Biology – Homeostasis in mammals | e-Consult

Glomerulus: The glomerulus is a network of capillaries enclosed by Bowman's capsule. Its structure is adapted for high filtration pressure. The afferent arteriole is wider than the efferent arteriole, creating a pressure gradient that forces water and solutes from the blood into the glomerular capillaries and then into Bowman's capsule. The fenestrations (pores) in the glomerular capillaries are large enough to allow passage of water and small solutes but are too small to allow passage of blood cells and proteins.

Proximal Convoluted Tubule (PCT): The PCT is highly adapted for reabsorbing solutes from the filtrate. The PCT cells have a large surface area due to the presence of microvilli (brush border) and numerous mitochondria. This allows for efficient active transport of substances like glucose, amino acids, ions (Na+, K+, Cl-), and water from the filtrate back into the peritubular capillaries. The tight junctions between PCT cells also play a role in regulating the movement of substances across the epithelium, ensuring that reabsorption occurs in a controlled manner. The high rate of reabsorption in the PCT contributes significantly to the high solute concentration in the filtrate as it leaves the glomerulus.

Relationship to Function: The glomerulus's structure ensures a high pressure filtration of blood, leading to a filtrate with a high solute concentration. The PCT then actively reabsorbs many of these solutes, further increasing the solute concentration in the filtrate as it moves towards the distal tubule and collecting duct. This process is crucial for maintaining the body's internal environment and regulating blood composition.