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Body Fluids and Transport
Water <ul><li>Body fluid is composed primarily of water </li></ul><ul><li>Water is the  solvent  in which all solutes in t...
Key concepts involving water <ul><li>Body water is contained in two major body compartments  (intracellular fluid compartm...
Key concepts involving water
Compartments <ul><li>Intracellular fluid (ICF) represents the  fluid inside the cells and is the largest   compartment (2/...
ECF divisions <ul><li>ISF occupies the space between cells and consists of 15% of total body fluid or ¾ of ECF </li></ul><...
BODY FLUIDS Distribution of Body Fluids  ICF ECF 40%  TBW 20%  TBW P IS 60-kg man TBW = 0.6 x 60 kg = 36 L ICF = 0.4 x 60 ...
Movement of molecule across cell membrane
<ul><li>The movement of molecules and ions both between cell organelles and the cytosol and between cytosol and extracellu...
Simple Diffusion <ul><li>The movement of molecules from one location to another as a result of their random thermal motion...
Membrane Permeability <ul><li>Diffusion through lipid bilayer </li></ul><ul><ul><li>Nonpolar, hydrophobic substances diffu...
Major characteristics of diffusion   pathways Yes No Chemical specificity Ions Nonpolar Typical molecules using pathway Ye...
Electric Forces and Ion Movement <ul><li>Separation of electric charge across plasma membrane known as  membrane potential...
Osmosis <ul><li>The net diffusion of water across a membrane is called  osmosis </li></ul><ul><li>Most plasma membrane hav...
Solutes <ul><li>Substances dissolved in a solution (sugar in your tea) </li></ul><ul><li>The addition of solute to water l...
Osmolarity <ul><li>The total concentration of a solution is known as  osmolarity. </li></ul><ul><li>It determine the water...
<ul><li>Isotonic : A solution containing 300 mOsmol/L of non penetrating solutes, </li></ul>
Solutes <ul><li>Substances dissolved in a solution (sugar in your tea) </li></ul><ul><li>These may be electrolytes or non-...
Diffusion Summary <ul><li>Diffusion is the movement of molecule from one location to another by random thermal motion </li...
<ul><li>Nonpolar molecule diffuse rapidly than do polar or ionized molecules </li></ul><ul><li>Mineral ions diffuse across...
Osmosis Summary <ul><li>Water crosses membranes by (1) diffusion through lipid by layer and (2) diffusing through protein ...
<ul><li>Osmosis across membrane permeable to water but impermeable to solute leads to increase volume in the compartment t...
 
Osmolality <ul><li>1 osmol solute dissolved in each kg of water </li></ul>
Permeable to water, Not permeable to solutes Presence of a membrane Impermeable to solute That leads to the volume Changes...
Osmotic Pressure <ul><li>The greater the osmolarity, the greater its osmotic pressure. </li></ul><ul><li>The lower the wat...
Tonicity <ul><li>Describes the behavior of a cell when it is placed in a solution </li></ul><ul><li>Depends not only on th...
Tonicity <ul><li>Describes the behavior of a cell when it is placed in a solution </li></ul><ul><li>Depends not only on th...
Water diffuses in Water diffuses out
-osmotic vs. -tonic <ul><li>Example:  1L solution containing 300 mOsm of non-penetrating NaCl and 100 mOsm of urea, which ...
Therapies Based on Two Basic Principles <ul><li>Water moves rapidly across cell membranes:  Osmolarities of ICF and ECF re...
Transport, the big picture fig 4-15
Facilitated diffusion (properties) Passive, carrier mediated Examples: glucose into most cells (not luminal membrane of ki...
Non-mediated vs. mediated transport fig 4-9
Primary active transport (Na + /K +  ATPase pump) 3 Na + ’s out, 2 K + ’s in, 1 ATP hydrolyzed fig 4-11
Primary active transport (Na + /K +  ATPase pump) 3 Na + ’s out, 2 K + ’s in, 1 ATP hydrolyzed fig 4-11
Primary active transport kinetics shows active transport shows carrier mediated
Effect of Na + /K +  ATPase pump fig 4-12
Secondary active transport fig 4-13
Secondary active transport properties Active (energy from ion gradient, usually Na + ) Carrier mediated  Can be cotranspor...
