The science of nutrition 4th edition thompson manore vaughan chapter 09

Chapter 9 Lecture

Chapter 9:
Nutrients Involved
in Fluid and
Electrolyte
Balance

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Body Fluids
• Body fluid is the liquid portion of cells and
tissues
• Characterized by its ability to move freely and
changeably, adapting to the shape of the
container that holds it
• About 50–70% of healthy adult body weight

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Body Fluids
• Intracelluar fluid: within the cell
• 2/3 of body fluid
• Extracellular fluid: outside the cell
• 1/3 of body fluid
• Interstitial fluid flows between cells that
make up a particular tissue or organ (muscle,
liver)
• Intravascular fluid is the water in the blood

and lymph
• Plasma transports blood cells within arteries,
veins, and capillaries
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© 2017 Pearson Education, Inc.


Body Fluids
• Fluid composition of tissue varies by:
• Tissue type: lean tissues have higher fluid
content than fat tissues
• Gender: males have more lean tissue and
therefore more body fluid than females
• Age: decrease in body water results partly
from loss of lean tissue as people age

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Electrolytes
• Electrolytes are dissolved substances that
disassociate in solution into electrically charged
particles called ions
• Positive charge (cations): sodium, potassium
• Negative charge (anions): chloride,
phosphorus
• Predominant electrolytes
• Extracellular fluid: sodium, chloride

• Intracellular fluid: potassium, phosphorus

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Functions of Body Fluids
• Fluids dissolve and transport substances
• Water is an excellent solvent because it
dissolves a variety of substances
• Water-soluble substances are readily
transported in the bloodstream: amino acids,
glucose, water-soluble vitamins, minerals,
some medications
• Fatty substances must be attached to or
surrounded by water-soluble proteins

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Functions of Body Fluids
• Fluids account for blood volume
• Appropriate body fluid levels are essential for
maintaining healthful blood volume
• Blood pressure increases when blood volume
rises
• High blood pressure (hypertension) is a risk
factor for heart disease and stroke
• Low blood pressure can cause people to feel
tired, confused, or dizzy
• Kidneys help to regulate blood volume and

blood pressure
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Functions of Body Fluids
• Fluids account for blood volume
• Antidiuretic hormone (ADH) released from
the pituitary gland stimulates the kidneys to
reabsorb water, reducing urine output
• Enzyme renin secreted from the kidneys
responds to decreased blood pressure;
catalyzes the conversion of blood protein
angiotensinogen to angiotensinogen I

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Functions of Body Fluids
• Fluids account for blood volume
• Angiotensin I is converted to Angiotensin II
(vasoconstrictor); increases blood pressure
• Hormone aldosterone secreted from the
adrenal glands signals the kidneys to retain
sodium and chloride, thereby retaining water,
increasing blood pressure, and decreasing
urine output

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© 2017 Pearson Education, Inc.


Functions of Body Fluids
• Fluids help maintain body temperature
• Fluids maintain body temperature within a
safe range
• Water has a high capacity for heat, which
means that only sustained high heat can
increase body temperature
• Sweating releases heat as the evaporation of
water from the skin cools the skin and blood

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Functions of Body Fluids
• Protect and lubricate tissues
• Cerebrospinal fluid protects the brain and
spinal cord
• Amniotic fluid protects the fetus
• Synovial fluid lubricates joints
• Tears cleanse and lubricate eyes
• Saliva moistens food for swallowing
• Pleural fluid allows lungs to expand and
retract without friction

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Functions of Electrolytes
• Electrolytes help regulate fluid balance
• Cell membranes are permeable to water, but
not freely permeable to electrolytes
• Water moves by osmosis to areas where the
concentration of solute is high
• This action provides a means to control
movement of water into and out of the cells
• Osmotic pressure keeps electrolytes in
solution from drawing liquid toward them
across a semipermeable membrane
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© 2017 Pearson Education, Inc.


Functions of Electrolytes
• Electrolytes enable nerves to respond to
stimuli
• Nerve impulses are initiated at nerve cell
membranes in response to a change in
electrical charge across the membrane
• Depolarization—Action Potential—
Repolarization
• Sodium and potassium ensure that nerve
impulses are generated, transmitted, and

completed

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© 2017 Pearson Education, Inc.


Functions of Electrolytes
• Electrolytes signal muscles to contract
• Muscles are stimulated to contract in
response to stimulation of nerve cells
• Increased flow of calcium ions from its
storage site into the muscle stimulates muscle
contraction
• Muscles can relax after contraction once the
electrical signal is complete and calcium is
pumped out of the muscle cell

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Fluid Balance
• Fluids gained through consumption and
metabolism
• As much as 90% of fluids needs met by
beverages and food
• Metabolic water formed from metabolic
reactions contributes 10–14% of the water the
body needs each day

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Fluid Balance
• Thirst mechanism (hypothalamus) prompts us
to drink. It is stimulated by:
• Increased concentration of salt and other
dissolved substances in the blood
• A reduction in blood volume and blood
pressure, such as during profuse sweating,
vomiting, diarrhea, or low fluid intake
• Dry mouth and throat from reduced saliva
• ADH signals the kidneys to retain water

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© 2017 Pearson Education, Inc.


Fluid Balance
• Sensible fluid loss
• Kidneys excrete water as urine
• Sweat during exercise or in hot environment
• Insensible fluid loss
• Skin (not sweating) or lungs during exhalation
• Significant loss
• Illness, traumatic injury, blood donation,
surgery, exercise, high altitude, low humidity,

pregnancy, breastfeeding, diuretics

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How Much Water Should We Drink?
• Requirements are individualized
• Amount needed varies with age, body size,
health status, physical activity level,
environment
• Athletes, highly active people, and people
working in hot environments may need
additional fluid to replace fluid lost in sweat
• Sources of drinking water: tap, carbonated,
mineral, bottled
• Distilled and purified water not suitable for
drinking
© 2017 Pearson Education, Inc.


© 2017 Pearson Education, Inc.