EXCRETORY SYSTEM

• Components of the Urinary System


  • Kidneys
  • Ureters
  • Urinary bladder
  • Urethra

  
• Functions of the Excretory System

  • Kidneys
  • Ureters
  • Urinary bladder
  • Urethra

  
• Kidneys


  • Regulate blood volume and composition
  • Help regulate blood pressure, pH, and blood glucose level
  • Produce 2 hormones (calcitriol and erythropoietin)
  • Excrete wastes in urine

  
• Ureters


  • Transport urine from kidneys to urinary bladder

  
• Urinary bladder


  • Stores urine and expels it into the urethra
• Urethra


  • Discharges urine from the body
• Kidneys


  Bean-shaped organ found in the retroperitoneal region, 150 grams, right kidney higher than left kidney, covered by the renal capsule and renal fascia

  
• Renal Cortex


  • Outer part of the kidney, characterized by a red and dotted appearance, contains glomeruli, proximal tubules, distal tubules, and cortical collecting ducts

  
• Renal Medulla


  • Inner part of the kidney, comprised of renal pyramids, contains loop of Henle and medullary collecting ducts, pale with a radial arrangement

  
• Urine Flow


  1. Minor Calyces collect urine

  2. Major Calyces further collect urine

  3. Renal Pelvis receives urine

  4. Ureter transports urine to bladder

  5. Bladder stores urine until excretion

  
• Functions of the Kidney

  • Excretion of wastes and foreign substances
  • Regulation of blood ionic composition
  • Regulation of blood pH
  • Regulation of blood volume
  • Regulation of blood pressure
  • Maintenance of blood osmolarity
  • Production of hormones
  • Regulation of blood glucose level

  
• Nephrons


  Structural and functional unit of the kidneys, 1.3 million per kidney, functioning decreases about 10% every 10 years after age 40
• Parts of the Nephrons

  • Renal Corpuscle
  • Renal Tubules
• Renal Corpuscle


  • Located in the kidney cortex, acts as the blood-filtering component, includes the glomerulus and Bowman's capsule

  
• Renal Tubules


  • Tubules that return nutrients, fluids, and other substances filtered from the blood back to the blood, consists of proximal convoluted tubules, loop of Henle, and distal convoluted tubule

  
• Glomerulus


  Tuft of glomerular capillaries with high hydrostatic pressure, surrounded by Bowman's capsule
• Parts of the Renal Tubules and Collecting Tubules


  • Proximal convoluted tubule
  • Loop of Henle
  • Distal convoluted tubule
  • Cortical collecting tubules
  • Collecting ducts
  • Vasa recta

  
• Superficial Cortical Nephrons


  • 85%-90% of nephrons, glomerulus in outer 2/3 of cortex, loop of Henle bends at cortex-medulla junction, small size with low reabsorption capacity
• Juxta Medullary Nephrons


  • 10%-15% of nephrons, glomerulus in outer 1/3 of cortex, loop of Henle bends at tip of inner medulla, large size with high reabsorption capacity
• Juxta-glomerular Apparatus


  • Composed of macula densa cells, juxtaglomerular cells, and extra glomerular mesangium cells, monitors sodium and chloride concentration in tubular fluid

  
• Stimuli and Mechanism for Renin Release

  1. Sympathetic Stimulation

  2. Renal Ischemia

  3. Decrease in sodium and chloride concentration in tubular fluid

  
• Renin Angiotensin Aldosterone System (RAAS)

  Crucial for regulating blood volume, electrolyte balance, and systemic vascular resistance

  
• Function of the Renin Angiotensin System

  • Salt and water retention
  • Vasoconstriction
  • Stimulates the adrenal cortex

  
• Inhibitors of Renin Release

  • Aldosterone
  • Atrial Natriuretic Peptide
  • Angiotensin II
  • Hypernatremia
• Pharmacologic Inhibitors of the RAAS

  • Angiotensin converting enzyme inhibitor
  • Angiotensin II Blockers
  • Beta blockers
• Renal Blood Flow


  • 1100 ml per minute or 22% of cardiac output, 94% goes to the cortex, high hydrostatic pressure in glomerular capillaries, low flow in renal medulla

  
• Renal Blood Flow and O2 Consumption

  Kidneys consume oxygen at twice the rate of the brain but have almost seven times the blood flow, O2 consumption is directly related to renal tubular Na-reabsorption

  
• Determinants of Renal Blood Flow

  • Renal artery pressure minus renal vein pressure over total renal vascular resistance, resistance controlled by sympathetic nervous system, hormones, and local mechanisms

  
• Regulation of Renal Blood Flow

  • Autoregulation
  • Myogenic response
  • Tubuloglomerular feedback
  • Neural regulation
  • Hormonal regulation

  
• Myogenic Response


  • Contraction of smooth muscle cells in efferent arterioles triggered by increased blood pressure

  
• Renal blood flow


  Calculated as the renal artery pressure minus the renal vein pressure over the total renal vascular resistance

  
• Renal artery pressure is almost the same as systemic arterial pressure

  
• Renal vein pressure is about 3 to 4 mmHg less than renal artery pressure

  
• Resistance in blood vessels

  • Controlled by the sympathetic nervous system, hormones, and local internal renal control mechanisms

  
• Increased resistance


  Decreases renal blood flow, and vice versa
• Kidneys


  • Have effective mechanisms to maintain renal blood flow and glomerular filtration rate (GFR) constant over arterial blood pressure between 82 to 170 mmHg through autoregulation

  
• Regulation of Renal Blood Flow

  • Autoregulation
  • Myogenic response
  • Tubuloglomerular feedback
  • Neural regulation
  • Hormonal regulation
  • Angiotensin II
  • Atrial natriuretic peptide

  
• Myogenic response

  Contraction of smooth muscle cells in the walls of efferent arterioles triggered by increased blood pressure

  
• Increased blood pressure


  Leads to increased renal blood flow and glomerular filtration rate (GFR)

  
• Elevated blood pressure


  Stretches walls of afferent arterioles, causing most muscle fibers to contract narrowing the arteriole and increasing renal blood flow