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Chapter 3 / Body Systems
121
Figure 3-60. The heart and its
chambers.
Superior
vena cava
Ascending
aorta
Right pulmonary
artery
Pulmonary valve
(semilunar valve)
Pulmonary
veins
Right atrium
Atrioventricular valve
(tricuspid valve)
Right ventricle
Inferior
vena cava
Unoxygenated blood
Oxygenated blood
Left common carotid artery
Left subclavian artery
Aortic arch
Left pulmonary artery
Pulmonary
veins
Left atrium
Aortic valve
(semilunar valve)
Mitral valve
(bicuspid valve)
Left ventricle
Descending
aorta
semilunar valves prevent the blood from leaking back into
the ventricles.
Blood follows a specific path through the heart:
1. Oxygen-depleted blood collects in the right atrium.
2. The right atrium contracts to push the blood through
an AV valve into the right ventricle.
3. The ventricle, full of oxygen-depleted blood, contracts
to push the blood through a semilunar valve into the
pulmonary artery in the lungs.
4. The blood receives additional oxygen in the lungs and
goes out through the pulmonary veins into the left
atrium.
5. The left atrium contracts and forces oxygen-rich blood
through an AV valve into the left ventricle.
6. The left ventricle contracts and forces oxygen-rich
blood through a semilunar valve into the aorta, where
it enters the arterial system and is delivered to the body.
Although there is a specific path, the left and right atria
contract at the same time, and the left and right ventricles
contract together.
Blood Vessels
The blood vessels transport blood from the heart to the
rest of the body and back to the heart. The arteries, veins,
and capillaries are collectively called the blood vessels. The
largest blood vessel is the aorta (ay-OR-tuh), which measures
about an inch across where it leaves the heart to transport
oxygenated blood to the entire body. The smallest blood vessels are the capillaries, which are less than a tenth of a millimeter in diameter. Their small size limits the passage of
molecules to a single file.
Arteries
An artery is a tube that carries blood away from the heart.
The strong mechanical pumping force of the heart pushes
the blood through the aorta and into its branches called
arteries. As an artery travels further from the heart, it
branches out, becoming smaller and thinner with distance.
Arterioles are small arteries that are far from the heart, delivering the oxygenated blood to the capillaries. Figure3-61
shows the arteries of the body. Gravity also helps the arteries move blood to different parts of the body. “Artery” is
derived from the Greek word arteria, meaning air pipe.
Originally, when they were discovered in corpses, the arteries were empty and assumed to transport air. Although it
has since been determined that they carry blood, the name
has not changed.
Arteries are constructed with three layers of tissues
(Fig. 3-62). The interior layer, called the tunica intima or
endothelium, is a layer of simple squamous epithelium that
is very smooth and slippery. The middle layer, called the
tunica media, is a layer of smooth muscle and elastic connective tissue. The smooth muscles keep the diameter of the
122 INTRODUCTION TO MASSAGE THERAPY
deoxygenated blood before it goes into the heart. Much of
the blood is moving against gravity, without the heart to
pump it.
To compensate for the disadvantages and prevent blood
Ascending aorta
Left and right common
carotid arteries
Subclavian
Axillary
from going the wrong direction, venous blood flow is aided
by valves and skeletal muscle contractions. The valves are
one-way gates that allow blood to flow in one direction only,
similar to doors that only open outward. There are more
valves in areas where blood typically must fight gravity to
Renal
Common
iliac
Internal
iliac
External
iliac
Brachial
Aorta
Ulnar
Radial
Palmar
arches
return to the heart, such as the legs. As the skeletal muscles
contract, they squeeze the veins, and blood can only flow
toward the heart. Figure 3-64 shows how the skeletal muscles work with the valves to encourage venous blood flow.
Veins are constructed with the same three layers as the
arteries and are similar in size to the arteries but have thinner walls (see Fig. 3-62). The tunica media, or smooth muscle layer, is thinner and, as a result, the lumens of the veins
are larger than those of arteries. The tunica externa of the
veins is thinner because blood pressure is much lower in the
veins, and they are not in danger of bursting.
