Download The Skeletal System

Human Biology and health
• The levels of organization in the human body
consist of cells, tissues, organs, and organ systems.
A cell is the basic unit of structure and function in a
living thing. Cells perform the basic processes that
keep organisms alive. Most cells are too small to
see without a microscope. In most animal cells, a
cell membrane forms the outside boundary of the
cell. Inside the cell membrane is a large structure
called the nucleus. The nucleus is the control center
that directs the cell’s activities and contains
information that determines the cell’s
characteristics. The area between the cell
membrane and the nucleus is called the cytoplasm
• A tissue is a group of similar cells that perform the
same function. The human body contains four basic
types of tissue: muscle tissue, nerve tissue, connective
tissue, and epithelial tissue. Muscle tissue can
contract, or shorten. This tissue is what makes parts of
your body move. Nervous tissue carries messages
back and forth between the brain and every other part
of the body. It directs and controls the body.
Connective tissue provides support for your body and
connects all its parts. Bone, fat, and blood ar e all
connective tissues. Epithelial tissue covers the
surfaces of your body. The skin and the lining of the
digestive system are examples of epithelial tissue.
• An organ is a structure that is composed of different
kinds of tissue. Like a tissue, an organ performs a
specific job. An organ’s job is usually more complex
than that of a tissue. The heart is an organ that pumps
blood throughout the body.
• Each organ in your body is part of an organ system. An
organ system is a group of organs that work together
to perform a major function. Your heart is part of an
organ system called the circulatory system. The blood
vessels are also part of the circulatory system. The
different organ systems work together and depend on
one another.
• All the systems of the body work together to maintain
homeostasis, the body’s tendency to keep an internal
balance. Homeostasis is the process by which an
organism’s internal environment is kept stable in
spite of changes in the external environment.
Sometimes, things can happen to throw off
homeostasis. As a result, your heart may beat more
rapidly or your breathing may quicken. These are signs
of stress, the reaction of your body to potentially
threatening, challenging, or disturbing events. When
the stress is over, homeostasis is restored, and the
body returns to its normal state.
The Skeletal System
Guide for Reading
■ What are the functions of the skeleton?
■ What role do joints play in the body?
■ What are the characteristics of bone, and
how can you keep your bones strong and
healthy?
Bones, Muscles, and Skin - The Skeletal System
What the Skeletal System Does
Your skeleton has five major
functions. It provides shape and
support, enables you to move,
protects your organs, produces
blood cells, and stores minerals
and other materials until your body
needs them.
The Skeletal System
• The skeleton is made up of all the bones in one’s
body. Your skeleton has five major functions. It
provides shape and support, enables you to
move, protects your organs, produces blood cells,
and stores minerals and other materials until
your body needs them. The backbone, or
vertebral column, is the center of the skeleton.
The backbone is made up of 26 small bones, or
vertebrae (singular vertebra). If your backbone
were just one bone, you would not be able to
bend or twist.
Bones, Muscles, and Skin - The Skeletal System
Joints of the Skeleton
A joint is a place in the body where two bones come
together. Joints allow bones to move in different ways.
The Skeletal System
• A joint is a place in the body where two bones
come together. Joints allow bones to move in
different ways. Immovable joints connect bones in
a way that allows little or no movement. Movable
joints allow the body to make a wide range of
movements. The bones in movable joints are held
together by a strong connective tissue called a
ligament. Cartilage is a connective tissue that is
more flexible than bone
The Skeletal System
• Bones are complex living structures that undergo
growth and development. A thin, tough
membrane covers all of a bone except the ends.
Blood vessels and nerves enter and leave the bone
through the membrane. Beneath the membrane is
a layer of compact bone, which is hard and dense,
but not solid.
The Skeletal System
• Small canals run through the compact bone,
carrying blood vessels and nerves from the bone’s
surface to the living cells within the bone. Just
inside the compact bone is a layer of spongy bone,
which has many small spaces within it. Spongy
bone is also found at the ends of the bone. The
spaces in bone contain a soft connective tissue
called marrow. There are two types of marrow—
red and yellow. Red bone marrow produces blood
cells. Yellow marrow stores fat that serves as an
energy reserve.
The Skeletal System
• A combination of a balanced diet and regular
exercise are important for a lifetime of healthy
bones. As people become older, their bones begin
to lose some minerals. Mineral loss can lead to
osteoporosis, a condition in which the body’s
bones become weak and break easily. Regular
exercise and a diet rich in calcium can help prevent
osteoporosis.
Bones, Muscles, and Skin - The Skeletal System
Bones—Strong and Living
Bones are complex living structures that undergo growth and
development.
