • Stimulatory neurone

- Inhibitory neurone

72
Q

What does the stimulatory neurone do?

A
  • Contains neuropeptide Y and agouti-related peptide. These promote hunger
73
Q

What do inhibitory neurones do?

A
  • Contain pro-opiomelancortin which yields several neurotransmitters including a-MSH and b-endorphin. These promote satiety.
74
Q

How is feeding behaviour altered?

A

Primary neurones synapse with secondary neurones in other regions of the hypothalamus.

75
Q

What is ghrelin and when is it released?

A
  • peptide hormone released from stomach wall when empty
76
Q

What is the function of ghrelin?

A
  • stimulates the excitatory primary neurones in accurate nucleus and therefore stimulates appetite.
77
Q

What inhibits the release of ghrelin?

A

Filling of the stomach

78
Q

What is peptide tyrosine tyrosine (PYY) and when is it released?

A
  • Short (36 amino acid) peptide hormone released by cells in the ileum and colon
  • In response to feeding
79
Q

What is the action of PYY?

A

Inhibits the excitatory primary neurones of the acrcuate nucleus ad stimulates the inhibitory neurones
effect is therefore to suppress appetite

80
Q

What is leptin and where is it made?

A
  • Peptide hormone

- Released into blood by fat cells (adipocytes)

81
Q

What effects does leptin have in arcuate nucleus?

A
  • Stimulates inhibitory (POMC) neurones

- Inhibits the excitatory (AgRP/NPY) neurones in arcuate nucleus

82
Q

What is the overall effect of leptin?

A

Suppress appetite

83
Q

What function does insulin have in controlling appetite?

A

Suppresses appetite by similar mechanism as leptin. Seems to be less important then leptin is in controlling appetite

84
Q

What is amylin and where is it secreted from?

A
  • Peptide hormone

- Secreted by B cells in pancreas

85
Q

What is the action of amylin?

A
  • Suppress appetite

- Decrease glucagon secretion and slow gastric emptying

MEH A (19 decks)

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