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Chapter 20, part B. Integrative Physiology II: Fluid and Electrolyte Balance. Sodium Recycling: Recycling and Excretion. Ascending loop of Henle H 2 O impermeable Na + Active Transport To ECF Gradient Diffuses to blood Collecting Duct: Aldosterone regulates
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Chapter 20, part B Integrative Physiology II: Fluid and Electrolyte Balance
Sodium Recycling: Recycling and Excretion • Ascending loop of Henle • H2O impermeable • Na+ Active Transport • To ECF • Gradient • Diffuses to blood • Collecting Duct: • Aldosterone regulates • Na+ recycled or excreted
Mechanism of Na+ Selective Reabsorption in Collecting Duct • Aldosterone: steroid H from adrenal cortex • Stimulates Na+ uptake (& K+ secretion) • channel synthesis
Mechanism of Na+ Selective Reabsorption in Collecting Duct Figure 20-12: Aldosterone action in principal cells
Angiotensin Pathway: Maintains BP , Volume & Osmolarity Angiotensinogen, ANGI, ANG II, rennin, & ACE Figure 20-13: The renin-angiotensin-aldosterone pathway
Artial Natruretic Peptide: Regulates Na+ & H2O Excretion • Hormone from myocardial cells • Stimulates: hypothalamus, kidney, adrenal, & medulla
Artial Natruretic Peptide: Regulates Na+ & H2O Excretion Figure 20-15: Atrial natriuretic peptide
Potassium Balance: Critical for Excitable Heart & Nervous Tissues • Hypokalemia – low [K+] in ECF, Hyperkalemia - high [K+] • Reabsorbed in Ascending Loop, secreted in Collecting duct
Potassium Balance: Critical for Excitable Heart & Nervous Tissues Figure 20-4: Osmolarity changes as fluid flows through the nephron
Potassium Balance: Critical for Excitable Heart & Nervous Tissues Figure 20-12: Aldosterone action in principal cells
Response to Dehydration & Osmolarity Imbalance • Thirst & "salt craving", or avoidance behavior • Integrated circulatory & excretory reflexes PLAY Animation: Fluids & Electrolytes: Water Homeostasis
Response to Dehydration & Osmolarity Imbalance Figure 20-17 : Homeostatic compensation for severe dehydration
Acid/Base Homeostasis: Overview • Acidosis: plasma pH • Protein damage • CNS depression • Alkalosis: plasma pH • Hyperexcitability • CNS & heart • Buffers: HCO3- & proteins • H+ input: diet & metabolic • H+ output: lungs & kidney
Acid/Base Homeostasis: Overview PLAY Animation: Fluids & Electrolytes: Acid/Base Homeostasis Figure 20-18: Hydrogen balance in the body
Kidney Hydrogen Ion Balancing: Proximal Tubule • H+ & NH4+ secreted into lumen and excreted • HCO3- is reabsorbed
Kidney Hydrogen Ion Balancing: Proximal Tubule Figure 20-21: Proximal tubule secretion and reabsorption of filtered HCO3-
Kidney Hydrogen Ion Balancing: Collecting Duct • Type A Intercalated cells excrete H+ absorb HCO3- • Type B intercalated cells absorb H+ secrete HCO3-
Kidney Hydrogen Ion Balancing: Collecting Duct Figure 20-22: Role of the intercalated cell in acidosis and alkalosis
Summary • Electrolyte balance depends on integration of circulatory, excretory and behavioral physiology • Water recycling and ECF/plasma balance depends on descending loop of Henle and vasopressin regulated collecting duct for conservation • Osmolarity depends on aldosterone and angiotensin pathway to regulate CNS & endocrine responses • Along with respiration, proximal tubule and collecting duct cells reabsorb or excrete H+ & HCO3- to balance pH