CHAPTER 1
Common cellular adaptations
Atrophy refers to a decrease in the size of cells, resulting in a reduced tissue
mass. Common causes include reduced use of the tissue, insufficient nutrition, decreased
neurologic or hormonal stimulation, and aging. An example is the shrinkage of skeletal muscle
that occurs when a limb is immobilized in a cast for several weeks.
• Hypertrophy refers to an increase in the size of individual cells, resulting in an enlarged tissue
mass. This increase may be caused by additional work by the tissue, as demonstrated by an
enlarged heart muscle resulting from increased demands. A common example of hypertrophy is
the effect of consistent exercise on skeletal muscle, leading to an enlarged muscle mass.
Excessive hormonal stimulation may also stimulate cell growth.
• Hyperplasia is defined as an increased number of cells resulting in an enlarged tissue mass. In
some cases, hypertrophy and hyperplasia occur simultaneously, as in the uterine enlargement that
occurs during pregnancy. Hyperplasia may be a compensatory mechanism to meet increased
demands, or it may be pathologic when there is a hormonal imbalance. In certain instances there
may be an increased risk of cancer when hyperplasia occurs.
• Metaplasia occurs when one mature cell type is replaced by a different mature cell type. This
change may result from a deficit of vitamin A. Sometimes, metaplasia may be an adaptive
mechanism that provides a more resistant tissue; for instance, when stratified squamous
epithelium replaces ciliated columnar epithelium in the respiratory tracts of cigarette smokers.
Although the new cells present a stronger barrier, they result in decreased defenses for the lungs
because cilia are no longer present as a defense mechanism for the simpler squamous cells in the
mucosa.
• Dysplasia is the term applied to tissue in which the cells vary in size and shape, large nuclei are
frequently present, and the rate of mitosis is increased. This situation may result from chronic
irritation infection, or it may be a precancerous change. Detection of dysplasia is the basis of
routine screening tests for atypical cells such as the Pap smear (Papanicolaou test on cervical
cells).
• Anaplasia refers to cells that are undifferentiated with variable nuclear and cell structures and
numerous mitotic figures. Anaplasia is characteristic of cancer and is the basis for grading the
aggressiveness of a tumor.
• Neoplasia means “new growth,” and a neoplasm is commonly called a tumor. Tumors are of
two types, benign and malignant. Malignant neoplasms are referred to as cancer. Benign tumors
do not necessarily become malignant. Benign tumors are usually considered less serious because
they do not spread and are not life threatening unless they are found in certain locations, such as
the brain, where they can cause pressure problems. The characteristics of each tumor depend on
the specific type of cell from which the tumor arises, resulting in a unique appearance and
growth pattern. Neoplasms are discussed further in
,Cell damage (Ischemia)
Apoptosis refers to programmed cell death, a normal occurrence in the body, which may increase
when cell development is abnormal, cell numbers are excessive, or cells are injured or aged.
Cells self-destruct, appearing to digest themselves enzymatically, and then disintegrate into
fragments.
There are many ways of injuring cells in the body, including:
•Ischemia, a decreased supply of oxygenated blood to a tissue or organ, due to circulatory
obstruction
•Physical agents, excessive heat or cold, or radiation exposure
•Mechanical damage such as pressure or tearing of tissue
•Chemical toxins
•Microorganisms such as bacteria, viruses, and parasites
•Abnormal metabolites accumulating in cells
•Nutritional deficits
•Imbalance of fluids or electrolytes
The most common cause of injury is ischemia or reduced blood supply to the tissue, which
results in insufficient oxygen and reduced cellular metabolism. Decreased oxygen in the tissue
may occur locally because of a blocked artery or systemically because of respiratory impairment.
Cells with a high demand for oxygen, such as those of the brain, heart, and kidney, are quickly
affected by hypoxia (reduced oxygen in the tissue). A severe oxygen deficit interferes with
energy (ATP) production in the cell, leading to loss of the sodium pump at the cell membrane as
well as loss of other cell functions. An increase in sodium ions inside the cell leads to swelling of
the cell and eventually to rupture of the cell membrane. At the same time, in the absence of
oxygen, anaerobic metabolism occurs in the cell, leading to a decrease in pH from build of lactic
acid and further metabolic impairment. A deficit of other essential nutrients such as vitamins may
also damage cells because normal metabolic processes cannot take place.
