Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5521_Библиотеки_им_академика_М_И_Перельмана.pdf
Chapter 3 / Body Systems
61
water from the side that has a lower concentration of these
molecules to the side with the higher concentration. The
addition of water effectively lowers the concentration of
these chemicals. Most people recognize that oil and water
do not mix. Because of its molecular structure, water is not
soluble in oil or fat. Although water is not a fat-soluble molecule and it would typically be repelled by the lipid bilayer,
water moves through the semipermeable cell membrane.
Osmosis is the specific passive transport mechanism by
which water crosses the membrane through channel proteins to balance concentrations on either side of the membrane. The best way to remember which direction water
moves through the membrane is the phrase “Water follows
concentration” (Fig.3-4B). If there is a higher concentration
of solutes outside the cell, water will move out of the cell
in an attempt to balance the solutions on either side of the
membrane. Conversely, if there is a higher concentration of
solutes inside the cell, water will flow into the cell to achieve
a balance.
Solutions possess tonicity, the amount of dissolved particles in the solution. A solution whose tonicity is the same
as that within our cells is called an isotonic (AHY-soh-TAHNik) solution. When an isotonic solution surrounds our cells,
water levels within the cells do not change. Intravenous
fluids such as Ringer’s lactate and 0.9% saline solution are
isotonic solutions that have the same concentrations as our
cells, so when they are injected into the bloodstream, the
cells do not absorb or eliminate water.
When solutions that do not have the same concentration as dissolved substances in our cells are introduced into our bodies, the water content within the cell
is adjusted to maintain a balance on either side of the cell
membrane. This homeostatic mechanism is used therapeutically when medical professionals give patients intravenous fluids. Hypotonic (HAHY-poh-TAHN-ik) solutions
have a lower osmotic pressure (are less concentrated)
than the fluid inside our cells and result in water moving
into the cell by osmosis. Conditions of dehydration are
sometimes treated with hypotonic solutions, which force
water to move into and rehydrate the cells. Hypertonic
(HAHY-per-TAHN-ik) solutions are used to treat edema,
which is swelling due to an excess of fluid between the
cells. The hypertonic solution, often 3% to 5% sodium
chloride solution, causes water to move toward the higher
concentration, outside the cells, and into the bloodstream
(Fig. 3-5). The excess fluid is then processed by the kidneys and excreted asurine.
Passive Transport Mechanism of
Facilitated Diffusion
Facilitated diffusion is a special form of passive membrane
transport. Molecules that are too large or that would be
repelled by the lipid bilayer use carrier proteins scattered
along the membrane as trap doors that allow them to pass
through easily. A carrier protein molecule will attach to the
oversized molecule, possibly altering its shape or enveloping
it, and will pull it through the membrane (see Fig. 3-4C). A
good example of facilitated diffusion is the passage of glucose through a cell membrane. Glucose is a large molecule
used for cellular metabolism that is not fat soluble but can
use a carrier protein to get through the membrane.
Passive Transport Mechanism of
Filtration
Filtration is another mode of passive transport whereby
water and dissolved substances (solutes) are pushed through
a membrane by fluid pressure. This process moves the solution from an area of higher pressure to an area of lower
pressure, again part of the homeostatic process of keeping
a balance on either side of the membrane (see Fig. 3-4D).
An example of filtration is urine formation in the kidneys,
where the fluid pressure in the blood capillaries is higher
than that in the kidney tubules. The difference in pressures
forces the solution out of the blood capillaries and into the
kidney tubules for elimination.
Figure 3-5. Effects of osmosis
on red blood cells in different
concentrations: isotonic, hypotonic,
and hypertonic solutions.
Normal
(isotonic)
solution
Hypotonic
solution
Hypertonic
solution
62 INTRODUCTION TO MASSAGE THERAPY
Active Transport Mechanisms
Active transport processes require ATP as a source of energy
to move chemicals through a membrane. There are several
different situations in which molecules cannot be transported passively and energy must be used to move them:
• Molecules that are too large to pass through the
membrane and cannot take advantage of carrier
proteins
• Molecules that have to move against the concentration gradient, or from an area where they are lower
in concentration to an area of higher concentration
• Molecules that are not fat soluble and cannot take
advantage of carrier proteins
Solute pumping is the active transport process that uses
energy from the breakdown of ATP to help protein carriers
pull amino acids, some sugars, and many ions through the
membrane.
