Animals move oxygen into—and carbon dioxide out of—the body with a respiratory system.
Although cellular respiration refers to an energy-releasing series of chemical reactions that occurs in
cells, the word respiration also means the process of exchanging gases. Finally, in many but not all
animals, air is physically pumped into and out of the body by the process of breathing.
GAS EXCHANGE SURFACES
All aerobic organisms—both plants and animals—exchange oxygen (O2) and carbon dioxide
(CO2) with their environment. For example, the single celled ameba exchanges these gases with the
watery environment in which it lives. Oxygen in the water and carbon dioxide in the ameba move by
diffusion across the cell membrane. As O2 gets metabolized inside the ameba, the concentration of O2
molecules in the cytoplasm becomes less than in the water outside the cell. Then, O2 diffuses into the
cell through the cell membrane. At the same time, CO2 diffuses out of the cell as its concentration
increases as a by-product of cellular respiration. Respiration in all organisms involves the diffusion of
gases across cell membranes. Gases must be moved to and from the environment. They must cross a
barrier to be moved in or out of the animal.
With the exception of a few snake species, all terrestrial vertebrates—animals with backbones
that live on land, such as frogs, snakes, birds, and humans—have two In shape, lungs look somewhat
like balloons. Located inside an animal, lungs are directly connected by tubes to the air outside. Blood
vessels next to the lungs transport gases to and from body cells.
The human respiratory system is similar to the respiratory system of other mammals. Air
moves through the nostrils into the nasal cavity, where dirt and other particles in the air are trapped by
hairs and mucus. The air is also warmed, humidified, and tested for odors. The nasal cavity leads to the
pharynx, where it meets air and food arriving from the mouth. Air continues flowing down, passing by
the larynx (lair inks). The vocal cords are in the larynx. When air moves out of the body, it passes over
the vocal cords. The air can cause the vocal cords to vibrate, producing the sounds of our voice. In
males, hormones increase the size of the voice box, providing a deeper sound. Continuing down the
tube, the trachea is surrounded by rings of stiff cartilage. The rings help maintain the tubelike shape of
the trachea, thus keeping it open.
The trachea branches into two bronchi. Each bronchus (singular) leads to a lung. In the lungs,
the bronchi continue branching into smaller and smaller tubes called bronchioles. Most of these tubes
are covered on the inside by mucus and by tiny hairlike extensions called cilia. The cilia move back
and forth in a wavelike motion. As dust and other particles in the air get trapped in the mucus, the
beating cilia help move them up the trachea.
The tiniest bronchioles end in bunches of microscopic hundreds of millions of air sacs, the
alveoli. The lining of the alveoli, just a little smaller than a handball court area, acts as our respiratory
surface. Blood vessels surround the alveoli. Only when oxygen molecules diffuse across this lining do
they enter into our blood and really enter our bodies.
All mammals, including humans, move air into their lungs by lowering the air pressure in the
lungs. Between your ribs are muscles. These muscles move your ribs. When the muscles move the ribs
upward and outward, the rib cage expands. At the same time, the diaphragm, a large flat muscle that
lies across the bottom of the chest cavity, contracts and moves down. This movement also increases the
size of the chest cavity. The air pressure lowers in the lungs because the same amount of air suddenly
has more space to fill. Inhalation occurs when air rushes into the lungs through the respiratory tubes.
The lungs fill with air. To move air out, the diaphragm and the muscles between the ribs relax. When
they return to their original positions, the volume of the chest cavity decreases. With less space to fill,
the pressure of the air in the lungs increases and air moves out. Exhalation occurs.
Respiratory Homeostatic disorders
• Bronchitis. This is an inflammation and swelling of the inside of the bronchial tubes. Mucus
accumulates, plugging up the air passages. Breathing is difficult and painful.
• Asthma. The walls of the bronchi contract. These narrowed passages restrict the flow of air.
People with asthma feel like they are suffocating. Asthma is now the most common chronic
childhood disease in the United States.
• Emphysema. This is a very serious chronic disease caused by smoking, in which the alveoli
break down, greatly reducing the total area of the respiratory surface. A person with
emphysema suffers from shortness of breath. Eventually, even the smallest physical effort
• Pneumonia. This disease is caused by a bacterial or viral infection that causes the alveoli to fill
with fluid. Breathing becomes difficult. There is a vaccine available that prevents certain types
of bacterial pneumonia.
To be transported to cells, materials must cross cell membranes from the outside environment
into the body. Absorption of food molecules occurs through the lining of the small intestine.
