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AQA A Level Biology 2018 > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

What is it?

A

The maintenance of a stable internal environment.

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2
Q

What happens if the temp/pH is too high?

A

Temp too high - enzymes could be denatured so homeostasis can aims to decrease it.

pH - needs to be perfect so enzymes don’t denature so if it’s too high homeostasis can decrease it.

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3
Q

Why do we need to control the conc of glucose in the blood?

A

Because cells need glucose for energy - it also effects the water potential of blood.

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4
Q

What happens if blood glucose conc is too high?

A

The water potential of blood is reduced to a point where water molecules diffuse out of cells into the blood by osmosis - cells shrivel and die.

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5
Q

What happens if blood glucose is too low?

A

Cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide energy.

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6
Q

Homeostatic systems detect…

A

A change and respond via negative feedback. They counteract the change to help keep things around the normal level.

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7
Q

Negative feedback only works with…

A

Certain limits - if the change is too big then the effectors may not be able to counteract it.

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8
Q

What are multiple negative feedback mechanisms?

A

Where more than one mechanism is used for each thing - gives more control.

Also means you can actively increase or decrease something until it turns back to normal.

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9
Q

If you only had one negative feedback mechanism…

A

All you could do would be turn it on and turn it off - would be slower and less control.

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10
Q

Some changes trigger a …

A

Positive feedback mechanism

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11
Q

What does a positive feedback mechanism do?

A

Rapidly activate something e.g. a blood clot after energy.

Platlets becomes activates and release a chemical - triggers more to be activated a this ends with negative feedback

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12
Q

How does Hypothermia involve positive feedback?

A

As body temp falls the brain doesn’t work properly and shivering stops - falls even more.

Positive takes the body temp even further away from normal level and it continues to decrease until action is taken.

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13
Q

Normal conc of glucose in blood:

A

90mg per 100cm3 of blood - monitored by pancreas cells.

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14
Q

When does glucose conc fall and rise?

A

Rises after eating foods containing carbohydrate

Falls after exercise as more glucose is used in respiration to release energy.

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15
Q

Two hormones released by pancreas:

A

Insulin

Glucose

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16
Q

What secrets the insulin and glucagon?

A

Islets of Langerhans - beta cells secrete insulin and alpha cells secrete glucagon into the blood.

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17
Q

How does insulin work?

When blood glucose conc is too high

A
  • binds to specific receptors on membranes of liver and muscle cells
  • increases permeability so cells take more glucose (increases number of channels)
  • also activates enzymes in liver and muscle cells that concert glucose to glycogen - glycogenesis
  • also increases rate of respiration.
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18
Q

How does glucagon work?

When blood glucose conc is too low

A
  • glucagon binds to specific receptors on cell membranes of liver cells
  • glucagon activates enzymes in liver cells that break down glycogen - glycogenolysis.
  • also activates enzymes in the formation of glucose from glycerol and amino acid - gluconeogenesis.
  • decreases rate of respiration.
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19
Q

Skeletal and cardiac muscle cells contain..

A

A channel protein called GLUT4 - this is a glucose transporter.

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20
Q

What happens to GLUT4 when insulin levels are low?

A

it’s stored in vesicles in the cytoplasm of cells and when insulin binds to receptors it triggers the movement of it to the membrane - glucose is then transported through it.

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21
Q

What is adrenaline?

A

A hormone that’s secretes from your adrenal grands when there’s a low conc of glucose in your blood.

22
Q

What does adrenaline do?

A

When it binds to receptors in the cell membrane of liver cells it:

Activated glycogenolysis (breakdown of glycogen to glucose)

Inhibits glycogenesis (synthesis of glycogen from glucose)

Activated glucagon secreteion and inhibits insulin secretion

23
Q

How can Adrenalin and glucagon activate glycogenolysis inside a cell? (3)

A
  • they bind to their receptors and activate an enzyme called adenylate cyclase.
  • this converts ATP into a chemical signal called second messenger - cyclic AMP.
  • this activates an enzyme called protein kinesis A - activates lots of reactions which break down glycogen into glucose.
24
Q

How can type 2 diabetes be prevented? (3)

A
  • regular exercise
  • eat a diet that’s low in fat sugar and salt
  • lose weight
25
Q

How have food companies responses to make their products more healthy: (2)

A
  • using sugar alternatives

- reducing the sugar fat and salt in their food

26
Q

When does type 2 diabetes occur?

