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Biology Paper 2 > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

What is homeostasis?

A

The maintenance of of the internal environment within an optimum range

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2
Q

What happens if body temperature is too high?

A

Enzymes denature, as the hydrogen bonds in the tertiary structure break, altering the shape of the active site

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3
Q

What happens if body temperature is too low?

A

Enzyme activity decreases, so important reactions slow down

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4
Q

What happens if pH is not maintained?

A

Enzymes will denature, so can no longer catalyse important reactions

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5
Q

What happens if blood glucose is high? (Ψ)

A
  • Ψ of blood is reduced, so water moves out of cells via osmosis and into the blood
  • This makes cells flaccid and kills them
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6
Q

What happens if blood glucose is low?

A
  • Insufficient glucose for respiration, so respiration rate decreases + energy falls
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7
Q

What is negative feedback?

A

A mechanism that restores the system to original level

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8
Q

How does negative feedback work?

A
  • Change in the internal environment is detected by receptors
  • Receptors are stimulated + send signal to effectors
  • The effectors counteract the change
  • But only in a specific range
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9
Q

Advantage of multiple feedback mechanisms

A

Faster response

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10
Q

What can cause changes in blood glucose conc? {2}

A
  • Eating carbs (increase)

- Exercise (decrease)

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11
Q

Where is blood glucose conc monitored?

A

Pancreas

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12
Q

What happens when blood glucose is too high?

A
  • Glycogenesis
  • Receptors in the pancreas detect change
  • Beta cells in the islets of Langerhans secrete insulin
  • Insulin binds to receptors on hepatocytes which activates the conversion of glucose to glycogen
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13
Q

What happens when insulin binds to receptors? {3}

A
  • Increases the permeability of cells by increasing the number of GLUT 4 channel proteins
  • Glucose is used during respiration
  • Glycogenesis
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14
Q

What happens when blood glucose is low (hepatocytes)?

A
  • Glycogenolysis
  • Receptors in the pancreas detect change
  • Alpha cells from the islets of Langerhans secrete glucagon
  • Glucagon binds to receptors on hepatocytes stimulating the conversion of glycogen to glucose
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15
Q

What happens when blood glucose is too low (muscle + cytoplasm of hepatocytes)?

A
  • Gluconeogenesis

- Glycerol and amino acids are converted to glucose

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16
Q

How else can glucagon reduce blood glucose

A
  • Slowing the rate of respiration
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17
Q

Why is insulin important? (Ψ)

A
  • As without it blood glucose would not decrease, so Ψ would decrease and move out of cells via osmosis causing them to die
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18
Q

Why is glucagon important?

A
  • As without it blood glucose would decrease, so there is not enough for respiration, therefore less energy to survive
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19
Q

How does adrenaline increase blood glucose?

A
  • It is secreted from the adrenal glands
  • It binds to receptors on hepatocytes
  • It inhibits glycogenesis and activates glycogenolysis
  • It also promotes the secretion of glucagon and inhibits the secretion of insulin
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20
Q

What are primary messengers?

A
  • Messengers that do not enter the cell
  • They exert an action on the cell membrane
  • They activate another molecule or initiate a reaction
  • Example; hormones
21
Q

What are secondary messengers?

A
  • They initiate and coordinate responses within a cell
  • They are activated by the binding of primary messengers
  • Example; cAMP (cyclic AMP)
22
Q

What is adenylate cyclase?

A
  • An enzyme that converts ATP to cAMP
23
Q

What is protein kinase A?

A
  • An enzyme activated by cAMP

- It triggers a cascade of reactions that results in glycogenolysis

24
Q

What are the causes of type 1 diabetes?

A
  • Beta cells are attacked by the immune system

- So become damaged and can no longer produce insulin

25
Q

What is hyperglycaemia?

A
  • When the body is unable to produce insulin to counteract the increase in blood glucose conc
  • So it continues to increase
  • Fatal if not treated
26
Q

Name a treatment for type 1 diabetes?

A
  • Insulin therapy; pump or injection
27
Q

What is hypoglycaemia?

A
  • When blood glucose conc is too low
28
Q

What are the causes of type II diabetes? {4}

A
  • Obesity
  • Lack of exercise
  • Age
  • Family history
29
Q

How does type II diabetes occur?

