histology - urinary system presentation
TRANSCRIPT
What we’ll talk about…
• Structure and function of nephrons
• Filtration barrier in renal corpuscles
• Segments of nephron that reabsorb solutes and water
• Feedback to regulate the filtration rate in individual nephrons
The kidney performs several critical functions.
• Excretion of metabolic waste products
• Water and electrolyte homeostasis
• pH homeostasis
• Renin production
• Vitamin D
Nephrons filter blood and reabsorb solutes and water.
• Filtration Unit - Renal Corpuscle
• Capillaries
• Basement Membrane
• Epithelium
• Reabsorption - Long Tubule
The kidney contains two types of nephrons to filter blood and regulate electrolyte concentration and pH.
Thin Descending
Thin Ascending
Collecting Duct
Medulla Cortex
Thick Ascending
Efferent Arteriole
Proximal Convoluted Tubule
Renal Corpuscle
Afferent Arteriole
Distal Convoluted Tubule
Connecting Tubule
Arcuate arteries define the border between cortex and medulla in the kidney.
Arcuate Artery
Collecting Ducts
Renal Corpuscle
Medulla Cortex
Renal corpuscles filter blood from a tuft of capillaries into Bowman’s space.
Distal Convoluted TubuleBowman’s Capsule
Podocyte
Capillary
Bowman’s Space
Mesangial CellArteriole
Macula Densa
Starling forces determine the direction of fluid flow in the glomerular capillaries.
Afferent Arteriole
Efferent Arteriole
Capillary Hydrostatic
Bowman’s Oncotic Bowman’s Hydrostatic
Capillary Oncotic
Renal corpuscles filter solutes based on size and charge.
1.8 2.2 2.6 3.43.0 3.8 4.2 4.60
0.2
0.4
0.6
0.8
1.0
Effective Molecular Radius (nm)
Cle
aran
ce R
atio
(Cx/
Cin)
Cationic Molecules
Neutral Molecules
Anionic Molecules
The filtration barrier consists of fenestrated endothelium, basement membrane and podocytes.
Foot Process
Slit Diaphragm
Basement MembraneEndothelial Cell
Fenestrae
Blood
Rara Interna
Rara Externa
Lamina Densa
Basement Membrane
Glycocalyx
Foot Process
Endothelium
Podocytes form foot processes that attach to the basement membrane.
Podocyte
Capillary Lumen
Bowman’s Space
Foot ProcessBasement Membrane
Endothelial Cell
Slit diaphagms span the distance between foot processes and contribute to the filtration barrier.
Basement Membrane
Endothelial Cell
Slit Diaphragm
Rara Externa
Lamina Densa
Rara Interna
Plasma
Urinary Space
Foot ProcessFoot Process
Foot processes from adjacent podocytes interdigitate and surround capillaries.
Foot Processes - Cell 1
Foot Processes - Cell 2
Podocyte
Podocyte Process
Different stains and microscopy methods are used to visualize features of renal corpuscles.
H&E PAS
Silver Stain Electron Micrograph
The proximal convoluted tubule absorbs most of the water and important biological solutes.
Proximal Convoluted Tubule
Microvilli on the apical surface and basal striations increase the surface area of epithelial cells.
Microvilli
Basal Striations
Mitochondrion
The loop of Henle in juxtamedullary nephrons increases the osmolality of the interstitium.
Thick Ascending Limb
Proximal Straight Tubule
Thin Limb
The distal convoluted tubule reabsorbs sodium and resides near the renal corpuscle.
Renal Corpuscle
Proximal Convoluted Tubule
Distal Convoluted Tubule
Cells of the distal convoluted tubule and afferent arteriole form the juxtamedullary complex.
Afferent Arteriole
Juxtaglomerular CellMacula Densa
Distal Convoluted Tubule
Macula densa cells sense sodium to regulate the glomerular filtration rate.
Proximal Convoluted Tubule
Distal Convoluted Tubule
Afferent Arteriole
Efferent Arteriole
Macula Densa Cells
Glomerulus
Juxtaglomerular Cells
Smooth Muscle
Sodium chloride uptake triggers release of ATP and adenosine which constricts the afferent arteriole.
Afferent Arteriole
DCT Lumen
NKCC2
Na2+ K+ Cl-
ATP
Macula Densa Cell
Ca2+
ATPAdenosine
AdenosineCl-
K+
Contraction
Collecting ducts contain intercalated cells and principle cells to regulate pH and water absorption.
Collecting Duct
The ureter is a muscular tube that connects the kidney to the urinary bladder.
Transitional Epithelium
Circular Smooth Muscle
Longitudinal Smooth Muscle
The urinary bladder is lined by a transitional epithelium that stretches as urine fills the bladder.
Transitional Epithelium
Basement Membrane
Smooth Muscle
Take home messages…
• Nephrons filter blood and reabsorb biologically important molecules.
• A filtration barrier of endothelium, basement membrane and podocyte determines what passes from blood into urine.
• Segments of the nephron tube have different properties to absorb biological molecules, ions and water.
• The juxtaglomerular complex generates feedback to regulate the glomerular filtration rate.