Sodium Reabsorption: Primary Active Transport <ul><li>Sodium  reabsorption is almost always by  active transport </li></ul...
Electrolytes-Sodium <ul><li>Major  cation in ECF   (positively charged) </li></ul><ul><li>Responsible for  90-95 % of extr...
Sodium Functions <ul><li>Sodium maintains ECF osmolality, ECF volume, and  influences water distribution   (where salt goe...
Sodium Recycling: Recycling and Excretion <ul><li>Ascending loop of Henle </li></ul><ul><ul><li>H 2 O impermeable </li></u...
<ul><li>Aldosterone: steroid H from adrenal cortex </li></ul><ul><ul><li>Stimulates Na +  uptake (& K +  secretion) </li><...
Mechanism of Na +  Selective Reabsorption in Collecting Duct Figure 20-12: Aldosterone action in principal cells
Imbalances <ul><li>Hyponatremia  (less than 130 mEq/L)-low sodium level-may cause seizures, headache, tachycardia, hypoten...
Artial Natruretic Peptide: Regulates Na +  & H2O Excretion <ul><li>Hormone from myocardial cells </li></ul><ul><li>Stimula...
Artial Natruretic Peptide: Regulates Na +  & H 2 O Excretion Figure 20-15: Atrial natriuretic peptide
Potassium Balance:  Critical for Excitable Heart & Nervous Tissues <ul><li>Hypokalemia – low [K + ] in ECF,  Hyperkalemia ...
Potassium Balance:  Critical for Excitable Heart & Nervous Tissues Figure 20-4: Osmolarity changes as fluid flows through ...
Potassium Balance:  Critical for Excitable Heart & Nervous Tissues Figure 20-12: Aldosterone action in principal cells
<ul><li>Thirst & &quot;salt craving&quot;, or avoidance behavior </li></ul><ul><li>Integrated circulatory & excretory refl...
Response to Dehydration & Osmolarity Imbalance
<ul><li>Acidosis:    plasma pH </li></ul><ul><ul><li>Protein damage </li></ul></ul><ul><ul><li>CNS depression </li></ul><...
Acid/Base Balance <ul><li>Homeostasis of hydrogen ion content </li></ul><ul><li>Body fluids are classified as either acids...
Acids <ul><li>During the process of cellular metabolism acids are continually being formed and excess hydrogen ions must b...
Non-volatile acids <ul><li>Cannot be eliminated by the lungs and  must be eliminated by the kidneys </li></ul><ul><li>All ...
Regulation of pH <ul><li>Three methods control pH </li></ul><ul><li>1.  chemical buffers-when   Hydrogen is removed a buff...
Chemical buffers <ul><li>These are  the first line of defense   against changes in pH </li></ul><ul><li>Act within a fract...
Buffers continued <ul><li>Carbonic acid-bicarbonate system is  most important extracellular buffer   because it can be reg...
Regulation of pH through kidneys <ul><li>Tubular secretion of H+ from convoluted tubules and collecting ducts so extra is ...
Acid/Base Homeostasis: Overview Figure 20-18: Hydrogen balance in the body
<ul><li>H +  & NH 4 +  secreted into lumen and excreted </li></ul><ul><li>HCO 3 -  is reabsorbed </li></ul>Kidney Hydrogen...
Kidney Hydrogen Ion Balancing: Proximal Tubule Figure 20-21: Proximal tubule secretion and reabsorption of filtered HCO 3 ...
<ul><li>Type A Intercalated cells excrete H +  absorb HCO 3 - </li></ul><ul><li>Type B intercalated cells absorb H +  secr...
Kidney Hydrogen Ion Balancing: Collecting Duct Figure 20-22: Role of the intercalated cell in acidosis and alkalosis
Ammonia <ul><li>Ammonia (NH3) is a weak base produced in cells of renal tubule by removal of amine group from some amino a...
