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Body CompartmentsRegulation of Fluid & Electrolyte
Balance Volume Osmolarity Disturbance Potassium Balance
Acid-Base Balance
OUTLINE
Body Compartments
Body Compartments
Fluid compartments are separated by membranes that are freely permeable to water
Movement of fluids due to: hydrostatic pressure osmotic pressure Starling forces
Fluid Movement
Starling Forces
Swelling of tissues due to excess interstitial fluidCauses:
Increased venous pressure (e.g. heart failure) Increased capillary permeability leak of plasma
proteins to interstitial fluid (e.g. anaphylactic shock)
Decreased plasma proteins (e.g. liver disease, malnutrition)
Inadequate lymph drainage (e.g. filariasis)
Edema
Body Compartments
All homeostatic mechanisms that monitor and adjust composition of body fluids respond to changes in ECF, not ICF
No receptors directly monitor fluid or electrolyte balance plasma volume & osmotic concentration
Cells cannot move water by active transport “water follows salt”
Regulation of Fluid & Electrolyte Balance
Osmolarity Tonicity Through water balance
Volume Blood Pressure Through salt balance
Regulation of ECF
Tonicity
Water Balance
Water Output
Regulation of Fluid Intake – Thirst
Regulation of Fluid Output – Urine
Kidneys conserve water by regulating urine concentration/osmolarity: 50-1200 mOsM
Countercurrent mechanism producing vertical osmotic gradient
Vasopressin/Antidiuretic Hormone (ADH) controls water reabsorption
Obligatory urine volume: 500 mL
Regulation of Fluid Output – Urine
Countercurrent Mechanism
Countercurrent Mechanism
Vasopressin/ADH
Vasopressin/ADH
Vasopressin/ADH
Short-term: Baroreceptor reflex cardiac output and
total peripheral resistance Fluid shifts due to Starling forces
Long-term: ECF volume salt balance
Regulation of Blood Pressure
Sodium account for >90% of ECF’s osmotic activity conservation of salt = conservation of water (“water follows salt”) primary determinant of ECF volume
Salt Balance
Intake: Poorly regulated; usually >>
Output: Obligatory loss in sweat and feces (0.5
g/day) Urine: controlled, very precise
Filtration: GFR Reabsorption: Renin-Angiotensin-Aldosterone
(RAA) system; Atrial Natriuretic Peptide (ANP)
Salt Balance
Salt Balance
RAA System
RAA System - Aldosterone
RAA System - Aldosterone
ANP
Integration of Fluid & Electrolyte Balance
Integration of Fluid & Electrolyte Balance
Disturbances of Fluid and Electrolyte Balance
98% in ICF
Intake: DietaryOutput: Urine
Disturbances in Potassium balance are less common than sodium balance, but significantly more dangerous
Potassium Balance
Factors affecting rate of K+ tubular secretion: K+ concentration in ECF (from dietary
intake) Aldosterone levels (promotes secretion) pH of ECF (acidosis: decreases secretion,
vice versa)
Potassium Balance
Potassium Balance
Acid-Base Balance
Buffer System
Buffer SystemLungs
Buffer System - Renal
Buffer System - Renal
Buffer System - Renal
Buffer System - Renal
Acid-Base Balance
Disturbances of Acid-Base Balance
SUMMARY
Guyton AC, Hall JE. Textbook of medical physiology.11th ed. Philadelphia. Elsevier, Inc. 2006.
Martini FH, Nath JL, Bartholomew EF. Fundamentals of anatomy & physiology. 9th ed. Boston. Benjamin Cummings. 2012
Sherwood L. Human Physiology from cells to system, 7th ed. Australia. Brooks/Cole Cengange Learning. 2011.
Silverthorn DU. Human physiology: an integrated approach. 5th ed. San Francisco. Pearson Education, Inc. 2010.
Tortora GJ, Derrickson B. Principles of anatomy and physiology. 12th ed. USA. John Wiley & Sons, Inc. 2009.
REFERENCES
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