Excretory System: Excretion is the process by which organisms remove waste products of metabolism from their bodies.

Metabolism: Metabolism encompasses all processes and chemical reactions that occur within a cell.

Examples of Metabolic Waste:

1. CO₂ – From respiration.
2. Excess Water – Resulting from excess fluid intake.
3. Nitrogenous Wastes – Such as urea, uric acid, and ammonia.
4. Waste Chemicals – Including hormones and drug by-products.
5. Bile Pigments – Produced from the breakdown of red blood cells.

Parts and Functions of the Excretory System:

1. Skin:
   • Removes excess water and mineral salts as sweat.
2. Lungs:
   • Eliminates CO₂ and water vapor.
3. Liver:
   • Removes bile pigments, dead cells, toxins, and medicine by-products.
4. Kidney:
   • Removes excess salts, water, and nitrogenous wastes in the form of urine.

Urinary System: Comprises:

• Kidney
• Urinary Bladder
• Ureter
• Urethra

Functions:

1. Urinary Bladder:
   • Temporarily stores urine.
2. Ureter:
   • Transports urine from the kidneys to the bladder.
3. Urethra:
   • Conducts urine from the bladder to the outside of the body through the penis.
4. Kidney:
   • Produces urine and eliminates other wastes.

Parts and Functions of the Kidney:

1. Cortex:
   • The outer part, lighter in color.
2. Medulla:
   • The inner part, darker in color.
3. Pelvis:
   • The widened end of the ureter that enters the kidney.
4. Nephrons:
   • Millions of tiny structures; the functional units of the kidney. Each kidney contains millions of nephrons, located in both the cortex and medulla.
5. Renal Vein:
   • Joins the vena cava, carrying blood from the kidney back to the general circulation.
6. Renal Artery:
   • Branches off from the aorta, supplying oxygenated blood rich in nutrients to the kidney.

The Kidney:

• There are two kidneys.
• Located near the back of the abdominal cavity.
• Each kidney weighs about 142.5 grams.
• Surrounded by a layer of fat that cushions it from physical damage.
• Bean-shaped.
• The main excretory organ.
• Excretes nitrogenous wastes in the form of urine.

Bowman’s Capsule:

• A cup-shaped structure where ultrafiltration occurs.
• Contains capillaries known as the glomerulus.

Glomerulus:

• A knot of capillaries branching from the afferent arteriole of the renal artery.
• Reunites to form the efferent arteriole, which channels blood away from the glomerulus.

Efferent Arteriole:

• Branches out into a second network of capillaries that surround the convoluted tubules and loop of Henle.
• Capillaries reunite to form venules, which then form the renal vein, taking blood out of the kidney to the heart via the vena cava.

Distal Convoluted Tubules:

• Formed from the ascending loop of Henle.
• Joins the collecting duct where urine is collected.

Kidney Function:

• The primary function of the kidney is to excrete urea in the form of urine.