Popliteal
Femoral
Peroneal
Anterior tibial
Posterior tibial
Dorsalis pedis
Figure 3-61. Arterial system.
arteries small, which increases the blood pressure the way a
pinched water hose increases the water pressure. The outer
layer of arteries is made of fibrous connective tissue called
the tunica externa. It protects the arteries from damage and
keeps the larger arteries from bursting as a result of the high
blood pressure exerted by the force of the heart contraction.
Capillaries
Capillaries are the smallest, finest branches of the blood
vessels where gases and fluids are exchanged. The capillary
walls are composed of only one layer of cells and a basement membrane (Fig. 3-62). All transfers between blood
and tissue cells occur at the capillary membranes via diffusion, osmosis, or filtration. Diffusion is a passive transport
mechanism that allows molecules to pass through semipermeable membranes without assistance. Respiratory gases
diffuse through the capillary walls and tissue cells. Osmosis
allows water molecules, which are not fat soluble and cannot diffuse through the lipid bilayer, to use channel proteins
to move through a membrane to balance concentrations on
either side. Osmosis carries fluid from the interstitial spaces
through the membrane and into the blood in the capillaries,
where the concentration of solutes is higher. Filtration is the
passive transport mechanism involving pressure gradients
that takes water and dissolved substances through a membrane from a higher pressure to a lower pressure in an effort
to balance concentrations on either side of the membrane.
Filtration occurs in the kidneys (discussed later in this chapter) as well as at the arteriolar end of all capillaries.
Blood Circuits
Veins
Veins transport blood from the capillaries of the body back
to the heart (Fig. 3-63). The smallest veins, called venules,
receive the blood from the capillaries immediately after
the blood has delivered its oxygen to and picked up carbon
dioxide from the tissues, and immediately after the blood
has picked up oxygen and dropped off carbon dioxide in
the lungs. The largest veins are the superior vena cava and
inferior vena cava, which are the last collection point of
The blood vessels can be separated into two separate pathways, called the pulmonary and systemic circuits. The pulmonary circuit takes blood to the lungs for gas exchange and
returns it to the heart. The systemic circuit transports blood
through the rest of the body.
Pulmonary Circuit
The pulmonary arteries carry deoxygenated blood from
the right ventricle to the lungs. There, carbon dioxide
Chapter 3 / Body Systems
Artery Vein
123
Elastic tissue
Tunica interna
(endothelium)
Tunica media
(smooth muscle)
Tunica externa
(connective tissue)
Blood flow
Arteriole
Capillary
Figure 3-62. Comparison of arterial, venous, and capillary walls.
diffuses out of the blood and into the lungs, where it is
exhaled into the external environment. Oxygen in the air
we inhale diffuses from the lungs into the blood, and the
pulmonary veins carry the oxygenated blood to the left
atrium of the heart.
Val ve
Venule
blood loss. The cardiovascular system is also involved in regulating our core body temperature and maintaining the correct acidity of our blood, measured as pH.
Transportation
Systemic Circuit
The systemic arteries carry oxygenated blood to the capillaries throughout the body. Oxygen in the blood at the capillaries diffuses out into the tissues. Carbon dioxide diffuses from
the tissues into the blood in the capillaries. The deoxygenated blood is then returned to the heart through the systemic
veins.
Functions of the Cardiovascular
System
The primary function of the cardiovascular system is to
transport blood and all of its components. In addition to
its important blood delivery service to all the cells of our
bodies, the cardiovascular system has some other important functions. It carries cells that protect us from infection
and diseases, provides immunity from disease, and prevents
The cardiovascular system is the delivery system within the
body. Using the blood as a transport mechanism, the cardiovascular system carries oxygen, carbon dioxide, hormones,
and nutrients to and from all parts of the body. There is
a certain pathway for taking blood from the heart to the
lungs to pick up oxygen, a separate path that delivers oxygen-rich blood from the heart to the cells of the body, and
yet another pathway for returning oxygen-deficient blood
to the heart.
