Vaccines have been around since 1796 preventing people from diseases and decreasing death rates. I believe due to the modern vaccines and medicine people have been living longer than life expectancies in the 1700's and 1800’s, which was between 30 and 40 years. Vaccines train the human body to recognize viruses or bacteria and the antigens (molecule capable of inducing an immune response) will start attacking the virus or bacteria before it tries to spread and cause sickness once it is has recognized it. However, vaccines are not always 100% safe because they can come with side effects. For example, the Hepatitis B vaccine had a severe allergic reaction, called anaphylaxis which caused difficulty breathing, dizziness, and skin rashes for a few people.
The pulmonary artery and its branches deliver blood rich in carbon dioxide (and lacking in oxygen) to the capillaries that surround the air sacs. The circulation of the blood through the lungs. The veins that return the oxygenated blood from the lungs to the left atrium of the heart.