Bulk transport is an active transport process that uses
energy to package molecules and carry them across the
membrane. Exocytosis is the bulk transport mechanism that
takes cellular products from the inside of the cell to the outside of the cell. The products in the cytoplasm are packaged
in a sac, the sac is incorporated into the membrane, and the
contents of the sac are released into the extracellular fluid
(the fluid that surrounds the cell). Mucus is released outside
the cell via exocytosis (Fig. 3-6B).
Endocytosis is another bulk transport mechanism that
works in the opposite direction of exocytosis. Substances
outside the cell are engulfed, transported inside the cell, and
usually digested by enzymes (Fig. 3-6A). Bacteria and dead
body cells are managed by the specific form of endocytosis
called phagocytosis (FAY-goh-sahy-TOH-sis). When liquids that
contain dissolved proteins or fats cannot diffuse through a cell
membrane, pinocytosis (PEE-noh-sahy-toh-sis) is the special
form of endocytosis that moves them into the cell. The prefix
“exo-” means to “move out” and “endo-” means to “move in.”
The cell membrane is a very active component of the
cell that is involved in homeostasis, but there are a number
of other structures that are equally important.
Cytoplasm
The cytoplasm is the liquid substance inside the plasma
membrane that houses most of the cellular activity, composed of a gel-like substance called cytosol that contains
nutrients, minerals, enzymes, and cytoplasmic organelles
suspended in it. The cytoplasm makes up 50% of the cell’s
volume and contains everything necessary for protein synthesis as well as the enzymes for building and breaking
down molecules (Fig. 3-7).
Cytoplasmic Organelles
The cytoplasmic organelles are the metabolic machinery of
the cell that keeps the cell alive and dynamic. Organelles,
including the nucleus, nucleolus, ribosomes, endoplasmic
reticulum, mitochondria, Golgi apparatus, lysosomes, and
Figure 3-6. Bulk transport
mechanisms. (A) Endocytosis.
(B) Exocytosis. (Reprinted from
Premkumar K. The Massage
Connection: Anatomy & Physiology.
2nd ed. Baltimore: Lippincott
Williams & Wilkins, 2004.)
Bacterium A
Cytoplasm
Cell membrane
Golgi
apparatus
Endocytosis
Lysosomes
Phagosome
Exocytosis
Phagosome fuses
with lysosome
Secondary
lysosome
B
Chapter 3 / Body Systems
63
Human cell
Microvilli
Cell
membrane
Mitochondrion
Nuclear
membrane
Nucleus
Nucleolus
Centriole
Ribonucleic
acid
Ribosomes
Chromatin
Endoplasmic
reticulum
Figure 3-7. Components of a cell. (Asset provided by Anatomical
Chart Co.)
Plasma
membrane
Golgi
apparatus
Cytosol
Lysosome
centrioles, are all suspended in the cytosol. They have different shapes and functions, and any disruption of their activity
will affect the homeostasis of the cell.
The largest organelle is the nucleus (NOOK-lee-us),
located somewhere near the center of the cell. The nucleus
is the control center for the cell. It is enveloped in a doublelayered membrane that is perforated with pores that allow
some molecules to pass between the nucleus and the cell.
Within the nucleus is a small, spherical structure called
a nucleolus (nook-lee-OH-lus) that builds the molecules
required for protein synthesis. Occasionally, cells have two
nucleoli, if there is a heavy demand for proteins. Among
other molecules, the nucleus contains DNA, which is necessary for building all proteins. Proteins are necessary components for building cell structures and carrying out cell
functions including cell reproduction.
Outside the nucleus are many organelles suspended in
the cytosol that carry out other cellular operations. There
are many ribosomes (RAHY-boh-zohmz) that serve as the
factory where proteins are put together with the help of
enzymes. Some ribosomes are suspended in the cytosol,
and some are attached to the rough endoplasmic reticulum. Within the cytosol, there are one or more endoplasmic
reticula, which are networks of tubes that modify and direct
newly made proteins to other cell organelles. The endoplasmic reticula also manufacture membrane lipids, synthesize
and break down cholesterol, and metabolize fat.
