homeostasis

Question 1

Humans can produce urine which is more concentrated than their blood plasma.

Explain the role of the loop of Henle in the absorption of water from the filtrate (6)

Answer 1

1. In the ascending limb sodium(ions) actively removed;
2. Ascending limb impermeable to water;
3. In descending limb sodium(ions) diffuse in;
4. Descending limb water moves out
5. Low water potential in the medulla / tissue fluid;
6. The longer the loop the lower the water potential in medulla / tissue fluid;
7. Water leaves collecting duct
8. By osmosis

Question 2

Explain the role of ADH in the production of concentrated urine (4)

Answer 2

1. When water potential of the blood too low;
2. Detected by receptors in the hypothalamus;
3. Pituitary secretes / releases (more) ADH;
4. ADH increases the permeability / recruitment of aquaporins / opens channels for water in the DCT / collecting duct;
5. More water is reabsorbed / leaves the nephron moves into the blood;
6. By osmosis down the water potential gradient;

Question 3

The kidney plays an important part in the regulation of blood water potential. This involves control of the amount of water reabsorbed from the filtrate produced in the kidney tubules. The amount of water reabsorbed affects the volume of urine produced, the rate at which the bladder fills and how often it has to be emptied.

Explain how the loop of Henle maintains the gradient of ions which allows water to be reabsorbed from filtrate in the collecting duct (5)

Answer 3

1. (epithelial cell) of tubule cells carry out active transport;
2. transport chloride / sodium ions out (of filtrate);
3. against concentration gradient;
4. into surrounding tissue / tissue fluid;
5. creates / maintains water potential gradient for water reabsorption;
6. countercurrent multiplier;

Question 4

Explain how ADH is involved in the control of the volume of urine produced (4)

Answer 4

1. if water potential of blood falls, detected by receptors in hypothalamus;
2. leads to ADH released from pituitary gland;
3. ADH makes cells of collecting duct permeable to water;
4. water leaves filtrate by osmosis;
5. smaller volume of urine produced;

Question 5

Describe how ultrafiltration produces glomerular filtrate (5)

Answer 5

1. hydrostatic pressure;
2. Small molecules / named example;
3. Pass through basement membrane /
4. Protein too large to go through / large so stays behind;
5. Presence of pores in capillaries

Question 6

Some people who have diabetes do not secrete insulin. Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin (4)

Answer 6

1. High concentration of glucose in blood;
2. High concentration in filtrate;
3. Reabsorbed by facilitated diffusion / active transport;
4. Requires proteins / carriers;
5. These are working at maximum rate / are saturated;
6. Not all glucose is reabsorbed from PCT

Question 7

Some desert mammals have long loops of Henle and secrete large amounts of antidiuretic hormone (ADH).

Explain how these two features are adaptations to living in desert conditions (6)

Answer 7

1. More water (from filtrate) reabsorbed
2. By osmosis;
3. From collecting duct
4. Due to longer loop of Henle;

For loop of Henle, maximum 2 marks:
5. Sodium ions absorbed from filtrate in ascending limb;

6. Gradient established in medulla

For ADH, maximum 2 marks:
7. Acts on collecting duct

8. Makes cells more permeable

Question 8

describe the second messenger model using adrenaline and glycogen

Answer 8

1. adrenaline binds to receptor proteins on CSM of liver cells
2. binding changes shape of protein receptors and activates adenyl cyclase
3. adenyl cyclase converts ATP into cyclic AMP
4. cyclic AMP acts as 2nd messenger and binds to kinase enzyme changing its shape and activating it
5. kinase converts glycogen into glucose
6. glucose leaves liver cell and enters blood by facilitated diffusion via protein channels

Question 9

what are the hormone producing cells of the pancreas called and what do they include