Protection
The cardiovascular system uses the blood to carry leukocytes, antibodies, and platelets throughout the body. The
leukocytes (also called white blood cells), along with the
antibodies, fight pathogens and destroy foreign substances. Their ability to protect us from infection and disease is
called immunity.
124 INTRODUCTION TO MASSAGE THERAPY
Brachiocephalic
Superior
vena cava
Renal
Common
iliac
Internal
iliac
External
iliac
Popliteal
Posterior tibial
Figure 3-63. Venous system.
Jugular
Subclavian
Axillary
Cephalic
Brachial
Basilic
Median
cubital
Ulnar
Radial
Palmar
arches
Femoral
Great
saphenous
Anterior tibial
Small
saphenous
Venous arch
Platelets in the blood activate hemostasis, a clotting process
that the body uses to automatically stop bleeding. By forming a
blood clot, our bodies protect us from losing too much blood.
When the clotting mechanism takes place on the integument, it
forms a scab that protects us from having bacteria in the external environment enter the body through the open wound.
The mechanism of hemostasis starts when blood vessels within a tissue are injured and localized vasoconstriction occurs. Blood platelets accumulate and stick together.
Once they adhere to each other, they release chemicals that
attract more platelets to the area, and they clump together to
form a platelet plug or clot to seal the hole in the blood vessel and slow the bleeding. Fibrinogen, a protein suspended in
the blood, is converted into strands of fibrin, which tangle
together at the injury site. As circulation continues, RBCs and
Figure 3-64. Skeletal muscle “pump” for venous blood flow.
Skeletal muscle contraction squeezes the veins and their valves,
causing venous blood to be forced through the one-way valves.
platelets are caught in the tangle, further reducing blood flow
in the area. Leukocytes also get caught, which remove cellular debris and fight infection. As the platelet plug shrinks,
the fibrin strands contract and pull the edges of the wound
together to provide a framework for tissue repair.
Regulation
The cardiovascular system also helps maintain body temperature by constriction and dilation of the blood vessels. A
thermostat in the brain maintains the body’s normal temperature at approximately 98.6°F. When external temperatures,
muscular exertion, or fever create excessive heat, vasodilation
(dilation of the blood vessels) in the skin allows more warm
blood to flow near the skin’s surface, where heat can dissipate. Conversely, the vessels constrict (vasoconstriction) in
the skin when the external environment is excessively cold,
in an effort to preserve body heat. The brain needs blood
to function properly and has priority over all other organs,
regardless of the body’s temperature or activity. In extreme
situations, more blood will be sent to the brain and less to
the rest of the body. Body heat is dissipated from the head,
despite the body’s core temperature. Thus, wearing a hat in
colder temperatures helps keep fingers and toes warmer.
The acidity or alkalinity of a substance is measured as
pH. Neutral pH, or pH balanced, indicates a substance that
is neither acidic nor alkaline and has a pH of 7. When the
pH is below 7, the solution is considered acidic, and above 7
it is considered basic, or alkaline. The interstitial fluids (also
called extracellular fluids or tissue fluids) are kept at pH 7.4,
which means that tissue fluids are slightly basic, or alkaline.
Chapter 3 / Body Systems 125
The blood has hemoglobin and plasma proteins that act as
buffers, or chemicals that stabilize pH levels.
Effects of Massage on the
Cardiovascular System
The effects of massage on the cardiovascular system are determined by where and how strokes are applied. Moderate pressure massage activates the parasympathetic nervous system,
which means that the heart rate slows down, the force of contractions decreases, and blood pressure decreases. See Research
Box 3.2. Percussive massage strokes initially cause the reflexive
effect of vasoconstriction (blood vessel constriction) to reduce
circulation to the area. Sustained percussion, however, can
result in vasodilation (blood vessel dilation) in the area.
Mechanically, pressure on the blood vessels increases
circulation. Capillaries with poor blood flow respond to
this kind of mechanical pressure remarkably well and can
then supply oxygenated blood to ischemic tissues. Massage
increases the permeability of the capillary walls, enhancing
the delivery of oxygen and nutrients as well as waste removal.