Also within the cytosol are several elongated oval organelles called mitochondria (MAHY-toh-KON-dree-uh). As the
powerhouses of cellular function, mitochondria break down
nutrients and release energy. Some of the energy is released
as heat, but most of the energy is converted to ATP molecules through the process of cellular respiration, which
is the primary source of energy for cellular metabolism.
Because oxygen is required for cellular respiration, the process is sometimes referred to as aerobic respiration. Without
oxygen, cells will suffer and eventually die. Generally, the
more active the cell, the more oxygen and energy it requires
and the more mitochondria it will have. Muscle cells that get
regular exercise increase their numbers of mitochondria to
generate more energy for the muscle cell.
The Golgi apparatus is an organelle that resembles a
stack of flattened sacs that are suspended in the cytosol.
Serving as a sort of packaging plant, the sacs receive proteins
by way of the endoplasmic reticulum. The proteins are modified, sorted, and gathered in sacs until the sacs swell to the
point that they pinch themselves off and become secretory
vesicles. The final destination of the vesicles depends on their
contents. Vesicles that contain substances destined for the
blood or a body tube fuse with the plasma membrane and
expel their contents outside the cell, illustrated above as the
active transport mechanism of exocytosis (see Fig. 3-6). Some
vesicles contain proteins and phospholipids that are taken to
the plasma membrane and become part of its structure.
Some of the smaller cytoplasmic organelles include lysosomes (LAHY-soh-zohmz) and centrioles (SEN-tree-ohlz).
Varied in size, lysosomes are essentially vesicles containing
digestive enzymes. Inside the cell, lysosomes engulf and
digest cellular waste, bacteria, and unwanted foreign substances. Centrioles are rod-shaped organelles located close
to the nucleus that aid in chromosome separation during
cell division. Some cells have cilia, which are small, hairlike
extensions of the plasma membrane on the outside of the
membrane that help sweep objects past the cell. They are
located in respiratory and reproductive tracts to push mucus
or an egg in a specific direction. An extra-long form of cilium
called a flagellum (fluh-JEL-uhm) is a whiplike extension that
propels the cell itself. The human sperm cell has a single flagellum that moves the sperm from one place to another.
The many structures of a cell, with their many activities, work cooperatively to maintain the life cycle of the
entire cell. As part of the whole picture, cells are the tiny
building blocks that make up tissues, organs, organ systems,
and the organism.
Tissues
A tissue is a group of cells that have a similar structure and
work together to accomplish a similar function. There are
four basic tissue types, each with a unique structure, a specific function, and its own rate of healing. Structure and
function are closely related, following the rule of “form
follows function.” Much of healing depends on nutrient
delivery and waste removal, so the healing rate tends to
64 INTRODUCTION TO MASSAGE THERAPY
be related to the tissue’s blood supply. Epithelial (EH-pihTHEE-lee-uhl) tissue, connective tissue, muscle tissue, and
nervous tissue are woven together within the body to provide coverings, support, movement, and control, respectively (Table 3-1). All tissues produce hormones. For example,
skin makes vitamin D, fat makes leptin (to regulate appetite), bone makes osteocalcin (to stimulate insulin and testosterone production) and growth factors, and kidneys
make erythropoietin.
Epithelial Tissue
Epithelial tissue, or epithelium (EH-pih-THEE-lee-uhm),
covers the outside of our bodies, lines cavities and tubes
inside our bodies, and forms the glands in the body.
Protection, absorption, filtration, excretion, and secretion
are functions specific to individual types of epithelia. All epithelial tissues share some common characteristics:
• Epithelial cells fit closely together without many
gaps, forming epithelial tissue that is a continuous
sheet of tightly joined cells.
• The top surface of epithelium is unattached and
exposed to an open space (or was at some point during its development), either the environment or an
internal body cavity.
