Kidneys and Homeostasis

Question 1

What are the main functions of the kidneys?

Answer 1

Control water content of the blood
Removal of urea from the blood
Removal of excess mineral salts from the blood

Question 2

Why do we produce urine?

Answer 2

It is a mixture of urea (made by the liver from proteins not needed in the body) and water, excreted because urea is poisonous and cannot be allowed to build up in the blood

Question 3

What do kidneys control?

Answer 3

Water levels

Ion levels

Question 4

What is urine concentration affected by?

Answer 4

Amount drunk

Temperature (if we sweat or not)

Question 5

Describe the structure of the excretory system

Answer 5

Blood enters kidney through RENAL ARTERY
Blood leaves kidney through RENAL VEIN
URETER carries urine from kidney to bladder
BLADDER stores urine
URETHRA carries urine out of the body

Question 6

What are the 3 main areas of the kidney?

Answer 6

Outer cortex (outer layer)
Inner medulla (inner layer)
Pelvis (where urine drains)

Question 7

What is the role of nephrons?

Answer 7

To remove urea, excess mineral salts and excess water from the blood to make urine

Question 8

What is the first stage of urine production in a nephron?

Answer 8

Ultrafiltration:
The blood capillaries form a tightly knotted cluster, squeezing out small particles from the blood and into the Bowman’s capsule
The blood is filtered and all water, urea and salts are removed from the blood.
Blood cells and proteins remain in the blood as they are too big to move across the capillary walls.

Question 9

What is the second stage of urine production in a nephron?

Answer 9

Selective reabsorption:
Useful molecules (e.g. glucose, salts and most water) are reabsorbed in the bloodstream. 
The remaining mixture forms urine which passes into the collecting ducts

Question 10

How many nephrons are in each kidney?

Answer 10

Around 1,000,000

Question 11

How does the capillary knot inside a nephron work?

Answer 11

Arterioles from the renal artery become very narrow and form a tight knot of capillaries. The arteriole leading into the knot is wider than the arteriole leading out the knot which increases blood pressure. Under this pressure, small molecules are filtered into the Bowman’s capsule.

Question 12

Describe the journey of molecules through a nephron

Answer 12

Capillary knot -> Bowman’s capsule -> Tubule -> Collecting ducts (urine) OR Capillary network (useful substances)

Question 13

What does presence of blood or cells in urine indicate?

Answer 13

Kidney disease

Question 14

How do useful substances get back into the bloodstream from the tubule during reabsorption?

Answer 14

Through the walls of the tubule and into the capillary network than travels alongside it

Question 15

What is another name for the capillary knot?

Answer 15

Glomerulus

Question 16

What osmoregulation and what is it controlled by?

Answer 16

Concentration of water in the blood - controlled by anti diuretic hormone (ADH)

Question 17

What path does ADH take?

Answer 17

Released by the pituitary gland in the brain, carried in the blood to the kidneys

Question 18

What happens when too little water is detected? (Concentrated blood)

Answer 18

Brain triggers release of ADH which increases permeability of nephron tubules, meaning more water is reabsorbed into the bloodstream.
Result is small volume of concentrated urine

Question 19

What happens when too much water is detected? (Dilute blood)

Answer 19

Brain signals to stop release of ADH which decreases permeability of nephron tubules, meaning less water is reabsorbed into the bloodstream.
Result is large volume of dilute urine

Question 20

Why is blood in urine a sign of kidney disease?

Answer 20

Blood cells and proteins are normally too large to pass through the capillary walls when the blood is filtered in the Bowman’s capsule. This means the nephron is damaged.

Question 21

What is glucose in urine a sign of?

Answer 21

Diabetes.
Blood glucose levels are so high that all of the glucose in the filtrate can’t be reabsorbed from the nephron tubules, so some glucose ends up in the urine.

Question 22

What are the two treatments available for kidney disease?

Answer 22

Kidney dialysis

Kidney transplant

Question 23

What is kidney dialysis?

Answer 23

Where a patient is attached to an artificial kidney machine which removes wastes and restores the balance of salts and water in their blood

Question 24

How does dialysis work?

Answer 24

1. Blood from patient taken from blood vessel in arm and pumped into machine.
2. Dialysate also put through machine, a fluid which contains the same concentration of glucose and salts as blood plasma.
3. Blood passes over a partially permeable membrane designed to replicate kidney tubules, with dialysis fluid on the other side.
4. A concentration gradient is established, allowing excess ions and urea to diffuse from an area of high concentration in the patient’s blood to an area of low concentration in the dialysis fluid.
5. Blood returned to body

Question 25

What are the advantages of dialysis?

Answer 25

Greatly reduced levels of urea – it is ‘cleaned blood’
No overall change in blood glucose levels
The correct water and ion balance maintained or restored (with only excess ions removed)
Gives a patient time to find a donor kidney

Question 26

What are the disadvantages of dialysis?

Answer 26

Requires expensive specialised machinery
Time consuming and restrictive - patient has to return 2-3 times a week for 3-4 hours at a time
Patients must monitor their diet carefully to ensure they don’t consume too much salt or protein
Increases risk of blood clots & infections
Dialysis only works for a certain amount of time before a transplant is needed - many die before a suitable donor is found

Question 27

Describe the concentration gradient in dialysis

Answer 27

Excess ions and urea diffuse from an area of high concentration (blood) to an area of low concentration (dialysate) across a semi-permeable membrane

Question 28

Why are kidney transplants possible?

Answer 28

We can survive with only one kidney, so can donate one of ours to someone with kidney failure (although donors put themselves at risk of complications)

Question 29

Where is a donor kidney implanted?

Answer 29

At the bottom of the abdomen close to the thigh, connected to the blood supply. The failed kidney is not usually removed

Question 30

How is risk of rejection reduced?

Answer 30

Before transplant: Doctors ensure tissue type of donor and recipient are similar (family members are more likely to have similar tissue)
After transplant: Patient has to take immunosuppressants for the rest of their life to suppress the immune system, preventing it from attempting to destroy the foreign cells

Question 31

What are the ethical issues involved with transplants?

Answer 31

Kidney donor schemes (e.g. presumed consent)
Living donors
Buying and selling of organs
Availability of dialysis machines

Question 32

What are the disadvantages of kidney transplants?

Answer 32

Kidney may be rejected by the body
Long waiting lists
Immunosuppressants make patient more prone to other infections

Question 33

What are the advantages of kidney transplants?

Answer 33

The patient does not need to have dialysis treatment, which is time-consuming
Transplants are cheaper than dialysis in the long run.

Question 34

Are kidney transplants a permanent solution to kidney failure?

Answer 34

No - transplanted kidneys usually have a lifespan of 40-50 years, so young patients may need to have multiple transplants in their lifetime

Question 35

How does blood enter the kidney?

Answer 35

Through the aorta and then renal artery

Question 36

How does filtered blood leave the kidney?

Answer 36

Through the renal veins and into the vena cava

Question 37

What happens in the renal cortex?

Answer 37

Blood is filtered

Question 38

What happens in the medulla?

Answer 38

Useful substances are reabsorbed into the bloodstream and urine is produced