Excretory System Reding

Functions of the Excretory System

  • Removal of metabolic waste:
    • Skin: Removes urea with sweat.
    • Lungs: Remove CO2CO_2 from blood.
    • Liver: Removes bilirubin from hemoglobin breakdown and puts it in bile.
    • Spleen: Puts bilirubin in plasma for kidney removal.
    • Kidneys: Remove nitrogenous waste.
  • Maintenance of the body's fluid and electrolyte balance:
    • Kidneys conserve water to maintain blood volume while excreting excess sodium.
    • Small volume of concentrated urine is produced.
  • Maintenance of the body's acid-base balance:
    • Kidneys secrete excess hydrogen ions (H+H^+).
    • Lungs remove CO2CO_2 to maintain blood pH.
    • Respiratory rate fluctuates with blood pH (increases if pH falls, decreases if pH rises).
  • Regulation of blood pressure:
    • Hypothalamus monitors blood sodium levels and increases thirst when sodium is high.
    • Kidneys produce more urine to reduce blood volume and pressure if fluid intake is excessive.

Effects of Aging on the Excretory System

  • Primarily affects the urinary system.
  • Kidney changes:
    • Kidney size and number of functioning nephrons decrease by about 1/3 by age 80.
    • Narrowing and hardening of arteries supplying kidneys and glomeruli.
    • Decreased glomerular filtration rate and reserve capacity.
    • Waste removal is usually sufficient, but system is more vulnerable to other diseases.
    • Drugs cleared less efficiently; dosages may need adjustment.
    • Decreased responsiveness to ADH, causing water balance problems.
    • Diminished sense of thirst, leading to dehydration.
  • Effects on voiding urine:
    • Men: 50% experience benign prostatic hyperplasia (BPH) by age 50, increasing to 80% by age 80. Prostate enlargement compresses the urethra, making bladder emptying difficult.
    • Women: Prone to incontinence (urine leakage), especially after vaginal childbirth due to weakened pelvic floor muscles and external urethral sphincter.

Diagnostic Tests for Excretory System Disorders

  • Biopsy: Tissue is collected and examined for abnormal cells.
  • Blood test: Analyzes blood composition to reveal kidney function problems.
  • CT scan: Imaging technique to visualize internal structures; used for changes in lower abdomen and pelvic regions.
  • Cystoscopy: Lighted cystoscope used to visualize the urinary bladder, lower urinary tract, and prostate.
  • Intravenous pyelography: X-ray of kidneys and urinary tract using contrast dye injected intravenously.
  • Ultrasound: Sound waves create visual images of internal structures; used to examine the urinary tract.
  • Urinalysis: Physical, chemical, and microscopic examination of urine; abnormal results may indicate a condition or disease.

Disorders of the Urinary Tract

  • Urinary Tract Infections (UTIs): Infections affecting any structure along the urinary tract (urethra, bladder, ureters, kidneys).
    • Urethritis: Infection of the urethra caused by bacteria, viruses, or fungi. More common in women due to shorter distance between urethra and anus. Symptoms include painful and frequent urination, and discharge.
    • Cystitis: Inflammation of the urinary bladder usually caused by a bacterial infection. More common in women due to shorter urethra. Symptoms include frequent passing of small amounts of urine with a burning sensation. Increased prevalence with sexual activity.
    • Pyelitis: Infection of the renal pelvis.
    • Pyelonephritis: Infection of the renal cortex.
    • Treatment: UTIs are treated with antibiotics.
  • Hydronephrosis: Buildup of urine in the kidneys due to blocked flow from kidney (kidney stones, blood clots, tumors, birth defects causing ureter narrowing). Causes kidneys to swell and increased pressure, leading to damage. Diagnosed with CT, intravenous pyelography, ultrasound, blood test, and urine test. Treatment involves removing obstruction.
  • Polycystic Kidney Disease (PKD): Inherited disorder causing multiple cysts on the kidneys, interrupting their normal function. Leads to high blood pressure and kidney infections. Diagnosed using CT, MRI, intravenous pyelography, and blood test. Genetic testing can determine risk.
    • Autosomal dominant trait: Offspring have a 50% chance of developing the disease if one parent carries the gene.
  • Kidney Stones: Solid stones formed in the renal pelvis from precipitated calcium or uric acid. Small stones may pass unnoticed; larger ones can block the renal pelvis or ureters. Blocked flow increases pressure within the kidney, damaging nephrons. Treatments include medication, lithotripsy (sound waves to break up stones), and surgery.
  • Glomerulonephritis: Inflammation of the filtration membrane and glomeruli of the nephron.
    • Acute: Occurs 1-3 weeks after a severe bacterial infection. Antibody-antigen complexes damage the glomeruli, causing inflammation and increased permeability. Results in higher urine volumes with protein and blood cells. Usually time-limited.
    • Chronic: Constant irritation to the filtration membrane causes it to thicken and be replaced by connective tissue, potentially leading to renal failure.
  • Renal Failure: Measured by assessing blood urea nitrogen (BUN) levels. Slightly higher levels indicate renal insufficiency (azotemia). Seriously elevated levels indicate uremia (vomiting, diarrhea, and arrhythmias). Complete kidney failure results in convulsions, coma and death. Treatment includes kidney transplantation or dialysis.