Tissue Type Function Location
Epithelium Lines
Covers
Produces
secretions
Connective
tissue
Muscle tissue
Cardiac Contracts the
Skeletal Moves and
Connects
Protects
Supports
heart
stabilizes
Skin, organs,
glands
Blood, bone,
cartilage,
fascia, fat,
ligament,
lymph, tendon
Heart
Attached to
skeleton
• The bottom surface of epithelium lies on a basement membrane, which is a material secreted by the
epithelial cells and has no structure.
• There are no blood vessels in epithelia (they are avascular), so they rely on diffusion of nutrients through
the basement membrane.
Epithelia are classified according to the arrangement and
shape of the cells within the tissue. By arrangement, epithelia are classified by the number of layers of cells. Simple epithelium is formed with only a single layer of cells. Stratified
epithelium has more than one layer of cells in its structure,
making it more durable. By cell shape, the classifications
include squamous (flat), cuboidal (cube-like), and columnar
(column-like). The different types of epithelia are generally
identified by their structural layers and cell shape (Fig. 3-8):
• Simple squamous—found in air sacs of the lungs,
walls of capillaries, and serous membranes
• Simple cuboidal—in glands and their ducts
• Simple columnar—in mucous membranes and the
lining of the digestive tract
• Pseudostratified columnar—in parts of the respiratory tract
• Stratified squamous—in the mouth, outer portion
of skin, and esophagus
• Stratified cuboidal—not very common, but found in
the ducts of large glands
• Stratified columnar—not very common, but found
in the ducts of large glands
• Transitional—highly modified epithelium found in
the lining of the urinary bladder, ureters, and part of
the urethra
There is a special type of epithelium that does not have lining
or covering functions. Glandular epithelium develops into
glands, which produce and secrete fluids that contain special
proteins. Exocrine (EK-soh-krihn) glands use ducts to deliver
their secretions to the top surface of the epithelium. Sweat
and oil glands are examples of exocrine glands that release
their secretions outside our bodies. The liver and the pancreas are exocrine glands that release their secretions inside our
bodies. Endocrine (EN-doh-krihn) glands, which also develop
from glandular epithelium, are ductless, so their secretions
diffuse directly into the bloodstream. The thyroid, adrenal,
and pituitary glands are examples of endocrine glands.
Smooth Produces
peristalsis
Nervous
tissue
Communication
and control
Organs
Brain, spinal
cord, nerves
Connective Tissue
Connective tissue serves many different functions and is
located throughout the body. It connects one part of the
body to another, it provides a gentle support structure to
various parts of the body, it protects internal organs, and it
Chapter 3 / Body Systems
Esophagus
(stratified squamous)
65
Stomach
(simple squamous)
Epithelium
Mucosa
Submucosa
Muscularis
externa
Epithelium
Mucosa
Submucosa
Muscularis
externa
Serosa
(pseudostratified columnar)
Trachea
Small intestines
(simple columnar)
Cilia
Epithelium
Mucosa
Submucosa
Tracheal
cartilage
Smooth
muscle
Blood
vessels
Villi
Epithelium
Mucosa
Submucosa
Muscularis
externa
Serosa
Urinary bladder
(transitional)
Epithelium
Smooth muscle bundles
and interstitial connective
tissue
Serosa
Figure 3-8. Examples of epithelia.
Palm
(simple cuboidal)
Stratified
squamous
keratinized
epithelium
Sweat
glands
Papillary
layer of the
dermis
66 INTRODUCTION TO MASSAGE THERAPY
serves as a defensive barrier against disease. It is composed
of living cells suspended in their own secretion of a nonliving structural material called the ground substance. The
ground substance is made up of water, protein fibers, and
sometimes hard minerals, collectively called the extracellular matrix. The consistency of the matrix can range from
fluid to solid, depending on the density of living cells in
the matrix, the kinds and quantities of protein fibers incorporated in the matrix, and the amount of minerals. The
matrix can provide a pathway for blood vessels and nerves.
Figure 3-9 illustrates connective tissues and their locations
in the body.
The protein fibers secreted by the cells and incorporated into the extracellular matrix that provide strength,
elasticity, and structural support to varying degrees include
collagen (CAHL-uh-jen), elastin (ee-LASS-tin), and reticular
(reh-TIK-yoo-lahr) fibers. Collagen fibers are white protein
Figure 3-9. Examples of connective
tissue in different locations in
thebody.
