Download the lymphatic system and immunity

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A & P II
SWARTZ
NOTES
Page 52
THE LYMPHATIC SYSTEM AND IMMUNITY
The lymphatic system consists of a fluid called lymph, vessels that convey lymph
called lymphatics, and a number of structures and organs, all of which contain
lymphatic (lymphoid) tissue. Essentially, lymphatic tissue is a specialized form
of reticular connective tissue that contains large numbers of lymphocytes. The
stroma (framework) of lymphatic tissue is a meshwork of reticular fibers and
reticular cells (fibroblasts and fixed macrophages). One exception to this is
the thymus gland, which has a stroma of epithelioreticular tissue.
Lymphatic tissue is organized in various ways. Accumulations of lymphatic tissue
not enclosed by a capsule are referred to as diffuse lymphatic tissue. This is
the
simplest
form
of
lymphatic
tissue
and
is
found
in
the
lamina
propria
(connective tissue) of mucous membranes of the gastrointestinal (GI) tract,
respiratory
passageways,
urinary
tract,
and reproductive
tract.
It
is
also
normally found in small amounts in the stroma of almost every organ of the body.
Lymphatic
nodules
are
unencapsulated
oval-shaped
concentrations
of
lymphatic
tissue that usually consist of a central, lighter-staining region consisting of
large lymphocytes (germinal center) and a peripheral, darker-staining region of
small lymphocytes (cortex).
Most lymphatic nodules are solitary, small, and
discrete.
Some lymphatic nodules occur in multiple, large aggregations in specific parts
of the body. Among these are the tonsils in the pharyngeal region and aggregated
lymphatic follicles (Peyer's patches) in the ileum of the small intestine.
Aggregations of lymphatic nodules also occur in the appendix. The lymphatic
organs of the body--the lymph nodes, spleen, and thymus gland--all contain
lymphatic tissue enclosed by a connective tissue capsule.
Since bone marrow
produces lymphocytes, it is also a component of the lymphatic system.
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The lymphatic system has several functions.
1.
Lymphatics drain protein-containing fluid from tissue spaces that escape
from blood capillaries. The proteins, which cannot be directly reabsorbed
by blood vessels, are returned to the cardiovascular system by lymphatics.
2.
Lymphatics also transport fats from the gastrointestinal (GI) tract to the
blood.
3.
Lymphatic tissue also functions in surveillance and defense, that is,
lymphocytes, with the aid of macrophages, protect the body from foreign
cells, microbes, and cancer cells.
4.
Lymphocytes recognize foreign cells and substances, microbes, and cancer
cells, and respond to them in two general ways. Some lymphocytes (T cells)
destroy them directly or indirectly by releasing various substances. Other
lymphocytes (B cells) differentiate into plasma cells that secrete
antibodies against foreign substances to help eliminate them.
Overall,
the
lymphatic
system
concentrates
foreign
substances
in
certain
lymphatic organs, circulates lymphocytes through the organs to make contact
with the foreign substances, and destroys the foreign substances and eliminates
them from the body.
LYMPHATIC VESSELS
Lymphatic vessels originate as microscopic vessels in spaces between cells
called lymph capillaries. Lymph capillaries may occur singly or in extensive
plexuses. They originate throughout the body, but not in avascular tissue, the
central nervous system, splenic pulp, nor bone marrow. They are slightly larger
and more permeable than blood capillaries.
Lymph capillaries also differ from blood capillaries in that they end blindly.
Blood
capillaries
have
an
arterial
and
a
venous
end.
In
addition,
lymph
capillaries are structurally adapted to ensure the return of proteins to the
circulation when they leak out of blood capillaries. The endothelial cells
lining lymph capillaries overlap one another forming pores which permits fluid
to flow easily into the capillary but prevents the flow of fluid out of the
capillary, much like a one-way valve would operate. During edema, there is an
excessive accumulation of fluid in the tissue, causing tissue swelling.
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Just as blood capillaries converge to form venules and veins, lymph capillaries
unite
to
form
larger
and
larger
lymph
vessels
called
lymphatics.
Lymphatics
resemble veins in structure, but have thinner walls and more valves, and contain
lymph
nodes
subcutaneous
at
various
tissue
and
intervals.
generally
Lymphatics
follow
of
veins.
the
skin
travel
Lymphatics
of
in
the
loose
viscera
generally follow arteries, forming plexuses around them. Ultimately, lymphatics
converge into two mid channels--the thoracic duct and the right lymphatic duct.
LYMPHATIC TISSUE
(1) Lymph Nodes: The oval or bean-shaped structures located along the length of
lymphatics are called lymph nodes. They are scattered throughout the body,
usually in groups, and range from 1 to 25 mm (0.04 to 1 inch) in length. A
lymph node contains a slight depression on one side called a hilus = hilum,
where blood vessels and efferent lymphatic vessels leave the node. Each node
is covered by a capsule of dense connective tissue that extends into the node.
The capsular extensions are called trabeculae,. Internal to the capsule is a
supporting network of reticular fibers and reticular cells (fibroblasts and
macrophages).
The
capsule,
trabeculae,
and
reticular
fibers
and
cells
constitute the stroma (framework) of a lymph node. The parenchyma of a lymph
node is specialized into two regions: cortex and medulla. The parenchyma is
the functional aspect of the lymph node. The outer cortex contains densely
packed lymphocytes arranged in masses called lymphatic nodules. The nodules
often contain lighter-staining central areas, the
germinal centers, where
lymphocytes are produced. The inner region of a lymph node is called the
medulla.
In
the
medulla,
the
lymphocytes
are
arranged
in
strands
called
medullary cords.
The circulation of lymph through a node involves afferent (to convey toward a
center) lymphatic vessels, sinuses in the node, and efferent (to convey away
from a center) lymphatic vessels. Afferent lymphatic vessels enter the convex
surface of the node at several points. They contain valves that open toward
the node so that the lymph is directed inward. Once inside the node,
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the lymph enters the sinuses, which are a series of irregular channels.
Lymph from the afferent lymphatic vessels enters the cortical sinuses just
inside the capsule. From here it circulates to the medullary sinuses between
the medullary cords. From these sinuses the lymph usually circulates into
one of two efferent lymphatic vessels. The efferent vessel is located at the
hilus of the lymph node. It is wider than the afferent vessels and contains
valves that open away from the node to convey the lymph out of the node.
Lymph nodes are scattered through the the body, usually in groups.
Typically, these groups are arranged in two sets: superficial and deep.
Lymph passing from tissue spaces through lymphatics on its way back to the
cardiovascular system is filtered through the lymph nodes. As lymph passes
through the nodes, it is filtered of foreign substances. These substances
are trapped by the reticular fibers within the node. Then, macrophages
destroy the foreign substances by phagocytosis, T cells may destroy them by
releasing various products, and/or
destroy them. Lymph
B cells may produce antibodies that
nodes also produce
lymphocytes, some
of
which can
circulate to other parts of the body.
-------------------Clinical Application
-------------------Knowledge of the location of lymph nodes and the direction of lymph flow is
important in the diagnosis and prognosis of the spread of cancer by metastasis.
Cancer
cells
usually
spread
by
way
of
the
lymphatic
system
and
produce
aggregates of tumor cells where they lodge. Such secondary tumor sites are
predictable by the direction of lymph flow from the organ primarily involved.
------------------------------------------------------------------------------(2)
Tonsils:
Tonsils
are
multiple
aggregations
of
large
lymphatic
nodules
embedded in a mucous membrane. The tonsils are arranged in a ring at the
junction of the oral cavity and pharynx. The single pharyngeal tonsil or
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adenoid
is
palatine
embedded
tonsils
in
are
the
posterior
situated
in
wall
of
the
nasopharynx.
the
tonsillar
fossae
The
paired
between
the
pharyngopalatine and glossopalatine arches. These are the ones commonly removed
by a tonsilectomy. The paired lingual tonsils are located at the base of the
tongue and may also have to be removed by a tonsillectomy.
The tonsils are situated strategically to protect against invasion of foreign
substances. Functionally, the tonsils produce lymphocytes and antibodies.
(3)Spleen: The oval spleen is the largest mass of lymphatic tissue in the body,
measuring
about
hypochondriac
12
cm
region
(5
inches)
between
the
in
length.
fundus
of
It
the
is
situated
stomach
and
in
the
left
diaphragm.
Its
visceral surface contains the contours of the organs adjacent to it, namely the
gastric
impression
(stomach),
renal
impression
(left
kidney),
and
colic
impression (left flexure of colon). The diaphragmatic surface of the spleen is
smooth and convex and conforms to the concave surface of the diaphragm to which
it is adjacent.
The spleen is surrounded by a capsule of dense connective tissue and scattered
smooth muscle fibers. The capsule, in turn, is covered by a serous membrane, the
peritoneum. Like lymph nodes, the spleen contains a hilus, trabeculae,
and
reticular fibers and cells. The capsule, trabeculae, and reticular fibers and
cells constitute the stroma of the spleen.
The parenchyma of the spleen consists of two different kinds of tissue called
white pulp and red pulp. White pulp is essentially lymphatic tissue, mostly
lymphocytes,
arranged
around
arteries
called
central
arteries.
In
various
areas, the lymphocytes are thickened into lymphatic nodules referred to as
splenic
nodules
(Malpighian
corpuscles).
The
red
pulp
consists
of
venous
sinuses filled with blood and cords of splenic tissue called splenic cords, or
cords of Billroth's. Veins are closely associated with the red pulp. Splenic
cords consist of erythrocytes, macrophages, lymphocytes, plasma cells, and
granulocytes.
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The splenic artery and vein and the efferent lymphatics pass through the
hilus. Since the spleen has no afferent lymphatic vessels or lymph sinuses,
it does not filter lymph. One key splenic function related to immunity is
the
production
of
B
lymphocytes,
which
develop
into
antibody-producing
plasma cells. The spleen also phagocytizes bacteria and worn-out and damaged
red blood cells and platelets. In addition, the spleen stores and releases
blood in case of demand, such as during hemorrhage. In this regard, the
spleen is considered to be a blood reservoir.
(4) Thymus Gland: Usually a bilobed lymphatic organ, the thymus eland is located
in the superior mediastinum, posterior to the sternum and between the lungs.
The two thymic lobes are held in close proximity by an enveloping layer of
connective tissue. Each lobe is enclosed by a connective tissue capsule. The
capsule gives off extensions into the lobes called trabeculae, which divide
the lobes into lobules. Each lobule consists of a deeply staining peripheral
cortex
and
a
lighter-staining
central
medulla.
The
medulla
contains
characteristic thymic corpuscles known as Hassall's corpuscles. Hassall's
corpuscles are concentric layers of epithelial cells. Their significance is
not known.
The thymus gland is conspicuous in the infant, and it reaches its maximum
size of about 40 grams during puberty. After puberty, most of the thymic
tissue is replaced by fat and connective tissue. By the time the person
reaches maturity, the gland has atrophied substantially. The role of the
thymus in immunity is to help produce T cells that destroy invading microbes
directly or indirectly by producing various substances.
