Formation of Urine

Question 1

Which is wider, the afferent or the efferent arteriole?

Answer 1

the efferent (ensures blood pressure in glomerulus is high, higher than pressure in Bowman’s capsule)

Question 2

What is ultrafiltration?

Answer 2

filtration at molecular level, in glomerulus: large mols and cells left in blood but smaller mols pass into Bowman’s capsule (pressure difference pushes mols)

Question 3

What are the three layers of the barrier between the blood in the capillary and the lumen of the Bowman’s capsule?

Answer 3

endothelium of capillary, basement membrane and epithelial cells of Bowman’s capsule

Question 4

What are the specialised cells that make up lining of Bowman’s capsule?

Answer 4

epithelial cells: podocytes, many finger-like projections: major/foot processes = ensure gaps between cells,

Question 5

How does the endothelium of the capillary allow mols to pass through?

Answer 5

narrow gaps between cells so blood plasma (and substances dissolved in it) can pass through

Question 6

What is the basement membrane?

Answer 6

fine mesh of collagen fibres and glycoproteins, act as filter for mols with mass larger than 69000, most proteins and all blood cells stay in glomerulus capillaries

Question 7

What does the blood plasma pushed into Bowman’s capsule contain?

Answer 7

water, amino acids, glucose, urea, inorganic ions (sodium, chloride, potassium)

Question 8

What substance has a much lower concentration in glomerular filtrate compared to blood plasma?

Answer 8

proteins

Question 9

What happens to the water potential of the blood left in the capillaries in glomerulus?

Answer 9

blood cells and proteins left so low water potential so retains some fluid (contains water and dissolved substances), helps reabsorb water at later stage

Question 10

What is the total volume of fluid filtered filtered out of the blood by both kidneys per minute? Per day?

Answer 10

125 cm3min-1, 180dm3day-1

Question 11

How are the cells of the proximal convoluted tubules specialised to help reabsorption?

Answer 11

microvilli on surface, co transporter proteins, sodium potassium pumps, many mitochondria

Question 12

What are microvilli?

Answer 12

microscopic folds of the cell surface membrane that increase surface area

Question 13

How do the microvilli on PCT cells help reabsorption?

Answer 13

on cell surface membrane in contact with tubule fluid = more surface area for reabsorption

Question 14

How do co transporter proteins in PCT cells help with reabsorption?

Answer 14

transport glucose or amino acids with sodium ions from tubule into cell - facilitated diffusion

Question 15

Why are the sodium potassium pumps helpful for reabsorption?

Answer 15

opposite membrane of cell (close to tissue fluid and capillaries), also folded for more SA, sodium ions out and potassium ions into cell

Question 16

What does the many mitochondria in the cytoplasm of PCT cells indicate?

Answer 16

active, energy requiring process involved in reabsorption, mitochondria produce ATP

Question 17

What is the first step of reabsorption?

Answer 17

sodium potassium pumps remove sodium ions from cells lining the PCT, reduces their concentration in the cells

Question 18

What happens when there is a low concentration of sodium ions in PCT cells?

Answer 18

sodium ions transported into cells along with glucose or amino acids by facilitated diffusion, glucose and amino concentrations in cells rise

Question 19

What happens when the glucose and amino acid concentrations in the PCT cells rise?

Answer 19

substances able to diffuse out of opposite side of cell into tissue fluid, may be increased by active removal of glucose and amino acids from cells

Question 20

What happens to glucose and amino acids in the tissue fluid?

Answer 20

substances diffuse into blood, carried away

Question 21

What happens to the water potential of PCT cells during reabsorption?

Answer 21

reabsorption of salts, glucose and amino acids reduces water potential of cells, increases in in the tubule fluid so water will enter cells and be reabsorbed into blood by osmosis

Question 22

How are larger mols in the tubule fluid absorbed?

Answer 22

endocytosis (e.g. small proteins)