Body Fluid Compartments

Give normal hematocrit for men and women and explain what hematocrit is?

The hematocrit is the fraction of the blood composed of red blood cells In men, the measured hematocrit is normally about 0.40, and in women, it is about 0.36.

List the major anions of the ECF?

The major anions of ECF are Cl- and HCO3-.

List the major anions of the ICF?

The major anions of ICF are protein and organic phosphates [ATP, ADP, AMP].

List the major cations of the ECF?

The major cation of ECF is Na+.

List the major cations of the ICF?

The major cations of ICF are K+ and Mg2+.

OVLT axons connect to the supraoptic nucleus in the hypothalamus, and therefore osmoreceptors regulate the release of ______________.

antidiuretic hormone

When osmolality of the blood or interstitial fluid _______, ADH secreting neurons are stimulated.

increases

Cl- level is controlled by?

indirectly by ADH and by processes that increase or decrease renal reabsorption of Na+.

Describe and give examples of Isosmotic volume expansion?

(1) Increase in ECF volume, but no change in osmolality and ICF volume. (2) Plasma protein concentration and hematocrit decrease. (3) Arterial blood pressure increases because ECF volume increases. Ex. = Isotonic NaCl infusion

Describe and give examples of Isosmotic volume contraction?

(1) Isosmotic volume contraction = Decrease in ECF Volume and no change in body osmolality and ICF Volume. (2) Plasma protein concentration and hematocrit increase because the loss of ECF concentrates the protein and RBCs. Because ECF osmolarity is unchanged, the RBCs will not shrink or swell. (3) Arterial blood pressure decreases because ECF volume decreases. Ex. = Acute fluid loss conditions like hemorrhage, diarrhea and vomiting. • Diarrhea causes loss of isosmotic fluid from the GI tract.

Describe and give examples of Hyposmotic volume contraction?

(1) The osmolarity of ECF decreases. (2) ECF volume decreases. Water shifts into the cells; as a result of this shift, ICF osmolarity decreases until it equals ECF osmolarity, and ICF volume increases. (3) Plasma protein concentration increases because of the decrease in ECF volume. Hematocrit increases because of the decreased ECF volume and because the RBCs swell as a result of water entry. (4) Arterial blood pressure decreases because of the decrease in ECF volume. Ex. = Adrenocortical insufficiency (loss of NaCl in urine due to lack of aldosterone) = Addison's disease

Describe and give examples of hyperosmotic volume contraction?

(1) The osmolarity of ECF increases because sweat is hyposmotic (relatively more water than salt is lost). (2) ECF volume decreases because of the loss of volume in the sweat. Water shifts out of ICF and therefore ICF volume decreases. In addition, Osmolarity of body increases. (3) Plasma protein concentration increases because of the decrease in ECF volume. Although hematocrit might also be expected to increase, it remains unchanged because water shifts out of the RBCs, decreasing their volume and offsetting the concentrating effect of the decreased ECF volume. Ex. = dehydration, diabetes insipidus, and alcoholism.

Describe the Body Fluid Compartments?

TBW (total body water) is divided into ICF and ECF. ECF is divided into the plasma and interstitial fluid. There is also transcellular fluid (synovial, peritoneal, pericardial, and intraocular space, as well as the cerebrospinal fluid) = specialized ECF.

Describe and give examples of Hyposmotic volume expansion?

1) The osmolarity of ECF decreases because excess water is retained. (2) ECF volume increases because of the water retention. Water shifts into the cells; as a result of this shift, ICF osmolarity decreases until it equals ECF osmolarity, and ICF volume increases. (3) Plasma protein concentration decreases because of the increase in ECF volume. Ex. = Conditions like excess water‐drinking and SIADH (syndrome of inappropriate ADH)

List the starling forces?