LYMPH CIRCULATION
When
plasma
is
filtered
by
blood
capillaries,
it
passes
into
interstitial
spaces. At this point it is known as interstitial fluid. When this fluid passes
from interstitial spaces into lymph capillaries, it is called lymph. Lymph from
lymph capillaries is then passed to lymphatics that run toward lymph nodes. At
the nodes, afferent vessels penetrate the capsules at numerous points, and the
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lymph passes through the sinuses of the nodes. Efferent vessels from the nodes
either run with afferent vessels into another node of the same group or pass on
to another group of nodes. From the most proximal group of each chain of nodes,
the efferent vessels unite to form lymph trunks. The principal trunks are the
lumbar, intestinal, bronchomediastinal, subclavian, and juglar trunks.
The principal trunks pass their lymph into two main channels, the thoracic duct
and the right lymphatic duct. The thoracic duct also known as the left lymphatic
duct is about 38 to 45 cm (15 to 18 inches) in length and begins as a dilation
in front of the second lumbar vetebra called the cisterna chyli. The thoracic
duct is the main collecting duct of the lymphatic system and receives lymph from
the left side of the head, neck, and chest, the left upper extremity, and the
entire body below the ribs.
The cisterna chyli receives lymph from the right and left lumbar trunks and from
the intestinal trunk. The lumbar trunks drain lymph from the lower extremities,
wall and viscera of the pelvis, kidneys, suprarenals, and the deep lymphatics
from most of the abdominal wall. The intestinal trunk drains lymph from the
stomach, intestines, pancreas, spleen, and visceral surface of the liver. In the
neck,
the
thoracic
duct
also
receives
lymph
from
the
left
jugular,
left
subclavian, and left bronchomediastinal trunks. The left jugular trunk drains
lymph from the left side of the head and neck; the left subclavian trunk drains
lymph from the upper left extremity; and the left bronchomediastinal trunk drains
lymph from the left side of the head and neck; the left subclavian trunk drains
lymph from the upper left extremity; and the left bronchomediastinal trunk drains
lymph from the left side of the deeper parts of the anterior thoracic wall, upper
part of the anterior abdominal wall, anterior part of the diaphragm, left lung,
and left side of the heart.
The right lymphatic duct is about 1.25 cm (0.5 inch) 1onz and drains lymph from
the upper right side of the body. The right lymphatic duct collects lymph from
its
trunks
as
follows.
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1.
2.
3.
It receives lymph from the right jugular trunk, which drains the right side
of the head and neck
From the right subclavian trunk, which drains the right upper extremity
And from the right bronchomediastinal trunk, which drains the right side of
the thorax, right lung, right side of the heart, and part of the convex
surface of the liver
Ultimately, the thoracic duct empties all of its lymph into the junction of the
left internal jugular vein and left subclavian vein, and the right lymphatic duct
empties all of its lymph into the junction of the right internal jugular vein and
right subclavian vein. Thus, lymph is drained back into the blood and the cycle
repeats itself continuously.
The
flow
of
lymph
from
tissue
spaces
to
the
large
lymphatic
ducts
to
the
subclavian veins is maintained primarily by the milking action of muscle tissue.
Skeletal muscle contractions compress lymph vessels and force lymph toward the
subclavian
veins.
Lymph
vessels,
like
veins,
contain
valves,
and
the
valves
ensure the movement of lymph toward the subclavian veins.
Another factor that maintains lymph flow is respiratory movements. These
movements create a pressure gradient between the two ends of the lymphatic
system.
Lymph
flows
from
the
abdominal
region,
where
the
pressure
is
higher, toward the thoracic region, where it is lower.
Edema: An excessive accumulation of interstitial fluid in tissue spaces may
be caused by an obstruction such as an infected node or a blockage of
vessels in the pathway between the lymphatic capillaries and the subclavian
veins. Another cause of edema is excessive lymph formation and increased
permeability of blood capillary walls. A rise in capillary blood pressure
in
which
lymphatics
interstitial
may
fluid
is
also
formed
faster
result
than
it
is
in
passed
into
edema.
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NONSPECIFIC RESISTANCE TO DISEASE
The human body continually attempts to maintain homeostasis by counteracting
harmful
stimuli
in
the
environment.
Frequently,
these
stimuli
are
disease-
producing organisms, called pathogens. or their toxins. The ability to ward off
disease
is
called
resistance.
Lack
of
resistance
is
called
susceptibility.
Defenses against disease may be grouped into two broad areas:
Nonspecific
resistance
and
specific
resistance.
Nonspecific
resistance
is
inherited and represents a wide variety of body reactions against a wide range
of pathogens. Specific resistance or immunity involves the production of a
specific
antibody
against
a
specific
pathogen
or
its
toxin.
Immunity
is
developed during a person's life; it is not inherited.
The skin and mucous membranes of the body are commonly regarded as the first
line of defense against
disease-causing
microorganism. They possess
certain
mechanical and chemical factors that are involved in combating the initial
attempt of a microbe to cause disease.
Mechanical Factors:
The intact skin consists of two distinct portions known as the dermis and
epidermis. Mucous membranes, like the skin, also consist of an epithelial layer
and
an
underlying
connective
tissue
layer.
But
unlike
the
skin,
a
mucous
membrane lines a body cavity that opens to the exterior. The epithelial layer of
a mucous membrane secretes a fluid called mucus, which prevents the cavities
from drying out. Since mucus is slightly viscous, it traps many microbes that
enter the respiratory and digestive tracts. The mucous membrane of the nose has
mucus-coated hairs that trap and filter air containing microbes, dust, and
pollutants. The mucous membrane of the upper respiratory tract contains cilia,
microscopic hairlike projections of the epithelial cells. These cilia move in
such a manner that they pass inhaled dust and microbes that have become trapped
in mucus toward the throat. This so-called "ciliary escalator" keeps the "mucus
blanket"
moving
'escalator."
toward
the
throat.
Coughing
and
sneezing
speed
up
the
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Since some pathogens can thrive on the moist secretions of a mucous membrane,
they are able to penetrate the membrane if present in sufficient numbers. This
penetration may be related to toxic products produced by the microbes, prior
injury by viral infections, or mucosal irritations. Although mucous membranes do
inhibit the entrance of many microbes, they are less effective than the skin.
There are several other mechanical factors that help to protect epithelial
surfaces of the skin and mucous membranes. One such mechanism that protects the
eyes
is
the
lacrimal
apparatus.
It consists of
a
group
of
structures
that
manufactures and drains away tears, which are spread over the surface of the
eyeball
by
blinking.
The
continual
washing
action
of
tears
helps
to
keep
microbes from settling on the surface of the eye.
Saliva produced by the salivary glands, washes microbes from the surfaces of the
teeth and the mucous membrane of the mouth, much as tears wash the eyes.
Microbes are additionally prevented from entering the lower respiratory tract by
a small lid of cartilage called the epiglottis that covers the voice box during
swallowing. The cleansing of the urethra by the flow of urine represents another
mechanical factor that prevents microbial colonization in the urinary system.
Chemical Factors:
Mechanical factors alone do not account for the high degree of resistance of
skin and mucous membranes to microbial invasion. Certain chemical factors play
an important role. Sebum, produced by the sebaceous (oil) glands of the skin,
forms a protective film over the surface of the skin and inhibits the growth of
certain bacteria. Perspiration flushes some microbes from the skin. Gastric
juice is a collection of hydrochloric acid, enzymes, and mucus produced by the
glands of the stomach. The very high acidity of gastric juice (pH 1.2-3.0) is
sufficient to preserve the usual sterility of the stomach. The acidity of
gastric juice destroys bacteria and almost all important bacterial toxins.
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The acidic pH of the skin , between 3.0 and 5.0, is due in part to the acid
products of bacterial metabolism. This acidity probably discou rages the growth
of
many
microbes
that
contact
the
skin.
One
of
the
components
of
sebum
is
unsaturated fatty acids. These fatty acids kill certain pathogenic bacteria.
Lysozyme is an enzyme capable of breaking down cell walls of various bacteria
under certain conditions . Lysozyme is normally found in perspiration, tears,
saliva, nasal secretions, and tissue fluids .
Antimicrobial Substances:
In
addition
to
the
mechanical
and
chemical
barriers
of
the
skin
and
mucous
membranes, the body also produces certain antimicrobial substances. Among these
are interferon, complement, and properdin.
Interferon:
Host cells infected with viruses produce a protein called interferon. There are
three principal types of interferon called alpha, beta, and gamma. In humans,
interferon has been shown to be produced by lymphocytes and other leucocytes and
fibroblasts.
uninfected
uninfected
Once
released
neighboring
cells
to
from
cells
virus -infected
and
synthesize
binds
to
another
cells,
"surface
antiviral
interferon
receptors.
protein
diffuses
This
that
to
induces
inhibits
intracellular viral replication. Interferon appears to be the body's first line
of defense against infection by many different viruses. It appears to decrease
the virulence (disease-producing power) of viruses associated with chicken -pox,
genital herpes, rabies, rubella, chronic hepatitis, shingles, eye infections,
encephalitis, and types of the common cold.
Complement:
Another
antimicrobial
resistance
(and
substance
immunity)
is
that
complement.
is
very
important
Complement
is
to
actually
nonspecific
a
group
of
eleven proteins found in normal blood serum . The system is called complement
because
it
P a g e | 63
"complements" certain immune and allergic reactions involving antibodies. The
function of antibody is to recogniz e the microbe as a foreign organism, form
an antigen-antibody complex, and activate complement for attack. The antigen antibody complex also fixes (attaches) the complement to the surface of the
invading
microbe.
Once
complement
is
activated,
it
destroys
microbes
as
follows:
1.
Some complement proteins initiate a series of reactions leading to cell
lysis caused by holes in the plasma membrane of the microbe.
2.
Some complement proteins interact with receptors on phagocytes,
promoting phagocytosis. This is called opsonization or immune adherence .
3.
Some complement proteins contribute to the development of inflammation
by causing the release of histamine from mast cells, leucocytes, and
platelets. Histamine increases the permeability of blood capillaries , a
process t hat enables leucocytes to penetrate tissues in order to combat
infection or allergy.
4.
Some complement proteins serve as chemotactic agents, attracting large
numbers of leucocytes to the area.
Properdin:
Properdin, like complement , is also a protein found in serum . It is a complex
consisting of three proteins. Properdin, acting together with complement, leads
to
the
destruction
of
several
types
of
bacteria,
the
enhancement
of
phagocytosis, and triggering of inflammatory responses.
PHAGOCYTOSIS
When
microbes
penetrate
the
skin
and
mucous
membranes,
or
bypass
the
antimicrobial substances in blood, there is another nonspecific resistance of
the body called phagocytosis. Very simply, phagocytosis means the ingestion and
destruction
of
microbes
called phagocytes.
or
any
foreign
p articulate
matter
by
certain
cells
P a g e | 64
Kinds of Phagocytes:
The
kinds
of
phagocytes
that
participate
in
the
process
fall
into
two
broad
categories: microphages and macrophages. The granulocytes of blood are called
microphages.
However,
capabilities.
not
all
Neutrophils
granulocytes
have
the
most
exhibit
the
prominent
same
phagocytic
phagocytic
activity.
Eosinophils are believed to have some phagocytic capability, and the role of
basophils in phagocytosis is debatable.
