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AQA A-Level Biology > Y2: Homeostasis > Flashcards

Y2: Homeostasis Flashcards

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1
Q

Define homeostasis?

long 4

A
  • The maintenance of a stable internal environment
  • it is controlled by nervous and hormonal system
  • keep conditions within a certain range (optimum)
  • keep the organism in a state of balanced equilibrium
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2
Q

Define homeostasis?

short, 1

A

Maintenance of the internal body conditions/environment

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3
Q

What is the hormonal system?

A

Input–>change detected–>info integrated–>brings about change–>return system to optimum

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4
Q

What are the two types of hormonal feedback systems?

A
  • Positive

- Negative

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5
Q

Define negative feedback

A

Response results in inhibition of corrective measures

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6
Q

Define positive feedback

A

Response stimulates corrective measures to remain on

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7
Q

What is end-point inhibition?

A

The product in a series of enzyme controlled reactions inhibits the first enzyme

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8
Q

What happens if the blood glucose levels get too high?

5

A
  • Beta-cells in the islets of langerhans detect increase in blood glucose levels
  • Release insulin into the blood
  • Insulin binds to glycoproteins in the phospholipid bilayer membranes
  • Results in measures to remove glucose from the blood and into cells
  • Decreases the concentration of glucose in the blood
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9
Q

What measures remove glucose from the blood into the cells?

4

A
  • More glycogenesis
  • Increased no. of glucose transporters (previously in vesicles that fuse w/ membrane)
  • Glucose transporters are activated (change in tertiary structure)
  • Activation of enzyme that converts glucose into fat
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10
Q

What happens if the blood glucose levels get too low?

4

A
  • Alpha-cells in the islets of langerhans detect decrease in blood glucose levels
  • Release glucagon into the blood
  • Binds to receptors on liver cells
  • Results in measures to increase the concentration of blood glucose
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11
Q

What measures increase the concentration of glucose in the blood?
2
where does it take place?
1

A
  • Activates enzymes that cause glycogenolysis
  • Activates enzymes that cause gluconeogenesis

-The liver

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12
Q

What is the second messenger model

4

A
  • Adrenaline binds to the adrenergic receptor in the phospholipid bilayer membrane
  • This activates adrenylate cyclase which catalyses the production of cAMP from ATP
  • cAMP is converted into pyruvate kinase
  • pyruvate kinase catalyses glycogenolysis
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13
Q

What is the difference between type 1 and type 2 diabetes?

Treatment

A
  • Type 1 requires injections of insulin

- Type 2 can be reversed sometimes by a low carb diet

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14
Q

What is the difference between type 1 and type 2 diabetes?

Science?

A

In type 1 the immune system attacks beta cells in the islets of langerhans so they no longer produce insulin

whereas in type 2 the cells no longer respond to insulin as the receptors are desensitised

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15
Q

What is the difference between type 1 and type 2 diabetes?

Cause?

A
  • Type 1: random

- Type 2: diet and genetic components

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16
Q

Why is gluconeogenesis needed?

A

The brain can only use glucose for respiration so cant use pyruvate made form amino acids or lipids

17
Q

Why are kidneys vunerable?

A

Because all the blood in the body goes through it

18
Q

What are the two ways to change the water potential of the blood?

A

Change solute

Change water

19
Q

Kidney: What is the pathway of the nephron?

A
  1. bowmans capsule
  2. proximal convoluted tubule
  3. loop of henle
  4. distal convoluted tubule
  5. collecting duct
20
Q

Kidney: Proximal convoluted tubule?

4

A
  1. the Na+-K+ pump actively transports Na+ out of the epithelial cell into the lumen of the capillary, generating and maintaining a conc gradient of Na+ from the lumen of the PCT to the ep cell
  2. Na+ binds to co-transporter and is transported down conc gradient taking one molecule of glucose or AA with it into ep cell
  3. glucose or AA going against its conc gradient
  4. glucose in ep cell travels down its gonc gradient to lumen of capillary via fac diffusion
21
Q

Kidney: loop of henle?

6

A
  1. Na+ is actively transported out of the ascending loop of henle into the interstitial space
  2. Cl- ions follow down electrical gradient via fac diff
  3. this lowers the water potential of the interstitial space
  4. t4 water moves out of descending loop of henle down water potential gradient via osmosis as ascending loop is impermeable to water
  5. makes the liquid at the bottom of the loop more conc , becoming more dilute w/ loss of ions going up ascending loop
  6. overall volume decreases
22
Q

Kidney: bowmans capsule, glomerular filtration?

4

A
  1. Blood into the glomerulus from wide afferent renal artery, and leaves through a narrower efferent renal artery. So blood is under high pressure
  2. causes the contents of the blood to be forced through the capillary wall, like a sieve, then through the basement membrane (a second ‘sieve’ made of collagen fibres and protein) into the nephron.
  3. The cells in the wall of the bowman’s capsule contain podocytes, with extensions called pedicels wrapped around the capillaries meaning any cells, large proteins or platelets which leave the capillary walls don’t enter the tubule.
  4. Filtrates include water, amino acids, glucose, ions and importantly: urea and other nitrogenous waste products.
23
Q

Kidney: collecting duct?

4

A
  1. The urine enters the collecting duct which transports it down through the medulla to the pelvis.
  2. The urine becomes more concentrated as it passes through the medulla, as the salty conditions created by the loop of henle mean water osmoses out down a potential gradient.
  3. ADH also controls the permeability of the collecting duct,
  4. more adh = more aquaporins in the membrane (from vesicles) which allow additional water to escape through.
24
Q

What are nephrons?

A

Millions of little filtering units that make up the kidneys

25
Q

What is the cortex?

A

The dark outer layer of the kidney, high density of capillaries as it is the site of blood filtration

26
Q

What is the medulla?

A

The lighter area of the kidney inside the cortex, contains nephron tubules that make the kidney pyramids and collecting ducts

27
Q

What is the pelvis?

A

The innermost part of the kidney, collects urine as it passes down to the bladder

28
Q

What is the uterer?

A

A tube that connects the kidney to the bladder

29
Q

What is the bladder?

A

Muscular sac for holding urine

30
Q

What is the urethra?

A

Tube that allows for urine in the bladder to be excreted from the body

31
Q

What do nephrons do?

A

remove nitrogenous waste, and balances mineral ions and water levels in the blood.

32
Q

Kidney; distal convoluted tubule: what happens if there is an increased water potential of the blood?

eg: low solute conc

5

A
  1. increased water potential detected by osmoreceptors in hypothalamus
  2. pituitary gland releases less ADH
  3. walls of distal convoluted tubule and collecting duct become less permeable to water
  4. more water leaves the body and urine is therefore more dilute
  5. therefore removal of water
33
Q

Kidney; distal convoluted tubule: what happens if there is an decreased water potential of the blood?

eg: high solute conc

ADH version

5

A
  1. decreased water potential detected by osmoreceptors in hypothalamus
  2. pituitary glands releases more ADH
  3. walls of distal convoluted tubule and collecting duct become more permeable to water
  4. less water leaves the body and urine is therefore more concentrated
  5. therefore conservation of water
34
Q

Kidney; distal convoluted tubule: what happens if there is an decreased water potential of the blood?

non-ADH version

4

A
  1. decreased water potential detected by osmoreceptors in hypothalamus
  2. stimulation of thirst centre in brain
  3. more water consumed
  4. therefore conservation of water

AQA A-Level Biology (11 decks)

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