Urinary System

• Urinary system


  Eliminates nitrogenous wastes from body

  Regulates water, electrolyte and acid-base balance of blood.
• function of kidneys


  - regulate H2O + electrolyte

  - Long-term acid-base balance

  - excretes metabolic wastes, toxins, drugs

  - produces erythropoietin (RBC prod.) and renin (bp reg.)

  - activates vit D
• Ureters


  transport urine from kidneys to urinary bladder
• Urinary bladder


  stores urine temporarily
• Urethra


  transports urine out of body
• renal cortex


  superficial region of kidney
• renal medulla


  inner region of the kidney composed of renal pyramids
• renal pelvis


  funnel-shaped tube continuous with ureter

  
• Renal Pelvis: minor calyces


  collect urine draining from pyramidal papillae

  
• Renal pelvis: major calyces


  collect urine from minor calyces

  
• urine flow


  Renal pyramid → minor calyx → major calyx → renal pelvis → ureter
• Blood and nerve supply to kidney

  Cleanses blood and adjust its composition so it has a rich blood supply
• renal arteries


  deliver 1/4 of CO to kidneys per min
• arterial flow in kidneys

  renal → segmental → interlobar

  → arcuate → cortical radiate (interlobular)
• venous flow in kidneys

  cortical radiate → arcuate → interlobar → renal veins
• Nephrons


  Functional units of kidneys

  
• glomerulus


  group of capillaries for filtration

  
• glomerular capsule


  surrounds glomerulus

  - parietal layer = simple squamous

  - visceral layer = epithelial podocytes

  
• proximal convoluted tubule (PCT)


  cuboidal cells w/ dense microvilli and large mitochondria

  function: reabsorption, secretion

  
• nephron loop (loop of Henle)


  u-shaped structure

  - descending limb = simple squamous

  - ascending limb = cuboidal/columnar cells

  
• distal convoluted tubule (DCT)


  Cuboidal cells with very few microvilli

  Function: mainly secretion

  
• Collecting Duct (CD)


  receive filtrate

  
  

  principal cells = short microvilli, maintain water/Na balance

  
  

  intercalated cells = abundant microvilli, cuboidal cells, maintain acid-base balance

  
• cortical nephrons


  - short nephron loop

  - glomerulus further from cortex-medulla junction

  - efferent arterioles supplies peritubular capillaries

  
• juxtamedullary nephrons


  - long nephron loop

  - glomerulus closer to the cortex-medulla junction

  - efferent arteriole supplies vasa recta

  
• peritubular capillaries


  capillaries for absorption of water and solutes

  
• vasa recta


  capillaries for urineformation

  
• The __ feeds into the glomerulus and the ___ drains the glomerulus.

  afferent arteriole, efferent arteriole
• juxtaglomerular complex


  regulate filtrate formation and BP

  
• macula densa


  - tall, packed cells

  - chemoreceptors that sense NaCl content of filtrate
• granular cells (JG cells)


  - smooth muscle cells of arteriole

  - sense BP in afferent arteriole

  - granules that have renin
• mesangial cells


  pass signals between macula densa and granular cells
• urine


  1.5 L made daily

  - metabolic wastes and unneeded substances
• 1. Glomerular Filtration


  passive movement of substances from blood through filtration membrane into glomerular capsule (no reabsorption)
• filtration membrane


  allow small molecules to pass (water, monomers, wastes)

  - no cells pass
• layers of filtration membrane

  fenestrated endothelium, basement membrane, foot processes of podocytes

  
• Hydrostatic pressure in glomerular capillaries (HPgc)

  - outward P

  - 55mmHg (high since efferent arteriole has higher resistance and smaller diameter than afferent)
• hydrostatic pressure in capsular space (HPcs)


  - inward P; filtrate P in capsule

  - 15 mm Hg
• Colloid osmotic pressure in capillaries (OPgc)


  - inward P; protein pull in blood

  - 30 mm Hg
• Net Filtration Pressure (NFP)

  total pressure that promotes filtration = 10 mm Hg
• Glomerular Filtration Rate (GFR)


  - volume of filtrate formed per minute by both kidneys (normal = 120-125 ml/min)

  - increase NFP, SA, permeability = increase GFR