When
an
infection
monocytes
enlarge
these
migrate
and
cells
wandering
occu rs,
to
develop
leave
both
microphages
the
infected
area.
into
actively
phagocytic
the
blood
macrophages.
Some
and
of
migrate
the
(especially
During
to
this
cells
migration,
called
infected
macrophages,
neutrophils)
monocytes
macrophages.
areas,
called
the
they
fixed
and
are
Since
called
macrophages
or
histiocytes enter certain tissues and organs of the body and remain there. Fixed
macrophages are found in the liver (stellate reticuloendothelial cells),
lungs
(alveolar macrophages), brain (microglia), spleen, lymph nodes, and bone marrow.
Mechanism:
Phagocytosis will be divided into two phases: adherence and ingestion. adherence
(attachment) is the formation of firm contact between the plasma membrane of t he
phagocyte and the microbe (or foreign material). In some instances, adherence
occurs
easily,
adherence
is
and
more
the
microbe
difficult,
is
but
readily
the
phagocytized.
particle
can
be
In
other
phagocytized
cases,
if
the
phagocyte traps the particle t o be ingested against a rough surface, like a
blood vessel, blood clot, or connective tissue fibers, where it cannot slide
away. This is sometimes called nonimmune (surface) phagocytosis. Bacteria can
also be phagocytized if they are first coated with comp lement or antibody to
promote the attachment of the microbe to the phagocyte. This is opsonization
(immune
adherence).
A
final
factor
that
helps
adherence
is
chemotaxis,
the
attraction of phagocytes to microbes by certain chemicals, such as microbial
products,
components
of
white
blood
cells
and
tissue
cells,
and
chemicals
derived from complement.
Following adherence, ingestion occurs. In the process of ingestion, projections
of the cell membrane of the phagocyte, called pseudopodia, engulf the microbe.
Once the microbe is surrounded, the membrane folds inward, forming a sac around
P a g e | 65
the
microbe
called
a
phagocytic
vesicle.
The
vesicle
pinches
off
from
the
membrane and enters the cytoplasm. Within the cytoplasm, the vesicle collides
with lysosomes that contain digestive enzymes and bactericidal substances. Upon
contact, the vesicular and lysosomal membranes fuse together to form a single,
larger
structure
called
a
phagolysosome
(digestive
vesicle).
Within
the
phagolysosome, most bacteria are usually killed within 30 minutes. It is assumed
that destruction occurs as a result of the contents of the lysosomes, namely
lactic acid which lowers the pH in the phagolysosome, the production of hydrogen
peroxide, lysozyme, and the destructive capabilities of enzymes that degrade
carbohydrates, proteins, lipids, and nucleic acids. Any indigestible materials
that cannot be degraded further are found in structures called residual bodies.
The cell disposes of materials in residual bodies by exocytosis, in which the
residual
body
migrates
to
the
plasma
membrane,
fuses
to
it,
ruptures,
and
releases its contents.
Inflammation:
When cells are damaged by microbes, physical agents, or chemical agents, the
injury sets of an inflammation (inflammatory response). The injury can be viewed
as a form of stress. They symptoms of inflammation are: redness, pain, heat, and
swelling. A fifth symptom can be the loss of function of the injured area. The
inflammatory response serves a protective and defensive role. It is an attempt
to neutralize and destroy toxic agents at the site of injury and to prevent
their spread to other organs. Thus the inflammatory response is an attempt to
restore tissue homeostasis.
The inflammatory response is one of the body's internal systems of defense. The
response of a tissue to a rusty nail wound is similar to other inflammatory
responses,
invasion.
such
The
as
the
basic
sore
throat
stages
of
that
the
results
from
bacterial
inflammatory
or
response
viral
are:
P a g e | 66
1. Vasodilation and increased permeability of blood vessels. Vasodilation is an
increase in diameter in the blood vessels. Increased permeability means that
substances normally retained in blood are permitted to pass from blood
vessels. Vasodilation allows more blood to go to the damaged area and
increased permeability permits defensive substances in the blood to enter
the injured area. The increased blood supply removes toxic products and dead
cells, preventing them from complicating the injury.
Vasodilation and increased permeability are caused by the release of certain
chemicals by damaged cells in response to injury. One such substance is
histamine It is present in many tissues of the body, especially in mast
cells
in
connective
tissue,
circulating
basophils
and
blood
platelets.
Histamine is released in direct response to any injured cells containing it.
Neutrophils, another type of white blood cell attracted to the site of
injury, can also produce chemicals that cause the release of histamine.
Other substances that play a role in vasodilation and increased permeability
of blood vessels are kinins. These chemicals also attract neutrophils to the
injured
area.
Prostaglandins
Inflammation
(PG).
also
results
Prostaglandins
are
in
an
strong
increased
synthesis
vasodilators
and
of
they
intensify the effect of histamine and kinins. Prostaglandins also bring
about increased permeability of blood vessels.
In addition to the responses in the area of injury, the body may also
respond by increasing the metabolic rate and quickening the heartbeat so
that more blood circulates to the injured area per minute. Within minutes
after the injury, the quickened metabolism and circulation, and especially,
the
dilation
and
increased
permeability
of
capillaries
produce
heat,
redness, and swelling.
Pain, whether immediate or delayed, is a cardinal symptom of inflammation.
2. Phagocyte migration: Generally, within an hour after the inflammatory
process is initiated, phagocytes (microphages and macrophages) appear on
P a g e | 67
the scene. As the flow of blood decreases, microphages (neutrophils) begin to
stick to the inner surface of the endothelial lining of blood
vessels. This is called margination. Then, the neutrophils begin to
squeeze through the wall of the blood vessel to reach the damaged area.
This migration, which resembles amoeboid m o v e m e n t , is called diapedesis.
The movement of neutrophils depends on chemotaxis which is the
attraction of neutrophils by certain chemicals. Neutrophils are
attracted by microbes, kinins, and other neutrophils. A steady
stream of neutrophils is ensured by the production and release of
additional cells from bone marrow. This is brought about by a substance
called leucocytosis-promoting factor, which is released from inflammed
tissues. Neutrophils attempt to destroy the invading microbes by
phagocytosis. Neutrophils also contain chemicals with antibiotic activity
called defensins, so named because of their apparent role in
preventing and overcoming infections. Defensins are active against
bacteria, fungi, and viruses, unlike other antibiotics that are directed
against specific microbes.
As the inflammatory response continues, monocytes follow the neutrophils into
the
infected
macrophages
area.
that
These
enhance
monocytes
the
then
phagocytic
become
activity
transformed
of
fixed
into
wandering
macrophages. Fixed
macrophages mobilize under the stimulus of inflammation and also migrate to the
infected area. The macrophages enter the picture during a later stage of the
infection. They are several
enough
to
engulf
tissue
that
times
has
more phagocytic than neutrophils and large
been
destroyed,
neutrophils
that
have
been
destroyed and invading microbes.
3.
4.
Release of nutrients : Nutrients stored in the body are used to support
the defensive cells. They are also used in the increased metabolic
reactions of the cells under attack.
Fibrin
formation :
The
blood
contains
a
soluble
protein
called
fibrinogen. Fibrinogen is then converted to an insoluble, thick network
called fibrin, which localizes and traps the invading organisms, preventing
their spread. This network event ually forms a fibrin clot that prevents
hemorrhage and isolates the infected area.
P a g e | 68
5. Pus formation: In all but very mild inflammations, pyogenesis occurs. Pus is a
thick fluid that contains living, as well as nonliving, white blood cells and
debris from other dead tissue.
If pus cannot drain out of the body, an abcess develops. An abscess is an
excess of accumulation of pus in a confined space. Common examples are
pimples and boils. When inflamed tissue is shed, many times it produces an
open sore called an ulcer on the surface of an organ or tissue. Ulcers may
result
from
prolonged
inflammatory
response
to
a
continuously
injured
tissue.
FEVER:
The most frequent cause of fever, an abnormally high body
temperature, is infection from bacteria and their toxins
and viruses. The high body temperature inhibits some
P a g e | 69
SUMMARY OF NONSPECIFIC RESISTANCE
Component
Functions
Component
Functions
Skin and mucous membranes
Acid pH of skin
Discourages growth of
microbes
Mechanical factors
Unsaturated fatty acids
Antibacterial substance in
sebum
Antimicrobial substance in
perspiration, tears,
saliva, nasal secretions,
and tissue fluids
Intact Skin
Forms a physical barrier
to the entrance of
microbes
Mucous membranes
Inhibit the entrance of
many microbes, but not as
effective as intact skin
Lysozyme
Mucus
Traps microbes in
respiratory and digestive
tracts
Antimicrobial substances
Hairs
Filter microbes and dust
in nose
Interferon (IFN)
Protects uninfected host
cells from viral infection
Cilia
Together with mucus, trap
and remove microbes and
dust from upper
respiratory tract
Complement
Causes lysis of microbes,
promotes phagocytosis,
contributes to
inflammation, serves as
chemotactic agent
Lacrimal apparatus
Tears dilute and wash
away irritating substances
and microbes
Properdin
Works with complement to
bring about same responses
as complement
Saliva
Washes microbes from
surfaces of teeth and
mucous membranes of mouth
Phagocytosis
Ingestion and destruction
of foreign particulate
matter by microphages and
macrophages
Epiglottis
Prevents microbes from
surfaces of teeth and
mucous membranes of mouth
Inflammation
Confines and destroys
microbes and repairs
tissues
Urine
Washes microbes from
urethra
Fever
Inhibits microbial growth
and speeds us body
reactions that aid repair
Chemical Factors
Gastric Juice
Destroys bacteria and most
toxins in stomach
P a g e | 70
IMMUNITY (SPECIFIC RESISTANCE TO DISEASE)
Despite the variety of mechanisms of nonspecific resistance, they all have one thing in
common. They are designed to protect the body from any kind of pathogen. They are not
specifically directed against a particular microbe. Specific resistance to disease, called
immunity, involves the production of a specific type of cell or specific molecule k n o w n
as an antibody to destroy a particular antigen. If antigen 1 invades the body, antibody 1
is produced against it. If antigen 2 invades the body, antibody 2 is produced against it,
and so on. The branch of science dealing with the responses of the body when challenged by
antigens is known as immunology.
Antigens:
An antigen or immunogen is any chemical substance that, when introduced into the body,
causes the body to produce specific antibodies, which can react with the antigen. Antigens
have two important characteristics. The first is immunogenicity which is the ability to
stimulate the formation of specific antibodies. The second is reactivity, the ability of
the antigen to react specifically with the produced antibodies. An antigen with both of
these characteristics is called a complete antigen.
Concerning the characteristics of antigens, chemically, the vast majority of a n t i g e n s are
proteins,
nucleoproteins
(nucleic
acid
+
protein),
lipoproteins
(lipid
+
protein),
glycoproteins (carbohydrate + protein), and certain large polysaccharides. In general, they
have molecular weights of 10,000 or more.
The entire microbe, such as a bacterium or virus, or components of microbes may act as an
antigen. Egg white is a nonmicrobial example of an antigen.
