Urinary System 1

• Components of the Urinary System

  1. Kidneys
  2. Ureters - Bring fluids from kidney to urinary bladder
  3. Urinary Bladder - storage tank for urine
  4. Urethra - carries fluid outside the body
• Functions of the Urinary System

  1. Fluid filtration - filter plasma of blood
  2. Regulates blood volume - by increasing amount of fluid filtered in the kidneys, blood volume decreases
  3. Maintains salt/water balance
  4. Maintains acid/base balance
  5. Gluconeogenesis - production of new glucose
  6. Renin production - leads to production of aldosterone
  7. Erythropoietin production - production of RBC
  8. Activates vitamin D
• Structure of the Kidney

  Capsule - external covering of the kidney

  Cortex - Outer region

  Medulla - inner region

  Renal Pelvis - flat region in the middle

  Renal Pyramids - triangle shaped structures

  Renal Columns - structures in between pyramids

  Major Calyces - where minor calyces empty

  Minor calyces - where collecting ducts end

  Collecting ducts - stripes in renal pyramids

  Hilum - indentation

  Renal Sinus - within the pelvis where major calyces dump into
• Supportive Layers of the Kidney

  Renal Capsule - outermost layer of the kidney

  Adipose Capsule - functions in protection and insulation

  Renal Fascia - holds kidney to abdominal wall
• The function unit of the kidney is the nephron
• Nephron


  Glomerulus - capillary bed of kidney between two arterioles; has high blood pressure

  Renal Tubule

  1. Glomerular Capsule
  2. Proximal Convoluted Tubule
  3. Loop of henle
  4. Distal Convoluted Tubule

  Collecting Ducts - make up renal pyramids

  Renal Corpuscle - glomerulus + bowman's capsule
• Nephron Vasculature

  Afferent Arteriole - deliver blood to glomerulus

  Efferent Arteriole - carry blood away from glomerulus

  Glomerulus - capillary bed

  Peritubular capillaries - fed by efferent arteriole, found in cortical nephron

  Vasa Recta - found in juxtamedullary nephron
• Juxtaglomerular Apparatus

  • Modification where the distal convoluted tubule runs against the afferent arteriole
  • In Afferent Arteriole
  • Juxtaglomerular Cells
  • Monitor blood pressure
  • Secrete renin
  • In Distal Convoluted Tubule
  • Macula Densa Cells
  • Affect diameter of the blood vessel
  • Monitor ion concentration
  • Activate JG cells
• Filtration Membrane


  Fenestrated Endothelium

  • Allows everything except blood cells

  Podocytes

  • Around basement membrane
  • Impermeable extensions called pedicels
  • Create filtration slits

  Basement Membrane

  • Wraps the capillaries
  • Limit size of what can pass - no proteins
  • Hold electrical charges
• Filtration Pressures


  Glomerular Hydrostatic Pressure

  • Pressure of blood inside the glomerulus

  Colloid osmotic pressure of intracapsular space

  • Pressure that draws fluid out into Bowman's capsule due to presence of proteins. Usually zero

  Colloid osmotic pressure of glomerular blood

  • Pressure that draws fluid into glomerulus from Bowman's capsule due to presence of proteins

  Capsular Hydrostatic Pressure

  • Fluid pressure inside the capsule
  • Works in opposition to glomerular hydrostatic pressure, usually lower
• When afferent arterioles constrict, renal blood flow decreases and glomerular filtration rate decreases
• When afferent arterioles dilate, renal blood flow increases and glomerular filtration rate increases
• When efferent arterioles constrict, renal blood flow decreases and glomerular filtration rate increases
• When efferent arterioles dilate, renal blood flow increases and glomerular filtration rate decreases
• Myogenic mechanism and tubuloglomerular mechanism of autoregulation are intrinsic
• Neural and hormonal control over filtration are extrinsic
• Myogenic Mechanism of Autoregulation

  When there is low bp, afferent arterioles will dilate which increases filtration rate
• Tubuloglomerular mechanism of autoregulation

  Macula densa cells detect low concentration of filtrate in distal convoluted tubule. Cause vasodilation which increases filtration rate
• Neural Control over Filtration regulation

  When BP is low sympathetic impulses cause release of norepinephrine which causes systemic vasoconstriction to increase BP which increases filtration
• Hormonal Control over filtration regulation

  JG cell in the afferent arteriole detect low BP and releases renin.