Summary <ul><li>Electrolyte balance depends on integration of circulatory, excretory and behavioral physiology </li></ul><...
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  1. 1. Body Fluids and Transport
  2. 2. Water <ul><li>Body fluid is composed primarily of water </li></ul><ul><li>Water is the solvent in which all solutes in the body are either dissolved or suspended </li></ul><ul><li>An average male has 60-63% of his body weight as water </li></ul><ul><li>An average female has 45-52%, due to extra body fat </li></ul><ul><li>Infants are 80% water, and this decreases as a child grows until about age 8. </li></ul>
  3. 3. Key concepts involving water <ul><li>Body water is contained in two major body compartments (intracellular fluid compartment and extracellular fluid compartment) </li></ul><ul><li>Fluid balance is maintained when input and output are equal </li></ul><ul><li>The primary source of intake is water ingestion (eating and drinking) </li></ul><ul><li>In addition, digestion and metabolism of carbohydrates, proteins, and fats provides another source of intake </li></ul>
  4. 4. Key concepts involving water
  5. 5. Compartments <ul><li>Intracellular fluid (ICF) represents the fluid inside the cells and is the largest compartment (2/3 of body water) </li></ul><ul><li>Extracellular fluid (ECF) represents the fluid outside the cells and is 1/3 of total. </li></ul><ul><li>ECF is further divided into interstitial (ISF) and is the plasma. </li></ul>
  6. 6. ECF divisions <ul><li>ISF occupies the space between cells and consists of 15% of total body fluid or ¾ of ECF </li></ul><ul><li>Plasma is the fluid portion of the blood and is 5% of total body fluid or ¼ of ECF </li></ul>
  7. 7. BODY FLUIDS Distribution of Body Fluids ICF ECF 40% TBW 20% TBW P IS 60-kg man TBW = 0.6 x 60 kg = 36 L ICF = 0.4 x 60 kg = 24 L ECF = 12 L 3L 9L
  8. 8. Movement of molecule across cell membrane
  9. 9. <ul><li>The movement of molecules and ions both between cell organelles and the cytosol and between cytosol and extracellular fluid depends on the properties of these membranes </li></ul><ul><ul><li>Impermeable membrane - membrane though which nothing can pass </li></ul></ul><ul><ul><li>Freely permeable membrane - any substance can pass through it </li></ul></ul><ul><ul><li>Selectively permeable membrane - permits free passage of some materials and restricts passage of others </li></ul></ul>Membrane Transport
  10. 10. Simple Diffusion <ul><li>The movement of molecules from one location to another as a result of their random thermal motion is known as diffusion </li></ul><ul><li>Net movement of particles from area of high concentration to area of low concentration </li></ul>
  11. 11. Membrane Permeability <ul><li>Diffusion through lipid bilayer </li></ul><ul><ul><li>Nonpolar, hydrophobic substances diffuse much more rapidly across plasma membrane </li></ul></ul><ul><li>Diffusion of Ions through channel proteins </li></ul><ul><ul><li>water and charged hydrophilic solutes diffuse through channel proteins; these are lipid insoluble substances </li></ul></ul><ul><li>Cells control permeability by regulating number of channel proteins </li></ul>
  12. 12. Major characteristics of diffusion pathways Yes No Chemical specificity Ions Nonpolar Typical molecules using pathway Yes No Use of integral membrane protein Through protein Channels Through lipid Bilayer
  13. 13. Electric Forces and Ion Movement <ul><li>Separation of electric charge across plasma membrane known as membrane potential </li></ul><ul><li>The direction of ion flux across membranes depend on: </li></ul><ul><li>Concentration difference </li></ul><ul><li>Electrical difference </li></ul><ul><li>These two driving forces known as electrochemical gardient </li></ul>