Antibodies do not form against the antigen. At specific regions on the surface of the
antigen called antigenic determinant sites, specific
P a g e | 71
chemical groups of the antigen combine with the antibody. This combination depends upon
the size and shape of the determinant site and the manner in which it corresponds to the
chemical structure of the antibody. The combination is very much like a lick and key.
The number of antigenic determinant sites on the surface of an antigen is called valence.
Most antigens are multivalent, that is, they have several antigenic determinant sites.
A determinant site that has reactivity but not immunogenicity is called a partial antigen
or hapten. A hapten can stimulate an immune response if it is attached to a larger carrier
molecule so that the combined molecule has two determinant sites.
As a rule, antigens are foreign substances. They are not usually part of the chemistry of
the
body.
The
body's
own
substances,
recognized
as
"self,"
do
not
act
as
antigens;
substances identified as "nonself," however, stimulate antibody production. However, there
are certain conditions in which the distinction between self and nonself breaks down, and
antibodies that attach the body are produced. These conditions result in what are called
autoimmune disease.
Antibodies:
An antibody is a protein produced by the body in response to the presence of an antigen
and
is
capable
of
combining
specifically
with
the
antigen.
This
is
essentially
the
complementary definition of an antigen.
The specific fit of the antibody with antigen depends not only on the size and shape of
the antigenic determinant site but also on the corresponding antibody site, much again
like a lock and key. An antibody, like an antigen, also has a valence. Most antigens are
multivalent, most antibodies
antibodies
are bivalent
or multivalent, and
are
the majority of
human
bivalent.
P a g e | 72
Antibodies belong to a group of proteins called globulins, and for this reason they are
known as immunoglobulins
or lg. Five different classes of
immunoglobulins are known to
exist in humans. These are designated as IgG, IgA, IgM, IgD, and IgE. Each has a distinct
chemical structure and a specific biological role. IgG antibodies enhance phagocytosis,
neutralize
toxins,
and
protect
the
fetus
and
newborn.
IgA
antibodies
provide
localized
projection on mucosal surfaces; IgM antibodies are especially effective against microbes
by
causing
agglutination
antibody-producing
cells
and
to
lysis.
IgD
manufacture
antibodies
may
be
antibodies.
IgE
antibodies
involved
in
are
stimulating
involved
in
allergic reactions. During stress IgA levels decrease. This decrease can lower resistance
to infection.
Structure:
Since antibodies are proteins, they consist of polypeptide chains. Most antibodies contain
two pairs of polypeptide chains. Overall the antibody molecule sometimes assumes the shape
of
the
letter
Y.
At
other
times,
it
resembles
the
letter
T.
In
performing
its
role
in
immunity, the antibody is believed to behave as a switch.
Cellular and Humoral Immunity:
The
ability
toxins,
of
the
viruses,
component
body
and
consists
of
to
foreign
the
defend
itself
tissues
formation
against
consists
of
of
specially
invading
two
agents
closely
sensitized
such
allied
as
bacteria,
components.
lymphocytes
that
have
One
the
capacity to attach to the foreign agent and destroy it. This is called cellular or cellmediated immunity
and
is
particularly
effective
against
fungi,
parasites,
intracellular
viral infections, cancer cells, and foreign tissue transplants. In the other component,
the body produces circulating antibo dies that are capable of attacking an invading agent.
This
is
against
called
humoral
or
bacterial
antibody -mediated
and
immunity
and
is
viral
particularly
effective
infections.
P a g e | 73
Cellular immunity and humoral immunity are the product of the body's lymphoid tissue. The
bulk of lymphoid tissue is located in the lymph nodes, but is also found in the spleen and
gastrointestinal tract, and to a lesser extent, in bone marrow. The placement of lymphoid
tissue is strategically designed to intercept an invading agent before it can spread too
extensively into the general circulation.
Formation of T Cells and B Cells:
Lymphoid tissue consists primarily of lymphocytes that may be distinguished into two kinds.
T cells are responsible for cellular immunity. B cells develop into specialized cells
(plasma cells) that produce antibodies and provide humoral immunity.
Both types of lymphocytes are derived originally in the embryo from lymphocytic stem cells
in bone marrow. Before migrating to their positions in lymphoid tissues, the descendants of
the stem cells follow two distinct pathways. About half of them first migrate to the thymus
gland, where they are processed to become T cells. The name T cell is derived from the
processing that occurs in the thymus gland. The thymus gland in some way confers what is
called immunologic competence on the T cells. This means that they develop the ability to
differentiate into cells that perform specific immune reactions. They then leave the thymus
gland and become embedded in lymphoid tissue. Immunologic competence is conferred by the
Thymus gland shortly before birth and for a few months after birth. The remaining stem
cells become B lymphocytes. They are given this name because in birds they are processed in
the Bursa of Fabricius, a small pouch of lymphoid tissue attached to the intestines. Once
processed, B cells migrate to lymphoid tissue and take up their positions there.
Unlike the various nonspecific resistance factors previously discussed, the responses of T
cells and B cells very much depend on the ability of the cells to recognize specific
antigens. Macrophages process and present antigens to T cells and B cells.
P a g e | 74
There are literally thousands of different T lymphocytes and each type is capable of
responding to a specific antigen or set of antigens. This forms the basis for cellular
immunity. At any given time, most T cells are inactive. When an antigen enters the body,
only the particular T cell specifically programmed to react with the antigen becomes
activated. Such an activated T cell is said to be sensitized. Activation occurs when
macrophages phagocytize the antigen and present it to the T cell. Sensitized T cells
increase in size, differentiate, and divide, each differentiated cell giving rise to a
clone, or population of cells identical to itself. Several subpopulations of cells within
the clone can be recognized: killer T cells, helper T cells, suppressor T cells, delayed
hypersensitivity T cells, amplifier T cells, and memory T cells.
Killer T Cells also known as Cytotoxic T cells are especially effective against slowly
developing bacterial diseases such as tuberculosis and brucellosis, some viruses, fungi,
transplanted cells, and cancer cells. Most of the protection provided by T cells is the
result of secretion of very powerful proteins called lymphokines.
Helper T cells which cooperate with B cells to help amplify antibody production also
secrete proteins that amplify the inflammatory response in killing by macrophages.
Suppressor T cells which dampen parts of the immune response inhibit production of
antibodies by plasma cells.
Delayed hypersensitivity T cells are the source of several lymphokines that are key factors
in the hypersensitivity or allergy response.
Amplifier T cells stimulate helper T cells, suppressor T cells, and B cells to exaggerated
levels of activity.
Memory T cells are programmed to recognize the original invading antigen.
P a g e | 75
Natural K i l l e r cells which are similar to T cells have the ability to kill certain cells
spontaneously without interacting with lymphocytes or antigens.
Whereas Killer T cells leave their reservoirs of lymphoid tissue to meet a foreign antigen,
B cells respond differently. They differentiate in the cells that produce specific antibodies
that can circulate in the lymph and blood to reach the site of invasion. When a foreign
antigen has been prepared and presented by macrophages to B cells and lymph nodes, the spleen
or lymphoid tissue in the gastrointestinal tract B cells specific for the a n t i g e n
are
activated. Some of them enlarge and divide and differentiate into a clone of plasma cells
under
the
influence
of
thymic
hormones.
Plasma
cells
secrete
the
antibody.
B
cells
proliferation and differentiation into plasma cells is also influenced by a substance as
interleukin 1, secreted by macrophages. The activated B cells that do not differentiate into
plasma cells remain as memory B cells, ready to respond more rapidly and forcefully should
the same antigen appear at a future time.
Different
antigens
stimulate different B cells to develop into plasma
cells
and
their
accompanying memory B cells because the B cells of a particular clone are capable of
secreting only one kind of antibody. In most cases only the interaction of macrophage and B
cell is required for the sequence of responses that results in antibody secretion. However,
in some cases, interaction of B cells with helper T cells and suppressor T cells is
involved.
Primary and anamnestic responses occur during microbial infection. When you recover from an
infection without taking antibiotics, it is usually because of the primary response. If at a
later time you contact the same microbe, the anamnestic response could be so swift that the
microbes are quickly destroyed and you do not exhibit any signs or symptoms.
P a g e | 76
The immune response of the body whether cellular or humoral is much more intense after a
second or subsequent exposure to an antigen than after the initial exposure. This can be
demonstrated by measuring the amount of antibody in serum called the antibody titer. Afte r
an initial contact with
an antigen, there
is a
period of
several
days during which
no
antibody is present. Then there is a slow rise in the antibody titer followed by a gradual
decline. Such a response of the body to the first contact is the primary response. During
the
primary
response
proliferation
of
in
which
the
immunocompetent
body
is
said
lymphocytes.
to
When
be
primed
the
or
antigen
sensitized,
is
there
contacted
is
again,
whether for the second t i m e , or for a time after the second time, there is a n i m m e d i a t e
proliferation of immunocompetent lymphocytes, and the antibody titer is far greater than
that
for
the
primary
response.
This
accelerated,
more
intense
response
is
called
the
anamnestic or secondary response. The reason for the anamnestic response is that some of
the immunocompetent lymphocytes formed during the primary response remain as memory cells.
These memory cells not only add to the pool of cells that can respond to the antigen -their response is more intense as well.
The Skin and Immunity
The skin not only provides nonspecific resistance to disease because of its mechanical and
chemical factors, but it is also an active component of the immune system. The epidermis of
the
skin contains four principal
kinds
of cells:
melanocytes, keratin ocytes,
Langerhans
cells, and Granstein cells. The last three types of cells assume a role in immunity.
When a normal cell becomes transformed into a cancer cell, the tumor cell assumes cell
surface components called tumor-specific antigens. It is believed that the immune system
usually recognizes tumor -specific antigens as "nonself" and destroys the cancer cells
carrying them. Such an immune response is called immunologic surveillance. Cellular immunity
is p r o b a b l y the basic mechanism involved in tumor de struction.
P a g e | 77
Despite the mechanism of immunologic surveillance, some cancer cells escape
destruction, a phenomenon called immunologic escape.
DEVELOPMENTAL ANATOMY OF THE LYMPHATIC SYSTEM
The lymphatic system begins its development by the end of the fifth week. Lymphatic
vessels develop from lymph sacs that arise from developing veins. Thus, the lymphatic
system is also derived from mesoderm.
DISORDERS AND HOMEOSTATIC IMBALANCES
Hypersensitivity (Allergy):
A person who is overly reactive to an antigen is said to be hypersensitive or allergic.
Whenever an allergic reaction occurs there is tissue injury. The antigens that induce an
allergic reaction are called allergens. Almost any substance can be an allergen for some
individuals. Common allergens include certain foods such as milk or eggs, antibiotics such
as penicillin, cosmetics, chemicals in plants such as poison ivy, pollens, dust, molds, and
even microbes.
There are four basis types of hypersensitivity reactions: Type I (anaphylaxis), Type II
(cytotoxic),
Type
III
(immune
complex),
and
Type
IV
(cell-mediated).
The
first
three
involve antibodies, and the last example involves T cells.
Type I (anaphylaxis) ___ Reactions: Occur within a few minutes after a person sensitized to
an allergen is reexposed to it. Anaphylaxis which means "against protection" results from
the interaction of humoral antibodies IgE with mast cells and basophils. In response to
certain allergens, some people produce IgE antibodies which bind to the surfaces of mast
cells and basophils. This binding is what causes a person to be allergic to the allergens.
