Kidney function 1 - excretion

Question 1

what are the two main processes in the Glomerlus/ PCT?

Answer 1

-ultrafiltration
-reabsorption

Question 2

what does ultrafiltration mean?

Answer 2

-the filtration of plasma and substances below a certain size into the Bowmans capsule

Question 3

where does ultrafiltration occur?

Answer 3

-the glomerulus

Question 4

does ultrafiltration recognize useful products?

Answer 4

-it doesn’t recognize useful products

Question 5

why is reabsorption necessary?

Answer 5

-as ultrafiltration is based purely on molecular size and not on whether or not the products are useful, it’s essential that filtered useful products are selectively reabsorbed back into the bloodstream in the nephron

Question 6

what kind of pressure does blood have when entering the glomerulus?

Answer 6

-a high hydrostatic pressure

Question 7

why does blood entering the glomerulus have a high hydrostatic pressure? (3 reasons)

Answer 7

-the short distance blood has to travel to get to the kidneys through the renal artery
-the fact that the afferent arteriole is wider than the efferent arteriole
-coiling of capillaries in glomerulus restricts blood flow and increases pressure

Question 8

what are the 5 small components in the blood that are forced out due to the high hydrostatic pressure?

Answer 8

-glucose
-amino acids
-salts
-water
-urea

Question 9

where are the 5 small blood components forced out to due to the high hydrostatic pressure?

Answer 9

-it forces these components out of the blood and into he Bowmans capsule

Question 10

can larger components of the blood pass to the Bowmans capsule, why? what are these components?

Answer 10

-they can’t because they are too large and ultrafiltration is based purely on molecular size
-red blood cells, white blood cells and large plasma proteins

Question 11

how is the process of ultrafiltration aided?

Answer 11

-by the structure of capillary walls and the lining of the Bowmans capsule
-both are very thin so blood can pass through easily

Question 12

what type of cells make up the walls of the glomerulus? what do these walls also have and why?

Answer 12

-single layer of flattened endothelial cells
-the walls contain pores

Question 13

what type of cells makeup the walls of the Bowmans capsule and what are their job?

Answer 13

-it’s lined with specialized cells known as podocytes which allow the filtered material to pass through easily

Question 14

what is the extension called that separates the capillary and podocytes?

Answer 14

-the basement membrane

Question 15

what is the job of the basement membrane?

Answer 15

-it is the effective filter which determines which components of the blood enter the Bowmans capsule
-it also prevents the blood cells and large plasma proteins from leaving the blood

Question 16

what are the three layers that separate the blood in the capillaries and the inside of the Bowmans capsule?

Answer 16

-capillary endothelial cells
-podocytes
-basement membrane

Question 17

how are each of the layers that separate blood in capillaries with the inside of the Bowmans capsule specialized?

Answer 17

-they are specialized by either being porous (capillary walls and podocytes) or through acting as a filter (basement membrane)

Question 18

what are the two forces that cause ultrafiltration?

Answer 18

-hydrostatic pressure which forces water and small components into the Bowmans capsule
-water potential on each side of the membrane

Question 19

what must the water potential be like for filtration to occur?

Answer 19

-the water potential within the Bowmans capsule (Bowmans filtrate) must have a more negative potential/ concentrated than blood in the glomerulus

Question 20

what are the two components of water potential?

Answer 20

-pressure potential and solute potential

Question 21

what is the hydrostatic pressure in the blood like compared to the pressure in the glomerular filtrate ?

Answer 21

-the hydrostatic pressure of the blood is much greater than the hydrostatic pressure created by the filtrate in the nephron

Question 22

by what blood component is the solute potential represented and why?

Answer 22

-plasma proteins
-this is because there are plasma proteins in the glomerulus capillaries but not in the filtrate

Question 23

what is the solute potential like in the filtrate compared to the blood? why is this not an issue?

Answer 23

-the filtrate has a less negative/ more dilute solute potential than in the blood
-although the difference opposes filtration the effect is insignificant when compared to the hydrostatic pressure

Question 24

look at worked example in book of pressure equation thing

Answer 24

hjdh

Question 25

due to filtration what happens to the useful products?

Answer 25

-useful blood products are temporarily lost to the glomerular filtrate

Question 26

where does selective reabsorption occur?

Answer 26

-in the PCT

Question 27

what are the two valuable products that are reabsorbed? why are they lost in the first place to the filtrate?

Answer 27

-glucose and amino acids
-they are small enough to pass through the basement membrane but are too valuable to be lost in the urine

Question 28

what are the 2 processes in which selective reabsorption occur?

Answer 28

-facilitated diffusion and active transport

Question 29

what is the osmotic effect of glucose and amino acids being selectively reabsorbed back into the blood?

Answer 29

-it causes over 70% of the water in the filtrate to be reabsorbed back into the blood via osmosis

Question 30

how are small plasma proteins reabsorbed back into the blood?

Answer 30

-through pinocytosis

Question 31

why is some urea also absorbed back into the blood?

Answer 31

-some passes from the nephron filtrate back into the blood via diffusion

Question 32

how is most of the glucose and amino acids reabsorbed back into the blood?

Answer 32

-through facilitated diffusion so long as the concentration gradient permits

Question 33

why is active transport necessary for selective reabsorption?

Answer 33

-its necessary to ensure that all the glucose is reabsorbed from the nephron back into the capillary network

Question 34

what are 5 adaptations of epithelial cells of the PCT for their high rate of metabolic activity?

Answer 34

-they contain lots of mitochondria that provide the ATP for active transport
-the infolding of the outer membrane increases the surface area for diffusion
-capillaries lie close to the cells lining the PCT
-microvilli on inner surface increases surface area further for selective reabsorption
-cell surface membrane of these cells contain protein carrier molecules for facilitated diffusion and active transport of glucose and amino acids

Question 35

when the filtrate reaches the end of the PCT what is it’s glucose and amino acid content like and why?

Answer 35

-it will have no glucose or amino acids present as they will have all been reabsorbed

Question 36

what is the concentration of urea like moving towards the end of the PCT despite some of it being reabsorbed into the blood?

Answer 36

-the concentration of urea in the filtrate increases along it’s length due to the reabsorption of water

Question 37

what is the water potential of both the filtrate and the blood plasma like at the end of the PCT?

Answer 37

-they are isotonic with each other

Question 38

where does further regulation of blood composition occur?

Answer 38

-in the DCT

Question 39

what is an example of another toxic substance that is secreted into the filtrate from the blood for disposal in the DCT?

Answer 39

-creatinine which is a byproduct from muscle metabolism