Kidney Tubular Function Flashcards
how much filtrate is produced every day in a healthy individual
180 litres
what proportion of total daily filtrate is reabsorbed in the renal tubules
99%
describe the filtration barriers main function
selects molecules to be filtered from blood plasma into the nephron based on their size and charge to form filtrate
how many times a day is the fluid in our body filtered through the kidneys
3-4 times a day
what are the components of the renal tubule
proximal convoluted tubule
loop of henle
distal convoluted tubule
what is the function of the renal tubule
reabsorption and secretion for conserving the water and electrolytes in the body
how much filtrate is immediately reabsorbed through the proximal convoluted tubule
two thirds
what does the transport of sodium in the proximal convoluted tubule also facilitate the reabsorptiono f
nutrients
water
ions
how much sodium is reabsorbed in the proximal convoluted tubule
65%
how much of the sodium in the filtrate is reabsorbed in the ascending loop of henle
25%
how much sodium is reabsorbed in the distal convoluted tubule
up to 8%, but this value depends on the hormonal regulation
how is sodium reabsorption in the distal convoluted tubule regulated
depending on the body’s requirements and therefore it is through hormonal regulation
how much of the sodium in the filtrate is reabsorbed in total
around 98%
how much of the kidneys energy requirement is dedicated to the reabsorption of sodium
80%
what is the role of proximal convoluted tubule
reabsorption and secretion
what is the role of the loop of henle
counter current multiplier
what is the role of the distal convoluted tubule
reabsorption and secretionw
what is the role of the collecting duct
urine collection
what is the function of the renal corpuscle
filtration
how is the proximal convoluted tubule designed
in order to facilitate its function: it is long, and is convoluted. this means it bends in on itself to maximise surface area for reabsorption
how does the glomerulus appear in the masson trichrome stain
black
where are the glomerular capillaries in the kidneys
the renal cortex
what are the vasa recta
these are the peritubular capillaries that are very closely associated with the nephrons to allow direction of movement of substances from the blood to the tubular lumen and vice versa
what specialisation is present in the epithelial lining of the proximal convoluted tubule
microvilli
what type of transport does sodium travel via
active transport
is urea reabsorbed
yes
is creatinine absorbed
no, this is why it is the value used in urine samples to measure the efficiency and health of the kidneys
describe the concentration gradient in the proximal convoluted tubule
the filtrate has a high concentration of solutes and water relative to the concentration in the peritubular capillaries.
this is what regulates the passive diffusion in the proximal convoluted, where half of the filtrate is reabsorbed immediately upon entering the proximal convoluted tubule
how many litres of filtrate are absorbed passively due to the laws of physics
90%
how is water reabsorption facilitated
using pores and carrier proteins to allow for the diffusion
what are aquaporins
these are protein pores in the bilayer that allow for free movement of water down its concentration gradient from the lumen across the epithelium into the peritubular capillaries
what is passive diffusion
the movement of molecules from high to low concentration until equilibrium is reached
what are the molecules commonly found in filtrate
sodium ions
water
chloride ions
glucose
amino acids
urea
creatinine
how do glucose and amion acids move across the apical surface for reabsorption
via sodium cotransporters: sodium is pumped and they hitch a ride
which molecules are important for facilitating the passive diffusion occurring in the proximal convoluted tubule
aquaporins and carrier proteins
how much of the filtrate urea can be reabsorbed
up to 50%
why does creatinine not get reabsorbed
it has no transporter protein
where are the sodium potassium pumps found in the proximal convoluted tubule
on the basolateral membrane
why does water follow sodium wherever it goes
osmosis
how do chloride and other negative ions get reabsorbed
they also follow sodium
how is sodium reabsorbed into the bloodstream
the sodium potassium pump disrupts equilibirum by moving sodium into the interstitial space
this causes an accumulation in the interstital space
as blood flows, the sodium moves down its concentration gradient into the peritubular capillaries
how many of the nutrients in the filtrate are reabsorbed
up to 100%
when might it be the case that not all nutrients are reabsorbed in the kidneys
diabetics with an excess of glucose in the blood
how many litres reabsorbed immediately
120
how does water reabsorb
follows sodium via osmosis
how does chloride reabsorb
follows electrical gradient
list all that the active transport of sodium facilitates
