Renal Anatomy Overview

Renal Anatomy

• Kidney:
  • Located retroperitoneally in the posterior abdominal region
  • Right kidney is slightly lower than the left
  • Left kidney is longer and more slender
• External features:
  • Renal capsule: fibrous connective tissue surrounding the kidney
  • Perirenal fat: adipose tissue cushioning the kidney
  • Renal fascia: connective tissue anchoring the kidney to the abdominal wall
  • Hilum: medial margin where renal artery, vein, lymphatics, nerves, and ureter enter/exit
• Internal features:
  • Renal cortex: pale tissue surrounding the medulla
  • Renal medulla: contains renal columns and renal pyramids
  • Renal columns: extensions of the cortex dividing the medulla into pyramids
  • Renal pyramids: triangular tissue with bases towards the cortex, apexes towards the renal sinus
  • Renal papilla: apical projections of pyramids surrounded by minor calices
  • Minor calices: several unite to form major calices
  • Major calices: two or three unite to form the renal pelvis
  • Renal pelvis: superior funnel-shaped end of the ureter
• Ureters:
  • Muscular tubes transporting urine from kidneys to bladder
  • Originate at the ureteropelvic junction
  • Descend retroperitoneally along the medial aspect of the psoas major muscle
  • Enter the pelvic cavity at the pelvic brim
• Bladder:
  • Situated in the pelvic cavity when empty, expands superiorly into abdomen when full
• Urethra:
  • Begins at the base of the bladder, ends with an external opening in the perineum
  • Location differs between males and females

Renal Function

• Primary function of the urinary system is to maintain homeostasis by regulating blood composition and volume
• Regulates pH balance, water balance, and electrolyte balance
• Excretes waste products
• Produces 0.6 to 2.5L of urine daily

Urine Composition

• Organic substances:
  • Urea: formed in the liver from ammonia and CO2
  • Uric acid: end product of purine oxidation
  • Creatinine: hydrated form of creatine
• Inorganic substances:
  • Chloride, phosphates, sulfates, and ammonia

Urine Physical Characteristics

• Colour:
  • Varies from light straw to amber
  • Milky appearance can indicate pus, bacteria, fat
  • Reddish colour can indicate urobilinogen
• Turbidity:
  • Fresh urine should be transparent
  • May become cloudy after standing
• Odour:
  • Usually odourless
• Other characteristics:
  • pH: usually 6 (range 4.8 – 7.5)
  • Specific gravity: indicates the kidney's ability to concentrate urine
    • High specific gravity can indicate a "wasting" process (e.g., cancer)
    • Low specific gravity (1.010) can indicate severe renal damage

Abnormal Urine Constituents

• Glucose: warning sign of diabetes mellitus (sweet urine)
• Ketones: intermediary products of fat and protein metabolism. Ketonuria occurs in diabetes mellitus and during periods of stress
• Blood: may indicate high altitudes, kidney stones, etc.
• Hemoglobin: Hemoglobinuria may indicate hemolytic anemia, transfusion reactions, smallpox, malaria, hepatitis, renal infections, etc.
• Bilirubin: Breakdown product of bile. May indicate blocked bile ducts, cirrhosis of the liver, or liver cancer
• Protein: high molecular weight molecule usually not excreted. May indicate impairment of kidney functioning

Urinalysis

• Measures urine volume, clarity, color, specific gravity, and pH
• Dipsticks are used for analysis
• Perform urinalysis on own urine to stay safe
• Gloves should be worn when analyzing unknown samples

Practical Considerations

• Follow the instructions for urinalysis experiments to ensure safety
• Consume light breakfast 2 hours before the experiment
• No coffee/tea, only 1 glass of water (250ml) until the experiment begins
• Collect urine samples at intervals
• Analyze urine for volume, pH, specific gravity, color, and clarity
• Document results in a table
• Discuss findings

Histology

• Kidney:
  • Identify the cortex, medulla (striated due to loop of Henle and collecting ducts), and glomeruli
• Bladder:
  • Identify the mucosa layer with transitional epithelium and lamina propria
• Ureter:
  • Identify the lumen, inner mucosa layer (comprising of transitional epithelium and lamina propria), and muscular layer (note longitudinal and circular muscle bands)