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MEH A > Session 6 Lecture 2 > Flashcards

Session 6 Lecture 2 Flashcards

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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
What monitors the osmotic pressure of blood plasma?
Osmoreceptors in hypothalamus
26
What is osmolarity?
The number of osmoles per litre of solution (related to VOLUME)
27
What is osmolality?
The number of osmoles per kg of solution (related to MASS)
28
Define osmole
The amount of substance that dissociates in solution to form one mole of osmotically active particles.
29
What is the osmolarity of 1mM of NaCl?
2mOsmol/L (1 each from Na and Cl)
30
When is serum osmolality useful?
When investigating hyponatraemia.
31
How many atom/molecules/ions in 1 mol?
6.02 x 10^23
32
What does a 1 molar (1M) solution contain?
1 mole substance in 1 litre
33
What happens immediately when you have high blood osmolality?
Detected by osmorecpetors in hypothalamus Feel thirsty Drinking reduces osmolality
34
What happens (more long term) when you have high blood osmolality?
Posterior pituitary releases more ADH which increases H2O absorption form ruin into blood
35
What is meant by high blood osmolality?
Body needs to conserve water
36
What is meant by low blood osmolality?
Body needs to excrete water
37
What happens when you have low blood osmolality?
- Detected by osmoreceptors - Posterior pituitary secretes less ADH - Decreased reabsorption of H2O from urine into blood
38
What releases insulin?
Beta cells of the pancreas
39
What is the endocrine system?
Collection of glands locates throughout the body
40
What are hormones?
Chemical signals produced in endocrine glands or tissues that travel in the bloodstream to cause an effect to other tissues.
41
Apart from endocrine glands, with other organs and tissues release important hormones?
- Heart (ANP & BNP) - Liver (IGF1) - Stomach (gastric, ghrelin) - Adipose (leptin)
42
What hormones does the placenta produce?
Inhibin, placental lactogen
43
What hormones does the kidney produce?
Erythropoietin, renin, calcitriol
44
Define autocrine
Hormone signal acts back on the cell of origin
45
Define paracrine
Hormone signal carried to adjacent cells over a short distance via interstitial fluid
46
Define endocrine
Hormone signal released into bloodstream and carried to distant target cells
47
Define neurocrine
Hormone originates in neurone and after transport down axon released into bloodstream and carries to distant target cells
48
What similarities do neurones and endocrine cells have?
Both can secrete and both can be depolarised
49
At what sort of concentration are hormones present in the blood?
- Very low concentrations | - Pico molar range
50
How can hormones be classified?
- By chemical type | - Water solubility
51
What are the different types of hormones based on their chemical structure?
- Peptide/polypeptide - Amino acid derivatives (amines) - Glycoproteins - Steroids
52
Peptide/polypeptide hormone characteristics
- Largest group - Short chains of amino acids - Water soluble - eg insulin, glucagon, growth hormone
53
Amino acid derivative (amine) hormone characteristics?
- Synthesised from aromatic amino acids - Adrenal medulla hormones water soluble - Thyroid hormones lipid soluble - eg adrenaline, noradrenaline, melatonin
54
Glycoprotein hormones characteristics?
- Large protein molecules - Often made up of subunits - Carbohydrate side chain - All water soluble - eg LH, FSH and TSH
55
Steroid hormones characteristics?
- All derived from cholesterol - Steroidogenic tissues convert cholesterol to different hormones - All lipid soluble - eg cortisol, aldosterone, testosterone
56
What is the significance of a hormone being lipid soluble?
Passes through the plasma membrane therefore the receptor is INISDE the cell
57
What are the two main ways hormones are transported in the body?
- travel in simple solution | - bind to protein
58
What type of hormone is biologically active?
Only free form hormone
59
What are the roles of carrier proteins?
- Increase solubility of hormone in plasma - Increase half life - Readily accessible reserve
60
Name two hormones that don't require a binding protein
Peptides and adrenaline
61
What factors determine hormone levels in the blood?
- Rate of production - Rate of delivery - Rate of degradation
62
Rate of production
Synthesis & secretion, the most highly regulated aspect of hormonal control
63
Rate of delivery
Higher blood flow to a particular organ will deliver more hormone
64
Rate of degradation
Hormones are metabolised and excreted from the body
65
How do hormones exert their effects?
By binding to specific receptors
66
What do water soluble hormones bind to?
Cell surface receptors
67
What do lipid soluble hormones bind to?
Intracellular receptors
68
What is obesity a result of?
Chronic imbalance between energy intake and energy expenditure BMI > 30Kg/m-2
69
Where is the appetite control centre?
Ar hate nucleus in the hypothalamus
70
What do the primary neurones in the accurate nuclear process?
Neuronal, nutrient and hormonal signals
71
What are the different types of primary neurone?
- Stimulatory neurone | - Inhibitory neurone
72
What does the stimulatory neurone do?
- Contains neuropeptide Y and agouti-related peptide. These promote hunger
73
What do inhibitory neurones do?
- Contain pro-opiomelancortin which yields several neurotransmitters including a-MSH and b-endorphin. These promote satiety.
74
How is feeding behaviour altered?
Primary neurones synapse with secondary neurones in other regions of the hypothalamus.
75
What is ghrelin and when is it released?
- peptide hormone released from stomach wall when empty
76
What is the function of ghrelin?
- stimulates the excitatory primary neurones in accurate nucleus and therefore stimulates appetite.
77
What inhibits the release of ghrelin?
Filling of the stomach
78
What is peptide tyrosine tyrosine (PYY) and when is it released?
- Short (36 amino acid) peptide hormone released by cells in the ileum and colon - In response to feeding
79
What is the action of PYY?
Inhibits the excitatory primary neurones of the acrcuate nucleus ad stimulates the inhibitory neurones effect is therefore to suppress appetite
80
What is leptin and where is it made?
- Peptide hormone | - Released into blood by fat cells (adipocytes)
81
What effects does leptin have in arcuate nucleus?
- Stimulates inhibitory (POMC) neurones | - Inhibits the excitatory (AgRP/NPY) neurones in arcuate nucleus
82
What is the overall effect of leptin?
Suppress appetite
83
What function does insulin have in controlling appetite?
Suppresses appetite by similar mechanism as leptin. Seems to be less important then leptin is in controlling appetite
84
What is amylin and where is it secreted from?
- Peptide hormone | - Secreted by B cells in pancreas
85
What is the action of amylin?
- Suppress appetite | - Decrease glucagon secretion and slow gastric emptying

MEH A (19 decks)

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