Ch. 25 - Body Fluids

A living cell requires…

a steady supply of reactants and a reliable system for removing waste

• Carried out by diffusion in simple organisms

• Complex organisms rely on a circulating system to prevent the depletion of the reactant and stop accumulation of wastes in the cell

Body Fluids

the average adult contains 42 L of fluids, which accounts for 2/3 of the total body weight

• located in the following regions of the body:

  • Interior of cells

  • Tissue spaces between cells

  • Blood vessels

Intracellular Fluid

Located inside cells

• Majority of body fluid (28 L)

• substance where vital life-maintaining reactions occur

Extracellular Fluid

Located outside of cells

• Provides a constant environment for the cells and transports substances to and from the cells

• Includes:

  • interstitial fluid

  • plasma

Interstitial Fluid

fluid that fills the space between tissue cells and moves in lymph vessels

• Constitutes about 25% (10.5 L) of the total body fluid

Plasma

Fluid of the bloodstream

• makes up about 8% (3.5 L) of the total body fluid

• Plasma and interstitial fluid are nearly identical, except plasma has more protein

Other Body Fluids

• urine

• digestive juices

• cerebrospinal fluid

Chemical Differences between ECF and ICF

Intracellular fluid

• Principle cation: K+

• Principle anion: Phosphate (HPO42−)

• Contains four times more protein than plasma

Extracellular fluid

• Principle cation: Na+

• Principle anion: Cl−

• Interstitial fluid contains very little protein and plasma contains high protein

How Oxygen gets Transported:

Oxygen required by the body is mostly carried by red blood cells in the form of oxyhemoglobin

• Limited solubility of oxygen in plasma only allows about 2% to be dissolved and transported in solution by hemoglobin

Oxyhemoglobin

Oxygen-hemoglobin combination

Deoxyhemoglobin (hemoglobin)

Nonoxygenated hemoglobin

How CO2 gets Transported:

When CO2 is present, hemoglobin can reversibly bind to it to form carbaminohemoglobin

• CO2 is transported from body tissues to the lungs

  • 25% is carried in the form of carbaminohemoglobin

  • 5% is dissolved in the plasma

  • 70% is transported as bicarbonate ions

Carbaminohemoglobin

Hemoglobin combined with carbon dioxide

How Oxygen Transports to Tissues (7 Steps):

1. Oxygen diffuses from the alveoli through capillary wall and into the red blood cells

2. Oxygen reacts with hemoglobin to form oxyhemoglobin and H+ ions inside the red blood cells

   • Oxyhemoglobin formation is favored by a high partial pressure of oxygen

3. Bicarbonate ions diffuse from the plasma into the red blood cells

   • Replaced in the plasma by chloride ions that diffuse from blood cells

   • chloride shift

4. Protons from the oxygenation of hemoglobin react with bicarbonate ions to form carbonic acid

5. Carbonic anhydrase (enzyme in the red blood cells) promotes the breakdown of carbonic acid to water and carbon dioxide

   • Formation of CO2 and water is favored by the low pressure of carbon dioxide in the lungs

6. Carbaminohemoglobin breaks apart to yield hemoglobin and carbon dioxide

7. Carbon dioxide molecules diffuse out of the red blood cells and into the lung because the CO2 pressure is high in red blood cells and low in the alveoli

   • Carbon dioxide and some water are expelled in the exhaled air

Chloride Shift

Maintains the charge balance and osmotic pressure relationships between the plasma and red blood cells

How CO2 gets Transported to the Lungs (8 Steps):

1. CO2 diffuses from the tissue cells into the interstitial fluid and into the red blood cells because of higher concentration of CO2 in tissue cells

2. CO2 reacts with water in the presence of carbonic anhydrase to produce carbonic acid inside the red blood cells

3. Carbonic acid dissociates to give hydrogen ions and bicarbonate ions

4. Bicarbonate ions diffuse into the plasma and transport most CO2 in bicarbonate form from the tissue cells to the lungs

5. Chloride shift occurs to maintain electrolyte balance

6. 25% of the CO2 from Step 1 reacts with hemoglobin to form carbaminohemoglobin for transport to the lungs

   • most CO2 is transported in the bicarbonate molecule

7. Increase of the H ion concentration inside the red blood cells promotes a reaction with oxyhemoglobin, which releases oxygen

8. Free oxygen diffuses out of the red blood cells through the plasma, capillary membrane, interstitial fluid, and into the tissue cells

Chemical Transport to the Cells:

Substances must become part of the moving bloodstream to be chemically transported

• May dissolve in water-based plasma

  • ex) Sugars and ions

• May bind to cellular components

  • ex) O2 and CO2 with hemoglobin

• May form a suspension in the plasma

  • ex) Lipids

Capillary walls behave as selectively permeable membranes to allow:

• Water containing dissolved nutrients (including O2) to pass in one direction

• Water containing dissolved wastes to pass in the other direction

Movement of water and dissolved materials is governed by:

• Pressure of blood against the capillary walls

• Differences in protein concentration on each side of the capillary walls

Protein concentration in plasma is…

higher than the protein concentration in the interstitial fluid outside blood vessels

• Results in osmotic pressure

Chemical Transport across Capillaries

• The pumping action of the heart creates pressure in the blood that is greater in the arterial end of a capillary than at the venous end

• At the arterial end, blood pressure is greater than the osmotic pressure, which results in a net outflow into the interstitial fluid

• At the venous end, blood pressure is less than the osmotic pressure, which results in a net inflow from the interstitial fluid

Components of Urine

• 96% water and 4% dissolved waste products

• Approximately 40–50 g of dissolved solids are found in daily urine output of an adult

• there is 25g of urea in daily urine output

What is the urine pH of a healthy person?

