Question

Which of the following is the correct flow of oxygen in the human body?

1. Oxygen moves from the alveolus and enters the bloodstream to capillaries.
2. Air moves down through trachea to lungs.
3. Blood full of oxygen moves to the heart and then out to body cells.
4. Breathing in air through nose & mouth.
5. Air moves to alveolus in the lungs. (Points : 2)
1,5,3,2,4
4,2,5,1,3
3,1,4,2,5
4,2,3,1,5

Answer 1

it is 4 - 2 - 5 - 1 - 3

From the external nares (nostrils), air, which is usually 21% oxygen mixed with 79% nitrogen, enters into the nasal cavity within the nose and passes over the nasal turbinates (shown but not labeled in the first link below) where it is warmed and humidified, and where nasal hairs remove larger particles of particulate matter from it.

The air then enters the upper part of the posterior oral cavity called the nasopharynx and flows down into the lower throat, or laryngopharynx.

From here it passes through the epiglottis into the larynx and through the vocal cords contained therein before entering the cartilagenous trachea, where a further set of hairs covered in a thin sheet of mucus removes smaller particulate matter missed in the upper respiratory tract.

From the trachea, the air passes into one of the two mainstem bronchi and then proceeds further down the respiratory tree which continues to branch into ever smaller generations of bronchioles. Finally, the air enters the terminal bronchioles, which deliver the inspired air into the air sacs, or alveoli, of the lung tissue.

The oxygen in the alveolar air then passes through the alveolar epithelial cells, through a basement membrane, and finally through the endothelial cells lining the pulmonary capillaries and enters the bloodstream.