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Chapter 3 / Body Systems
131
the digestive system to take the food we eat and transform
it into a substance that can release the nutrients. The capillaries absorb the nutrients and deliver them throughout the
body by way of the blood. The organ systems must work
together for our bodies to function normally.
Structures of the Digestive
System
The digestive system can be broken into two sets of structures: the alimentary canal and the accessory organs. The
alimentary (AL-ih-MEN-tah-ree) canal is the passageway that
includes the oral cavity, pharynx, esophagus, stomach, small
intestine, and large intestine. The accessory digestive organs
include the pancreas, liver, gallbladder, and salivary glands
that produce chemicals necessary for digestion. Figure 3-68
shows the structures of the alimentary canal and the accessory digestive organs.
The Alimentary Canal
The alimentary canal, or digestive tract, is where food is broken down and eventually absorbed. It includes the oral cavity, pharynx, esophagus, stomach, small intestine, and large
intestine. The canal is constructed of four layers, including
the mucous membrane, submucosa, external muscle layer,
and serous membrane. The deepest layer is the mucous
membrane. It secretes mucus to lubricate the passage of
food through the canal and secretes digestive enzymes to
encourage the breakdown of food. Just outside the mucous
membrane is the submucosa, which is a layer of connective tissue filled with blood vessels and lymph vessels. The
external muscle layer is made of smooth muscle for most
of the length of the canal, but the esophagus contains skeletal muscle. The outermost layer of the alimentary canal is
fibrous connective tissue above the diaphragm, but below
the diaphragm, most of the outer layer is a serous membrane called the visceral peritoneum.
Small
intestine
Duodenum
Jejunum
IIeum
Oral cavity
Submandibular and
sublingual salivary
glands
Liver
Gallbladder
Large intestine
Ascending
colon
Cecum
Parotid salivary gland
Pharynx
Esophagus
Stomach
Pancreas
Transverse
colon
Small
intestine
Descending
colon
Appendix
Figure 3-68. Structures of the digestive system.
Anus
Rectum
Sigmoid
colon
132 INTRODUCTION TO MASSAGE THERAPY
Oral Cavity
The oral cavity contains the teeth and tongue, which begin
the process of digestion. Teeth grind food into smaller pieces while the tongue circulates the food to make sure everything gets evenly chewed. The salivary glands are located
below the tongue, above, below, and behind the TMJ. The
saliva contains enzymes that chemically break down food
even further.
Pharynx
The pharynx has overlapping layers of skeletal muscle
whose fibers run perpendicular to each other. When these
muscles rhythmically contract, they create peristalsis: wavelike contractions that move substances through a tube.
Esophagus
The esophagus is a tube that runs from the pharynx to the
stomach, moving the food with peristaltic action.
Stomach
Once food reaches the stomach, it is stored and chemically
broken down even further. The smooth muscles churn the
food mechanically while gastric juice continues the chemical breakdown. The resulting chyme (KAHYM) exits the
stomach.
Small Intestine
The chyme formed in the stomach then enters the small
intestine, the major organ for absorption. Nutrients, water,
and electrolytes are absorbed in the small intestine as the
chyme passes through.
Large Intestine
The chyme leaves the small intestine and enters the large
intestine, where more water and minerals are absorbed.
Bacteria in the large intestine feed on fecal material and
release gas as a byproduct. The remaining fiber and other
indigestible wastes are eliminated at the exit of the large
intestine, the anus.
fat, the gallbladder releases bile to emulsify it. The salivary
glands, located anterior to the ears (parotid glands), under
the tongue (sublingual glands), and just under the lower jaw
(submandibular glands), all produce saliva, which chemically
breaks down starches, inhibits bacterial growth, and eases
the processes of chewing and swallowing.
Functions of the Digestive
System
Our digestive system is responsible for taking the food we
consume and delivering the nutrients to the body. It does
this by mechanically and chemically breaking down food,
absorbing it, and eliminating the indigestible remains, all the
while moving it through the digestive tract by propulsion
and smooth muscle contractions called peristalsis.
Digestion
Digestion is the process of breaking food down by mechanical and chemical activity. When food enters the mouth, we
chew it up and mechanically grind the food into smaller
pieces. Saliva, secreted by three pairs of salivary glands and
delivered to the oral cavity through ducts, contains a digestive enzyme that can chemically break down some foods.