Cancer of the Excretory System

  • Kidney Cancer: Most common type is renal cell carcinoma (tumors originating in glandular epithelial tissue). Affects people ages 50-70, more often men. Risk factors include smoking, obesity, drug use, chemical exposure, and polycystic kidney disease. Symptoms include blood in urine (hematuria), flank pain, fever, and a mass. Diagnosed by CT scan or MRI. Treatment depends on stage; nephrectomy (kidney removal) may be performed.
  • Bladder Cancer: Usually caused by transitional cell carcinoma. Risk factors include smoking and exposure to certain drugs and chemicals. Symptoms include hematuria, anemia, dysuria, and pelvic pain. Diagnosis involves cystoscopy and biopsy. Treatment includes removal of cancerous tissue and chemotherapy; cystectomy (bladder removal) may be necessary in severe cases.

Summary of Diseases

  • Urinary Tract Infections (UTIs):
    • Cystitis: Inflammation of the urinary bladder (bacterial).
    • Pyelitis: Infection of the renal pelvis.
    • Pyelonephritis: Infection of the renal cortex.
    • Urethritis: Infection of the urethra (bacteria, viruses, fungi).
  • Kidney Disorders:
    • Glomerulonephritis: Inflammation of the filtration membrane in the glomerulus (acute or chronic).
    • Hydronephrosis: Buildup of urine in the kidney (obstructed flow).
    • Kidney Stones: Solid stones in the renal pelvis (calcium or uric acid).
    • Polycystic Kidney Disease (PKD): Inherited disorder causing cysts on kidneys.
    • Renal Failure: Failure to clear waste from blood (azotemia).
  • Cancers:
    • Bladder Cancer: Tumor of the bladder (transitional cell carcinoma).
    • Kidney Cancer: Tumor of the kidney (renal cell carcinoma).
  • Other Excretory Disorders:
    • Benign Prostatic Hyperplasia (BPH): Enlargement of the prostate gland.
    • Incontinence: Urine leakage.

Overview of Excretion

  • Removal of metabolic waste in the body.
  • Skin, lungs, liver, and kidneys remove metabolic waste.
  • Nitrogenous waste includes ammonia, urea, uric acid, and creatinine.

Overview of Kidney Function

  • Kidneys function in the integumentary, skeletal, cardiovascular, and excretory systems.

Anatomy of a Kidney

  • Retroperitoneal.
  • Three layers: renal capsule, renal cortex, and renal medulla.
  • Pyramids are in the renal medulla.
  • Calyces collect urine from pyramids and deliver it to the renal pelvis.
  • Renal sinus: Space occupied by renal artery, renal vein, and renal pelvis.

Anatomy of a Nephron

  • Two basic parts: renal corpuscle and renal tubule.
  • Renal corpuscle: glomerulus and glomerular capsule.
  • Renal tubule: proximal convoluted tubule, nephron loop, and distal convoluted tubule.
  • Renal corpuscle and convoluted tubules are in the renal cortex.
  • Nephron loop and collecting duct are in the pyramid.
  • Juxtaglomerular apparatus: Located between afferent and efferent arterioles and distal convoluted tubule.

Flow of Urine

  • Glomerular capsule → proximal convoluted tubule → nephron loop → distal convoluted tubule → collecting duct → minor calyx.

Blood Flow to a Nephron

  • Renal artery → smaller arteries → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries → venules → larger veins → renal vein.

Physiology of Urine Production

  • Three processes: filtration, reabsorption, and secretion.
  • Filtration:
    • Happens in the renal corpuscle.
    • Materials move from glomerulus to glomerular capsule.
    • Materials moved: water, glucose, amino acids, some nitrogenous waste, and mineral salts.
  • Reabsorption:
    • Happens along the renal tubule.
    • Materials move from tubules to peritubular capillaries.
    • Materials moved: 100% of glucose, 100% of amino acids, variable amounts of mineral salts, and water.
  • Secretion:
    • Happens along the renal tubule.
    • Materials move from peritubular capillaries to tubules.
    • Materials moved: nitrogenous waste, excess hydrogen ions, excess potassium ions, and some drugs.
    • Secretion of hydrogen ions helps maintain blood's acid-base balance.

Water Conservation

  • Human body is 50-75% water.
  • Water is held in two fluid compartments: intracellular (65%) and extracellular (35%).
  • Water moves easily between compartments by osmosis to minimize concentration gradients.
  • Daily water intake should equal daily output.

Regulation of Urine Volume and Concentration

  • Regulated through hormones, the nervous system, and diuretics.
  • Hormonal Mechanisms of Control:
    • Hormones that control urine production: ADH, aldosterone, and ANH.
  • Nervous System Mechanisms of Control:
    • Sympathetic nervous system reduces urine production.
  • Diuretics:
    • Increase urine production.

Anatomy of Ureters, Urinary Bladder, and Urethra

  • Ureters:
    • Retroperitoneal.
    • Deliver urine from the renal pelvis to the urinary bladder.
    • Go posterior to the bladder and enter at its base.
  • Urinary Bladder:
    • Storage sac with smooth muscle in its walls.
    • Trigone: Triangular area of bladder floor defined by openings of ureters and urethra.
    • Detrusor muscle thickens to form the internal urinary sphincter.
  • Urethra:
    • Delivers urine from the urinary bladder to the outside.
    • Male urethra is longer than female urethra.
    • Surrounded by the external urinary sphincter (skeletal muscle).
    • Male urethra sections: prostatic, membranous, and penile.

Physiology of Passing Urine

  • Passing urine is called micturition.
  • Micturition reflex controls passing of urine in infants.
  • Higher brain centers influence the reflex after toilet training.