URINARY

• Urinary System


  • Major excretory system of the body
  • Consists of 2 kidneys, 2 ureters, urinary bladder, and urethra
  • Filters the blood
• Functions of the Urinary System

  • Excretion: Waste products such as ammonia, creatinine, and urea are excreted
  • Regulation of blood volume and pressure
  • Regulation of blood solute concentrations
  • Regulation of extracellular fluid pH
  • Regulation of red blood cell synthesis
  • Regulation of vitamin D synthesis
• Renal hypertension


  Kidneys are inducing high blood pressure
• Erythropoietin


  Responsible for red blood cell production
• Calcitriol


  Secreted by the kidney and helps to stimulate calcium ion production for vitamin D synthesis
• Kidney


  • Primary excretory organ
  • Retroperitoneal; behind the peritoneum or abdominal cavity
  • Located on each side of the vertebral column
  • Bean-shaped organs
  • Size equivalent to tightly clenched fist and bar soap
  • Length: 10-12 cm (4-5")
  • Width: 5-7 cm (2-3")
  • Thickness: 3cm (1')
  • Mass: 135-150 g
  • Right kidney is lower than the left as the upper superior part of the right side is occupied by the liver
• External Layers of Kidney

  • Renal corpuscles: Deep layer of connective tissue
  • Adipose corpuscles: Middle fatty layer
  • Renal fascia: Outer layer that helps secure the kidney
• Inner Layers of Kidney

  • Cortex: Outer layer after renal capsule
  • Medulla: Inner layer
  • Renal Pyramid: Cone-shaped structures in the medulla
  • Renal Papilla: Tips of the renal pyramid
  • Renal Column: Area where cortex extends between renal pyramids
  • Hilum: Medial side of each kidney
  • Renal Sinus: Where blood vessels, nerves, and lymphatic vessels pass through
• Urine Flow


  1. Renal papilla

  2. Minor Calyx

  3. Major Calyx

  4. Renal pelvis

  5. Ureters

  6. Urinary bladder

  7. Urethra
• Nephron


  • Functional unit of kidney where filtration occurs
  • Approx. 1.3 million in each kidney
• Regions of Nephron


  • Renal Capsule (corpuscles)
  • Proximal convoluted tubule
  • Loop of Henle
  • Distal convoluted tubule and collecting ducts
  • Collecting Ducts
  • Papillary Ducts
  • Calyx
• Renal Capsule (corpuscles)


  • Consists of a glomerulus and bowman's capsule
  • Glomerulus: Network of capillaries from afferent arterioles and exits via efferent arterioles
  • Bowman capsule: Cup-like structure surrounding the glomerulus
  • Parietal layer: Outer layer with podocytes
  • Visceral layer: Closes to the organ
• Macula densa


  • Group of crowded columnar tubule cells of ascending limb of the loop of Henle or distal convoluted tubule
• Juxtaglomerular cells (JG)


  • Modified smooth muscle fibers on the wall of afferent arteriole
• Juxtaglomerular Apparatus


  Juxtaglomerular cells + Macula densa. It helps to regulate blood pressure within the kidneys.
• Types of Nephrons


  • Cortical Nephrons (80-85%)
  • Juxtamedullary Nephrons (15-20%)
• Cortical Nephrons


  • Renal corpuscles lie in the outer portion of the renal cortex
  • Short loops of Henle in the cortex and penetrate only outer region of renal medulla
  • Receives blood supply from peritubular capillaries from efferent arterioles
  • Ascending loop of Henle has 2 portions: thin ascending and thick ascending
• Juxtamedullary Nephrons


  • Renal corpuscles lie deep in the cortex close to the medulla
  • Long loops of Henle extending into deep regions of the medulla (for water conservation)
  • Receives blood supply from peritubular capillaries and from the vasa recta from efferent arterioles
• Blood Supply to Kidney

  • Renal artery
  • Interlobar arteries
  • Arcuate arteries
  • Interlobular veins
  • Efferent arteriole
  • Peritubular capillaries
  • Interlobular veins
  • Arcuate veins
  • Interlobar veins
  • Renal vein
• Vasa recta


  Branches from afferent arteriole near the loop of henle
• Substances in Urine


  • Excess water
  • Excess ions
  • Metabolic wastes
  • Toxic substances
• Protein (0.1%) is not supposed to be filtered in the kidneys. However, small proteins like albumin in blood plasma are sometimes able to get through.
• Urine Production


  1. Glomerular Filtration

  2. Tubular Reabsorption

  3. Tubular Secretion
• Glomerular Filtration


  • Main site: renal corpuscles
  • Driven by blood pressure that forces water and solutes out in the blood plasma to go to the bowman capsule and prevent red blood cells, white blood cells, and proteins from exiting
  • Glomerular filtrate: fluid which enters the capsular space
• Filtration Membrane


  • Capillary endothelium
  • Basement membrane
  • Podocytes of the bowman capsule
• Fenestration or pores


  Allow water and solutes from going out of the blood plasma
• Net Filtration Pressure (NFP)

  • Combination of three forces: one pressure which promotes filtration (going out) and two opposing pressures (going in)
  • A net outward pressure
  • 10mm Hg
• Glomerular blood hydrostatic pressure (GBHP)

  • Blood pressure in glomerular capillaries
  • 50 to 55mm Hg
  • Promotes filtration by forcing water and solutes in blood plasma through the filtration membrane
• Capsular hydrostatic pressure (CHP)

  • Hydrostatic pressure opposing the filtration membrane by fluid already in the capsular space and renal tubule
  • 15mmHg
  • Inward pressure
• Blood colloid osmotic pressure (BCOP)


  • Due to proteins in blood plasma
  • Opposes filtration
  • 30mm Hg
  • Inward pressure
• Glomerular Filtration Rate (GFR)


  • Amount of filtrate formed in all renal corpuscles each minute
  • Males: 125mL/min
• Glomerular filtration pressure


  The driving force of glomerular filtration
• Glomerular filtration pressure


  • Combination of three forces: one pressure which promotes filtration (going out) and two opposing pressures (going in)
  • A net outward pressure
  • 10mm Hg
• NFP


  Net filtration pressure = GBHP - CHP - BCOP
• Glomerular blood hydrostatic pressure (GBHP)

  • Blood pressure in glomerular capillaries
  • 50 to 55mm Hg
  • Promotes filtration by forcing water and solutes in blood plasma through the filtration membrane
  • The efferent arteriole has a smaller diameter than the afferent arterioles which provides an increase in resistance and pressure. It helps to build up GBHP.
• Capsular hydrostatic pressure (CHP)

  • Hydrostatic pressure opposing the filtration membrane by fluid already in the capsular space and renal tubule
  • 15mmHg
  • Inward pressure
• Blood colloid osmotic pressure (BCOP)


  • Due to proteins in blood plasma
  • Opposes filtration
  • 30mm Hg
  • Inward pressure
• Glomerular Filtration Rate (GFR)


  • Amount of filtrate formed in all renal corpuscles each minute
  • Males: 125mL/min
  • Females: 105 mL/min
  • Directly related to pressures that determine net filtration pressure
• Regulation of GFR


  1. Blood flow into and out of glomerulus eg by constriction of afferent and efferent

  2. Altering the GFR surface area available for filtration
• Tubular reabsorption


  • Transport of water and solutes from the filtrate back into the blood
  • 99% of water and solutes are reabsorbed
  • Main site: Proximal convoluted tubule