Transcript Skeletal, Muscular, and Integumentary Systems

Skeletal, Muscular, and Integumentary Systems
• The explosive speed
needed for speed
skating comes from a
well-developed
muscular
Skeletal, Muscular, and Integumentary Systems
The Skeletal System
• To retain their shapes, all organisms need some type
of structural support
• Single-celled organisms have a cytoskeleton that
provides structural support
• In multicellular animals, support is provided by some
form of skeleton, including the external exoskeletons
of arthropods and the internal endoskeletons of
vertebrates
• The human skeleton is composed of a type of
connective tissue called bone
– Bones and other connective tissues, such as
cartilage and ligaments, form the skeletal system
The Skeletal System
• Scientists can infer a lot about the behavior
of extinct species by studying fossil bones
and reconstructing skeletons
• The human skeleton also contains important
clues
– The shape of your hip bones shows that you walk
upright on two legs
– The structure of the bones in your hands,
especially your opposable thumbs, indicates that
you have the ability to grasp objects
– The size and shape of your skull is a clue that you
have a well-developed brain
The Skeleton
• The skeletal system has many important functions
• The skeleton supports the body, protects internal
organs, provides for movement, stores mineral
reserves, and provides a site for blood cell formation
• The bones that make up the skeletal system support
and shape the body much like an internal wooden
frame supports a house
– Just as a house could not stand without its wooden frame, the
human body would collapse without its bony skeleton
• Bones protect the delicate internal organs of the
body
– For example, the skull forms a protective shell around the brain,
and the ribs form a basketlike cage that protects the heart and
lungs
The Skeleton
• Bones provide a system of levers on which
muscles act to produce movement
– Levers are rigid rods that can be moved about a fixed
point
• In addition, bones contain reserves of
minerals, mainly calcium salts, that are
important to many body processes
• Finally, bones are the site of blood cell
formation
– Blood cells are produced in the soft marrow tissue
that fills the internal cavities in some bones
SKELETON
• Human body contains 206 bones
• Human skeleton is an internal structure referred to as a
Endoskeleton
• Bones:
– Support the muscles and organs
– Give shape and structure to the body
– Store calcium and phosphorous which are important
minerals used by the body in certain metabolic processes
– Internal portions of certain bones manufacture blood cells
– Protect delicate internal organs
• Cranium (skull): protects the brain
• Ribs: curved bones that form a cage to protect the heart and lungs
The Skeleton
• There are 206 bones in the adult human
skeleton
• These bones can be divided into two parts:
– Axial skeleton: supports the central axis of
the body
• Consists of the skull, the vertebral column,
and the rib cage
– Appendicular skeleton:
• The bones of the arms and legs, along with
the bones of the pelvis and shoulder area
SKELETON STRUCTURE
• Composed of two parts:
– Axial skeleton: consisting of about 80 bones,
including the spine, ribs, sacrum, sternum,
and cranium
– Appendicular skeleton: contains 126 bones,
including the bones of the arms, legs, pelvis,
and shoulders
The Human Skeleton
• The skeleton
supports the body
• The human skeleton
is divided into two
parts:
– Axial skeleton
– Appendicular skeleton
The Human Skeleton
Structure of Bones
• It is easy to think of bones as nonliving
– After all, most of the mass of bone is
mineral salts—mainly calcium and
phosphorus
• However, bones are living tissue
– Bones are a solid network of living cells
and protein fibers that are surrounded by
deposits of calcium salts
Structure of Bones
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The figure at right shows the
structure of a typical bone
The bone is surrounded by a
tough layer of connective tissue
called the periosteum
Blood vessels that pass through
the periosteum carry oxygen and
nutrients to the bone
Beneath the periosteum is a
thick layer of compact bone
– Although compact bone is
dense, it is far from being solid
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Running through compact bone
is a network of tubes called
Haversian canals that contain
blood vessels and nerves
Structure of Bones
• Bones are a solid
network of living cells
and protein fibers that
are supported by
deposits of calcium
salts
• A typical long bone
such as the femur
contains spongy bone
and compact bone
• Within compact bone
are Haversian canals,
which contain blood
vessels
BONE STRUCTURE
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Bones are made up of both organic and inorganic material
Internal structure of long bones (arms/legs)