1. Capillary hydrostatic pressure (blood pressure) forces fluid out of the capillary to the interstitial space. 2. Capillary (plasma) oncotic pressure pulls fluid from the interstitial space back into the capillary. 3. Interstitial hydrostatic pressure‐forces fluid back into the capillary 4. Interstitial oncotic pressure pulls fluid out of the capillary back into the interstitial space. Net Filtration=K [(HP + π = filtration)-(P + π = absoption)] OR J = K (HP - P) - (πc - πi)

Dehydration with accompanying hypertonicity can be brought about in three different ways. What are the three different ways?

1. Insufficient H2O intake (desert, difficulty swallowing) 2. Excessive H2O loss (diarrhea, vomiting, heavy sweating) 3. Diabetes insipidus (deficiency of ADH)

Usually, any surplus free H2O is promptly excreted in the urine, so hypotonicity generally does not occur. However, hypotonicity of the ECF may arise in three ways. What are the three ways?

1. Renal failure (can't excrete dilute urine) 2. Excessive and rapid H2O ingestion (overhydration) 3. syndrome of inappropriate vasopressin secretion(SIADH) - excessive ADH and therefore excessive fluid retention.

What are the two factors make the free movement of fluid between ICF and ECF possible?

1. water molecules diffuse through capillary walls faster than blood 2. There is a pressure difference between the inside and outside of the vessels (capillary filtration pressure)

How does one estimate plasma osmolarity?

2 (serum Na+) + serum glucose/18 + serum blood urea nitrogen (BUN)/2.8 = 275‐295 mOsm/kg

About ______ percent of the blood is plasma and _____ percent is red blood cells

60, 40

What two mechanisms are available to the body to correct serum hyperosmolarity

ADH and thirst ADH is released at a lower osmolarity than thirst. "The first sign of dehydration is darkening of the urine. If you wait until you are thirsty, you arealready in a water deficit."

What percent of body weight is TBW (total body water), ICF, ECF, Interstitial Fluid, and plasma?

TBW is 60% of body weight (40 L). ICF is 40% of body weight. ECF is 20% of body weight. Interstitial fluid is 15% of body weight and Plasma is 5% of body weight.

What is TBW (total body water) dependent on?

Age, gender, % of body fat. The percentage of TBW is highest in newborns and adult males and lowest in adult females and in adults with a large amount of adipose tissue

Describe Antidiuretic hormone (ADH)?

Also known as vasopressin. Produced by the hypothalamus and released by the posterior pituitary. Constricts arterioles and increases reabsoption of water in the kidney.

Describe the influence of the Gibbs-Donnan Effect on concentration of plasma electrolytes.

Because cell membranes are impermeable to proteins but permeable to ions both osmotic and electrochemical gradients are generated across the membrane. Cumulative effect is referred to as Gibbs‐Donnan effect. Specifically, Presence of negatively charge proteins (anions) creates two events. 1. Protein particles create an oncotic gradient favoring the movement of water into the cell 2. Negative charges on proteins create an electrical environment, favoring movement of charges into the cell.

Compare the concentration of cations/anions in the plasma and in the interstitial fluid. Explain why any differences occur.

Because of the Donnan effect, the concentration of cations is greater in the plasma than in the interstitial fluid (plasma proteins have a net negative charge and bind cations). Negatively charged ions (anions) tend to have a slightly higher concentration in the interstitial fluid compared with the plasma because the negative charges of the plasma proteins repel the negatively charged anions.

____________ are the second most abundant anion in extracellular fluid.

Bicarbonate ions (HCO3)

What percent of body fluid is blood?

Blood contains both ECF (plasma) and ICF (RBCs) 7% or about 5 liters.

Compare Colloids to Crystalloids?

Crystalloids do not cross plasma membrane and remain in ECF. In addition, they are distributed evenly within ECF, readily diffusing across capillary walls to equilibrate between intravascular (plasma, ECV) and interstitial volume. Colloids contain large molecules that don't pass through semipermeable membranes. When infused, they remain in the intravascular compartment and expand intravascular volume by drawing fluid from extravascular spaces via their higher oncotic pressure.