4.5–8.0

• 6.6 is a reasonable average for an ordinary diet

  • Fruits and vegetables make urine alkaline/basic

  • High-protein foods make urine acidic

How urine composition can be used for diagnosis:

• Urine specimen can be checked with paper test strip

  • Contains bands of reagents that react with the abnormal components of urine

• Quickly checks for indications of pathological conditions

Fluid and Electrolyte Balance

• Fluid balance within the body is maintained by:

  • Balance in the total amount

  • Normal and stable distribution of fluid inside the cells, in the interstitial spaces, and in the blood vessels

• When the fluid balance deviates, the electrolyte balance deviates as well

• Fluid output and intake must be equal

• Fluid balance is maintained or restored by variations in urine output

  • Urine output - 1400 mL/day

Thirst Mechanism

Regulates water intake

• Stimulated when the body loses large amounts of water, salivary secretions decrease and a dry feeling develops in the mouth

Water leaves the body through the:

• Kidneys (urine)

• Lungs (water vapor in expired air)

• Skin (diffusion and perspiration)

• Intestines (feces)

Abnormally high fluid losses, and possibly dehydration, can be caused by hyperventilation, excessive sweating, vomiting, or diarrhea

What controls urine production?

The rate of water reabsorption from the renal tubules in the kidneys controls urine production

How is urine production regulated?

Regulated by vasopressin (or antidiuretic hormone, ADH) and the adrenal cortex hormone aldosterone

• Vasopressin regulates urine production by affecting the permeability of the renal tubules to water

When bodily fluid levels run low, what happens?

• aldosterone is secreted, which then stimulates the reabsorption of Na +

  • Chloride ions follow the sodium ions to maintain electrical neutrality, and water follows sodium chloride

  • Conserves salt and water in the body

  • Amount of aldosterone secretion decreases when the fluid level is back to normal

Acid-Base Balance

Normal blood pH is 7.35 to 7.45

• Death can result when pH value falls below 6.8 or rises above 7.8

• Large amounts of acids and smaller amount of bases enter the blood

  • Constant pH is maintained by the interactive operation of

    • buffer systems

    • respiratory systems

    • urinary systems

Alkalosis Vs. Acidosis

Alkalosis: Abnormally high blood pH

Acidosis: Abnormally low blood pH

Buffer Control of Blood pH

• Types of buffer systems

  • Bicarbonate buffer - Consists of a mixture of bicarbonate ions (HCO 3−) and carbonic acid (H2CO 3)

    • regulated by the kidneys and the respiratory system

  • Phosphate buffer

  • Plasma proteins

Buffers are resistant to pH changes

Respiratory Control of Blood pH

Respiratory system helps control the acidity of blood by regulating the elimination of CO2 and H2O

• When more CO2 and H2O are exhaled, more carbonic acid is removed from the blood

  • Blood pH is raised to a more alkaline/basic level

Hyperventilation

Rapid, deep breathing that is caused by an increase in the CO2 of arterial blood or a decrease in the arterial pH level below 7.38

Hypoventilation

Slow, shallow breathing

• Less CO2 is exhaled, and higher concentration of carbonic acid remaining in the blood lowers the pH back to normal

Urinary Control of Blood pH:

• Reactions involved in the excretion of H+ ions by the kidneys

  • breathing in CO2 gives us a lot of bicarbonate ions, which dissociates rapidly

  • Hydrogen ions diffuse into the developing urine

  • A Na+ ion passes into the tubule cells for every H+ ion that enters the urine

• Decrease in CO2 and increase in HCO3− increases the blood pH levels back to normal

• Developing urine picks up the hydrogen ions, which react with

  buffering ions present in the urine

• Presence of phosphate buffer system

Respiratory Acid–Base Imbalances

Respiratory acidosis and alkalosis

• Result from abnormal breathing patterns

Respiratory Alkalosis

Caused by hyperventilation that increases loss of CO2

• Increases blood pH

Treatment

• Rebreathing one's own exhaled air by breathing into a paper bag

• Administering CO2

• Treating the causes of hyperventilation

Respiratory Acidosis

Result of hypoventilation that decreases the loss of CO2

• Decreases blood pH

Causes:

• Overdose of narcotics or barbiturates

• Anesthesia

• Lung disease, such as emphysema and pneumonia

• Object lodged in the windpipe

Treatments:

• Identifying the underlying cause

• IV administration of isotonic sodium bicarbonate solution or hemodialysis

Metabolic Acidosis

Caused by factors other than abnormal breathing

• Serious problem in diabetes mellitus

• Occurs temporarily after heavy exercise

• Caused by severe diarrhea and aspirin overdose

• Triggered by the increase in H + that leads to lower blood pH

Symptoms and Treatment of Metabolic Acidosis

Symptoms:

• Hyperventilation

• Increased urine formation

• Thirst

• Drowsiness

• Headache

• Disorientation

Treatment:

• Insulin therapy

• Intravenous bicarbonate

• Hemodialysis

Metabolic Alkalosis

Caused by factors other than abnormal breathing

• Body loses acid because of prolonged vomiting or ingestion of alkaline substances

• Decrease in H + in bodily fluids leads to an increase in blood

  pH

• Symptoms

  • Hypoventilation

  • Numbness

  • Tingling

  • Headache

• Causes:

  • Kidney disease, prolonged vomiting, excessive intake of baking soda