A
  • When beta cells no longer produce enough insulin

- When the hepatocytes and muscle cells stop responding to insulin

30
Q

Name treatments for type II diabetes

A
  • Healthy diet
  • Exercise
  • Medication to lower glucose levels
  • Insulin injections(rare)
31
Q

Where does osmoregulation take place?

A

The nephron of the kidneys

32
Q

What do the kidneys do if blood Ψ is too high?

A
  • The blood reabsorbs less water from the kidneys

- So more is excreted making urine dilute

33
Q

What do the kidneys do if blood Ψ is too low?

A
  • The blood reabsorbs more water from the kidneys

- So less water is excreted and urine is more concentrated

34
Q

What happens during filtration in the kidneys?

A
  • Blood flows through the afferent arteriole at high hydrostatic Pa into the glomerulus
  • As the afferent arteriole has a larger diameter than the efferent arteriole
  • Small molecules forced out of the blood to the bowman’s capsule creating glomerular filtrate
  • The efferent arteriole takes filtered blood back to the body
35
Q

What happens during selective reabsorption? {3}

A
  • Sugars such as glucose move back into the blood from the glomerular filtrate via active transport
  • It takes place in the proximal convoluted tube (PCT), distal convoluted tube and loop of Henle
  • Water moves back into the blood via osmosis as the Ψ of the blood is lower than the Ψ of the glomerular filtrate
36
Q

What occurs after selective reabsorption?

A
  • The rest of the filtrate(urine) enters the collecting duct and passes out of the kidneys down the ureters, into the bladder
37
Q

Which limb is permeable to water?

A

Descending limb

38
Q

How are substances selectively reabsorbed by the PCT?

A
  • Na⁺ ions actively transported out of PCT to the blood via the Na-K pump, K⁺ ions are transported into the epithelium
  • The conc in the epithelial cells decrease
  • Na⁺ ions diffuse down the conc gradient to epithelial cells via co-transporter proteins
  • AA + glucose are also co-transported in, increasing their conc
  • Glucose + AA diffuse down conc gradient into the blood, maintaining a steep conc gradient
  • Ψ of the blood decreases, in PCT increase, so water diffuses via osmosis into the blood
39
Q

How is water reabsorbed in the collecting duct?

A
  • Na⁺ ions are actively transported out of the A limb into medulla
  • This decreases the Ψ in the medulla, A limb is impermeable to water so does not diffuse out
  • D limb is permeable to water so water diffuses out to increase Ψ, + is reabsorbed by the blood
  • Na⁺ ions diffuse out at the bottom of A limb decreasing Ψ in the medulla
  • Collecting duct is permeable to water, so it diffuses out via osmosis + reabsorbed by the blood
40
Q

Why is the ascending limb less permeable to water?

A

Due to its thick walls

41
Q

What monitors blood Ψ?

A

Osmoreceptors in the hypothalamus

42
Q

What does ADH stand for?

A

Anti diuretic hormone

43
Q

What stimulates the release of ADH?

A
  • When Ψ is low, water moves out of osmoreceptors via osmosis
  • Causing the cell to shrink which is detected by the posterior pituitary gland
  • The gland then releases ADH into the blood
44
Q

What is ADH?

A

A hormone that binds to receptors on the cell membrane of the DCT and collecting duct

45
Q

What happens when ADH binds to the receptors on the cell membrane?

A
  • Vesicles containing aquaporins fuse with the cell membrane
  • Aquaporins increase the permeability of the DCT and collecting duct
  • So more water in reabsorbed into the blood
46
Q

What is the special name given to epithelial cells of the Bowman’s capsule?

A

Podocytes

47
Q

What happens if Ψ of the blood is low?

A
  • The change is detected by osmoreceptors in the hypothalamus
  • Stimulating the posterior pituitary gland to release lots of ADH
  • ADH binds to receptors of cells lining DCT + collecting duct
  • Causing more aquaporins to move to cell membrane
  • DCT + collecting duct become more permeable to water
  • So lots of water leaves via osmosis into the medulla
  • So lots of water is reabsorbed by the blood so Ψ increases
48
Q

What happens if Ψ of the blood is high?

A
  • The change is detected by osmoreceptors in the hypothalamus
  • Stimulating the posterior pituitary gland to release less ADH
  • ADH bind to receptors on cells lining DCT + collecting duct
  • So less aquaporins move to cell membrane
  • So DCT + collecting duct are less permeable to water and less leaves via osmosis into the medulla
  • So less water is reabsorbed by the blood so Ψ decreases

Biology Paper 2 (10 decks)

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