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Periosteum: outer membrane of the bone which contains a network of blood vessels that supplies living
bone cells with oxygen and nutrients and carries away carbon dioxide
Compact bone:
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Under the periosteum
Hard material
Composed of rings of mineral crystals and protein fibers
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Osteocytes:
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Haversian Canal:
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Channel in the center of each mineral ring in the Compact Bone containing nerves and blood vessels
Spongy bone:
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Living bone cells interspersed throughout the mineral rings of the Compact Bone
Connective tissue interior to the Compact Bone and at end of long bones
Lacy structure adds strength to the bone without adding weight
Bone marrow:
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Red:
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Consist of blood vessels, fibers, cells
Manufactures erythrocytes and white blood cells
Found in spongy bone /ends of long bones/ribs/vertebrate/sternum/pelvis
Yellow
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Consist mostly of fat cells
Serves as energy reserve
Fill shafts of the long bones
Structure of Bones
Structure of Bones
• A less dense tissue known as spongy bone
is found inside the outer layer of compact
bone
– It is found in the ends of long bones and in the
middle part of short, flat bones
• Despite its name, spongy bone is not soft
and spongy; it is actually quite strong
– Near the ends of bones where force is applied,
spongy bone is organized into structures that
resemble the supporting girders in a bridge
• This latticework structure of spongy bone helps to add
strength to bone without adding mass
Structure of Bones
• Osteocytes, which are mature bone cells, are
embedded in the bone matrix
• Two other kinds of bone cells—osteoclasts and
osteoblasts line the Haversian canals and the
surfaces of compact and spongy bone
– Osteoclasts break down bone
– Osteoblasts produce bone
• Although we stop growing in our late teens, our
bones are continuously remodeled through the
activity of osteoclasts and osteoblasts
Structure of Bones
• Within bones are cavities that contain a
soft tissue called bone marrow
• There are two types of bone marrow:
– Yellow:
• Made up primarily of fat cells
– Red:
• Produces red blood cells, some kinds of white
blood cells, and cell fragments called platelets
Development of Bones
• The skeleton of an embryo is composed almost
entirely of a type of connective tissue called
cartilage
• The cells that make up cartilage are scattered in a
network of protein fibers including both tough
collagen and flexible elastin
• Unlike bone, cartilage does not contain blood
vessels
– Cartilage cells must rely on the diffusion of
nutrients from the tiny blood vessels in
surrounding tissues
• Because cartilage is dense and fibrous, it can
support weight, despite its extreme flexibility
Development of Bones
• Cartilage is replaced by bone during the
process of bone formation called ossification
– Ossification begins to take place up to seven months
before birth
• Bone tissue forms as osteoblasts secrete
mineral deposits that replace the cartilage in
developing bones
• When the osteoblasts become surrounded
by bone tissue, they mature into osteocytes
Development of Bones
• Many long bones, including those of the
arms and legs, have growth plates at either
end
– The growth of cartilage at these plates causes the
bones to lengthen
– Gradually, this new growth of cartilage is replaced
by bone tissue, and the bones become larger and
stronger
– During late adolescence or early adulthood, the
cartilage in the growth plates is replaced by bone,
the bones become completely ossified, and the
person “stops growing”
Development of Bones
• In adults, cartilage is found in those
parts of the body that are flexible, such
as the tip of the nose and the external
ears
• Cartilage also is found where the ribs
are attached to the sternum, which
allows the rib cage to move during
breathing
BONE DEVELOPMENT
• Ossification: process by which bones develop
– Two types:
• Long bones first develop as cartilage that is later
replaced by bone
– Cartilage: tough, flexible connective tissue
» Once osteocytes develop in the cartilage, they release
minerals that lodge in the spaces between cartilage cells
eventually replacing the cartilage
» Some cartilage is never replaced: disc between vertebrae,
joints, end of nose, external ear, trachea
» Makes area flexible
• Other bones develop directly from embryonic connective
tissue without forming cartilage first
– Clavicle, some parts of the skull
Types of Joints
• A place where one bone attaches to another
bone is called a joint
– Joints permit bones to move without damaging
each other
– Some joints, such as those of the shoulder, allow
