HUMAN RESPIRATORY AND CIRCULATORY SYSTEM

HUMAN RESPIRATORY AND CIRCULATORY SYSTEM

Breathing

Air enters the body through the nostrils. The nostrils lead into nasal passage or nasal cavity. Dust and bacteria are trapped by the hair and mucus in the nasal passage. The air is also warmed and moistened in the nasal passage. From here, air is passed to windpipe or trachea through larynx or voice box. The opening of air passage in the larynx is called glottis which has a lid called epiglottis. The epiglottis prevents food from entering the trachea. Trachea divides into two tubes called bronchi (singular: bronchus). The bronchi carry air into the lungs one to each lung. The walls of the trachea and bronchi bear cilia and have mucus which trap dust particles and bacteria. Inside the lung the bronchi branch into smaller tubes called bronchioles. Each bronchioles ends in a group of sacs or alveoli (singular; alveolus). The lung look like sponges due to the presence of alveoli. Millions of alveoli are found the lungs. They are surrounded by thick network of blood capillaries.

REPIRATORY SYSTEM IN MAN.

Breathing

Gaseous exchange takes place in the alveoli. Oxygen from the air diffuses into blood through the walls of the alveoli. At the same time carbon dioxide carried by the blood from the body cells diffuses out into the alveoli. From the alveoli it passes out of the body. Blood circulation supplies each of the body cells with oxygen and collects carbon dioxide produced in the cell during oxidation of food.