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Kidney and Nephron
UBSDM 2015 Histology
Question | Answer |
---|---|
Urinary System | Two kidneys that purify the blood and concentrate urine. Two ureters that convey urine to bladder. One bladder that stores urine. Urethra conveys urine from bladder to outside. |
Kidney structures | Hilum (opening), interior cavity (sinus), vascular tree, pelvis of ureter and calyces. Connective tissue capsule. |
Kidney – Parenchyma | Lies between capsule and sinus. Made of cortex and medulla. Medulla contains pyramids, apex of pyramid is papilla. Cortical tissue along the pyramids are renal (Bertin) columns. |
Nephron | Million of so functional units that create urine. Long, Twisted, looping tubule that begins at renal corpuscle. |
Nephron – Segments | Renal Corpuscle, proximal convoluted & straight tubule, thin tubule, distal straight & convoluted tubule. |
Nephron – 3 types | Cortical Nephron which have short loops of Henle, Juxtamedullary Nephron (15%) have long loops, and intermediate nephrons. |
Loop of Henle | the proximal straight tubule (thick descending), thin tubule , and the distal straight tubule (thick Ascending). *Not a consistent definition |
Renal Corpuscle | Proximal tubule is a closed sac with glomerulus capillary bed and inner visceral & outer parietal layer of Bowman’s Capsule. |
Capsular, Urinary, Filtration or Bowman's space | The space between the inner and outer layers of Bowman’s Capsule where filtrate of blood is collected. |
Renal Cortex – Subdivisions – Pars Convoluta | Proximal and Distal convoluted tubules and renal corpuscles are confined here. |
Renal Cortex – Subdivisions – Pars Radiata (Medullary Ray) | Proximal and Distal Straight & Collecting tubules & Ducts are found here. |
Uriniferous Tubule | Nephron and collecting tubule |
Renal Lobule | Located in the cortex, poorly defined as a medullary ray and ½ of the surrounding convoluted cortex. |
Renal Lobe | A pyramid and the overlying cortex. |
Area Cribrosa | Area on a papilla of a pyramid that is punctuated by ducts. |
Renal Arteries – Names | Interlobar (Between Lobes), arcuate (Arch Like), interlobular (Between Lobules) – Arteries. Afferent Arterioles supply glomeruli and drained by Efferent Arterioles |
Renal Veins – Names | The venous drainage of blood from the kidney is through companion veins that follow the course of the arteries. There are interlobular veins, arcuate veins, and interlobar veins. |
Renal Capillary Beds – Types | The Glomerulus, Peritubular bed of the cortex, Vasa Recta of the Medulla. |
Renal Capillary Beds – Glomerulus | Afferent Arterioles enter a dense capillary bed around the Glomerulus. Helps remove urea, creatinine, & Uric acid. |
Renal Capillary Beds – Peritubular | The Efferent Arterioles (Leaving the glomerulus) make a capillary bed around the renal tubules of the cortex. Retrieves Water, amino acids, NaCl, & Glucose from urine. Releases ammonia and penicillin into urine. |
Renal Capillary Bed – Vasa Recta | Formed from efferent arterioles deep in the cortex. They are straight branching capillaries around the tubules. Primarily responsible for concentration of urine through water absorption. |
Ureter & Bladder – microscopic layers | Central Cavity, lumen lined with transitional epithelium, supported by lamina propria, submucosa, inner longitudinal and outer circular layer, 3rd outer longitudinal in lower ureter & Blader. Adventitia or serosa. |
Transitional Epithelium | Several layers thick. Superficial, desmosome connected middle layer and basal layer attached to lamina propria by hemidesmosomes. |
Transitional Epithelium – Umbrella Cells | The superficial layer with tight junctions that prevent urine from crossing cells. Covered in glycosaminoglycans to prevent urine passing through. Change shape as bladder distends. |
Ureter & Bladder – Smooth Muscle | Peristaltic contractions move urine away from kidneys and toward bladder. In the bladder they constrict to push urine out into urethra. Unidirectional flow. |
Ureter & Bladder – Connective Tissue | Folds in the mucoas of the bladder and ureter are formed by the submucosal connective tissue. The unfolding of the mucosa allows lumens to expand when urine is present. |
Urethra | begins as a transitional epithelium but then changes to pseudostratified or stratified columnar before becoming stratified squamous 2) lamina propria 3) submucosa 4) muscularis of inner longitudinal and outer circular muscle 5) an adventitia. |
Renal Corpuscle - Podocytes | Cell found in Glomerulus with a nuclei bulge into Bowman’s Space can be identified. They form the visceral layer of Bowman’s Capsule. |
Renal Corpuscle - Mesangial Cell | Acidophilic cytoplasm. Smooth muscles that help control flow through the glomerulus. Supports endothelium. Captures escaped molecules. |
Renal Corpuscle - Parietal Cell | Form the outer boundary of Bowman’s Capsule. |
Renal Corpuscle - Endothelial Cell | Cells of the fenestrated capillary bed in Bowman’s Capsule. Covered in podocalyxin “-“ charge. Water, glucose, small proteins and small neutral molecules pass freely through fenestrations (70- 90 nm), e.g., platelets RBC are too big |
Renal Corpuscle – Urinary Pole | The end of the corpuscle that is continuous with the proximal convoluted tubule. |
Renal Corpuscle – Vascular Pole | The end of the corpuscle that is continuous with the afferent and efferent arterioles |
Renal Corpuscle – Basal Lamina | Fused layer of endothelium/podocytes. Contains lamina densa and lamina Rara/Lucidae. CollagenIV and L.Densa form barrier. Heparin Sulfate repels –charges. Principle structure of permeability. |
Podocytes – Details | Contain cytoplasmic processes and pedicels that rest on basal lamina. EM visible. Interdigitate with other podocytes. Create filtration slits covered by diaphragm made of nephrin. |
Type 1 Cortical Interstitial Cell | Resembles a fibroblast and secretes erythropoietin. Found in the cortex. |
Proximal Convoluted Tubule Cells | Basolateral membranes folded to form microvilli, apical canaliculi, and basolateral interdigitations. Has brush border. Lots of mitochondria making basal striations. Glyclocalyx coat. 65% of NaCl & H2O resorption. |
Proximal Straight Tubule Cells | similar to those of the proximal convoluted tubule except that the membrane specializations and organelles are fewer in number |
Distal Tubule Cells | Smooth luminal surface. Nuclei are on apical membrane. May have macula densa. Lightly stained and smaller than Proximal. |
Thin Tubules | Like a capillary but nuclei bulge into lumen & have thicker cytoplasm. Both Surfaces of cell can be seen. No blood cells inside. |
Collecting Ducts | Poorly staining cytoplasm and cell borders are visible. Halo around nucleus. Dome shaped luminal surface. |
Collecting Tubule Cells – Principal | (light) cells have defined cell borders, and a light cytoplasm. Ultrastructure reveals poorly developed lateral folds and basal. Impermeable to H2O. ADH present becomes permeable. tight junctions, few organelles and a smooth surface. |
Collecting Tubule Cells- Intercalated | (dark) cells stain more darkly, have apical vesicles, microvilli, more mitochondria than principle cells and mitochondria surround the nucleus. cells secrete hydrogen ions and regulate acid-base balance |
Macula Densa | Narrower & Taller than distal tubule cells they are bunched together. |
Juxtaglomerular Apparatus (JGA) | Formed at vascular pole of glomerulus by afferent/efferent arteriole extraglomerular mesangial cells, macula densa. Plays role in blood pressure regulation. |