Nephron Function and Filtration

Nephron Function

• The nephron has vascular (glomerulus, peritubular capillaries) and tubular (Bowman's capsule, proximal and distal convoluted tubules, collecting ducts) components vital for urine formation.

Glomerular Filtration

• Filtration occurs in the glomerulus, a specialized capillary bed.
• The filtration membrane, a selectively permeable barrier, prevents large molecules (proteins) from entering the filtrate.
• A pressure gradient between the glomerular capillaries and Bowman's capsule (filtration pressure) drives filtration.
• Filtrate consists primarily of water, electrolytes, glucose, amino acids, and nitrogenous wastes.

Sympathetic Activity and Glomerular Pressure

• Increased sympathetic nervous system activity constricts afferent arterioles, reducing glomerular pressure and filtration.

Proximal Convoluted Tubule Reabsorption

• The proximal convoluted tubule (PCT) is responsible for significant reabsorption of water and solutes.
• Complete reabsorption of glucose, amino acids, and most of the filtered bicarbonate occurs here.
• Partial reabsorption of other substances like electrolytes (e.g., sodium, chloride) occurs in this section.
• Reabsorption mechanisms include active transport (for solutes) and osmosis (for water).

Distal Convoluted Tubule and Collecting Duct

• Distal convoluted tubule (DCT) and collecting ducts modify filtrate further.
• Reabsorption, secretion, and exchange mechanisms are crucial here.
• Active transport of sodium and potassium regulate osmotic balance.
• Water reabsorption in the DCT and collecting ducts is regulated by hormones like ADH (antidiuretic hormone).

Urine Concentration/Dilution

• The nephron is responsible for creating both concentrated and diluted urine based on body needs. This is achieved through adjustments in the reabsorption of water and solutes in the DCT and collecting ducts in response to hormones like ADH (antidiuretic hormone).