extensive movement
– Others, like the joints of the fully developed skull,
allow no movement at all
• Depending on its type of movement, a joint is
classified as immovable, slightly movable, or
freely movable
JOINTS
• Location where two bones meet
• Ligaments: tough bands of connective tissue that holds
the bones of a joint in place
– Stretch as the bones move
• Three kinds:
– Fixed: skull
– Semimovable(bend and twist): vertebral column, ribs
– Movable:
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Hinge (back and forth movement): elbow
Ball and socket (circular motion): hip, shoulder
Pivot (side to side / up and down): cervical vertebrae
Angular (twisting): wrists, ankles
Gliding (slide against each other): small bones of the hand and feet
Immovable Joints
• Immovable joints, often called fixed
joints, allow no movement
– The bones at an immovable joint are
interlocked and held together by
connective tissue, or they are fused
– The places where the bones in the skull
meet are examples of immovable joints
Slightly Movable Joints
• Slightly movable joints permit a small
amount of restricted movement
– Unlike the bones of immovable joints, the
bones of slightly movable joints are
separated from each other
– The joints between the two bones of the
lower leg and the joints between adjacent
vertebrae are examples of slightly movable
joints
Freely Movable Joints
• Freely movable joints permit movement
in one or more directions
– Freely movable joints are grouped
according to the shapes of the surfaces of
the adjacent bones
Freely Movable Joints
• Ball-and-socket joints permit movement in
many directions
– They allow the widest range of movement of any
joint
• Hinge joints permit back-and-forth motion,
like the opening and closing of a door
• Pivot joints allow one bone to rotate around
another
• Saddle joints permit one bone to slide in two
directions
Types of Freely Movable Joints
• Freely movable
joints are classified
by the type of
movement they
permit
• The joints illustrated
are in the shoulder,
knee, elbow, and
hand
Types of Freely Movable Joints
FUNCTIONING OF JOINTS
• Joints are subject to a great deal of pressure
and stress
• Connective tissue near the joints secretes
synovial fluid which cushions the bones thus
preventing the bones from wearing away
• Fluid filled sac called the bursa is found in
the knee and shoulder joints adding an
additional cushion between the bones
Structure of Joints
• In freely movable joints, cartilage
covers the surfaces where two bones
come together
– This protects the bones as they move
against each other
• The joints are also surrounded by a
fibrous joint capsule that helps hold the
bones together while still allowing them
to move
Structure of Joints
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The joint capsule consists of
two layers
One layer forms strips of tough
connective tissue called
ligaments
– Ligaments, which hold bones
together in a joint, are attached
to the membranes that
surround bones
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Cells in the other layer of the
joint capsule produce a
substance called synovial fluid,
which forms a thin film on the
cartilage that covers the bony
surfaces that form the joint
– This lubricating film enables the
surfaces of the joint to slide
over each other smoothly
Structure of Joints
• In some freely movable
joints, such as the knee in
the figure, small sacs of
synovial fluid called
bursae (singular: bursa)
form
• A bursa reduces the
friction between the
bones of a joint and
also acts as a tiny
shock absorber.
Knee Joint
• The knee joint is
protected by
cartilage and bursae
• The ligaments hold
the bones
composing the knee
joint—femur, patella,
tibia, and fibula—
together
Knee Joint
Skeletal System Disorders
• Bones and joints can be damaged, just like
any other tissue
• Excessive strain on a joint may produce
inflammation, a response in which excess
fluid causes swelling, pain, heat, and
redness
• Inflammation of a bursa is called bursitis
• A more serious disorder is arthritis, which
involves inflammation of the joint itself
• Arthritis affects approximately 10 percent of the
world's population
JOINT INJURY
• Bursitis: inflammation of the bursa
• Sprain: torn ligament
• Arthritis:
– Synovial membranes become inflamed and
grow thicker
– Fibrous tissues in the joints may become
ossified, immobilizing the joint and fusing
the bones together
Skeletal System Disorders
• Because bone is living tissue, calcium is
moved between it and the rest of the body to
maintain homeostasis of this important
mineral
• In older people, especially women, loss of
calcium can lead to a weakening of the
bones, a condition known as osteoporosis
– Osteoporosis can cause many serious fractures
• Sound nutrition, including plenty of calcium
in the diet, and weight-bearing exercise are
among the best ways to prevent this serious
problem
The Muscular System
