Overview
This lecture covers the microanatomy of the kidney, focusing on the structure and function of the nephron—the kidney's basic functional unit.
Nephron Structure and Types
- The nephron is the kidney's functional unit, responsible for filtering waste from blood.
- Each kidney contains approximately one million nephrons.
- Nephrons have two main parts: the renal corpuscle and the tubular network.
- The renal corpuscle consists of Bowman's capsule surrounding a glomerulus (a tuft of capillaries).
- There are two types of nephrons: cortical (located mainly in the cortex) and juxtamedullary (dive deep into the medulla).
- Cortical nephrons are more numerous; juxtamedullary nephrons have longer loops of Henle for effective concentration of urine.
Blood Supply and Filtration
- Renal blood flow: renal artery → lobar arteries → segmental arteries → arcuate arteries → cortical radiate arteries → glomerulus.
- The glomerulus receives blood from an afferent arteriole and drains via an efferent arteriole.
- Bowman's capsule collects the filtrate that passes from blood through the glomerulus.
Renal Corpuscle and Associated Cells
- The glomerulus is surrounded by Bowman's capsule, which has visceral (inner) and parietal (outer) layers.
- Intraglomerular mesangial cells provide structural support and phagocytosis within the glomerulus.
- Extraglomerular mesangial cells are located near the glomerulus and aid in regulation.
- The macula densa, specialized cells near the distal convoluted tubule, sense tubular content and help regulate filtration rate.
- Granulosa (granular) cells are specialized smooth muscle cells involved in regulation.
Tubular System Anatomy
- Filtrate flows from Bowman's capsule to the proximal convoluted tubule (PCT).
- The filtrate passes through the descending thick limb, descending thin limb, ascending thin limb, and ascending thick limb of the loop of Henle.
- Then, filtrate enters the distal convoluted tubule (DCT), draining into a collecting duct.
- Collecting ducts run through the medulla, converge at the papilla, and collect urine for excretion.
Key Terms & Definitions
- Nephron — the kidney's functional unit that filters blood and forms urine.
- Renal corpuscle — part of the nephron; includes Bowman's capsule and the glomerulus.
- Glomerulus — tuft of capillaries inside Bowman's capsule where filtration occurs.
- Bowman’s capsule — double-layered sac surrounding the glomerulus, collects filtrate.
- Mesangial cells — support and regulate the glomerulus; intraglomerular (inside) and extraglomerular (outside).
- Macula densa — cells in the distal tubule that sense sodium/chloride and regulate filtration.
- Granulosa cells — specialized smooth muscle cells involved in nephron regulation.
- Proximal convoluted tubule (PCT) — first tubular segment after Bowman's capsule for reabsorption.
- Loop of Henle — tubule section with descending and ascending limbs, crucial for urine concentration.
- Distal convoluted tubule (DCT) — segment after the loop of Henle that fine-tunes filtrate.
- Collecting duct — receives filtrate from several nephrons and delivers urine to the papilla.
Action Items / Next Steps
- Review diagrams of nephron anatomy for visual reinforcement.
- Memorize the flow of filtrate through the nephron segments.
- Study the roles of different cell types (mesangial, macula densa, granular).