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URO revision (Kidney SA (BC and glomerulus (Afferent (Hydrostatic pressure…
URO revision
Kidney SA
Why?
- Kidney + gonads intermediate mesoderm: urogenital ridge (nephrogenic cord)
- Pronephros: Cervical end forms nephrostomes
- Grow, fuse and extend in caudal direction, form pronephric duct
- Arterioles extend from aorta to give glomeruli
- Pronephros never functions properly and degenerates
- Mesonephros
- Wolffian/mesonephric ducts forms caudal to pronephros
- 7-10 tubules drain into duct with glomeruli invaginating from capillaries
- Function until 4th month
- Degenerates after
- Metanephros
- Ureteric bud forms as outgrowth of Wolffian duct
- Mesenchyme develops from mesoderm and partly the duct
- Migration intermediate mesoderm differentiates into nephrons
- Migrates upwards towards lumbar region as ureters (ureteric bud)
- Elongates 6-9 week
- Gonads
- IM gives mesothelium and primordial germ cells
- Migrate along dorsal mesentery to gonadal ridges
- Diff around 7 weeks
- SRY causes gonads descend into labioscrotal swellings
Blood supply and Innervation
- Parasympathetic: Vagus nerve - Vasoconstriction
- Sympathetic T5-T9 outflow - greater splanchnic nerve - coeliac ganglion - kidney
- T9-T11: lesser splanchnic nerve - Coeliac/articorenal ganglion - Kidney
- T12: Least splanchnic nerve - renal plexus/ganglion - Kidney
- Renal artery (directly off aorta just inferior to SMA) (right longer than left)
- Renal veins directly into IVC - Left longer than right
Nephrons
Juxtamedullary
(15-20%)
- BC and glomerulus in deep cortex with long nephron loop extending into mddep medulla
- Surrounded by vasa recta and peritubular capillaries
Cortical
(80-85%)
- Bowman's capsule and glomerulus in outer cortex with short nephron loops
- Extends into outer medulla
- Surrounded by peritubular capillaries
BC and glomerulus
Afferent
- Hydrostatic pressure 50mmHg- DRIVING FORCE
- Plasma proteins don't pass through - draws water towards plasma - Colloid osmotic/oncotic pressure - 25mmHg
- Presence of fluid in nephron exerts pressure towards plasma - back or filtrate or tubular pressure - 10mmHg
- NET filtration = 50- (25+10) 15mmHg piushing into nephron
Efferent
- Hydrostatic pressure = 45mmHg
- Oncotic pressure = 35mmHg- less water in plasma relative to proteins so protein conc increases
- Tubular pressure = 10mmHg
- Net filtration = 45- (35+10) = 0mmHg pushing fluid into nephron
- NOT NET FILTRATION
Afferent more dilated efferent: High hydrostatic pressure
Filter:
- Capillary endothelial cells: free passage
- Basement membrane
- Lamina rara interna: fused to capillaries
- Lamina densa: thick
- Lamina rara externa: fused to podocytes (-ive charge, repels proteins MOST EFFECTIVE FILTER)
- Podocytes: foot processes, cross over: filtration slits: prevent proteins + large molecules entering
GFR: Amount water and unbound, small blood products filtered from glomerulus into Bowman's capsule unit of time
Totally inert substances can pass through
- Inulin: not practical clinically but highly accurate
- Creatinine: Little excretion/secretion but time consuming
-
Prediction from serum creatinine and patient characteristics
- Age, weight,gender and ethnicity
- CKD-EPI most accurate
Kidney Parts
-
Loop of Henle
CCM
Thick Ascending limb
- 3Na+/2K+ ATPase pumps sodium interstitium creating gradient
- Sodium moves through Na+/K+/Cl- co transporter
- Moves down conc gradient, creates energy to pump K+ and Cl- into cells
- Potassium and chloride move into interstitium via ion channels
- K+ secreted into tubule via ROMK to maintain K+ balance
- Presence of NACl in interstitium creates osmotic gradient at attracts water