In response to the attachment of IgE antibodies to basophils and mast cells, the cells
release
chemicals
called
mediators
of
anaphylaxis,
among
which
prostaglandins. Collectively, the mediators increase blood capillary
are
histamine
and
P a g e | 78
permeability,
result,
a
increase
person
may
smooth
muscle
experience
contraction,
edema
and
and
increase
redness,
along
mucus
with
secretion.
other
As
a
inflammatory
responses; difficulty in breathing from constricted bronchial tubes; and a "runny" nose
from excess mucus secretion.
Some anaphylactic reactions, such as hay fever, bronchial asthma, hives, and eczema, are
referred to as localized. Other anaphylactic reactions are considered systemic. An example
is acute anaphylaxis (anaphylactic shock), which can produce life-threatening system effects
such as circulatory shock and asphyxia and can be fatal within a few minutes.
Transplantation
Transplantation involves the replacement of an injured or diseased tissue or organ. Usually
the
body
recognizes
the
proteins
in
the
transplanted
tissue
or
organ
as
foreign
and
produces antibodies against them. This phenomenon is known as tissue resection. Rejection
can be somewhat reduced by matching donor and recipient HLA antigens by administering drugs
that inhibit the body's ability to form antibodies. White blood cells and other nucleated
cells have surface antigens called HLA antigens. These are unique for each person, except
for identical twins. The more closely matched the HLA antigens between donor and recipient,
the less the likelihood of tissue rejection.
Immunosuppressive Therapv
Until
recently,
immunosuppressive
drugs
suppressed
not
only
the
recipient's
immune
rejection of the donor organ, but also the immune response to all antigens as well. This
causes
patients
to
become
very
susceptible
to
infectious
diseases.
A
drug
called
cyclosporine derived from a fungus, fungi imperfecti, has largely overcome this problem
with regard to kidney, heart, and liver transplants.
P a g e | 79
Autoimmune Disease
At times immunologic tolerance breaks down and the body has difficulty in discriminating
between its own antigens and foreign antigens. This loss of immunologic tolerance leads to
an autoimmune disease (autoimmunity). Such diseases are immunologic responses mediated by
antibodies against a person's own tissue antigens.
Hodgkin's Disease
Hodgkin's disease is a malignant disorder, usually arising in lymph nodes, the cause of
which is unknown. The disease is initially characterized by a painless, nontender lymph node
most commonly in the neck but occasionally in the axilla, inguinal, or femoral region. About
one-quarter to one-third of patients also have an unexplained and persistent fever and/or
night
sweats.
Fatigue
and
weight
loss
are
also
associated
complaints,
as
is
pruritus.
Treatment consists of radiation therapy, chemotherapy, and combinations of the two. Hodgkin's
disease is curable.
AIDS (Acquired Immune Deficiency Syndrome)
This is a disease which threatens to run to epidemic proportions in the United States and
worldwide unless a cure is found for it. The cause of AIDS is a virus called human Tlymphotropic virus, type III (HTLV-III). A variant of this virus known as HTLV-I causes a
rare type of leukemia in humans and attacks and transforms T cells. The reason the AIDS
virus lowers the body's immune system is that the virus primarily attacks helper T cells. As
a consequence, several key roles of helper T cells in the immune response are inhibited.
Symptoms of AIDS may develop for months or years and include malaise; a low-grade fever or
night sweats; coughing; shortness of breath; sore throat; extreme fatigue; muscle aches;
unexplained weight loss; enlarged lymph nodes in the neck, axilla, and groin; and blueviolet or brownish spots on the skin known as Kaposi's sarcoma. These spots are usually
found on the legs, the lower extremities.
P a g e | 80
The deterioration of host defenses allows for the development of cancer and opportunistic
infections
of
various
kinds.
The
two
diseases
that
most
often
kill
AIDS
victims
are
Kaposi's sarcoma and Pneumocystis carinii pneumonia. Kaposi's sarcoma is a deadly form of
skin cancer prevalent in equatorial Africa but previously almost unknown in the United
States. Pneumocystis carinii pneumonia is a rare form of pneumonia caused by the protozoan
Pneumocystis carinii. It results in shortness of breath, persistent dry cough, sharp chest
pains, and difficulty in breathing. AIDS victims are also subject to a form of herpes that
attacks
the
central
nervous
system
and
a
bacterial
infection
that
usually
causes
tuberculosis in chickens and pigs.
Among the high-risk groups who are susceptible to AIDS are homosexual and bisexual males,
intravenous drug abusers, sexual partners of individuals in AIDS risk groups, and infants
born to mothers at risk. Other risk groups include hemophiliacs under treatment with blood
plasma products, and Haitian immigrants. It is also found among infants in other patients
who have received blood transfusions. Current testing of blood has virtually eliminated
future contamination by blood transfusion or therapy.
The pattern of AIDS transmission closely resembles the occurrence of hepatitis B (serum
hepatitis), a liver disease that commonly strikes homosexual drug addicts using contaminated
needles and sometimes patients getting blood transfusions. Like hepatitis B, AIDS appears
to be transmitted by intimate direct contact involving muscosal surfaces or by parenteral
routes, which means by injection. Two fluids considered most highly contagious are semen
and blood. Airborne transmission and spread via food, water, insects, and casual contact
seem unlikely.
Treatment of AIDS is currently by means of various drugs such as AZT. Some people who
carry the AIDS virus will develop the AIDS-related complex (ARC). This condition may
include fever, diarrhea, malaise, and a generalized swelling of lymph nodes. ARC may follow
several courses. It may resolve, persist for a long period, or progress to full-blown
AIDS.
P a g e | 81
----------TERMS RELATED TO LYMPHATIC SYSTEM AND IMMUNITY ----------------------------------1.
Adenitis
Enlarged,
t e n d e r , and
inflamed
nod
e sinfection.
resulting from
an
2.
Elephantiasis
Great
enlargement
of a limb ( e s p e c i a l l y
limbs) lower
and scrotum resulting from obstruction
of
lymph glands
or vessels by a parasitic worm.
3.
4.
Lymphadnectomy
Lymphadenopathy
Removal of a lymph node.
Enlarged, sometimes tender lymph glands.
5.
Lymphangioma
Benign tumor of the lymph vessels.
6.
Lymphangitis
Inflammation of the lymphatic vessels.
7.
Lymphedema
Accumulation of lymph fluid producing subcutaneous
tissue swelling.
8.
9.
Lymphoma
Lymphostasis
10. Splenomegaly
Any tumor composed of lymph tissue.
A lymph flow stoppage.
Enlarged spleen.
lymph
P a g e | 82
Swartz
NHCC
THE RESPIRATORY SYSTEM _____ CHAP. 16 ________ Page 82
THESE NOTES ARE ONLY AN OUTLINE OF THE MATERIAL PRESENTED IN CHAP.
16, HUMAN ANATOMY AND PHYSIOLOGY, HOLE, 4TH ED., PP. 571-609. YOUR
LECTURE EXAM. # 3 ILL COVER ALL OF THE MATERIAL IN YOUR TEXTBOOK ON THE
ABOVE-MENTIONED PAGES, BUT NO OTHER MATERIAL. BE SURE TO READ ALL OF IT.
The Respiratory System: primary functions- obtaining 0 & removing C O 2 .
filter particles from incoming air, help to control the temp. &
water content of the air, aid in producing sounds used in speech, & func. in
the sensation of smell & the regulation of pH.
Resp. organs
Respiration = exchanging gases between the atmosphere & the body cells
Parts of respiration: (1) breathing or pulmonary ventilation = movement of
air in & out of the lungs. (2) exchange of gases between the air in the
lungs & the blood. (3) transport of gases by the blood between the lungs &
the body cells. ( 4 ) exchange of gases between the blood & the body cells.
Cellular resp. = utilization of 0 2 & the production of CO 2 .
Organs of resp. system: nose, nasal cavity, sinuses, pharynx, larynx,
trachea, bronchial tree, & lungs. Upper resp. tract = resp. organs outside
the thorax. Lower resp. tract = resp. organs inside the thorax . Nosenostrils let air in. Hairs help prevent entrance of coarse particles in
air. Nasal cavity- nasal septum divides this cavity into left & rt.
portions. Nasal cavity is separated from the cranial cavity by the
cribriform plate of the ethmoid bone & from the mouth by the hard palate.
Nasal conchae = turbinate bones- divide nasal cavity into superior, middle,
& inferior meatuses. Conchae also support the mucous membrane lining nasal
cavity & increase its surface area, Upper portion of nasal cavity contains
olfactory receptors (func. in smell). Nest of cavity conducts air to & from
nasopharynx. Mucous membrane lining nasal cavity has pseudostratified
ciliated columnar epithelium with many mucus-secreting goblet cells. Also,
this membrane is highly vascular.
Air passes over the membrane, heat radiates from the blood & warms the air,
thus, temp. of incoming air adjusts to body temp. Incoming air also mois tened by mucous membrane. Sticky mucus traps dust & other entering part icles.
Paranasal sinuses are air-filled spaces in the maxillary, frontal,
ethmoid, & sphenoid bones o f t h e s k u l l . T h e s e spaces open into the nasal
cavity & are lined with mucous membranes. Mucus drains from these sinuses
i n t o t h e n a s a l c a v i t y . S i n u s e s reduce weight of the skull & are resonant
chambers that affect the quality of the voice.
The pharynx = throat- located behind the mouth cavity & between the
nasal cavity & the larynx. Func.- passageway for food & air & aids in
c r e a t i n g s o u n d s . The larynx = an enlargement in the airway at the top of t h e
t r a c h e a & below the p h a r y n x . F u n c . - passageway for air & prevents foreign
objects from entering the trachea. It also houses t h e v o c a l c o r d s & is called
the voice box. Larynx is composed of muscles & cartilages bound together by
elastic tissues. The thyroid cartilage = Adam ' s apple is more prominent in
males because of effect of male sex hormones on develop ment of the larynx.
The cricoid cartilage- below the thyroid cartilage
& is the lowest portion of the larynx. The epiglottic cartilage is attach-
P a g e | 83
ed to the upper border of the thyroid cartilage & supports a flaplike
structure called the epiglottis. The epiglottis usually stands upright &
allows air to enter the larynx. During swallowing, however, the larynx is
raised by muscular contractions, & the epiglottis is pressed downward by
the base of the tongue. This allows the epiglottis to partially cover the
opening into the larynx, thereby helping to prevent foods & liquids from
entering the air passages.
The arytenoid cartilages are located above & on either side of the
cricoid cartilage. The corniculate cartilages are attached to the tips of
the aryytenoid cartilages. The corniculate cartilages serve as attachments
for muscles that help to regulate tension on the vocal cords during speech &
aid in closing the larynx during swallowing. The cuneiform cartilages, found
in the mucous membrane between the epiglottic & the arytenoid cartilages,
stiffen soft tissues in this region. Inside the larynx there are 2 pairs of
horizontal folds: the upper ones are the vestibular folds & are known as the
false vocal cords- they do not function in the production of sounds. Muscle
fibers within these folds help to close the larynx during swallowing. The
lower folds are the true vocal cords. They contain elastic fibers & they
are responsible for vocal sounds, which are created by forcing air between
the vocal cords, causing them to vibrate from side to side. This action
generates sound waves that can be formed into words by changing the shapes
of the pharynx & oral cavity & by using the tongue & lips.
