Urinary Flashcards: Nephron Types

Nephron Types

• Cortical nephrons (85%): Short nephron loops with glomeruli in the outer renal cortex; responsible for excretory and regulatory kidney functions.
• Juxtamedullary nephrons (15%): Long loops of Henle that penetrate deeply into the medulla; crucial for maintaining osmotic gradient and concentrating urine.

Osmolarity

• Blood plasma osmolarity is crucial for physiological functions, while renal medulla osmolarity is involved in urine concentration and water balance.

Loop of Henle Function

• Establishes osmotic gradient in the renal medulla, preventing excessive production of dilute urine.
• Ascent and descent differ in permeability: descending limb is permeable to water; ascending limb is impermeable to water but allows solute diffusion.

Vasa Recta Structure and Function

• Vasa recta provides blood supply to the medulla with high permeability to solutes and water.
• Responsible for nutrient delivery and efficient removal of excess solutes and water from the interstitium.

Renal Autoregulation of GFR

• Nephrons can self-regulate blood flow and GFR, maintaining stable filtration rates despite fluctuations in arterial blood pressure.

ANS and GFR Control

• Sympathetic nervous system stimulation constricts afferent arterioles during stress, reducing GFR and redirecting blood to vital organs.

Renin-Angiotensin System

• Drop in blood pressure activates baroreceptors, stimulating renin release, which triggers a cascade increasing blood volume and pressure via angiotensin II.

Peritubular Capillaries

• High colloid osmotic pressure (COP) and low blood hydrostatic pressure (BHP) favor reabsorption of water and solutes back into circulation.

Nephron Components and Functions

• Different nephron segments (proximal convoluted tubule, loop of Henle, distal convoluted tubule) are specialized for filtration, absorption, and secretion.

Proximal Convoluted Tubule Functions

• Reabsorbs 65% of glomerular filtrate, including NaCl, K, water, glucose, and bicarbonate.
• Secretes waste products such as urea and ammonium ions.

Urea Recycling

• Occurs in the collecting duct and medulla; urea contributes to the osmolarity gradient, aiding in urine concentration.

Aldosterone and ADH Effects

• Aldosterone promotes sodium and water reabsorption in the distal tubule and collecting duct.
• ADH increases water reabsorption in the collecting duct, concentrating urine and reducing volume.
• Atrial Natriuretic Peptide (ANP) has opposite effects, promoting sodium and water excretion.

Renin-Angiotensin-Aldosterone Pathway

• Involves complex interactions starting from renin release to increasing blood pressure and fluid balance through angiotensin II and aldosterone.

Urine Composition

• Normal urine composition: 95% water, 5% solutes (urea, NaCl, KCl, creatinine).
• pH typically ranges from 4.5 to 8.2, usually around 6.0; elevated solutes like proteins should not be present.

Transport Maxima and GFR

• Transport maximum influences reabsorption capacity; if limits are exceeded, certain substances may remain in filtrate despite normal GFR levels.