Circulatory System
How the Blood Gets Around the Body
The circulatory system is made up of the vessels and the muscles that help and control the
flow of the blood around the body. This process is called circulation. The main parts of the
system are the heart, arteries, capillaries and veins.
As blood begins to circulate, it leaves the heart from the left ventricle and goes into the aorta.
The aorta is the largest artery in the body. The blood leaving the aorta is full of oxygen. This
is important for the cells in the brain and the body to do their work. The oxygen rich blood
travels throughout the body in its system of arteries into the smallest arterioles.
On its way back to the heart, the blood travels through a system of veins. As it reaches the
lungs, the carbon dioxide (a waste product) is removed from the blood and replace with fresh
oxygen that we have inhaled through the lungs.
Veins and Arteries
Arteries are tough, elastic tubes that carry blood away from the heart. As the arteries move
away from the heart, they divide into smaller vessels. The largest arteries are about as thick
as a thumb. The smallest arteries are thinner than hair. These thinner arteries are called
arterioles. Arteries carry bright red blood! The color comes from the oxygen that it carries.
Heart
Did you know that your heart is the strongest muscle? Your heart is divided into two sides.
The right side pumps blood to your lungs where it picks up oxygen. The left side pumps
oxygen-soaked blood out to your body. They do not work on their own, but together as a
team. The body's blood is circulated through the heart more than 1,000 times per day.
Between five and six thousand quarts of blood are pumped each day. Your heart is about the
same size as your fist.
Your heart's job is to pump blood around your body. Its muscles
contract and squeeze out blood. The left-hand side pumps blood
from the lungs to the rest of your body. The right-hand side pumps
stale blood from your body back to your lungs for a fresh supply of
oxygen.
What is Blood?
Blood is thicker than water and has a little bit salty taste. In an adults body there is 10.6 pints
of blood circulating around. In their blood there is billions of living blood cells floating in a
liquid called plasma. If you took a small sample of this blood and poured it into a test tube
and then put it in a machine called a centrifuge, you would be able to see the layers of this
blood. This machine spins the blood around so fast that it separates the red blood cells, from
the white blood cells, from the platelets. The red blood cells sink to the bottom because they
are the heavier, more solid parts, but the plasma remains at the top because it is lighter. The
plasma is 95% water and the other 5% is made up of dissolved substances including salts.
The Digestive System
The human body needs fuel to live. We eat food for fuel. But just getting the food into the
body is only a small part of the process. The food must be broken down into chemicals that
the body can use. This whole process is called digestion. Some of the organs involved in
digestion are the mouth, esophagus, stomach, small and large intestines, gallbladder,
pancreas and liver.
Mouth and Teeth
The mouth and teeth are the first step in breaking food down. During the process of chewing,
food is shredded and ground. Powerful muscles move the mandible, or lower jaw, while the
food is chewed. The front teeth cut the food and the back teeth grind the food.
There are three main parts to the tooth: the root, the neck and the crown. The root is the part
inside the jaw. The neck is a narrow connection between the root and the crown. The crown
of the tooth is above the gum.
First teeth come in between 6 and 8 months. By age 6, baby teeth are gradually replaced by
permanent teeth. There are 32 permanent teeth.
When food is being chewed, saliva is squirted into the mouth. Saliva helps to soften the food.
It contains an enzyme that helps break down the starch in the food.
After chewing, the food is swallowed and passes down the esophagus to the stomach. The
esophagus is about ten inches long. The tongue helps push the food to the back of the
mouth, and the muscles in the esophagus move the food down the tube.
Travelling Food
The stomach is a sac shaped like a "j" and is about eight inches long. In the stomach, food is
mixed with acids. The muscles in the stomach move, which helps break down the food. The
stomach is protected from the acid by a lining. From the stomach, the food pulp is sent to the
small intestine. Food leaves the stomach a little bit at a time.
The small intestine is the final place for digestion. Measuring about twenty feet in length, the
small intestine is one inch in diameter. Digestive juices released in the small intestine finish
breaking down the food.
The food is moved along the small intestine in a squeezing motion known as peristalsis. This
motion is much the same as squeezing a tube of toothpaste. All of this movement causes the
noise when we say our stomach is "growling."
