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cardiovascular
Your cardiovascular system is a network made up of blood vessels and your heart, which is responsible for pumping blood and oxygen around your body. It also transports carbon dioxide, a waste product, from your body to your lungs – breathing out removes carbon dioxide from your body. How does your cardiovascular system work?

When you breathe in air through your mouth and nose it travels to your lungs. Oxygen from the air is absorbed into your bloodstream through your lungs. Your heart then pumps oxygen-rich (oxygenated) blood through a network of blood vessels (arteries) to tissues including your organs, muscles and nerves, all around your body.

When blood reaches the capillaries in your tissues it releases oxygen, which cells use to function. Cells release waste products, such as carbon dioxide and water, which your blood absorbs and carries away. The used (deoxygenated) blood then travels through your veins and back towards your heart. Your heart pumps the deoxygenated blood back to your lungs, where it absorbs fresh oxygen, releases the carbon dioxide and the cycle starts again. Your lifestyle plays an essential part in maintaining your long-term cardiovascular health. Eating a healthy diet, getting plenty of exercise and not smoking can all help you to maintain a healthy cardiovascular system.

Respiratory

The primary function of the respiratory system is to supply the blood with oxygen in order for the blood to deliver oxygen to all parts of the body. The respiratory system does this through breathing. When we breathe, we inhale oxygen and exhale carbon dioxide. This exchange of gases is the respiratory system's means of getting oxygen to the blood. Respiration is achieved through the mouth, nose, trachea, lungs, and diaphragm. Oxygen enters the respiratory system through the mouth and the nose. The oxygen then passes through the larynx (where speech sounds are produced) and the trachea which is a tube that enters the chest cavity. In the chest cavity, the trachea splits into two smaller tubes called the bronchi. Each bronchus then divides again forming the bronchial tubes. The bronchial tubes lead directly into the lungs where they divide into many smaller tubes which connect to tiny sacs called alveoli. The average adult's lungs contain about 600 million of these spongy, air-filled sacs that are surrounded by capillaries. The inhaled oxygen passes into the alveoli and then diffuses through the capillaries into the arterial blood. Meanwhile, the waste-rich blood from the veins releases its carbon dioxide into the alveoli. The carbon dioxide follows the same path out of the lungs when you exhale. The diaphragm's job is to help pump the carbon dioxide out of the lungs and pull the oxygen into the lungs. The diaphragm is a sheet of muscles that lies across the bottom of the chest cavity. As the diaphragm contracts and relaxes, breathing takes place. When the diaphragm contracts, oxygen is pulled into the lungs. When the diaphragm relaxes, carbon dioxide is pumped out of the lungs.

Digestive system
Uniquely designed to turn the food you eat into energy your body needs to survive. Here's how it works.

Mouth; the mouth is the beginning of the digestive tract. In fact, digestion starts here as soon as you take the first bite of a meal. Chewing breaks the food into pieces that are more easily digested, while saliva mixes with food to begin the process of breaking it down into a form your body can absorb and use. Throat; also called the pharynx, the throat is the next destination for food you've eaten. From here, food travels to the oesophagus or swallowing tube.

Oesophagus; the oesophagus is a muscular tube extending from the pharynx to the stomach. By means of a series of contractions, called peristalsis, the oesophagus delivers food to the stomach. Just before the connection to the stomach there is a "zone of high pressure," called the lower oesophageal sphincter; this is a "valve" meant...
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