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= __**The Human Circulatory System**__ = = The Human Circulatory System is made up of several key components. =

__** The Heart **__

The above diagram should be learnt with approropriate labels.

The heart is the pump of the body. It is what pushes the blood around the arteries and allows nutrients to be moved around our bodies.
The heart has four chambers, the Left and Right Atria, and Left and Right Ventricals. There are also major blood vessels that enter and exit our heart, they are: Aorta, Vena Cava, Pulmonary Artery, and Pulmonary Vein. The heart pumps both oxygenated and non-oxygenated blood around our bodies.

As the diagram shows, non-oygenated blood enters the heart from the body through the Vena Cava and fills the Right Atrium. The blood is then pushed through a valve into the Right Ventrical with the first contraction (beat) of the heart. On the second contraction (beat) the non-oxygenated blood is pushed out of the Right Ventrical into the Pulmonary Artery to the Lungs. Oygenated blood then returns from the Lungs through the Pulmonary Vein and into the Left Atrium. With the first contraction (beat) oxygenated blood is pushed through a valve to the Left Ventrical. On the second contraction (beat) oxygenated blood is pushed out of the Left Ventriacal into the Aorta, where the oxygenated blood is then dispersed throughout the body.

__**The vessels of the Human Circulatory system:**__
- Arteries - Veins - Capillaries

- Arteries are muscular and are responsible for taking oxygenated blood from the heart to the organs and tissues of the body. (With the exception of the Pulmonary system)

- Veins use a valve system to transport non- oxygenated blood from the tissues back to the heart. (With the exception of the Pulmonary system)

- Capillaries are the small vessels that allow the blood to move throughout the body between the tissues, Veins and Arteries. Look at the image below see how the wall of the Capillary is only one cell thick.

Look at the following diagram and note that the Veins from the body carry non- oxygenated blood from the body, but oxygenated blood from the Lungs.

__**The Red Stuff:**__
Blood is made up of several components; the ones that are important for you to know are: Red blood cells (containing Hemoglobin) White blood cells (immune system) And water (Plasma)

Below is a diagram of a red blood cell. Oxygen attaches to the Hemoglobin and this is what carries it around the body. (It’s like the bus for people, it stops and drops off oxygen where it is needed)

__**Diffusion:**__ Diffusion is the movement of molecules from high concentration to low. In this case it is the movement of oxygen and carbon dioxide to and from the tissues and vessels.

When a tissue such as the bicep muscle is working out, it is in demand of oxygen and is producing carbon dioxide. Carbon dioxide is a toxin and the muscle wants to get rid of it. As the red blood cells travel through the Capillaries containing oxygen filled Hemoglobin, the gradient causes the oxygen to diffuse across the membranes and into the muscle cells. In the same way that the carbon dioxide gradient causes it to move into the blood.

Below is a diagram that shows diffusion in the lungs.
 * Note alveolus is tissue of the lung