Filtration Membrane – Urine Formation (Nursing)

00:01 So let's take a closer look at each of these steps individually.

00:06 Starting with glomerular filtration.

00:09 This is going to be a passive process that takes place in the glomerulus of the nephron.

00:16 This is going to be made up of glomerular capillaries surrounded by a glomerular capsule.

00:23 The capsule is a double-walled epithelium where the inner wall is going to be closest to the capillary and made up of podocytes and the outer wall is going to surround a space known as the capsular space.

00:39 Because this is a passive process.

00:41 No metabolic energy is expended during filtration.

00:48 Instead we have hydrostatic pressure forces, which are going to force fluids and solutes through a filtration membrane into the glomerular capsule.

01:00 In the glomerular capsular space, recall that hydrostatic pressure is the pushing pressure of a fluid against the walls of a capillary due to gravity and that causes fluid to move out of the capillaries into the capsular.

01:19 There is no reabsorption of any materials from the glomerular capsular space back into the blood.

01:29 Glomerular filtration is going to happen across the filtration membrane.

01:35 This is a porous membrane between the blood and the interior of the glomerular capsule.

01:41 This membrane allows water and solutes that are smaller than plasma proteins to pass.

01:48 And normally no cells are able to pass through this membrane.

01:54 The filtration membrane is going to make up three layers.

01:58 First, on the glomerular capillary.

02:01 We have the fenestrated endothelium.

02:04 This is going to be an endothelium that has holes or fenestrations that allow fluid to flow or leak out of the capillary.

02:15 Then we have the basement membrane what is which is actually a fusion of the basal lamina of both the capillaries as well as the podocytes of the glomerular capsule.

02:29 Then we have the foot processes of the podocytes.

02:34 The podocytes are going to come from the visceral layer of the glomerular capsule.

02:39 On the podocytes, there are filtration slits, which are going to have slit diaphragms which are going to repel larger macromolecules.

02:51 So to recap using a diagram, plasma and the glomerular capillaries are going to be filtered through the fenestrations of the capillary endothelia.

03:03 Then they're going to go through the basement membrane of the capillary as well as the glomerular capsule and finally through this slit diaphragms of the podocytes of the glomerular capsule wall.

03:17 From there, the filtrate is going to go into the capsular space.

03:24 Again, the filtration membranes main function is to allow smaller molecules like that are smaller than about three nanometers to pass.

03:34 These includes molecules, like water, glucose, amino acids, and nitrogenous waste.

03:42 Larger molecules such as plasma proteins are going to remain in the blood and this is necessary to maintain colloid osmotic pressure.

03:53 This prevents the loss of all water to the capsular space and if there are proteins in the filtrate, it could indicate that there is a problem with the filtration membrane.