How do you find the volume of a specific compartment

Dilution method (conservation of mass principle) = the total mass of a substance after dispersion in the fluid compartment will be the same as the total mass injected into the compartment. Total mass of the substance injected = Total mass of substance in the compartment OR Volume A x Concentration A = Volume B x Concentration B

How does excess water intake affect the ECF?

ECF osmolarity decreases (ECF becomes hypotonic) therefore water moves into the cells and they swell.

How will the following disturbances affect hematocrit? ECF volume Loss ECF volume gain ICF volume Loss ICF volume gain

ECF volume loss = increased hematocrit (concentration) ECF volume gain = decreased hematocrit (dilution) ICF volume loss = decreased hematocrit (shrinkage of red blood cells) ICF volume gain = increased hematocrit (swelling of red blood cells)

How will the following disturbances affect plasma protein concentration? ECF volume loss ECF volume gain

ECF volume loss = increased total plasma protein (concentration) ECF volume gain = decreased total plasma protein (dilution)

Which has a greater ability to cause fluid shift... Electrolytes or Non-electrolytes?

Electrolytes have a greater ability to cause fluid shift

When capillary blood pressure exceeds plasma colloid osmotic pressure what occurs?

Filtration When capillary blood pressure falls below plasma colloid osmotic pressure, then water returns to capillaries. (absorption)

What percent of ECF is intersitial fluid and plasma?

Interstitial fluid = 3/4 of the ECF Plasma = 1/4 of the ECF

What would happen if Gibbs‐Donnan effects were not countered?

Intracellular proteins would result in an influx of water into the cell=resulting in cell swelling and eventually death. Na/K Atpase pump counter acts the inward force + created by the Gibbs -Donnan effect by pumping 3Na ions out in exchange for 2K+ ions pumped in. This action maintains a high sodium concentration outside of the cell which ultimately protects cells from swelling and rupturing. Net balance prevents excessive inward movement of water.

What is the contribution of the "third space" to alterations in body fluid balance?

Intravascular, intracellular, or interstitial spaces usually contain most of the fluid, however, a shift can occur to third spacing ("nonfunctional" area of cells) from the intravascular space. This can be problematic. Examples of this shift are ascites(fluid buildup in peritoneal cavity in abdomen) and pulmonary edema.

Cells have a NaCl concentration equal to 0.85%. Given this compare isotonic, hypertonic and hypotonic cell environments?

Isotonic = NaCl concentration = 0.85% Hypertonic = NaCl concentration > 0.85% Hypotonic = NaCl concentration < 0.85%

Diarrhea and excessive sweating can lead to what type of dehydration?

Isotonic or (isonatremic) dehydration

What is the most common cause of dehydration?

Isotonic or isosmotic (Isonatremic) Dehydration

Explain what would happen if a cell were placed in an isotonic, hypertonic, or hypotonic solution

Isotonic solution = equal movement of water in and out of cell. Hypertonic solution = net movement of water out of the cell (cell shrinkage). Hypotonic solution = net movement of water into the cell (cell swelling)

How does one measure interstitial Fluid?

Measured indirectly (ECF volume-plasma volume)

List major Substances used to measure ICF?

Measured indirectly (TBW-ECF volume)

What does long-term control of arterial blood pressure ultimately depend on?

Na+ regulating mechanisms *Remember water follows Na+ osmotically* Expansion of ECF Volume results in an increase in BP AND reduction of ECF volume results in a decrease in BP.

Compare and contrast the ionic and nonelectrolyte composition of the ECF, including plasma and interstitial fluid, to the ICF.

Nonelectrolytes contain covalent bonds that prevent them form dissociating in solution and therefore have no electrical charge (egs. glucose, lipids, and urea)

Compare nonelectrolytes and electrolytes?

Nonelectrolytes contain covalent bonds that prevent them form dissociating in solution and therefore have no electrical charge (egs. glucose, lipids, and urea). Electrolytes dissociate into ions (ionize) in water; Electrolyte examples ‐‐> Mg+, Na+, Cl‐, K+. Electrolytes have a higher osmotic power than nonelectrolytes because each electrolyte molecule dissociates into at least two ions.

