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7/30/2019 CH 25 of Guyton
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ABCJJKKMP- Batch 2017 Page 1
Lectured on: August 29, 2013
Lectured by: Dra. Felices Emerita Pascual - Perez
RENAL PHYSIOLOGY
Topic: THE BODY FLUIDS COMPARTMENTS : ECF & ICF
Maintenance of a relatively constant volume and a stable composition of the
body fluids is essential for homeostasis
Water Balance to maintain a steady state, water intake must equal water
excretion.
Average INTAKE per day 2300 mL
2100 mL from ingested
food and beverages
200 mL from metabolism
Average OUTPUT per day 2300 mL
100 mL feces (4%)
100 mL sweat (8%)
700 mL insensible losses via skin and lungs (25%)
1400 mL urine (60%)
BALANCE CONCEPTS
Balance is necessary, in the long-term,
to maintain life.
Fluid Loss = Fluid Intake
Electrolyte Loss = Electrolyte Intake
Fluid Intake: regulated by thirst mechanism, habits
Electrolyte intake: governed by dietary habits
Fluid Output: regulated mainly by kidneys
Electrolyte output: regulated mainly by kidneys
BODY FLUIDS COMPARTMENTS
FLUID BALANCE (ml/day)70 kg
Adult
TOTAL BODY WATER IN RELATION TO BODY WEIGHT: EFFECTS OF GENDER,
BODY BUILD AND AGE
Transcellular fluid compartmenta specialized type of ECF 1-2liter
- Synovial fuid- Peritoneal fluid- Pericardial fluid- CSF (cerebrospinal fluid)
BODY FLUID COMPARTMENTS
ECF ICF
20% of body weight = 14 L 40% of total body weight = 28 L
(++) Na+, Cl- and Bicarbonate ions Only small amount of Na+ and Cl-ions and almost no Calcium
Has small amount of Potassium,
Calcium, Magnesium phosphate and
organic acids
Proteins: Plasma > ISF
Large amount of K+ and PO4- ions.
Moderate quantities of Mg++ and
Sulfate ions
Proteins -4x greater than ECF
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BLOOD VOLUME
Both ECF & ICF Average blood volume = 5 L (7 % of body weight) 60% plasma, 40% RBC Hematocrit
- Fraction of the blood composed of RBC- Men 0.40- Females 0.36- Anemia low levels- Polycythemia excessive production
COMPUTATION OF BODY WATER
(for a 70 kg man)
Total Body Water (TBW)
= 60% or 0.6 x Body weight (BW)
42L
ECF ICF
=20% or 0.2 x BW =40% or 0.4 x BW
13L 28L
MEASUREMENT OF BLOOD VOLUME
Total Volume = Plasma volume1-Hematocrit
An average 70 kg man:
Total blood volume = 3.5 L / 1-0.40
= 5.8 L
Blood volume = 7% of body weight
Hct in male = .40
REGULATION OF FLUID EXCHANGE AND OSMOTIC EQUILIBRIUM
b/w ICF & ECF
The distribution of fluids between ECF and ICF is determinedmainly by the osmotic effect of smaller solutes.
- Sp. NaCl and other electrolyte acting across the cellmembrane
Involves semi-permeable cell membrane- Permeability: Water >>> NaCl- Thus water moves very rapidly across the membrane
so that the ICF remains isotonic with the ECF.
CONTROL OF BODY FLUID DISTRIBUTION
Distribution across cell membranes determined by osmotic forces (mainly
from electrolytes)
Distribution across capillaries determined by hydrostatic and colloid
osmotic forces.
BASIC PRINCIPLES OF OSMOSIS AND OSMOTIC PRESSURE
Osmosis Net diffusion of water across a selectively permeable membrane
from a region of high water concentration that has a lower water
concentration.
-The higher the solute concentration the lower the waterconcentration.
Rate of osmosis Rate of diffusion of water
WHAT IS THE DIRECTION OF OSMOSIS?
A.
Pure water
B.
C.
With solute
Osmole - refers to the number of osmotically active particles in a solution.
