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Cell function depends not only on a continuous supply of nutrients and removal of metabolic wastes, but also on...

physical & chemical homeostasis of the surrounding fluids

Major fluid compartments of the body

Intracellular fluid (ICF) (40% body weight)
Interstitial fluid (IF) (80% of ECF)
Plasma (20% of ECF)

Total body water is a function of...

body mass
sex (gender)
relative amount of body fat

Infants are 73% or more water. Why is this?

Their low body fat & low bone mass.
(This level of hydration accounts for their "dewy" skin, like that of a freshly picked peach)

T/F: Women have relatively more body fat & relatively less skeletal muscle than males.


Of all body tissues, which is the least hydrated?

Adipose tissue

T/F: Bone contains more water than does fat.


People with greater muscle mass have proportionately ______ (more or less?) body water.


Water occupies two main fluid compartments within the body. What are they?

Intracellular fluid (ICF) compartment &
Extracellular fluid (ECF) compartment

Intracellular fluid is fluid...

within the cells

What fluid compartment is most occupied?

Intracellular fluid compartment (little less than 2/3)

The _____________ constitutes the body's internal environment & is the external environment of each cell.

Extracellular fluid (ECF) compartment

The ECF compartment is divisible into two subcompartments. What are they?

Plasma (fluid portion of blood)
Interstitial fluid (IF) (fluid in the microscopic spaces between tissue cells)

The fluid portion of the blood is the


The fluid in the microscopic spaces between tissue cells is known as the

interstitial fluid (IF)

What are some examples of ECF that are distinct from plasma & interstitial fluid (IF)?

Cerebrospinal fluid
Humors of the eye
Synovial fluid
Serous fluid
Secretions of gastrointestinal tract

Universal solvent in which a variety of solutes are dissolved.


Solutes may be classified broadly as ____________ & _____________.

electrolytes & nonelectrolytes


-Have bonds (usually covalent) that prevent them from dissociating in solution
-Most are organic molecules (glucose, lipids, creatinine, urea, etc.)

No electrically charged species are created when nonelectrolytes dissolve in water. Why?

Because nonelectrolytes have bonds (usually covalent) that prevent them from dissociating in solution

Most are organic molecules (glucose, lipids, creatinine, urea, etc.) are nonelectrolytes or electrolytes?



-chemical compounds that dissociate into ions in water
-Typically include inorganic salts, both inorganic & organic acids & bases, and some proteins

Typically, electrolytes include..


Which has greater osmotic power? Electrolytes or nonelectrolytes?

Electrolytes have a much greater osmotic power than nonelectrolytes because each electrolyte molecule dissociates into atleast 2 ions.

Regardless of the type of solute particle, water moves according to ______________.

osmotic gradients (from an area of lesser osmolarity to an area of greater osmolarity)

Is it electrolytes or nonelectrolytes that have the greatest ability to cause fluid shifts?

Electrolytes (due to osmotic gradients)

Except for the relatively high ________ content in plasma, the extracellular fluids are very similar.


Chief cation in extracellular fluids.


Major anion in extracellular fluids.


Most abundant cation in intracellular fluids.


Major anion in intracellular fluids.


T/F: Intracellular fluid cells contain substantial quantities of soluble proteins.

True; about 3x the amount found in plasma

Sodium & potassium ion concentrations in ECF & ICF are nearly ___________.


Sodium & potassium ion concentrations in ECF & ICF are nearly opposite. This reflects the activity of ________________

ATP-dependent sodium-potassium pumps (which keep intracellular Na+ concentrations low & K+ concentrations high)

The most abundant solutes in body fluids, which determines most of their physical & chemical reactions.


T/F: Electrolytes do not constitute the bulk of dissolved solutes in the body fluids.

True (proteins & some nonelectrolytes like phospholipids, cholesterol, & triglycerides are large molecules that account for 90% of the mass of dissolved solutes in plasma, 60% in IF, & 97% in the ICF)

The continuous exchange and mixing of body fluids are regulated by

osmotic & hydrostatic pressures.

