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Chapter 20a Integrative Physiology II: Fluid and Electrolyte Balance.

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Presentation on theme: "Chapter 20a Integrative Physiology II: Fluid and Electrolyte Balance."— Presentation transcript:

1 Chapter 20a Integrative Physiology II: Fluid and Electrolyte Balance

2 About this Chapter Fluid and electrolyte homeostasis Water balance Sodium balance and ECF volume Potassium balance Behavioral mechanism in salt and water balance Integrated control of volume and osmolarity Acid-base balance

3 Na + and waterECF volume and osmolarity K+K+ Cardiac and muscle function Ca 2+ Exocytosis, muscle contractions, and other functions H + and HCO 3 – pH balance Body must maintain mass balance Excretion routes: kidney and lungs Fluid and Electrolyte Homeostasis

4 The body’s integrated responses to changes in blood volume and blood pressure Figure 20-1a Blood volume Blood pressure Volume receptors in atria and carotid and aortic baroreceptors Cardiovascular system Cardiac output, vasoconstriction Thirst causes water intake ECF and ICF volume Behavior Kidneys Conserve H 2 O to minimize further volume loss Blood pressure trigger homeostatic reflexes Stimulus Receptor Effector Tissue response Systemic response (a) KEY

5 Blood volume Blood pressure Volume receptors in atria, endocrine cells in atria, and carotid and aortic baroreceptors Cardiac output, vasodilation Excrete salts and H 2 O in urine Kidneys Cardiovascular system ECF and ICF volume Blood pressure trigger homeostatic reflexes Stimulus Receptor Effector Tissue response Systemic response (b) KEY Fluid and Electrolyte Homeostasis Figure 20-1b

6 Urine Lungs Feces Skin Water lossWater gain Totals 1.5 L/day 0.1 L/day Food and drink Metabolism 2.2 L/day 2.5 L/day 0.3 L/day Insensible water loss 0.9 L/day Intake 2.2 L/day Metabolic production 0.3 L/day Output 2.5 L/day +–= 0 Water Balance Figure 20-2

7 Water Balance The kidneys conserve volume but cannot replace lost volume Figure 20-3 Volume gainVolume loss GFR can be adjusted. Glomerular filtration rate (GFR) If volume falls too low, GFR stops. Regulated H 2 O reabsorption Volume loss in the urine Body fluid volume Kidneys conserve volume. Kidneys recycle fluid.

8 Urine Concentration Osmolarity changes as filtrate flows through the nephron Figure –1200 mOsM urine excreted 300 mOsM 600 mOsM 900 mOsM 1200 mOsM Distal tubule Proximal tubule Collecting duct Loop of Henle CORTEX MEDULLA Permeability to water and solutes is regulated by hormones. Variable reabsorption of water and solutes Ions reabsorbed but no water Only water reabsorbed Isosmotic fluid leaving the proximal tubule becomes progressively more concentrated in the descending limb. Removal of solute in the thick ascending limb creates hyposmotic fluid. Hormones control distal nephron permeability to water and solutes. Urine osmolarity depends on reabsorption in the collecting duct

9 Urine Concentration Figure 20-4, step 1 50–1200 mOsM urine excreted 300 mOsM 600 mOsM 900 mOsM 1200 mOsM Distal tubule Proximal tubule Loop of Henle CORTEX MEDULLA Permeability to water and solutes is regulated by hormones. Variable reabsorption of water and solutes Ions reabsorbed but no water Only water reabsorbed Isosmotic fluid leaving the proximal tubule becomes progressively more concentrated in the descending limb. 1 1 Collecting duct

10 Water Reabsorption Vasopressin makes the collecting duct permeable to water Figure 20-5a

11 Water Reabsorption Figure 20-5b

12 Collecting duct cell Second messenger signal Collecting duct lumen Medullary interstitial fluid Vasa recta Filtrate 300 mOsM cAMP Exocytosis of vesicles Vasopressin receptor 700 mOsM 600 mOsM Aquaporin-2 water pores 600 mOsM Cross section of kidney tubule Vasopressin Vasopressin binds to membrane receptor. Receptor activates cAMP second messenger system. Water is absorbed by osmosis into the blood. Storage vesicles Cell inserts AQP2 water pores into apical membrane. H2OH2O H2OH2O H2OH2O H2OH2O Water Reabsorption Vasopressin causes insertion of water pores into the apical membrane Figure 20-6