  14. 14. Osmosis <ul><li>The net diffusion of water across a membrane is called osmosis </li></ul><ul><li>Most plasma membrane have permeability to water. </li></ul><ul><li>A group of membrane protein known as aquaporins form channel through which water can diffuse </li></ul>
  15. 15. Solutes <ul><li>Substances dissolved in a solution (sugar in your tea) </li></ul><ul><li>The addition of solute to water lowers the concentration of water in the solution </li></ul><ul><li>The greater the solute concentration the lower the water concentration </li></ul><ul><li>It does not depend on chemical nature </li></ul><ul><li>A molecule that ionizes in solution decreases the water concentration in proportion to the number of ion formed. </li></ul>
  16. 16. Osmolarity <ul><li>The total concentration of a solution is known as osmolarity. </li></ul><ul><li>It determine the water concentration in the solution. Higher osmolarity lower water concentration. </li></ul><ul><li>Osmotic pressure is the pressure that must be applied to the solution to prevent net flow of water. </li></ul>
  17. 17. <ul><li>Isotonic : A solution containing 300 mOsmol/L of non penetrating solutes, </li></ul>
  18. 18. Solutes <ul><li>Substances dissolved in a solution (sugar in your tea) </li></ul><ul><li>These may be electrolytes or non-electrolytes </li></ul><ul><li>Electrolytes have an electrical charge when they are dissolved in water </li></ul><ul><li>Electrolytes that have a positive charge are called cations </li></ul><ul><li>Electrolytes with negative charge are anions </li></ul>
  19. 19. Diffusion Summary <ul><li>Diffusion is the movement of molecule from one location to another by random thermal motion </li></ul><ul><li>The net flux between the two compartments always proceed from higher to lower concentration </li></ul><ul><li>Diffusion equilibirum is reached when the two concentration become equal </li></ul>
  20. 20. <ul><li>Nonpolar molecule diffuse rapidly than do polar or ionized molecules </li></ul><ul><li>Mineral ions diffuse across membranes by passing through ion channels formed by integral proteins </li></ul><ul><li>Diffusion of ions across membrane depends on both concentration difference and the membrane potential. </li></ul><ul><li>The flux of ions across a membrane can be altered by opening and closing ion channels </li></ul>Diffusion Summary
  21. 21. Osmosis Summary <ul><li>Water crosses membranes by (1) diffusion through lipid by layer and (2) diffusing through protein channels in the membrane </li></ul><ul><li>Osmosis is the diffusion of water from higher water concentration to lower water concentration. Osmolarity total solute concentration in the solution. The higher osmolarity of a solution the lower the water concentration. </li></ul>
  22. 22. <ul><li>Osmosis across membrane permeable to water but impermeable to solute leads to increase volume in the compartment that initially had higher osmolarity. </li></ul><ul><li>Application to a solution of sufficient pressure will prevent the osmotic flow of water into the solution from the compartment of pure water. This pressure is osmotic pressure. </li></ul>Osmosis Summary
  23. 24. Osmolality <ul><li>1 osmol solute dissolved in each kg of water </li></ul>
  24. 25. Permeable to water, Not permeable to solutes Presence of a membrane Impermeable to solute That leads to the volume Changes associated with Osmosis.
