homeostasis and the kidney

Question 1

Explain the function of the loop of henle is osmoregulation (4)

Answer 1

• water leaves the descending limb
• at apex Na+ is very concentrated
• Na+ is pumped out of the ascending limg
• lowering the water potential in the medulla
• ascending limb is impermeable to water
• counter current system = neutral

Question 2

Describe how hormonal control affects the final concenrtration and volume of urine produced when someone is dehydrated (4)

Answer 2

• low water potential of blood detected by osmoreceptors/hypothalmus
• secretion of ADH by posterior pituitary gland
• causes collecting duct to become more pereable to water
• water moves into the medulla vi osmosis
• quickly removed by the vasa reca
• low volumes of concentrated urine produced

Question 3

Explain what is meant by the term homeostasis (2)

Answer 3

• maintenance of an intrnaal environmenrt
• despite internal and external changes

Question 4

Apart from water and glucose name two substances which will be present in the filtrate (1)

Answer 4

• urea
• amino acids
• fatty acids /glycerol
• small proteins
• inorganic ions
• salt

Question 5

Name the process which seperates these molecules from the blood plasma (1)

Answer 5

ultrafiltration

Question 6

The filtration rate is the total volume of filtrate formed per minute. explain the effect of a large loss of blood from the body on the filtration rate (2)

Answer 6

• blood pressure decreases
• less filtrate formed

Question 7

Name the part of the nephron which provies the osmotic gradient for reabsorption (1)

Answer 7

loop of henle

Question 8

Suggest one way in which the loop of henle might be modified in desert animals (1)

Answer 8

increased length/longer

Question 9

What i the main excretorry product for freshwater fish , bird and mammals (3)

Answer 9

• fish - ammonia
• bird - uric acid
• mammal - urea

Question 10

Wich excretory product requires the least volume of water for it’s excretion (1)
explain one further advantage of the excretory product (1)

Answer 10

• uric acid
• little mass for storage in eggs/light for flight

Question 11

Describe the mechanisms that are triggered in the mammalian body when water intake is reduced (6)

Answer 11

• low water levels/ low water potential in blood
• detected by osmoreceptor
• in hypothalmus
• more ADH secreted from posteriori pituitary gland
• travels into blood
• collecting duct/ distal convoluted tubule becomes more permeable/more aquaporins
• water absorbed
• because of low water potential in the medulla

Question 12

Suggest a condition which might stimulate ADH secretion (1)

Answer 12

• blood loss
• vomiting

Question 13

Explain how the nephron and its blood supply is adapted for ultrafiltration (5)

Answer 13

• mention of glomerelus and bowmans capsule
• glomerlus has a high blood pressure
• fferent arterioles is wider than efferent
• glomerelus capillaries have manhy fenstrations
• basement membrane allows filtrate throguh
• allowings small molecules -large proteins throguh
• coorect function of podocytes and filtration slits

Question 14

Use you knowledge of the role of the kidney suggest why a protein controlled diet and low sodium chloride intake is recommended (3)

Answer 14

• protein controlled diet - high protein more urea cannot be removed
• low sodium chloride - excess salt does not need to be removed
• high salt cuases high blood pressure

Question 15

Give two eamples of what might cuse a rie in blood solute concentration (1)

Answer 15

• high solute intake
• sweating / low water intake / vomiting / diahrrea

Question 16

What would be the result of high levels of ADH at the collecting duct (1)

Answer 16

• increased peremeability of the collectinf duct to water
• more aquaporines

Question 17

Explain how chlroide ions are selectivley reabsorbed (2)

Answer 17

• facilitated diffusion
• down a concentration gradient

Question 18

Describe how water is selectivley reabsorbed (3)

Answer 18

• osmosis
• high wter potential to low water potential
• patially permebale membrane

Question 19

Describe how sodium ions are selectivley reabsorbed (3)

Answer 19

• facilitted diffusion into cell from glomerular filtrate
• sodium potassium pump
• ATP used

Question 20

Describe how glucose and aino acids are selectivley reabsorbed (3)

Answer 20

• facilitated diffusion
• glucose and amino acids diffuse with sodium ions
• glucose and amino acids diffuse fand glucose activley transported from PCT cell into blood

Question 21

Suggest why the sodium chloride nd glucose improve water reabsorpetion by the kidneys (3)

Answer 21

• more sodium and glucose absorbed from gut into blood
• more glucose and sodium ions in glomerular filtrate
• more sodium ions diffuse into PCT higher gradient
• more glucose co transported
• lower water potential - more water reabsrobed by osmosis
• reference to loop of Henle/collecting ducts

Question 22

State two variable whcih would need to be considered when comparing results form a numbeer of people who have drunk similar volumes of water (2)

Answer 22

• age
• sex
• activity levels
• diey
• previous fluid intakr
• mass
• external temperature
• normal kidney function

Question 23

Explain how high hydrostatic pressure is achieed in the glomerlus (1)

Answer 23

affrent arteriole is wider than effernet arteriole

Question 24

Suggest which type of organic molecule in the blood is responsible for mainintaining the blood osmotic pressure (1)