urinary system 1: the nephrone

Overview of Nephrons

• Definition: Nephrons are the structural and functional units of the kidney, crucial for kidney function as a filter.

• Quantity: Approximately 1,200,000 nephrons per kidney.

• Location: Located in both the cortex (outer part) and the medulla (inner part).

Structure of Nephrons

• Two Main Parts:

  • Renal Corpuscle:

  • Composed of:

    • Glomerulus: A ball of fenestrated capillaries where blood is filtered under high pressure.

    • Bowman's Capsule: Encases the glomerulus; has two poles:

    • Vascular Pole (VP): Where blood enters through the afferent arteriole.

    • Urinary Pole (UP): Where filtrate exits into the renal tubule.

  • Renal Tubule:

  • Composed of three segments:

    • Proximal Convoluted Tubule (PCT): Twisted tubule nearest to the renal corpuscle.

    • Nephron Loop (Loop of Henle):

    • Contains descending and ascending limbs.

    • Has thick and thin segments.

    • Distal Convoluted Tubule (DCT): Further from the glomerulus, also twisted.

Urine Formation Process

• Filtration:

  • High-pressure blood enters the glomerulus, facilitating the removal of water and solutes into the capsular space, termed as filtrate.

• Filtrate Pathway:

  • Filtrate moves from the capsular space via the urinary pole into the PCT, descends through the nephron loop, ascends through the loop, and finally into the DCT, before entering the collecting duct.

Collecting Duct

• Function: Not considered part of the nephron itself; collects filtrate from multiple nephrons.

• Location: Plays a role in urine concentration and forms striations in the renal medulla.

Afferent vs Efferent Arterioles

• Afferent Arteriole: Larger diameter, allows for high pressure to facilitate filtration.

• Efferent Arteriole: Smaller diameter, helps maintain pressure for filtration in the glomerulus.

Types of Nephrons

• Cortical Nephrons:

  • Majority (about 85%); short nephron loop, most structures remain in the cortex.

• Juxtamedullary Nephrons:

  • Less common; have long nephron loops that dip deep into the medulla, essential for urine concentration due to osmolarity gradient.

Function of Nephrons

• Three Main Functions:

  1. Filtration:

  • Occurs in the renal corpuscle; removal of water and solutes from blood to form filtrate.

  1. Reabsorption:

  • Occurs in the renal tubule; reclaiming and returning substances (like water and salts) from filtrate back into the blood.

  1. Secretion:

  • Also occurs in the renal tubule; removal of additional wastes and excess substances from blood into the tubule for elimination.

Summary of Functions by Location

• Renal Corpuscle: Responsible for filtration.

• Renal Tubule: Responsible for reabsorption and secretion, processing the filtrate to maintain homeostasis and clear waste.

Conclusion

• Understanding the nephron's structure and function is essential for understanding how kidneys filter blood, restore balance, and produce urine.