Nephron Structure and Urine Formation

Nephron Structure

• A nephron is the functional unit of the kidney, with approximately 1 million nephrons per kidney.
• A nephron consists of small tubules and associated blood vessels.
• The glomerular (Bowman's) capsule surrounds the glomerulus, forming the renal corpuscle.

Urine Formation Process

• The process involves four key steps: filtration, reabsorption, secretion, and excretion.
• Filtration: blood plasma is filtered through the glomerulus, forming the filtrate.
• Reabsorption: essential nutrients, solutes, and water are reabsorbed from the filtrate into the bloodstream.
• Secretion: certain substances are actively secreted from the blood into the filtrate.
• Excretion: the refined filtrate, now called urine, is passed through the collecting ducts to the renal pelvis and out of the body.

Filtration Mechanism

• The fluid in blood plasma must pass through three layers of selective filters before entering the glomerular capsule:
• The fenestrae of the endothelial cells of the glomerular capillaries: large pores that allow water and soluble material to pass through.
• The glomerular basement membrane: a thick structure that restricts the rate of fluid flow into the capsule lumen.
• The slit diaphragm: the inner layer of the glomerular capsule, composed of podocytes with pedicels that form filtration slits.

Nephron Pathway

• Filtrate produced in the renal corpuscle passes into the proximal convoluted tubule.
• Fluid then passes into the descending and ascending limbs of the loop of Henle.
• After the loop of Henle, fluid passes into the distal convoluted tubule.
• Finally, fluid passes into the collecting duct, where it is now urine and will drain into a minor calyx.