Osmoregulation

Osmoregulation

Formation of Glomerular Filtrate:

Blood enters the kidney via the renal artery which branches into smaller arterioles that enter the cup-shaped opening of each nephron, the Bowman's capsule. The afferent arteriole has a larger diameter than the efferent arteriole which creates a high hydrostatic pressure of the blood in the capillary network, called the glomerulus. The high blood pressure forces all small molecules and ions in the blood through into the lumen of the nephron, so forming the glomerular filtrate. Large molecules such as proteins cannot enter the filtrate and neither can cells.

The blood leaves the Borman's capsule via the efferent arteriole which then branches into a capillary network surrounding the rest of the sections of the nephron. Eventually, the capillaries form venules which then merge into the larger vessel leaving the kidney - the renal vein.

Reabsorption in the Proximal Convuluted Tubule:

The glomerular filtrate flows into the proximal convuluted tubule. Here, the cells making up the wall have adaptations to provide a large surface area for absorption - the micro-villi and many mitochondria to provide energy for active transport. There are also numerous carrier proteins in the cell surface membranes to allow specific molecules/ions to be transported across into the blood.

All glucose is reabsorbed back into the blood from the filtrate in the proximal convuluted tubule, there should be none found in the urine (except in diabetics where they are unable to lower blood glucose to within normal limits). Some active transport must be involved here because facilitated diffusion alone as a transport method could potentially reach equilibrium between glucose in the filtrate and the blood preventing further reabsorption.

Some water is reabsorbed back into the blood from the filtrate in the proximal convuluted tubule. This happens by the process of osmosis as water travels down a water potential gradient.…