The stomach contains acids and enzymes to chemically
break down food particles even more.
Several muscles are involved in the process of digestion.
The process of chewing requires muscles to move the mandible, or lower jaw. The muscles of the tongue push food
around the mouth to be chewed completely. Both skeletal
and smooth muscles create peristalsis.
Absorption
Food that has been mechanically broken down into a substance called chyme can be chemically digested into absorbable nutrients. The nutrients are absorbed into the blood
and lymph in the intestines. From there, the nutrients can
be delivered throughout the body via the circulatory vessels.
Accessory Digestive Organs
The accessory organs of the digestive system include the
pancreas, liver, gallbladder, and salivary glands. They secrete
enzymes and hormones that are required for digestion. The
pancreas also produces the hormones insulin and glucagon,
which are critical for the regulation of blood sugar levels.
The liver makes bile, which breaks fats into smaller pieces
that are more easily digested, and it detoxifies and excretes
wastes and toxins. Fats and glycogen for energy are stored
in the liver, as are many vitamins, and iron for hemoglobin
formation. The gallbladder is a small organ just below the
liver that acts as a sort of holding tank for bile that is not
being used. When the body must process large amounts of
Elimination
Because we cannot digest every component of food we eat,
such as cellulose from plants, the digestive system eliminates
the parts we cannot digest. The indigestible material, along
with water and bacteria in the digestive tract, is called fecal
matter. The fecal matter is propelled through the digestive
tract and eliminated through the anus to the external environment, at which point it is called feces.
Peristalsis
The smooth muscles of the digestive tract, as discussed in
the muscular system section, are layered structures capable
Chapter 3 / Body Systems
133
of long, sustained contractions. The rhythmic contractions
of the layers propel the contents of the digestive system
through the digestive tract from oral cavity to anus.
Effects of Massage on the
Digestive System
Massage generally stimulates cellular metabolism and
increases the delivery of nutrients to cells and tissues. As
the nutrients are used up, the body may recognize the need
for more nutrients by triggering the appetite. Massage can
mechanically push the indigestible waste through the intestines, but massage also evokes the parasympathetic nervous
response that encourages digestive activity, so hunger can be
a subtle reflexive effect of massage.
Urinary System
The urinary system is primarily responsible for forming and
excreting urine; however, in doing so, it also performs many
regulatory functions. There are nitrogen-based wastes produced during cellular metabolism that are only eliminated
with the passive transport mechanism of filtration. Many of
the harmful wastes are actively transported from the blood
to become part of the urine. The creatine phosphate mechanism for creating ATP in muscles generates some of the
wastes that are removed by the kidneys, demonstrating the
interdependence of the muscular system, circulatory system, and urinary system.
Structures of the Urinary
System
The urinary system includes the kidneys, ureters, urinary
bladder, and urethra (Fig. 3-69).
Kidneys
Our two kidneys are located against the posterior wall of the
abdominal cavity, on either side of the spine, at the level of the
superior lumbar vertebrae. Each kidney is the shape of a kidney bean and measures about 5 inches long, 2.5 inches wide,
and 1 inch thick. These organs are suspended in the abdominal
cavity by a fatty mass called the adipose capsule and a renal fascia, and are not well protected by bones, which is why they are
such vulnerable organs. Losing weight too rapidly can reduce
the size of the adipose capsule and change the position of the
kidneys. If they shift inferiorly, the ureters can develop kinks,
and eventually, if the urine cannot flow down to the urinary
bladder, the urine can back up and damage the kidneys.
Figure 3-69. Structures of the urinary
system.
Adrenal
gland
Right
kidney
Ureter
Urinary
bladder
Prostate
gland
Hepatic veins
Diaphragm
Inferior
vena cava
Abdominal aorta
Renal artery
Renal vein
Common iliac
vein
Common iliac
artery
Internal iliac
vein
Internal iliac
artery
External iliac
vein
Urethra
External iliac
artery
134 INTRODUCTION TO MASSAGE THERAPY
The functional part of the kidney is called the nephron, of which there are over a million in each kidney. They
filter the blood; reabsorb needed water, ions, and nutrients
from the filtered fluid; and secrete harmful substances from
the blood into the nephron fluid and thus into the urine.
Adequate amounts of water must be consumed for the urinary system to function properly.