Bones, Muscles, and Skin - The Skeletal System
Asking Questions
Before you read, preview the red headings. In a graphic
organizer like the one below, ask a what or how question for
each heading. As you read, write answers to your questions.
Question
Answer
What does the skeleton do?
The skeleton provides shape and support, helps
you to move, protects organs, produces blood
cells, and stores minerals and other materials.
Joints can move forward or backward,
in a circle, in a rotating motion, and in a
gliding motion.
How do joints move?
How strong are bones?
Bones can absorb more force without
breaking than granite or concrete.
What can I do to care for my bones?
Eat a well balanced diet and get
plenty of exercise.
Diagnosing Bone and Joint Injuries
Three common skeletal system injuries are
fractures, dislocations, and sprains. A fracture, or a
break in a bone, can occur when you fall so that all
of your weight is placed on only a few bones. A
dislocation occurs when a bone comes out of its
joint. A sprain occurs when ligaments are stretched
too far and tear in places. Sprains are the most
common joint injuries.
Diagnosing Bone and Joint Injuries
Two ways to identify injuries of the skeletal system
are X-rays and magnetic resonance imaging. X-ray
images can determine whether bones have been
broken. X-rays are a form of energy that travels in
waves. Because most X-rays pass through the skin
and other body tissues, the X-rays strike the
photographic film beneath the area. Unlike other
body tissues, bone absorbs X-rays. Absorbed X-rays
do not reach the film. After the film is developed, it
shows bones as clearly defined white areas. X-rays
cannot be used to view injuries to soft tissues, such
as muscle, and internal organs.
Diagnosing Bone and Joint Injuries
A more recently developed method for taking clear
images of both the bones and soft tissues of the
body is called magnetic resonance imaging, or MRI.
In MRI, a person is exposed to short bursts of
magnetic energy. This magnetic energy causes atoms
within the body to vibrate, or resonate. A computer
then analyzes the vibration patterns and produces
an image of the area. MRI can show clear images of
muscles and other soft tissues that an
X-ray image cannot show.
Diagnosing Bone and Joint Injuries
If a doctor determines that you have a broken bone,
you will usually have to wear a cast. In addition to
wearing a cast, two other ways to treat skeletal
system injuries include surgical procedures such as
joint replacement and arthroscopy.
The Muscular System
Guide for Reading
■ What types of muscles are found in the
body?
■ Why do skeletal muscles work in pairs?
The Muscular System
There are about 600 muscles in your body.
The muscles that are not under your conscious
control are called involuntary muscles.
Involuntary muscles are responsible for
activities such as breathing and digesting food.
The muscles that are under your control are
called voluntary muscles. Smiling and turning
the pages in a book are actions of voluntary
muscles.
The Muscular System
• Your body has three types of muscle tissue—skeletal
muscle, smooth muscle, and cardiac muscle. Some of
these muscle tissues are involuntary, and some are
voluntary. Skeletal muscles are attached to the bones of
your skeleton. At the end of a skeletal muscle is a tendon.
A tendon is a strong connective tissue that attaches
muscle to bone. Because you have conscious control of
skeletal muscles, they are classified as voluntary muscles.
These muscles provide the force that moves your bones.
Skeletal muscles react quickly and tire quickly. Skeletal
muscle cells appear banded, or striated. For this reason,
they are sometimes called striated muscles.
The Muscular System
• Smooth muscles are called involuntary
muscles because they work automatically.
They are inside many internal organs of the
body, and control many types of movements
inside your body, such as those involved in
the process of digestion. Smooth muscles
react more slowly and tire more slowly than
skeletal muscles. Cardiac muscles are
involuntary muscles found only in the heart.
Cardiac muscles do not get tired.
The Muscular System
• Muscles work by contracting, or becoming shorter and
thicker. Because muscle cells can only contract, not
extend, skeletal muscles must work in pairs. While one
muscle contracts, the other muscle in the pair relaxes to
its original length. For example, in order to move the
lower arm, the biceps muscle on the front of the upper
arm contracts to bend the elbow. This lifts the forearm
and hand. As the biceps contracts, the triceps on the back
of the upper arm returns to its original length. To
straighten the elbow, the triceps muscle contracts while
the biceps returns to its original length.
The Muscular System
Exercise is important for maintaining both
muscular strength and flexibility. Exercise
makes individual muscle cells grow wider,
thicker, and stronger. Sometimes, muscle
injuries such as strains and cramps, can
occur. Resting the injured area can help it
heal.
The Skin
Guide for Reading
■ What are the functions and the structures of
skin?
■ What habits can help keep your skin
healthy?
