Pathophysiology 1 Exam 3 - Chapter 24

Body fluid =

water within the body and the particles dissolved in it

body fluid flows in

arteries, veins, and lymph vessels

Body fluid is contained in 2 major compartments

• extracellular (outside of cell; 1/3 of total)

• intracellular (inside of cell; 2/3 of total)

body fluids are also secreted into specialized compartments:

• joints

• cerebral ventricles (as CSF)

• intestinal lumen

Location

Dynamic processes in fluid homeostasis results from interplay of the four subprocesses:

1. fluid intake

2. fluid absorption

3. fluid distribution

4. fluid excretion

Fluid intake is entry of fluid into

the body by any route

Thirst is triggered by

• increased concentration of extracellular fluid (osmolality)

• decreased circulating blood volume

• dryness of the mucous membrane

• in older adults, cerebral osmoreceptor-mediated thirst diminishes

• habit is also important in fluid regulation

Two forces tend to move fluid from blood vessels to the interstitial compartment:

• capillary hydrostatic pressure

• interstitial fluid colloid osmotic pressure

Capillary hydrostatic pressure

Outward-pushing vascular fluid against vessel wall

Interstitial fluid colloid osmotic pressure

inward-pulling force of particles in the interstitial fluid

Fluid distribution between vascular and interstitial compartments is like

two groups of people pushing on the opposite sides of a swinging door

The two capillary forces move fluid from interstitial compartment into capillaries:

• capillary osmotic pressure

• interstitial fluid hydrostatic pressure

Capillary osmotic pressure

Inward-pulling force of particles in vascular fluid

Interstitial fluid hydrostatic pressure

Outward push of interstitial fluid against outside of capillary walls

Fluid distribution between interstitial and intracellular compartments causing

water that moves in and out of cells by osmosis

Water goes to the ___ osmolality

higher

Visible fluid excretion include

• urine (kidneys)

• sweat (skin)

Invisible fluid excretion include

insensible perspiration (skin) and water loss (bowels, lungs)

Abnormal route fluid excretion

• emesis

• wound drainage

Healthy kidneys adjust fluid excretion in response to

blood pressure and several hormones

Hormones involved with fluid excretion through kidneys

• antidiuretic hormone (ADH)

• aldosterone

• natriuretic peptides (ANP and BNP)

Urine volume and concentration are important indicators of what?

body fluid balance

ADH

responds to high osmolality or decreased volume

• causes kidneys to retain water (not salt)

Aldosterone

responds to angiotensin II levels or increased plasma potassium

• induces kidneys to conserve saline (salt and water)

ANP and BNP

responds to vascular volume

• promotes saline (salt and water) excretion

Imbalances of extracellular fluid volume (ECV)

• saline imbalances

• imbalances of amount of extracellular fluid

Imbalances of body fluid concentration

• water imbalances

• imbalances of concentration of extracellular fluid

Etiology of extracellular fluid (ECV) deficit

• removal of a sodium-containing fluid from the extracellular compartment

  • GI excretion or loss of sodium-containing fluid (vomit/diarrhea)

  • Renal excretion of sodium-containing fluid (adrenal insufficiency; salt-wasting renal disorders)

  • Other losses of sodium-containing fluid (burns/hemorrhage)

Clinical manifestation of ECV deficit

Fluid loss is from the vascular and interstitial areas

Etiology of ECV excess

Caused by addition or retention of isotonic saline; sometimes termed saline excess

• excessive secretion of hormone aldosterone causes kidneys to retain too much saline

ECV excess compensatory mechanism can accompany

chronic heart failure

Imbalances are disorders of concentration and not the

amount of extracellular fluid

Serum sodium concentration reflects

osmolality (concentratedness) of blood

water imbalances are recognized by abnormal

serum sodium concentration

Hyponatremia is

too little sodium in the blood

Hyponatremia serum sodium concentration is

below the lower limit of the normal 135-145 mEq/L level

In hyponatremia, extracellular fluid is

more dilute than normal

Hyponatremia is also called

• hypotonic syndrome

• hypo-osmolality

• water intoxication

Two primary causes of hyponatremia

• gain of relatively more water than salt

• loss of relatively more salt than water

Hyponatremia clinical manifestations

• mild central nervous system dysfunction

• severe central nervous system dysfunction

Hypernatremia is

too much sodium in blood

In hypernatremia, serum sodium concentration is

above upper limit of normal

Cells in hypernatremia

shrivel

Etiology of hypernatremia

• gain of more salt than water

• loss of more water than salt

Hypernatremia clinical manifestations

mild

• thirst

• oliguria

• confusion

• lethargy

severe

• seizures

• coma

• death

Clinical dehydration is a

combination of extracellular volume deficit and hypernatremia

• too small a volume of fluid in extracellular compartment and too-concentrated body fluids