  25. 26. Osmotic Pressure <ul><li>The greater the osmolarity, the greater its osmotic pressure. </li></ul><ul><li>The lower the water concentration, the higher the osmotic pressure. </li></ul>
  26. 27. Tonicity <ul><li>Describes the behavior of a cell when it is placed in a solution </li></ul><ul><li>Depends not only on the number of particles in solution, but also on the NATURE of the solute </li></ul>
  27. 28. Tonicity <ul><li>Describes the behavior of a cell when it is placed in a solution </li></ul><ul><li>Depends not only on the number of particles in solution, but also on the NATURE of the solute </li></ul>
  28. 29. Water diffuses in Water diffuses out
  29. 30. -osmotic vs. -tonic <ul><li>Example: 1L solution containing 300 mOsm of non-penetrating NaCl and 100 mOsm of urea, which can cross the membrane would have a total osmolarity of 400 mOsm and would be hyperosmotic. However, it would be an isotonic solution producing no change in the equilibrium volume of cells immersed in it. </li></ul>
  30. 31. Therapies Based on Two Basic Principles <ul><li>Water moves rapidly across cell membranes: Osmolarities of ICF and ECF remain almost exactly equal </li></ul><ul><li>Cell membranes are almost completely impermeable to many solutes: the number of osmoles in the ECF or ICF remains constant unless solutes are added or lost from the ECF compartment </li></ul>
  31. 32. Transport, the big picture fig 4-15
  32. 33. Facilitated diffusion (properties) Passive, carrier mediated Examples: glucose into most cells (not luminal membrane of kidney or intestine), urea, some amino acids Kinetics: shows: passive shows: carrier mediated
  33. 34. Non-mediated vs. mediated transport fig 4-9
  34. 35. Primary active transport (Na + /K + ATPase pump) 3 Na + ’s out, 2 K + ’s in, 1 ATP hydrolyzed fig 4-11
  35. 36. Primary active transport (Na + /K + ATPase pump) 3 Na + ’s out, 2 K + ’s in, 1 ATP hydrolyzed fig 4-11
  36. 37. Primary active transport kinetics shows active transport shows carrier mediated
  37. 38. Effect of Na + /K + ATPase pump fig 4-12
  38. 39. Secondary active transport fig 4-13
  39. 40. Secondary active transport properties Active (energy from ion gradient, usually Na + ) Carrier mediated Can be cotransport (symport) or countertransport (antiport) Examples (many): Na + /amino acids, Na + /glucose (luminal membrane kidney, GI tract), *Na + /H + kidney, *Ca ++ /3Na + muscle, *Cl - /HCO 3 - red cell. (* = countertransport) Kinetics see primary active transport graphs
  40. 41. Sodium Reabsorption: Primary Active Transport <ul><li>Sodium reabsorption is almost always by active transport </li></ul><ul><ul><li>Na + enters the tubule cells at the luminal membrane </li></ul></ul><ul><ul><li>Is actively transported out of the tubules by a Na + -K + ATPase pump </li></ul></ul><ul><li>From there it moves to peritubular capillaries due to: </li></ul><ul><ul><li>Low hydrostatic pressure </li></ul></ul><ul><ul><li>High osmotic pressure of the blood </li></ul></ul><ul><li>Na + reabsorption provides the energy and the means for reabsorbing most other solutes </li></ul>
  41. 42. Electrolytes-Sodium <ul><li>Major cation in ECF (positively charged) </li></ul><ul><li>Responsible for 90-95 % of extracellular osmotic pressure </li></ul><ul><li>Regulated by aldosterone and the kidneys </li></ul><ul><ul><li>Increases sodium reabsorption in DCT of nephron </li></ul></ul><ul><ul><li>Also regulates K+ (secretion) </li></ul></ul><ul><li>Normal serum concentration in ECF ranges from 135-146 mEq/L </li></ul>
  42. 43. Sodium Functions <ul><li>Sodium maintains ECF osmolality, ECF volume, and influences water distribution (where salt goes water follows) </li></ul><ul><li>It affects the concentration, secretion, and adsorption of potassium and chloride ions, and can combine with bicarbonate ions and chloride ions to help regulate acid/base balance </li></ul><ul><li>It also help aid the impulse transmission of nerve and muscle fibers </li></ul>