Answer 9

islets of langerhans

include:
- a cells
- B cells

Question 10

what hormone do a cells make

Answer 10

glucagon

Question 11

what hormone do B cells make

Answer 11

insulin

Question 12

what is glycogenesis

Answer 12

making glycogen from glucose

when blood glucose is too high

Question 13

glycogenolysis

Answer 13

converting glycogen into glucose

when blood glucose is too low

Question 14

gluconeogenesis

Answer 14

when glycogen too low we can make glucose from other non carb sources- glycerol and amino acids

when blood glucose too low

glycerol and amino acids converted to glucose

Question 15

explain the roles of insulin from B cells when glucose concentration is too high

Answer 15

B cells have receptors- detect rise in blood glucose and secrete insulin

1. insulin binds to glucose transporter carrier proteins- changes their tertiary structure, become more open so more glucose into cells by FD
2. increases number of glucose transporter proteins in membrane- more transport channels for glucose to enter cells
3. activates enzymes that convert glucose into glycogen and fats to be stored in liver and muscle cells

Question 16

which hormone is secreted when blood glucose is too high

Answer 16

insulin

from b cells of islets of langerhans from pancreas

Question 17

which hormones is secreted when blood glucose is too low

Answer 17

glucagon

from a cells of islets of langerhans from pancreas

Question 18

explain the steps of lowering blood glucose concentration using glucagon secreted from a cells

Answer 18

1. a cells have receptors and detect fall in blood glucose so secrete glucagon into blood plasma
2. glucagon binds to specific receptors on CSM of liver cells
3. activates enzymes that convert glycogen into glucose
   (glycogenolysis)
4. activates enzymes that convert glycerol and amino acids into glucose (gluconeogenesis)

Question 19

why do people with type 1 diabetes have glucose in urine

Answer 19

type 1 diabetes can’t make insulin so glucose remains in blood- high glucose concentration

glucose is reabsorbed in nephron but not all can be reabsorbed- too high concentration so glucose remains and passes out as urine

Question 20

what causes type 1 diabetes

Answer 20

autoimmune response- destroys B cells of islets of langerhans so can’t make insulin

Question 21

what is type 1 diabetes

Answer 21

can’t make insulin

Question 22

what is type 2 diabetes

Answer 22

receptors on body cells lose responsiveness to insulin

Question 23

explain how to treat type 1 diabetes

Answer 23

insulin injections

dose must match exactly the glucose intake- if too much insulin given then blood glucose falls too low and causes unconsciousness

Question 24

explain how to treat type 2 diabetes

Answer 24

control diet- control carbohydrate and sugar intake, less glucose intake= lower blood glucose

increase exercise- increasing the rate at which glucose is removed from body and metabolised

Question 25

factors affecting type 2 diabetes

Answer 25

diet exercise

Question 26

Using your knowledge of the kidney, explain why glucose is found in the urine of a person with untreated diabetes (3)

Answer 26

1. High concentration of glucose in blood/filtrate; 2. Not all the glucose is (re)absorbed at the proximal convoluted tubule; 3. Carrier proteins are working at maximum rate/ saturated

Question 27

Describe the role of glucagon in gluconeogenesis (2)

Answer 27

1. (Attaches to receptors on target cells) Activates enzymes; 2. Glycerol/amino acids into glucose;

Question 28

Metformin is a drug used to treat type II diabetes. it lowers blood glucose by: * increasing a cell’s sensitivity to insulin * inhibiting adenylate cyclase. Explain how increasing a cell’s sensitivity to insulin will lower blood glucose concentration. Explain how inhibiting adenylate cyclase may help to lower blood glucose concentration. (4)

Answer 28

1. (More) insulin binds to receptors; 2. (Stimulates) uptake of glucose by transport proteins OR Activates enzymes which convert glucose to glycogen; 3. Less/no ATP is converted to cyclic AMP/cAMP; 4. Less/no kinase is activated; 5. Less/no glycogen is converted to glucose

Question 29

Each year, people with type I diabetes are given a pancreas transplant. Pancreas transplants are not used to treat people with type II diabetes. Give two reasons why pancreas transplants are not used for the treatment of type II diabetes. (2)

Answer 29

1. Type II produce insulin; 2. Cells less responsive to insulin 3. (Treated / controlled by) diet / exercise;

Question 30

Give two ways in which people with type 1 diabetes control their blood glucose concentration (2)

Answer 30

1. treat with insulin injections 2. control sugar intake