Ligaments
fibers that provide strength in structures such as the bones
and tendons. Elastin is a yellow protein fiber with an elastic
or stretchy quality that allows structures such as the vocal
cords and walls of large blood vessels to return to their original length after being stretched. Reticular fibers are threads
of a few collagen fibers that create a delicate, mesh-like web
material often found in areolar tissue. The reticular fibers
support large numbers of free blood cells in the spleen,
lymph nodes, and liver. Figure 3-10 shows the difference
between collagen and elastin protein fibers in the extracellular matrix of areolar connective tissue.
The density and arrangement of any one or a combination
of these protein fibers contribute to the strength and elasticity
of a particular tissue. Dense fibers tend to result in stronger,
harder connective tissues. The more loosely these fibers are
packed in the matrix, the more pliable the tissue. Fiber arrangements can be random or aligned. When the fibers are aligned
Tendons
Muscle
Bones
Blood vessels
Adipose tissue
Cartilage
Chapter 3 / Body Systems
67
Collagen fibers
Areolar connective tissue
Figure 3-10. Collagen and elastin fibers in an extracellular matrix.
Elastin fiber
in the same direction, the tissue resembles ropelike cords, as in
the tendons and ligaments. Scar tissue has a random arrangement and has a patchwork-like quality. Connective tissue can
be categorized into four groups: hard, fibrous, soft, and liquid.
Figure 3-11 illustrates the four types of connective tissues.
Hard Connective Tissue
The hard connective tissues are very firm and not very pliable, and some contain hardened minerals that further solidify their structure. The two forms of hard connective tissue
in our bodies include cartilage and bones.
Cartilage
Cartilage is a form of hard connective tissue that is firm,
smooth, and bendable. It is composed of living chondrocytes
(KON-droh-sahytz), or cartilage cells, suspended in a nonliving extracellular matrix that contains collagen and elastin
protein fibers. It functions as a shock absorber that can bear
mechanical stress without permanent distortion and reduce
friction between moving parts, as in the knee joint. Cartilage
can also be used as a material for structural support, as in
the outer ear. Cartilage is avascular, which makes it slow to
heal after injury. It can only receive nourishment via diffusion
from capillaries in the adjacent tissues or from the synovial
fluid that bathes and lubricates freely movable joints. While
temporary cartilage forms the fetal skeleton and is later ossified and converted to bone, permanent cartilage remains
throughout life. The three major types of cartilage are hyaline cartilage, fibrocartilage, and elastic cartilage (Table 3-2).
Adipose tissue
(soft)
Areolar
(soft)
Collagen
fiber
Cell
Fat-filled cells
Blood (liquid)
Red blood
cells
Channel (for nerves
and blood vessels)
Bone cells
Bone
(hard)
Collagen
bundles
Cells
Muscle
cells
Figure 3-11. Examples of the four types of connective tissue: soft, liquid, hard, and fibrous.
Tendon
(fibrous)
Cartilage
(hard)
68 INTRODUCTION TO MASSAGE THERAPY
Cartilage Characteristics Examples
Hyaline Strong, not very flexible Costal cartilage
Hyaline cartilage
(costal cartilage)
Fibrocartilage Strongest Intervertebral discs
Elastic Most flexible Outer ear
Fibrocartilage
(intervertebral discs)
Elastic cartilage
(external ear)
Hyaline cartilage is the most common form of permanent
cartilage and provides strength and shock absorption but not
much flexibility. It appears white or whitish blue because of its
avascularity and the predominance of white collagen protein
fibers. It is found where two bones come together and need
some padding, for example, where the ribs contact the sternum
and at the growth zones at the ends of long bones. Hyaline cartilage also provides a structural framework in the walls of large
respiratory passages that go from outside the body to the lungs,
including the nose, trachea, and bronchi.
Chapter 3 / Body Systems
69
Elastic cartilage has an abundance of elastic fibers,
which give it a yellowish color and make it the most flexible type of cartilage. It can be bent and return to its normal shape, providing a structural framework for parts of the
body that are subjected to higher amounts of movement,
such as the external part of the ear, the ear canal, the eustachian tube, and the epiglottis.
