Chapter 19 The Kidneys

About this Chapter Anatomy of the excretory system How the kidney is organized How the nephron works to filter blood, recycle, secrete, and excrete How filtration is regulated Urination reflex

Kidney Functions: Overview Homeostatic regulation: ECF volume, osmolarity, ion & pH balance Excretion: Metabolic wastes & foreign molecules Regulating hormones & enzymes

Kidney Functions: Overview Figure 19-3: The excretion of a substance depends on the amount that was filtered, reabsorbed, and secreted

Excretory System: Anatomy Review Kidney Cortex Medulla Pelvis Nephrons Ureter Bladder Urethra Figure 19-1: Anatomy Summary: The Urinary System

Nephron Functions: Overview Figure 19-2: Filtration, reabsorption, secretion, and excretion

Glomerulus & Bowman's Capsule: Blood Filtration Capillaries Podocytes Mesanglial cells Bulk flow Solutes Water (Few proteins) (Not cells)

Glomerulus & Bowman's Capsule: Blood Filtration Figure 19-4: Structure of the renal corpuscle

Glomerular Flow Rate (GFR) Capillary Hydrostatic pressure Colloidal Capsule pressure Back pressure Net Filtration p GFR  180L/day (about 1% is excreted) Figure 19-6: Filtration pressure in the renal corpuscle

Glomerular Flow Rate (GFR) Figure 19-5: The filtration fraction

Regulation of GFR Autoregulation Myogenic stretch Tubuloglomerular feedback Macula densa J G cells ANS-Sympathetic Arteriole vasoconstriction Hormones/paracrines Angiotensin II Prostaglandins

Figure 19-9: The juxtaglomerular apparatus Regulation of GFR Figure 19-9: The juxtaglomerular apparatus

Reabsorption: 10 Active Transport (Passive diffusion in) Active Transport Na+ to ECF K+ into cell ATP-ase Uses energy Na+ ECF peritubular capillaries Reabsorption  blood

Reabsorption: 10 Active Transport Figure 19-11: Sodium reabsorption in the proximal tubule

Reabsorption: Secondary Active Transport Na+ linked 20 transport Symport Glucose Ions Amino acids Proximal tubule, key site Figure 19-12: Sodium-linked glucose reabsorption in the proximal tubule

Reabsorption: Passive Transport & Trancytosis Passive Transport of urea Na+ pumped out H2O follows Passive  [urea] [urea] higher than ECF passive diffusion to ECF Trancytosis of proteins

Reabsorption: Passive Transport & Trancytosis Figure 19-13: Passive reabsorption of urea in the proximal tubule

Reabsorption: Receptors can Limit Transport maximum Saturation (# of receptors) Competition Specificity Renal Threshold Example: glucosuria

Reabsorption: Receptors can Limit Figure 19-15: Glucose handling by the nephron

Secretion: From Peritubular Blood vessels & ECF Figure 19-2 : Filtration, reabsorption, secretion, and excretion

Solute Clearance: Rate of removal from the Blood Information on Kidney Function GFR Reabsorption rates Secretion rates Figure 19-16: Inulin clearance

Excretion: All Filtration Products that are not reabsorbed Excess ions, H2O, molecules, toxins, "foreign molecules" "nitrogenous waste": NH4+ and excess urea Kidney Ureter  bladder urethra out of body

Excretion: All Filtration Products that are not reabsorbed Figure 19-5: The filtration fraction

Urination: Micturation reflex Bladder: smooth muscles internal sphincter external sphincter Regulation

Urination: Micturation reflex Figure 19-18: The micturition reflex

Summary Kidney produces urine, ureter bladder urethra Nephron filters, reabsorbs, secretes and excretes Arteriole pressure dictates GFR through autoregulation, ANS and hormonal influences Most filtrate is reabsorbed & returned via peritubular blood vessels; excess & toxic remains are excreted Urination reflex uses involuntary and voluntary paths