Kidney function 1 - excretion Flashcards
what are the two main processes in the Glomerlus/ PCT?
-ultrafiltration
-reabsorption
what does ultrafiltration mean?
-the filtration of plasma and substances below a certain size into the Bowmans capsule
where does ultrafiltration occur?
-the glomerulus
does ultrafiltration recognize useful products?
-it doesn’t recognize useful products
why is reabsorption necessary?
-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
what kind of pressure does blood have when entering the glomerulus?
-a high hydrostatic pressure
why does blood entering the glomerulus have a high hydrostatic pressure? (3 reasons)
-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
what are the 5 small components in the blood that are forced out due to the high hydrostatic pressure?
-glucose
-amino acids
-salts
-water
-urea
where are the 5 small blood components forced out to due to the high hydrostatic pressure?
-it forces these components out of the blood and into he Bowmans capsule
can larger components of the blood pass to the Bowmans capsule, why? what are these components?
-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
how is the process of ultrafiltration aided?
-by the structure of capillary walls and the lining of the Bowmans capsule
-both are very thin so blood can pass through easily
what type of cells make up the walls of the glomerulus? what do these walls also have and why?
-single layer of flattened endothelial cells
-the walls contain pores
what type of cells makeup the walls of the Bowmans capsule and what are their job?
-it’s lined with specialized cells known as podocytes which allow the filtered material to pass through easily
what is the extension called that separates the capillary and podocytes?
-the basement membrane
what is the job of the basement membrane?
-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
what are the three layers that separate the blood in the capillaries and the inside of the Bowmans capsule?
-capillary endothelial cells
-podocytes
-basement membrane
how are each of the layers that separate blood in capillaries with the inside of the Bowmans capsule specialized?
-they are specialized by either being porous (capillary walls and podocytes) or through acting as a filter (basement membrane)
what are the two forces that cause ultrafiltration?
-hydrostatic pressure which forces water and small components into the Bowmans capsule
-water potential on each side of the membrane
what must the water potential be like for filtration to occur?
-the water potential within the Bowmans capsule (Bowmans filtrate) must have a more negative potential/ concentrated than blood in the glomerulus
what are the two components of water potential?
-pressure potential and solute potential
what is the hydrostatic pressure in the blood like compared to the pressure in the glomerular filtrate ?
-the hydrostatic pressure of the blood is much greater than the hydrostatic pressure created by the filtrate in the nephron
by what blood component is the solute potential represented and why?
-plasma proteins
-this is because there are plasma proteins in the glomerulus capillaries but not in the filtrate
what is the solute potential like in the filtrate compared to the blood? why is this not an issue?
-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
look at worked example in book of pressure equation thing
hjdh
due to filtration what happens to the useful products?
-useful blood products are temporarily lost to the glomerular filtrate
where does selective reabsorption occur?
-in the PCT
what are the two valuable products that are reabsorbed? why are they lost in the first place to the filtrate?
-glucose and amino acids
-they are small enough to pass through the basement membrane but are too valuable to be lost in the urine
what are the 2 processes in which selective reabsorption occur?
-facilitated diffusion and active transport
what is the osmotic effect of glucose and amino acids being selectively reabsorbed back into the blood?
-it causes over 70% of the water in the filtrate to be reabsorbed back into the blood via osmosis
how are small plasma proteins reabsorbed back into the blood?
-through pinocytosis
why is some urea also absorbed back into the blood?
-some passes from the nephron filtrate back into the blood via diffusion
how is most of the glucose and amino acids reabsorbed back into the blood?
-through facilitated diffusion so long as the concentration gradient permits
why is active transport necessary for selective reabsorption?
-its necessary to ensure that all the glucose is reabsorbed from the nephron back into the capillary network
what are 5 adaptations of epithelial cells of the PCT for their high rate of metabolic activity?
-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
when the filtrate reaches the end of the PCT what is it’s glucose and amino acid content like and why?
-it will have no glucose or amino acids present as they will have all been reabsorbed
what is the concentration of urea like moving towards the end of the PCT despite some of it being reabsorbed into the blood?
-the concentration of urea in the filtrate increases along it’s length due to the reabsorption of water
what is the water potential of both the filtrate and the blood plasma like at the end of the PCT?
-they are isotonic with each other
where does further regulation of blood composition occur?
-in the DCT
what is an example of another toxic substance that is secreted into the filtrate from the blood for disposal in the DCT?
-creatinine which is a byproduct from muscle metabolism