  • Renin can increase BP intrinsic and extrinsically

  1. Extrinsic

  • Cause systemic vasoconstriction

  2. Intrinsic

  • Renin combines with angiotensinogen to make angiotensin II which releases aldosterone. Aldosterone increases sodium reabsorption which increases blood volume, BP, and filtration
• Other factors affecting filtration rate

  Prostalglandins

  • Vasodilators, increase GFR

  Nitric Oxide

  • Vasodilators, increase GFR

  Adenosine

  • Vasoconstrictor, decrease GFR

  Endothelin

  • Vasoconstrictor, decrease GFR
• Types of Nephrone

  Cortical

  • More common
  • Mostly in cortex
  • Less concentrated urine

  Juxtamedullary

  • Less common
  • Mostly in medulla
  • More concentrated urine
• The deeper into the medulla the more concentrated the urine
• If were dehydrated, our blood flow will go to more juxtamedullary nephrons to conserve water
• Glomerular Filtration

  • Activate process
  • Occurs in glomerulus
  • Nonselective
  • Affected by basement membrane and pedicles
  • Movement of Flow:
  • Blood (afferent arteriole) -> tubule
• Tubular Reabsorption

  • Both active and passive process
  • Occurs after bowman's capsule
  • Selective
  • Controlled by hormones
  • Movement of fluid:
  • Tubule -> blood (capillaries)
• Tubular Secretion

  • Both active and passive process
  • Occurs mainly in proximal convoluted tubule
  • Also minimally in DCT
  • Selective
  • Movement of fluid:
  • Blood (capillaries) -> tubule
• During Tubular reabsorption, glucose and amino acids are completely reabsorbed in the proximal convoluted tubule under normal conditions

  Water and ionic reabsorption is under hormonal control
• Glomerular Hydrostatic Pressure

  Source of pressure: fluids in the blood

  Drives or limits exchange: drives

  Where is it pushing fluid: toward capsule
• Capsular Hydrostatic Pressure

  Source of pressure: fluid in the capsule

  Drives or limits exchange: limits

  Where is it pushing fluid: toward glomerulus
• Colloid Osmotic Pressure of Intracapsular Space

  Source of pressure: Proteins in the capsule

  Where is it pulling fluid: Into capsule, out of glomerulus

  Amount of effect: should be zero
• Colloid Osmotic Pressure of Glomerular Blood

  Source of pressure: fluids in the glomerulus/blood

  Where is it pulling fluid: into glomerulus/blood, out of capsule

  Amount of effect: minimal
• The most important pressure determining movement is glomerular hydrostatic pressure
• Tubular Reabsorption


  Begins immediately in proximal convoluted tubule

  • 99% of water, 99.5% of sodium, 100% of glucose
  • 3 fluid compartment: tubule, interstitial space, blood vessel
  • Transepithelial process: lumen -> cell of tubule wall -> epithelial space -> blood vessel
  • Tight junctions
  • Paracellular channels: ions can cross as shortcut and get to interstitial space first
• Action by Region


  Proximal Convoluted Tubule

  • Most reabsorption takes place here
  • Both active and passive process

  Loop of Henle

  • Controls urine concentration
  • Descending Limb
  • Permeable to water - makes filtrate more concentrated
  • Passive process
  • Ascending Limb
  • Impermeable to water - makes filtrate less concentrated
• The highest concentration of ions is at the bottom of the loop of Henle because the filtrate is most concentrated after the descending limb
• Countercurrent Mechanism

  Two Examples

  1. The descending and ascending loop run next to each other in opposite directions which increases efficiency
  2. Blood flow from cappilaries run in the opposite direction of the tubule which increases efficiency
• Renal Gradient

  To change concentration of urine: switch from cortical nephron to juxtamedullary nephron

  Deeper into medulla -> more reabsoprtion of water -> tissue gets more concentrated
• Urine Formation

  • Concentration of urine dependent on ADH secretion
  • Less -> produces dilute urine
  • More -> produces more concentrated urine
  • ADH production increases water reabsorption from collecting duct
  • Opens aquaporins
• Micturition is the act of emptying the bladder aka peeing