The Respiratory and Circulatory System in Mammals

Windpipe

• Mammals take air in through the windpipe. In humans and many other mammals, this is called the trachea. Air breathed in through the mouth or nose travels down the trachea until it reaches the lungs. Fresh air full of oxygen travels through the trachea, as does air leaving the lungs laden with carbon dioxide. Since the mouth is used for eating and drinking as well as breathing, the epiglottis in the back of the mouth closes off the trachea during eating or drinking so food or liquid does not enter the lungs.

Lungs

• The lungs are the main respiration organs in mammals. The lungs capture oxygen from the air and dissolve it in the blood so it can be transported throughout the body. Blood that has been depleted of oxygen --- deoxygenated blood --- also passes through the lungs so they can remove the excess carbon dioxide and release it from the body.

Heart

• The heart is the part of the circulatory system responsible for pumping the blood throughout the body. Mammal hearts contain four chambers: two atria and two ventricles. One half of the heart pumps oxygenated blood from the lungs throughout the body while the other half receives the deoxygenated blood from the body and directs it to the lungs to be filtered.

Blood Vessels

• Mammals have a closed circulatory system, which means blood is distributed throughout the body via a series of blood vessels. Arteries transport blood from the heart while veins carry blood back to the heart. Usually arteries transport oxygenated blood and veins transport deoxygenated blood; however, for arteries and veins that extend between the lungs and the heart, the reverse is true. The smallest blood vessels, capillaries, are where the exchange of water and nutrients actually takes place.

Blood

• Blood is a bodily fluid that carries oxygen and nutrients to all the cells of the body and transports waste materials away from the cells. In mammals, blood cells are suspended in plasma, which allows them to flow easily. Red blood cells, also called erythrocytes, bind with oxygen in the lungs and transport the oxygen through the body. Some carbon dioxide is removed from the body via erythrocytes, but the majority is carried back to the lungs in the form of bicarbonate dissolved in the blood plasma.