The Kidneys Flashcards
What are the 3 major functions of the kidneys?
- Endocrine function (secreting hormones)
- Maintain balance of water, Salt and pH
- Excrete waste products
How much cardiac output does each kidney receive?
20% of cardiac output
5L/min
What is total renal blood flow?
1L/min
What is total urine flow?
1L/min
What is the pathway of renal blood supply from the renal artery?
Renal artery Segmental artery Interlobar artery Arcuate artery Interlobular artery Afferent arteriole (Nephron) glomerular capillary Efferent arteriole (Nephron) peritubular capillary
Each nephron has how many capillary beds and where?
2 capillary beds
One at the glomerulus and one of the peritubular area
Within each nephron, how many sets of capillaries are there and which ones?
2 sets of capillaries
Glomerular capillaries (glomeruli)
Peritubular capillaries
How are the 2 capillaries connected together?
By an efferent arteriole, the vessel that allows blood to leave the glomerulus
What is unusual about renal circulation?
2 sets of arterioles and capillaries
Where do peritubular capillaries supply blood to and why?
Supply the tubules with blood
Many of the tubular processes of secretion and reabsorption so are active (thus require oxygen and energy) so blood supply is crucial
Where do the peritubular capillaries go after?
Form the veins and blood leaves the kidneys
What is the entire capillary covered by?
Podocytes
What happens in glomerular filtration?
Where does fluid go from and to?
Passage of fluid from the blood into Bowman’s space to form filtrate
What is the distal part of the nephron (tubule) responsible for?
Secretion and reabsorption
What are the layers of the glomerular filtration barrier?
Capillary Capillary endothelium Basement membrane (basal lamina) Podocytes Bowman’s capsule
What factors determine what crosses the filtration barrier?
Pressure
Size and charge of molecule
Rate of blood flow
Binding to plasma proteins eg. Calcium, hormones such as thyroxine
What can pass the filtration barrier?
Small molecules and ions up to 10 kDa can pass freely eg. Glucose, Uric acid, potassium and creatine
What molecules are restricted?
Larger molecules are increasingly restricted
What charges are able to pass?
Fixed negative charge in the glomerular basement membrane repels negatively charges anions eg, albumin
Can albumin pass into the tubule and why?
Albumin has a molecular weight around 66kDa and is negatively charged so it cannot pass into the tubule easily
Is protein found in the filtered fluid in the tubules?
It is protein free
Only protein found is Tamm horsfall protein in urine which is produced by tubule
What can pressure determine in the kidneys?
Glomerular filtration rate
What are the 2 types of pressure found in the glomerular filtration?
Hydrostatic pressure (of glomerular capillary and bowman’s space - GC and BS) P(gc) bigger & P(bs) smaller
Osmotic pressure
ℼ(gc) - increases as you go along glomerular capillary ad proteins become more concentrated
ℼ(bs) - no osmotic pressure as there are no proteins = 0
What is the glomerular filtration rate?
It is the filtration volume from glomeruli into Bowman’s space per unit time (minutes)
