Kidney + Nephron

Question 1

what is the role of the kidney?

Answer 1

the kidney filters the blood and removes any excess materials and passes them to the bladder to be excreted

Question 2

what are the three main sections of the kidney?

Answer 2

1. around the outside and a lighter colour is the cortex
2. in the middle are the triangular shaped medulla
3. in the centre is the pelvis (the yellowy section)

Question 3

what are the nephrons?

Answer 3

millions of tiny structures that filter the blood

Question 4

what is stage 1 of kidney filtration?

Answer 4

ultrafiltration

Question 5

what is ultrafiltration?

Answer 5

1. the diameter of the efferent arteriole at the exit of the glomerulus is smaller than the diameter of the afferent arteriole at the entrance - this creates a build up of pressure in the capillaries forming the glomerulus
2. this pressure forces small molecules such as urea, glucose, amino acids and salts out of the capillaries of the glomerulus and into the Bowman’s Capsule - this forms the glomerular filtrate
3. larger molecules like proteins or red blood cells are too big to fit across the capillary walls and therefore stay in the blood

Question 6

what does the basement membrane which surrounds the capillaries control?

Answer 6

which molecules can pass into the Bowman’s capsule

Question 7

what is stage 2 of kidney filtration?

Answer 7

selective reabsorption

Question 8

what is the process of selected reabsorption?

Answer 8

1. the filtrate travels to the proximal convoluted tubule (PCT) - however it contains a lot of useful materials such a glucose would be wasted unless they were recovered
2. there are specialised cells within the walls of the PCT which move the useful materials back into the blood stream - initially, molecules will move by diffusion, but some substances are moved against a concentration gradient using ATP (this is called active transport)

Question 9

what materials are reabsorbed into the blood in the PCT?

Answer 9

all of the glucose and amino acids, along with some salts and 80% of the water

Question 10

how are the cells lining the PCT specialised for movement of molecules?

Answer 10

they have a folded membrane to increase surface area, and many mitochondria to provide ATP for active transport

Question 11

what is stage 3 of kidney filtration?

Answer 11

water reabsorption

Question 12

what is the process of water reabsorption?

Answer 12

• the Loop of Henle and collecting duct are both involved in reabsorbing water if needed, and the Loop of Henle concentrates the urine by transporting salt into the blood by active transport - this causes water to diffuse into the blood by osmosis
• if you have lost a lot of water through sweating or perhaps haven’t taken any in your body will try and reabsorb as much water from the filtrate as it can - this makes the urine very concentrated, with a lower volume of water and therefore is a darker browner colour

Question 13

what is osmoregulation?

Answer 13

when the collecting duct responds to a hormone called ADH to vary how much water is reabsorbed