Quartz 5

Renal Physiology

2 min read

Blood Supply

Intrinsic Regulation - GFR Maintenance

Purpose: Maintain GFR- H2O and Solute Homeostasis

  • Mechanism: Smooth muscle contraction in Afferent Arteriole / Macula Densa

State: GFR too high
Solution: Constrict afferent arteriole

  • Triggered by:
  1. Afferent arteriole stretch (mildly elevated BP): too much blood going into glomerulus
  2. High [NaCl] concentration : too much tubular fluid solute
  • Reaction:
  1. Myogenic Response: Intra-arteriole Ca2+ release causes SMC contraction in afferent arteriole
  2. Tubuloglomerular Mechanism: Macula Densa releases “vasoactive magic stuff” that constricts afferent arteriole

State- GFR too low
Solution- Relax afferent arteriole / Constrict efferent arteriole

  • Triggered by:
  1. Afferent arteriole shrinkage (mildly lowered BP): not enough blood going into glomerulus
  2. Low [NaCl] concentration : not enough tubular fluid solute
  • Reaction:
  1. Myogenic Response: SMC relaxes in afferent arteriole
  2. Tubuloglomerular Mechanism: Macula Densa releases prostaglandin/renin, that constricts efferent arteriole

Extrinsic Regulation - BP Maintenance

Purpose: Maintain BP- something bad happened (BP/Blood Volume (BV) too low!)
Mechanisms: Hormones and Sympathetic Nervous System

State- BP/blood volume too high
Solution- Constrict afferent arteriole

  • Triggered by:
  1. R Atrium Stretch: ANP released
  2. High [NaCl] concentration: too much tubular fluid solute
  • Reaction:
  1. Myogenic Response: Intra-arteriole Ca2+ release causes SMC contraction in afferent arteriole
  2. Tubuloglomerular Mechanism: Macula Densa releases “vasoactive magic stuff” that constricts afferent arteriole

State- BP/blood volume too low
Solution- Relax afferent arteriole / Constrict efferent arteriole

  • Sympathetic (neurotransmitter or circulating catecholamine), e.g., hemorrhaging
  • Granular cells release renin.
  • Constrict afferent (far more a1 receptors) more than efferent arterioles (fewer a1 receptors)to decrease filtration to conserve blood volume.
  • This also indirectly triggers the Renin-Angiotensin-Aldosterone system.

Juxtaglomerular Apparatus

Graph View

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