1 / 66

Homeostasis.

Homeostasis. Definition : Processes by which bodily equilibrium is maintained constant. Examples of Bodily homeostasis: temperature blood pressure heart rate blood glucose level, etc. body fluid composition. BODY FLUID COMPARTMENTS.

gwydion
Download Presentation

Homeostasis.

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Homeostasis. • Definition: Processes by which bodily equilibrium is maintained constant. • Examples of Bodily homeostasis: • temperature • blood pressure • heart rate • blood glucose level, etc. • body fluid composition

  2. BODY FLUID COMPARTMENTS • General Goal:To describe the major body fluid compartments, and the general processes involved in movement of water between extracellular and intracellular compartments.

  3. The Body as an Open System • “Open System”. The body exchanges material and energy with its surroundings.

  4. Water Steady State. • Amount Ingested = Amount Eliminated

  5. Water Ingestion • Drinking (1.4 L/day). • Water contained in Food (0.85L/day). • Metabolism ----> CO2 and H2O (0.35 L/day).

  6. Water Elimination • Urinary loss (1.5 L/day). • Fecal loss (0.2 L/day). • Insensible H2O loss (0.9 L/day) • Sweat Losses. • Pathological losses. • vascular bleeding (H20, Na+) • vomiting (H20, H+) • diarrhea (H20, HCO3-).

  7. Electrolyte (Na+, K+, Ca++) Steady State. • Amount Ingested = Amount Excreted. • Normal entry: Mainly ingestion in food. • Clinical entry: Can include parenteral administration.

  8. Electrolyte losses • Renal excretion. • Stool losses. • Sweating. • Abnormal routes: e.g.. vomit and diarrhea.

  9. Metabolized Substances. • Chemically altered substances must also be in balance • Balance sheet: conservation between substrates and end products.

  10. Compartment. • DEFINITION. A non-specific term to refer to a region in the body with a unique chemical composition or a unique behavior. • Distribution of substances within the body is NOTHOMOGENEOUS.

  11. Compartment Properties. • Can be spatially dispersed. • Separated by membranes • Epithelial (or endothelial) barriers (cells joined by tight junctions)

  12. II. EXPRESSING FLUID COMPOSITION

  13. Gram Molecular Weight (GMW). • Mole (mol) (6.02x1023 molecules). • Atomic weight in grams • Molecules: sum atomic weight individual atoms.

  14. Physiological Molecular Weights

  15. Expressing Fluid Composition • Percentage • Molality • Molarity • Equivalence

  16. Percent Concentrations: (Solute / Solvent) x 100 • Body solvent is H2O • 1 ml weighs 1 g. • (weight/volume) percentages (w/v). • (weight/weight) percentages (w/w). • Clinical chemistries: mg % or mg / dl.

  17. Molality. • Concentration expressed as:moles per kilogram of solvent. • Rarely used

  18. Molarity (M). • Concentration expressed as:moles per liter of solution. • Symbol “M” means moles/liter not moles. • Physiological concentrations are low. • millimolar (mM) = 10-3 M • micromolar (mM) = 10-6 M • nanomolar (nM) = 10-9 M • picomolar (pM) = 10-12 M

  19. Electrochemical Equivalence (Eq). • Equivalent -- weight of an ionic substance in grams that replaces or combines with one gram (mole) of monovalent H+ ions. • Physiological Concentration: milliequivalent.

  20. Electrochemical Equivalence (Eq). • Monovalent Ions (Na+, K+, Cl-): • One equivalent is equal to one GMW. • 1 milliequivalent = 1 millimole • Divalent Ions (Ca++, Mg++, and HPO42-) • One equivalent is equal to one-half a GMW. • 1 milliequivalent = 0.5 millimole

  21. Complications in Determining Plasma Concentrations. • Incomplete dissociation (e.g. NaCl). • Protein binding (e.g. Ca++) • Plasma volume is only 93% water. • The other 7% is protein and lipid. • Hyperlipidemia • Hyperproteinemia.

  22. III. Distribution and Composition of Body Fluid Compartments

  23. Input PLASMA WATER RBC 3 L BONE 4.5% 3% 2 L INTERSTITIAL FLUID COMPARTMENT ECF CELL WATER 36% 25 L 24% 17 L DENSE CONNECTIVE 11.5% 8 L 4.5% 3 L TRANSCELLULAR WATER 1.5% 1 L Fig 2: Body Water Distribution

  24. Total Body Water • Individual variability = f(lean body mass) • 55 - 60% of body weight in adult males • 50 - 55% of body weight in adult female • ~42 L For a 70 Kg man.

  25. Extracellular Water vs. Intracellular Water • Intracellular fluid • ~36% of body weight • 25 L in a 70 Kg man. • Extracellular fluid • ~24% of body weight • 17 L in a 70 Kg man.

