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Biology > Topic 6C: Homeostasis > Flashcards

Topic 6C: Homeostasis Flashcards

1
Q

Define homeostasis

A

Maintenance of a constant / stable internal environment within set limits

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2
Q

What happens if the body is too hot?

A
  • Enzymes denature
  • Molecules vibrate too much, breaks hydrogen bonds, changes shape of active site, substrate cannot bind, no ESC
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3
Q

What happens if the body is too cold?

A
  • Enzyme activity reduced
  • Slows rate of metabolic reactions
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4
Q

What happens if blood pH too high or low?

A
  • Enzymes denature
  • Hydrogen bonds break
  • Active site changes shape
  • No ESC
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5
Q

What happens to cells when blood glucose conc too high?

A
  • Water potential decreases in blood
  • Water moves out of cells by osmosis
  • Cells shrivel and die
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6
Q

What happens when blood glucose conc too low?

A
  • Cannot perform their function
  • Can’t respire
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7
Q

Define negative feedback?

A
  • Change from normal conditions causes a series of changes that result in a level being restored to normal
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8
Q

What is the negative feedback for a level increasing?

A
  • Detected by receptors
  • Effectors bring a return to normal
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9
Q

What is the negative feedback for a level decreasing?

A
  • Detected by receptors
  • Effectors bring a return to normal
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10
Q

Why is it important to have separate mechanisms for departures in different directions?

A
  • Means you can increase or decrease to return the level to normal
  • If there was only 1 - would only be able to turn it on and off
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11
Q

Define positive feedback

A
  • A deviation from the normal conditions is amplified leading to further deviation
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12
Q

How are neurones examples of positive feedback?

A
  • Na+ channels open
  • If threshold reached more channels open and more Na+ move in
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13
Q

How is blood clots an example of positive feedback?

A
  • Platelets are activated
  • Release a chemical triggering more platelets
  • Allows a clot to be formed quickly
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14
Q

Where in the pancreas secrete hormones for BG control?

A
  • Islets of Langerhans
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15
Q

What cells produce glucagon?

A

alpha cells

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16
Q

What cells produce insulin?

A

beta cells

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17
Q

What is the simple negative feedback for high BG conc?

A
  • Detected by beta cells
  • Increased insulin secretion
  • Reduce to normal
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18
Q

What is the simple negative feedback for low BG conc?

A
  • Detected by alpha cells
  • Increase glucagon secretion
  • Increase to normal
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19
Q

What is glycogenesis?

A

glucose to glycogen

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20
Q

What hormone stimulates glycogenesis?

A

insulin

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21
Q

What hormone inhibits glycogenesis?

A

adrenaline

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22
Q

What is glycogenolysis?

A

glycogen to glucose

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23
Q

What hormones stimulate glycogenolysis?

A

glucagon and adrenaline

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24
Q

What is gluconeogenesis?

