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AQA A Level Biology > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

Define homeostasis

A

Physiological control systems that maintain a constant internal environment

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2
Q

Why does a constant internal temperature need to be maintained?

A
  • Metabolism is controlled by enzymes- Enzymes have an optimum temperature- Too hot = denatured enzymes- Too cold = slow rate of reaction
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3
Q

Why does a constant internal pH need to be maintained?

A
  • Metabolism is controlled by pH- Enzymes have an optimum pH- Away from optimum pH rate of reaction decreases and then beyond a point enzymes denature
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4
Q

Why does a constant internal glucose concentration need to be maintained?

A

A minimum amount of glucose is needed as a respiratory substrate

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5
Q

What happens if glucose concentration is too high?

A
  • Decreases water potential- Water moves out of cells by osmosis- Cells shrivel up
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6
Q

What is negative feedback?

A
  • Receptors detect a change away from the normal/optimum and effectors activate mechanisms to return the body to normal/optimum- Control and regulation- e.g. blood temp, pH, glucose- Separate negative feedback systems give you more control
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7
Q

What is positive feedback?

A
  • A response that results in the effectors further amplifying the change away from the normal - Rapid changes and responses- e.g. giving birth, hypothermia, blood clotting, depolarisation
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8
Q

What happens when there’s an increase to the blood glucose concentration

A
  • Receptors in the pancreas detect an increase in blood glucose- Beta cells in the islets of Langahans (pancreas) secrete insulin- Insulin binds to receptors in liver + muscles- Increases permeability to glucose- More glucose absorbed by facilitated diffusion- Glycogenesis converts glucose into glycogen- Increases rate of respiration
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9
Q

What happens when there’s an decrease to the blood glucose concentration

A
  • Receptors in the pancreas detect blood glucose is low - Alpha cells in the islets of Langahans (pancreas) secrete glucagon - Glucagon binds to receptors on liver cells- Decreases rate of respiration - Glycogenolysis (glycogen to glucose)- Gluconeogenesis (non carbs to glucose)
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10
Q

What is glycogenesis?

A

Makes glycogen and is promoted by insulin when blood glucose is high

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11
Q

What is glycogenolysis?

A

Splits glycogen to produce glucose when blood glucose is low, it is promoted by glucagon and adrenaline

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12
Q

What is glyconeogenesis?

A

Makes glucose from non carbs when blood glucose is low , is promoted by glucagon

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13
Q

What is glucagon secreted by?

A

Alpha cells in the islets of Langahans in the pancreas

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14
Q

When is glucagon secreted?

A

When blood glucose is low

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15
Q

What receptors does glucagon bind to?

A

Liver cells

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16
Q

What is the effect on blood glucose when glucagon binds to receptors on liver cells?

A

Blood glucose increases

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17
Q

What are the mechanisms of glucagon?

A
  • decreases respiration- gluconeogenesis- glycogenolysis
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18
Q

What is adrenaline secreted by?

A

Adrenal glands

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19
Q

When is adrenaline secreted?

A

When blood glucose is low

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20
Q

What receptors does adrenaline bind to?

A

Liver cells

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21
Q

What is the effect on blood glucose when adrenaline binds to receptors on liver cells?

A

Blood glucose increases

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22
Q

What are the mechanisms of adrenaline?

A
  • activates glycogenolysis by secretion of glucagon- inhibits glycogenesis
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23
Q

What is insulin secreted by?

A

Beta cells in the islets of Langahans in the pancreas

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24
Q

When is insulin secreted?

A

When blood glucose is high

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25
Q

What receptors does insulin bind to?

A

Liver and muscle cells

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26
Q

What is the effect on blood glucose when insulin binds to receptors on liver and muscle cells?

A

Blood glucose decreases

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27
Q

What are the mechanisms of insulin?

A
  • increases respiration- glycogenesis- increases permeability of liver and muscle cells
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28
Q

How does insulin cause an increase in liver and muscle cell permeability?

A
  • glucose carrier proteins are stored in vesicles inside liver and muscle cells - insulin binds with receptors on the cell membrane of the target cells- causes vesicles to fuse with cell membranes- carrier proteins join the membrane and glucose is absorbed by fascillitated diffusion
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29
Q

What is diabetes meilitus?

A

An illness where blood glucose levels are not controlled

30
Q

What is hyperglycemia?

A

Dangerously high blood glucose concentration

31
Q

What is hypoglycemia?

A

Dangerously low blood glucose concentration

32
Q

What are the causes of type 1 diabetes?

A

Immune system kills beta cells in the islets of Langerhans therefore insulin cannot be made

33
Q

What effect does type 1 diabetes have on blood glucose?

A

Hyperglycemia

34
Q

What age groups are most effected by type 1 diabetes?

A

Children and young adults

35
Q

What is the treatment for type 1 diabetes?

A
  • insulin injections - avoid simple carbs- eat at regular intervals- regular exercise to use up glucose
36
Q

What are the causes of type 2 diabetes?

A
  • obesity - lack of exercise- poor diet - beta cells dont make enough insulin - liver + muscle cells stop responding to insulin
37
Q

What effect does type 2 diabetes have on blood glucose?

A

Hyperglycaemia

38
Q

What age groups are most effected by type 2 diabetes?

A

Adults/elderly

39
Q

What is the treatment for type 2 diabetes?

