Ultrafiltration

This lesson covers: 

1. Ultrafiltration in the glomerulus
2. Movement of substances from blood into the glomerular filtrate

Ultrafiltration in the glomerulus

Ultrafiltration is the process by which small molecules like water, glucose, mineral ions, and urea are filtered out of the blood and into the Bowman's capsule to form glomerular filtrate. Larger molecules remain in the bloodstream.

This selective movement is essential for filtering blood and maintaining a balance of substances in the body.

The ultrafiltration process:

1. Blood enters the glomerulus through the afferent arteriole.
2. Blood leaves the glomerulus via the smaller efferent arteriole, maintaining a high hydrostatic pressure.
3. This high pressure forces molecules, like water and small solutes, out of the blood through pores in the capillary endothelium.
4. The molecules move through the basement membrane, which has collagen fibres that act as a selective filter preventing large molecules and blood cells from passing into the Bowman’s capsule.
5. The molecules move through the Bowman's capsule epithelium, which has specialised cells called podocytes with extensions known as pedicels that wrap around capillaries and help to filter the blood.
6. Filtered fluid collects in Bowman's capsule.

Glomerular filtrate formation

The liquid part of blood that enters Bowman’s capsule is known as the glomerular filtrate.

Some useful substances in the glomerular filtrate are reabsorbed back into the blood in subsequent sections of the nephron. This reabsorption is vital for retaining essential nutrients and maintaining the body's chemical balance.

The glomerular filtration rate (GFR) measures the volume of glomerular filtrate formed per minute. Effectively, it is the volume of blood that is filtered through the kidneys in a given time. This rate is a key indicator of how efficiently the kidneys filter blood.