Overview
This lecture provides an overview of kidney structure and function, focusing on the nephron as the key unit responsible for filtration, reabsorption, and urine formation.
Structure and Function of the Kidney
- Kidneys maintain water balance, electrolyte levels, blood pressure, and excrete waste.
- Each kidney contains about one million microscopic nephrons.
- The kidney has two main regions: the outer renal cortex and the inner renal medulla.
The Nephron: Functional Unit of the Kidney
- The nephron is the site of blood filtration and selective reabsorption.
- Blood enters the nephron via the afferent arteriole into the glomerulus (a porous capillary network).
- The glomerulus is surrounded by Bowman's capsule, where initial filtration occurs.
- About one-fifth of blood plasma is filtered into Bowman's space as filtrate.
Filtration and Reabsorption Process
- Filtrate contains small ions (e.g., sodium), glucose, and amino acids; large proteins and red blood cells remain in blood.
- Proximal convoluted tubule reabsorbs glucose, sodium, amino acids, and some water back into blood via active transport using ATP.
- Remaining filtrate moves to the loop of Henle.
The Role of the Loop of Henle
- The descending limb is permeable only to water, allowing water to be reabsorbed due to the salty medulla.
- The ascending limb actively pumps out salts (sodium, potassium, chloride) to create a hypertonic medulla, but is impermeable to water.
- This process concentrates the filtrate and conserves water.
Distal Tubule and Collecting Duct
- Filtrate enters the distal convoluted tubule for further reabsorption of sodium, calcium, and water.
- Processed filtrate (mainly waste and excess water) goes to the collecting duct.
- Collecting ducts pass through salty medulla; permeability is regulated by antidiuretic hormone (ADH) to control final water reabsorption and urine concentration.
Key Terms & Definitions
- Nephron — functional microscopic unit of the kidney performing filtration and reabsorption.
- Renal cortex — outer kidney region.
- Renal medulla — inner kidney region.
- Glomerulus — capillary bundle where blood filtration begins.
- Bowman's capsule — structure surrounding glomerulus; collects filtrate.
- Proximal convoluted tubule — tubule section reabsorbing nutrients and water.
- Loop of Henle — segment regulating water and salt reabsorption.
- Distal convoluted tubule — further reabsorbs salts and water.
- Collecting duct — final channel for urine concentration.
- Antidiuretic hormone (ADH) — hormone controlling collecting duct permeability to water.
Action Items / Next Steps
- Review the structure and function of each nephron section.
- Study how active transport and osmosis contribute to nephron function.
- Prepare for deeper analysis of proximal tubule cell structure in future lessons.