Session 3: GFR and Filtration Flashcards
Basic functions of the kidneys.
Regulation and control of concentrations of key substances in the ECF. Excretion of waste products. Synthesis of renin, EPO and prostaglandins. Activation of vitamin D, catabolism of insulin and PTH + calcitonin.
What does the kidney filter?
The extra cellular fluid which includes interstitial fluid and the plasma of the blood.
How much ECF does the kidney filter?
180L/day
Where does the main filtration occur?
In the glomerulus of a nephron in the kidney into Bowman’s capsule.
What is being filtered?
Most water Almost all of the salts Almost all of the glucose Almost all of the urea
What is not being filtered?
Proteins and large molecules.
What is ultra-filtrate?
It is more or less plasma but without the proteins and large molecules. It is what has been filtered into Bowman’s capsule.
How much of the ultra-filtrate will be recovered and reabsorbed into system circulation?
99% water 99% sodium and chloride ions 100% bicarbonate 100% glucose and amino acids
How much fluid is excreted by the kidneys daily?
Around 1.5L of urine per day
What is osmolality?
Solute per kilogram of solvent Measured in milliosmoles
What is osmolarity?
Number of osmoles of solute per litre
What is the glomerulus?
A small tuft of capillaries which are specialised and have fenestrations in order for increased permeability.
What is the specialised basement membrane of the glomerulus? What is its purpose?
It is an acellular glycoprotein membrane which has a negative charge. It provides further selectivity to ions.
What are podocytes?
Specialised type of epithelial cells which directly invest the glomerular capillaries.
They are critical for selectivity of glomerular filtration.
The podocytes contact the glomerular capillaries’ basement membrane using thin outpouchings known as foot processes.
The narrow area between adjacent foot processes forms an extremely thin slit which is sometimes termed the slit diaphragm.
After the podocytes where will the ultra-filtrate go?
Into the Bowman’s space which is between the glomerular capillaries and the Bowman’s capsule. After this it will go into Bowman’s capsule.
What is Bowman’s capsule?
A layer of epithelial cells that surrounds the glomerular capillaries and is continuous with the epithelium of the proximal convoluted tubule.
Where can the glomerulus be found?
Only in the cortex of the kidney.
What is glomerular filtrate rate? (GFR)
How much filtration of ECF (ml) occurs per min.
What is a normal GFR?
90-125 ml/min