The Skin
The skin performs several major functions in
the body. The skin covers and
protects the body from injury, infection, and
water loss. The skin also helps
regulate body temperature, eliminate wastes,
gather information about the
environment, and produce vitamin D.
The Skin
The skin is organized into two main layers, the epidermis
and the dermis. The epidermis is the outermost layer of the
skin. The epidermis does not have nerves or blood vessels.
Cells in the epidermis have a definite life cycle. New cells
form deep in the epidermis, gradually mature, and move
upward. When these cells die, they become part of the
surface layer of the epidermis. Soon, these cells are shed
and replaced by the dead cells below them. Cells deep in
the epidermis produce melanin, a pigment, or colored
substance, that gives skin its color. The more melanin in
your skin,
the darker it is. Melanin production helps to protect the skin
from burning.
The Skin
The skin is organized into two main layers, the epidermis
and the dermis. The epidermis is the outermost layer of the
skin. The epidermis does not have nerves or blood vessels.
Cells in the epidermis have a definite life cycle. New cells
form deep in the epidermis, gradually mature, and move
upward. When these cells die, they become part of the
surface layer of the epidermis. Soon, these cells are shed
and replaced by the dead cells below them. Cells deep in
the epidermis produce melanin, a pigment, or colored
substance, that gives skin its color. The more melanin in
your skin,
the darker it is. Melanin production helps to protect the skin
from burning.
The Skin
The dermis is the inner layer of the skin. It contains
nerves, blood vessels, sweat glands, hairs, and oil
glands. Sweat glands produce perspiration , which
reaches the surface through openings called pores.
Strands of hair grow within the dermis in structures
called follicles. Oil produced in glands around the
hair follicles waterproofs the hair. In addition, oil
helps to keep the skin moist
The Skin
Three simple habits can help you keep your skin healthy.
Eat a healthful diet. Keep your skin clean and dry. Limit
your exposure to the sun.
Eating a well-balanced diet and drinking plenty of water are
important for healthy skin. Good washing habits can get rid
of dirt and harmful bacteria, and can help control oiliness.
The Skin
Repeated exposure to sunlight can damage skin cells and
cause them to become cancerous. Cancer is a disease in
which some body cells divide uncontrollably. Wearing
sunscreen and limiting sun exposure can protect skin from
sun damage.
Food and Energy
Foods provide your body with materials for
growing and for repairing tissues. Food also
provides energy for everything you do.
• Your body breaks down the foods you eat
into nutrients. Nutrients are the substances
in food that provide the raw materials and
energy the body needs to carry out all its
essential processes. There are six kinds of
nutrients necessary for human health
carbohydrates, fats, proteins, vitamins,
minerals, and water.
Food and Energy
The amount of energy released by nutrients
can be measured in units called calories. One
calorie is the amount of energy needed to
raise the temperature of one gram of water by
one degree Celsius
Food and Energy
Carbohydrates are nutrients composed of carbon, oxygen,
and hydrogen. They are a major source of energy. In
addition to providing energy, carbohydrates provide the
raw materials to make parts of cells. Carbohydrates are
either simple or complex. Simple carbohydrates are sugars.
One sugar, glucose, is the major source of energy for your
body’s cells. Complex carbohydrates are made up of many
sugar molecules linked together in a chain. Starch is a
complex carbohydrate found in some plant foods. Fiber is a
complex carbohydrate found in plant foods. Fiber keeps the
digestive system functioning properly.
Food and Energy
Like carbohydrates, fats are energy-containing
nutrients that are composed of carbon, oxygen, and
hydrogen. They contain twice as much energy as an
equal amount of carbohydrates. In addition to
providing energy, fats have other important
functions. Fats form part of the cell membrane, the
structure that forms the boundary of a cell. Fatty
tissue protects and supports your internal organs and
insulates your body.
Food and Energy
Unsaturated fats are usually liquid at room
temperature. Saturated fats are usually solid at
room temperature. trans fats are found in
many commercially baked goods. Cholesterol
is a waxy, fatlike substance found only in
animal products. Large amounts of cholesterol,
saturated fats, and trans fats can lead to heart
disease.
Food and Energy
Proteins are nutrients that contain nitrogen as
well as carbon, hydrogen, and oxygen.
Proteins are needed for tissue growth and
repair. They also play an important part in
chemical reactions within cells. Proteins are
made up of small units called amino acids
Food and Energy
Vitamins act as helper molecules in a variety of chemical
reactions within the body. Minerals are nutrients that are
not made by living things. You obtain minerals by eating
plant foods or animals that have eaten plants. Both vitamins
and minerals are needed by your body in small amounts to
carry out chemical processes.
