Cell Membrane

Chapter 1
Cell Structure and Function
 The cell is the building
 Each cell is a self-contained
 Cells tissues organs
body systems.
Physiologic Concepts
Cell Structure
 A cell is made up of internal
structures bound together inside
one cell membrane.
 All cells contain the same
internal structures.
 The inside of each cell can be
divided into cytoplasm and
The cytoplasm includes everything
inside the cell but outside the
 mitochondria energy
sources of the cell,
 endoplasmic reticulum
and ribosomes, protein
 The Golgi apparatus
secretion of proteins
synthesized on the
 Intracellular lysosomes
are vesicles that contain
potent digestive enzymes.
 The internal skeleton, called
cytoskeleton, supports the cell
from the inside and allows for the
movement of substances inside the
The Nucleus: a large, membranebound organelle that contains
deoxyribonucleic acid (DNA), the
genetic material of the cell. To
protect itself from breakage, the
DNA is folded up inside the
nucleus. Proteins responsible for
folding and protecting the DNA
are called histones.
Cell Membrane; encircles each
cell, semipermeable barrier
composed of a bilayer of
phospholipids, with interspersed,
freely moving, protein molecules.
 Diffusion through the lipid
bilayer is limited to lipidsoluble substances.
Movement through the
- Lipid-soluble substances, such as
oxygen, carbon dioxide, alcohol,
and urea, move across the lipid
bilayer by simple diffusion.
- Other substances that are not
lipid soluble, move through pores
provided by the integral proteins or
through carrier-mediated transport
Through the Cell Membrane
This process does not require
energy, a substance that is
permeable across the cell
membrane will diffuse into or out
of the cell until its concentration is
equal on both sides
The diffusion of water into the cell
is called osmosis; water moves
down its concentration gradient
(i.e., from high concentration to
low). According to osmotic
 The osmotic pressure of a
solution depends on the number
of particles or ions present in
the water solution. The more
ions that are present in the
solution, the less the water
concentration and the greater
the osmotic pressure (i.e., the
pressure for water to diffuse
into the solution).
 A cell also has osmotic
pressure. A dehydrated cell has
high osmotic pressure, Water
would diffuse into this cell if
 An overhydrated cell has low
osmotic pressure , Water would
diffuse out of this cell if
Simple Diffusion through Protein
These protein channels are usually
selective about which ions they
allow to pass. Like all types of
simple diffusion, diffusion through
a gate continues until the
concentrations on either side of the
membrane are equal or the gate is
Mediated Transport
For many substances like glucose
and amino acids, simple diffusion
is impossible. These molecules are
too charged large to pass through a
pore. Instead, these substances, are
transported across the membrane
with the assistance of a carrier.
This type of movement is called
mediated transport .
. With active transport, energy is
used by the cell to maintain a
substance at higher concentration
on one side of the membrane than
the other. Examples of substances
moved by active transport
include Na, K, Ca, and the
amino acids.
 Facilitated diffusion is similar
to simple diffusion in that no
energy is used by the cell to
transport a substance but differs
from simple diffusion in that it
is assisted (facilitated) by a
carrier and so can cross the
membrane. Glucose moves into
most cells by facilitated
When large substances cannot
enter the cell by diffusion or
mediated transport, endocytosis
(engulfment) of the substance by
the cell membrane occurs.
- Pinocytosis is the engulfment of
macromolecules, such as protein,
by vesicles.
- Phagocytosis is the engulfment
of dead cells or bacteria. Both
processes require energy. Only
cells of the immune system (i.e.,
macrophages and neutrophils)
perform phagocytosis.
Energy Production
Cells are required to produce
energy for their own use. Cells do
this by extracting the energy
contained in the chemical bonds of
food molecules by combining the
food molecules with oxygen inside
the mitochondria of the cell. The
food molecules used are glucose
from carbohydrate metabolism,
amino acids from protein
metabolism, and fatty acids and
glycerol from fat metabolism.
The Sodium-Potassium Pump
An important example of active
transport is the pumping of sodium
and potassium across cell
membranes. This transport
depends on an integral carrier
protein known as the sodiumpotassium pump. Associated with
the pump is an enzyme that splits
ATP and provides the energy
needed for the pump to function.
This enzyme is known as the
sodium-potassium ATPase. The
sodium-potassium pump transports
sodium ions out of and potassium
ions into the cell. This transport
causes greater sodium
concentration in the extracellular
fluid (142 mEq/L) compared to the
intracellular fluid (14 mEq/L), and
greater potassium concentration in
the intracellular fluid (140 mEq/L)
compared to the extracellular fluid
(4 mEq/L).