• Despite the fantasies of Hollywood horror films, a
skeleton cannot move by itself
• Movement is the function of the muscular system
• More than 40 percent of the mass of the average
human body is muscle
• The muscular system includes the large muscles
displayed by some athletes
• It also includes thousands of tiny muscles throughout the
body that help to regulate blood pressure, move food
through the digestive system, and power every
movement of the body—from the blink of an eye to
the hint of a smile
Types of Muscle Tissue
• Muscle tissue is found everywhere in the
body—not only just beneath the skin but
also deep within the body
• There are three different types of
muscle tissue: skeletal, smooth, and
cardiac
– Each type of muscle is specialized for a
specific function in the body
MUSCLE
• Contractile organ consisting of many cells
• Three types:
– Skeletal
– Cardiac
– Smooth
Muscle Tissue
• There are three types of
muscle tissue: skeletal,
smooth, and cardiac
• Skeletal muscle cells
have striations, or stripes,
and many nuclei
• Smooth muscle cells
are spindle-shaped and
have one nucleus and no
striations
• Cardiac muscle cells
have striations and
usually only one nucleus
Muscle Tissue
Skeletal Muscles
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Skeletal muscles are usually
attached to bones
Skeletal muscles are
responsible for such voluntary
movements as typing on a
computer keyboard, dancing, or
winking an eye
When viewed under a microscope
at high magnification, skeletal
muscle appears to have
alternating light and dark bands
called striations
For this reason, skeletal muscle
is sometimes called striated
muscle
Most skeletal muscles are
consciously controlled by the
central nervous system
Skeletal Muscles
• Skeletal muscle cells are
large, have many nuclei, and
vary in length from 1 millimeter
to about 30 centimeters
• Because skeletal muscle
cells are long and slender,
they are often called muscle
fibers
• Complete skeletal muscles
consist of muscle fibers,
connective tissues, blood
vessels, and nerves
• The figure at right shows the
structure of a skeletal muscle
in the leg
MUSCLE CELL
• Muscle cell is also known as a fiber
– Within each fiber are many smaller units called
myofibrils (1,000 to 2,000)
• Each myofibril appears banded
– Bands referred to as Z lines
– Area between Z lines is called a sarcomere (functional unit
of contraction)
» Striated appearance of a sarcomere results from the
presence of two types of protein filaments, myosin and
actin
» The thicker myosin filaments have lateral extensions
called cross-bridges which are attached to the thinner
actin filaments that lie beside the myosin filaments
Skeletal Muscle Structure
• Skeletal muscles are made
up of bundles of muscle
fibers, which in turn are
composed of myofibrils
• Each myofibril contains thin
filaments made of actin and
thick filaments made of
myosin
• Muscle fibers are divided
into functional units called
sarcomeres
• What nervous system
structures carry messages to
skeletal muscles?
SKELETAL MUSCLE
• Attached to the periosteum of bone
– Either directly or by a tough connective tissue
called a tendon
• Striated: dark bands located at right angles to
the long axis of the muscle
• Voluntary: muscle contractions can be
controlled
• Nucleus in each cell but the separate cells
are harder to see
• Cell can sometimes be almost half a meter long
Skeletal Muscle Structure
Smooth Muscles
• Smooth muscles are usually not under voluntary control
• A smooth muscle cell is spindle-shaped, has one nucleus, and
is not striated
• Smooth muscles are found in the walls of hollow structures such
as the stomach, blood vessels, and intestines
• Smooth muscles move food through your digestive tract, control
the way blood flows through your circulatory system, and
decrease the size of the pupils of your eyes in bright light
• Most smooth muscle cells can function without nervous
stimulation
– They are connected to one another by gap junctions that allow
electrical impulses to travel directly from one muscle cell to a
neighboring muscle cell
SMOOTH MUSCLE
• Found in the walls of the stomach,
intestines, and blood vessels
• Not striated
– Actin and myosin fibers are present but in the
cytoplasm but not arranged in repeating units
• Involuntary
• Long spindle-shaped cells that contain a
single nucleus
Cardiac Muscle
• Cardiac muscle is found in just one place in the body—the
heart
– The prefix cardio comes from a Greek word meaning “heart”
• Cardiac muscle shares features with both skeletal muscle and
smooth muscle
• Cardiac muscle is striated like skeletal muscle, although its cells
are smaller
• Cardiac muscle cells usually have one nucleus, but they may have
two
• Cardiac muscle is similar to smooth muscle because it is
usually not under the direct control of the central nervous
system and cardiac cells are connected to their neighbors by
gap junctions
• You will learn more about cardiac muscle in Chapter 37.
