In details

The human respiratory system

The human respiratory system

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At nasal cavities (or nasal cavities) and the mouth are the air inlets to our respiratory system.

The air that enters the nasal passages is filtered, moistened and heated, before going to the trachea. Eyelashes lining the epithelium of the nasal cavities trap particles of dirt and microorganisms that exist in the air. The particles adhere to the mucus produced by the epithelial cells and are subsequently expelled from the nasal cavities.

Then the air passes through the larynx (where our vocal cords - or vocal folds) meet, crossing the glottis that is the entrance to the larynx. Just above it is a cartilaginous structure, the epiglottis, which closes the passage of food to the larynx, with no danger of food entering the airways. Then air enters the trachea, which forks into two main bronchi. Each bronchus branches numerous times and causes progressively less caliber bronchioles until the terminal bronchioles form. These, in turn, end up in extremely thin-walled pouches, the pulmonary alveoli.

Gas exchange: happen in the alveoli

Gas exchange occurs between the alveolar air and the blood contained in the capillaries. The blood from the tissues is high in carbon dioxide and low in oxygen. Alveolar air is rich in oxygen and low in carbon dioxide.
Carbon dioxide diffuses from the blood into the alveolar air, leaving the hemoglobin molecules in the red cells free. In turn, oxygen diffuses from the alveolar air into the blood, occupying the vacant places in the hemoglobin molecules.


1- oxygen 2- Carbon dioxide
3- arterial blood 4- Inhaled / Exhaled Air
5- venous blood 6- blood capillary