RESEARCH BOX 3-2
Lymphatic System
The lymphatic system is similar to the cardiovascular system
because of its many vessels, but it is not a true circulatory
system. This branching network of lymph vessels is a oneway road that transports lymphatic fluid from all over the
body and drains it into the bloodstream at a location near
the heart. Although the cardiovascular system has the heart
to push the blood through the blood vessels, the lymphatic
system does not have a major pump. The lymphatic system
of vessels and valves is able to function primarily via rhythmic contraction of the skeletal muscles and gravity. As the
fluid is being moved toward the heart, it passes through several structures that filter out large and foreign particles so
they do not enter the bloodstream. There are also structures
of the lymphatic system that provide immunity by producing cells that destroy pathogens and other foreign particles.
Structures of the Lymphatic
System
The lymphatic system includes the lymph, lymph vessels, lymph nodes, lymphatic organs including the spleen
and thymus gland, and some lymph tissue in the intestine
andtonsils.
Massage and High Blood
Pressure
High blood pressure is associated with elevated
anxiety, stress and stress hormones, hostility, depression and catecholamines. Massage therapy
and progressive muscle relaxation were evaluated
as treatments for reducing blood pressure and
these associated symptoms. Adults who had been
diagnosed as hypertensive received ten 30 min
massage sessions over five weeks or they were
given progressive muscle relaxation instructions
(control group). Sitting diastolic blood pressure
decreased after the first and last massage therapy
sessions and reclining diastolic blood pressure decreased from the first to the last day of the study.
Although both groups reported less anxiety, only
the massage therapy group reported less depression and hostility and showed decreased urinary
and salivary stress hormone levels (cortisol). Massage therapy may be effective in reducing diastolic
blood pressure and symptoms associated with hypertension.
Hernandez-Reif M, Field T, Krasnegor J, Hossain Z, Theakston H, Burman I.
(2000). High blood pressure and associated symptoms were reduced by
massage therapy. J Bodyw Mov Ther 2000;4:31–38.
Lymph
Remember that in the capillaries, blood plasma seeps
through the capillaries to fill the interstitial space, or the
space between cells. There, it acquires cellular debris and
foreign substances that are eliminated by the surrounding
cells. The interstitial fluid that is taken from all over the
body into the lymphatic system is called lymphatic fluid ,
or lymph . The additional components of lymph include the
lymphocytes, monocytes, proteins, and cellular waste.
Lymph Vessels
The interstitial fluids are first collected by the lymph capillaries throughout the body. The lymph capillaries join to form
larger lymphatic vessels that carry the lymph back to the
heart. The lymph from the upper right quadrant of the body
exits the lymphatic system at the right lymphatic duct, which
drains into the right subclavian vein. The lymph from the rest
of the body drains out of the lymphatic system through the
thoracic duct and into the left subclavian vein. The subclavian veins join together and empty lymph and deoxygenated
blood into the heart (Fig. 3-65 illustrates the lymph vessels).
Lymph vessels have the same basic structure as veins
but are smaller and more delicate. The vessels have valves to
ensure lymph flows in one direction, and they have smooth
muscles within their walls. The sections of the lymph vessels between the valves are called lymphangions, and the
126 INTRODUCTION TO MASSAGE THERAPY
Right lymphatic duct
Right subclavian vein
Left subclavian vein
Axillary nodes
Occipital
nodes
Parotid
Cervical
nodes
Lymph nodes and
vessels of the head
Vessels in purple area drain
into right lymphatic duct
Vessels in remaining area drain
into thoracic duct
Figure 3-65. Lymph vessels and areas with many lymph nodes.
nodes
Mandibular
nodes
Mammary
vessels
Lumbar
nodes
Femoral
vessels
Poplitieal
nodes
Tibial
vessels
Thoracic duct
Cisterna chyli
Cubital nodes
Mesenteric nodes
Iliac nodes
Iliac vessels
Inguinal nodes
peristaltic contractions of the smooth muscles assist the
flow of lymph very slightly. Being a one-way system without a mechanical pump behind it, the lymphatic system puts
minimal pressure on the walls of the vessels, so the layers
of muscle and fibrous connective tissue covering are thin.
