Lecture 2 Flashcards
How many times a day is plasma filtered?
65
How much filtrate is produced a day?
85 litres
What is filtered in the glomerulus?
Water, ions and small proteins that are reabsorbed
What is the glomerulus and what percentage of plasma is filtered?
Is a capillary bed- blood comes in from afferent and leaves from efferent. 20% is filtered into Bowman’s capsule
What 3 layers does the filtrate need to cross?
1) Endothelial cells of the blood capillary
2) Basement membrane= thin and main determinant for filtration
3) Epithelial cells= podocytes
What are the features if endothelial cells?
1) Flat, large nuclei
2) circular fenestrations
3) Allow water solutes and ions to pass but not blood cells or platelets
What are the features of the basement membrane?
1) Continuous membrane that surrounds the glomerular capillaries
2) Made from glycoproteins e.g. laminin fibronectin and collagen that make a mesh to form the main barrier
3) Negative charge- sorts out by size, charge then shape
What is the structure of the epithelial cells in a glomerulus?
Provide structural support and consist of podocytes that are involved in phagocytosis. They have trabeculae which have projections that interdigit to form slit pores.
What determines filtration and use dextran as an example of how this can be tested?
Filtration is measured via ration= filtrate/plasma
As the Mr increases, the likelihood of being filtered decreases. Negatively charged molecules find it more difficult to be filtered unless they are small enough (small MR).
Can use dextran which is a molecule that can have modified charge and modified Mr. For the same Mr of dextran, removal of charge allows it to be filtered more easily.
What is Kf and how is filtration rate measured?
Is the filtration co-efficient and is essentially a constant. The starlings forces dictate that GFR is proportional to forces favouring - forces opposing= kf(Pcap + IIbc) - (Pbc + IIcap). Balance of all 4 determines filtration rate.
What does P mean?
hydrostatic pressure - pressure of plasma pushing against endothelial layer
what is II?
oncotic pressure - pressure generated by proteins in the plasma
How does GFR change as you go down the capillary?
Is essentially a constant.
1) IIbc is approximately 0 due to no proteins
2) Pbc is 20mmHG and remains constant due to the volume in Bowman’s capsule being constant
3) IIcap= 30mmHG and increases as you go along the capillary due to the protein conc increasing as fluid is lost
4) Pcap= 60 mmHG and decreases slightly due to loss of fluid down the capillary
How is Kf measured?
Difficult to measure experimentally therefore the clearance technique is used. Found that single glomerular filtration rate= 50nl/min
How does resistance in the arteries effect the filtration?
In control conditions afferent and efferent arteriole resistance are equal.
Increase in afferent resistance= decrease in RBF, Pcap and GFR
decrease in afferent resistance= increase in RBF, GFR and Pcap (increase in blood flow increases hydrostatic pressure
