Kidney Functions

9-26-08 Renal Introduction

Kidney Functions

Fluid Composition – controls fluid volume, osmolarity, electrolyte content, and pH
Metabolic End Products – excretes metabolic products, foreign substances (durgs), & hormones (insulin)
Enyzme/Hormone Production – creates renin, erythropoietin, vitamin D, prostaglandins

Body Water Composition Review

~60% of body weight is water:
2/3 of water is intracellular
1/3 of water is extracellular:
1/4 of extracellular water (1/12 of total) is circulating plasma
Hematocrit is about 40%, and thus total blood volume = (Plasma volume)/(1 – Hct)

Renal Failure EKG

K+is normally excreted by kidneys in larger amounts than Na+ or Cl-
Renal failure can’t excrete K+hyperkalemia more intense repolarization very large T-wave

Kidney Anatomy

Medulla – inner layer of renal pyramids  ascending/descending limbs of nephrons
Cortex – surrounding outer layer w/glomeruli, w/ portions penetrating between pyramids = renal columns
Renal Pelvis – collection of all renal pyramids
Renal Artery – gets 20% of cardiac output  important to filter blood
Arcuate Arteries – divide medulla from cortex, travel horizontally
Glomeruli – branches off arcuate artery into cortex, site of filtration
Afferent arteriole – leads from arcuate artery  glomeruli
Efferent arteriole – leads from glomeruli peritubular capillaries around nephrons
Bowman’s Space – outside of arteriole, but inside glomerulus, site of filtration
Plasma enters nephron at Bowman’s space, and re-enters blood at peritubular network

Kidney Plasma Journey

Afferent arteriole Bowman’s space & capsule  Proximal convoluted tubule  Thin descending limb (permeable only to water, gets sucked out)  Loop of Henle  Thin ascending limb (permeable only to ions, actively transports Na+ out) Thick ascending limb  Distal convoluted tubule (reg. signal to nephron) & Macula densa collecting duct  minor/major calyces  renal pelvis.
Bold = cortex, Regular = medulla
Proximal Convoluted Tubule – thicker epithelial lining, bulk of filtration work
Distal Convoluted Tubule – thinner epithelial lining, fine-tuning of filtration

Kidney Function

Creatinine – muscle breakdown product excreted at constant rate, thus great kidney function marker
High Creatinine – not being reabsorbed by kidneys, and thus renal failure
Low Creatinine – kidneys functioning properly to re-absorb creatinine (good = 1)
Na+/K+ ATPase – present in epithelial cells of nephron, function to generate osmotic gradient for filtration
Apical Microvilli – lumen-facing villi in tubules, break off and excreted in urine if in kidney failure
Casts – remnants of cells excreted in kidneys pathological, means kidneys aren’t filtering properly

Kidney X-ray

Visualization – patient ingests contrast agent, take x-ray of kidneys to assess function as contrast passes by
Abnormalities – will see blockages where contrast builds up in disease states

End-Stage Kidney Disease Treatments