Topics: Respiratory system, Oxygen, Thoracic cavity Pages: 6 (1978 words) Published: December 21, 2012

Biology Take-Home Assignment

Describe the process of respiration in man and toad using suitable diagrams

BY: Nwaezeigwe Franklin

The Process of Respiration in Man
The Respiratory system in Man: The human respiratory system is typical of the respiratory systems of mammals in general. It includes the nasal passages or nostrils, the pharynx, the larynx, the bronchi and the lungs. The respiratory system starts with the nose that encloses the nasal cavity. The nasal cavity opens outside through the openings called the nostrils. The nasal cavity is divided into two portions by a cartilaginous septum and is lined by fine hairs that filter the dust particles from the air. The nasal cavity is separated from the mouth by hard and soft palate that forms its floor. It opens into the region called the pharynx. The pharynx leads into the larynx or the voice box. The larynx is held open with the help of cartilages. 'Adam's apple' is a prominent cartilage of larynx. The larynx leads into the trachea or wind pipe. The trachea is held open with the help of C-shaped cartilaginous rings. The open ends of the rings are towards the oesophagus also known as the food pipe, it lies just behind the trachea and it prevents food particles from falling into the larynx and trachea when food is being swallowed. The trachea then branch into two main branches called bronchi. Each bronchus is also supported by the cartilaginous rings. The bronchus then branches into smaller tubes called bronchioles. The bronchioles progressively lose the cartilages as they become narrower. The bronchioles end as fine tubules called the alveolar ducts. The alveoli communicates with the atmosphere through a continuous air passage leading from them to the bronchioles, bronchi, trachea, larynx, pharynx, nostrils, and mouth. The mass of each lung consists mainly of numerous air sacs and the small tubes (bronchioles) which lead into them. The alveoli are richly supplied with blood capillaries. Each lung is enclosed by two membranes called the outer and the inner pleural membrane. The membranes enclose a space called the pleural cavity that contains a fluid. The lungs are capable of expanding and contracting as they are elastic organs. Lubrication for their free movement is provided by the fluid in the pleural cavity.

Breathing in Man
Breathing is the process that moves air in and out of the lungs. Breathing goes on automatically. But if you want to take a deep breath, you can do so. Therefore, we say that respiration is partly involuntary (automatic), and partly voluntary (by will). Respiration is controlled by a small centre located in the posterior part of the brain. This centre is called respiratory centre. The chest cavity is an air-tight chamber, bounded by the thoracic wall which contains the rib cage, and by the diaphragm. In between the ribs are two layers of muscles known as the internal and external intercostal muscles. When the external intercostal muscles contract and the internal intercostals muscles relax, the ribs are moved upward and outward to increase the volume of the thoracic cavity. When the internal intercostals muscles contact, while the external intercostals muscles relax the ribs move downward and inward, thus reducing the volume of the thoracic cavity. When the muscles of the diaphragm contract, the diaphragm assumes a flat position, thus decreasing the volume of the thoracic cavity. Breathing in and out of man is brought about by the alternative increase and decrease in the size of the thoracic cavity as a result of the actions of the intercostals muscles and the diaphragm. Inspiration: The manner in which the air is brought into the lungs is called inspiration. It occurs as follows: The diaphragm contracts and changes from a dome to a flat shape while the external intercostals muscles contract causing the ribs to move upward and outward. Those two actions increase the volume of the thoracic cavity. As the thoracic...
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