CARDIAC MUSCLE
• Makes up the walls of the heart
• Striated
• Involuntary: movements cannot be
controlled
• Many mitochondria
• Cell much shorter than skeletal cell
• Cell nucleus is present, but separate
cells are easier to see
Muscle Contraction
• The muscle fibers in skeletal muscles are composed
of smaller structures called myofibrils
– Each myofibril is made up of even smaller structures called
filaments
• The striations in skeletal muscle cells are formed by
an alternating pattern of thick and thin filaments
– The thick filaments contain a protein called myosin
– The thin filaments are made up mainly of a protein called
actin
• The filaments are arranged along the muscle fiber in
units called sarcomeres, which are separated from each
other by regions called Z lines
Muscle Contraction
• During muscle
contraction, the
actin filaments slide
over the myosin
filaments,
decreasing the
distance between
the Z lines
Muscle Contraction
Muscle Contraction
• The tiny myosin and actin filaments are the forceproducing engines that cause a muscle to contract
• A muscle contracts when the thin filaments in the
muscle fiber slide over the thick filaments
– This process is called the sliding-filament model of muscle
contraction
• For a muscle to contract, the thick myosin filament
must form a cross-bridge with the thin actin filament
– As the cross-bridge changes shape, it pulls on the actin
filament, which slides toward the center of the sarcomere
– The distance between the Z lines decreases
– The cross-bridge detaches from the actin filament
• The cycle is repeated when the myosin binds to
another site on the actin filament
Muscle Contraction
• When hundreds of thousands of myosin crossbridges change shape in a fraction of a second, the
muscle fiber shortens with considerable force
• The energy for muscle contraction is supplied by
ATP
• Because one molecule of ATP supplies the energy
for one interaction between a myosin cross-bridge
and an actin filament, the cell needs plenty of ATP
molecules for a strong contraction
• Recall that the cell can produce ATP in two ways—by
cellular respiration and by fermentation
MUSCLE CONTRACTION
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Begins when a nerve impulse reaches a muscle (junction of a nerve branch and a muscle is
called a motor end plate)
Stimulus reaching the motor end plate causes a specialized membrane of the muscle to
release calcium (Ca) into the muscle cytoplasm
Before the nerve impulse (myosin cannot bind to actin)
Attachment of calcium to muscle protein causes a change in their shapes allowing the
binding of the myosin heads to the actin filament
– Myosin heads then bend inward, pulling the actin filament toward the center of the
sarcomere
• Myosin is then released from the actin and uses the energy of ATP to bend the
myosin heads back to their original position
• Process is repeated with the myosin heads moving down the actin filament and
reattaching to a new position
– Z lines move closer to each other
– The entire sarcomere contracts
Synchronized shortening of sarcomeres along the full length of a muscle fiber causes the
whole fiber, and hence the muscle, to contract
Contraction process continues until calcium and ATP supplies are depleted or nerve stimulation
stops
When a single muscle fiber is stimulated, an all-or-none response occurs (no in-between
state)
– As more muscle fibers are activated, the force of the contraction increases
Control of Muscle Contraction
• Skeletal muscles are useful only if they
contract in a controlled fashion
• Remember that motor neurons connect
the central nervous system to skeletal
muscle cells
• Impulses from motor neurons control
the contraction of skeletal muscle
fibers
Control of Muscle Contraction
• A neuromuscular junction is the point of contact between a
motor neuron and a skeletal muscle cell
• Vesicles, or pockets, in the axon terminals of the motor neuron
release a neurotransmitter called acetylcholine
– Acetylcholine molecules diffuse across the synapse,
producing an impulse in the cell membrane of the muscle
fiber
– The impulse causes the release of calcium ions (Ca2+)
within the fiber
– The calcium ions affect regulatory proteins that allow actin
and myosin filaments to interact
• From the time a nerve impulse reaches a muscle cell, it is only a few
milliseconds before these events occur and the muscle cell
contracts
Control of Muscle Contraction
• A muscle cell remains contracted until
the release of acetylcholine stops and
an enzyme produced at the axon
terminal destroys any remaining
acetylcholine
– Then, the cell pumps calcium ions back
into storage, the cross-bridges stop
forming, and contraction ends
Control of Muscle Contraction
• What is the difference between a strong
contraction and a weak contraction?