Ureters
The ureters are tubes about 12 inches long and 0.25 inches
in diameter that carry urine away from the kidneys. They
have an inner lining of mucous membrane, but their outer
walls are made of overlapping layers of smooth muscle and
an outer connective tissue layer. Gravity and the peristaltic
contractions of the ureters propel urine through the ureters
toward the urinary bladder.
Urinary Bladder
The urinary bladder is a storage site for urine, located just
behind the pubic symphysis. It is made of three layers of
smooth muscle and has a mucous membrane lining of transitional epithelium. It can expand from its normal size of
about 2 inches long to a distended size of about 5 inches
long when full of urine.
that serve the kidneys. The blood traveling through the
kidneys is under a high pressure that forces water and dissolved substances through the capillary walls. Second, the
filtrate, or the solution that comes through the membrane,
undergoes reabsorption. All of the dissolved material is not
waste, so the body reabsorbs the substances that are useful,
such as amino acids to build proteins, ions to use in cellular functions, glucose to use for creating ATP, and water to
keep cells and tissues hydrated. Most of the substances must
be actively or passively transported out of the kidney and
back into the blood capillaries, but water passes through
via osmosis. The third step of urine formation is secretion,
which is how some additional ions, creatinine, and many
drugs, such as penicillin, are removed.
Excretion
Once the urine has been produced, it is excreted from the
body by the other structures of the urinary system. The
urine travels from the kidneys through a pair of tubes called
the ureters (YOO-rih-terz) to the urinary bladder. Urine
is stored in the bladder temporarily, and is carried to the
external environment through a tube called the urethra
(yoo-REETH-rah).
Regulation
Urethra
From the urinary bladder, the urethra carries urine to the
exterior of the body for elimination, called urination. An
involuntary smooth muscle sphincter at the exit of the urinary bladder closes the urethra when urine is being stored.
There is also a voluntary skeletal muscle sphincter farther
down the urethra that we control. When we contract the
skeletal muscle sphincter, urine flow is stopped, and when
we relax the sphincter, urine is excreted through the urethra
to the external environment.
Functions of the Urinary
System
The structures of the urinary system accomplish several
tasks. They filter the blood to remove chemical wastes and
excrete the wastes in the form of urine. The system regulates the volume of blood, pH of body fluids, and RBC
formation in red bone marrow. The kidneys control blood
volume (and thus blood pressure) by controlling how much
water is lost in the urine.
Urine Formation
The urinary system goes through a series of steps to eliminate chemical wastes in the form of urine. First, the passive
transport mechanism of filtration occurs in the capillaries
In the process of making urine, the complex structure and
functions of the kidney also regulate blood volume, chemical content of blood, pH of body fluids, and RBC formation.
Blood Volume
The reabsorption activity of the kidney moves water from
the kidney back into the blood capillaries via osmosis. The
amount of water reabsorbed in the kidneys is a homeostatic
mechanism that keeps the blood volume stable after water
is lost through the skin as perspiration, out the lungs as
water vapor, or out the digestive tract in the feces. The kidneys work at keeping blood volume constant despite widely
changing patterns of fluid intake.
Chemical Balance
Once the blood has been filtered in the kidneys, the filtrate
contains ions and other molecules that are necessary for cellular metabolism. Regulating the reabsorption of substances
is another homeostatic mechanism for maintaining chemical
balance in the blood and body fluids.
pH Balance
As mentioned in the cardiovascular system section, the pH
of blood is normally kept at 7.4. The body constantly creates
byproducts of cellular metabolism that affect pH levels, but
homeostatic mechanisms maintain a stable pH in body fluids.
The kidneys are the primary structures for regulating pH,
although respiratory activity can also change pH levels. The
Chapter 3 / Body Systems
kidneys can excrete bicarbonate ions and hydrogen ions, and
can create and reabsorb bicarbonate ions to change the pH.
135
Pineal
Red Blood Cell Formation
The kidneys are the primary structures that secrete erythropoietin, a hormone that stimulates RBC formation in the red
marrow of bones. A small amount is present in the blood all
the time, but when oxygen levels in blood are low, the kidneys
secrete extra erythropoietin to increase the production of RBCs.
Effects of Massage on the
Urinary System
The mechanical effects of massage result in more cellular and chemical waste to be excreted through the urine.
