In: Anatomy and Physiology
Glomerular filtration is the process by which the blood is
filtered while passing through the glomerular capillaries by
filtration membrane. It is the first process of urine formation.
The structure of filtration membrane is well suited for
Filtration membrane is formed by three layers: 1. Glomerular capillary membrane
2. Basement membrane
3. Visceral layer of Bowman capsule.
1. Glomerular capillary membrane
Glomerular capillary membrane is formed by single layer of endothelial cells, which are attached to the basement membrane. The capillary membrane has many pores called fenestrae or filtration pores with a diameter of 0.1 μ.
2. Basement membrane
Basement membrane of glomerular capillaries and the basement membrane of visceral layer of Bowman capsule fuse together. The fused basement membrane separates the endothelium of glomerular capillary and the epithelium of visceral layer of Bowman capsule.
3. Visceral layer of Bowman capsule
This layer is formed by a single layer of flattened epi thelial cells resting on a basement membrane. Each cell is connected with the basement membrane by cytoplasmic extensions called pedicles or feet. Epithelial cells with pedicles are called podocytes . Pedicles interdigitate leaving small cleftlike spaces in between. The cleftlike space is called slit pore or filtration slit. Filtration takes place through these slit pores.
Process of Glomerular Filtration
When blood passes through glomerular capillaries, the plasma is filtered into the Bowman capsule. All the substances of plasma are filtered except the plasma proteins. The filtered fluid is called glomerular filtrate.
Glomerular filtration is called ultrafiltration because even the minute particles are filtered. But, the plasma proteins are not filtered due to their large molecular size. The protein molecules are larger than the slit pores present in the endothelium of capillaries. Thus, the glomerular filtrate contains all the substances present in plasma except the plasma proteins.