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FINAL:Urinary System

chapter 25

Kidney Functions - Removal of toxins, metabolic waste, and excess ions from the blood - Regulation of blood volume, chemical composition, and pH - Gluconeogenesis during prolonged fasting - Activation of vitamin D - Endocrine functions (renin and erythropoietin)
Renin regulation of blood pressure and kidney function
Erythropoietin regulation of RBC production
Vascular Resistance in Microcirculation High resistance in afferent and efferent arterioles Causes blood pressure to decline from ~95 mm Hg to ~8 mm Hg in kidneys
Mechanisms of Urine Formation Glomerular filtration Tubular reabsorption Tubular Secretion
Tubular Reabsorption Returns all glucose and amino acids, 99% of water, salt, and other components to the blood
Tubular Secretion Reverse of reabsoprtion: selective addition to urine
Glomerular Filtration Passive process driven by hydrostatic pressure Molecules >5 nm are not filtered (e.g., plasma proteins) and function to maintain colloid osmotic pressure of the blood
Why is the glomerulus an efficient filter -Its filtration membrane is very permeable and it has a large surface area - Glomerular blood pressure is higher (55 mm Hg) than other capillaries
Net Filtration Pressure (NFP) The pressure responsible for filtrate formation (10 mm Hg)
Net Filtration Equation NFP = HPg – (OPg + HPc) net filtration pressure = glomular hydrostatic pressure - (Colloid osmotic pressure of glomerular blood - capsular pressure)
NFP determined by... Glomerular hydrostatic pressure (HPg) the chief force Two opposing forces: Colloid osmotic pressure of glomerular blood (OPg) Capsular pressure (HPc)
Glomerular Filtration Rate (GFR) Volume of filtrate formed per minute by the kidneys (120–125 ml/min)
GFR determined by... - Total surface area available for filtration - Filtration membrane permeability - NFP
GFR mechanisms Intrinsic controls (renal autoregulation) Extrinsic controls
Intrinsic control of GFR Act locally within the kidney Maintains a nearly constant GFR Two types of renal autoregulation - myogenic mechanism - Tubuloglomerylar feedback mechanism, which senses changes in the juxtaglomerular apparatus
Extrinsic control of GFR Nervous and endocrine mechanisms that maintain blood pressure, but affect kidney function
Myogenic Mechanism increased BP: contraction of afferent arterioles - Helps maintain normal GFR - Protects glomeruli from damaging high BP decreased BP: dilation of afferent arterioles - Helps maintain normal GFR
tubular reabsoprtion routes transcellular paracellular
transcellular route (tubular reabsorption) Apical membrane of tubule cells -> Cytosol of tubule cells -> Basolateral membranes of tubule cells -> Endothelium of peritubular capillaries
paracellular route (tubular reabsorption) Between cells - Movement through the interstitial fluid and into the capillary - Limited by tight junctions, but leaky in proximal nephron - Water, Ca2+, Mg2+, K+, and some Na+ in the PCT
What gets reabsorbed in tubular reabsoption - all nutrients -> glucose & amino acids - Ions: Na+, Ca2+, Mg2+, K+ - water
urinary bladder function - temporary urine reservoir
paired ureters - transport urine from the kidneys to the bladder
urethra - transports urine from the bladder out of the body
kidney anatomy - Retroperitoneal and in superior lumbar region - Right kidney is lower than the left - Convex lateral surface, concave medial surface - Renal hilum ->renal sinus - Ureters, renal blood vessels, lymphatics, and nerves enter and exit at the hilum
kidney layers - renal fascia - perirenal fat capsule - fibrous capsule
Renal fascia - The anchoring outer layer of dense fibrous connective tissue
Perirenal fat capsule - A fatty cushion
Fibrous capsule - Prevents spread of infection to kidney
Renal cortex - A granular superficial region
Renal capsule - The cone-shaped medullary (renal) pyramids separated by renal columns
Lobe - A medullary pyramid and its surrounding cortical tissue
Papillary - Tip of pyramid; releases urine into minor calyx
Renal Pelvis - The funnel-shaped tube within the renal sinus
regions of internal kidney - renal cortex - renal medulla - renal pelvis
Renal cortex - granular-appearing superficial region
Renal medulla - medullary renal pyramids: cone shaped - pyramids separated by renal columns (made of cortical tissue) - Lobe: medullary pyramid and its surrounding cortical tissue; about eight lobes per kidney
Renal pelvis - Funnel-shaped tube continuous with ureter -minor calyces - Cup-shaped areas that collect urine draining from pyramidal papillae -major calyces - Areas that collect urine from minor calyces + Empty urine into renal pelvis
Flow of urine - Renal pyramid -> minor calyx -> major calyx -> renal pelvis -> ureter
Blood and Nerve supply - 1/4 (1200 ml) of cardiac output to the kidneys each minute - Arterial flow into and venous flow out of the kidneys follow similar paths - Nerve supply is via sympathetic fibers from the renal plexus
Nephrons - Structural and functional units that form urine - 1 mill. per kidney - 2 main parts - renal corpuscle - glomerulus - bowman's capsule (surrounds glomerulus) - renal tubule: tube
Glomerular capsule - Parietal layer: simple squamous epithelium - Visceral layer: branching epithelial podocytes
Renal Tubule - single layer of epithelial cells - Proximal convoluted tubule (PCT) - Proximal, closest to renal corpuscle - Nephron loop - ascending and descending loops - Distal convoluted tubule (DCT) - Distal, farthest from renal corpuscl
PCT histology - Cuboidal cells - Functions in reabsorption and secretion - Confined to the cortex
Loop of Henle histology - Thin segment usually in descending limb - Simple squamous epithelium - Freely permeable to water Thick segment of ascending limb - Cuboidal to columnar cells
DCT histology - Cuboidal cells with very few microvilli - Function more in secretion than reabsorption - Confined to the cortex
Collecting ducts - receive filtrate from many nephrons - Fuse together to deliver urine through papillae into minor calyces - 2 types of cells - intercalated cells - principal cells
intercalated cells - Cuboidal cells with microvilli - Function in maintaining the acid base balance of the body
principal cells - Cuboidal cells without microvilli - Help maintain the body’s water and salt balance
types of nephrons - cortical nephrons - juxtamedullary nephrons
Cortical nephrons - 85% of nephrons; almost entirely in the cortex
Juxtamedullary nephrons - Long loops of Henle deeply invade the medulla - Extensive thin segments - Important in the production of concentrated urine
Created by: davisobr



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