-
1 osmole is equal to 1 molecule of solute
1 mole of Glucose L = 1 osmole L 1 mole of NaCl L = 2 osmoles L 1 mole of Na2SO4 L = Osmoles L 1 milliosmole = 1 1000 osmole
ISF
of ECF
10.5L
Plasma
1/3 of
ECF
3.5L
*
* *
*
* *
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OSMOLARITY AND OSMOLALITY
Osmolality- Osmolal concentration of solution- OSmoles per kg of water (osm/kg H2O)
Osmolarity- Osmoles per literof solution (osm/L)
OSMOLARITY
Fluid Osmolarity:-
ECF: Na and Cl ions- ICF: 50% due to K+- Corrected osmolarity is 282 mosm/L
RELATION BETWEEN OSMOTIC PRESSURE AND OSMOLARITY
Osmotic pressure of a solution is directly proportional to theconcentration of osmotically active substances regardless of the
size of the solute/
Which has a higher osmotic pressure? Albumin, Glucose, NaCl
OSMOTIC PRESSURE : VAN HOFFS LAW
PRINCIPLES OF OSMOTIC EQUILIBRIUM
CALCULATION OF THE OSMOLARITY AND OSMOTIC PRESSURE OF A
SOLUTION
What is the osmotic pressure of a -.9% NaCl solution? Is this isotonic, hypotonic or hypertonic?
OSMOLARITY OF A 0.9% NaCl SOLUTION
OSMOLARITY
Plasma mosm/L ISF ICF
Total mosm/L 301.8* 300.8 300.8
Corrected** 282 mosm/L 281 mosm/L 281 mosm/L
Total osm.
Pressure at 37C
5443 5423 5423
*Slightly higher in plasma due to osmotic effects of plasma
proteins
**Correction factor (osmotic coefficient) for NaCl is 0.93
EFFECTS OF DIFFERENT CONCENTRATION OF IMPERMEANT
SOLUTES IN ECF ON CELL VOLUME
Tonicity of solution, refers to whether solution will cause a change
in a cell volume; depends on concentration of impermeant solute.
Isosmotic solution has same osmolarity as body fluids
Hyperosmotic higher osmolarity than body fluids
Hyposmotic lower osmolarity than body fluids
Osmolarity of solution refers to solution with higher or lower
osmolarity compared with Normal ECF without regard for
whether it can permeate the cell membrane.
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REVIEW: WHATS THE EFFECT OF SOLUTIONS OF CARYING
TONICITY ON RBC?
280 mOsm/L 200 mOsm/L 360 mOsm/L
QUESTIONS:
What is the osmolarity of a 5% glucose solution? (MW is 180g/mol)
Is the solution hyperosmotic, hypo-osmotic or isosmotic? What is a hypo-osmotic solution?
OSMOLARITY OF A 5% GLUCOSE SOLUTION
REMEMBER!!!
Water moves rapidly across cell membranes, thus osmolaritiesbetween ECF & ICF remain almost equal.
Cell membrane are almost impermeable to many solutestherefore the number of osmoles in ECF or ICF generally are
constant unless solutes.
WHAT ARE THE CHANGES IN THE FF VARIABLES AFTER GIVING 2.0 L OF
WATER I.V.?
ECF Volume? Increase
ECF Osmolarity? Decrease
ICF Volume? Increase
ICF Osmolarity? Decrease
WHAT ARE THE CHANGES IN THE FF VARIABLES AFTER GIVING 2L OF 3%
NaCl I.V.?
ECF Volume? Increase > 2.0 L
ECF Osmolarity? Increase
ICF Volume? Decrease
ICF Osmolarity? Increase
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SUMMARY
ABNORMALITIES OF ECF FLUID Na+ CONCENTRATION
ECF solute is 90% due to NaCl, hence an indicator of plasma osmolarity.
CONSEQUENCES OF HYPONATREMIA AND HYPERNATREMIA
Water moves in and out of cells cells swell or shrink
This has profound effects on the brain.- Neurologic function is altered- Rapid shrinking can tear vessels and cause hemorrhage- Rapid swelling can cause herniation because the skull
is rigid, the brain cannot increase its volume by more
than 10% without being forced down the neck
(herniation).
