Respiration in man
The respiratory arrangement of man comprises of lungs and air sections. The air sections convey natural air to the respiratory locales.
Air passage ways or respiratory system of man
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Air passage ways consists of nostrils, nasal cavities, pharynx, larynx, trachea, bronchi bronchioles, alveolar ducts and alveolar sacs.
1. Nasal cavities
Nasal cavities are lined with mucous membrane. Mucous membrane is composed of ciliated epithelium. There is projection of bones from the wall of the internal nose. These bones subdivide each nasal cavity into three passage ways. The nasal cavities open into throat or pharynx by two openings. There are following functions of nasal cavities.
(a) Air enters the nasal cavity through nostrils.
(b) The hairs and mucous of nostrils trap the large duct particles.
(c) the mucous membrane of nasal cavity makes the air moist and warm. It also filters the small foreign particles.
2. Throat or pharynx
The pharynx is a muscular passage. It is also lined with mucous membrane. The air is transferred from the pharynx into the larynx.
3. Larynx or voice box
The larynx is a complex cartilaginous structure. It surround the upper end of the trachea. One of the cartilages of the larynx is epiglottis. The epiglottis is muscularly controlled structure. It shows hinge like action. It acts as a lid. It automatically closes the opening of the larynx during the act of swallowing. So the epiglottis forestalls the section of food or fluid into the larynx. The opening of the larynx is called glottis. The glottis is lined by mucous membrane. The mucous membrane of glottis forms two thin edged fibrous bands called vocal cords. These vocal cords are stretched across the glottis. The vocal cords vibrate by air and produce voice.
4. Trachea or wind pipe
Trachea is a tubular structure. It lies ventral to the oesophagus. It extends into the chest cavity or thorax. There are series of C-shaped cartilage ring in the wall of trachea. The cartilaginous ring keeps the windpipe from imploding. So they keep the trachea open.
5. Bronchi and bronchioles
Trachea divides into right and light bronchi in the thorax. Each bronchus enter into the lung. Each bronchus in lungs divides and subdivides into small bronchi. The bronchi with diameter less than1 mm are called bronchioles. The bronchi have similar cartilaginous plates. These cartilaginous plates are irregularly distributed. The cartilages are totally absent in bronchioles. Bronchioles are made up of mainly circular smooth muscles.
6. Air sacs and alveoli
The bronchioles continue to divide and subdivide deep into the lungs. These bronchioles are at long last opened into an enormous number of air sacs. Air sac is the practical unit of the lung. Each air sac comprises of alveoli. The alveoli are infinitesimal single layered structures. There is a rich organization of blood vessels overlying the alveoli. These capillaries produce an excellent site for the exchange of gases.
7. Lungs
The lungs are closed sacs. They are connected to the outside through trachea and nostril or mouth. The lungs have millions of alveoli. So they spongy in nature. Lungs are placed in the chest cavity. The floor of the chest is called diaphragm. Diaphragm is a sheet of skeletal muscles. It isolates the chest depression from the stomach pit. Lungs are covered with pleura. The pleura are double layered thin membrane sacs.
Breathing
Mechanics of the voluntary and involuntary regulation of breathing in ma. The pumping of oxygen containing fresh air into the lungs and pumping of the carbon dioxide containing air out of the lungs is called breathing. Breathing is a mechanical process. It comprises of two stages, motivation and termination. Breathing occurs rhythmically. The frequency of breathing in man at rest is 15 to 20 times per minute.
Inspiration
The moving of the fresh air in the lungs is called inspiration. The space inside the chest cavity is increased during inspiration. This space is increased by two ways:
(a) The muscles of the ribs contract and elevate the ribs upward and forward.
(b) The muscles of the diaphragm also contract and diaphragm becomes less domelike.
Expiration
The removal of the consumed air from the lungs is called expiration. The space in the chest cavity is decreased by two different ways:
(a) The intercostals muscles of the ribs are relaxed during expiration. Therefore the ribs move downward and inward. So the space in the sides of the chest cavity is diminished.
(b)At the same time the muscles of the diaphragm are relaxed and the diaphragm becomes more domelike. So the chest cavity is also reduced from the floor.