- nutrient reabsorbtion
- water reabsorption
- negative ions follow the electrical gradient
does sodium transport affect waste removal
no, urea is reabsorbed via passive diffusion and creatinine is not reabsorbed
how much remaining filtrate is in the loop of henle
60 litres
where does the counter current multiplication system occur
in the juxtamedullary nephrons
what are the sections in the loop of henle
thin descending limb
thin ascending limb
thick ascending limb
what are the loop rules
the idea that each limb in the nephron has different permeability and transport properties
what do aquaporins do
they allow for free movement of water out of the filtrate
which part of the loop of henle has aquaporins
the thin descending limb
describe the thin descending limbs loop rules
- aquaporins
- freely permeable to water
- does not contain active sodium pumps
describe the loop rules of the thin ascending limbs
- no aquaporins
- impermeable to water
describe the loop rules of the thick ascending limb
- site of active sodium reabsorption
- no aquaporins
- impermeable to water
what drug is used to inhibit the action of the NKCC2 pump
furosemide
what conditions are created in the medulla as sodium is actively reabsorbed from the filtrate
it becomes salty as there is an increase in sodium concentration
what happens to water in the filtrate as it enters the loop of henle
the medulla is salty, so the water wants to follow the sodium and is drawn out from the filtrate into the medulla as well
what happens to the concentration of the filtrate as it descends the thin ascending limb
it becomes more concentrated as the sodium ions are retained and water diffuses out
what is the typical concentration of our bodily fluids
300 mini osmoles per litre
how does the concentration of the filtrate change as you go from the medulla up through the ascending limbs
it decreases because sodium is being pumped out but the water is remaining
what is the concentration of sodium ions at the top of the loop of henle
around 100 mini osmols
what is the importance of the counter current multiplication
to save water and sodium from excretion - primary function of the loop of henle is water retention
what is the counter current multiplication
the mechanism in the loop of henle for water reabsorption
counter current because the filtrate flows in two opposite directions
multipilication because the concentrtion is multiplied as you go deeper into the medulla
how do the vasa recta work to ensure the concentration gradient is not washed away
the blood flow is slow, and at each level the blood concentration gradient will equalise with the medulla
what supports the concentration gradient of the medulla
blood flow from the vasa recta
what is the function of the distal convoluted tubule
site of fluid volume and electrolyte regulation
which three hormones are involved in regulating the distal convoluted tubule
anti diuretic hormone
aldosterone
atrial natriuretic hormone
what does ADH do
increase water reabsorption
what does aldosterone do
increase sodium reabsorption
what does ANH do
promote sodium secretion
what is the by product of the kidneys main function
production of urine
are there aquaporins in the distal convoluted tubule
no
is filtrate hypotonic or hypertonic in the absence of hormone regulation
hypotonic
describe the pathway that ADH follows
- lost fluids detected by a change in blood pressure or increased serum osmorality
- detected by the pituitary gland which will produce ADH
- one ADH target is the epithelial lining of the distal convoluted tubule and cells of the collecting duct
- cells insert aquaporins in the cell membrane
describe urine production when ADH acts on the distal convoluted tubule
smaller volume, more concentrated
what is the vasopressin receptor
a cell surface membrane receptor called AVPR2
describe how ADH/vasopressin leads to production of aquaporin channels
activates a signal transduction pathway in the target cell when it binds to its extracellular receptor
this regulates transcription factors to lead to transcription and translation of proteins
aquaporin channels inserted into the membrane to allow water to flow passively
describe the action of aldosterone on the distal convoluted tubule
upregulates the activity and insertion of the sodium potassium pumps and channels
steroid hormone so it enters the cell and acts directly on the transcription factors
which two hormones work together to increase the internal fluid volume
adh and aldosterone
describe the action of ANH on the distal convoluted tubule
counteracts the effects of ADH and aldosterone to produce large volumes of diluted urine
body gets rid of excess fluid if blood pressure is too high, and acts on the cells in the same place as others
aquaporins are removed from the cell membrane of the sites, and activity of sodium potassium pumps are removed
salt and water are retained in the tubule, and excreted in the body