Clinical dehydration etiology

vomiting and diarrhea

Edema

Excess fluid in the interstitial compartment

• may be manifestation of excess extracellular fluid volume

• decreased capillary osmotic pressure: plasma proteins decreased: extensive edema

Edema leads to increased ________________ which leads to increased local capillary flow that accompanies inflamation

capillary hydrostatic pressure

Increased interstitial fluid osmotic pressure leads to

inflammation that causes protein to leak out from vascular permeability

Causes of edema

• increased capillary hydrostatic pressure

• increased interstitial fluid colloid pressure

• tumor blocking lymphatic drainage

• decreased capillary colloid osmotic pressure

Lymphedema

Blockage of lymphatic drainage; frequently localized

Edema from increased capillary hydrostatic pressure can be caused by

Hypertension

Edema caused by increased interstitial fluid colloid osmotic pressure can be caused by

Ruptured vessel 

Vasodilation caused by inflammation

Decreased capillary colloid osmotic pressure leads to

Less albumin in the blood

• Indication of nephron or kidney damage

• Or it could be from being an athlete in a sport that goes against gravity

• Starving: lack of protein in body

Electrolytes are

ionized salts dissolved in water

Cells contain higher concentrations of

Potassium, magnesium, and phosphate ions

Extracellular fluid contains higher concentrations of

Sodium, chloride, calcium, and bicarbonate ions

Dynamic control of electrolyte homeostasis

• concentration of an electrolyte in plasma is different from its concentration in the cell

Concentration of an electrolyte in the plasma is the net result of four processes

• electrolyte intake

• electrolyte absorption

• electrolyte distribution

• electrolyte excretion

True or False: Absorption is essential if electrolyte is to be useful metabolically

True

Bone and cells are often referred to as

electrolyte pools

Electrolytes are primarily influenced by the hormones:

• epinephrine (potassium ions)

• insulin (potassium and phosphate)

• parathyroid hormone (calcium ions)

*causes mobilization of electrolyte into the blood stream

Electrolyte excretion occurs through

urine, feces, sweat

Electrolyte excretion is influenced by

hormones

Excess electrolytes may be caused by

• increased intake

• increased absorption

• shift into extracellular fluid

• decreased excretion

Deficit electrolytes may be caused by

• decreased intake

• decreased absorption

• shift into electrolyte pools

• increased excretion

• loss through abnormal route

Electrolyte imbalances can be

• total imbalances

• imbalances in distribution between compartments

True or False: Most of potassium is inside the cell

True

Normal concentration of potassium:

3.5 - 5 mEq/L

Hypokalemia is

decreased potassium ion concentration in extracellular fluid

Hypokalemia etiology

• decreased intake: usually n conditions that cause decrease oral intake

• increased excretion: usually renal but can be through feces, sweat, GI, diuretics

Hypokalemia clinical manifestations

altered smooth, skeletal, cardiac muscle function because of changes in resting membrane potential

Hyperkalemia is

rise of serum potassium above 5 mEq/L

Hyperkalemia etiology

• increased potassium intake: rapid or excessive IV infusion

• decreased potassium excretion: oliguria, potassium-sparing diuretics, drugs that reduce aldosterone

Hyperkalemia clinical manifestations

Muscle dysfunction because of changes in resting membrane potential

*cardiac dysrhythmias and even cardiac arrest

Plasma calcium presents in three forms

• bound to plasma proteins (such as albumin)

• bound to small organic ions (such as citrate)

• unbound

Only free (unbound) ionized calcium is

physiologically active

Hypocalcemia is

Low concentration of calcium

Hypocalcemia etiology

• decreased calcium intake or absorption

• decreased physiologic availability of calcium

• increased calcium excretion

Hypocalcemia clinical manifestations

decreases the threshold potential, causing hyperexcitability of neuromuscular cells

Hypercalcemia

Serum calcium concentration rises normal limit

Hypercalcemia causes

decreased neuromuscular excitability caused by elevation of the threshold potential of excitable cells

Hypercalcemia etiology

• increased calcium intake or absorption

• shift of calcium from bone to extracellular fluid

• decreased calcium excretion

Hypomagnesemia

Indicates a decreased concentration of magnesium in the extracellular fluid but does not necessarily indicate a deficit in the total body magnesium

Hypomagnesemia clinical manifestations

Increased neuromuscular excitability from excessive amount of acetylcholine

More magnesium =

Less acetylcholine

Hypermagnesemia is

Too much magnesium

Hypermagnesemia etiology

• increased magnesium intake or absorption

• decreased magnesium excretion

Hypermagnesemia clinical manifestations

depression of neuromuscular function related to decreased release of acetylcholine at neuromuscular junctions

Hypophosphatemia is caused by

• Decreased phosphate intake or absorption

• shift of phosphate from extracellular fluid to cells

• increased phosphate excretion

Hypophosphatemia clinical manifestations

due in part to decreased ATP within the cells (phosphate is a major component of ATP)

*look over geriatric considerations for fluid and electrolyte imbalances slide