Solutes are unequally distributed in the body because of their...

size, electrical charge, or dependence on transport proteins

In general, substances must pass through both the plasma & interstitial fluid (IF) in order to reach the...

intracellular fluid

Exchanges between the outside world & the plasma occur almost continuously in what three areas?

Gastrointestinal tract

Serves as the highway for delivering substances throughout the body.


Exchanges between plasma and interstitial fluid (IF) occur...

across capillary membranes

Under normal circumstances, the small net leakage that remains behind in the interstitial space is picked up by ____________ & returned to the blood.

lymphatic vessels

Exchanges between IF & ICF occur across ___________ & depend on ___________.

plasma membranes ; membranes' complex permeability properties

T/F: Movements of nutrients, respiratory gases, & wastes are typically unidirectional.


T/F: Osmolarities of all body fluids are equal.


Increasing extracellular fluid (ECF) content can be expected to cause

a shift in water out of the cells

Intracellular fluid volume is determined by the

Extracellular fluid (ECF) solute concentration

T/F: For the body to remain properly hydrated, water intake must be equal to water output.


Most water enters the body through..

ingested liquids & solid foods.

Body water produced by cellular metabolism is called

metabolic water (or water of oxidation)

Water that vaporizes out of the lungs in expired air or diffuses directly through the skin is called

insensible water loss

A rise in plasma osmolarity triggers:

1) thirst (which prompts us to drink water)
2) release of antidiuretic hormone (ADH), which causes kidneys to conserve water & excrete concentrated urine

A decline in plasma osmolarity...

inhibits thirst & ADH release

The driving force for water intake.

The thirst mechanism

Output of certain amounts of water is unavoidable. These outputs are known as

obligatory water losses

______________ help explain why we cannot survive for long without drinking.

Obligatory water losses

Obligatory water loss includes:

insensible water losses & sensible water losses

The body's water volume is closely tied to a powerful water magnet known as

ionic sodium (Na+)

Factors that trigger ADH release by reducing blood volume include:

-prolonged fever
-excessive sweating
-vomiting or diarrhea
-severe blood loss
-traumatic burns
(under these conditions ADH also acts to constrict arterioles which directly increases blood pressure; hense ADH's other name, vasopressin)

Principle abnormalities or disorders of water balance are

-Hypotonic hydration

When water output exceeds intake over a period of time & the body is in negative fluid balance, the result is


Dehydration is a common resulting factor to:

-severe burns
-prolonged vomiting or diarrhea
-profuse sweating
-water deprivation
-diuretic abuse

T/F: Dehydration may also be caused by endocrine disturbances, such as diabetes mellitus or diabetes insipidus.


Decreased urine output is known as


If prolonged, dehydration can lead to

weight loss
mental confusion

One serious consequence of water loss from plasma is inadequate blood volume to maintain normal circulation. This results in

hypovolemic shock

In dehydration, water is lost from the

extracellular fluid (ECF)

When there is renal insufficiency or when an extraordinary amount of water is drunk very quickly, a type of cellular overhydration occurs known as

hypotonic hydration.

The hallmark of hypotonic hydration is

hyponatremia (low ECF Na+ concentration)

Hypotonic hydration leads to severe metabolic disturbances evidenced by

-muscular cramping
-cerebral edema

Hypotonic hydration is particularly damaging to


Left untreated, cerebral edema quickly leads to...


___________ is an atypical accumulation of fluid in the interstitial space, leading to tissue (but not cell) swelling


T/F: Edema is an increase in volume of ONLY the IF (interstitial fluid)


Factors that accelerate fluid loss from the blood include

increases in capillary hydrostatic pressure & permeability

Increased capillary permeability is usually due to...

an ongoing inflammatory response.

A condition of unusually low levels of plasma proteins, results in tissue edema because protein-deficient plasma has an abnormally low colloid osmotic pressure.


Hypoproteinemia may result from:

-protein malnutrition
-liver disease

______________ is in which plasma proteins pass through "leaky" renal filtration membranes and are lost in urine.


What happens when lymphatic vessels are blocked?