Like venous blood, much of the lymph travels against gravity. Skeletal muscle movements encourage lymph through
the lymph vessels and valves, similar to the mechanism that
encourages venous flow (see Fig. 3-64).
The flow of lymph through the vessels is also aided by
the contraction of the diaphragm muscle during inspiration,
which creates a vacuum-like suction that pulls blood and
lymph upward and toward the heart. There are many lymph
vessels in the central tendon of the diaphragm, so when
it contracts, lymph is pushed through the one-way valves.
Also, contraction of the diaphragm creates a vacuum in
the thoracic cavity that pulls both lymph and venous blood
through their respective vessels and one-way valves.
Lymph Nodes
Lymph nodes are oval, bean-shaped structures that house
and produce lymphocytes and filter the lymphatic fluid.
Thousands of lymph nodes can be found in groups along
the lymph vessels, and large concentrations of lymph nodes
are found in the cervical, inguinal, and axillary regions
(Fig.3-65). Lymph nodes contain lots of macrophages and
lymphocytes and have a structural framework of reticular connective tissue that creates a meshwork for filtering
lymph. Pathogens and toxins in the lymph are destroyed or
inactivated and filtered out with a series of fibrous traps.
The clean lymphatic fluid flows out of the node and continues on its path toward the heart.
Lymph Organs and Tissues
The largest lymph organ is the spleen, which is approximately the size of the heart. The spleen produces lymphocytes,
filters the blood, and removes old, worn-out erythrocytes
from the blood. In the process of removing erythrocytes,
iron is extracted for future use. The spleen also functions as
a storage container for extra blood, releasing it when necessary. It acts as a conference center for immune cells and
blood cells, providing a meeting place and activity center
for them. Macrophages destroy foreign substances that have
with chemical antigens on their surface that stimulate the
Chapter 3 / Body Systems 127
immune response. Macrophages destroy foreign substances
such as bacteria, pollen, and viruses that have antigens (proteins) on their surfaces that activate the immune response.
To destroy antigenic cells and substances with antigenic proteins on them, the spleen has B cells that produce antibodies,
proteins that recognize and bond to specific antigens. The
antibodies coat the foreign substances, inactivating them or
attracting macrophages to them. The process of inactivating
foreign substances is called the immune response.
The thymus gland in children is located deep to the
sternum, but as we age, the thymus gland shrinks and only
a small amount of tissue remains in adults, superior to the
heart. It is the site where some lymphocytes mature.
There are areas of clustered lymph tissue found in the
tonsils and intestines. Tonsils are small masses of lymph tissue on either side of the soft palate at the back of the throat.
These areas of moist epithelium are in contact with the
external environment, so the tonsils help prevent bacteria
and other pathogens from entering the throat. Some pathogens get past the tonsils and are able to get further into the
gastrointestinal tract. If they get into the intestines, they are
subjected to Peyer’s patches, lymph tissue in the lining of
the intestines, loaded with white blood cells that fight bacteria, viruses, and other microorganisms.
Functions of the Lymphatic
System
The lymphatic system has transportation, immune, and
homeostatic functions. The lymph vessels provide a roadway for lymph, which can carry nutrients as well as waste.
The lymphatic system also provides immunity by producing
cells that destroy foreign particles, pathogens, and toxins.
Finally, the lymph vessels help maintain blood volume and
blood pressure.
are critical to immunity, are made in the bone marrow and
are divided in the lymphatic tissue. The fluid that is drained
from the interstitial spaces by the lymphatic system carries
the leukocytes known as lymphocytes and monocytes. As
the fluid is transported to the heart to be added to the blood,
it is filtered in lymph nodes where antibodies and macrophages destroy or inactivate pathogens that cause illness.