Massage encourages smooth muscle contraction of the urinary bladder to eliminate more urine as a reflexive response
of the parasympathetic nervous system to rest and digest.
Endocrine System
The endocrine system is a regulating control system of the
body. It is made up of several ductless glands and some
organs that are involved in other systems. Endocrine system hormones are secreted directly into the blood and
circulate through the body. The hormones have specific
effects on their target tissues to keep metabolic and developmental processes of the body functioning normally. They
work both antagonistically and cooperatively to maintain
homeostasis.
Structures of the Endocrine
System
The major endocrine structures are the pituitary (pih-TOOih-tair-ee), thyroid (THAHY-royd), parathyroid, adrenal
(a-DREE-nul), pineal (PAHY-nee-ahl), and thymus glands, as
well as parts of the hypothalamus, pancreas, ovaries, testes,
and placenta (Fig. 3-70).
Pituitary Gland
The pituitary gland is often called the master gland of the
body (Fig. 3-71). Located at the base of the brain, it secretes
six different hormones that stimulate other glands and
organs to act. In addition to its six secretions, it stores and
releases the two hormones secreted by the hypothalamus:
• Growth hormone (GH) primarily stimulates muscles
and long bones to grow and regulates blood sugar.
• Prolactin (PRL) is similar to GH, but only activates
milk production in the breasts.
Pituitary
Thyroid
Parathyroids
(posterior)
Thymus
Adrenal
Islets of
Langerhans
(in pancreas)
Ovaries
Te st e s
Figure 3-70. Structures of the endocrine system.
• Thyroid-stimulating hormone (TSH) regulates the
thyroid gland.
• Adrenocorticotropic hormone (ACTH) regulates the
adrenal gland.
• Follicle-stimulating hormone (FSH) promotes the
maturation of eggs, the production of estrogen, and
development of sperm production.
• Luteinizing hormone (LH) signals the ovary to
release an egg and produce progesterone or the testes to produce testosterone.
• Oxytocin, secreted by the hypothalamus, stimulates
contractions of the uterus and the milk “letdown”
reflex of new mothers.
• Antidiuretic hormone (ADH), secreted by the hypothalamus, promotes water retention in the kidneys.
Thyroid Gland
The thyroid gland is slightly larger than the other glands
and is located in the anterior neck area in two lobes
on either side of the trachea. Its hormones, including
136 INTRODUCTION TO MASSAGE THERAPY
Internal-external stimuli
Neurotransmitters
Hypothalamus
Hormones
feed back to
anterior pituitary
and hypothalamus
ADH
Oxytocin
Posterior
Breast
Uterus
Kidney
pituitary
Oxytocin
ADH
Prolactin
GH
FSH
LH
FSH
LH
Anterior
pituitary
Portal system
TSH
ACTH
Thyroid
Thyroid
hormones
Adrenal
Adrenocorticosteroids
Ovary
Breast
Bone and
soft tissues
Figure 3-71. Pituitary gland activity.
thyroxin and triiodothyronine, regulate metabolism and
reduce blood calcium levels by triggering calcium from the
blood to be deposited in the bones. The thyroid requires
iodine to produce its hormones; without enough dietary
iodine, the thyroid overworks and becomes enlarged, creating a goiter. Since iodine was added to table salt, goiters
are fairly rare.
Parathyroid Glands
There are at least four small, pea-shaped parathyroid
glands that are usually embedded in the posterior wall
of the thyroid. Their hormone, aptly called parathyroid
hormone, increases calcium levels in the blood by triggering the bones to release calcium into the blood when
calcium is needed. Parathyroid hormone also stimulates
vitamin D synthesis (which stimulates the uptake of calcium in the intestine) and promotes calcium retention in
the kidneys.
Progesterone
Te st e s
Corpus luteum
Testosterone
Estrogen
Adrenal Glands
The adrenal glands sit on the superior surface of the kidneys. The hormones they secrete include adrenal epinephrine (adrenaline), norepinephrine (noradrenaline),
glucocorticoids, and mineralocorticoids. The adrenal hormones promote sodium and water conservation; they also
help cope with long-term stress, reduce inflammation and
edema, and reduce pain. In addition, adrenaline cooperates
with the sympathetic nervous system to initiate the alarm
response.
