# Science: An Elementary Teacher’s Guide/The Human Body: The Circulatory System

* Content
* The Heart
* The Blood Vessel
* The Blood
* The Lymphatic System

## The Circulatory System

The circulatory system is a vast network of organs and vessels that is responsible for the flow of blood, nutrients, hormones, oxygen and other gases to and from cells. Without the circulatory system, the body would not be able to fight disease or maintain a stable internal environment — such as proper temperature and pH — known as homeostasis. Circulatory system, also known as the cardiovascular system, as simply a highway for blood, it is made up of three independent systems that work together: the heart (cardiovascular); lungs (pulmonary); and arteries, veins, coronary and portal vessels (systemic) In the average human, about 2,000 gallons (7,572 liters) of blood travel daily through about 60,000 miles (96,560 kilometers) of blood vessels. An average adult has 5 to 6 quarts (4.7 to 5.6 liters) of blood, which is made up of plasma, red blood cells, white blood cells and platelets. In addition to blood, the circulatory system moves lymph, which is a clear fluid that helps rid the body of unwanted material. The heart, blood, and blood vessels make up the cardiovascular component of the circulatory system. It includes the pulmonary circulation, a "loop" through the lungs where blood is oxygenated. It also incorporates the systemic circulation, which runs through the rest of the body to provide oxygenated blood.
Homeostasis
Homeostasis refers to "keeping cells in the body relatively constant and balanced".
Homeostasis does not only balance pH levels, but it can also help regulate numerous variables such as temperature levels, water content, blood levels, sugar levels, calcium levels, and plenty of other ions found in the body systems. Homeostasis does not only occur in the circulatory system, it can be found in multiple body systems.
Some examples in which homeostasis fails to regulate include:
* Diabetes
* Anemia
* Hypothermia
* Heart Failure

## The Heart

The heart, is defined as a pump that is responsible for the continuous blood flow through the blood vessels. This vital organ is the size of a human fist, and is lies in the middle of the chest and slightly towards the left of the breastbone. The heart is enclosed in the pericardium which is a double layer, and it is protected by the rib cage. Basically our blood is pumped through a network of vessels that is approximately 75,000 miles, and the excess body fat increases the workload of the heart by adding about 200 miles of capillaries. A mature heart pumps an average of 4,000 gallons a day.
The human heart has four pumping chambers the two located at the upper region are called auricles (also called atriums) and the other two are located further down, are called ventricles. Blood flows from large veins into the auricles, which contract to force it into the ventricles.When the ventricles contract, blood is involuntary push out though large arteries to commence its journey. The two auricles are separated by a divider called a septum, as are two ventricles, so the two heart is essentially a dual pump, with the left and right sides forming completely distinct blood pathways. The right side of the heart takes blood from the body and pumps into the lungs. Blood moves from the right side of the heart to the lungs through the pulmonary arteries. The left side takes the blood from the lungs, and pumps it directly to the body. Valves in the heart and veins avoid blood from moving in the wrong direction as the organ alternately pumps and relaxes.
Here is a video link that demonstrates the circulatory system of blood flow through a heart: https://www.youtube.com/watch?v=7XaftdE_h60

## Quiz

Take this quiz and test your knowledge!

## Blood Vessels

System of blood vessels includes arteries, veins and capillaries. The arteries transport blood away from the heart and veins bring blood toward the heart. Blood moves from the right side of the heart to the lungs through pulmonary arteries and returns to the left side of the heart through the pulmonary veins. The left side of the heart pumps blood into an artery aorta this leads other arteries like highways. Capillaries are the smallest of the blood vessels are at the end of the supply line they receive and distribute the goods. Capillary walls are so thin that molecules of oxygen and nutrients pass right through into the cells and molecules of carbon dioxide and other waste products pass from the cells into the blood. Then when is through with the delivery and taking on a new load of waste products blood flows into tiny veins in turn lead to larger veins on the return trip to the heart.

## Blood

The blood consists of a liquid called plasma, solid material, red cells, white cells, and platelets.

## Plasma

This brings nutrients to the cells and carries away waste materials. It contains hormones this control many activities in the body and fibrinogen helps the blood to clot.
Plasma is just a liquid portion within our body blood, as we know this is something that can be donated and it reproduces itself as the days go by.

## Red Blood Cells

Are the most abundant solid material in human blood with about 5 million of them in each milliliter. Red blood cells pick up oxygen from the lungs and deliver it to the cells of the body and is exchanged for carbon dioxide then return the carbon dioxide to the lungs to be exhaled. The blood gets its red color from an iron compound called hemoglobin is contained in the red blood cells and which is responsible for their ability to transport oxygen. Each red blood cell has a life span of about 120 days. During that time they make approximately 75,000 round trips from the heart to other parts of the body.Also,Red blood cells can be located in marrow, within the hallow bones.

## White Blood Cells

Are larger but much less numerous than red blood cells. Colorless and spherical in shape, irregular protrusions, and defend the body against infection and disease.White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders.

## Platelets

Are colorless, irregularly shaped, and even smaller than the red blood cells. It give off a chemical that reacts with fibrinogen in plasma to cause clotting when exposed to the air at a wound site.

## Lymphatic System

Works very close with the circulatory system of the blood. As blood moves through capillaries around the body cells white blood cells pass through the capillary walls and move among the cells collecting harmful bacteria and other disease causing organisms. Some of the blood plasma seeps through also flows freely among the cells bathing them with nutrients and picking up waste materials some white cells go along with other matter in the plasma.

## Lymph Nodes

The nodes it is a concentration of white blood cells that kill harmful bacteria that might have been picked up from the cells by the lymph. The lymph is filtered and purified before being returned to the blood.

## Respiratory System

Is to supply the body with oxygen and to discard carbon dioxide which is product of cells. Blood transports oxygen from the lungs to the cells of the body and transport carbon dioxide back to the lungs to be exhaled.'
The main parts are- Nose Lungs Mouth Throat Heart'