ABNORMALITIES OF BODY FLUID VOLUME REGULATION
ABN Cause Plasma
Na+ Conc
ECF Vol ICF Vol
Hyponatremic
Dehydration
Diarrhea,
vomiting,
adrenal insuff;
overuse of
diuretics,
Addisons
Hyponatremic
overhydration
Excess ADH,
bronchogenictumor
Hypernatremic
dehydration
Lack ADH,
Diabetes
insipidus,
excessive
sweating
Hypernatremic
overhydration
Cushingsm
primary
aldosteronism
HYPO/HYPER OSMOTIC REFERS TO PLASMA Na+ CONCENTRATION
EDEMA
Presence of excess fluid in the body tissues.INTRACELLULAR EDEMA
Depression of tissue metabolic systems(e.g. hypothyroidism)
Inadequate tissue nutrition(e.g. ischemia)
Inflammation of tissues (increased cellmembrane permeability)
EXTRACELLULAR EDEMA
Causes of increased interstitial fluid volume
Increased Capillary Filtration Failure of lymphatics to return interstitial fluid to circulation
3 Factors that can increase capillary filtration
1. Increased capillary hydrostatic pressure (Pc)2. Decreased plasma colloid osmotic pressure3. Increased capillary filtration coefficient (permeability) (Kf)
DETERMINANTS OF CAPILLARY FILTRATION
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XLymphatic
Failure = Edema
CAUSES OF INCREASED CAPILLARY FILTRATION
NORMAL FILTRATION
FILT = Kfx Net Filt Pressure
= 6.6 x ( 17.3 - (-3) - 28 +8)
= 6.6 x ( + 0.3)
= 1.89 ml/min
FILT = 2722 ml/day
Where does all of this fluid (and protein in it) go?
FUNCTION OF LYMPHATICS
CAUSES OF ECF EDEMA
Lymphatic blockage Infection Cancer Surgery Congenital absence of lymphatics
SAFETY FACTORS AGAINST EDEMA
Low compliance of interstitium when = 3 mmHginterstitial fluid pressure is negative
Increased lymph flow = 7 mmHg Washdown of interstitial protein = 7 mmHgat high lymph flow rates
TOTAL SAFETY FACTORY = 17 mmHg
NEGATIVE PRESSURE SUCKS. (If negative IFPr, IF volume does NOT
change much if +3 fluid start to accumulate), because tissue
became highly compliant,
LOW TISSUE COMPLIANCE AND NEGATIVE INTERSTITIAL FLUID
HYDROSTATIC PRESSURE
INCREASED LYMPH FLOW
EFFECT OF INTERSTITIAL FLUID PRESSURE ON LYMPH FLOW
Increases lymph flow 10-50x
Lymph
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PITTING VS NON PITTING EDEMA
Thumbprint - When the thumb press against the tissue area, it pushes
the fluid away from the area.
When tissue cell swells instead of interstitium, fluid do not move away
from the area.
WASHDOWN OF INTERSTITIAL PROTEINS
CONDITIONS CAUSING EDEMA
1. High capillary hydrostatic pressure
Excess fluid retention by kidneys- acute or chronic kidney fa ilure- glomerulonephritis- mineralocorticoid excess
Decreased arteriolar resistance- vasodilator drugs- autonomic insufficiency
Increased venous pressure- congestive heart failure- high output heart fa ilure (e.g. anemia)- -venous obstruction- venous valve failure- cirrhosis
2. Decreased plasma proteins
(low oncotic pressure)
Loss of proteins- burns, wounds
- nephrosis
- gastroenteropathy
Failure to produce proteins- malnutrition (kwashiorkor)
- cirrhosis
- analbuminemia
3. Increased capillary permeability
Immune reactions (histamine) Toxins Burns Prolonged ischemia Vitamin deficiency (e.g. vitamin C) Pre-eclampsia and eclampsia in
Pregnancy
4. Blockage of lymphatics
Cancer Surgery Infections (e.g. filaria nematodes)
FLUIDS IN THE POTENTIAL SPACES OF THE BODY
Pleural, peritoneal, pericardial, synovial cavities Fluid is exchanged between the capillaries and the potential
spaces
Lymphatic vessels drain protein from the potential spaces Effusion- Edema fluid in the potential spaces- Abdominal cavityascites- Normal Interstitial hydrostatic pressure of
Pleural cavity (-) 7 to (-) 8 mmHg Pericardial cavity (-) 5 to (-) 6 mmHg Joint spaces (-3) to (-) 5 mmHg
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