Respiratory system

Respiration has two distinct meanings. It refers to the oxidative degradation of nutrients such as glucose through metabolic reactions within the cell, resulting in the production of carbon dioxide, water, and energy. Respiration also refers to the exchange of gases between the cells of an organism and the external environment. Many different methods for exchange are utilized by different organisms. In man, respiration can be categorized by three phases: ventilation (breathing), external respiration, and internal respiration.

Breathing may be defined as the mechanical process of taking air into the lungs (inspiration) and expelling it (expiration). It does not include the exchange of gases between the bloodstream and the alveoli. Breathing must occur in order for respiration to occur; that is, air must be brought to the alveolar cells before exchange can be effective. One distinction that can be made between respiration and breathing is that the former ultimately results in energy production in the cells. Breathing, on the other hand, is solely an energy consuming process because of the muscular activity required to move the diaphragm.

The phenomenon in which the cells of an organism exchange oxygen and carbon dioxide directly with the surrounding environment is termed direct respiration. This form of respiration is a fairly simple process and occurs in small, aquatic animals such as paramecia or hydras. In these animals, dissolved oxygen from the surrounding water diffuses into the cells, while carbon dioxide within the cell diffuses out; no special respiratory system is needed.

With the evolution of animals into larger and more complex forms, it became impossible for each cell to exchange gases directly with the external environment. Consequently, it became necessary for these organisms to have a specialized organ system that would function in gas exchange with the environment. This structure must be thin-walled, and its membrane must be differentially permeable. In addition, the membrane must be kept moist so that oxygen and carbon dioxide could dissolve in it, and it must have a good blood supply. The process of respiration employing this organ system is called indirect respiration. For indirect respiration, the lower vertebrates developed gills and the higher vertebrates developed lungs.

During indirect respiration, gas exchange between the body cells and the environment may be categorized into two phases: an external and an internal phase. External respiration is the exchange of gases by diffusion that occurs between the lungs and the bloodstream. Oxygen passes from the lungs to the blood and carbon dioxide passes from the blood to the lungs. Internal respiration takes place throughout the body. In the latter, there is an exchange of gases between the blood and other tissues of the body, with oxygen passing from the blood to the tissue cells and carbon dioxide passing from the cells to the blood. This phase, along with the external phase, relies on the movement of gases from a region of higher concentration to one of lower concentration.

2. POST-READING TASKS.

1. Define the following concepts: respiration, breathing, direct (indirect) respiration, external (internal) respiration.

1. Explain the difference between:

I. breathing and respiration,

II. direct and indirect respiration,

III. external and internal respiration.

3. Write an essay describing respiration and its phases.

Дата добавления: 2015-09-03