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Chapter 17 Physiology of the Kidneys

Chapter 17 Physiology of the Kidneys

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Chapter 17 Physiology of the Kidneys

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  1. Chapter 17 Physiology of the Kidneys Dr. David Washington

  2. 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

  3. Uv p GFR = 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,

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

  5. Cortex Outer Medula Inner Medulla Counter-Current Mechanism(Urine Formation) K+ Na+ K+ Na+ H2O H2O Glucose Amino acid 300 400 600 320 400 600 200 400 H2O Na+ 800 1000 600 800 800 1000 Na+ Na+ Diffusion passive active 1200 Highly permeable to Na Impermeable to H2O

  6. Cortex Outer Medula Inner Medulla Counter-Current Mechanism(Urine Formation) Net action in loop of Henle - H2O reabsorption Net action at distal tubule: a. ADH - increases reabsorption b. Aldosterone - increases Na reabsorption

  7. Countercurrent Multiplier Mechanism Proximal Tubule Tubular lumen Peritubular fluid Na+ K + H2O Glucose Amino acids Glucose 70%

  8. Countercurrent Multiplier Mechanism Loop of Henle (Descending limb) H2O Na+ (Ascending limb) Na+ H2O Distal Tubule Na+ H2O 15% 14% x membrane impermeable K+ Diabetes insipidus

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

  10. Renin-Angiotensin-Aldosterone Pathway 14 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 10 8

  11. 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 Compensation for Low Sodium Low Na+ Intake Na+ retention in blood Sympathetic nerve activity

  12. H H O H H O H H O Acids, Bases and Buffers H+ OH- H+ OH- H - O - H H+ + OH- hydroxide H2O

  13. H H O H H O H H O Acids, Bases and Buffers HCL CL- H+ H+ CL- H+ CL- HCL H+ + CL- Acid in H2O

  14. H H O H H O H H O Acids, Bases and Buffers NaOH H+ H+ OH- Na+ OH- NAOH Na+ + OH- Base in H2O

  15. Bicarbonate Buffer System Contains mixture for converting strong acids + bases to weak acids and bases. Example: (H2CO3 and NaHCO3) a) HCL + NaHCO3 H2Co3 + NaCL sodium bi- carbonic carbonate acid b) NaOH + H2Co3 NaHCO3 + H20 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

  16. Bicarbonate Buffer System Buffer Curve: 0 25 50 75 100 75 50 25 Acid added H2CO3 NaHCO3 Base added pk 6.1 4 5 6 7 8 ph

  17. Henderson-Hasselbalch Equarion (pH caused by the concentration of CO2 in blood) HA H+ + A- 1) H2 CO3 H++ HCO3- carbonic bicarbonate ion acid Extracellular Fluid pH

  18. 2) KA = 3) KA = 4) log KA = log (H+) + log 5) - log(H+) = -logKA + log (HCO3-) (CO2) (HCO3-) (CO2) (H+)x(HCO3-) (H2CO3) (H+)x(HCO3-) (CO3) Extracellular Fluid pH Since [H2CO3] in extra-cellular fluids is an express of [CO2], we write --- equation 3.

  19. 6) pH = pKA + 7) pH =p KA + log pKA= 6.1; [HCO3-] = 24mM/L in arterial blood pH = 6.1 + log = 6.1 + log 20 = 6.1 + 1.3 = 7.4 24 0.03 x 40 (HCO3-) (CO2) (HCO3-) 0.03 x Pco2 Extracellular Fluid pH (solubility coefficient in mM/L)