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Biology: Response > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

What is homeostasis?

A

The maintenance of a stable internal environment.

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2
Q

Why is it important to maintain a stable body temperature?

A
  1. If the temperature is too low the enzyme activity is reduced. This lowers the rate of metabolic reactions.
  2. As the temperature increases the particles have more energy and love faster. This means there are more frequent and successful collisions between the substrates and enzymes. The increased formation of enzyme-substrate complexes increases enzyme activity and the rate of metabolic reactions.
  3. If the temperature gets too high the enzymes will denature meaning they will no longer be able to catalyse metabolic reactions and the rate increases.
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3
Q

Why is it important to maintain stable blood pH levels?

A

If the blood pH levels are too high or too low the ionic bonds that hold the tertiary structure of the enzymes together will break. This means the active site of the enzymes will change shape and it will no longer be able to form an enzyme-substrate complex. This decreases enzyme activity and the rate of metabolic reactions. The highest rate of enzyme activity and metabolic reactions is at optimum pH.

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4
Q

Why is it important to maintain a stable blood glucose concentration?

A
  1. If the blood glucose levels are too high water will diffuse out of cells via osmosis. This causes cells to shrivel up and die.
  2. If the blood glucose levels are too low water will diffuse into cells which will cause them to burst. There also won’t be enough to carry out respiration, which releases energy for metabolic reactions.
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5
Q

What is a negative feedback mechanism?

A

The effectors counteract the change to restore levels to normal.

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6
Q

What is a positive feedback mechanism?

A

The effectors amplify the change to raise the levels away from the normal.

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7
Q

How do blood glucose levels rise?

A

When we eat food that contains carbohydrates.

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8
Q

How do blood glucose levels fall?

A

When the glucose is used for respiration and the release of energy.

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9
Q

What is the role of the beta cells in the islet of Langerhans?

A

They release insulin

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10
Q

What is the role of the alpha cells in the islet of Langerhans?

A

They release glucagon.

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11
Q

Describe what happens when the blood glucose levels are too high.

A
  1. The beta cells in the islet of Langerhans detect the increase in blood glucose levels and release insulin.
  2. The insulin binds to receptors on the cell membrane of the liver cells.
  3. This triggers the release of GLUT-4 from the vesicles in the cells. These then move to the membrane and allow the movement of glucose into the cell via facilitated diffusion.
  4. The insulin activates enzymes that convert glucose into glycogen via glucogenesis.
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12
Q

Describe what happens when the blood glucose levels are too high.

A
  1. The alpha cells in the islet of Langerhans detect the increase in blood glucose levels and release glucagon.
  2. The glucagon binds to receptors on the cell membrane of the liver cells.
  3. It activates enzymes that convert glycogen into glucose via glycogenolysis.
  4. It activates enzymes that make glucose from other biological molecules, like lipids, via gluconeogenesis.
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13
Q

When is adrenaline released?

A

It is secreted from the adrenal glands when the blood glucose levels are low and the body needs to get ready for action.

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14
Q

What is the role of adrenaline?

A

It activates glycogenolysis and inhibits glycogenesis. It activates glucagon secretion and inhibits the secretion of insulin.

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15
Q

What is the second messenger model?

A

It describes how glucagon and adrenaline activate glycogenolysis.

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16
Q

Describe the second messenger model.

A
  1. When glucagon binds to receptors on the cell membrane of liver cells, it activates adenylate cyclase.
  2. The adenylate cyclase converts ATP into cAMP.
  3. The cAMP activates protein kinase A.
  4. The protein kinase A triggers a cascade of reactions that turn glycogen into glucose.
17
Q

What is type 1 diabetes?

A

The immune system attacks the beat cells so they can’t produce enough insulin.

18
Q

How is type 1 diabetes dealt with?

A

Regular insulin injections.

19
Q

What is type 2 diabetes?

A

The liver cells no longer respond to insulin. This could be due to the receptors on the cell membrane being damaged.

20
Q

How is type 2 diabetes dealt with?

A
  1. Regular exercise.
  2. Healthy diet.
21
Q

Draw the structure of a kidney.

A
22
Q

How does the glomerular filtrate form in the nephrons?

A
  1. The efferent arterioles are smaller than the afferent arterioles, which means that the glomerulus is under high pressure.
  2. This pushes water and other small molecules out of the capillary and into the Bowman’s capsule.
  3. The filtrate then passes through the capsule and enters the nephron.
23
Q

Why are proteins and other large molecules not part of the glomerular filtrate?

A
24
Q

What happens in the PCT?

A
  1. Useful solutes like glucose are reabsorbed into the blood via active transport and facilitated diffusion.
  2. Water is reabsorbed via osmosis into the blood.
25
Q

What is the control of the blood water potential called?

A

osmoregulation

26
Q

How do mammals lose water?

A

They lose it in urine and sweat.

27
Q

Where is water reabsorbed in the nephrons?

A
  1. In the PCT.
  2. In the DCT and collecting duct.
  3. The loop of Henle.
28
Q

Describe how water is reabsorbed in the loop of Henle.

A
  1. The ascending limb is permeable to sodium ions and not water.
  2. Sodium ions are actively pumped out of the ascending limb, which decreases the water potential of the medulla.
  3. The water potential inside the descending limb is higher than the water potential of the medulla, so water moves out of it via osmosis.
  4. Water also moves out of the DCT and collecting duct via osmosis.
  5. The water is reabsorbed into the blood via a capillary network.
29
Q

Describe how water is reabsorbed in the DCT and collecting duct.

A
  1. ADH binds to receptors on the walls of the DCT and collecting duct.
  2. This causes the cells to release aquaporins.
  3. The aquaporins allow water to move from the DCT and collecting duct into the medulla.
  4. The water is reabsorbed into the bloodstream via osmosis.
30
Q

How does the amount of ADH in the blood change when the blood water potential is too high? What effect does this have?

A
  1. The osmoreceptors in the hypothalamus detect an increase in the blood water potential.
  2. They send an impulse along the sensory neuron to the posterior pituitary gland.
  3. The posterior pituitary gland releases less ADH, which makes the walls of the DCT and collecting duct less permeable to water.
  4. Less water is reabsorbed into the blood. The water potential decreases.
31
Q

How does the amount of ADH in the blood change when the blood water potential is too low? What effect does this have?

A
  1. The osmoreceptors in the hypothalamus detect a decrease in the blood water potential.
  2. They send an impulse along the sensory neuron to the posterior pituitary gland.
  3. The posterior pituitary gland releases more ADH, which makes the walls of the DCT and collecting duct more permeable.
  4. More water is reabsorbed into the blood. The water potential increases.

Biology: Response (7 decks)

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