Urinary System Anatomy and Function

Urinary System Anatomy and Function

• The urinary system maintains homeostasis by removing waste, excess water, and electrolytes from the blood, concentrating them into urine. It also produces erythropoietin, stimulating red blood cell production.
• The system comprises two kidneys, two ureters, the bladder, and the urethra.
• Kidneys are situated behind the peritoneum, roughly 4-5 inches long, 2-3 inches wide, and 1 inch thick. The right kidney is slightly lower than the left, due to the liver's position.
• Each kidney is encased in adipose tissue. The hilus is a notch where the ureter, blood vessels, and nerves enter and exit.

Kidney Gross Anatomy

• Renal Capsule: The strong outer covering of connective tissue.
• Renal Cortex: Inner layer beneath the capsule containing renal tubules (1.25 million per kidney).
• Renal Medulla: Located beneath the cortex, darker in appearance and comprised of pyramids.
• Papillae: The pointed tips of the pyramids, draining urine into calyces.
• Calyces: Collecting chambers draining into the renal pelvis.
• Renal Pelvis: The upper part of the ureters, receiving urine from the calyces.
• Ureters: Transport urine to the bladder.
• Bladder: Stores urine.
• Urethra: Transports urine from the bladder to the exterior.

Microscopic Kidney Structure (Nephron)

• The nephron is the functional unit, with over 1 million per kidney.
• It filters blood and processes urine, performing vital functions like:
  • Regulating fluid levels
  • Controlling blood pH
  • Removing waste.
• Two main parts:
  • Renal Corpuscle: A glomerulus (a network of capillaries) and Bowman's capsule (cup-like structure enclosing the glomerulus).
    • Blood enters the glomerulus via the afferent arteriole and leaves via the efferent arteriole. The diameter difference controls filtration rate.
  • Renal Tubule: Composed of the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.
    • Filtrate travels through the tubule: Water and electrolytes are reabsorbed or secreted to regulate homeostasis. This is controlled by ADH and aldosterone.
    • Juxtaglomerular apparatus (adjacent to the glomerulus) regulates nephron function and systemic blood pressure. When blood pressure is low, renin is released to activate the renin-angiotensin mechanism, leading to hypertension.

Urine Formation

• Three phases:
  • Filtration: Water and blood products filtered in the glomerulus and Bowman's capsule.
  • Reabsorption: Water, glucose, and necessary ions return to the blood in the proximal convoluted tubules, loop of Henle, and distal convoluted tubules.
  • Secretion: Ions, waste, and drugs move from the blood to the filtrate in the distal convoluted tubule.

Hormonal Influences

• ADH (antidiuretic hormone): Increases water reabsorption in the distal convoluted tubules in response to fluid loss (e.g., hemorrhage).

Urine Composition and Characteristics

• Urine is mostly water (95%) with nitrogenous waste and salts.
• Yellow color due to urochrome (pigment from hemoglobin breakdown).
• Normal pH: 4.6-8.0; specific gravity: 1.003-1.030.
• Urine is normally sterile, but decomposes rapidly at room temperature.
• Urine abnormalities are evaluated in diagnostic testing.

Urinary System Disorders in Aging Adults

• Aging kidneys: Decreased blood supply and nephron loss cause reduced filtering capacity, especially by age 70.
• Incontinence: Women face issues with bladder tone and perineal muscle relaxation. Men experience prostate enlargement, constricting the urethra and potentially leading to incomplete bladder emptying.
• Risk Factors for UTI: Incomplete bladder emptying in both men and women increases UTI risk.

Urinary System Diagnostic Tests

• Routine Urinalysis:
  • Evaluates physical characteristics (color, clarity, odor), pH, specific gravity, and presence of proteins, glucose, ketones, blood cells, crystals.
• 24-Hour Urine Collection: Measures excreted substances to assess kidney function.
• Urine Culture and Sensitivity: Identifies causative organisms for infections and determines appropriate antibiotics.
• Urine Specific Gravity: Determines fluid balance. Affected by factors like dehydration, excessive fluid intake, and some disorders.
• Blood Tests:
  • BUN (Blood Urea Nitrogen): Measures urea, a non-protein waste. Reflects renal function and protein intake, but not as reliable as serum creatinine.
  • Serum Creatinine: Measures creatinine, which is excreted entirely by the kidneys Reflects renal function, less affected by factors like hydration and malnutrition compared to BUN.
• Creatinine Clearance Test: Measures creatinine levels in blood and urine to assess kidney function.
• PSA (Prostate Specific Antigen): Normal PSA is less than 4 ng/mL; elevated levels indicate potential prostate disorders.
• Urine Osmolality: Measures the number of particles per volume of urine, providing information about the kidneys' ability to concentrate urine.

Imaging and Endoscopic Procedures

• KUB (Kidney-Ureter-Bladder) radiography

• IVP/IVU (Intravenous pyelography/urography): Examines the urinary tract, using contrast dye. Preparation includes a light supper, laxative, and NPO status.

• Retrograde Pyelography: Injects contrast into ureters to view upper urinary tract structures.

• Voiding Cystourethrography: Evaluates bladder and urethra, often using an indwelling catheter.

• Cystoscopy: Visual examination of the urinary bladder. Procedures often include biopsy, urine samples, and other treatments.

• Nephroscopy (Renal Endoscopy): Direct visualization of upper urinary structures.

• Renal Angiography: Evaluates blood supply to kidneys, often using contrast dye.

• Renal Venography: Evaluates venous drainage of the kidneys.

• CT (Computed Tomography), MRI (Magnetic Resonance Imaging): Non-invasive imaging procedures, using contrast for certain cases.

• Renal Biopsy: Obtaining tissue samples from kidneys.

• Other procedures like Transrectal Ultrasound (for prostate), Urodynamic Studies (bladder function assessment) are also detailed.

Explore the anatomy and function of the urinary system in this quiz. Learn about the components including the kidneys, ureters, bladder, and their roles in maintaining homeostasis. Test your knowledge on kidney structure and function.