Absorption of gas molecules occurs through the lining of the lungs’ alveoli. Then materials must be
circulated throughout the body to where they are needed. Transport involves absorption and
Human hearts are four chambered double pump systems. One system pumps blood to the lungs
and back. This pulmonary circulation on the right side of the heart carries oxygen-depleted blood away
from the heart, to the lungs, and returns oxygenated blood back to the heart. The other system pumps
this oxygen rich blood to the rest of the body. This systemic circulation on the left side of the heart
carries oxygenated blood away from the heart, to the body, and returns deoxygenated blood back to the
heart. In the heart the atria receive the blood and pump it into the ventricles, which pump the blood out
of the heart. The right ventricle pumps blood to the lungs and the left ventricle pumps blood to the
body. Since the body is a much longer journey the left ventricle is a larger and thicker walled
Arteries have thick, muscular walls, are very elastic, and carry blood away from the heart.
Blood pressure is measured in the arteries. While the heart is pumping the pressure is higher and is
called systolic pressure, normal level is 120. When the heart is relaxing there is some pressure
remaining, called diastolic, normal is 80.
As blood moves further from the heart is passes into smaller and smaller vessels. The smallest
arteries are called arterioles. The arterioles help control where the blood will flow by muscular
contraction. From these arterioles the blood passes into the capillaries. The capillaries are a single cell
thick and allow diffusion of nutrients into the cells and waste materials out of the cells. Additionally
the blood circulates hormones that will also diffuse at the capillaries. The capillaries are so numerous
that if one person’s were laid end to end they would be long enough to circle the world at the equator.
After moving through capillaries, blood returns through the thin-walled veins, which get larger
and larger closer to the heart. Unlike the walls of arteries, the walls of veins have little elasticity; blood
is under low pressure in them. To prevent the blood in veins from moving backward, one-way valves
work to trap the blood. The blood is moved along with the help of these valves and muscular activities,
such as the contracting of leg muscles that force the blood back toward the heart.
Blood itself is a tissue. But unlike any other tissue in the body, blood is a liquid. Blood is made
up of cells, cell parts, and a clear, light yellow colored liquid called plasma. Plasma is 90 percent
water, plus many important proteins, salts, vitamins, hormones, gases, sugars, and other nutrients. The
cells in the blood include red blood cells, which contain the oxygen-carrying protein hemoglobin, and
white blood cells. Red blood cells, RBCs, lose their nuclei before entering the bloodstream and live
about 120 days. There are five types of white blood cells, all of which are involved in protecting the
body from disease-causing foreign substances. The white blood cells are identified by their
appearances, including different shaped nuclei. Some of these cells live only a few days, while others
live for many years. Blood also contains platelets—fragments of cells that with the aid of a plasma
protein, fibrinogen, plug “leaks” where an injury occurs. Platelets also begin the complex chemical
process that results in production of a blood clot. A blood clot stops the flow of blood out of a
damaged blood vessel. Platelets live about 8-10 days.
Circulatory Homeostatic disorders: Cardiovascular disease
• Heart attack occurs when muscle tissue in the heart dies. When the coronary arteries that bring
blood to the walls of the heart get blocked, the heart tissue beyond the clot is not supplied with
• Atherosclerosis is the gradual buildup of layers of fatty deposits on the insides of arteries.
Because of these deposits, the inside diameter of the blood vessel becomes smaller and the
blood cannot flow so easily. In time, the arteries become “hardened”; the less flexible walls do
not expand and contract as easily with each beat of the heart.
• Strokes that may block an artery in the brain. Depending on what area of the brain is affected,
strokes damage a person’s ability to feel things or to speak and move.
• Hypertension, or high blood pressure increase a person’s chances for atherosclerosis, heart
attacks, and strokes. Sometimes called the “silent killer,” abnormally high blood pressure often
shows no symptoms.
Use the words in the box to fill in the blanks. Words may be repeated.
veins transport circulatory blood
arteries oxygen lungs heart
capillaries ATP carbon dioxide pumped
atmosphere heat to intestine
All animals need to ________________ materials around to the different parts of their body. This is
the job of the ________________ system. The circulatory system consists of a liquid called
_______________, a pump called the ________________ and a series of vessels called
_________________ and ________________.
One thing that must be transported around is a gas called _____________. This gas, _____________,
enters the blood through the ______________. It is then ____________ through the heart and around
the body where it is used along with food to make ______________. The body produces another gas
called _______________, which is a waste product. This gas is carried back to the heart and then to the
lungs where it is released back into the _______________.
The vessels that transport blood away from the heart are called ___________. The blood in arteries is
bright red because it is rich in oxygen. The vessels that transport blood toward the heart are called
_____________. The blood in veins is dark red because it is low in oxygen. ________________ are
small vessels that join the arteries and veins and allow diffusion of materials with the cells.
