Question

Describe the process of ultrafiltration.

Answer 1

Hint:Urine formation includes glomerular filtration or ultrafiltration, selective absorption, and tubular absorption. It leads to removal of excess water and wastes.

Complete answer:
Glomerular filtration or ultrafiltration begins in the nephron of the kidney. The steps of ultrafiltration are discussed below:

i. The Blood travels through a coiled structure of capillaries called the glomerulus surrounded by the Bowman's capsule.
ii. The capillaries of the glomerulus are narrower than the afferent renal arterioles. Hence, the blood pressure in the glomerular capillaries becomes very high so that ultrafiltration occurs continuously through the semi-permeable glomerular capillaries.
iii. The hydrostatic pressure of the flow of blood allows small molecules such as sodium and potassium, glucose, water, urea, and amino acids present within the blood, to pass through the capillary membrane and through the gaps in the podocytes surrounding the Bowman's capsule.
iv. The fluid in the capsule is now referred to as the glomerular filtrate. This filtrate then enters the proximal convoluted tubule (PCT), where the majority of glucose and amino acids are selectively reabsorbed.
v. This filtrate then passes to the Loop of Henle, which is responsible for the transport of salts and creates an osmotic gradient in the surrounding tissue to aid the absorption of water. Sodium and potassium ions are pumped out of the loop to decrease the water potential of the surrounding fluid, thus creating an osmotic gradient that drives water out of the fluid and into the tissue.
vi. Then, the water re enters the filtrate in the distal convoluted tubule (DCT) and collects ducts due to the negative osmotic gradient created by the remaining urea in the filtrate.
vii. The volume of water absorbed in the collecting ducts is controlled by a hormone called antidiuretic hormone (ADH).

Note:It is to be noted that urea decreases the water potential of the filtrate, therefore some water moves into the filtrate due to the process of osmosis. On an average 1100 -1200 ml of blood is filtered by the kidneys per minute.