ch 25

• ~200 liters of fluid filtered from blood by kidneys every single day
• Functions of the kidneys

  • Regulate total body water volume and concentration of solutes in water
  • Regulate concentration of ions in ECF
  • Acid-base balance
  • Remove toxins, metabolic wastes, & other foreign substances
  • Hormone production- EPO and renin
• Kidneys

  • Each kidney lies between the parietal peritoneum and dorsal body wall
  • Kidneys are retroperitoneal organs
• Renal hilum


  • Ureters, renal blood vessels, lymphatics, and renal nerve supply enter here
• Adrenal gland


  • Sits immediately superior to each kidney
• Supporting external structures of the kidneys

  • Renal fascia (dense connective tissue that anchors kidneys to surrounding structures)
  • Perirenal fat capsule (fat mass surrounding kidneys that cushions them from physical trauma)
  • Fibrous capsule (thin, transparent capsule that prevents disease from spreading to kidneys from other parts of body)
• Renal Cortex


  • Provides area for glomerular capillaries and blood vessel passage, EPO produced here
• Renal Medulla


  • Contains renal pyramids packed with capillaries & urine-collecting tubules
• Renal Pelvis


  • Open space in center of each kidney, branches to form major calyces that lead into minor calyces at tip of each renal pyramid, function is urine collection from renal medulla
• Blood vessels supplying the kidneys

  • Renal arteries
  • Segmental arteries
  • Interlobar arteries
  • Arcuate arteries
  • Cortical radiate arteries
• Veins draining the kidneys

  • Cortical radiate veins
  • Arcuate veins
  • Interlobar veins
  • Renal veins
• Renal plexus


  • Autonomic nerve fibers & ganglia, sympathetic vasomotor fibers regulate blood supply to each kidney
• Nephron

  Functional unit of the kidney, responsible for forming filtrate and eventually urine
• Renal corpuscle


  • Located entirely within renal cortex, contains glomerulus and glomerular capsule
• Glomerulus

  Cluster of blood vessels, blood enters via afferent arteriole and leaves via efferent arteriole, capillaries are very porous allowing fluid to pass from blood into glomerular capsule to form filtrate
• Glomerular capsule

  • Double-layered structure that completely surrounds glomerular capillaries, inner layer has podocytes with foot processes
• Proximal convoluted tubule (PCT)

  • Leads immediately off from glomerulus, located in renal cortex, has large cuboidal epithelia cells with dense microvilli
• Nephron Loop (Loop of Henle)

  • Travels between renal cortex and renal medulla, descending limb is highly permeable to H2O and low permeability to solutes, ascending limb is highly permeable to solutes and low permeability to H2O, allows kidneys to vary concentration of urine
• Distal convoluted tubule (DCT)

  • Located in cortex, composed of small cuboidal epithelia, smaller diameter than PCT and contain no microvilli
• Collecting Ducts

  • Important cell types are principal cells that maintain Na+ balance and intercalated cells that help maintain acid-base balance, each collecting duct receives filtrate from tubules of multiple nephrons and fuse together to dump urine into minor calyces
• Types of Nephrons

  • Cortical Nephrons (located almost entirely in the cortex with small portion of nephron loop in medulla)
  • Juxtamedullary Nephrons (nephron loops deeply invade renal medulla)
• Glomerulus


  • Maintains high pressure to increase filtrate production
• Peritubular Capillaries


  • Low pressure capillaries arising from efferent arteriole, cling to proximal & distal tubules of cortical nephrons, reabsorb water & solutes from tubule cells, empty into venules
• Vasa Recta

  • Found only on juxtamedullary nephrons, run parallel to long nephron loop, help form concentrated urine
• Juxtaglomerular complex

  • Portion of nephron where distal ascending limb lies against arterioles, regulates blood pressure & filtration rate of the glomerulus
• Macula densa

  • Chemoreceptor cells that monitor NaCl content of filtrate entering distal convoluted tubule
• Granular cells (Juxtaglomerular cells)


  • Specialized smooth muscle cells found in arteriolar walls of afferent arteriole, can sense blood pressure and secrete renin
• Extraglomerular mesangial cells are packed between tubule and arterioles but their function is unclear
• Glomerular Filtration

  1. Production of a cell and protein-free filtrate that serves as the raw material for urine

  2. Pressure forces fluid out of glomerular capillary & into glomerular capsule

  3. Filtration membrane allows passage of water, small solutes into glomerular capsule
• Filtration membrane

  • 3 layers: fenestrated endothelium of capillaries, basement membrane, foot processes of podocytes
• Hydrostatic pressure in glomerular capillaries (HPgc)

  Blood pressure of the glomerular capillaries that forces fluid into the surrounding space
• Hydrostatic pressure in capsular space (HPcs)


  Pressure exerted by filtrate that is already in the glomerular capsule
• Colloid osmotic pressure in glomerular capillaries (OPgc)


  Proteins that are still in capillaries will "pull" water back in
• Glomerular Filtration Rate (GFR)


  The total volume of filtrate formed per minute for all nephrons in the kidneys
• Factors affecting GFR

  • Net Filtration Pressure (NFP)
  • Surface area of capillaries
  • Filtration membrane permeability
• Regulation of GFR


  1. Tightly regulated to maintain extracellular homeostasis and regulate blood pressure

  2. Primary variable controlled is HPgc, when HPgc increases NFP & GFR also increase, when HPgc decreases NFP & GFR decrease

  3. Can be regulated by intrinsic (renal autoregulation) or extrinsic (neural, hormonal) mechanisms
• Renal autoregulation (Intrinsic)


  • Myogenic mechanism (smooth muscle contracts when stretched)
  • Tubuloglomerular Feedback Mechanism (controlled by macula densa monitoring NaCl concentrations)
• Neural Mechanisms (Extrinsic)


  • Sympathetic nervous system releases norepinephrine in response to low blood pressure, causing vascular smooth muscle contraction
• Hormonal Mechanisms (Extrinsic)


  • Renin-Angiotensin-Aldosterone mechanism, overall effect is to increase blood pressure
• Reabsorption


  Selectively moving substances from the filtrate back into the blood, 99% of filtrate is reabsorbed