Pineal Gland
The tiny pineal gland hangs from the roof of the third ventricle in the brain and is responsible for producing melatonin. Although not proven, melatonin is commonly known
to help the body recognize and move through sleep/wake
cycles. When nerves in the eyes are exposed to light, the
Chapter 3 / Body Systems 137
pineal gland is triggered to produce less melatonin. As night
falls and environmental light diminishes, the pineal gland
produces more melatonin.
Thymus Gland
The thymus gland, discussed in the lymphatic system section, is located posterior to the sternum and decreases in
size as we get older. It produces thymosin, which triggers
leukocytes to mature into T lymphocytes, special immune
cells that help the body recognize foreign substances.
Other Endocrine Organs
Parts of the hypothalamus, pancreas, ovaries, testes, and placenta are considered components of the endocrine system
because of their secretions.
The hypothalamus sits just above the pituitary gland and
controls its hormone release, giving them a close, cooperative
relationship. It produces ADH and oxytocin but immediately
stores them in the pituitary gland. Once the hypothalamus
stimulates the pituitary gland to release them, ADH causes
the kidneys to reabsorb more water instead of excreting it in
the urine, and oxytocin stimulates uterine contractions during childbirth and the initial milk letdown in the breasts.
The pancreas secretes glucagon and insulin, the hormones involved in metabolizing carbohydrates. Insulin is
also very important in stimulating fat and protein synthesis.
The ovaries produce the hormones estrogen and progesterone, and the testes produce testosterone. These hormones
are responsible for sexual maturation and development.
The placenta develops in the uterus during pregnancy.
It is the organ that serves as the intermediary between the
mother and the fetus, made of tissue from both. It provides
fetal nutrition, eliminates fetal wastes, and produces estrogen and progesterone. These hormones help maintain the
pregnancy by preventing contractions that can cause miscarriage, and they prepare the mother’s body for breastfeeding.
Effects of Massage on the
Endocrine System
The glands of the endocrine system help maintain homeostasis via hormones and other chemicals secreted into the
bloodstream. As massage increases circulation of blood and
lymph, the effectiveness of the endocrine system is enhanced.
Research has repeatedly shown that massage reduces levels
of cortisol and epinephrine, stress-related hormones.
offspring. The female reproductive system is slightly more
complex than the male reproductive system, and the structures perform very different activities.
Structures of the Female
Reproductive System
The many structures of the female reproductive system
include the ovaries, uterine tubes (fallopian tubes), uterus,
vagina, and mammary glands. The female reproductive
organs are located in pelvis, except for the mammary glands,
located in the breasts (Fig. 3-72).
Ovaries
The ovaries are the primary female sex organs that secrete
the sex hormones estrogen and progesterone. Within the
ovaries are immature egg cells that develop over time in
response to sex hormones. LH, secreted by the pituitary
gland, stimulates the ovaries to typically release one egg per
menstrual cycle.
Fallopian Tubes
The fallopian tubes receive the eggs from the ovaries and
transport the eggs to the uterus. Incidentally, fertilization
usually occurs in the fallopian tubes. To transport the egg,
the smooth muscles of the fallopian tubes use peristalsis
to encourage the egg to move toward the uterus, and ciliated cells along the lining of the tubes rhythmically sweep
toward the uterus.
Uterus
The uterus is the organ that serves as the incubator for the
growing fetus. It is constructed with three layers. The inner
layer is a lining of mucous membrane called the endometrium.
The thick middle layer, the myometrium, is made of smooth
muscle that expands to accommodate the growing fetus, and
rhythmically contracts to deliver the baby. The outer layer of
the uterus is a serous membrane called the perimetrium.
Vagina
The vagina is a muscular tube that connects the uterus to
the external environment. It provides a pathway for sperm
and becomes the infant’s birth canal during delivery.
Mammary Glands
The reproductive system is relatively inactive in humans
until puberty; then the overall function is to produce
The mammary glands are modified sweat glands that produce milk and release it through the nipple to provide nourishment to the infant. Estrogen and progesterone promote
breast development, PRL stimulates the initial production of
milk, and oxytocin stimulates the continued production of
milk as well as the release of the milk (letdown).
