Kidney Function and Structure: Nephrons, Filtration, and Homeostasis

Kidney

Organ that removes nitrogenous wastes, regulates water balance, regulates ion concentration, maintains blood pH, and maintains homeostasis.

Nitrogenous Waste

Main waste product is urea, produced in the liver from amino acid breakdown.

Cortex

Region of the kidney that contains glomeruli and convoluted tubules.

Medulla

Region of the kidney that contains loops of Henle and collecting ducts.

Renal pelvis

Collects urine from the kidney.

Nephron

Functional unit of the kidney, with each kidney containing approximately 1 million nephrons.

Bowman's capsule

Structure that collects filtrate in the nephron.

Glomerulus

Network of capillaries inside Bowman's capsule responsible for ultrafiltration.

Ultrafiltration

Pressure-driven filtration of blood from glomerulus into Bowman's capsule.

Filtrate

Fluid entering Bowman's capsule after ultrafiltration.

Selective Reabsorption

Process where useful substances are reabsorbed back into blood.

Proximal convoluted tubule (PCT)

Main site for reabsorption of useful substances.

Loop of Henle

Creates osmotic gradient in medulla.

Countercurrent Multiplier

Mechanism producing concentration gradient in medulla.

Distal Convoluted Tubule (DCT)

Functions in ion regulation, pH regulation, and hormone-controlled transport.

Collecting duct

Adjusts final water content of urine.

Osmoregulation

Control of water potential and solute concentration in body fluids.

Antidiuretic Hormone (ADH)

Hormone produced by hypothalamus that increases water reabsorption in collecting duct.

Aquaporins

Water channel proteins that increase water permeability in collecting duct cells.

Osmolarity

Concentration of dissolved solutes in solution.

Kidney Failure

Results in buildup of wastes, fluid imbalance, and electrolyte imbalance.

Dialysis

Artificial removal of wastes and excess water from blood.

Comparison of Blood, Filtrate, and Urine

Glucose is present in blood and filtrate but normally absent in urine; proteins are present in blood but absent in filtrate and urine; urea is present in blood and filtrate with high concentration in urine.