CHAPTER 2
Fluid deficit- Dehydration
Dehydration refers to insufficient body fluid resulting from inadequate intake or excessive loss
of fluids or a combination of the two. Losses are more common and affect the extracellular
compartment first. Water can shift within the extracellular compartments. For example, if fluid is
lost from the digestive tract because of vomiting, water shifts from the vascular compartment
,into the digestive tract to replace the lost secretions. If the deficit continues, eventually fluid is
lost from the cells, impairing cell function.
Fluid loss is often measured by a change in body weight; knowing the usual body weight of a
person is very helpful in assessment of the extent of loss. As a general guide to extracellular fluid
loss, a mild deficit is defined as a decrease of 2% in body weight, a moderate deficit as a 5%
weight loss, and severe dehydration is a decrease of 8%. This figure should be adjusted for the
individual's age, body size, and condition.
Dehydration is a more serious problem for infants and elderly people, who lack significant fluid
reserves as well as the ability to conserve fluid quickly. Infants also experience not only greater
insensible water losses through their proportionately larger body surface area but also an
increased need for water owing to their higher metabolic rate. The vascular compartment is
rapidly depleted in an infant (hypovolemia), affecting the heart, brain, and kidneys. This is
indicated by decreased urine output (number of wet diapers), increased lethargy, and dry mucosal
membranes.
Water loss is often accompanied by a loss of electrolytes and sometimes of proteins, depending
on the specific cause of the loss. For example, sweating results in a loss of water and sodium
chloride. Electrolyte losses can influence water balance significantly because electrolyte changes
lead to osmotic pressure change between compartments. To restore balance, electrolytes as well
as fluid must be replaced. Isotonic dehydration refers to a proportionate loss of fluid and
electrolytes, hypotonic dehydration to a loss of more electrolytes than water, and
hypertonic dehydration to a loss of more fluid than electrolytes. The latter two types
of dehydration cause signs of electrolyte imbalance and influence the movement of water
between the intracellular and extracellular compartments (see Electrolyte Imbalances).
Causes of Dehydration
Common causes of dehydration include:
1.Vomiting and diarrhea, both of which result in loss of numerous electrolytes and nutrients such
as glucose, as well as water; drainage or suction of any portion of the digestive system can also
result in deficits
2.Excessive sweating with loss of sodium and water
3.Diabetic ketoacidosis with loss of fluid, electrolytes, and glucose in the urine
4.Insufficient water intake in an elderly or unconscious person
5.Use of a concentrated formula in an attempt to provide more nutrition to an infant
Effects of Dehydration
Initially, dehydration involves a decrease in interstitial and intravascular fluids. These losses may
produce direct effects such as:
•Dry mucous membranes in the mouth (see Table 2-3)
, Decreased skin turgor or elasticity (Fig. 2-4)
•Lower blood pressure, weak pulse, and a feeling of fatigue
•Increased hematocrit, indicating a higher proportion of red blood cells compared with water in
the blood
•Decreasing mental function, confusion, and loss of consciousness, which develop as brain cells
lose water and reduce function
The body attempts to compensate for the fluid loss by:
•Increasing thirst
•Increasing the heart rate
•Constricting the cutaneous blood vessels, leading to pale and cool skin
•Producing less urine and concentrating the urine, increasing the specific gravity, as a result of
renal vasoconstriction and increased secretion of ADH and aldosterone
CHAPTER 5
Acute inflammation (Local and Systemic effects)
The cardinal signs of inflammation are redness (rubor or erythema), heat, swelling, and pain:
•Redness and warmth are caused by increased blood flow into the damaged area (Fig. 5-
Swelling or edema is caused by the shift of protein and fluid into the interstitial space.
•Pain results from the increased pressure of fluid on the nerves, especially in enclosed areas, and
by the local irritation of nerves by chemical mediators such as bradykinins.
•Loss of function may develop if the cells lack nutrients or swelling interferes mechanically with
function, as happens in restricted joint movement.
Exudate refers to a collection of interstitial fluid formed in the inflamed area. The characteristics
of the exudate vary with the cause of the trauma:
•Serous or watery exudates consist primarily of fluid with small amounts of protein and white
blood cells. Common examples of serous exudates occur with allergic reactions or burns.
•Fibrinous exudates are thick and sticky and have a high cell and fibrin content. This type of
exudate increases the risk of scar tissue in the area.
•Purulent exudates are thick, yellow-green in color, and contain more leukocytes and cell debris
as well as microorganisms. Typically, this type of exudate indicates bacterial infection, and the
exudate is often referred to as “pus.”