  43. 44. Sodium Recycling: Recycling and Excretion <ul><li>Ascending loop of Henle </li></ul><ul><ul><li>H 2 O impermeable </li></ul></ul><ul><ul><li>Na + Active Transport </li></ul></ul><ul><ul><ul><li>To ECF </li></ul></ul></ul><ul><ul><ul><li>Gradient </li></ul></ul></ul><ul><ul><ul><li>Diffuses to blood </li></ul></ul></ul><ul><li>Collecting Duct: </li></ul><ul><ul><li>Aldosterone regulates </li></ul></ul><ul><ul><li>Na + recycled or excreted </li></ul></ul>
  44. 45. <ul><li>Aldosterone: steroid H from adrenal cortex </li></ul><ul><ul><li>Stimulates Na + uptake (& K + secretion) </li></ul></ul><ul><ul><li> channel synthesis </li></ul></ul>Mechanism of Na + Selective Reabsorption in Collecting Duct
  45. 46. Mechanism of Na + Selective Reabsorption in Collecting Duct Figure 20-12: Aldosterone action in principal cells
  46. 47. Imbalances <ul><li>Hyponatremia (less than 130 mEq/L)-low sodium level-may cause seizures, headache, tachycardia, hypotension, cramps, muscle twitching, irritability, decreased body temp, nausea, vomiting, and possible coma (polyuria due to diabetes insipidis may be one cause), </li></ul><ul><li>Hypernatremia (more than 150 mEq/L) -high sodium level-usually indicates water deficit in ECF-symptoms include thirst, tachycardia, dry sticky tongue, disorientation, hallucination, lethargy, seizures, coma, hypotension, agitation, low fever </li></ul>
  47. 48. Artial Natruretic Peptide: Regulates Na + & H2O Excretion <ul><li>Hormone from myocardial cells </li></ul><ul><li>Stimulates: hypothalamus, kidney, adrenal, & medulla </li></ul>
  48. 49. Artial Natruretic Peptide: Regulates Na + & H 2 O Excretion Figure 20-15: Atrial natriuretic peptide
  49. 50. Potassium Balance: Critical for Excitable Heart & Nervous Tissues <ul><li>Hypokalemia – low [K + ] in ECF, Hyperkalemia - high [K + ] </li></ul><ul><li>Reabsorbed in Ascending Loop, secreted in Collecting duct </li></ul>
  50. 51. Potassium Balance: Critical for Excitable Heart & Nervous Tissues Figure 20-4: Osmolarity changes as fluid flows through the nephron
  51. 52. Potassium Balance: Critical for Excitable Heart & Nervous Tissues Figure 20-12: Aldosterone action in principal cells
  52. 53. <ul><li>Thirst & &quot;salt craving&quot;, or avoidance behavior </li></ul><ul><li>Integrated circulatory & excretory reflexes </li></ul>Response to Dehydration & Osmolarity Imbalance
  53. 54. Response to Dehydration & Osmolarity Imbalance
  54. 55. <ul><li>Acidosis:  plasma pH </li></ul><ul><ul><li>Protein damage </li></ul></ul><ul><ul><li>CNS depression </li></ul></ul><ul><li>Alkalosis:  plasma pH </li></ul><ul><ul><li>Hyperexcitability </li></ul></ul><ul><ul><li>CNS & heart </li></ul></ul><ul><li>Buffers: HCO 3 - & proteins </li></ul><ul><li>H + input: diet & metabolic </li></ul><ul><li>H + output: lungs & kidney </li></ul>Acid/Base Homeostasis: Overview
  55. 56. Acid/Base Balance <ul><li>Homeostasis of hydrogen ion content </li></ul><ul><li>Body fluids are classified as either acids or bases depending on H ion concentration </li></ul><ul><li>Acid is an H donor and elevates the hydrogen ion content of the solution to which it is added </li></ul><ul><li>Base is an H acceptor and can bind hydrogen ions </li></ul><ul><li>Concentration is expressed as pH </li></ul><ul><li>Normal pH of blood is 7.35-7.45 (alkaline) </li></ul><ul><li>pH below 6.8 or above 7.8 is incompatible with life </li></ul>
  56. 57. Acids <ul><li>During the process of cellular metabolism acids are continually being formed and excess hydrogen ions must be eliminated </li></ul><ul><li>There are two types of acids formed: volatile acids are excreted by the lungs and nonvolatile acids are excreted by the kidney </li></ul><ul><li>Volatile acids can be excreted from the body as gas. Carbonic acid produced by the hydration of carbon dioxide is a volatile acid </li></ul><ul><li>Normally carbon dioxide is excreted by the lungs as fast as metabolism produces it, so carbonic acid is not allowed to accumulate and alter pH </li></ul>