Compare Capillary hydrostatic pressure in the arteriole vs the venule end of the capillary?

Normally, capillary blood pressure exceeds plasma colloid osmotic pressure in the arteriole end and falls below it in the venule end.

Large proteins such as albumin normally can't pass through capillary membranes. The osmotic, pulling, force of albumin (magnetic‐like) in the intravascular space attracts water and holds it inside the blood vessel is referred to as _______________.

Plasma colloid osmotic pressure

List major Substances used to measure plasma?

Radioiodinated serum albumin (RISA) and Evans blue

Hematocrit of 0.10 would be indicative of what?

Severe anemia

List major Substances used to measure ECF?

Sulfate, mannitol, and inulin.

List potential abnormalities of ADH secretion?

Syndrome of inappropriate hypersecretion of ADH. Diabetes insipidus

Na+ level is controlled by what hormonally?

aldosterone, antidiuretic hormone (ADH), and atrial natriuretic peptide (ANP).

Compare Osmolality and Osmolarity?

The terms are bascially interchangeable Osmolality = measure of the number of osmotically active particles per kilogram of H2O. Osmolarity = the number of osmotically active particles per liter of total solution. All body fluid compartments have approximately the same osmolality— expressed as the number of osmotically active particles per kilogram of water—of ~290 milliosmoles/kg H2O (290 mOsm).

List method for measurement of blood volume?

Total Blood Volume = Plasma Volume / (1-Hematocrit)

List major Substances used to measure TBW?

Tritiated water, D2O, and antipyrene

Define the following fluid characteristic categories: Volume contraction, Volume expansion, isosmotic, hyperosmotic, and hypoosmotic?

Volume Contraction = decrease in ECF volume Volume Expansion = increase in ECF volume Isosmotic = no change in body fluid osmolarity Hyperosmotic = body fluid osmolarity is increased Hyposmotic = body fluid osmolarity is decreased

K+ level is controlled by which hormone?

aldosterone

Osmolality in the plasma (291) and interstitial fluid (290) differs. What accounts for this 1 mOsm difference?

colloid osmotic pressure or oncotic pressure

One of the methods for treating fluid and electrolyte alterations is the infusion of I.V. solutions. I.V. solutions for fluid replacement may be placed in two general categories. What are they?

colloids and crystalloids

Hypertonicity of the ECF, is usually associated with ___________.

dehydration

What are the Most commonly used solutes in crystalloids?

glucose and sodium chloride. Normal saline (0.9 % sodium chloride ) and lactated Ringer's (LR) are commonly used. D5W ‐5 % dextrose in water

List the types of dehydration?

hypernatremic, hyponatremic or isonatremic

Where are Osmoreceptors found in the body?

in the brain in the organum vasculosum of the laminae terminalis (OVLT)

The internal measurement of the body's osmolality belongs to a group of neurons called ____________. These cells are defined by their intrinsic capacity to both sense and respond to the changes in serum osmolality.

osmoreceptors

Control of __________ is primarily important in regulating ECF volume.

salt balance

Describe osmosis?

water moves from an area of higher concentration of water (more dilute solution, lower solute concentation) to an area of lower concentration of water (more concentrated solution, higher solute concentration)

Describe hypotonic (hyponatremic) dehydration

• Loss of sodium is greater than the loss of water in ECF. • Serum sodium concentration in the ICF is greater than that of the ECF. • Water shifts from the ECF to the ICF to establish osmotic equilibrium. • Serum sodium and serum osmolality will be less than the normal range.

Describe Isotonic (Isonatremic) Dehydration?

• Loss of water along with sodium that is normally in water (diarrhea, excessive sweating). • Both water and sodium are lost proportionally to the serum concentration • Water and sodium move out of the cells to replace the extracellular fluid loss.

Describe hypertonic (hypernatremic) dehydration

• Loss of water is greater than the loss of sodium in ECF. • Serum sodium concentration in the ECF is greater than in the ICF, water shifts from the ICF to the ECF.