Chapter 27: Water, Electrolytes, and Acid-Base Balance

Identify the major fluid compartments of the body and their subdivisions:

Intracellular fluid compartment:

• all fluids inside cells of body

~40-50% of total body weight

Identify the major fluid compartments of the body and their subdivisions:

Extracellular fluid compartment:

• All fluids outside cells

~25-30% of total body weight

Identify the major fluid compartments of the body and their subdivisions:

• Subcompartments

—> interstitial fluid, plasma, lymph, CSF, synovial fluid

List the dominant cations and anions in the major fluid compartments:

Intracellular fluid:

• K+: primary cation inside

• PO3-: primary anion inside

List the dominant cations and anions in the major fluid compartments:

Extracellular fluid:

• interstitial fluid/ plasma(blood):

• Na+: primary cation

• Cl-: primary anion

Regulation of body fluid concentration and volume:

*content regulated so total volume of water in body remains constant

Regulation of body fluid concentration and volume:

Kidneys:

• primary regulators of water excretion

Regulation of body fluid concentration and volume:

Regulation process:

• osmosis

• osmolality

• baroreceptors

• learned behavior

Regulation of body fluid concentration and volume:

Sources of water:

• ingestion

• cellular metabolism

Regulation of body fluid concentration and volume:

Routes of water loss:

• urine

• evaporation

-perspiration (sweat)

-respiratory passages

• feces

Osmolality:

*Measure of water vs. solute concentration in a solution

• the higher the solute concentration, the higher the osmolality

• adding or removing water from a solution changes osmolality

Increased osmolality:

• triggers thirst

• stimulates ADH secretion

Decreased osmolality:

• inhibits thirst

• inhibits ADH secretion

Explain the four mechanisms that regulate blood (extracellular fluid) volume:

**ECF volume can increase or decrease even if osmolality is maintained

**ECF volume regulatory mechanisms include:

• neural

• renin-angiotensin aldosterone

• atrial natriuretic hormone (ANH)

• antidiuretic hormone (ADH)

Describe how intracellular fluid composition is maintained.

1) Large organic molecules, such as proteins, which cannot cross the plasma membrane, are synthesized inside cells and influence the concentration of solutes inside the cells

2) The transport ions, such as Na+, K+, and Ca2+, across the plasma membrane influences the concentration of ions inside and outside the cell

3) An electrical charge difference across the plasma membrane influences the distribution of ions inside and outside the cell

4) the distribution of water inside and outside the cell is determined by osmosis

How is sodium ion concentration is regulated:

Regulation of Na+-

• kidneys major route of excretion

• small quantities lost in sweat

Insensible perspiration:

• water evaporating from skin

Sensible perspiration:

• secreted by the sweat glands

• contains solutes

Hypernatremia:

*Abnormally high blood Na+

• thirst, fever, dry mucous membranes

Hyponatremia:

*Abnormally low blood Na+

• lethargy, confusion, apprehension, seizures

Explain potassium ion homeostasis:

• maintained in narrow range

• affect resting membrane potentials

• aldosterone increases amount secreted

Hyperkalemia:

*abnormally high blood K+

• symptoms: intestinal cramping and diarrhea

Hypokalemia:

*abnormally low blood K+

• symptoms: bradycardia, delayed ventricular depolarization

Explain calcium ion homeostasis (PTH, Vitamin D, Calcitonin)

—> regulated within a narrow range:

• elevated extracellular levels prevent membrane depolarization

• decreased levels lead to spontaneous action potential generation

*PTH:

• increases extracellular Ca2+ levels and decreases extracellular phosphate levels

*Vitamin D:

• stimulates Ca2+ uptake in the intestines

*Calcitonin:

• decreases extracellular Ca2+ levels

Hypocalcemia:

*Abnormally low blood Ca2+

• confusion, muscle spasms

Hypercalcemia:

*abnormally high blood Ca2+

• fatigue, weakness

Describe the three mechanisms of acid-base balance:

1) Buffers

• respond almost instantaneously to changes in pH

*Prevent large shifts in pH of blood and body fluids

*Protein buffer:

• intracellular and plasma proteins absorb H+

• provide ¾ of buffering in body

• EX) hemoglobin

*Bicarbonate buffering system:

• important in the plasma

*Phosphate buffer system:

• important as an intracellular buffer

2) Respiratory center:

• takes minutes to respond to changes in pH

*If pH rises: We hypoventilate

• respiratory rate decreases (retaining more Co2)

*If pH falls: We hyperventilate

• respiratory rate increases (fewer hydrogen ions in blood)

3) Renal regulation:

• may take hours to days to respond to changes in pH

• the kidneys have the greatest ability to regulate pH precisely

Hypoventilation:

• increases blood Co2 levels

Hyperventilation:

• decreases blood Co2 levels

*Acidosis:

1) respiratory

2) metabolic

*body fluid pH below 7.35

1) caused by hypoventilation

• reduced elimination of Co2, asthma, damage to respiratory center in brain, emphysema

2) Results from all conditions other than respiratory that decrease pH

• diarrhea, vomiting

*Alkalosis:

1) Respiratory

2) Metabolic

*Body fluid pH above 7.45

1) caused by hyperventilation

• high altitude reduced partial pressure of O2

2) All conditions other than respiratory

• severe vomiting, too much aldosterone