13 Water Reabsorption Figure 20-6, steps 1–4 Collecting duct cell Second messenger signal Collecting duct lumen Medullary interstitial fluid Vasa recta Filtrate 300 mOsM cAMP Exocytosis of vesicles Vasopressin receptor 700 mOsM 600 mOsM Aquaporin-2 water pores 600 mOsM Cross section of kidney tubule Vasopressin Vasopressin binds to membrane receptor. Receptor activates cAMP second messenger system. Water is absorbed by osmosis into the blood. Storage vesicles Cell inserts AQP2 water pores into apical membrane. H2OH2O H2OH2O H2OH2O H2OH2O

14 Factors Affecting Vasopressin Release Figure 20-7

15 Water Balance The effect of plasma osmolarity on vasopressin secretion by the posterior pituitary Figure 20-8

16 Countercurrent Heat Exchanger Figure 20-9 Warm blood (a)(b) Limb Warm blood Cold blood Heat lost to external environment

17 H 2 O = Cl – = KEY Na + = K + = Blood in the vasa recta Filtrate entering the descending limb The ascending limb pumps out Na +, K +, and Cl – 100 mOsM 300 mOsM 1200 mOsM Loop of Henle (a) Vasa recta Water Balance Countercurrent exchange in the medulla of the kidney Figure 20-10a

18 Ion reabsorption Active reabsorption of ions in the thick ascending limb creates a dilute filtrate in the lumen Figure 20-10b (b) KEY 1200 mOsm entering ascending loop of Henle Salt reabsorption Water cannot follow solute Cells of ascending loop of Henle Interstitial fluid 100 mOsm leaving the loop H 2 O = Cl – = Na + = K + =

19 Fluid and Electrolyte Balance Vasa recta removes water Close anatomical association of the loop of Henle and the vasa recta Urea increases the osmolarity of the medullary interstitium

20 Sodium Balance Homeostatic responses to salt ingestion Figure 20-11

21 Sodium Balance Figure New channels P cell of distal nephron Translation and protein synthesis Proteins modulate existing channels and pumps New pumps K+K+ Na + K + secreted Na + reabsorbed Lumen of distal tubule Interstitial fluid Blood Aldosterone Aldosterone receptor K+K+ Na + Aldosterone combines with a cytoplasmic receptor. Hormone-receptor complex initiates transcription in the nucleus. New protein channels and pumps are made. Aldosterone-induced proteins modify existing proteins. Result is increased Na + reabsorption and K + secretion. K+K+ ATP

22 Sodium Balance The renin-angiotensin-aldosterone system (RAAS) Figure Blood pressure Angiotensinogen in the plasma ANG I in plasma Granular cells (kidney) Renin Liver constantly produces produce contains Blood vessel endothelium ACE (enzyme) Volume and maintain osmolarity Hypothalamus Cardiovascular control center in medulla oblongata Adrenal cortex Blood pressure Arterioles Vasoconstrict Cardiovascular response Na + reabsorptionThirst Vasopressin Aldosterone ANG II in plasma

23 Sodium Balance Decreased blood pressure stimulates renin secretion Figure Blood pressure Cardio- vascular control center Paracrines Granular cells of afferent arteriole Macula densa of distal tubule Sympathetic activity NaCl transport Renin secretion GFR across direct effect

24 Increased blood volume causes increased atrial stretch Myocardial cells stretch and release Natriuretic peptides Kidney Adrenal cortex Medulla oblongata Hypothalamus Less vasopressin Decreased renin Less aldosterone Decreased blood pressure Increased GFR NaCl and H 2 O excretion Sodium Balance Natriuretic peptides promote salt and water excretion Figure 20-15


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