The pitch of the vocal sound is controlled by changing the tension on
the cords. Increasing the tension produces higher pitched sounds &
decreasing the tension creates a lower pitch. The intensity or loudness of a
vocal sound is related to the force of the air passing over the vocal
cords.
During normal breathing, the vocal cords remain relaxed, & the opening
between the vocal cords are called the glottis, appears as a triangular slit.
When food or liquid is swallowed, muscles within the larynx close the
glottis, & this prevents foreign substances from entering the trachea.
The trachea is a flexible cylindrical tube about 2.5 cm. in diamet er &
12.5 cm. long. It extends downward in front of the esophagus & into the
thoracic cavity, where it splits into the right & left primary bronchi. The
inner wall of the trachea is lined with ciliated pseudostratified columnar
eipthelium containing numerous goblet cells. This membrane, like the one
lining the larynx, continues to filter incoming air, thereby moving
entrapped particles upward to the pharynx. Within the tracheal wall there
are about 20 C-shaped pieces of hyaline cartilage arranged one above the
other. Smooth muscle & conn. tissue fill the posterior aspect of these
cartilagenous rings, which prevent the trachea from collapsing & blocking
the airway. The smooth muscle & c.t. allow the esophagus to expand as it
carries food to the stomach.
The bronchial tree consists of the branched airways leading from the
trachea to the microscopic alveolar air sacs. It begins with the right &
Left primary bronchi arising from the trachea at the level of T-5
(vertebra). The openings of these tubes are separated by a ridge of
cartilage_ called the carina. Each bronchus, accompanied by large blood
vessels, enters its respective lung. A short distance from its
P a g e | 84
origin, each primary bronchus divides into secondary or lobar bronchi-2 on
the left & 3 on the right, which in turn branch into finer & finer tubes.
The branching is as follows (largest to smallest). Tertiary or segmental
bronchi-supply a portion of the lung called a bronchopulmonary segment. There
are 10 of these segments in the right lung & 8 in the left lung. Bronchioles
are small branches of segmental bronchi. They enter the lobules, which are
the basic units of the lung. Terminal bronchioles branch from a bronchiole.
There are 50 to 80 terminal bronchioles within a lung lobule. Two or more
respiratory bronchioles branch from each terminal bronchiole. They are
relatively short & they have a few air sacs branching from their sides &
they can therefore en-gage in gas exchange, being the first structures in
the resp. system that can do so. Alveolar ducts branch & extens from each
respiratory bronchiole. They are from 2 to 10 long. Alveolar sacs are thinwalled closely packed outpouchings of the alveolar ducts. Alveoli are thinwalled microscopic air sacs opening only on the side communicating with the
alveolar sac. Air can therefore diffuse freely into the alveoli.
The structure of the bronchus, a respiratory tube, is similar to that
of the trachea. The cartilagenous rings are replaced with cartilagenous
plates, however, & they completely surround the tube giving it a
cylindrical form. The percentage of cartilage gradually decreases as finer
branch tubes appear, & the cartilage completely disappears at the level of
the bronchioles. Smooth muscle becomes more prominent as the cartilage
decreases. The amount of muscle is limited in the alveolar ducts, however.
Elastic fibers are abundant in the conn. tissue surrounding the resp.
tubes. These fibers play an important role in the breathing mechanism. The
lining of the larger tubes consists of a layer of ciliated pseudostratified
columnar cells, while a single layer of simple squamous cells lines the
alveoli.
Concerning the functions of the respiratory tubes, the branches of the
bronchial tree serve as air passages that continue filtering incominc_ air &
distribute it to alveoli in all parts of the lungs. The alveoli provide a
large surface area of thin epithelial cells through which gas exchange
occurs. During these exchanges, 0 diffuses through the alveolar walls &
enters the blood in nearby capillaries, while CO 2 diffuses through these
walls from the blood & enters the alveoli. There are about 300 million
alveoli in a normal adult lung & these spaces have a total surface area of 70
to 80 square meters!
The lungs are soft spongy cone-shaped organs located in the thoracic
cavity. The right & Left lungs are separated medially by the heart & the
mediastinum, & the lungs are enclosed by the diaphragm & the thoracic cage.
Each lung occupies most of the thoracic space on its side, & is suspended in
the cavity by its attachments, including a bronchus & some large blood
vessels. These tubes enter the lung on its medial surface through a region
called the hilus. A layer of serous membrane, the visceral pleura, is firmly
attached to the surface of each lung, & this membrane folds back at the
hilus to become the parietal pleura. The parietal pleura forms part of the
mediastinum & lines the inner wall of the thoracic cavity. The potential
space between the visceral & parietal pleura is called the pleural cavity, &
it contains a thin film of serous fluid. This fluid lubricates the adjacent
pleural surfaces, thereby reducing friction as they move against one another
during breathing. The fluid also helps to hold the pleural membranes
together.
P a g e | 85
The right lung is larger than the left one. The right lung is divided
into 3 lobes: a superior, middle, & inferior lobe. The left lung is divided
into 2 lobes: a superior lobe & an inferior lobe. (obvious test questions!)
Each lobe is supplied by a lobar bronchus. Lobes are subdivided by conn.
tissue into lobules, each lobule containing terminal bronchioles, alveolar
ducts, alveolar sacs, alveoli, nerves, blood vessels & Lymphatic vessels.
PLEASE TAKE TIME TO STUDY THE CHART IN THE BLUE BOX (CHART 16.1- PARTS OF
THE RESPIRATORY SYSTEM) AT THE TOP OF PAGE 585 IN YOUR TEXTBOOK. THERE WILL
BE A FEW TEST QUESTIONS FROM THIS CHART.
Breathing, or pulmonary ventilation, is the movement of air from outside the
body into the bronchial tree & alveoli followed by a reversal of the air
movement. These actions are termed inspiration or inhalation & expiration or
exhalation. Concerning inspiration, atmospheric pressure is the force that
causes air to move into the lungs. Atmospheric pressure is due to the weight
of the air. Normal air pressure at sea level = 760 mm Hg. (millimeters of
mercury). The air pressure on the inside of the lungs, the alveoli, & on the
outside of the thoracic wall is about the same. If the pressure on the
inside of the lungs & alveoli (intra-alveolar pressure) decreases, air from
the outside will be pushed into the airways by atmospheric pressure. This
happens
during
normal
inspiration.
Muscle
fibers
in
the
dome-shaped
diaphragm below the lungs are stimulated to contract by impulses from the
phrenic nerves. The diaphragm moves downward, the size of the thoracic
cavity increases, & the intra-alveolar pressure decreases slightly below
that of normal atmospheric pressure. Air is forced into the airways by
atmospheric pressure & the lungs expand.
The external intercostal muscles may be stimulated to contract while
the diaphragm is contracting & moving downward. This raises the ribs &
elevates the sternum, increasing the size of the thoracic cavity still
further. Air pressure inside is thus further reduced & more air is forced
into the airways. The expansion of the lungs is aided by the fact that the
parietal & visceral pleura are separated by only a thin film of serous
fluid. The water molecules in this fluid have a great attraction for one
another, & the resulting surface tension holds the 1.1oist surfaces of the
pleural membranes tightly together. PLEASE STUDY THE BRIEF CHART (CHART 16.2MAJOR EVENTS IN INSPIRATION) IN THE BLUE BOX AT THE TOP OF PAGE 587 IN YOUR
TEXTBOOK. THERE WILL BE A FEW TEST QUESTIONS FROM IT. The alveolar cells
secrete a substance called surfactant that reduces surface tension &
decreases the tendency of the alveoli to collapse. The ease with which the
lungs can be expanded as a result of pressure changes occurring during
breathing is called compliance or distensibility. In a normal lung,
compliance decreases as the lung volume increases. (I love these types of
relationships & they lend them-selves beautifully to test questions!) The
reason for this inverse relationship is because an inflated lung is more
difficult to expand than a deflated one. Conditions that obstruct air
passages, destroy lung tissue or impede lung expansion will decrease
compliance.
The forces responsible for normal expiration come from elastic recoil of
tissues & surface tension. The lungs contain a lot of elastic tissue & as
they expand during inspiration, the elastic tissue is stretched. The
diaphragm lowers compressing the abdominal organs beneath it. As the
P a g e | 86
diaphragm & the external intercostal muscles relax following inspiration,'
the elastic tissues cause the lungs & the thoracic cage to recoil, & they
return to their original positions. Elastic tissues within abdominal organs
cause them to spring back into their original locations, there -by pushing the
diaphragm upward. At the same time, surface tension that develops between
the moist surfaces of the alveolar linings tends to cause the alveoli to
decrease in diameter. Each of these factors tends to increase the intraalveolar pressure slightly above atmospheric pressure, thereby forcing the
air inside the lungs out through the respiratory passageways. Normal
expiration is, therefore, a passive process. The recoil of elastic fibers
within the lung tissues tends to reduce the pressure in the pleural cavity.
The pressure between the pleural membranes (intrapleural pressure) is
usually slightly less than atmospheric pressure.
If a person needs to exhale more air than normal, the posterior
internal intercostal muscles can be contracted. These muscles pull the ribs
& , the sternum down & inward increasing the pressure in the lungs. The
abdominal wall muscles squeeze (if you can think of a better scrabble word
than squeeze, you ' re a better man than I am- equinox is a few less points
than squeeze because " q " & " z" are 10 point letters & " x" is only an 8 point
letter) the abdominal organs inward, causing the pressure in the abdominal
cavity to increase thereby forcing the diaphragm still higher against the
lungs. These actions squeeze abdominal air out of the lungs. PLEASE STUDY
CHART 16.3- MAJOR EVENTS IN EXPIRATION ON PAGE 5 8 8 IN YOUR TEXTBOOK.- A FEW
MORE TEST QUESTIONS!
I AM GOING TO ASK A NUMBER OF TEST QUESTIONS ON THE VARIOUS
RESPIRATORY AIR VOLUMES. _ I SUGGEST YOU STUDY THEM CAREFULLY IN YOUR
BOOK ON PAGE 5 8 9 , INCLUDING THE MATERIAL IN THE TEXT AS WELL AS THE
MATERAL IN THE BLUE BOX- CHART 16.4- RESPIRATORY AIR VOLUMES. _ IN OTHER
WORDS, BE THOROUGHLY FAMILIAR WITH THE TERMS TIDAL VOLUME, INSPIRATORY
RESERVE VOLUME, EXPIRATORY RESERVE VOLUME, VITAL CAPACITY, RESIDUAL
VOLUME, & TOTAL LUNG CAPACITY. _ KNOW WHAT LUNG VOLUMES MAKE UP THE VITAL
CAPACITY & WHAT LUNG VOLUMES MAKE UP THE TOTAL LUNG CAPACITY. _ KNOW ALL
THE LUNG VOLUMES IN CC (CUBIC CENTIMETERS) OR LITERS. __ BE THOROUGHLY
FAMILIAR WITH THE TERMS ANATOMIC DEAD SPACE & PHYSIOLOGIC DEAD SPACE &
WHAT THESE TWO VOLUMES EQUAL IN CC. __ BE FAMILIAR WITH THE GRAPH FROM
THE SPIROMETER IN THE GREEN BOX AT THE TOP OF PAGE 5 8 9 IN YOUR TEXTBOOK. IF
YOU DON ' T KNOW HOW TO READ THE GRAPH VALUES, PLEASE COME & SEE ME BEFORE
THE EXAM! The white line on the graph is formed by a stylus with ink as you
breathe.
