Urinary System

• Urinary System


  Consists of the paired kidneys and ureters, the bladder, and the urethra

  
• Urinary System


  • Rids the body of nitrogenous wastes while regulating water, electrolyte, and acid-base balance of the blood
  • Primary role is to ensure optimal properties of the blood, which the kidneys continuously monitor

  
• Kidney functions


  1. Secretion of RENIN

  2. Secretion of ERYTHROPOIETIN

  3. Conversion of VITAMIN D to active form

  4. GLUCONEOGENESIS during starvation or prolonged fasting
• Organs of the Urinary System

  • Kidneys
  • Ureters
  • Urinary Bladder
  • Urethra

  
• Kidneys


  • Small, dark red organs, kidney-bean shape
  • Right kidney is slightly lower than the left
  • Approximately 12-cm long, 6-cm wide, and 2.5-cm thick in adults

  
• Kidney location


  • Located in the lower back and extended from the T12 to the L3 vertebra, receive some protection from the lower part of the rib cage
  • Lie against the dorsal body wall in a retroperitoneal position (beneath the parietal peritoneum) in the superior lumbar region
• Kidney functions


  • Maintain the purity and constancy of our internal fluids
  • Filter gallons of fluid from the bloodstream
  • Regulate the blood's volume and chemical makeup to maintain the proper balance between water and salts and between acids and bases

  
• Adrenal Gland


  Found at the top of the kidney, part of the endocrine system and is a separate organ functionally

  
• Renal Hilum


  Concave medial border of the kidney, where several structures including the ureters, the renal blood vessels, and nerves, enter or exit the kidney

  
• Calyces


  Collect urine, which continuously drains from the tips of the pyramids into the renal pelvis

  
• Renal Pelvis


  Flat, funnel-shaped tube that is continuous with the ureter leaving the hilum

  
• Major & Minor Calyces


  Extensions of the pelvis, cup-shaped formed areas that enclose the tips of the pyramids
• Fibrous Capsule


  Transparent, encloses each kidney and gives a fresh kidney a glistening appearance

  
• Perirenal Fat Capsule


  Fatty mass that surrounds each kidney and cushions it against blows
• Renal Fascia


  An outer layer of dense fibrous connective tissue that anchors the kidney and adrenal gland to surrounding structures

  
• Nephrons


  The structural and functional units of the kidneys, responsible for forming urine

  
• Renal Corpuscle


  An initial dilated part enclosing a tuft of capillary loops and the site of blood filtration, always located in the cortex

  
• Glomerulus


  A knot of capillaries, and a cup shaped hollow structure that completely surrounds the glomerulus like a well-worn baseball glove encloses a ball
• Bowman's Capsule


  The portion of the renal corpuscle that surrounds the glomerulus

  
• Podocytes


  Highly modified octopus-like cells that make up the inner (visceral) layer of the Bowman's capsule, with long branching processes called foot processes that intertwine and cling to the glomerulus
• Renal Tubules


  Make up the rest of the nephron, about 3 cm long, with a long-convoluted part located entirely in the cortex and a shorter straight part that enters the medulla

  
• Regions of the Renal Tubule

  • Proximal Convoluted Tubule (PCT)
  • Nephron Loop (Loop of Henle)
  • Distal Convoluted Tubule (DCT)

  
• Cortical Nephrons


  • Include most nephrons, located almost entirely within the cortex, responsible for reabsorption of nutrients
• Juxtamedullary Nephrons


  • Situated close to the cortex-medulla junction, their nephron loops dip deep into the medulla, responsible for urine concentration
• Collecting Ducts


  Receive urine from many nephrons, run downward through the medullary pyramids, deliver the final urine product into the calyces and renal pelvis

  
• Glomerular Capillary Bed


  • Specialized for filtration, with afferent and efferent arterioles that have high resistance, resulting in high blood pressure in the glomerular capillaries
• Peritubular Capillary Bed


  • Specialized for absorption, arises from the efferent arteriole that drains the glomerulus, low-pressure, porous vessels adapted for absorption instead of filtration
• Urine Formation


  1. Glomerular Filtration

  2. Tubular Reabsorption

  3. Tubular Secretion

  
• Glomerular Filtration


  Nonselective, passive process in which fluid passes from the blood into the glomerular capsule part of the renal tubule, at a rate of 125mL/min

  
• Tubular Reabsorption


  Begins as soon as the filtrate enters the PCT, reabsorption of most substances depends on active transport processes and are very selective, peritubular capillaries reabsorb several materials
• Tubular Secretion


  Essentially tubular reabsorption in reverse, regulates acid base-balance and eliminates waste products not filtered by glomerulus
• In 24 hours, the kidney filters 150-180 liters of blood plasma and produces 1-1.8 liters of urine

  
• Filtrate


  Contains everything that blood plasma does (except proteins), but by the time it reaches the collecting ducts, the filtrate has lost most of its water and just about all of its nutrients and necessary ions
• Urine


  Contains nitrogenous wastes and unneeded substances, generally clear and pale to deep yellow, with normal yellow color from urochrome pigment
• Acids


  Used to produce energy
• Uric acid


  Released when nucleic acids are metabolized
• Creatinine


  Associated with creatine metabolism in muscle tissue
• Tubular secretion


  1. Tubular reabsorption in reverse

  2. Regulates acid base-balance

  3. Elimination of waste products not filtered by glomerulus
• Kidney filters 150-180 liters of blood plasma in 24 hours

  
• 1. 1.8 liters of Urine is produced in 24 hours