The Renal System: Overview

Components of the Renal System

• Kidneys: Paired bean-shaped organs located outside the peritoneal cavity in the upper abdomen.
• Connecting Arteries and Veins: Supply blood to and from the kidneys.
• Urinary Tract: Includes the ureters, bladder, and urethra.

Functions of the Kidneys

• Main excretory organs that filter metabolic waste products from the blood.
• Urine Formation: Unneeded substances are filtered from the blood forming urine that travels via the ureters to the bladder, then expelled through the urethra.
• Blood Composition Regulation:
  • Maintain blood volume and pressure.
  • Ensure balance of electrolytes: sodium, chloride, potassium, calcium, hydrogen phosphate.
  • Regulate pH levels.
  • Eliminate metabolic waste: urea, uric acid, creatinine.

Structural Overview

• Hylas: The medial border of the kidney with a deep fissure where blood vessels, nerves, and ureters connect.
• Lobes and Nephrons:
  • Up to 18 lobes per kidney.
  • Each lobe contains nephrons (over 1 million per kidney).
• Nephron Components:
  • Glomerulus: High-pressure capillaries that filter blood, encased in Bowman's capsule.
  • Bowman's Capsule and Space: Filters plasma-like fluid from blood, forms the primary urine.

Nephron Tubule System

• Proximal Convoluted Tubules: Coiled segment where most nutrient absorption occurs.
• Loop of Henle: Loop structure for water and ion reabsorption and urine concentration control.
• Distal Convoluted Tubules: Regulates potassium, sodium, pH, and dilutes urine further.
• Collecting Tubules: Final sodium regulation, joining multiple tubules to collect filtrate.

Blood Supply and Filtration Process

• Renal Artery: Supplies each kidney, branches into segmental and lobular arteries.
• Afferent/Efferent Arterioles: Regulate glomerular capillary pressure.
• Peritubular Capillary Network: Low-pressure system surrounding tubules for rapid solute and water movement.

Urine Formation Process

1. Filtration: Blood flows into glomerulus, plasma moves to Bowman's space.
2. Tubular Reabsorption: Electrolytes and nutrients move back into bloodstream from filtrate.
3. Tubular Secretion: Substances from peritubular capillaries move into urine filtrate.
4. Final Urine Concentration: Occurs in collecting tubules, then directed to renal pelvis, ureter, bladder, and urethra for elimination.

Summary

• The kidneys filter blood, reabsorb necessary substances, and excrete waste.
• The nephron is the functional unit of the kidney, composed of a glomerulus and a tubular component for filtering and reabsorption processes.

These notes summarize the structure and functions of the renal system, focusing on the roles of the kidneys and nephrons in maintaining body homeostasis.