138 INTRODUCTION TO MASSAGE THERAPY
Sacrum
Ureter
Ovary
Fallopian
tube
Rectum
Uterus
Urinary bladder
Pubic symphysis
Urethra
Clitoris
Urethral orifice
Vaginal orifice
A
Abdominal
opening of
fallopian tube
Fallopian tube
Fimbria
Secondary
oocyte
Corpus luteum
of menstruation
Uterus
Perimetrium
(serosa)
Myometrium
Endometrium
(glandular mucosa)
Cervix
Vagina
Anus
Ovary
Cavity of uterus
Cervix
Vagina
B
Figure 3-72. Structures of the female reproductive system. (A) Sagittal view (provided by the
Anatomical Chart Co.) (B) Frontal view.
Chapter 3 / Body Systems 139
Pectoralis major
Intercostal
muscle
C
Figure 3-72. (continued) (C) Breast mammary gland.
Rib
Deep fascia
Fat pad
Alveolus
(Acinus)
Ductule
Contractile unit
Myoepithelial
cell
Secretory
cell
Lactiferous
(mammary) duct
Lactiferous sinus
(ampulla)
Nipple
(mammary papilla)
Nipple opening
Areola
Lobe
Suspensory ligament
of the breast
Functions of the Female
Reproductive System
The primary goal of the female reproductive system is to
reproduce. To reach that goal, the system must produce sex
hormones, produce and release ova (OH-vah), incubate the
growing fetus in a safe nurturing environment, deliver the
infant, and nourish the infant.
Sex Hormones
The hormones produced by the female reproductive system
include estrogen and progesterone. They are released by the
ovaries in varying amounts during the menstrual cycle. Estrogen
promotes maturation of the eggs and helps prepare the uterus
prior to implantation. Progesterone maximizes the ability of the
uterus to maintain pregnancy by promoting blood vessel and
gland formation in the uterine lining and inhibiting contractions
of the uterus to prevent miscarriage. There are some physical
changes that occur with the increased production of hormones
during the teen years: the breasts enlarge, the reproductive
organs enlarge, more body hair grows in the axillary and pubic
areas, increased amounts of fat are deposited in the subcutaneous layer, the pelvis widens, and the menstrual cycle begins.
Ova
ovary and mature over time. Ovulation is the release of a
mature egg from the ovary, stimulated by a hormone called
luteinizing hormone.
Maternal Reproductive System
Functions
Once an egg has been fertilized and has been implanted
in the uterine lining, the female reproductive system is
responsible for incubating the growing fetus in a safe, nurturing environment, delivering the baby, and nourishing
the baby.
Delivering the baby, also called parturition or birth,
is also a responsibility of the female reproductive system. During pregnancy, the smooth muscles of the uterus
increase in size to expand with the growing fetus and to
accomplish the delivery. In a normal pregnancy, the fullterm fetus is squeezed out of the uterus by strong, smooth
muscle contractions and through the vagina to the external
environment. The smooth muscles work very hard to deliver the baby, and most women are encouraged to contract
their abdominal muscles to reduce the size of the abdominal
cavity and help push the baby out.
The mammary glands in the breasts are specialized
sweat glands, as discussed in the integumentary system section. Once the baby is born, oxytocin stimulates the release
of milk to feed the baby.
Structures of the Male
Reproductive System
The male reproductive system includes the testes, ducts,
accessory organs, and external genitalia (Fig. 3-73).
Testes
There are two testes, each about 1.5 inches long and 1 inch
wide. Outside, they are encased in a fibrous connective tissue. Inside, they contain structures that form sperm and testosterone. The epididymis, where the sperm mature, is the
beginning of the delivery system for the sperm, and it starts
in the testes.
Ducts
Mature sperm travel through a series of ducts in their quest
for an ovum:
1. Epididymis
2. Ductus deferens (vas deferens)
3. Urethra
The eggs produced by the female reproductive system are
referred to as ova. They start out as immature cells in the
Smooth muscles in the ducts propel the sperm toward
the external environment with peristalsis.
140 INTRODUCTION TO MASSAGE THERAPY
Sagittal section
Sacrum
Ureter
Peritoneum
Prostate gland
Membranous
urethra
Ductus deferens
Pubic symphysis
Urinary bladder
Rectum
Seminal vesicle
Ejaculatory duct
Penis
External
urethral
opening
Epididymis
A
Figure 3-73. Structures of the male reproductive system. (A) Sagittal view.
Bulbourethral
gland and duct
External anal sphincter