Urinary System and Diabetes

Urine Characteristics

• Urine is colored yellow due to the pigment urochrome
• Urine is sterile and slightly aromatic
• Normal pH of urine is around 6
• Specific gravity of urine is between 1.001 to 1.035
• Urine composition differs based on diet, metabolic activity, and urine output
• Urine is made up of 95% water, contains urea, uric acid, electrolytes, and amino acids

Urinary Bladder

• The bladder wall has three layers of smooth muscle (detrusor muscle)
• The mucosa is made of transitional epithelium
• The bladder can expand significantly without increasing internal pressure
• A moderately full bladder can hold around 500mL (1 pint), and a full bladder can stretch to hold more than twice that amount

Ureter

• The ureter is a slender tube that attaches the kidney to the bladder
• The mucosal lining is continuous with that of the renal pelvis and bladder
• The ureter runs behind the peritoneum and enters the posterior aspect of the bladder at a slight angle
• Peristalsis aids gravity in urine transport from the kidneys to the bladder

Micturition (Voiding)

• Both internal and external urethral sphincters must open to allow voiding
• The internal urethral sphincter relaxes after the bladder stretches to around 200mL
• Activation of micturition is from an impulse sent to the spinal cord and then back via the pelvic nerves
• The external urethral sphincter must be voluntarily relaxed
• Incontinence is the inability to control micturition, and retention is the inability to micturate

Urethra

• The urethra is a thin-walled tube that carries urine from the bladder to the outside of the body by peristalsis
• The release of urine is controlled by two sphincters: internal urethral sphincter and external urethral sphincter
• The internal urethral sphincter is a thickening of smooth muscle at the bladder-urethra junction
• The external urethral sphincter is a voluntary skeletal muscle that controls urine as the urethra passes through the pelvic floor

Urethra Gender Differences

• Female urethra is shorter (3-4 cm or 1-1.5 inches) and located along the wall of the vagina
• Male urethra is longer (20 cm or 7-8 inches) and passes through the prostate and penis