Homeostasis
Once outside the cells, interstitial fluid can either diffuse
back through the capillary walls into the blood or it can
be drained via the lymphatic system. This is an important
homeostatic mechanism for maintaining proper blood volume and blood pressure. If our blood volume or blood
pressure is low, interstitial fluid will diffuse through the capillaries to be added to the blood. As a result, blood volume
and blood pressure increase.
Effects of Massage on the
Lymphatic System
Massage is especially beneficial to the lymphatic system.
Because there are so many lymph vessels in the diaphragm
muscle, massage therapists can utilize the diaphragm to
increase lymphatic flow by asking clients to use deep breathing techniques.
Numerous lymph vessels travel through the superficial and deep fascia, and the mechanical pressure of massage strokes on these vessels increases the flow of lymph.
Similarly, skeletal muscle contractions put pressure on the
lymph vessels and pump lymph through the one-way valves.
Joint movement and passive contractions applied during a
massage activate this skeletal muscle pump, though not as
effectively as active contractions.
Transportation
Interstitial fluid, the fluid that surrounds our cells, contains
chemicals and metabolic wastes that have been transported
out of the cells. The lymphatic system is most commonly
known for transporting “bad” things away from our tissues so they can be destroyed or removed from our bodies.
However, there are some beneficial substances produced in
the body that can only get to the bloodstream for delivery
to the rest of the body by way of the lymph system. Fatty
acids and vitamin A are end products of digestion found in
the small intestine. From there, they are absorbed into the
lymphatic system and eventually added to the bloodstream
to nourish cells throughout the body.
Immunity
The lymphatic system helps us fight bacteria and other foreign substances. Leukocytes, or white blood cells, which
Respiratory System
The respiratory system allows us to breathe, which is an activity controlled by the CNS. Awake or asleep, breathing continues as long as we are alive. The nervous system controls
contractions of the diaphragm muscle, which pulls air into
the respiratory system. In the lungs, oxygen diffuses from the
air we breathe into the blood in the capillaries, and the circulatory system delivers the oxygen throughout the body. This is
also where carbon dioxide is eliminated via exhalation.
Structures of the Respiratory
System
The structures of the respiratory system include the nose, nasal
cavity, pharynx (FAIR-inks), larynx, trachea (TRAY-kee-ah),
128 INTRODUCTION TO MASSAGE THERAPY
Nasal cavity
Pharynx
Larynx
Trachea
Lungs
Bronchi
Bronchioles
Diaphragm
Figure 3-66. Respiratory system.
bronchi (BRAHN-kahy), bronchioles, alveoli (al-VEE-oh-lahy),
and lungs (Fig. 3-66). These structures can be separated into
two groups: the upper and lower respiratory tracts.
Upper Respiratory Tract
The upper respiratory tract includes the nose, nasal cavity, pharynx, larynx, and the upper part of the trachea.
Cartilage, mucus, and ciliated cells are present in all of the
structures of the upper respiratory tract. Cartilage maintains the shape of the structures to prevent the airway from
collapsing and stopping air flow. The mucus traps foreign
particles that are then swept toward the external environment by ciliated cells. The lungs are a good breeding ground
for infection because they are moist and warm, so it is very
important to have the cells that secrete mucus and the ciliated cells functioning properly.
Nose and Nasal Cavity
The first part of the respiratory tract to receive air from the
external environment is the nose and the nasal cavity. The
cartilage in the nose holds it open to allow air to enter easily. There, the mucous secretions moisten the air to keep the
lungs from drying out. The capillaries lying just beneath the
surface of the epithelium warm the air, again for the benefit
of the delicate tissues of the lungs. There are olfactory cells
within the nasal cavity that are the sensory receptors for smell.
Cilia
the respiratory and digestive systems. Eustachian tubes
connect the upper part of the pharynx to the middle ear,
equalizing air pressure on either side of the ear’s tympanic
membrane. The pharyngeal tonsils, also called adenoids, are
made of lymphatic tissue in the pharynx and are discussed in
the lymphatic system section above. If the lymphatic activity
is high enough, the tonsils can enlarge and the air passage
can actually be obstructed.