• Each muscle contains hundreds of cells
• When you lift something light, such as a
sheet of paper, your brain stimulates only a
few cells in your arm muscles to contract
• However, as you exert maximum effort,
almost all the muscle cells in your arm are
stimulated to contract
How Muscles and Bones Interact
• Skeletal muscles generate
force and produce
movement by contracting, or
pulling on body parts
• Individual muscles can only
pull in one direction
• Yet, you know from
experience that your legs
bend when you sit and
extend when you stand up
• How is this possible?
How Muscles and Bones Interact
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Skeletal muscles are joined to
bones by tough connective
tissues called tendons
Tendons are attached in such a
way that they pull on the bones
and make them work like levers
The joint functions as a
fulcrum—the fixed point around
which the lever moves
The muscles provide the force to
move the lever
Usually, there are several muscles
surrounding each joint that pull in
different directions
How Muscles and Bones Interact
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Most skeletal muscles work in opposing
pairs
– When one muscle contracts, the
other relaxes
The muscles of the upper arm shown in the
figure are a good example of this dual action
When the biceps muscle contracts, it
bends, or flexes, the elbow joint
When the triceps muscle contracts, it
opens, or extends, the elbow joint
A controlled movement, however,
requires contraction by both muscles
To hold a tennis racket or a violin, both
the biceps and triceps must contract in
balance
This is why the training of athletes and
musicians is so difficult
The brain must learn how to work
opposing muscle groups in just the right
ways to make the joint move precisely
Arm Movement
• By contracting and
relaxing, the triceps
and biceps in the
upper arm enable you
to bend or straighten
your elbow
Arm Movement
BONE MOVEMENT
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Skeletal muscle pulls at the base of a joint
Point of attachment on the moving bone is called the insertion
Point of attachment on the stationary bone is the origin
Most skeletal muscles form antagonistic pairs
– When one contracts, the other usually relaxes
– One muscle in a pair moves a body part in one direction, and the
other muscle moves it in the opposite direction
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Flexors: bend joints (biceps)
Extensors: straighten joints (triceps)
Abductors: move limb away from body (deltoid)
Adductors: move a limb toward the body (pectorals)
• Isometric contraction: exercise in which both antagonistic pairs
contract (joint does not move)
Exercise and Health
• Skeletal muscles generally remain in a
state of partial contraction called
resting muscle tone
• Muscle tone is responsible for keeping
the back and legs straight and the head
upright, even when you are relaxed
Exercise and Health
• Regular exercise is important in
maintaining muscular strength and
flexibility
• Muscles that are exercised regularly
stay firm and increase in size and
strength by adding actin and myosin
filaments
– Muscles that are not used become weak and
can visibly decrease in size
Exercise and Health
• Aerobic exercises—such as running and
swimming—cause the body's systems to
become more efficient
– For example, aerobic exercise helps your heart
and lungs become more efficient
• This, in turn, increases physical endurance—the
ability to perform an activity without fatigue
• Regular exercise also strengthens your
bones, making them thicker and stronger
• Strong bones and muscles are less likely to
become injured
Exercise and Health
• Resistance exercises, such as weight
lifting, increase muscle size and
strength
• Resistance exercises also decrease
body fat and increase muscle mass
• Over time, weight-training exercises
will help to maintain coordination and
flexibility
The Integumentary System
• “Good fences make good neighbors,”
wrote the American poet Robert Frost as