Fibrocartilage has dense collagen fibers surrounding rows
or groups of chondrocytes, making it extremely resilient.
Providing a cushion between bones that are only slightly movable, fibrocartilage is found between adjacent vertebrae (bones
in the spine) and in the sutures between the cranial bones.
Bone
Bone is the other form of hard connective tissue. Calcium
and phosphate salts that accompany the dense collagen
fibers in the extracellular matrix create the hardness of bone.
There are three different kinds of living cells suspended in
the matrix of bone: osteoblasts (AHS-tee-oh-blastz), or boneforming cells; osteocytes (AHS-tee-oh-sahytz), or mature
bone cells; and osteoclasts (AHS-tee-oh-klastz), or bonedestroying cells. Figure 3-12 shows the difference between
the matrix of bone and the matrix of hyaline cartilage.
Bones are much more than a compilation of proteins
and minerals. Their structure is a highly organized series
of bundles of osteocytes and blood vessels. Because of its
high vascularity, bone heals quickly, relative to other tissues.
Bone, which is the main component of the skeletal system,
has many functions:
• Bones are the main storage place for calcium and
other ions.
• Bones act as a lever system for converting muscle
contraction into movement.
• Blood cells are formed inside many bones.
• Bones protect soft tissue structures in the body.
Fibrous Connective Tissue
Fibrous connective tissues, sometimes called dense connective
tissues, are found as tendons, ligaments, and scar tissue. Most of
the protein fibers in the extracellular matrix are collagen fibers
that are all aligned in the same direction, giving the fibrous connective tissues a cord-like structure that is strong and flexible.
Tendons connect muscles to bones and, as part of the
muscle–tendon (musculotendinous) unit, create skeletal
movement. Almost every muscle has at least one tendon
attached to it, and some muscles have more than one tendon. Because the tendons themselves do not actively contract or relax, they vary in tension, depending on the activity
of the muscles to which they attach. For example, a tendon
attached to a muscle that is working against a lot of resistance will feel tight and not very pliable, like an elastic band
that has been stretched almost to its limit. A tendon attached
to a muscle that is relaxed will feel looser, like a rubber band
lying on a table. Specialized tendons that are broad and flat
called are called aponeuroses (AP-poh-nur-OH-seez). They
provide attachment for broad muscles to connect to bone or
for one set of muscles to connect toanother.
As a form of fibrous connective tissue, tendons have
parallel collagen fibers that are dense and regular. The dense
arrangement and poor blood supply make it difficult for the
nutrient–waste exchange to occur. Because this exchange
occurs mostly through diffusion from the surrounding tissues, injured tendons heal slowly.
Ligaments are fibrous connective tissue structures
that connect bones to bones at a joint. They stabilize and
strengthen the joints of the body that must withstand great
mechanical force, such as the knee and the hip. As in tendons,
most of the protein fibers are dense, regular, parallel strands
of collagen. Ligaments are more flexible than tendons because
there are more elastin fibers and the proportion of ground
substance to protein is larger. Ligaments remain tight despite
movement or various states of contraction and are more
Figure 3-12. Hard connective tissue
matrix: hyaline cartilage and compact
bone.
Matrix Chondrocytes Osteocytes
Hyaline cartilage Compact bone
Matrix
70 INTRODUCTION TO MASSAGE THERAPY
difficult to palpate because of their location within joints.
Because of the minimal blood supply to the ligaments at their
attachment sites, the healing process is very slow.
Scar tissue is a special kind of fibrous connective tissue
that forms when tissues are injured. It is unique because,
unlike those in tendons and ligaments, the collagen fibers are
not arranged in a parallel pattern. Because of the abundance
of dense and irregular collagen fibers, scar tissue is strong but
not as pliable as normal, healthy tissue. Serving as a replacement for other injured tissue, it cannot perform the functions of the tissue it replaces, and its blood supply is minimal.
Extensive scarring can restrict normal movement, reduce or
prevent normal circulation of blood and lymph, and impede
or even prevent injured tissue from functioning properly. The
structure of scar tissue depends on where the injury occurs,
but it usually contains the same components as the original
tissue, accompanied by an abundance of extra collagen fibers.