READ THE MATERIAL CAREFULLY ON PAGES 5 9 2 & 5 9 3 IN YOUR TEXTBOOK
CONCERNING RESPIRATORY DISORDERS (PARALYSIS OF BREATHING MUSCLES,
BRONCHIAL ASTHMA, EMPHYSEMA, LUNG CANCER, & PRIMARY PULMONARY CANCER).
THERE WILL BE SOME QUESTIONS ON THIS MATERIAL IN THE TEST!
Concerning alveolar ventilation, the amount of new atmospheric air
that is moved into the respiratory passages each minute is called the
minute respiratory volume. This vol. can be calculated by multiplying the
tidal volume by the breathing rate. e.g., if the tidal vol. is 500 cc &
the breathing rate is 12 breaths/min., then the minute resp. vol. = 5 0 0 c c
12 = 6,000 cc per minute. Not all of this new air reaches the
alveoli. Must of it remain in the air passages in the physiologic dead
X
P a g e | 87
space. The amount of new air that does reach the alveoli & is available for
gas exchange is calculated by subtracting the physiologic dead space (150
cc) from the tidal volume (500 cc). If the resulting volume (350 cc) is
multiplied by the breathing rate (12 breaths per minute in an average
normal healthy adult), the alveolar ventilation rate (4,200 cc/min.) is
obtained. This ventilation rate is a major factor affecting the
concentration of 0 2 & CO in the alveoli. It affects the exchange of gases
between the alveoli & the blood. (Do you get the feeling that I ' m going to
do something with these numbers & computations? You ' re right!)
PLEASE STUDY THE NONRESPIRATORY AIR MOVEMENTS (COUGHING, SNEEZING,
LAUGHING, CRYING, HICCUPING, YAWNING, & SPEECH) IN YOUR TEXTBOOK ON PAGES
590 & 591. BE SURE TO READ THE MATERIAL ON THESE 2 PAGES IN YOUR TEXTBOOK
AS WELL AS STUDY THE CHART- CHART 16.5- NONRESPIRATORY AIR
MOVEMENTS, ON PAGE 591 (BLUE BOX AT TOP OF PAGE). THERE WILL BE SOME
TEST QUESTIONS FROM THIS MATERIAL!
Control of Breathing: Respiratory muscles can be controlled voluntarily. Normal breathing, however, is a rhythmic involuntary act that
continues even when a person is unconscious.
The Respiratory Center: Breathing is controlled by a poorly defined
collection of neurons in the brain stem called the respiratory center.
Cranial & Spinal nerves transmit impulses from this center periodically to
various breathing muscles causing inspiration & expiration. The center can
also adjust the rate & depth of breathing. Therefore cellular 0 2 needs & the
removal of CO 2 are met even in strenuous exercise.
Components of the resp. center are widely scattered throughout the pons
& Medulla oblongata. The medullary rhythmicity area (obviously in the medulla
oblongata) includes 2 groups of neurons extending throughout the entire
length of the medulla oblongata. They are termed the dorsal respiratory group
& the ventral respiratory group. The dorsal resp. group is responsible for
the basic rhythm of breathing (good test question). Neurons of this group
send impulses to the diaphragm & other resp. muscles to contract. The vol. of
air entering the lungs increases.
The
there is
impulses
impulses
ventral respiratory group is quiet during normal breathing. When
a need for more forceful breathing, neurons in this group send
that increase resp. movement. Other neurons in this group send
which activate muscles associated with forceful expiration.
Neurons in the pneumotaxic area transmit impulses to the dorsal resp.
group continuously & regulate the duration of inspiratory bursts originating
from the dorsal group. In this way the pneumotaxic neurons control the rate
of breathing. When pneumotaxic signals are strong, the inspiratory bursts are
of short duration, & the rate of breathing is increased. Conversely, when the
pneumotaxic signals are weak, the inspiratory bursts are of longer duration, &
the rate of breathing is decreased.
Factors Affecting Breathing: Breathing rate & depth are influenced by
respiratory center controls & several other factors. These other factors
include the presence of certain chemicals in body fluids, the degree to which
the lung tissues are stretched, & the person ' s emotional state.
P a g e | 88
There are chemosensitive areas within the resp. center. These areas
are located within the ventral portion of the medulla oblongata near the
origins of the vagus nerves (tenth cranial nerves), & they are very sensitive to changes in the blood concentrations of CO 2 & H ions. If the conc.
of CO, or H ions rises, the chemosensitive areas signal the resp. center, &
t e rate of breathing is increased. CO 2 combines with water in the blood or
CSF (cerebrospinal fluid) to form carbonic acid (H 2 CO 3 ). This carbonic acid
becomes ionized releasing H ions & HCO 3 ions (bicarbonate ions). The
hydrogen ions influence the chemosensitive areas, not the presence of
carbon dioxide molecules. A person's breathing rate increases when air rich
in CO is inhaled. As a result of increased breathing rate, more CO 2 is lost
in exhaled air, & the blood conc. of CO 2 & H ions are reduced.
Low blood 0 2 conc. has little effect on the chemosensitive areas
in the resp. center. Changes in blood 0 2 conc. are sensed by chemoreceptors
within carotid & aortic bodies. These are located within the walls of large
arteries (carotid arteries & aorta) in the neck & thorax. When these
receptors are stimulated by low 0 2 conc., impulses are transmitted to the
resp. center & the breathing rate is increased. The blood 0 2 conc. must reach
a very low level to trigger this mechanism. 0 2 plays only a minor role in the
control of normal resp.
Although the chemoreceptors of the carotid &
stimulated by changes in the blood conc. of CO 2 7
have a much more powerful effect when they act on
the resp. center. The effects of CO 2 & H + ions on
bodies are, therefore, relatively unimportant.
aortic bodies are
H + ions, these substances
the chemosensitive areas of
the carotid & aortic
An exception to the normal pattern of chemical control may occur
in patients suffering from COPD (chronic obstructive pulmonary diseases), such
as asthma & bronchitis. Over a period of time, these pts. seem to adapt to
the presence of high levels of CO 2 , & in these pts. (patients) low 0 2 levels
may serve as effective respiratory stimuli.
An inflation reflex, the Hering-Breuer reflex, helps to regulate
the depth of breathing. This reflex occurs when stretch receptors in the
visceral pleura, bronchioles, & alveoli are stimulated as a result of lung
tissues being overstretched. The vagus nerves (10th cranial nerves are
involved) send sensory impulses to the pneumotaxic area, & the duration of
inspiratory movements is reduced. This action prevents overinflation of the
lungs during forceful breathing. An emotional upset can also alter the
normal breathing pattern. Fear increases the breathing rate. Pain also
increases breathing rate. Thus, a person may gasp due to a sudden fright or
initially in a cold shower.
The resp. muscles are voluntary & the breathing pattern can there -fore
be altered consciously. Breathing can be stopped altogether for a time. If
a person decides to stop breathing, the blood conc. of CO 2 & H + ions rise,
& the conc. of 0 2 falls. These changes stimulate the resp. center & soon
the need to inhale overpowers the desire to hold the breath. On the other
hand, a person can hold his breath for a longer period of time by
hyperventilating = breathing rapidly & deeply in advance. This action
lowers
blood
CO 2
conc.
P a g e | 89
STUDY CHART 16.6- FACTORS AFFECTING BREATHING- ON PAGE 596 IN YOUR
TEXTBOOK (BLUE BOX MIDDLE OF THE PAGE).
ALSO READ EXERCISE & BREATHINGOF
PAGE 596.
A FEW
A PRACTICAL APPLICATION IN THE BROWN BOX AT THE TOP
TEST QUESTIONS WILL COME FROM THIS MATERIAL!
ALSO READ
THE MATERIAL ON
HAND
COLUMN OF PAGE
HYPERVENTILATION IN BROWN TYPE AT THE BOTTOM RIGHT
596.
Alveolar Gas Exchange: The alveoli exchange gases between the air & the
blood. Other parts of the resp. system merely move air in & out of the air
passages. The alveoli are microscopic air sacs clustered at the distal ends of the
finest resp. tubes- the alveolar ducts, like a sprig of grapes. Each alveolus
consists of a tiny space surrounded by a thin wall separating it from adjacent
alveoli. There are minute openings called alveolar pores in the walls of some
alveoli.
The Respiratory Membrane: The alveloar wall is lined by a single layer of
simple squamous cells. (Squamous is another great scrabble word even though it has 8
letters. You can run it from a preexisting word on the board with your 7 letters &
you also have the advantage that a nonscientific person might challenge you & lose
his turn). There are also a dense network of capillaries (also lined with a single
layer of simple squamous cells termed an endothelium rather than an epithelium)
surrounding the alveoli. There are at least 2 thicknesses of epithelial cells &
basement membranes between the air in an alveolus & the blood in a capillary. These
layers make up the respiratory membrane, through which gas exchange occurs between
alveolar air & blood.
Diffusion through the Respiratory Membrane: Gas molecules diffuse from areas
of high conc. to areas of lower conc. of the gas. Gas molecules also move from
areas of high pressure to areas of lower pressure. The pressure of a gas
determines its rate of diffusion.
Ordinary air is approximately 78% nitrogen, 21% oxygen, & 0.04% CO 2 by
volume. In a mixture of gases like air, each gas is responsible for a portion of
the total weight or pressure produced by the mixture. The amount of pressure that
each gas creates is called the partial pressure of that gas, & this pressure is
directly related to the conc. of the gas in the mixture. The partial pressure of
oxygen (PO 2 ) = 160 mm Hg. (21% of 760 mm Hg. or .21 X 760 mm Hg). Similarly,
the 2 PCO 2 = 0.3 mm Hg. (.0004 X 760 mm Hg.) & the PN 2 = approx. 593 mm Hg. (.78 X
760 mm Hg). When a mixture of gases dissolves in blood, each gas exerts its own
partial pressure in proportion to its own conc. Each gas will diffuse between the
liquid & its surroundings, & this movement will tend to equalize its partial
pressure in the 2 regions. For example, the P0 2 of capillary blood is less than the
PO of alveolar air. The 0 2 , therefore, diffuses from the alveolar air into the
blood.
Transport of Gases: The transport of 0 & CO 2 between the lungs & the body
cells is a function of the blood. As these gases enter the blood, they dissolve in
the plasma (liquid portion) & they combine chemically with other substances & are
carried in that form.