The Effects of Pumping Sodium
and Potassium
1- allows nerve and muscle
function and action potentials to
occur .
Because sodium and potassium are
cations (carrying a positive
charge), the transport of three
sodium ions out of the cell and
only two potassium ions into the
cell creates an electrical gradient
across the cell membrane.
2- controlling cell volume
The presence of intracellular
proteins and other organic
substances that cannot cross the
cell membrane increases
intracellular osmotic pressure and
creates a tendency for water to
diffuse into the cell. This diffusion
of water, if unlimited, would cause
the cell to swell and eventually
burst. However, with the active
transport of sodium ions out of the
cell, the osmotic pressure inside
the cell is reduced and the
diffusion of water into the cell is
Cellular Reproduction
Many cells of the body reproduce
and make copies of themselves
throughout an organism's lifetime.
To reproduce, a cell has to
replicate its genetic material and
then split in two. Replication and
division of a cell occurs during the
cell cycle .
To replicate, the DNA double helix
uncoils and each strand of DNA
serves as a template for a new
strand. Replication of the
chromosome pairs and the DNA
occurs in the nucleus of the cell.
Various enzymes participate in
DNA replication, which results in
each chromosome being exactly
copied or duplicated.
Cell Division
Once duplicated, the chromosome
pairs pull apart and the original
cell splits into two cells. Each new
cell contains the entire genetic
information in 23 pairs of
chromosomes. The process
whereby a cell divides to produce
two identical daughter cells is
called mitosis.
Meiosis, another type of cell
division, occurs in the reproductive
cells, the egg and sperm. Meiosis
involves two cell divisions
resulting in a total of four daughter
cells produced, each containing 23
single chromosomes rather than 23
Cellular Replication and Division
- Some cells, such as liver, bone
marrow, and gut cells, undergo
replication and mitosis
- Nerve and cardiac muscle
cells, do not replicate or divide
except during fetal development
or in the neonatal period.
Pathophysiologic Concepts
Cells are continually exposed to
changing conditions and
potentially damaging stimuli. If
these changes and stimuli are
minor or brief, the cell adapts to
them. Cellular adaptations include
atrophy, hypertrophy, hyperplasia,
metaplasia and dysplasia. More
prolonged or intense stimuli can
cause cell injury or death.
Atrophy is a decrease in the size of
a cell or tissue. Atrophy can occur
as a result of
- disuse, for
instance, as seen in the muscles of
an individual who is immobilized .
- decreased hormonal or neural
stimulation of a cell or tissue,
which is seen in the breasts of
women after menopause or in
skeletal muscle after spinal cord
injury .
- nutritional deficiency and is seen
in malnourished or starving
- insufficient blood supply to cells,
which cuts off vital nutrient and
oxygen supply.
Hypertrophy is the increase in the
size of a cell or tissue.
Hypertrophy is an adaptive
response that occurs when there is
an increase in the workload of a
cell. The cell's demand for oxygen
and nutrients increases, causing
growth of most intracellular
Hypertrophy is primarily seen in
cells that cannot adapt to increased
work by increasing their numbers
through mitosis. Examples of cells
that cannot undergo mitosis but
experience hypertrophy are cardiac
and skeletal muscle cells. There
are three main types of
-Physiologic hypertrophy occurs as
a result of a healthy increase in the
workload of a cell (i.e., increased
muscle bulk through exercise).
-Pathologic hypertrophy occurs in
response to a disease state, for
example, hypertrophy of the left
ventricle in response to
longstanding hypertension .
-Compensatory hypertrophy occurs
when cells grow to take over the
role of other cells that have died.
For example, the loss of one
kidney causes the cells of the
remaining kidney to undergo
Hyperplasia is the increase in cell
number as a result of increased
mitosis stimulated by an increased
workload, or by hormonal signals.
It can only occur in cells that
undergo mitosis, such as liver,
kidney, and connective tissue cells.
Hyperplasia may be:
Physiologic hyperplasia occurs
monthly in uterine endometrial
cells .
Pathophysiologic hyperplasia can
occur with excessive hormonal
stimulation, which is seen in
acromegaly .
Compensatory hyperplasia occurs
when cells of a tissue reproduce to
make up for a previous decrease in
cells as what occurs in liver cells
after surgical removal of sections
of liver tissue. The compensation
is striking in its rapidity.