A
  • drugs to increase sensitivity to insulin, make more insulin, reduce amount of glucose released - eat healthy- lose weight - regular exercise- insulin injections
40
Q

What is the mechanism by which cAMP acts as a second messenger?

A
  • A hormone (first messenger), such as adrenaline or glucagon, is complimentary to the receptor protein on the cell membrane of the target cell (liver cell)- This activates adenyl cyclate (enzyme)- Adenyl cyclate connects ATP to form cAMP- cAMP activates protein kinase A by altering its tertiary structure allowing glycogenolysis to take place
41
Q

In what part of the nephron is the glomerus?

A

Cortex

42
Q

In what part of the nephron is the bowmans capsule?

A

Cortex

43
Q

In what part of the nephron is the proximal conviluted tubule?

A

Cortex

44
Q

In what part of the nephron is the loop of henle?

A

Medulla

45
Q

In what part of the nephron is the distal conviluted tubule?

A

Cortex

46
Q

In what part of the nephron is the collecting duct?

A

Medulla

47
Q

Compare the afferent arteriole and the efferent arteriole

A

Upon entering the glomerus the afferent arteriole has a considerably larger surface area when comparing it to the efferent arteriole (by which the blood leaves the glomerus and the bowmans capsule). This allows for the mechanism of ultrafiltration

48
Q

What happens at the proximal conviluted tubule?

A

Most of reabsorption from the filtrate that passes trough the glomerus, this is supported by numerous microvilli (increase the surface area). Most of reabsorption takes place through active transport, therefore the proximal conviluted tubule contains many mitochondria

49
Q

What happens at the distal convoluted tubule?

A

Reabsorption of Na+ ions and osmoregulation

50
Q

What happens after the collecting duct?

A

Urine passes to the ureter, bladder and finally the urethra

51
Q

What happens at the collecting duct?

A

Osmoregulation

52
Q

What is the order of the parts in a nephron?

A

1 - Glomerus2 - Bowmans capsule3 - Proximal conviluted tubule4 - Descending limb of the loop of henle5 - Ascending limb of the loop of henle6 - Distal conviluted tubule7 - Collecting duct

53
Q

What does the nephron have?

A

A really good blood supply

54
Q

How does ultrafiltration take place?

A

High hydrostatic pressure forms due to the change in width from the afferent arteriole to the efferent arteriole, this forces small molecules into the bowmans capsule (which form the filtrate). Larger molecules will not fit throgh the gaps in the capillary wall, basement membrane and the podocytes

55
Q

Why does ultrafiltration take place?

A

To filter the blood

56
Q

Where does ultrafiltration take place?

A

At the glomerus which is surrounded by the Bowmans capsule

57
Q

What is the filtrate made up of?

A
  • Water- Glucose- Amino acids- Ions (Sodium and chloride)- Urea
58
Q

What molecules are too big to filter out of the blood and into the filtrate?

A

Red blood cells and other proteins

59
Q

What is the role of the basement membrane and the podocytes in the process of ultrafiltration?

A

They prevent large molecules entering the filtrate

60
Q

What is selective reabsorption?

A

Useful products are reabsorbed from the glomerular filtrate mostly by the proximal convoluted tubule but also by the distal convoluted tubule, the loop of Henle and the collecting duct

61
Q

What is ultrafiltration and what does it produce?

A

The process of filtering under pressure to produce the glomerular filtrate

62
Q

What is the process of selective reabsorption?

A

Useful molecules are absorbed into the epithelial cells lining the PCT from the lumen of the nephron where they can be transported into the surrounding capillaries

63
Q

What part of the nephron does the most selective reabsorption?

A

The proximal convoluted tubule

64
Q

How is the PCT adapted for selective reabsorption?

A
  • Microvilli increase SA- Mitochondria provide ATP for active transport
65
Q

What does urine contain?

A
  • Water- Ions- Urea- Excess vitamins- Glucose if diabetic
66
Q

What happens at the descending limb of the loop of Henle?

A
  • Permeable to water- Water moves out by osmosis - Water absorbed by capillaries- Increases conc of urine
67
Q

What happens at the ascending limb of the loop of Henle?

A
  • Sodium and chlorine ions pumped out- Using ATP- Decreases water potential of the medulla- Impermeable to water (Water cannot move in or out)
68
Q

What effect does ADH have on the collecting duct?

A
  • ADH changes the collecting ducts permeability to water- More ADH = less piss
69
Q

What happens if you have a longer loop of Henle and what is an example of mammals with a longer loop of Henle?

A
  • Longer loop of henle = more concentrated medulla - More water reabsorbed by the capillaries- More concentrated urine- Dessert animals such as camels
70
Q

How is dehydration detected by the body and dealt with?

A
  • Low water potential of the blood is detected by the osmoreceptors in the hypothalimus - The posterior pituitary secretes antidiuretic hormone which is carried in the blood stream - ADH binds to specific receptor proteins on the collecting duct (and DCT)- Increases permeability to water- Water moves out of collecting duct (and dct) by osmosis (medulla now has a lower water potential) and more water is reabsorbed into the blood
71
Q

What happens when there is more ADH?

A
  • Collecting duct wall more permeable to water- More water moves out of collecting duct by osmosis- Less piss

AQA A Level Biology (13 decks)

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