Physiology 3 Flashcards
What is the osmolarity in the cortex?
Same as the rest of the body 300
What happens to the concentration as we move deeper into the medulla?
It increases - eventually gets to 1200
What is the basis of healthy kidney function?
The ability to form a cortico-medullary concentration gradient
What is the innermost part of the medulla called?
The papilla
How thick is the boundary around the tubule?
1 epithelial cell thick
what is the concentration of the fluid entering into the thick descending loop?
It is iso-osmotic
What is the fluid percentage remaining after the proximal tubule?
1/3 of original
Two membranes:
Luminal
Basolateral
What happens in the thin descending loop?
It increases
Why is the descending loop thin?
The cells do not contain much (i.e. mitochondria etc)
What are the properties of thin descending loop?
It is permeable to water
It is impermeable to almost everything else
Why are lipids hard to get rid of?
They can diffuse across membranes very easily
Does the descending loop have aquaporins?
Yes
What is the relationship between depth and concentration?
The deeper you go the higher the concentration
Why does water leave the lumen?
It is drawn out osmotically (because of the high osmolarity of interstitial fluid)
What happens to the concentrations of sodium and chloride at the bottom of the loop?
It is 4x normal
What makes up the high osmolar concentration in the deep medulla?
Urea - it is trapped allowing for the movement of water
What happens in the thin ascending limb to sodium and water permeability?
It is high but the water permeability is low
What happens in the ascending limb?
There is an enormous passive movement of sodium into the interstitium
i.e. sodium is reabsorbed
How much sodium is reabsorbed in the thick ascending limb?
25%
How much water is reabsorbed by the descending limb?
10-15%
What would be expected of the urine at the macula densa?
It should be dilute
What is specific about the distal tubule?
It responds to circumstances
Specifically regulates sodium balance
What is the sodium concentration in the urine
50mOsM
What does the collecting duct primarily regulate?
The water concentration
What regulates the expression of aquaporins and water reabsorbtion?
Adh
It regualtes aquaporin expression and binding
What is seen in the urine of someone with kidney failure?
It has the same specific gravity of plasma
What drives the majority of tubular reabsorption?
Active transport of Na
What does the Na/kATPase do?
It maintains the the intracellular concentration inside the cells
What occurs at the basolateral membrane?
Always the same mechanism (sodium/potassium ATPase)
What occurs at the luminal membrane?
A series of different transporters including co-transporters.
It is made up of a variety of co-transporters
What type of co-transporters are there?
Lots - glucose etc etc
How do co-transporters act?
They do not use energy, but rather use the concentration gradient
How many amino acid co-transporters are there?
About 5-6 (transport more than one amino acid)
Where is the sodium phosphate transporter?
It is in the proximal tubule
how much sodium phosphate transporter is there?
No that much and as such not all phosphate is reabsorbed (unlike glucose which is there in high concentration)
How is chloride reabsorbed?
The sodium is absorbed and causes a electrochemical gradient.
Sodium is absorbed trans-cellularly
the sodium and the water which are dragged behind take the para-cellular route.
The occurs for a number of other molecules in the proximal tubule. As water moves across there is a growing concentration gradient which allows movement via bulk flow.
Where is the sodium hydrogen exchanger?
Luminal membrane
Why doesn’t sodium flow back into the lumen?
It does - as the concentration is higher in the interstium
Where are potassium channels?
They are present at the basolateral membrane and not at the apical membrane.
The potassium diffuses out back into the interstitium and not
How much oxygen in used by the kidney for active transport?
80%
What is reabsorbed via the movement of sodium?
Water, chloride, glucose, amino acids, urea
Where does sodium diffuse back into the lumen through?
Tight junctions between cells
