Circulatory and respiratory

Blood carries all the nutrients ingested in food around our bodies, its main function is to carry oxygen around our body this is so our cells can function properly. Blood is pumped around the body by the heart which is connected to the body by lots of different vessels. Blood also collects oxygen from the lungs and delivers it to the body.
Veins are tubes which form part of the blood circulation system of the body, carrying mainly oxygen-depleted blood towards the heart.
Arteries are the blood vessels that deliver oxygen-rich blood from the heart to the tissues of the body. Every artery is a muscular tube lined with smooth tissue and has three layers: * The intima, the inner layer lined by a smooth tissue called endothelium * The media, a layer of muscle that lets arteries handle the high pressures from the heart * The adventitia, connective tissue anchoring arteries to nearby tissues
The largest artery is the aorta, the main high-pressure pipeline connected to the heart's left ventricle. The aorta branches into a network of smaller arteries that extend throughout the body. The arteries' smaller branches are called arterioles and capillaries. The pulmonary arteries carry oxygen-poor blood from the heart to the lungs under low pressure, making these arteries unique.
Capillary’s are extremely small blood vessel which are located within the tissues of the body, they transport blood from arteries to veins. Capillaries are most abundant in tissues and organs that are metabolically active. For example, muscle tissues and the kidneys have a greater amount of capillary networks than do connective tissues.

Capillaries are so small that red blood cells can only travel through them in single file. Capillary walls are thin and are composed of endothelium. Oxygen, carbon dioxide, nutrients, wastes, and fluids are exchanged through the