Glomerular filtration Flashcards
What does the glomerulus restrict the passage of into Bowman’s capsule
Blood cells and proteins
How many litres of filtrate does the glomerulus filter per day
180l
How many times is the plasma filtered per day
65 times
How and what do endothelial cells filter
The flat cells with large nuclei have circular fenestrations in contact with each other - these keep out blood cells and platelets
How does the basement membrane of the glomerulus filter the incoming fluid
A continuous, main barrier, consists of glycoproteins, laminin, collagen and fibronectin, negatively charged - filtration is therefore based on size and charge of the molecule
How do epithelial cells interact with the filtrate?
Trabeculae (columns of connective tissue) with pedicels interdigitating between them creating slit pores into Bowman’s capsule - Site for maintenance of the structural barrier and phagocytosis
What is the equation for glomerular filtration rate
Kf(Pcap + OncoticPbc) - (Pbc + OncoticPcap)
Kf is the filtration co-efficient -
Pcap = hydorstatic pressure in capillary
Oncotic P = oncotic pressure
bc = Bowman’s capsule
How do the oncotic and hydrostatic pressures change along the glomerular capillary
Pbc = remains constant as fluid moves on to the proximal tubule - 20mmHg
OncoticPcap = Increases as fluid levels drop but protein conc remains constant = 30mmHg
Pcap starts >60mmHg but drops due to loss of fluid - 60mmHg
Net filtration pressure = 10mmHg
How does the action of the afferent arteriole regulate renal blood flow/GFR through changes in mean arterial blood pressure
See changes in Pcap
But: when MABP rises - afferent arteriole contracts smooth muscle and constricts - This reduces renal blood flow and lowers Pcap/GFR
When there’s a decrease the opposite process occurs
What is the average GFR
125ml/min
What is the myogenic theory behind the control by the afferent arteriole
Property of smooth muscle - when arterial BP rises this stretches the afferent arteriole leading to its constriction therefore increasing afferent arteriole resistance
What is the tubuloglomerular feedback theory behind GFR control
Macula densa cells found in the thick ascending limb that runs past its own glomerulus - look at rate of flow - able to release vasoactive chemicals - respond depending on increased or decreased BP - increased release of vasoconstrictors or dilators