  26. Major Extracellular Fluid Compartments (11L of ECF) • Plasma (blood minus the red and white cells) • ~3 L in a 70 Kg man • ~4.5% of body weight. • Interstitial space (between organ cells) • ~8 L in a 70 Kg man • ~11.5% of body weight.

  27. Minor Extracellular Compartments (6 L of ECF) • Bone and dense connective tissue • Transcellular water (secretions) • digestive secretions • intraocular fluid • cerebrospinal fluid • sweat • synovial fluid.

  28. Blood is Composed of Cells and Plasma. • Hematocrit (Hct). • Fraction of blood that is cells. • Often expressed as percentage. • Plasma volume = Blood volume x (1-Hct).

  29. Ingress and Egress • Plasma water • Ingested nutrients pass through plasma on way to cells • Cellular waste products pass through plasma before elimination • Interstitial space. • Direct access point for almost all cells of the body • Exception -- red and white blood cells

  30. Solute Overview: Intracellular vs. Extracellular • Ionic composition very different • Total ionic concentration very similar • Total osmotic concentrations virtually identical

  31. Plasma Interstitial Cell H2O H2O H2O Figure 3: Summary of Ionic composition

  32. IV. PROTEINS, OSMOTIC CONCEPTS, DONNAN MEMBRANE EQUILIBRIUM

  33. Net Osmotic Force Development • Semipermeable membrane. • Movement some solute obstructed. • H2O (solvent) crosses freely. • End point: • Water moves until solute concentration on both sides of the membrane is equal. • OR, an opposing force prevents further movement.

  34. p = p S S S S S S S S S S S S S Osmotic Pressure (p). • The force/area tending to cause water movement.

  35. Initial Gl Gl Gl Gl 10 L 10 L Final Gl Gl Gl Gl 15 L 5 L Glucose Example

  36. Osmotic Concentration. • Proportional to the number of osmotic particles formed. • Assuming complete dissociation: • 1.0 mole of NaCl forms a 2.0 osmolar solution in 1L. • 1.0 mole of CaCl2 forms a 3.0 osmolar solution in 1L.

  37. Osmotic Concentration • Physiological concentrations: • milliOsmolar units most appropriate. • 1 mOSM = 10-3 osmoles/L

  38. Biological membranes are not impermeable to all solutes. • Endothelial Cell Barriers • All ions can freely cross the capillary wall. • Only proteins exert important net osmotic forces. • Cell Membrane Barriers • Membrane pumps effectively keep Na+ from entering cells, thus forming a virtual barrier. • Proteins can’t escape the cell interior.

  39. Gibbs-Donnan Membrane Equilibrium. • Proteins are not only large, osmotically active, particles, but they are also negatively charged anions. • Proteins influence the distribution of other ions so that electrochemical equilibrium is maintained.

  40. Total Volume 100 ml 50 K+ 50 K+ Initial 50 Cl- 50 Pr - 100 Osmoles 100 Osmoles 67 K+ Ions Move 33 K+ Step 2 17 Cl- 33 Cl- 50 Pr - 66 Osmoles 134 Osmoles 67 K+ H2O moves 33 K+ Final 17 Cl- 33 Cl- 50 Pr - 33 ml 67 ml Figure 5: Donnan’s Law • The product of Diffusible Ions is the same on the two sides of a membrane.

  41. Amount Injected Concentration = Volume of Distribution Measurement of Body Fluid Compartments • Based on concentration in a well-mixed compartment:

  42. Amount Injected - Amount Excreted Vd = Concentration after Equilibrium Measurement of Body Fluid Compartments • Requires substance that distributes itself only in the compartment of interest.

  43. Total Body Water (TBW) • Deuterated water (D2O) • Tritiated water (THO) • Antipyrine

  44. Extracellular Fluid Volume (ECFV) • Labeled inulin • Sucrose • Mannitol • Sulfate

  45. Plasma Volume (PV) • Radiolabeled albumin • Evans Blue Dye (which binds to albumin)

  46. Compartments with no Compartment-Specific Substance • Determine by subtraction: • Intracellular Fluid Volume (ICFV). ICFV = TBW - ECFV • Interstitial Fluid Volume (ISFV). ISFV = ECFV - PV

  47. VI. PRINCIPLES OF H2O MOVEMENT BETWEEN BODY COMPARTMENTS Intracellular vs. Extracellular

  48. Principles of Body Water Distribution. • Body control systems regulate ingestion and excretion: • constant total body water • constant total body osmolarity • Osmolarity is identical in all body fluid compartments (steady state conditions) • Body water will redistribute itself as necessary to accomplish this.

  49. Intra-ECF Water RedistributionPlasma vs. Interstitium • Balance of Starling Forces acting across the capillary membrane. • osmotic forces • hydrostatic forces • Discussed in more detail later in course

  50. Intracellular Fluid Volume • ICFV altered by: changes in extracellular fluid osmolarity. • ICFV NOT altered by:iso-osmotic changes in extracellular fluid volume. • ECF undergoes proportional changes in: • Interstitial water volume • Plasma water volume

More Related