Water is the most important nutrient because the body’s
vital processes— including chemical reactions such as the
breakdown of nutrients—take place in water. People
cannot live without fresh water.
Healthy Eating
Guide for Reading
■ How can the Food Guide Pyramid help you
plan a healthy diet?
■ What kind of information is included on
food labels?
Healthy Eating
The Food Guide Pyramid was developed by
nutritionists to help people plan a healthy diet.
The Food Guide Pyramid classifies foods into
six groups. It also indicates how many
servings from each group should be eaten
every day to maintain a healthy diet.
Healthy Eating
The pyramid has four levels. The base of the
pyramid includes foods made from grains, such
as bread, cereals, rice, and pasta. This bottom
level is the widest part of the pyramid. This
means that these foods should make up the
largest part of the diet. The second level is
made of two food groups, the Fruit group and
the Vegetable group. People need fewer
servings of these foods than of foods from the
bottom level.
Healthy Eating
The third level contains the Milk, Yogurt, and
Cheese group, and the Meat, Poultry, Fish, Dry
Beans, Eggs, and Nuts group. People need still
smaller amounts of food from this level. At the
top of the pyramid are foods containing large
amounts of fat, sugar, or both. Only small
amounts of these foods should be eaten.
Healthy Eating
• Food labels contain information that can
help you to eat wisely. The serving size and
the number of servings in the container are
listed at the top of the label. Food labels
allow you to evaluate a single food as well
as to compare the nutritional value of two
different foods.
Healthy Eating
A food label also has a column called Percent
Daily Value. The Percent Daily Value indicates
how the nutritional content of one serving fits
into the diet of a person who consumes a total
of 2,000 Calories a day. For example, suppose
the label lists 12 percent for Total
Carbohydrates
Healthy Eating
• This means that the food supplies 12 percent of
the carbohydrates that an average person should
eat each day. Food labels also list ingredients in
order by weight, starting with the main ingredient.
By reading ingredient lists, people can avoid foods
that contain substances they should not eat.
• Dietary Reference Intakes (DRIs) are guidelines
that show the amounts of nutrients needed every
day. DRIs also show how the Calories that people
eat each day should be split among carbohydrates,
fats, and proteins.
The Digestive Process Begins
Guide for Reading
■ What functions are carried out in the digestive
system?
■ What roles do the mouth, esophagus, and
stomach play in digestion?
The Digestive Process Begins
The digestive system has three main functions.
First, it breaks down food into molecules the body
can use. Then, the molecules are absorbed into the
blood and carried throughout the body. Finally,
wastes are eliminated from the body.
The Digestive Process Begins
The process by which the body breaks down
food into small nutrient molecules is called
digestion. There are two kinds of digestion—
mechanical and chemical. In mechanical
digestion, foods are physically broken down
into smaller pieces. In chemical digestion,
chemicals produced by the body break foods
into their smaller chemical building blocks.
The Digestive Process Begins
• After food is digested, the molecules are
ready to be transported throughout your
body. Absorption is the process by which
nutrient molecules pass through the wall of
your digestive system into your blood.
Materials that are not absorbed are
eliminated as wastes.
The Digestive Process Begins
Both mechanical digestion and chemical digestion
begin in the mouth. The fluid released when your
mouth waters is called saliva. Saliva plays an
important role in both mechanical and chemical
digestion.
Your teeth carry out the first stage of mechanical
digestion. As the teeth break foods into smaller
pieces, saliva mixes with the pieces of food and
moistens them. Chemical digestion is accomplished
by enzymes. An enzyme is a protein that speeds up
chemical reactions in the body.
The Digestive Process Begins
As you swallow, muscles in your throat move the
food downward. As this happens, a flap of tissue
called the epiglottis seals off your windpipe,
preventing the food from entering. Food moves into
the esophagus, a muscular tube that connects the
mouth to the stomach. The esophagus is lined with
mucus. Mucus is a thick, slippery substance
produced by the body. Mucus makes food easier to
swallow. Food remains in the esophagus for only
about 10 seconds. After food enters the esophagus,
contractions of smooth muscles push the food toward the
stomach. These involuntary waves of muscle contractions
are called peristalsis.
The Digestive Process Begins
Food leaves the esophagus and enters the stomach. The
stomach is a J-shaped muscular pouch located in the
abdomen. Most mechanical digestion and some chemical
digestion occur in the stomach. Mechanical digestion
occurs as three strong layers of muscle contract to produce
a churning motion. Chemical digestion is carried out in the
stomach by digestive juice that contains enzymes and
hydrochloric acid. When the food has been digested into a
liquid form, it moves into the next part of the digestive
system.