THE CIRCULATORY SYSTEM


The circulatory system transports nutrients and oxygen to our cells .

* The heart is a muscular organ that pumps blood around the body.
* The blood collects oxygen from the alveoli and nutrients from the    small intestine and transports them to all the cells . 
* The blood vessels are the tubes through which blood circulates.        There are  three types of blood vessels : arteries , veins and              capillaries.



THE BLOOD

Blood is a red liquid tissue made up of cells that float in a liquid called plasma.

* Red blood cells carry oxygen .
* White blood cells remove bacteria and viruses from the blood .
* Platelets are small fragments of cells that form blood clots when a    blood vessels breaks.


RED BLOOD CELL               WHITE BLOOD CELL         PLATELETS 


THE HEART 

The heart uses rhythmic systole and diastole movements to pump the blood around the body .
Blood enters the atria through the veins and passes to the ventricles . Between the atria and ventricles, there are valves that prevent blood from flowing back to the atria .




HUMAN CIRCULATION 

* Human circulation is closed. In mammals, the heart septum              separates the two halves of the heart. 
* Human circulation is double. 
   - Pulmonary circulation. The blood releases carbon dioxide in it        comes out of the right ventricle through the pulmonary artery. 
     Then, in the alveoli, the blood releases carbon dioxide and takes      oxygen. 
     Finally, the blood with oxygen in it reaches the heart´s left                atrium through the pulmonary veins.
   - Systemic circulation. The blood with oxygen in it leaves the left      ventricle throgh the aorta. 
     Finally, the blood with carbon dioxide in it returns to the heart.        It reaches the right atrium throuht the vena cava.