Metaplasia is the change
in a cell from one subtype
to another, i.e change in
the cells of the respiratory
passages from ciliated
columnar epithelial cells to
stratified squamous
epithelial cells (smokers).
Stratified epithelial cells
are better able to survive
smoke damage.
Unfortunately, they do not
assume the vital protective
role of ciliated cells.
Dysplasia is a
derangement in cell growth
that results in cells that
differ in shape, size, and
appearance from their
predecessors, due to
exposure to chronic
irritation and
inflammation. (dangerous,
mey be precancerous).
Again, respiratory tract
(especially the squamous
cells is the most common
site as well as the cervix.
Cervical dysplasia usually
results from infection of
the cells with the human
papilloma virus (HPV).
Dysplasia is usually rated
on a scale to reflect its
degree, from minor to
Cell Injury
Cell injury occurs when a
cell can no longer adapt to
stimuli. This can occur if
the stimuli are too long or
too severe. Hypoxia,
microorganism infection,
temperature extremes,
physical trauma, and
radiation, cause cell injury.
Cell Death
There are two main
categories of cell death:
1-necrotic cell death,
characterized by cell
swelling and rupture of
internal organelles.
Common causes of
necrotic cell death include
prolonged hypoxia and
infection .
2- apoptosis, is not
characterized by that dying
cell shrinks on itself and
then is engulfed by
neighboring cells.
Programmed cell death
begins during
embryogenesis and
continues throughout the
lifetime of an organism.
Viral infection of a cell
will often turn on
apoptosis. Deficiencies in
apoptosis have been
implicated in the
development of cancer .
Results of Cell Death
Dead cells are removed
from the area or isolated
from the rest of the tissue
by immune cells in the
process of phagocytosis. If
mitosis is possible and the
area of necrosis is not too
large, new cells of the
same type fill in the empty
space. Scar tissue will
form in the vacated space
if cell division is
impossible or if the area of
necrosis is extensive.
Gangrene refers to the
death of a large mass of
cells. Gangrene may be
classified as dry or wet.
Dry gangrene spreads
slowly with few symptoms
and is frequently seen in
the extremities, often as a
result of prolonged
Wet gangrene is a rapidly
spreading area of dead
tissue, often of internal
organs, and is associated
with bacterial invasion of
the dead tissue. It exudes a
strong odor and is usually
accompanied by systemic
Gas gangrene is a special
type of gangrene that
occurs in response to an
infection of the tissue by a
type of anaerobic bacteria
called clostridium. It is
seen most often after
significant trauma. Gas
gangrene rapidly spreads to
neighboring tissue as the
bacteria release deadly
toxins that kill neighboring
cells. Muscle cells are
specially susceptible and
release characteristic
hydrogen sulfide gas when
affected. This type of
gangrene may prove fatal.
Wound Repair
Destroyed or injured
tissues must be repaired by
regeneration of the cells or
the formation of scar
tissue. The goal of both
types of repair is to fill in
the areas of
damage.Tissues that heal
cleanly and quickly are
said to heal by primary
intention. Large wounds
that heal slowly and with a
great deal of scar tissue
heal by secondary
Delayed Healing and
Tissue repair can be
delayed if the host has:
malnutrition, systemic
disease, poorly functioning
immune system or if there
is reduced blood flow to
the injured tissue or if an
infection develops.
Conditions of Disease or
Hypoxia is the decreased
concentration of oxygen in
the tissues.
 inadequate intake of
oxygen by the
respiratory system,
 inadequate delivery of
oxygen by the
cardiovascular system,
 a lack of hemoglobin.
Oxygen is required by the
mitochondria for oxidative
phosphorylation and the
production of ATP.
Without oxygen, this
process cannot occur.
Consequences of Hypoxia
When cells are deprived of
ATP, they can no longer
maintain cellular functions,
including the transport of
sodium and potassium
through the sodiumpotassium pump. Without
pumping, cells begin to
accumulate sodium as it
diffuses into the cell down
its concentration and
electrical gradients.
Osmotic pressure inside
the cell increases, drawing
water into the cell and
begins to swell and burst.
Another consequence of
hypoxia is the production
of lactic acid, (which
occurs during anaerobic
glycolysis). Decreased ph
causes damage to the
nuclear structures.
The effects of hypoxia are
reversible if oxygen is
returned within a certain
period of time, the amount
of which varies and
depends on the tissue.
Clinical Manifestations
If the source of hypoxia is
respiratory failure or
myocardial infarct, all
tissues will be affected.