he explained the importance of property
boundaries
• Living things have their own “fences,”
and none is as important as the skin—
the boundary that separates the human
body from the outside world
INTEGUMENTARY SYSTEM
• Consist of the skin, hair, and nails
• Protective barrier between the body and
the outside world
• Helps retain body fluids
• Barrier against disease
• Helps eliminate waste products
• Helps regulates body temperature
The Integumentary System
• The skin, the single largest organ of the
body, is part of the integumentary system
• The word integument comes from a Latin
word that means “to cover,” reflecting the
fact that the skin and its related structures
form a covering over the entire body
• Skin and its related structures—the hair,
nails, and a variety of glands—make up the
integumentary system
The Skin
• The skin has many different functions, but its most
important function is protection
• The integumentary system serves as a barrier
against infection and injury, helps to regulate body
temperature, removes waste products from the body,
and provides protection against ultraviolet radiation
from the sun
• Because the largest component of the
integumentary system—the skin—contains several
types of sensory receptors, it serves as the gateway
through which sensations such as pressure, heat,
cold, and pain are transmitted to the nervous system
The Skin
• The skin is made up of two main
layers—the epidermis and the dermis
• Beneath the dermis is a subcutaneous
layer of fat (the hypodermis) and loose
connective tissue that help insulate the
body
SKIN
• Largest organ of the human body
• Two parts:
– Epidermis
– Dermis
EPIDERMIS
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Outer part of the skin
Composed of many cell layers (epithelial cells)
Protects the body from harmful UV light
Outer layer of cells are dead and are constantly
being shed and replaced by new cells from the
rapidly dividing lower layer by mitosis
– New cells are pushed toward the surface
• Cells fills with a protein called keratin
– Gives the skin its rough, leathery texture and its
waterproof quality
Epidermis
• The outer layer of the
skin is the epidermis
• The epidermis itself has
two layers:
– The outside of the
epidermis—the part that
comes in contact with the
environment—is made up
of dead cells
– The inner layer of the
epidermis is made up of
living cells
Epidermis
• Cells in the inner layer
of the epidermis
undergo rapid cell
division, producing new
cells that push older
cells to the surface of
the skin
• As they move upward,
the older cells become
flattened and their
organelles disintegrate
• They also begin making
keratin, a tough, fibrous
protein
Epidermis
• Eventually, the keratinproducing cells die and
form a tough, flexible,
waterproof covering on
the surface of the skin
• This outer layer of dead
cells is shed or washed
away at a surprising
rate—once every four to
five weeks
MELANIN
• Pigment produced in the lower layers of the
epidermis:
– Gives color to the skin
– Absorbs harmful ultraviolet light
– Determines the color of the skin
• Large amount: darker the skin
• Small amount: lighter the skin
• In some individuals exposure to sunlight
increases the production causing the skin to
become darker (tan)
Epidermis
•
•
•
•
The epidermis also contains
melanocytes
Melanocytes are cells that
produce melanin, a dark brown
pigment
Melanin helps protect the skin
from damage by absorbing
ultraviolet rays from the sun
Although most people have
roughly the same number of
melanocytes in their skin,
differences in skin color are
caused by the different amount
of melanin the melanocytes
produce and where these cells
are distributed
Epidermis
• Look closely at the
figure at right and
you will see that
there are no blood
vessels in the
epidermis
• This explains why a
slight scratch will
not cause bleeding
Layers of the Skin
• The skin has an outer
layer called the
epidermis and an
inner layer called the
dermis
• What is the function
of the dermis?