A

fatty acids and amino acids to glucose

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25
What hormone stimulates gluconeogenesis?
glucagon
26
What does insulin do?
- Binds to complimentary receptors on target cell membranes - Cells add more glucose transporter proteins to cell membranes - increase permeability to glucose - Rate of facilitated diffusion of glucose into cells increases, decreases BG conc - Binds to receptors on the liver - stimulates glycogenesis - Increases rate of respiration of glucose
27
What does glucagon do?
- Activates enzymes for glycogenolysis - Activates enzymes for gluconeogenesis - Causes a decrease in rate of respiration of glucose
28
What does adrenaline do?
- Secreted from adrenal glands when BG conc low, exercise or stress - Activates glycogenolysis and inhibits glycogenesis - Activates secretion of glucagon and inhibits secretion of insulin - Increased glucose conc so more available for respiration
29
How does the second messenger model work?
- Adrenaline / glucagon binds to receptor on target cell - Activates adenylate cyclase to catalyse the conversion of ATP to cyclic AMP (cAMP) - 2nd messenger - cAMP activated protein kinase A - Causes cascade of reactions of glycogenolysis
30
Describe Type 1 diabetes (cause, treatment etc)
- Autoimmune - Can’t produce insulin - Glucose levels remain high - kidneys can’t reabsorb it all - Insulin therapy
31
Describe type 2 diabetes (cause, treatment etc)
- Risk factors (obesity, lack of exercise, diet, age) - Not enough insulin produced or cells no longer responsive to it - Diet, exercise, weight loss
32
What is the advice of healthcare professionals about type 2 diabetes?
- Eat low fat, sugar and salt diet - Eat whole grains, fruit and vegetables - Exercise - NHS change4life - education on healthy eating and lifestyle changes - Challenge the food industry for advertising junk food and to improve nutritional values
33
What is the response of food companies?
- Making healthier products - sugar alternatives, reducing sugar, fat and salt contents - Still pressure to increase profits - need public perception of healthy eating to change
34
What happens if blood water potential too low?
- Water leaves cells by osmosis - Cells shrivel and die
35
What happens if blood water potential too high?
- Water moves into cells by osmosis - Cells swell and burst
36
What is the structure of the kidneys?
- Cortex = outer layer - Medulla = inner layer - Renal artery - brings blood in - Renal vein - takes blood away - Ureter - takes urine to the bladder
37
What is the structure of the bowman’s capsule?
- Afferent arteriole brings blood in (wider) - Efferent takes blood away (narrower) - Glomerelus - Bundle of capillaries
38
How does ultrafiltration occur?
- Blood enters glomerleus from wide afferent arteriole - High pressure because efferent arteriole is narrower - High hydrostatic pressure forces liquid and small molecules from blood into bowman’s capsule as filtrate - Larger molecules (proteins and blood cells) can’t pass through
39
What 3 layers does the filtrate have to pass through?
- Capillary wall - Basement membrane - Epithelial cells of bowman’s capsule
40
Where does selective reabsorption happen?
- Proximal convoluted tubule
41
How are the cells of the PCT epithelium adapted?
- Microvilli - high SA for reabsorption - Mitochondria - provide ATP for active transport - Carrier and channel proteins - allow active transport and facilitated diffusion
42
How is glucose reabsorbed?
- Active transport into the epithelial cells - Diffusion into the blood
43
How is Na+ reabsorbed?
- Facilitated diffusion into the epithelial cell - Active transport into the blood
44
How is water reabsorbed?
- Osmosis - Other molecules removed into the blood - blood has lower water potential - water moves in
45
What substances does urine contain?
- Water - Dissolved salts - Urea - Other substances such as hormones, excess vitamins
46
What substances does urine not usually contain and why?
- Proteins and blood cells - too large to be filtered out - Glucose - actively reabsorbed into the blood
47
What system does the loop of Henle make and what is it?
- Counter current multiplier system - Flows in opposite directions - Longer loop - bigger gradient - Creates an ion gradient in medulla
48
What is the descending limb of the loop of Henle permeable to?
- Water
49
What is the ascending limb of the loop of Henle permeable to?
ions Not permeable to water
50
What directions is the water potential gradient in the medulla?
- More negative as you go down - Ion conc increases
51
How does the counter current multiplier system begin?
- Na+, Cl- actively transported out of the ascending limb - This lowers the water potential in the medulla
52
How does the loss of ions from the ascending limb impact the descending limb?
- The low water potential in the medulla means water moves out of the ascending limb by osmosis down the water potential gradient into the medulla
53
How does this loss of water impact the loop?
- Filtrate in the lower part of the loop now has a lower water potential (lost water) so has a higher ion concentration - Na+, Cl- at the lower end of the loop move out by facilitated diffusion - fluid around then has a very low water potential
54
What happens to water in the interstitial fluid of the medulla?
- Reabsorbed into the blood
55
What happens in the distal convoluted tubule?
- Water potential of the filtrate higher than in plasma - Water moves out by osmosis into capillaries - Ions have moved out of the filtrate so have higher water potential
56
How does the body detect a decrease in water potential?
- Osmoreceptors in the hypothalamus - lose water by osmosis in low blood water potential - Decrease in volume - Send action potentials to the posterior pituitary gland
57
How does the body respond to a low water potential?
- Posterior pituitary gland secretes more ADH
58
What effect does ADH have?
- Bind to complimentary receptors on the distal convoluted tubule and collecting duct - More aquaporins added to the membranes of the DCT and CD - Increases their permeability to water
59
What is the negative feedback system for too high blood water potential?
- Detected by osmoreceptors in the hypothalamus - Less ADH secretion by posterior pituitary gland - Less permeability of DCT + CD to water - Less water reabsorbed - Less concentrated and more volume of urine
60
What is the negative feedback system for too low blood water potential?
- Detected by osmoreceptors in the hypothalamus - More ADH secretion by posterior pituitary gland - More permeability of DCT + CD to water - More water reabsorbed - More concentrated and less volume of urine

Biology (22 decks)

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