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Fluid and Electrolyte Homeostasis  Na + and water: ECF volume and osmolarity  K + : cardiac and muscle function  Ca 2+ : exocytosis, muscle contractions,

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Presentation on theme: "Fluid and Electrolyte Homeostasis  Na + and water: ECF volume and osmolarity  K + : cardiac and muscle function  Ca 2+ : exocytosis, muscle contractions,"— Presentation transcript:

1 Fluid and Electrolyte Homeostasis  Na + and water: ECF volume and osmolarity  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

2 Figure 20-2 Water Balance in the Body

3 Figure 20-3 Water Balance A model of the role of the kidneys in water balance

4 Fluid and Electrolyte Homeostasis The body’s integrated response to changes in blood volume and blood pressure Figure 20-1a

5 Figure 20-1b Fluid and Electrolyte Homeostasis

6 Figure 20-4 Urine Concentration Osmolarity changes as filtrate flows through the nephron

7 Figure 20-5a Water Reabsorption Water movement in the collecting duct in the presence and absence of vasopressin

8 Figure 20-5b Water Reabsorption

9 Figure 20-6, step 1 Water Reabsorption Collecting duct lumen Filtrate 300 mOsm Cross-section of kidney tubule Collecting duct cell Medullary interstitial fluid Vasopressin receptor Vasa recta Vasopressin binds to mem- brane receptor mOsM 700 mOsM The mechanism of vasopressin action

10 Figure 20-6, steps 1–2 Water Reabsorption Collecting duct lumen Filtrate 300 mOsm Cross-section of kidney tubule Collecting duct cell Second messenger signal cAMP Medullary interstitial fluid Vasopressin receptor Vasa recta Vasopressin binds to mem- brane receptor. Receptor activates cAMP second messenger system mOsM 700 mOsM

11 Figure 20-6, steps 1–3 Water Reabsorption Collecting duct lumen Filtrate 300 mOsm Exocytosis of vesicles Cross-section of kidney tubule Collecting duct cell Second messenger signal cAMP Storage vesicles Aquaporin-2 water pores Medullary interstitial fluid Vasopressin receptor Vasa recta Vasopressin binds to mem- brane receptor. Receptor activates cAMP second messenger system. Cell inserts AQP2 water pores into apical membrane mOsM 700 mOsM

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

13 Figure 20-7 Factors Affecting Vasopressin Release Main Trigger

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

15 Figure 20-9 Countercurrent Heat Exchanger

16 Figure Water Balance Countercurrent exchange in the medulla of the kidney

17 Figure Ion reabsorption Active reabsorption of ions in the thick ascending limb creates a dilute filtrate in the lumen “Loop Diuretics” furosemide (Lasix) x

18 Fluid and Electrolyte Balance  Vasa recta removes water  Close anatomical association of the loop of Henle and the vasa recta--“countercurrent exchange”  Urea increases the osmolarity of the medullary interstitium--urea is 50% of solutes

19 Figure Sodium Balance Homeostatic responses to salt ingestion

20 Figure Sodium Balance Aldosterone action in principle cells Interstitial fluid Blood Aldosterone ATP Aldosterone receptor New channels P cell of distal nephron Translation and protein synthesis Proteins modulate existing channels and pumps. New pumps K+K+ Na + K+K+ K+K+ ATP K + secreted Na + reabsorbed Lumen of distal tubule 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 Transcription mRNA

21 Figure Sodium Balance The renin-angiotensin-aldosterone pathway

22 Figure Sodium Balance Decreased blood pressure stimulates renin secretion

23 Figure Sodium Balance Action of natriuretic peptides

24 Potassium Balance  Regulatory mechanisms keep plasma potassium in narrow range  Aldosterone plays a critical role (mentioned earlier)  Hypokalemia  Muscle weakness and failure of respiratory muscles and the heart  Hyperkalemia  Can lead to cardiac arrhythmias  Causes include kidney disease, diarrhea, and diuretics

25 Disturbances in Volume and Osmolarity Figure 20-17

26 Volume and Osmolarity

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29 Figure (1 of 6) Volume and Osmolarity Blood volume/ Blood pressure CVCC Parasympathetic output Sympathetic output Heart ForceRate Cardiac output Vasoconstriction Peripheral resistance Arterioles DEHYDRATION CARDIOVASCULAR MECHANISMS Carotid and aortic baroreceptors Blood pressure

30 Figure (2 of 6) Volume and Osmolarity Blood volume/ Blood pressure Osmolarity accompanied by Distal nephron Vasopressin release from posterior pituitary Volume H 2 O reabsorption H 2 O intake Thirst Hypothalamus DEHYDRATION HYPOTHALAMIC MECHANISMS Hypothalamic osmoreceptors Atrial volume receptors; carotid and aortic baroreceptors Osmolarity Blood pressure + +

31 Figure (3 of 6) Volume and Osmolarity Blood volume/ Blood pressure Granular cells GFR Flow at macula densa Angiotensinogen ANG I ACE ANG II Volume conserved DEHYDRATION RENIN-ANGIOTENSIN SYSTEM RENAL MECHANISMS + + Renin

32 Figure (4 of 6) Volume and Osmolarity Blood volume/ Blood pressure Osmolarity Granular cells accompanied by CVCC Angiotensinogen ANG I ACE ANG II Aldosterone Na + reabsorption Distal nephron Vasopressin release from posterior pituitary Arterioles Thirst Adrenal cortex DEHYDRATION RENIN-ANGIOTENSIN SYSTEM Renin osmolarity inhibits

33 Figure (6 of 6) Volume and Osmolarity Blood volume/ Blood pressure Osmolarity Granular cells GFR Flow at macula densa accompanied by CVCC Parasympathetic output Sympathetic output Heart ForceRate Cardiac output Vasoconstriction Peripheral resistance Angiotensinogen ANG I ACE ANG II Aldosterone Na + reabsorption Distal nephron Distal nephron Vasopressin release from posterior pituitary Arterioles Volume H 2 O reabsorption H 2 O intake Thirst Volume conserved Hypothalamus Adrenal cortex DEHYDRATION CARDIOVASCULAR MECHANISMS RENIN-ANGIOTENSIN SYSTEM RENAL MECHANISMS HYPOTHALAMIC MECHANISMS Carotid and aortic baroreceptors Hypothalamic osmoreceptors Atrial volume receptors; carotid and aortic baroreceptors Osmolarity Blood pressure Renin osmolarity inhibits


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