-The small amount of plasma proteins that seep out of the blood stream are not returned to the blood as usual
-As leaked proteins accumulate in the IF, they exert an increasing colloid osmotic pressure, which draws fluid from the blood & holds it in the interstitial space

Edema can impair tissue function because

excess fluid in the interstitial space increases the distance nutrients and oxygen must diffuse between the blood & the cells

The most serious problems resulting from edema affect what system?

Cardiovascular system

The salt balance of the body is known as

electrolyte balance

What are the functions of salt in the body?

-important in controlling fluid movements
-provide minerals essential for excitability, secretory activity, and membrane permeability

Salts are lost from the body in..


Addison's disease

disorder entailing deficient mineralcorticoid hormone production by the adrenal cortex

The appetite for abnormal substancs such as chalk, clay, starch, or burnt match tips is known as


____________ holds a central position in fluid and electrolyte balance and overall body homeostasis


In normal plasma, _______ is the single most abundant cation in the ECF and the only one exerting significant osmotic pressure.

Na+ (sodium)

T/F: While sodium content of the body may change, its ECF concentration normally remains stable.

True (because of immediate movement of water into or out of the ICF and longer-term adjustments due to the ADH & thirst mechanisms)

T/F: Salt follows water.

False; water follows salt!!

Regulation of the Na+-water balance involves a variety of ________ & _________ controls.

neural & hormonal controls

What hormone "has the most to say" about renal regulation of sodium ion concentration in the ECF?


Aldosterone's central role

maintaining blood volume & blood pressure

T/F: Water always follows Na+


T/F: Aldosterone increases ECF volume


The most important trigger for aldosterone release from the adrenal cortex is...

the renin-angiotensin mechanism mediated by the juxtaglomerular apparatus of the renal tubules

What 3 situations make the juxtaglomerular apparatus respond by making its granular cells to release renin?

-Sympathetic stimulation
-Decreased filtrate NaCl concentration
-Decreased stretch (due to decreased blood pressure)

____________ catalyzes the initial step in the reactions that produce angiotensin II, which prompts aldosterone release.


____________ is an important intermediate pathway linking renin to aldosterone release.

Angiotensin II

Functions of angiontensin II

-prods adrenal cortex to release aldosterone
-directly increases Na+ reabsorption by kidney tubules
-a number of other actions which all raise blood pressure & blood volume

The principal effects of aldosterone are to

-diminish urinary output
-increase blood volume

People with _________ lose tremendous amounts of NaCl and water to urine.

Addison's disease (hypoaldosteronism)

The influence atrial natriuretic peptide (ANP) can be summarized in one sentence:

It reduces blood pressure & blood volume by inhibiting nearly all events that promote vasoconstriction & Na+ and water retention.

___________ are chemically similar to aldosterone, and like aldosterone, enhance NaCl reabsorption by the renal tubules.


____________ decreases Na+ reabsorption by blocking the effect aldosterone has on the renal tubules.


The usual effect of glucocorticoids (such as cortisol & hydrocortisol) is to

-enhance tubular reabsorption of Na+
-promote an increased glomerular filtration rate that may mask their effects on the tubules

Most important effect of ionic calcium in the ECF

is on neuromuscular excitability

ECF calcium ion levels are closely regulation by what hormone?

PTH (parathyroid hormone)

Whenever the pH of arterial blood rises above 7.45, a person is said to have

alkalosis (or alkalemia)

A drop in arterial pH to below 7.35 results in

acidosis (acidemia)

Any arterial pH between 7.35 & 7.0 is called

physiological acidosis

The H+ concentration in blood is regulated sequentially by:

1) chemical buffers
2) brain stem respiratory centers
3) renal mechanisms

System of one or more compounds that acts to resist changes in pH when a strong acid or base is added.

Chemical buffer

Three major chemical buffer systems in the body are:

-bicarbonate buffer system
-phosphate buffer system
-protein buffer system

Mixture of carbonic acid (H2CO3) and its salt, sodium bicarbonate (NaHCO3) in the same solution.

Bicarbonate buffer system

All the available HCO3- ions

alkaline reserve

Single protein molecule that can function reversibly as either an acid or base depending on the pH of its environment. Molecules with this ability are known as

amphoteric molecules

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