Lining the small intestine are millions of fingers called villi. These absorb the chemicals that
we need from the food into the body. It is at this point the food is actually in the body.
Waste products and food that are not absorbed in the small intestine pass into the large
intestine. This waste material is called feces. The large intestine is only five feet long but is
larger in diameter than the small intestine. The large intestine includes the colon.
In the large intestine, feces are formed from water, undigested food and bacteria. Water is
absorbed back into the body so the waste material becomes more solid as it travels through
the colon. It may take as long as twenty hours for food to pass completely through the large
intestine.
Gall Bladder Pancreas and Liver
The pancreas is an elongated gland that is below the stomach. It produces pancreatic juice
that contains digestive enzymes. The pancreas also secretes insulin into the blood. Insulin is
needed to allow glucose or sugar from food to get into the bloodstream. People who cannot
produce insulin are diabetics.
The largest gland in the body is the liver. It is on the right side of the body underneath the
ribs. It weighs about three pounds and is eight inches long. The liver stores a form of glucose
called glycogen. Vitamin A is manufactured in the liver. Bile which is needed to breakdown
fat, is made in the liver. This organ is also where alcohol, drugs, bacteria and old blood cells
are broken down and removed from the body. Damage to the liver can be serious because
this organ is extremely necessary to life.
The gallbladder is a small sac on the underside of the right lobe of the liver. It stores bile that
is made by the liver. Bile travels from the liver through the hepatic ducts to the gallbladder. It
holds about two ounces of bile. Bile is needed to breakdown the fat that is in food.
Respiratory System
All animals need oxygen to live. Land animals get oxygen from the air. Without the oxygen in
the air we cannot survive more than a few minutes. Breathing happens automatically, we do
not have to even think about it.
We breathe in order to take oxygen into our bodies and get rid of carbon dioxide. The oxygen
is carried in the blood to all the body's cells. The air we breath out has 100 times more
carbon dioxide than the air we breath in.
Nose and Nasal Cavity
The respiratory system is made of body parts that are in charge of your breathing. It includes
your nose and nasal cavity. You inhale air though your nose. As you inhale, small specks of
dirt are trapped by many tiny hairs in your nose. This cleans the air. The hairs stop the dirt
from going further in your body. The moist inside surface in your nose traps even smaller
pieces of dirt. The nasal cavity, the air passage behind the nose, plays an important role in
breathing. The nasal cavity is divided into a right and left passageway. The tissue that covers
the wall of your nasal cavity contains many blood vessels. Heat from the blood in the vessels
helps warm the air as you breath. Moisture is added to the air you breath by special cells in
the walls of the nasal cavity. The air is warmed and moistened before it reaches your lungs.
You usually cannot see the air you breathe out. But on cold days the air you exhale is visible.
This is because your breath contains water vapor, as well as carbon dioxide. As the water
vapor meets cold air, it condenses and turns into tiny droplets of liquid water which look like
white puffs of steam.
Windpipe and Bronchial Tree
The windpipe (trachea) joins the the the upper respiratory tract to the lungs. If you gently
touch the front of your throat you can feel the trachea. The bottom of the trachea splits into
two branches called bronchi. One enters the right lung and one goes to the left lung.
The bronchial tree's job is to spread the air from the trachea over a very wide area as quickly
as possible. The air passing through the windpipe divides into two branches. These divide
into twigs called bronchioles. These twigs open into little bags called alveoli.
We have about 300 million alveoli (air sacs) in each lung. The alveoli gives our lungs a huge
surface for absorbing oxygen from the air.
When you breathe in your chest muscles pull your ribs up and out. Your diaphragm, the
muscle under your chest, moves down. Your chest expands and your lungs fill with air. When
you breathe out, the muscles relax. Your ribs move down, and your diaphragm moves up to
squeeze air out.
Lungs
Lungs provide the breath of life. Our lungs are about the size of a pair of footballs. They fill
our chest from the neck to the ribs. The lungs are protected by our ribs. The lungs are the
pickup place for oxygen and the drop off place for carbon dioxide. The lungs are always
working, breathing in oxygen and breathing out carbon dioxide.
Blood is pumped into the lungs from the heart through the pulmonary arteries. Blood with
oxygen leaves the lungs through the pulmonary veins and travels to the heart. Oxygen is the
fuel that makes all the body processes run.
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