Layers of the Skin
DERMIS
•
•
•
•
Inner layer of skin
Thickest layer
Composed of living cells
Contains:
– Nerves: receive environmental stimuli
– Blood: release heat helping the body
maintain a comfortable temperature
– Lymph vessels: helps the skin fight against
infection
DERMIS
• Layer of fat cells (adipose tissue)
below:
– Enables the skin to store food for energy
– Provides protection to the body
– Insulates the body against heat loss
DERMIS
• Location of hair follicles:
– Cells at the base produce hair
– Blood vessels surround the hair follicles
nourishing the root hair
– Shaft of hair that extends beyond the skin
consist mostly of keratin and requires no
nourishment
Dermis
• The inner layer of the skin
is the dermis
• The dermis lies beneath
the epidermis and
contains collagen
fibers, blood vessels,
nerve endings, glands,
sensory receptors,
smooth muscles, and
hair follicles
NERVES
• Special sensory neuron receptors send
a great deal of information to the brain
from the environment
• Types of sensory neuron receptors:
– Pressure
– Touch
– Heat
– Cold
– Pain
Dermis
• The skin interacts with other
body systems to maintain
homeostasis by helping to
regulate body temperature
• When the body needs to
conserve heat on a cold day,
the blood vessels in the
dermis narrow, helping to
limit heat loss
• On hot days, the blood
vessels widen, bringing heat
from the body's core to the
skin and increasing heat
loss
Dermis
•
•
The dermis contains two major
types of glands: sweat glands and
sebaceous, or oil, glands
If your body gets too hot, sweat
glands produce perspiration, or
sweat
–
–
–
–
•
Sweat contains water, salts, and other
compounds
When sweat evaporates, it takes
heat away from your body
Sweat also gets rid of wastes from
the blood, along with water
In this way, the skin acts as an organ
of excretion
Sebaceous glands produce an oily
secretion called sebum
–
Sebum spreads out along the
surface of the skin and helps to keep
the keratin-rich epidermis flexible
and waterproof
SEBACEOUS GLAND
• Oil gland
• Secretes a substance called sebum
– Production controlled by hormones
• Exocrine gland (gland that releases fluid
through a duct)
• Next to each hair follicle
• Oil from these glands help prevent the
skin’s outer layer from drying and
cracking keeping it soft and waterproof
SWEAT GLANDS
• Function as excretory organs by releasing
excess water, salts, and urea
• Releasing excess water helps regulate the
body temperature
– When the body temperature rises, the circulation
increases, and the skin becomes warm and
flushed
• Sweat glands then release sweat and as the water
evaporates the skin is cooled
• Helps maintain homeostasis by regulating
heat loss
Skin Cancer
• Excessive exposure to the ultraviolet
radiation in sunlight can produce skin
cancer, an abnormal growth of cells in the
skin
• You can help protect yourself from this
dangerous disease by wearing a hat,
sunglasses, and protective clothing whenever
you plan to spend time outside
• In addition, you should always use a
sunscreen with a sun protection factor (SPF)
of at least 15
The UV Index and Sunburn
• Ultraviolet (UV) radiation is one type of energy from the sun
• UV rays cause sunburn, some cataracts, and skin cancer
• There are many factors that affect the amount of UV radiation to
which you are exposed
• These include the time of day, the season, the weather conditions,
and your location
• Recently, the National Weather Service, the Environmental
Protection Agency, and the Centers for Disease Control agreed
upon a national UV index
• The UV index is issued daily to advise you of conditions in your
region of the country
The UV Index and Sunburn
The UV Index and Sunburn
• Describe the trend in
the amount of time it
takes to sunburn,
from a minimal UV
index level to a very
high UV index level
The UV Index and Sunburn
• Why do you think
applying sunscreen is
always
recommended?
The UV Index and Sunburn
• Why should a hat
worn as protection
against UV rays have
a brim?
The UV Index and Sunburn
• The minutes-to-burn
data apply to most
people
• What variable could
cause the time for a
particular person to
burn to be shorter or
to be longer?
The UV Index and Sunburn
• Use the data in the
table to construct a
bar graph
• Place the UV index
levels on the x-axis
and the minutes to
burn on the y-axis
Hair and Nails
• The basic structure of human hair and
nails is keratin
• In other animals, keratin forms a variety of
structures, including bull horns, reptile
scales, bird feathers, and porcupine quills
Hair
• Hair covers almost every exposed surface
of the body and has important functions
– Hair on the head protects the scalp from
ultraviolet light from the sun and provides
insulation from the cold
– Hairs in the nostrils, external ear canals,
and around the eyes (eyelashes) prevent
dirt and other particles from entering the body
Hair
• Hair is produced by cells at the base of structures called hair
follicles
• Hair follicles are tubelike pockets of epidermal cells that extend
into the dermis
• An individual hair is actually a large column of cells that have
filled with keratin and then died
– Rapid cell growth at the base of the hair follicle causes the hair
to grow longer
– Hair follicles are in close contact with sebaceous glands
• The oily secretions of these glands help maintain the
condition of each individual hair
Nails
• Nails grow from an area of rapidly dividing
cells known as the nail root
• The nail root is located near the tips of the
fingers and toes
• During cell division, the cells of the nail root
fill with keratin and produce a tough,
platelike nail that covers and protects the
tips of the fingers and toes
• Nails grow at an average rate of 3 millimeters
per month, with fingernails growing more
rapidly than toenails—about four times as
fast