Body Fluids

Percentage of body fluid

• Body is 45%-75%

• Depends on age and amount of adipose tissue and muscle tissue

Infants

Highest percent of fluid

Elderly

Lowest percent of fluid

Body fluids decreases…

With age and increased body fat

Adipose

20% water

Skeletal muscle

75% water

Fluid compartments

• intracellular

• extracellular

Intracellular fluid

• 2/3 of total body fluid

• Fluid within our cells

• Contains more K+, Mg2+, PO4 3- and negatively charged proteins

Extracellular fluid

• 1/3 of total body fluid

• Fluid outside of our cells

• More Na+, Ca2+, Cl-, HCO3-

Interstitial fluid

• 2/3 of the 1/3 of ECF

• Extracellular fluid surrounding cells (not in blood vessel)

Blood plasma

• 1/3 of 1/3 of ECF

• Extracellular fluid within blood vessels

• More dissolved proteins

Extracellular fluids examples

• cerebrospinal fluid

• synovial joint fluid

• aqueous and vitreous humor of the eye

• fluids of inner ear

• serous fluid within body cavity

Fluid movement between compartments

1. Drinking water

2. Digestive system

3. Blood (hypotonic)

4. Interstitial fluid

5. Cells

Reversed if water is lost

Fluid balance

(Fluid intake= fluid output) is the normal distribution of water and solutes

Fluid intake

2500 mL/day or 2.5 L

• Addition of water to body

• Ingested water (2300 mL/day)

• Metabolic water (200 mL/day)

Fluid output

2500 mL/day or 2.5 L

• loss of water from body

• Breathing (300mL)

• Sweating (100mL)

• Cutaneous transpiration (400mL)

• Defamation (200mL)

• Urination (1000mL)

Sensible

Water loss that is measured

Insensible

Water loss that cant be measured

Obligatory

Water loss that occurs because of normal bodily processes

Facultative

Controlled water loss

Fluid imbalance with constant osmolarity

Does not move from H to L

• Volume depletion

Volume depletion

Occurs when an isotonic fluid loss is greater than isotonic fluid gain

• hemorrhage

• severe burns

• chronic vomiting

• diarrhea

• hyposecretion of aldosterone

Volume excess

Isotonic fluid gain is greater than isotonic fluid loss

• fluid intake normal but decreased fluid loss through kidneys

Fluid imbalance with changes in osmolarity

Moves from high to low and higher concentration of solutes over water

• dehydration

• hypotonic hydration

Dehydration

Water loss greater than loss of solutes

• profuse sweating

• diabetes

• intake of alcohol

• hyposecretion of ADH

• insufficient water intake

• overexposure to cold weather

Blood becomes hypertonic

Water shift in dehydration

Cells to interstitial fluid to blood plasma

Hypotonic hydration

Water gain or retention that is greater than solute gain or retention (water intoxication)

• can result from ADH hypersecretion of large amounts of plain water

Na+ and water loss during sweating and drinking water only replaces water not solutes so plasma becomes hypotonic

Hypotonic hydration fluid movement

Blood plasma to interstitial fluid to cells

• possible swelling of cells

Fluid sequestration

Total body fluid is normal but distributed abnormally (keeping fluid from going outside)

• edema

• ascites

• pericardial effusion

• pleural effusion

Edema

Puffiness with fluid accumulation in interstitial space

Ascites

Accumulation of fluid within peritoneal cavity

Pericardial effusion

Accumulation of fluid in pericardial cavity

Pleural effusion

Accumulation of fluid in pleural cavity

Regulating fluid balance (fluid intake)

• increases blood volume

• increases blood pressure

• decreases blood osmolarity if water gain exceeds solute gain

Regulating fluid balance (fluid output)

• decreases blood volume

• decreases blood pressure

• increases blood osmolarity if water loss is greater than solute loss

Regulating fluid intake (stimuli turn on)

• Turns on thirst center

• Blood volume and pressure decreases

• Increases angiotensin II which stimulates thirst center

• Blood osmolarity and ADH increases due to insufficient water intake

• Salivary secretions decrease

Regulating fluid intake (stimuli to turn off)

• Stimuli to turn off thirst center

• Blood volume and blood pressure increases

• Decrease in angiotensin II results in reduced stimulation of thirst center

• Decreased blood osmolarity

• Increased salivary secretions

• Distension of stomach

Regulating fluid output

• through kidneys by controlling urine output done by 4 hormones

Hormones that regulate urine output

• Angiotensin II, Antidiuretic hormone, and aldosterone decrease urine output to increase blood volume and pressure

• Atrial natriuretic peptide (ANP) increases urine output to decrease blood volume and pressure

Fixed acid

• Wastes produced from metabolic processes

• Regulated by the kidney

Volatile acid

• An acid produced from carbon dioxide

• Regulated by respiratory system

Chemical buffers

Not regulated by kidneys or respiratory system

• act in seconds to temporarily prevent small changes in pH such as eating food

• either putting in a lot of H+ or absorbing a lot of H+

• composed of weak base and weak acid

Weak base

Can bind excess H+

Weak acid

Can release H+

Absorbing in chemical buffer systems

Lowers H+ available which increases pH

• mixes with something other than acid or base

Chemical buffer systems

• proteins- within cells and blood

• phosphate- within cells

• bicarbonate- within ECF (particularly bloods)