In-Depth Notes on Excretory System

Excretory System Overview

  • The excretory system is responsible for removing waste products from the body.
    • Organs involved: Liver, Lungs, Skin, Colon, Kidneys.

Liver

  • Produces waste but primarily excretes it via other organs (e.g. kidneys).
  • Types of waste formed:
    • Nitrogenous Waste:
    • Urea: Created from breakdown of amino acids (deamination of amino acids yields ammonia, which is converted to urea).
    • Uric Acid: Result of nucleic acid breakdown.
    • Creatinine: Formed from creatine phosphate in muscle cells.
    • Non-nitrogenous Waste:
    • Toxins and drugs, alcohol.

Lungs

  • Excretes carbon dioxide, a byproduct of cellular respiration, as well as heat and water in small amounts.

Skin

  • Releases water and salts through sweat, which aids in cooling the body.
  • Sweat Mechanism:
    • Evaporation of sweat cools the body as heat is lost.

Colon

  • Excretes bile pigments, which are byproducts from the breakdown of blood cells, and cholesterol produced by the liver.
  • These are eliminated in feces, along with mucus.

Kidneys

  • Main organs for excreting nitrogenous waste (urea) and non-nitrogenous waste (carbon dioxide, water, ions, hormones, poisons, drugs, bacteria).

Anatomy of the Excretory System (Kidneys)

  • Renal Capsule: Covers kidney surface to prevent infection.
  • Adipose Tissue: Holds kidneys in place and cushions against blows.
  • Renal Fascia: Binds kidneys to surrounding structures.
  • Cortex: Contains renal corpuscles.
  • Medullary Pyramids: Tips (papilla) fit into calyces, which collect urine.

Nephron Structure

  1. Afferent Arteriole: Blood enters under high pressure.
  2. Glomerulus: Filters blood; contents include glucose, water, amino acids, vitamins, urea, uric acid, creatinine (excludes proteins and RBCs).
  3. Bowman's Capsule: Encases glomerulus.
  4. Distal Convoluted Tubule: Reabsorbs sodium, chloride, water, and secretes hydrogen ions, creatinine, drugs.
  5. Loop of Henle:
    • Function: Concentrates salts and regulates water absorption.
    • Active Transport: Involves sodium and chloride reabsorption; plays a role in blood pressure and pH balance.
  6. Collecting Duct: Final site of water reabsorption; urine is collected here.

Kidney Function and Dialysis

  • Dialysis: Temporary solution for kidney failure by diffusing waste substances through semipermeable membranes.
    • Process: Blood is circulated through a dialyzer where waste diffuses into a dialysate resembling blood plasma.
    • Disadvantages: Time-consuming (4-6 hours per session) and expensive.

Kidney Failure

  • Occurs when kidneys cannot concentrate urine, leading to nitrogenous waste accumulation in the blood.
  • Causes include bacterial infections (e.g. cystitis), excessive analgesic use, and loss of nephrons with age.

Kidney Stones

  • Solidified salts that crystallize in the kidneys, caused by dehydration, excessive calcium intake, or abnormal urine pH.
  • Symptoms: Pain during urination, possible blood in urine if stones are present.
  • Treatment: Small stones (<5mm) may pass naturally; larger stones can be treated with lithotripsy (sound waves to shatter the stone).

Urinary Infections

  • Infection in the bladder and urethra, resulting in inflammation.
  • Symptoms: Frequent urination with small amounts, painful urination.

Kidney Trauma

  • Can be blunt (impact without skin break) or penetrating (object piercing skin).
  • Diagnosis: Detection of blood in urine, ultrasound, or X-ray with contrast to visualize kidney function.