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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
Q

What hormone stimulates gluconeogenesis?

26
Q

What does insulin do?

A
  • 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
Q

What does glucagon do?

A
  • Activates enzymes for glycogenolysis
  • Activates enzymes for gluconeogenesis
  • Causes a decrease in rate of respiration of glucose
28
Q

What does adrenaline do?

A
  • 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
Q

How does the second messenger model work?

A
  • 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
Q

Describe Type 1 diabetes (cause, treatment etc)

A
  • Autoimmune
  • Can’t produce insulin
  • Glucose levels remain high - kidneys can’t reabsorb it all
  • Insulin therapy
31
Q

Describe type 2 diabetes (cause, treatment etc)

A
  • Risk factors (obesity, lack of exercise, diet, age)
  • Not enough insulin produced or cells no longer responsive to it
  • Diet, exercise, weight loss
32
Q

What is the advice of healthcare professionals about type 2 diabetes?

A
  • 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
Q

What is the response of food companies?

A
  • 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
Q

What happens if blood water potential too low?

A
  • Water leaves cells by osmosis
  • Cells shrivel and die
35
Q

What happens if blood water potential too high?

A
  • Water moves into cells by osmosis
  • Cells swell and burst
36
Q

What is the structure of the kidneys?

A
  • Cortex = outer layer
  • Medulla = inner layer
  • Renal artery - brings blood in
  • Renal vein - takes blood away
  • Ureter - takes urine to the bladder
37
Q

What is the structure of the bowman’s capsule?

A
  • Afferent arteriole brings blood in (wider)
  • Efferent takes blood away (narrower)
  • Glomerelus - Bundle of capillaries
38
Q

How does ultrafiltration occur?

A
  • 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
Q

What 3 layers does the filtrate have to pass through?

A
  • Capillary wall
  • Basement membrane
  • Epithelial cells of bowman’s capsule
40
Q

Where does selective reabsorption happen?

A
  • Proximal convoluted tubule
41
Q

How are the cells of the PCT epithelium adapted?

A
  • Microvilli - high SA for reabsorption
  • Mitochondria - provide ATP for active transport
  • Carrier and channel proteins - allow active transport and facilitated diffusion
42
Q

How is glucose reabsorbed?

A
  • Active transport into the epithelial cells
  • Diffusion into the blood
43
Q

How is Na+ reabsorbed?

A
  • Facilitated diffusion into the epithelial cell
  • Active transport into the blood
44
Q

How is water reabsorbed?

A
  • Osmosis
  • Other molecules removed into the blood - blood has lower water potential - water moves in
45
Q

What substances does urine contain?

A
  • Water
  • Dissolved salts
  • Urea
  • Other substances such as hormones, excess vitamins
46
Q

What substances does urine not usually contain and why?

A
  • Proteins and blood cells - too large to be filtered out
  • Glucose - actively reabsorbed into the blood
47
Q

What system does the loop of Henle make and what is it?

A
  • Counter current multiplier system
  • Flows in opposite directions
  • Longer loop - bigger gradient
  • Creates an ion gradient in medulla
48
Q

What is the descending limb of the loop of Henle permeable to?

49
Q

What is the ascending limb of the loop of Henle permeable to?

A

ions
Not permeable to water

50
Q

What directions is the water potential gradient in the medulla?

A
  • More negative as you go down
  • Ion conc increases
51
Q

How does the counter current multiplier system begin?

A
  • Na+, Cl- actively transported out of the ascending limb
  • This lowers the water potential in the medulla
52
Q

How does the loss of ions from the ascending limb impact the descending limb?

A
  • 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
Q

How does this loss of water impact the loop?

A
  • 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
Q

What happens to water in the interstitial fluid of the medulla?

A
  • Reabsorbed into the blood
55
Q

What happens in the distal convoluted tubule?

A
  • 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
Q

How does the body detect a decrease in water potential?

A
  • 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
Q

How does the body respond to a low water potential?

A
  • Posterior pituitary gland secretes more ADH
58
Q

What effect does ADH have?

A
  • 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
Q

What is the negative feedback system for too high blood water potential?

A
  • 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
Q

What is the negative feedback system for too low blood water potential?

A
  • 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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