The Journey of Blood: From the Heart to the Body & The Protective Layers of the Respiratory System

'1. Blood flows out from the left ventricle and enters the aorta - the largest artery in the body. From there, the vessels continuously branch out into smaller and larger blood vessels, reaching every part of the body.

2. The entire respiratory tract is protected by three layers of barriers. Firstly, nasal hairs block foreign substances such as bacteria, viruses, and dust from entering the respiratory tract. Secondly, the mucus secreted by the tracheal epithelial cells traps the foreign substances and is then expelled by the movement of cilia on the epithelial lining. Thirdly, there are cells in the alveoli that can engulf foreign substances in the lungs.'