Lecture 21 - Urinary System: Anatomy

Urinary System Overview

• Kidneys, Ureters, Urinary bladder & urethra

• Kidneys - bilateral

  • Filter blood plasma → urine

• Ureters - Carries urine from kidneys to bladders

• Bladder - Holding area for urine before release

• Urethra - area of release

• Urine flows from each kidney > down ureter → bladder → outside via urethra

• Filter blood & return most of water & solutes to bloodstream

  • Filters plasma portion of blood

1. Kidneys cone in contact w/ blood

2. Pulls out portion of blood plasma - Filtrate

3. Move filtrate through series of tubes

   1. Pull back things we dont want body to lose (ions, glucose)

   2. Pull things OUT of blood (toxins)

4. Filtrate makes it to exit point → fully waste products - Urine

5. Moves towards bladder

• Right/Left Renal Artery - From abdominal aorta, carries blood INTO kidneys

• Right/Left Renal Veins - Carries blood back to inferior vena cava

  • Large - Kidneys filter blood, need to send large volumes of blood to kidneys for filtration → large diameter vasculature

  • 20-25% cardiac output sent to kidneys during resting condition

Overview of Kidney Functions

• Excretion - Removal of waste products from blood plasma

  • Breakdown of amino acids

    • Excreting ammonia in urine or turn it into Urea

  • Bilirubin from Hemoglobin → Urobilin

  • Phosphocreatine → creatine

  • Nucleic Acids → Uric acid

  • Removal of toxins

    • Drugs, environmental toxins, etc

• Regulation of Blood Volume/Pressure

  • Blood pressure too high → decrease blood volume

  • Blood pressure too low → increase blood volume

  • Kidneys change blood volume

• Regulation of Solute Concentrations in Blood

  • Sodium/potassium/calcium/chloride/phosphate levels

  • Maintains solute concentrations

• Regulation of pH

  • Larger number of hydrogen ions → creating acidic environment

  • Smaller number of hydrogen ions → alkaline/basic environment

  • Increase/decrease excretion of hydrogen ions

• Regulation of RBC Synthesis

  • Release hormone - Erythropoietin → Stimulates RBC production in red bone marrow

• Vitamin D Synthesis

  • Active form of vitamin D produced → increasing absorption of Calcium from food in GI tract

Anatomy of Kidneys

• Above waist, retroperitoneal

  • Behind parietal peritoneum

  • Posterior portion of abdominal cavity

• Protected by 11th & 12th ribs (Floating ribs)

  • Right kidney lower → accommodate mass of liver

External Anatomy of Kidneys

• Kidneys not entirely surrounded by ribs

  • Additional layers for protection

• Layers Surrounding Kidneys:

  1. Renal Capsule - Dense irregular connective tissue

     • Walls of kidneys

     • Maintain shape of kidney

  2. Adipose Capsule - Layer of fat

  3. Renal Fascia - Dense, irregular connective tissue

     • Anchor kidney to other structures in abdomen

       • Abdominal wall

  4. Peritoneum - Anterior & lateral sides

     • Kidneys - retroperitoneum (behind peritoneum)

• Renal Hilum - Where Renal artery/vein enters from

Internal Anatomy of Kidney

1. Renal Capsule

2. Renal Cortex - Tissue deep to renal capsule

3. Renal Medulla - Near hilum area

   • Shaped into structures - Renal Pyramids

   • 8-18 renal pyramids

   • Region closest to cortex - Base

   • Region closest to hilum region - Renal Papilla

4. Renal Column - Extension of cortex between each renal pyramid

• Renal Lobe:

  • Individual pyramid + cortex + portions of renal columns on either side

  • Creating portions of urine

• Renal Hilum:

  • Region where blood vessels come in/out

  • Region where ureter exits

• Renal Sinus:

  • Cavity deep within the renal hilum

Path of Urine Drainage

• Nephron:

  • Functional unit of kidney where urine being produced

  • Start in cortex region just at base of pyramids

  • Takes portion of blood plasma through series of tubes

  • Fluids inside nephron join to form urine

• Collecting Duct:

  • Tube bringing nephrons together from filtrate region towards center

• Papillary Ducts:

  • Collecting ducts joining together

  • Final place for filtration before exiting

• Minor Calyx:

  • Funnel like region where urine drips into

  • Minor calyx for each renal lobe

• Major Calyx:

  • Minor calyx joint together

  • 2-3 in each kidney

• Renal Pelvis:

  • Creates small reservoir in region of renal sinus

  • Where all urine collects before exiting to ureters

Blood Supply of Kidney

• Renal Artery → Blood into kidney

  • In Renal Pelvis → branches → Segmental Arteries

  • Splits at renal lobes → Interlobar Arteries

    • moves on outside of pyramids

  • At cortex levels - Arcuate Arteries

  • Final branches → Cortical Radiate Arteries/Interlobular Arteries

• Highly structured network of blood vessels surrounding each nephron

  • Cortical Radiate Artery → Afferent Arteriole

  • Reaches nephron → Glomerulus (ball like capillary network)

    • Pull plasma portion out of blood supply → into nerphon

  • Whats left over from afferent arteriole enters Efferent Arteriole → blood into capillary network surrounding rest of nephron

  • Network - Peritubular Capillaries/Vasa Recta

    • Vasa Recta - surrounds loops of nephron in medulla region

    • Peritubular Capillaries - Capillary beds surrounding tubes of nephron in cortical region

  • Both join together → Cortical Radiate Vein

  • Cortical Radiate veins merge together → Arcuate Veins

  • Arcuate veins → Interlobar Veins

  • Interlobar vein → Renal Vein

Passageway/Order of Vasculature:

1. Renal artery

2. Segmental arteries

3. Interlobar arteries

4. Arcuate arteries

5. Cortical radiate Arteries

6. Afferent Arterioles

7. Glomerular Capillaries

   • Plasma portion removed

8. Efferent Arterioles

9. Peritubular Capillaries/Vasa Recta

   • Surrounds nephron

   • Gas exchange

10. Cortical Radiate Veins

11. Arcuate Veins

12. Interlobar Veins

13. Renal Vein