Urinary System: Functions and Anatomy

Functions of the Urinary System

• Production of urine: The primary function of the urinary system is to produce urine for eliminating waste from the body.

  • Storage: Urine is stored in the bladder until it is expelled.

  • Elimination: Urine is eliminated from the body, not transported within it.

• Filtration of blood: The kidneys filter the blood to remove waste products, specifically focusing on nitrogenous waste.

  • Nitrogenous waste includes:

  • Urea: A product of protein metabolism.

  • Uric acid: Produced from the breakdown of purines.

  • Creatinine: A waste product from muscle metabolism.

  • Ammonia (NH₄): A byproduct of amino acid breakdown.

  • These compounds can accumulate in cases of renal failure, necessitating dialysis to prevent uremia, a condition characterized by elevated urea levels in blood.

• Regulation of blood pH:

  • Kidneys regulate blood pH through:

  • Excretion of hydrogen ions: When acidity increases, excess hydrogen is eliminated into the urine.

  • Bicarbonate production: Bicarbonate acts as a buffer to maintain pH levels in the blood.

• Regulation of blood pressure:

  • The renin-angiotensin-aldosterone system (RAAS) is crucial for managing blood pressure, emphasizing the kidneys' role in this physiological process rather than the heart.

• Control of electrolyte balance: The kidneys help regulate sodium, potassium, chloride, and calcium levels in the blood.

• Synthesis of vitamin D: The kidneys convert vitamin D into its active form, crucial for calcium absorption.

• Production of red blood cells:

  • The hormone Erythropoietin (EPO) secreted by the kidneys stimulates red blood cell production in the bone marrow.

Anatomy of the Kidneys

• Renal Capsule: Protective fibrous layer surrounding each kidney.

• External Structure:

  • Renal Cortex: The outer layer of the kidney, responsible for filtering blood.

  • Renal Medulla: The inner layer, contains structures critical to urine formation.

• Renal Structures:

  • Renal Pyramids: Triangular structures in the medulla where urine is collected.

  • Renal Columns: Areas of tissue between the pyramids.

  • Renal Papillae: The tips of the pyramids that deliver urine to the minor calices.

• Calices Structure:

  • Minor Calices: Surround each renal papilla and collect urine from the pyramids.

  • Major Calices: Formed from multiple minor calices, these lead into the renal pelvis.

  • Renal Pelvis: A funnel-shaped structure that collects urine from the major calices and drains into the ureter, which transports urine to the bladder.

Blood Supply to the Kidneys

• Blood enters the kidney through the Renal Artery, which branches into:

  • Segmental Arteries

  • Interlobular Arteries

  • Arcuate Arteries

  • Afferent Arterioles: Transport blood into the glomerulus.

• Glomerulus: A network of capillaries where filtration occurs.

• Blood exits the glomerulus via Efferent Arterioles and continues into Peritubular Capillaries for nutrient absorption and waste secretion.

Urine Formation

• Urine is formed from the filtration of blood within the kidneys:

  • Blood enters the nephron, is filtered in the glomerulus, and metabolites are removed, creating urine that passes through the renal tubules into the collecting ducts, calices, pelvis, and then the ureter.