Larynx
The larynx, or voice box, is made of cartilage and lies just
inferior to the pharynx. The thyroid cartilage, commonly
referred to as the Adam’s apple, is part of the larynx. The
epiglottis is a little structure in the larynx that prevents food
from going down the airway. The vocal cords are connected to the larynx’s cartilage, and as air moves by them, they
vibrate and create sound.
Upper Trachea
The trachea is a tubelike structure that connects the larynx
to the bronchi in the lungs. The trachea has cilia that sweep
foreign particles caught in mucus up toward the external
environment. These unwanted particles are coughed out,
spat out, or swallowed.
Lower Respiratory Tract
Pharynx
As the incoming air leaves the nasal cavity, the air is received
by the pharynx. The pharynx acts as a passageway for both
The structures of the lower respiratory tract include the
lower part of the trachea, the bronchi, bronchioles, alveoli,
and lungs.
Chapter 3 / Body Systems
129
Lower Trachea
At the inferior end of the trachea, the airway splits into two
separate paths. Rings of hyaline cartilage hold the trachea
open, and mucus and cilia cooperate to remove foreign matter from the respiratory path.
Bronchi
The left and right branches of the airway following the trachea are called the bronchi. The bronchi enter the lungs and
each of the bronchi branches into finer and finer airways.
Bronchioles are the smallest airways inside the lungs and
they do not contain any cartilage. Their walls are mostly
made of smooth muscles that are controlled by the ANS.
Although the air that reaches the bronchi is usually warm,
moist, and particle-free, mucus and cilia are still present to
sweep foreign particles out to the environment.
Alveoli
At the ends of the tiny bronchioles, air enters the pulmonary alveoli, which resemble clusters of grapes. They have
thin walls of simple squamous epithelium that allow gases
to be exchanged with the blood in the capillaries that wrap
around them. Diffusion allows oxygen to move into the capillaries and carbon dioxide to move into the alveoli (Fig. 3-67).
Surfactants are secreted by cells in the alveoli to reduce surface tension and allow the alveoli to expand without stress.
The tops of the lungs are just inferior to the clavicles and
the bottoms of the lungs rest on the diaphragm. The lungs
are enveloped in a serous membrane called the visceral
pleura, and the thoracic cavity is lined with a serous membrane called the parietal pleura. The serous fluid that these
membranes secrete provides lubrication to prevent friction
between the two membranes and also helps keep the separate layers of membranes together. The concept is similar
to how water between two layers of plastic wrap keeps the
layers close together while allowing them to slip past each
other easily.
Functions of the Respiratory
System
The respiratory system moves air in and out of the lungs,
which is also known as ventilation. In addition to ventilation, the respiratory system cooperates with the circulatory
system to perform respiration, which provides oxygen to the
body and removes carbon dioxide. Carbon dioxide removal
is very important. People actually die faster from carbon
dioxide accumulation than oxygen depletion.
The respiratory system also allows us to maintain the
proper pH level for interstitial fluids and produce speech,
and it provides body defenses by coughing and sneezing
unwanted particles out of the airway.
Lungs
The left and right lungs are separated by the section of the
thoracic cavity that holds the heart and large blood vessels
and is called the mediastinum (MEE-dee-ah-STAHY-num).
Figure 3-67. Alveoli and gas exchange.
Ventilation
Ventilation moves air in and out of the lungs, and respiration takes the carbon dioxide out of the body and brings
Alveolus
(air sac)
Oxygen
molecule
Carbon dioxide
molecule
Wall of
alveolus
Wall of
capillary
Capillary
Erythrocyte
130 INTRODUCTION TO MASSAGE THERAPY
oxygen in. The gas exchange must occur in both directions
to maintain homeostasis.
Inhalation
Inhalation, also known as inspiration, draws air into the
lungs. It occurs as the diaphragm and external intercostal
muscles contract. The floor of the thoracic cavity is pulled
downward as a result of the diaphragm contraction, and the
walls of the thoracic cavity are widened by the contraction
of the external intercostals. The parietal pleural membranes
are attached to the walls of the thoracic cavity and expand
along with it, pulling air from the external environment into
the respiratory pathway.
