Nephron Structure and Function

Structure and Function of the Nephron

• Proximal convoluted tubule reabsorbs water through osmosis, and utilizes active transport for complete reabsorption of glucose and amino acids.
• Most mineral salts are primarily reabsorbed in the proximal convoluted tubule via diffusion and active transport.
• Loop of Henlé facilitates some water reabsorption by osmosis and mineral salts through active transport.
• Distal convoluted tubule continues water reabsorption by osmosis and reabsorbs additional mineral salts through active transport.
• Collecting duct plays a key role in final water reabsorption by osmosis.

Waste Products and Excretion

• Excretory products include urea, uric acid, and creatinine, eliminated by kidneys through urine.

Components of the Human Urinary System

• Kidneys: Primary organs for waste excretion and osmoregulation.
• Ureter: Transports urine from kidneys to bladder.
• Bladder: Stores urine until excretion.
• Urethra: Conducts urine out of the body.

Blood Circulation at the Nephron

• Blood enters the kidneys via the renal artery, branching into arterioles.
• Arterioles lead to the glomerulus, a network of capillaries where filtration occurs.
• After passing through the glomerulus, blood enters surrounding nephron capillaries, merging into venules that form the renal vein, allowing blood to exit the kidney.

Urine Formation

• Two processes essential for urine formation: ultrafiltration and selective reabsorption.
• Ultrafiltration occurs in the renal corpuscle (Bowman’s capsule + glomerulus), requiring high hydrostatic pressure to push small molecules through the basement membrane into Bowman’s capsule.
• Small molecules such as water, glucose, amino acids, and mineral salts pass through; larger molecules remain in the bloodstream.
• This process results in the formation of urine, containing excess water, salts, and metabolic waste.

Osmoregulation and Role of ADH

• Blood plasma water potential is determined by the balance of water and solutes.
• Anti-diuretic hormone (ADH), produced by the hypothalamus and released by the pituitary gland, regulates water potential in blood plasma.
• Increased ADH secretion enhances water absorption in the nephron, aiding in osmoregulation.

Mechanism of Dialysis in Kidney Failure

• Kidney functions include excretion and osmoregulation; kidney failure can be treated with transplants or dialysis.
• Dialysis machines simulate kidney function by filtering blood.
• Blood is drawn from a vein and passed through a partially permeable tubing immersed in dialysis fluid.
• Small waste molecules diffuse from blood into dialysis fluid due to concentration gradients, while blood cells and large molecules remain within the tubing.
• Filtered blood is returned to the patient after purification.