Nursing Entrance Exam

Chapter 8: Anatomy & Physiology – Part 3 8.1 The Respiratory System – Tour of the System Life itself depends on the ability of the blood to deliver oxygen to and remove carbon dioxide from every cell, tissue, and organ of the body, which is the responsibility of the respiratory system. This system also works very closely with other body systems, including the circulatory system. The respiratory system has six basic functions: 1. To transport air into and from the lungs for gas exchange 2. To provide an extensive surface area for gas exchange between air and circulating blood within the lungs 3. To protect respiratory surfaces from dehydration, temperature changes, and other environmental variations 4. To defend the respiratory system and other tissues from invasion by irritants and pathogens 5. To produce sounds involved in speaking, singing, and verbal communication 6. To detect olfactory stimuli by the receptors in the superior region of the nasal cavity. In addition, the lungs’ capillaries indirectly assist with the regulation of blood pressure and blood volume. The medulla regulates the breathing rate based on the carbon dioxide content of the blood. Breathing is automatic, although under “normal” conditions, humans have the ability to consciously alter their breathing rates. The respiratory system consists of two main processes – inhalation and exhalation – which occur in the thoracic cavity. There is around 21% oxygen inhaled from the air and around 16% oxygen exhaled, which is why resuscitation can be effective in saving lives. 8.1.1 Inhalation Inhalation begins when the diaphragm (located at the base of the rib cage) contracts. The ribs move outward and upward, creating more space in the pleural cavity (the space between the lining and covering of the lung). This action changes the air pressure via a vacuum mechanism, forcing air into the lungs. The air enters the nose through the nostrils (nares). In the nasal cavity, air passes through nasal conchae. The nasal conchae are mucosal tissues in the nose. In addition to directing the movement of air, they also heat, moisten, and filter the air. The air then passes through the pharynx, the larynx, and into the trachea. The trachea is ciliated and secretes mucus. Mucus is required to keep the airways lubricated and to trap foreign particles, such as bacteria. The cilia move mucus steadily upwards until it can be swallowed and passed through the digestive system. This process is called the mucocilliary escalator. As air passes through the trachea towards the lungs, the trachea divides into two main branches, the right and left primary bronchi. The bronchi enter the lung with blood vessels, lymphatics, and nerves at a point known as the root of the lung. The bronchi repeatedly branch until the branches become very tiny; these small branches are bronchioles. Bronchioles eventually end at the thin-walled alveoli of the lungs, where gas exchange takes place by way of diffusion.

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