The Respiratory System
With normal breathing, the average person moves more than 10000L
of air in and out of the lungs each day.
The respiratory system is responsible for providing the oxygen
needed by the body and for removing the carbon dioxide produced
as your body uses energy for growth, repair, and movement. The
respiratory system works in close collaboration with the circulatory
system.
STRUCTURAL FEATURES
The respiratory system consists of the lungs and the other organs
that connect the lungs to the outside. Air enters through the mouth
and the nose, passes through the pharynx, and travels down the
trachea. The trachea separates into two branches called bronchi.
Some of the epithelial cells that line the trachea and bronchi produce
mucus, similar to those in the digestive system. Many of the
epithelial cells have cilia. Cilia help move mucus and filter out any
foreign material that might enter the system. The bronchi deliver air
into the lungs. The trachea is supported by rings of cartilage. This
keeps the trachea open and allows the air to flow freely.
GAS EXCHANGE
The main purpose of the respiratory system is gas exchange.
Oxygen enters the bloodstream in the lungs by diffusion. Carbon
dioxide leaves the blood in the same way. The respiratory system is
adapted in several ways to make these processes as efficient as
possible.
Each of the bronchi branch again and again, ending in tiny air sacs
called alveoli. The alveoli have very thin walls. Each alveolus is
surrounded by a network of capillaries. Oxygen and carbon dioxide
have only to diffuse through two thin walls.
BREATHING
Breathing involves alternately drawing air into the lungs (inhalation)
and then pushing air out (exhalation). This process involves muscles
that move the ribs, making the rib cage expand and contract.
Breathing also involves the diaphragm, a large sheet of muscle
underneath the lungs. Together, the diaphragm and the muscles
between the ribs increase or decrease the volume of the lungs. As
the volume of the lungs changes, the pressure inside them also
changes. In this way, fresh air flows into and out of the alveoli.
The control over our breathing is involuntary. We can override the
involuntary system and stop breathing or control it while we talk.
Breathing is controlled by a part of the brain that detects the
concentration of carbon dioxide in the blood. As the level of carbon
dioxide increases, the brain sends signals to the diaphragm, the
muscles between the ribs, and the heart. The breathing rate
increases and the heart beats faster.
Homework
1. What is the role of the epithelial tissue that lines the trachea
and bronchi?
2. Explain the difference between breathing and gas exchange.
3. Identify what function the cilia have and give an example of how
they might work.
4. What might happen if the trachea did not have rings of cartilage
to support it.
The Musculoskeletal System
The musculoskeletal system is made up of all the bones in the body
and the muscles that make them move.
The skeleton consists of three different types of connective tissue:
bones, ligaments, and cartilage. Bone tissue is hard and dense. It
consists of bone cells within a matrix of minerals (mainly calcium and
phosphorus) and collagen fibres. Canals inside the bones contain
nerves and blood vessels. Only a small percentage of bone tissue is
actually living.
Ligaments are tough, elastic connective tissues that hold bones
together at the joints. They are made up mostly of long fibres of
collagen. Cartilage is a dense connective tissue found in the ear,
nose, esophagus, the disks between our vertebrae, and joints.
Cartilage is made up of special cells in a matrix of collagen fibres. It
provides a strong, flexible, low friction support for bones and other
tissues.
The other part of the
musculoskeletal system is the
muscle. Muscle tissue consists of
bundles of long cells called muscle
fibres that contain specialized
proteins. These proteins contract
when signalled by nerve cells.
When they contract, the muscles
get shorter and thicker. Skeletal
muscle tissue is one of the three
types of muscle tissue. The others
are smooth muscle, mostly located
in the intestines and cardiac
muscle in the heart.
SUPPORT, PROTECTION, and MOVEMENT
The main role of the skeleton is to provide structure and support for
our bodies and anchor points for our muscles. Some bones also
protect the soft internal organs and the brain. Bones also store
calcium and other minerals needed by the organism, and some
bones contain marrow, which produces red and white blood cells.
Cartilage provides a smooth surface where bones come together at
a joint, preventing damage to the ends of the bones. We use skeletal
muscle for voluntary movements of the body, such as walking.
HOW MUSCLES MAKE BONES MOVE
Each end of a skeletal muscle is connected by tendons to one or
more different bones in the skeleton. Tendons are similar to
ligaments but are less elastic and
connect muscles to bones. When
muscles contract in response to
signals from the nervous system,
they exert a force. This force
moves one or both of the bones to
which the muscle is connected.
Muscles can pull, but they cannot
push, so skeletal muscles always
work in opposing pairs or groups.
HOMEWORK
1. List the main functions of the musculoskeletal muscle system
2. Differentiate between a tendon and a ligament
3. Use a simple diagram to describe how opposing muscle pairs
produce movement of the lower leg (Quadraceps, hamstring)