Cell death may occur.
- Increased heart rate.
- Increased respiratory rate.
- Muscle weakness.
- Decreased level of
- Altered consciousness
progressing to coma and
death if prolonged cerebral
(brain) hypoxia occurs.
-Organ failure, including
adult respiratory distress
syndrome, cardiac failure,
or kidney failure, may
occur if hypoxia is
Increase oxygen in inspired
air through a mask or
mechanical ventilation.
2-Temperature Extremes
- Exposure to very high
temperatures can cause
burn injuries, which
directly kill cells or
indirectly by causing
coagulation of blood
vessels or the breakdown
of cell membranes (brain,
boiled eggs).
- Exposure to very cold
temperatures injures cells
in two ways: constriction
of the blood vessels that
deliver nutrients and
oxygen to the extremities
and the formation of ice
crystals in the cells. These
crystals directly damage
the cells and can lead to
cell lysis (bursting).
Prolonged exposure to the
cold can lead to
Clinical Manifestations of
Cold Exposure and
- Numbness or tingling of
the skin or extremities.
- Pale or blue skin that is
cool to the touch.
- Shivering early on, then
lack of shivering as
condition worsens.
- Decreased level of
consciousness, drowsiness,
and confusion.
- Blood clotting,
characterized by pain and a
decrease in pulse
downstream from the clot.
If blood flow is inadequate
for an extended time,
gangrene may result.
- --- Frostbite.
- Ventricular dysrhythmia.
3-Radiation Injury
Radiation energy may be
in the visible range of
light, or it invisible light.
High-energy radiation
(UV) is called ionizing
radiation because it has the
capability of knocking
electrons off atoms or
molecules, thereby
ionizing them. Low-energy
radiation is called nonionizing radiation because
it cannot displace electrons
off atoms or molecules.
Effects of Ionizing
Ionizing radiation may
injure or kill cells directly
by destroying the cell
membrane and causing
intracellular swelling and
cell lysis. As cells are
killed or injured, the
inflammatory response is
stimulated, causing
capillary leakiness,
interstitial edema, white
blood cell accumulation,
and tissue scarring.
Ionizing radiation may also
lead to mistakes in DNA
replication or transcription
which may cause
programmed cell death or
subsequent cancer .
cells Susceptible to
Ionizing Radiation
Cells most susceptible to
damage by ionizing
radiation are cells that
undergo frequent divisions,
including cells of the
gastrointestinal (GI) tract,
the integument (skin and
hair), and the bloodforming cells of the bone
marrow and FETUS.
Ionizing radiation is
emitted by the sun, in x-
rays, and in nuclear
Effects of Non-Ionizing
Non-ionizing radiation
includes microwave and
ultrasound radiation. The
energy of this radiation is
too low to break DNA
bonds or damage the cell
Clinical Manifestations of
Ionizing Radiation
- Skin redness or
- With high doses,
vomiting and nausea
caused by GI damage.
- Anemia if the bone
marrow is destroyed.
- Cancer may develop
years after the exposure .
- Damage caused by low
doses will be repaired and
does not require treatment.
- Cancers should be treated
Pediatric Consideration
Fetal cells rapidly undergo
cellular division and are
highly susceptible to the
damaging effects of
ionizing radiation. Infants
and young children also
experience periods of rapid
cellular growth and are at
risk of genetic damage
from ionizing radiation.
Studies suggest that there
are no apparent health risks
to fetuses exposed to non-
ionizing radiation .
4-Injury Caused by
Microorganisms infectious
to humans include
bacteria, viruses,
mycoplasmas, rickettsiae,
chlamydiae, fungi, and
protozoa. Some of these
organisms infect humans
a. direct access, such as
b. intermediate vector,
such as from an insect
bite. Cells of the body
may be destroyed :
a. directly by the
microorganism or
b. by a toxin released
from MO , or may be
c. indirectly injured as a
result of the immune
and inflammatory
reactions .
Clinical Manifestations
Infection by bacteria and
viruses, often results in:
- Regional lymph node
- Fever (usually low-grade
with a viral infection)
- Body aches
- Skin rash or eruption,
especially with viral
- Site-specific responses,
such as pharyngitis, cough,
otitis media
- Bacteria and
mycoplasmas are treated
with antibiotics, preferably
- Certain viral infections
may be treated with
antiviral agents. Other viral
infections usually are left
to resolve on their own,
with care taken that a
subsequent bacterial
infection does not infect
the original site or