Excretion, Osmoregulation and Homeostasis

Excretion, Osmoregulation and Homeostasis
• Excretion: nitrogenous wastes (urea, uric acid), excess salts, excess water.
• Osmoregulation: maintaining the blood at a suitable constant concentration.
• Homeostasis: maintaining a suitable constant internal environment to sustain efficient metabolism.
Urinary System
Textbook Diagram: urinary system.
• The kidneys are a pair of fist-sized red-brown bean-shaped structures.
• The kidneys are attached to the back wall of the abdominal cavity.
• They lie on either side of the backbone just above the pelvis.
• Each kidney receives a good supply of oxygenated blood from the renal artery, a branch of the dorsal aorta.
• The renal vein takes the deoxygenated blood from the kidneys to the inferior vena cava.
• The blood in the renal vein has less oxygen, salt, urea and uric acid than the renal artery.
• Urine is carried to the bladder along the ureter by peristalsis for temporary in the bladder.
• A sphincter muscle at the junction of the bladder and urethra regulates the retention and release of urine.
• Urine is channelled to the exterior along the urethra.

Kidney Structure
Textbook Diagram: longitudinal section of a kidney showing its internal structure.
• A smooth thin protective cover called the capsule surrounds each kidney.
• Below the capsule is a thick reddish granular layer, the cortex.
• The central part of the series of triangular structures is reddish-brown, the renal pyramids, the tips of which project into the upper expanded end of the ureter known as the pelvis.

Textbook diagram: structure and blood supply of the nephron.
• The nephron or renal tubule is the functional unit of the kidney.
• The nephron has a number of functionally distinct parts.
• Each human kidney has about one million nephrons.
• Urine is manufactured by the nephrons.
Production of Urine: Filtration and Selective Reabsorption

Details of Urine Formation