The Urinary System: Structure and Function

The Urinary System

Overview of Urinary System Organs

The urinary system is essential for the removal of metabolic wastes and the regulation of fluid and electrolyte balance in the body. It consists of several organs, each with a specialized function.

• Kidneys: Major excretory organs responsible for filtering blood and forming urine.

• Urinary bladder: Temporary storage reservoir for urine.

• Ureters: Tubes that transport urine from the kidneys to the bladder.

• Urethra: Tube that transports urine out of the body.

Example: The kidneys filter blood to remove toxins, which are then excreted as urine through the ureters, stored in the bladder, and eliminated via the urethra.

Kidney Functions

The kidneys perform several vital functions to maintain homeostasis.

• Removal of toxins, metabolic wastes, and excess ions: Ensures the body's internal environment remains stable.

• Regulation of blood volume, blood pressure, chemical composition, and pH: Kidneys adjust the amount of water and solutes reabsorbed or excreted.

• Gluconeogenesis during prolonged fasting: Production of glucose from non-carbohydrate sources.

• Endocrine functions:

  • Renin: Regulates blood pressure and kidney function.

  • Erythropoietin: Stimulates red blood cell production.

• Activation of vitamin D: Converts vitamin D to its active form, aiding calcium absorption.

Additional info: The kidneys also help maintain acid-base balance and electrolyte concentrations.

Kidney Anatomy

Location and Structure

The kidneys are retroperitoneal organs located in the posterior abdominal region, specifically between the 12th thoracic and 3rd lumbar vertebrae.

• Right kidney is lower than the left: Due to the position of the liver.

• Shape: Convex lateral surface and concave medial surface.

• Renal hilum: The entry and exit site for ureters, blood vessels, lymphatics, and nerves.

Example: The renal hilum is a central indentation on the medial side of the kidney where structures enter and leave.

Supportive Tissue Layers

The kidneys are protected and stabilized by three layers of supportive tissue:

• Renal fascia: Outer layer of dense fibrous connective tissue anchoring the kidney.

• Perirenal fat capsule: Fatty cushion that stabilizes and protects the kidney.

• Fibrous capsule: Thin layer that prevents the spread of infection to the kidney.

Additional info: These layers help maintain the position of the kidneys and shield them from trauma.

Internal Anatomy of the Kidney

The kidney is divided into distinct regions, each with specialized structures.

• Renal cortex: The outer, granular region.

• Renal medulla: Inner region containing cone-shaped renal pyramids separated by renal columns.

• Lobe: A renal pyramid and its surrounding cortical tissue.

• Renal pelvis: Funnel-shaped tube within the renal sinus that joins the ureter.

• Minor and major calyces: Branching channels that collect urine from the pyramids and empty it into the renal pelvis.

Example: Urine flows from the renal pyramids into minor calyces, then major calyces, renal pelvis, ureter, and finally the bladder.

Blood and Nerve Supply

The kidneys receive a rich blood supply and are innervated by sympathetic nerves.

• Renal arteries: Deliver approximately 1200 ml of cardiac output to the kidneys each minute.

• Venous flow: Follows a similar path as arterial flow.

• Nerve supply: Sympathetic fibers from the renal plexus regulate blood flow and influence urine formation.

Additional info: The high rate of blood flow is necessary for efficient filtration and waste removal.

Structure	Function
Kidney	Filters blood, forms urine
Ureter	Transports urine to bladder
Urinary bladder	Stores urine
Urethra	Eliminates urine from body