Nutrients from food are also transported around the body by the circulatory system. They enter the
blood from the small _________________. The circulatory system also helps to regulate temperature
by transporting _________________ around the body.
Type of Blood Component Function Length of survival (for the cells)
THE HUMAN RESPIRATORY SYSTEM
Match the words to the function in the right column. BRONCHIOLES, LARYNX, ALVEOLI,
BRONCHI, PHARYNX, DIAPHRAGM, NOSE, TRACHEA
♦ When we swallow food, a flap called the
epiglottis closes over the top of the larynx and
below it, the trachea (windpipe) to prevent food
entering the lungs
♦ As air passes through the vocal cords, different
pitches of sound are produced
♦ Air, containing 20% oxygen, enters the body
♦ Air is cleaned and warmed as it passes through
the nasal cavity
♦ Mucus and hairs serve to filter dust from the air
♦ Mucus also moistens the inhaled air
♦ The trachea branches into these 2 tubes – one
going to each lung
♦ Mucus and cilia cover the walls
♦ Large, dome-shaped muscle that lies at the
base of the chest cavity
♦ Contracts during inhalation, and relaxes during
♦ These are balloon –like air sacs at the ends of
♦ The walls are very thin, and are surrounded by
fine blood capillaries
♦ Exchange or diffusion of oxygen into the blood
from the inhaled air, and of carbon dioxide out
of the blood to the exhaled air takes place
♦ Lies in front of the esophagus (food tube)
♦ Protected at the front by C-shaped cartilage
♦ Fine hair-like hairs called cilia on the walls of the
trachea ‘brush’ dust upwards and out of the
♦ Cavity at back of nose and mouth
♦ Both food and air pass through
♦ The right and left bronchi branch into many
♦ Walls are lined with mucus and cilia
Define each of these terms in your own words. (Do on separate paper)
alveoli, arteries, atrium, bronchi, bronchioles, capillaries, cilia, circulation, diastolic pressure,
exhalation, inhalation, nasal cavity, plasma, platelets, pulmonary, respiratory surface, systemic,
systolic pressure, trachea, tracheae, veins, ventricle
Use the words in the box to fill in the blanks.
air alveoli sneeze water vapor
lungs oxygen capillaries blood
carbon dioxide trachea inhale exhale
hiccup yawn respiratory cough
mouth diaphragm bronchi pharynx
All animals need ________________ to make energy from food. We get this oxygen
from the _____________ that we breathe. In order to get the oxygen into the blood where it
can be transported to the rest of the body, the air travels through a system of organs called
the _______________ system.
When you ________________, air enters the body through the _______________ or
the ____________. From there it passes through the ______________, air continues into the
_______________ and food into the esophagus. The air travels down the trachea into two
branching tubes called ________________ and then on into the ________________, and
finally into the _________________.
In the lungs oxygen from the air enters the _______________ and into the
_________________. At the same time, the waste gas ____________________ leaves the
blood and then leaves the body when you ___________________. Some
__________________ also leaves the body when you exhale, which is why mirrors get foggy
when you breathe on them. The ______________ is the muscle that controls the lungs.
It is important to keep the respiratory system clear so oxygen can keep flowing into
your body. If something gets in your nose and irritates it, you ___________________. If
something gets in your trachea or bronchi and irritates it, you _________________. If
something irritates your diaphragm, you _________________. Finally, if the brain thinks you
are not getting enough oxygen, then it forces you to _________________.
THE HUMAN CIRCULATORY SYSTEM
Match the words to the function in the right column. Heart, Artery, Vein, Capillary, Atria, Ventricle,
Circulatory Organ Function
♦ Carries blood toward the heart
♦ Relatively thin walled, low pressure system
♦ Contains valves
♦ Most carry deoxygenated blood. Exception is
♦ Blood pumped from the left ventricle to the aorta
♦ Circulates blood to most of the body
♦ Blood exchanges nutrients to cells and picks up
♦ Blood returns to heart via vena cava into right
♦ Carries blood away from the heart
♦ Thick muscular elastic walled, high pressure
♦ Most carry oxygenated blood. Exception is
♦ Largest is aorta
♦ Receives blood from the atria
♦ Pumps blood through a valve to the arteries
♦ Receives blood from the veins
♦ Pumps blood through a valve to the ventricles
♦ Four chambered double pump system
♦ Lies in the thoracic cavity between the lungs
♦ Left side larger because blood must be pumped
♦ Has rich supply of blood vessels to serve itself
♦ Blood pumped from the right ventricle to the
♦ Circulates blood to lungs to pick up Oxygen and
give off carbon dioxide
♦ Blood returns to heart via vein into left atria
♦ Single cell thick
♦ Site of exchange of materials between blood
and cells of the body
♦ Small diameter. Blood cells line up single file to