- Hyperosmotic solution
Thin Ascending limb
- Impermeable to water by permeable to Cl-
- Moves into interstitium down electrochemical gradient
- Na+ moves paracellularly
Thin Descending limb
- Solution entering ascending limb then more conc as water has been removed
- More conc ions enter institium at bottom of loop
- Creates larger osmotic gradient
- More water leaves descending lub to reduce gradeint
- Even more conc ions enter interstitium
- More water leaves
- Continues until maximal gradient is established, largest in deep medulla
- Impermeable to ions, permeable to water
- Hyperosmotic fluid arrives and moves down osmotic gradient via osmosis into interstitium
- Reduces osmotic gradient from top of loop down
DCT and Collecting Duct
Collecting duct
- Very dilute solution enters
- Regulated by ADH
Released in response to increase plasma osmolarity or reduced mean arterial BP
- Binds to V2 receptors
- Water into AQP2 vesicles fuse with apical membrane
- Water moves via AQP2 and AQP3 (basolateral membrane) down osmotic gradient
- Into blood and interstitium
Urea
- Both impermeable to urea - permeable with ADH
- ADH binds to V2R: vesicles containing urea transporters fuse with apical membrane (basolateral)
- Urea reabsorbed via dacilitated diffusion into interstitum and blood
Contributes to osmotic gradient in medulla
- Enters LoH via UT and can be excreted or recycled
DCT
- Fluid entering very low NaCl conc
- 3Na+/2K+ ATPase pumps sodium into blood creating gradient
- Na+ mainly moves through ENac into blood
- Cl- moves paracellularly into blood but also via Cl- channels and Na+/Cl- cotransporter
- Lumen very -ive despite ROMK allowing K+ to move in
- Cl- moves into cell via Cl- channels
- Into blood via Cl-/HCO3- antiporter
Autoregulation
Reduced renal perfusion
- Increased vasoconstriction of efferent
- Reduced vasoconstriction of afferent
Increased renal perfusion/BP
- Stretching of afferent arterioles: vasoconstriction
- Increased vasoconstriction afferent
- Reduced vasoconstriction of efferent
Anatomy urinary system
Kidneys:
Function
- Water and electrolyte balance
- Maintain acid-base balance blood
Position
- Behind peritoneum, high posterior abdo wall, either side vertebral column
- Right kidney lower due to liver
- Left; under ribs XI and XII
- Right: rib XII
- Ureter: transverse process lumbar vertebrae
Coverings
- Fibrous capsule
- Perirenal fat (sep renal fascia)
- Pararenal fat
- Renal fascia
- Fascia transversalis
- Quadratus lumborium and Psoas major
Anterior relations
- Right: liver: suprarenal gland, descedning part of duodenum, right colic flexure, SI
- Left: Suprarenal glands, stomach, spleen, pancreas, left colic flexure, descending colon, and jejunum
Structure
- Cortex: renal Columns
- Medulla:12 renal pyramids
- Base (contains nephrons)
- Apex (renal papilla)
- Minor and major calyx
- Renal pelvis
- Hilum
- Ureter
- Renal vein
- Renal artery (superior to ureter and posterior to vein)
- Pyramid has base containing nephrons
- Apex which from renal papilla
- Collecting duct drains to
- Papilla drains to minor calyx
- Several minor calyces drain to major calyx
- Major calyces drain to renal pelvis
- Drain to ureter
Tubular system
- Collecting ducts
- Minor calyx
- Major calyx
- Renal pelvis
- Ureter
- Bowman's capsule: Ultrafiltration
- PCT: selective reabsorption
- Loop Henle: Osmoregulation (salt gradient)
- DCT: Selective reabosrption
- Collecting duct: Osmoregulation (water retention)
Erythropoiesis
- Produced by fibroblast like interstitial cells
- Hypoxia- Reduced pO2 in blood
- Erythropoietin secretion
- Stimulates red bone to produce RBC
- PO2 returned back to normal