Soft Connective Tissue
Soft connective tissues are also called loose connective tissues. They have more living cells and fewer protein fibers in
their matrix and are highly vascular, giving them a relatively
fast healing rate.
Areolar (ah-REE-oh-lahr) tissue is a form of soft connective tissue that is highly vascular, delicate, and somewhat
resistant to stress. Phagocytes, living cells that engulf bacteria or cellular debris, are present in the matrix, accompanied
by few collagen and elastin fibers. Found just below the skin,
in membranes around blood and lymph vessels, around
organs, and between muscles, areolar tissue cushions and
protects the structures it surrounds.
Adipose tissue, commonly called fat, is basically areolar
tissue with adipose cells suspended in the matrix. Adipose cells
can synthesize fat and store it as a large droplet of oil. When
the body needs a source of energy, it can use fat released by
adipose cells. Besides its function as a source of energy, adipose
tissue acts as a thermal insulator. Heat is not conducted well
through the fat, which means that if there are different temperatures on either side of the adipose tissue, those temperatures
will be maintained. Adipose tissue also provides padding and
protection for organs in its locations just beneath the skin in the
superficial fascia, around organs, between muscles, in the marrow of the long bone shafts, and in the breasts and hips.
Liquid Connective Tissue
Blood and lymph are sometimes called liquid connective
tissues because they have living cells suspended in a nonliving matrix and they “connect” different parts of the body.
Technically, however, neither blood nor lymph has an extracellular matrix that is secreted by the living cells. Moreover,
blood has protein fibers present in the matrix only during the
process of blood clotting. Blood flows through the blood vessels of the cardiovascular system, and lymph flows through
the lymphatic vessels in the lymphatic system. Blood and
lymph are described in more detail in the sections on the cardiovascular system and the lymphatic system, respectively.
Muscle Tissue
Tissues are a group of cells with similar structure and function. Muscle tissue is a group of muscle cells that are grouped
together with blood vessels and packaged with connective
tissue in a specific organization, more commonly called a
muscle . These cells have an elongated shape and are sometimes referred to as muscle fibers. Muscle cells have the
special ability to contract and relax, resulting in their primary
function of creating movement. Skeletal, cardiac, and smooth
muscle tissues are the three types of muscle tissue that have
slightly different characteristics and arrangements. Some have
striations (strahy-AY-shunz), which are microscopic structural features that look like stripes. Some muscle cells contain
more than one nucleus, and some muscle cells form branching networks of cells. The control mechanism for muscle
cells can also differ. Some are involuntary, meaning that they
contract without our conscious effort, and others are voluntary, which means that we have to consciously make an effort
to contract the muscle to create movement. Table 3-3 characterizes the different types of muscle tissue. This section of
the body systems chapter briefly introduces and compares
the different kinds of muscle tissue. There is a comprehensive
discussion of skeletal muscle tissue below in this chapter.
Skeletal Muscle
Skeletal muscle is tissue that attaches to the skeleton. The
cells are long and cylindrical with multiple nuclei and heavy
striations. Skeletal muscle tissue is under voluntary control,
meaning that we consciously make skeletal muscles contract
to move our bodies. When actively contracted, skeletal muscles are shortened and the muscles cells are closer together.
As a result, blood vessels are constricted, and the delivery
of nutrients and elimination of cellular metabolic waste is
limited. Healthy muscles at their normal resting length have
more space between the cells and the exchange of oxygen,
nutrients, and waste is more efficient. Skeletal muscle tissue
is responsible for producing body movement and holding our
bodies up against the force of gravity. Simply, gravity is the
force that pulls us to the earth, and except when we are lying
down, we use skeletal muscles to hold ourselves upright.
Massage deals with movement, restriction of movement, and restoration of health to the skeletal muscle system. Understanding skeletal muscle tissue and how it functions
is fundamental to massage.
(tense) skeletal muscles by using the help of the nervous system to stop triggering muscles to contract. Once the muscles
stop receiving signals from the nervous system to contract,
they can relax, and then other massage techniques can help
return skeletal muscles to their normal resting lengths.
Using massage to return skeletal muscles to their normal
Massage can relax hypertonic