Exhalation
The ventilation process that moves air out of the lungs is called
exhalation, or expiration. Normal exhalation is a passive process that mostly results from the relaxation of the diaphragm
and external intercostals. Some activities require additional,
forced exhalation, such as speaking, singing, or blowing. The
internal intercostal muscles can be contracted to reduce the
size of the thoracic cavity, and the abdominal muscles can be
contracted to push the floor of the thoracic cavity upward.
Respiration
The exchange of oxygen and carbon dioxide that occurs in
the respiratory system is called external respiration because
the gas exchange occurs between our tissues and the external environment. As discussed above, internal respiration,
or cellular respiration, occurs within the cells and tissues.
Inhalation and exhalation are equally important for maintaining proper chemical levels in the blood. The respiratory
and circulatory systems cooperate to provide a transport
mechanism for the blood gas exchange.
The nervous system and chemical signals can trigger
increased ventilation to provide more gas exchange via external
respiration. The brain and motor nerves control the muscles
that set the rate and depth of respiration. If you think about
how we breathe when we cry, laugh, or exercise, you will see
how emotions and physical activity affect our breathing patterns. Emotions are associated with chemicals produced in the
brain, and those chemicals can stimulate or alter respiration.
The proprioceptors of the nervous system play an important part in respiratory activity. Muscle spindles sense tension
in the muscle fibers. Low levels of oxygen can cause the respiratory muscles to contract insufficiently, which can be detected by the muscle spindles. To maintain homeostasis, the CNS
will increase ventilation to increase external respiration.
tissues. When the pH is too low, the body will try to raise
the pH by increasing the breathing rate, exposing the lungs
to more oxygen, getting rid of carbon dioxide, thus raising
the proportion of oxygen levels in the tissues. When the pH
is too high and the fluids are too basic, the body can respond
by reducing respiratory activity to build up carbon dioxide
and acidify the fluids. The cooperation between the respiratory and circulatory systems is an obvious example of how
interdependent the body systems are from the cellular level
all the way up to the organism level.
Speech Production
The larynx (LAIR-inks), or voice box, is part of the respiratory system where sounds can be created. Specifically, the
vocal cords vibrate as air passes over them, creating sound.
By combining movement of the tongue, lips, and cheeks
and the speed of exhalation, we can control our voices to
create precise sounds.
Body Defenses
There are some reflexive activities of the respiratory system
that protect us from irritating objects in the airway. Irritation
of the mucous membrane at the back of the throat or farther down the respiratory pathway can cause a cough, our
body’s attempt to eliminate unwanted material through the
mouth. When the mucous membrane of the nasal passages
is irritated, our body sneezes reflexively in an attempt to
expel unwanted material through the nose.
Effects of Massage on the
Respiratory System
The process of cellular respiration is enhanced by massage and manipulation of the tissues, partly as a result of
the increased circulation. As muscles are massaged, the
heat of friction and the oxidation of glycogen create additional amounts of carbon dioxide that the body has to expel
to maintain homeostasis. We eliminate carbon dioxide by
exhaling it through the lungs and can eliminate unusually
high amounts by simply breathing deeply and more effectively. Furthermore, massage that lasts longer than 10 to 15
minutes activates the parasympathetic nervous response,
which encourages slow, deep contractions of the diaphragm.
When excessive mucus accumulates in the respiratory
tract, rhythmic tapotement can help loosen it and make it
easier to cough out for relief from respiratory congestion.
pH Maintenance
The amount of carbon dioxide in the blood affects the pH.
Too much carbon dioxide lowers the pH and makes blood
more acidic than normal. Acidic fluids can destroy the cellular membrane and are harmful to the health of the cells and
Digestive System
The digestive system is the pathway for food from the
moment it enters the mouth until it is eliminated at the anus.
The nervous system sends motor signals to the structures of