Chapter 17 Physiology of the Kidneys Dr. David Washington

Glomerular Filtration A person with a cardiac output of 5,600 ml/min would have a flow rate through the kidneys of about 1,200 ml/min, or 21% of the C.O. (renal fraction = = 21%) The glomeruli filter particles up to 80 A, therefore; proteins and blood cells are not filterable. 1,200 5,600 o

Measurement of GFR (Glomerular Filtration Rate) U = concentration of substance in urine P = concentration of substance in plasma V = volume of urine example (inulin) U = 125 mg/ml P = 1 mg/ml V = 1ml/min therefore, GFR = Uv p

Measurement of GFR (Glomerular Filtration Rate) That is; 125 ml of plasma had to be filtered to get 125 mg of inulin in the urine. GFR = 125 ml/min U = 125 mg/ml P = 1 mg/ml V = 1ml/min therefore, GFR = 125 mg/ml X 1 ml/min 1 mg/ml

Counter-Current Mechanism (Urine Formation) Highly permeable to Na Impermeable to H 2 O H2OH2O Diffusion passive active Cortex Outer Medula Inner Medulla H2OH2O H2OH2O Na + K+K+ K+K Glucose Amino acid

Counter-Current Mechanism (Urine Formation) Net action in loop of Henle - H 2 O reabsorption Net action at distal tubule: a. ADH - increases reabsorption b. Aldosterone - increases Na reabsorption Cortex Outer Medula Inner Medulla

Countercurrent Multiplier Mechanism Proximal Tubule Tubular lumenPeritubular fluid Na + K + H 2 O Glucose Amino acids Glucose 70%

Countercurrent Multiplier Mechanism Loop of Henle (Descending limb) H 2 O Na + (Ascending limb) Na + H 2 O Distal Tubule Na + H 2 O x K+K+ membrane impermeable Diabetes insipidus 15% 14%

Autoregulation of Glomerular Filtration Rate (J-G apparatus) Bowman’s capsule Glomerulus Juxtaglomerular cells Macula densa cells Afferent arteriole Efferent arteriole Distal tubule

Renin-Angiotensin-Aldosterone Pathway Angiotensinogen Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Leu-Val-Tyr-Ser Renin Angiotensin I Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu Ang.I Converting enzyme (in lungs) Angiotensin II Asp-Arg-Val-Tyr-Ile-His-Pro-Phe Vasoconstriction Aldosterone

Compensation for Low Sodium Low plasma Na + concentration Hypothalamus Posterior pituitary ADH Water reabsorption in collecting ducts Urine Vol Blood Vol Na + reabsorption in distal tubules Aldosterone Adrenal cortex Angiotensin II Renin Juxtaglomerular apparratus Low Na + IntakeNa + retention in blood Sympathetic nerve activity

Acids, Bases and Buffers H O H O H O OH - H+H+ H+H+ H - O - H H + + OH - hydroxide H2OH2O

Acids, Bases and Buffers H O H O H O CL - H+H+ H+H+ HCL H + + CL - Acid in H 2 O HCL H+H+ CL -

Acids, Bases and Buffers H O H O H O OH - H+H+ Na + NAOH Na + + OH - Base in H 2 O NaOH OH - H+H+

Bicarbonate Buffer System Contains mixture for converting strong acids + bases to weak acids and bases. Example: (H 2 CO 3 and NaHCO 3 ) a) HCL + NaHCO 3 H 2 Co 3 + NaCL sodium bi- carbonic carbonate acid b) NaOH + H 2 Co 3 NaHCO 3 + H 2 0 pk - the ph at which the concentration of the two portions of the buffer are equal. Buffer power - ability to maintain a ph following the addition of acid or base

Bicarbonate Buffer System Buffer Curve: pk 6.1 ph NaHCO 3 Base added Acid added H 2 CO 3

Extracellular Fluid pH n Henderson-Hasselbalch Equarion (pH caused by the concentration of CO 2 in blood) HA H + + A - 1) H 2 CO 3 H + + HCO 3 - carbonic bicarbonate ion acid

Extracellular Fluid pH 2) K A = 3) K A = 4) log K A = log (H + ) + log 5) - log(H + ) = -logK A + log (H + )x(HCO 3 - ) (H 2 CO 3 ) (H + )x(HCO 3 - ) (CO 3 ) (HCO 3 - ) (CO 2 ) (HCO 3 - ) (CO 2 ) Since [H 2 CO 3 ] in extra-cellular fluids is an express of [CO 2 ], we write --- equation 3.

Extracellular Fluid pH 6) pH = pK A + 7) pH =p K A + log pK A = 6.1; [HCO 3 - ] = 24mM/L in arterial blood pH = log = log 20 = = 7.4 (HCO 3 - ) 0.03 x Pco x 40 (HCO 3 - ) (CO 2 ) (solubility coefficient in mM/L)