READ SOME DISORDERS INVOLVING GAS EXCHANGE- A CLINICAL APPLICATION IN THE
BROWN BOX AT THE TOP OF PAGE 598 IN YOUR TEXTBOOK. _____________ ALSO READ
THE SECTION IN BROWN TYPE AT THE BOTTOM OF THE LEFT HAND COLUMN ON PAGE
P a g e | 90
599 CONCERNING HYPOXIA. PAY PARTICULAR ATTENTION TO THE SX (SYMPTOMS)!
Oxygen Transport: Almost all of the oxygen carried in the blood is
combined with hemoglobin that occurs in the r.b.c.'s. The Hgb is responsible
for the color of these cells. Hgb (hemoglobin) has a complex structure
consisting of 2 subunits called heme & globin. Globin is a protein
consisting of 574 amino acids arranged in 4 polypeptide chains. Each chain
is associated with a heme group, & Each heme group contains an iron atom.
Each iron atom can combine loosely with an oxygen atom. As 02 dissolves in
the blood, it combines radidly with Hgb, thereby forming oxyhemoglobin. The
amount of 02 that combines with Hgb is determined by the P02. The greaer the
P 0 , the more O2 that will combine with Hgb, until the Hgb molecules are
saturated with 02. The chemical bonds that form between 02 & Hgb are
relatively unstable, & as the P02 decreases, 02 is released from oxyhemoglobin molecules. This happens in tissues where cells have used 02 in their
respiratory processes & the free 02 diffuses from the blood into nearby
cells.
As the conc. of CO2 increases, oxyhemoglobin tends to release more
02. As the blood becomes more acidic or as the temp. increases, more 02
is released. The amount of 02 released from oxyhemoglobin increases as
the PCO2 increases. The amount of 02 released from oxyhemoglobin increases
as the pH decreases. The amount of oxygen released from oxyhemoglobin
increases as the temp. increases. (These relationships make for good test
questions!) Because of the above mentioned factors, more 02 is released to
skeletal muscles from the blood during periods of exercise, since the
increased muscular activity causes an increase in the PCO2, a decrease in
the pH value, & a rise in the local temp. Similarly, less active cells
receive smaller amounts of 02.
Carbon Monoxide: CO is a gasproduced in gasoline engines because of
incomplete combustion of fuel. It has a toxic effect because it combines
with Hgb more effectively than 02. CO does not dissolve readily from Hgb.
When a person breathes CO, increasing quantities of Hgb become unavailable
for 02 transport, & the body cells suffer. Read the tx (treatment ) of CO
poisoning in brown type on page 600.__ Note particularly that both 02 & CO2
are administered to the victim & why!
Carbon Dioxide Transport: READ THIS SECTION IN YOUR TEXTBOOK ON PAGES
602 & 603, PAYING PARTICULAR ATTENTION TO THE TERMS CARBAMINOHEMOGLOBIN,
THE ROLE OF BICARBONATE IONS (HCO__ minus) IN CARBON DIOXIDE TRANSPORT, THE
TERM CARBONIC ANHYDRASE, THE CONCEPT OF THE CHLORIDE SHIFT. THESE CONCEPTS
ARE ESPECIALLY IMPORTANT AND WE WILL DISCUSS THEM IN LECTURE
THOROUGHLY.__ THEY WILL DEFINITELY COME UP ON THE EXAM!
READ CHART 16.7- GASES TRANSPORTED IN THE BLOOD (BLUE BOX, TOP OF
PAGE 604).
STUDY THE MATERIAL ON PAGES 604 & 605 VERY CAREFULLY (UTILIZATION OF
OXYGEN- (1) CELLULAR RESPIRATION & (2) CITRIC ACID CYCLE.__ MEMORIZE THE
COMPONENTS OF THE ANAEROBIC & AEROBIC PHASES OF CELLULAR RESPIRATION ON
PAGE 605.__ PAY PARTICULAR ATTENTION TO THE CITRIC ACID CYCLE ON PAGE 605,
LEARNING THE NAMES OF THE VARIOUS COMPONENTS OF THE CYLCE & PAYING
ATTENTION TO THE NUMBER OF CARBON ATOMS IN EACH COMPONENT.
THROUGHOUT THE COURSE, I HAVE EMPHASIZED SOME OF THE TERMS AT THE END
P a g e | 91
Page 91
OF EACH CHAPTER IN YOUR TEXTBOOK IN THE SECTION ENTITLED " CLINICAL TERMS
RELATED TO THE SYSTEM UNDER DISCUSSION. " IN MANY INSTANCES, ONLY SOME OF THE
TERMS ARE IMPORTANT & OTHERS ARE RELATIVELY UNIMPORTANT. ______ IT IS MY
SINCERE BELIEF, BASED ON MY CLINICAL EXPERIENCE & EDUCATIONAL BACKGROUND,
THAT ALL OF THE TERMS IN THE " CLINICAL TERMS RELATED TO THE RESPIRATORY
SYSTEM, " ON PAGE 606 OF YOUR TEXTBOOK ARE IMPORTANT. I WILL INCLUDE MANY OF
THEM ON YOUR EXAMINATION. THE TERMS YOU SHOULD KNOW INCLUDE ANOXIA, APNEA,
ASPHYXIA, ATELECTASIS, BRADYPNEA, BRONCHIOLECTASIS, BRONCHITIS, CHEYNESTOKES RESPIRATION (PAY PARTICULAR ATTENTION TO THIS TERM), DYSPNEA, EUPNEA,
HEMOTHORAX, HYPERCAPNIA, HYPERPNEA, HYPERVENTILATION, HYPDXEMIA, HYPDXIA,
LOBAR PNEUMONIA, PLEURISY, PNEUMOCONIOSIS, PNEUMOTHORAX, RHINITIS, SINUSITIS,
TACHYPNEA, & TRACHEOTOMY.
Good luck on the exam. The following is a copy of the aerobic & the anaerobic
phases of cellular respiration taken from your textbook (page 605).
Glucose
(6 Carbon Atoms)
Energy
Pyruvic Acid
(3 Carbon atoms)
2 molecules
Of ATP
ATP
Acetyl Coenzyme A
(2 Carbon atoms)
Oxaloacetic acid
(4 Carbon Atoms)
Citric
Acid
Cycle
Citric Acid
CO2
O2
2H+
Ketoglutaric acid
(5 Carbon atoms)
H2O
CO2 + H20 + Energy
36 ATP molecules
Heat
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Page 91B
The following are important air volumes and lung capacities that one can measure:
(1) Tidal Volume :"'V)-- Formal breathing, that is, the volume of air inhaled and
exhaled in a normal respiratory cycle (approximately 500 ml. in both males and
females).
(2) Inspiratory Reserve Volume (IPV)-- The maximum volume of air that one can inhale at
the end of the inspiratory position (approximately 3,300 ml. in the male & 1,900 ml. in
the female).
(3) Expiratory Reserve Volume (ERV)-- The maximum volume of air that one can exhale at
the end of the expiratory _position (approximately 1,000 ml. in males & 700 ml. in
females).
(4) Residual Volume (RV)-- The volume of air remaining in the lungs that can never be
expired even with the maximum effort (approximately 1,200 ml. in the male & 1,100 ml. in
the female).
(5) Vital Capacity (VC)-- The maximum volume of air that one can expire immediately
following a maximum inspiratory effort (approximately 4,900 mi. in the male & 3,100
ml. in the female).
(6) Inspiratory Capacity (IC)-- The maximum volume of air that can be inspired from the
resting respiratory level (approximately 3,800 ml. in the male & 2,400 ml. in the
female).
(7) Functional Residual Capacity (FRC)-- The volume of air remaining in the lungs at
the resting expiratory level (approximately 2,200 ml. in the male & 1,800 ml. in the
female).
(8) Total Lung Capacity (TLC)-- The amount of air contained in the lungs at the
end of maximum inspiration (approximately 6,000 ml. in the male & 4,200 ml. in the
female).
Any increase in the partial pressure of CO in the arterial blood is called hypercapnia. This
stimulates the chemosensitive area in the medulla & chemoreceptors in the carotid & aortic
bodies. This causes the inspiratory area to become active, & the rate & depth of respiration
increases. If arterial blood PCO2 is less than 40 mm Hg., the condition is called hypocapnia.
Cheyne-Stokes respiration is a repeated cycle of irregular breathing beginning with shallow
breaths that increase in depth & rapidity, then decrease & cease altogether for 15 to 20
seconds. Cheyne-Stokes is normal in infants. It is also often seen just before death from
pulmonary, cerebral, cardiac, & kidney disease.
Oxygen is carried in the blood in the form of oxyhemoglobin. Carbon dioxide
is carried in the deoxygenated blood in several forms. The smallest percentage, 7%, is
dissolved in plasma. 23% of the carbon dioxide combines with the globin portion of
hemoglobin to form carbaminohemoglobin. 70% of the CO2 is transported in the plasma in the
form of bicarbonate ions. The reaction is:
carbonic anhydrase
CO2 + H2O --------------- H2C03 ↔ H+ + HCOcarbon water
carbonic hydrogen bicarbonate
dioxide
acid
ions
ions
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Page 91C
As CO2 diffuses into tissue capillaries & enters rbc's, it reacts with water
in
the presence of carbonic anhydrase, to form carbonic acid. The
carbonic acid dissociates into hydrogen ions & bicarbonate ions. The hydrogen
ions combine mainly with Hgb (hemoglobin). The bicarbonate ions leave the rbc's
& enter the plasma. In exchange chloride ions (Cl-) diffuse from plasma into the
rbc's. This exchange of negative ions maintains the ionic balance between plasma
& rbc's & is known as the chloride shift.
Just as an increase in CO2 in the blood causes oxygen to split from Hgb, the binding
of 02 to Hgb causes the release of CO2 from blood. In the presence of 02, less COi binds in
the blood. This reaction, called the Haldane effect, occurs because when 02 combines with
Hgb, the Hgb becomes a stronger acid. In this state, Hgb combines with less CO,. Also, the
more acidic Hgb releases more hydrogen ions that bind to bicarbonate ions to orm carbonic
acid. The carbonic acid breaks down into water & carbon dioxide. The CO2 is released from
the blood into the alveoli. In tissue capillaries, blood picks up more CO2 as 02 is removed
from Hgb. In pulmonary capillaries, blood releases more CO2 as 02 is picked up by Hgb.
The apneustic center in the lower pons coordinates the transition between inspiration &
expiration.
Boyle's
Law
states
that
the
pressure
of
a
gas
in
a
closed
container
is
inversely
proportional to the volume of the container. Eupnea = normal quiet breathing. Shallow
chest breathing = costal breathing. Deep abdominal breathing = diaphragmatic breathing.
Charles' Law states that the volume of a gas is directly proportional to its absolute
temperature, assuming that the pressure remains constant. Dalton's Law states that each
gas in a mixture of gases exerts its own pressure as if all the other gases were not
present. Henry's Law states that the quantity of a gas that will dissolve in a liquid is
proportional to the partial pressure of the gas & its solubility coefficient, when the
temperature remains constant.
The amount of oxygen released from Hgb is determined by several factors in addition to
the P02. For example, in an acid environment, oxygen splits more readily from Hgb. This
is referred to as the Bohr effect, & is based on the belief that when hydrogen ions bind
to the Hgb, they alter the structure of Hgb & thereby decrease its oxygen-carrying
capacity.
Hypoxia refers to a general low level of oxygen availability.
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