Urinary System

• Kidney Characteristics

  • bean shaped
  • weigh 5 ounces
• Kidney Structures

  • Renal capsule
  • Hilum
  • Renal sinus
  • Renal cortex
  • Renal medulla
  • Renal pyramid
  • Renal papillae
  • Renal pelvis
• Renal capsule - a connective tissue around each kidney. Protects and acts as a barrier
• Hilum - an indentation, contains renal artery, veins, nerves, ureter
• Renal sinus - contains renal pelvis, blood vessels, and fats
• Renal cortex - outer portion of the kidney
• Renal medulla - inner portion of the kidney.
• Renal pyramid - cone shaped structures in the medulla whose bases project into the cortex.
• Renal papillae - tip of pyramids which drain into calyces.
• Renal pelvis - where calyces join together, it narrows to form ureter.
• Nephron is the functional unit of the kidney. Each kidney has over one million nephrons. Approximately 15% are juxtamedullary.
• The nephron includes:

  • renal corpuscle
  • proximal convoluted tubule
  • loop of Henle
  • distal convoluted tubule
  • collecting duct
• Types of Nephrons

  • Juxtamedullary nephrons
  • Cortical nephrons
• Juxtamedullary nephrons

  • renal corpuscles are deep in the cortex near the medulla
  • long loops of Henle extend deep into the medulla
  • Well adapted for water conservation
  • About 15% of nephrons
• Cortical nephrons

  • Renal corpuscles distributed throughout the cortex
  • Loops of Henle are shorter and closer to the outer edge of the cortex than juxtamedullary nephrons
• Renal Corpuscle, the filtration portion of the nephron.
• Glomerulus

  • A network of capillaries twisted around each other like a ball of yarn
• Bowman’s capsule

  • enlarged end of nephron surrounds glomerulus
  • opens into proximal convoluted tubule
  • contains podocytes (specialized cells around glomerular capillaries)
• Renal corpuscle (Bowman capsule) consists of two layers:

  • Outer layer - simple squamous epithelial cells that become cube-shaped at the beginning of the proximal convoluted tubule.
  • Inner layer - cells called podocytes, which wrap around the glomerular capillaries.
• Characteristics of Renal Corpuscle

  • High pressure
  • An afferent ateriole supplies blood to the glomerulus for filtration
  • An efferent arteriole transports the filtered blood away from the glomerulus.
  • Efferent arteriole has smaller diameter than afferent arteriole creating a high pressure in the capillaries
• The structures in the corpuscle make up the filtration membrane.

  • Consists of capillary endothelium, the basement membrane, and the podocytes of the Bowman capsule
  • Filtrate is the fluid filtered from the glomerular capillaries. Enters the lumen inside the Bowman capsule.
• Juxtaglomerular apparatus – specialized cells of the afferent arteriole and distal convoluted tubule in close contact with each other.
• Juxtaglomerular cells – specialized smooth muscle cells located where the afferent arteriole enters the renal corpuscle
• Macula densa - part of the distal convoluted tubule that lies between the afferent and efferent arterioles next to the renal corpuscle.
• Secretion of the enzyme renin by the juxtaglomerular apparatus plays an important role in the regulation of filtrate formation and blood pressure.
• Nephron Components

  Proximal convulated tubule:

  • where filtrate passes first
  • drains filtrate from Bowman capsule
• Nephron Components

  Loop of Henle

  • contains descending and ascending loops
  • water and solutes pass through thin walls by diffusion
• Nephron Components

  Distal convoluted tubule

  • structure between Loop of Henle and collecting duct
• Nephron Components

  Collecting duct

  • empties into calyces
  • carry fluid from cortex through medulla
• Flow of Filtrate through Nephron

  1. Renal corpuscle
  2. Proximal convoluted tubule
  3. Descending loop of Henle
  4. Ascending loop of Henle
  5. Distal convoluted tubule
  6. Collecting duct
  7. Papillary duct
• Blood Flow through Kidney

  1. Renal artery
  2. Interlobar artery
  3. Arcuate artery
  4. Interlobular artery
  5. Afferent arteriole
  6. Glomerulus
  7. Efferent arteriole
  8. Peritubular capillaries
  9. Vasa recta
  10. Interlobular vein
  11. Arcuate vein
  12. Interlobar vein
• Urine Formation

  • Filtration – occurs in the renal corpuscle, blood plasma leave glomerulus and enters Bowman space.
  • Tubular Reabsorption – involves removing substances from the filtrate and placing them back into the blood.
  • Secretion – involves taking substances from the blood at a nephron area other than the renal corpuscle and putting back into the nephron tubule.
• Urine Formation-Filtration

  • Movement of water, ions, small molecules through filtration membrane into Bowman’s capsule
  • 19% of plasma becomes filtrate
  • 180 Liters of filtrate are produced by the nephrons each day
  • 1% of filtrate (1.8 liters) become urine, the rest is reabsorbed
• Urine Formation

  A) FILTRATION

  B) REABSORPTION

  C) SECRETION

  
• Filtration Pressure

  A) 10 mm Hg

  B) 50 mm Hg

  C) 30 mm Hg
• Urine Production-Reabsorption

  • 99% of filtrate is reabsorbed and reenters circulation
  • The proximal convoluted tubule is the primary site for reabsorption of solutes and water
  • The descending Loop of Henle concentrates filtrate
  • Reabsorption of water and solutes from distal convoluted tubule and collecting duct is controlled by hormones
• Urine Production—Secretion

  • Ammonia secretion is passive.
  • Secretion of H+, K+, creatinine, histamine, and penicillin is by active transport.
  • These substances are actively transported into the nephron.
  • The secretion of H+ plays an important role in regulating the body fluid pH.
• Urine Concentration Mechanism

  • The kidneys regulate blood composition and are able to produce very dilute or very concentrated urine to maintain the extracellular fluid concentration close to 300 mOsm/L.
  • The ability to control the volume and concentration of the urine depends on: (1) countercurrent mechanisms, (2) a medullary concentration gradient, and (3) hormonal mechanisms.
• Urine Concentration Mechanism

  • Countercurrent mechanism - fluids in separate structures flow in opposite directions relative to each other. As they pass by each other, materials can be exchanged between them.
  • The countercurrent mechanism creates a very high solute concentration in the medulla compared to the cortex. Called the medullary concentration gradient.
• Filtration Pressure

  A) 50 mm Hg

  B) 10 mm Hg

  C) 30 mm Hg