  57. 58. Non-volatile acids <ul><li>Cannot be eliminated by the lungs and must be eliminated by the kidneys </li></ul><ul><li>All metabolic acids except carbolic are non-volatile acids </li></ul><ul><li>These include sulfuric acid, phosphoric acid, lactic acid, ketoacids like acetoacetic acid and beta hydroxybutyric acid, and small amounts of other inorganic and organic acids </li></ul>
  58. 59. Regulation of pH <ul><li>Three methods control pH </li></ul><ul><li>1. chemical buffers-when Hydrogen is removed a buffer replaces it </li></ul><ul><li>2. regulation of carbon dioxide by respiratory system </li></ul><ul><li>3. regulation of plasma bicarbonate concentration by the kidneys-slower, second line of defense </li></ul>
  59. 60. Chemical buffers <ul><li>These are the first line of defense against changes in pH </li></ul><ul><li>Act within a fraction of a second for immediate defense against H+ shift </li></ul><ul><li>These are a mixture of 2 or more chemicals that minimize changes in pH </li></ul><ul><li>Convert strong acids into weak acids and strong bases into weak bases </li></ul>
  60. 61. Buffers continued <ul><li>Carbonic acid-bicarbonate system is most important extracellular buffer because it can be regulated by both lungs and kidneys </li></ul><ul><li>Carbonic acid/bicarbonate ratio is usually 1:20 </li></ul><ul><li>CO 2 + H 2 O↔H 2 CO 3 ↔H + + HCO 3 - </li></ul><ul><li>Phosphates act as a buffer like the bicarbonate system does and protein buffers are the most abundant buffers in body cells and blood </li></ul>
  61. 62. Regulation of pH through kidneys <ul><li>Tubular secretion of H+ from convoluted tubules and collecting ducts so extra is excreted in urine </li></ul><ul><li>Helps regulate sulfuric acid and phosphoric acid, and other organic acids in body fluids as a result of metabolism </li></ul><ul><li>Diets high in protein generate more acid, so kidneys respond by secreting more hydrogen ion. (Atkins Diet) </li></ul><ul><li>In urine, hydrogen ion is buffered by phosphate and ammonia </li></ul>
  62. 63. Acid/Base Homeostasis: Overview Figure 20-18: Hydrogen balance in the body
  63. 64. <ul><li>H + & NH 4 + secreted into lumen and excreted </li></ul><ul><li>HCO 3 - is reabsorbed </li></ul>Kidney Hydrogen Ion Balancing: Proximal Tubule
  64. 65. Kidney Hydrogen Ion Balancing: Proximal Tubule Figure 20-21: Proximal tubule secretion and reabsorption of filtered HCO 3 -
  65. 66. <ul><li>Type A Intercalated cells excrete H + absorb HCO 3 - </li></ul><ul><li>Type B intercalated cells absorb H + secrete HCO 3 - </li></ul>Kidney Hydrogen Ion Balancing: Collecting Duct
  66. 67. Kidney Hydrogen Ion Balancing: Collecting Duct Figure 20-22: Role of the intercalated cell in acidosis and alkalosis
  67. 68. Ammonia <ul><li>Ammonia (NH3) is a weak base produced in cells of renal tubule by removal of amine group from some amino acids (deamination) </li></ul><ul><li>It diffuses into the tubule and accepts hydrogen ions to become NH4+ which is trapped in the tubule and excreted </li></ul>
  68. 69. Summary <ul><li>Electrolyte balance depends on integration of circulatory, excretory and behavioral physiology </li></ul><ul><li>Water recycling and ECF/plasma balance depends on descending loop of Henle and vasopressin regulated collecting duct for conservation </li></ul><ul><li>Osmolarity depends on aldosterone and angiotensin pathway to regulate CNS & endocrine responses </li></ul><ul><li>Along with respiration, proximal tubule and collecting duct cells reabsorb or excrete H + & HCO 3 - to balance pH </li></ul>

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