Kidney-Ultra-filtration and Selective Re-absorption

Question 1

Where does ultra-filtration happen?

Answer 1

Between glomerular capillaries and tubule of Bowmans Capsule

Question 2

What is filtered out of blood?

Answer 2

Anything which is small enough to leave the glomerular capillaries

Question 3

What can get out of the glomerular capillaries?

Answer 3

-Water
-H2O
-Ions/Electrolytes (NA+, Cl-, K+)
-O2/CO2
-Glucose
-Amino Acids
-Urea
-Vitamins
-Hormones e.g hCG
-Some drugs e.g. steroids

Question 4

What can’t get out of the glomerular capillaries?

Answer 4

-Plasma proteins e.g albumin
-RBC’s
-WBC’s
-Platelets

Question 5

What is the first way ultra-filtration happens?

Answer 5

Filtration Pressure

Question 6

Explain Filtration Pressure.

Answer 6

Solutes are forced out of glomerular capillaries due to high hydrostatic pressure

Question 7

How is this hydrostatic pressure achieved?

Answer 7

Because the diameter of the afferent arteriole is wider than efferent creating a bottle-neck effect

Question 8

What is the second way ultra-filtration happens?

Answer 8

Three layered Filtration System

Question 9

What are the three layers in the Three layered Filtration System?

Answer 9

1-Endothelium of glomerular capillaries
2-Basement membranes
3-Epithelium of Bowmans Capsule (made of podocytes)

Question 10

What features does the glomerulaar capillary have?

Answer 10

-Pores; 10nm
-Fenestrations/Slits; 50 to 100nm

Question 11

What can and can’t get in and out of the glomerular capillary?

Answer 11

RBC’s, WBC’s and Platelets =CAN’T
Plasma Proteins=CAN

Question 12

What is the basement membrane made out of?

Answer 12

Fibres, Collagen and Glycoproteins

Question 13

What do the fibres, collagen and glycoproteins in the basement membrane form?

Answer 13

Molecular Mesh

Question 14

What size substances can get through the basement membrane?

Answer 14

if <69,000 RMM

Question 15

What happens to the plasma proteins that get through the glomerular capillary and into the basement membrane?

Answer 15

Come out and go straight back to the glomerular capillary

Question 16

Why cant the plasma proteins get through the basement membrane?

Answer 16

are >69,000 RMM so can’t get through unless basement membrane is damaged

Question 17

How can the basement membrane be damaged?

Answer 17

By high blood pressure

Question 18

What is another reason why plasma proteins are sent back to the glomerular capillary?

Answer 18

They are ‘repelled’ back into blood by negative charge of basement membrane

Question 19

What do podocytes have on them?

Answer 19

Prejections called pedocils

Question 20

What is the function of the pedocils?

Answer 20

Hold podocytes away from capillaries so space for fluid/solutes to get through and they hold adjacent podocytes together so no gap between each podocyte

Question 21

What do the fenestration’s at bottom of basement membrane/top of podocyte do?

Answer 21

Back up in case capillary endothelium/basement membrane is broken

Question 22

Where does selective re-absorption happen?

Answer 22

In PCT

Question 23

What are the 4 adaptations of the PCT to increase the rate of re-absorption?

Answer 23

-Tubule is convoluted to increase time
-Microvili to increase SA
-Flattened cells to decrease distance
-Lots of mitochondria in cells lining PCT

Question 24

Approximately how much of filtrate is re-absorbed into blood?

Answer 24

85%

Question 25

What does this 85% of filtrate include?

Answer 25

-60% of H20
-All glucose (unless diabetic)
-Some electrolytes/ions
-Most amino acids
-Most vitamins
-Most hormones (e.g. not all hCG=pregnancy test)
-50% or urea

Question 26

Why is not all glucose re-absorbed into blood if diabetic?

Answer 26

Protein carriers become saturated so not all glucose can be reabsorbed

Question 27

What is the first step in how selective re-absorption happens?

Answer 27

Sodium-potassium pumps, pump NA+ and K+ into cell by using ATP which causes the sodium concentration in cell to decrease

Question 28

What is the second step in how selective re-absorption happens?

Answer 28

NA+ moves into cell via co-transport protein which brings either glucose or amino acid with it
-NA+ moves down conc grad and gluc/a-acids move against concentration gradient

Question 29

What is the third step in how selective re-absorption happens?

Answer 29

Glucose/amino acids move into blood via facilitated diffusion

Question 30

What is the fourth step in how selective re-absorption happens?

Answer 30

As solutes (NA+/g/aa) leave the filtrate, the water potential of filtrate increases so H2O moves into cell then blood via osmosis
-Either directly through permeable membrane or via aquaporins

Question 31

What is the fifth step in how selective re-absorption happens?

Answer 31

As H20 moves out of filtrate the concentration of urea and Cl- increase so they diffuse into blood

Question 32

How does urea and Cl- diffuse into blood?

Answer 32

U;with or without protein carrier
Cl-; needs protein channel as polar