Glomerular Filtration and its Control Flashcards
List the functions of the kidneys
- Regulation of ECF volume and BP,
- Regulation of osmolality of plasma and ECF,
- Maintenance of ion balance,
- Regulation of pH,
- Excretion of waste,
- Production of hormones
Describe the structure of a nephron
- Corpuscle,
- Procimal convoluted tubule,
- Proximal straight tubule.
- Thin descending limb of Henle.
- Thin ascending limb of henle,
- Thick ascending loop of henle,
- Distal convoluted tubule,
- Connecting tubule,
- Initial collecting tubule,
- Cortical collecting tubule,
- Outer medullary collecting duct,
- Inner medullary collecting duct
- Duct of Bellini
What are the main processes that occur in the nephron?
1) Filtration by the glomerulus,
2) Obligatory absorption and secretion by proximal tubule,
3) Generation of osmotic gradient by loop of henle,
4) Regulated absorption and secretion by distal tubule,
5) Regulation of water uptake by collecting ducts
What is glomerular filtration?
A passive process which forces fluid and solutes out of blood due to hydrostatic pressure.
Why does the glomerulus produce such a large quantity of filtrate?
1) Filtration membrane is very permeable to water and solutes.
2) Glomerular blood pressure it much higher than in other capillary beds in the body.
Formation of filtrate occurs by crossing a triple barrier, name and explain these layers
1) Epithelial lining of capillaries.
2) Basement membrane of capillaries (triple layer)
3) Foot processes of epithelial cells (podocytes).
What does the triple barrier allows for?
Opposition movement of cells and large proteins.
Negatively charged molecules are filtered less easily than positively charged molecules
What are the different about the blood supply that goes through glomerulus
It is both fed and drained by arterioles. Fed by afferent and drained by efferent.
What are some of the barriers for filtration?
Endothelial fenestrations,
Basement membrane repels proteins and filtration slit diaphragms
Define what RBF and RPF is
RBF - Total amount of blood that traverses renal artery/vein per unit time.
RPF - Total amount of plasma that traverses renal artery/vein per unit time
Describe how the different pressure values result in net movement into tubules
Blood Hydrostatic pressure - +55mmHg.
Hydrostatic pressure of tubule = -15mmHg
Oncotic pressure of blood = - 30mmHg
So total net filtration = + 10mmHg
What are some of the regulation mechanisms of glomerular filtration?
Autoregulation Mechanisms; myogenic mechanism and tubuloglomerular feedback (nephrogenic). When afferent dilation then increase in GFR, when efferent dilation then decrease in GFR
Describe the myogenic autoregulation
In the afferent arteriole when constriction occurs this reduces filtration pressure and glomerular filtration rate falls. With dilation there is an increase in pressure driving ultrafiltration so GFR increases.
Efferent arterioles - Constriction causes pressure to back up in capillary so GFR increases. With Dilation it allows blood to easily escape so pressure falls and GFR decreases. (Done by stretch receptors)
Describe the tubuloglomerular feedback control mechanism when there is low filtrate flow rate
When macula densa cells are exposed to low filtration flow there is low concs of NaCl entry. This results in release of prostaglandins E1 which activates endothelial NO synthase. There is increased cell cAMP and then muscle relaxation and vasodilation and increased GFR
Describe the tubuloglomerular feedback control mechanism when there is high filtrate flow rate
There is increased NaCl entry into macula densa cells. This causes them to swell, depolarise and release ATP. The adenosine binds to A1 receptors causing constriction of afferent arterioles, reducing GFR
