Excretion and the Excretory System

Study Notes

Process of removing chemical wastes, primarily nitrogenous wastes, from the body.
Critical for maintaining homeostasis (steady state condition) in the body.

Composed of organs involved in the formation, storage, and elimination of urine.

Carbon Dioxide and Water
- Carbon dioxide eliminated through the lungs.
- Excess water released as sweat.
Nitrogenous Wastes
- Includes urea, uric acid, and ammonia.
- Urea is mainly excreted through kidneys.
Excess Salts and Water-Soluble Vitamins
- Common salt (NaCl) and excess B and C vitamins eliminated primarily through kidneys.

Bean-shaped organs located on either side of the backbone, protected by the last two ribs.
Ureters connect each kidney to the urinary bladder; the ureter expands into the pelvis of the kidney.
Urine collects in the urinary bladder, expelled through the urethra during micturition.
A sphincter muscle controls the bladder opening, relaxing only during urination.

Two primary regions: dark outer cortex and lighter inner medulla.
Medulla contains conical pyramids with apices known as papillae.
Composed of numerous nephrons (uriniferous tubules) as structural and functional units.

Ultrafiltration
- Blood flows through the glomerulus under high pressure, causing filtration.
- Resulting fluid is called glomerular filtrate, containing water, urea, salts, glucose, and plasma solutes.
Reabsorption
- Glomerular filtrate is an extremely dilute solution, with useful materials (e.g., glucose, some salts).
- Selective absorption occurs to maintain blood concentration.
Tubular Secretion
- Potassium (K+) and foreign chemicals are added to the urine via tubular walls, a process called tubular secretion.

Colour: Clear yellow, attributed to pigment urochrome.
Volume: Typically 1 to 1.5 litres per day, varying with hydration and other factors.
pH: Ranges from 5 to 8.
Odour: Ammonia-like scent.
Specific Gravity: Between 1.003 and 1.035.

Normal urine consists of approximately 95% water and 5% dissolved solid wastes.
Abnormal Constituents:
- Blood Cells: Indicates hematuria.
- Glucose: Indicates glycosuria.
- Albumin: Presence known as albuminuria.
- Bile Pigments: May appear due to conditions such as anemia or liver disease.