A

When the B cells don’t produce enough insulin or when the body’s cells don’t respond properly to insulin - means the glucose conc is higher than normal.

27
Q

What happens in Type 1 diabetes?

A

The immune system attacks the B cells so they can’t produce any insulin - this means after eating blood glucose levels remain and stay high (hyperglycaemia)

28
Q

How is type 1 diabetes treated?

A

Insulin therapy - using an insulin pump and injections.

29
Q

One of the main functions of the kidneys:

A

To excrete waste products e.g. urea.

As blood is passed through capillaries, substances are filtered out of the blood into long tubules - ultrafiltration.

Useful ones are reabsorbed and unwanted are urine.

30
Q

What are nephrons?

A

The long tubules with the bundle of capillaries where the blood is filtered.

31
Q

How does ultrafiltration start?

A

When blood from the renal artery enters the smaller arterioles in the vortex of the kidney

Each arteriolar splits into a structure called glomerulus.

32
Q

Ultrafiltration:

A
  • high pressure forces liquid and small molecules in the blood out of the capillary and into the bowman’s capsule
  • these pass through 3 layers before they get to it and enter the nephron tubules (capilarrybwall, membrane and epithelium)
  • large molecules can’t pass so they stay in the blood.
33
Q

Substances that enter the bowman’s capsule are known as:

A

Glomerular filtrate.

34
Q

What is the arteriole takes blood into each glomerulus is called…

A

The afferent arteriole.

35
Q

The arteriole that takes the filtered blood away from the glomerulus is called..

A

The efferent arteriole

36
Q

What forces the liquid and small molecules out of capillary?

A

The high pressure

37
Q

The end of ultrafiltration:

A
  • the glomerular filtrate passed along the rest of the nephron and useful substances are reabsorbed.
  • finally the filtrate flows through the collecting duct and passed out of the kidney along the ureter.
38
Q

Urine is usually made of: (3)

A

Urea

Water

Hormones and excess vitamins

39
Q

Where does selective reabsorbtion happen?

A

Along the proximal convoluted tubule through loop of henle and along the distal convoluted tubule.

40
Q

How is the epithelium of the wall of the PCT adapted?

A

Microvilli provide a large surface area for the reabsorption of useful materials from the glomerular filtrate into the blood.

41
Q

What is osmoregulation?

A

It’s the way in which kidneys regulate the water potential of the blood and urine so the body has just the right amount of water.

42
Q

What happens if the blood water potential is too low?

A

More water is reabsorbed by osmosis into the blood from the tubules of the nephrons - means urine is more concentrated so less water lost.

43
Q

What happens if water potential of the blood is too high?

A

Less water is reabsorbed by osmosis into the blood from the tubules of the nephrons - means the urine is more dilute so more water is lost during excretion.

44
Q

Where is the loop of Henle and what is it?

A

It’s made up of two lines which control the movement of sodium ions so that water can be reabsorbed by the blood - locates in the medulla of kidneys.

45
Q

Loop of henle made of…

A

Ascending limb

Descending limb

46
Q

Step 1

A
  • at ascending limb, Na+ ions pumped out into the medulla - this is impermeable to water so water stays inside tubules so there’s a lower water potential in medulla - higher conc of ions.
47
Q

Step 2

A
  • lower potential in medulla than descending means water moves out into medulla - filtrate is more concentrated, water in the medulla reabsorbed into the blood.
48
Q

Step 3

A

Near the bottom of ascending limb na* diffuse out into the medulla further lowering the water potential - this is impermeable to water so it stays in tubule

Water moves out of distal convoluted tubule and reabsorbed into blood

49
Q

How is the water potential of blood monitored?

A

By cells called osmoreceptrs in a part of a brain called the hypothalamus.

50
Q

What happens when you’re dehydrated? (5)

A
  • water content of blood drops
  • detected by osmoreceptors in hypothalamus
  • posterior pituitary gland is stimulated to release more ADHD in blood
  • more ADHD means the DCT and collecting duct are more permeable so more water is reabsorbed into blood
  • small amount of highly concentrated urine is produced and less water is lost.
51
Q

What happens when you’re hydrated?

A
  • water content rises
  • detected by osmoreceptors
  • PPG releases less ADHD in blood
  • less ADH means that the DCT and collecting dust becomes less permeable so less water is reabsorbed into blood by osmosis
  • large amount of dilute urine is produced and more water is lost.

AQA A Level Biology 2018 (17 decks)

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