respitory cavity Flashcards
Front: Structure of the Lungs
Location: The lungs occupy the entire thoracic cavity except for the central area, the mediastinum, which houses the heart, great blood vessels, bronchi, esophagus, and other organs.
Apex: The narrow top portion of each lung, located just below the clavicle.
Base: The broad bottom portion of each lung resting on the diaphragm.
Lobes:
Left lung: 2 lobes
Right lung: 3 lobes
Fissures: Divide the lungs into lobes.
Pleurae and Their Role in Breathing
Visceral pleura (pulmonary pleura): Covers the surface of the lungs.
Parietal pleura: Lines the walls of the thoracic cavity (chest wall).
Pleural fluid: Slippery, serous fluid between the pleurae, allowing smooth lung movement during breathing.
Function of pleurae:
The pleurae slide easily over each other but resist being pulled apart.
This tight adherence keeps the lungs securely against the chest wall.
The pleural space is a potential space, not a true cavity.
Importance: The pleurae’s tight adherence is essential for normal lung function and breathing.
Pleurisy (ploo′rĭ-se), side affect of pleurae
inflammation of the pleurae, can be caused by insufficient secretion of pleural fluid. The pleural surfaces become dry and rough, resulting in friction and stabbing pain with each breath. Conversely, the pleurae may produce excessive amounts of fluid, which exerts pressure on the lungs. This type of pleurisy hinders breathing movements, but it is much less painful than the dry rubbing type.
What is the Bronchial Tree and its function?
After entering the lungs, the main bronchi subdivide into smaller and smaller branches (secondary and tertiary bronchi, and so on), finally ending in the smallest of the conducting passageways, the bronchioles (brong′ke-ōlz). Because of this branching and rebranching of the respiratory passageways within the lungs, the network formed is often referred to as the bronchial, or respiratory, tree. All but the smallest branches have reinforcing cartilage in their walls. The bronchial tree is the branching system of airways in the lungs that allows air to travel from the trachea to the alveoli, where gas exchange occurs. It resembles an upside-down tree and consists of several parts:
What is the function of the respiratory zone, and what structures make it up?
The terminal bronchioles lead into respiratory zone structures, even smaller conduits that eventually terminate in alveoli (al-ve′o-li; alveol = small cavity), or air sacs. The respiratory zone, which includes the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli, is the only site of gas exchange (Figure 13.5). All other respiratory passages are conducting zone structures that serve as conduits to and from the respiratory zone. There are millions of the clustered alveoli, which resemble bunches of grapes, and they make up the bulk of the lungs. Consequently, the lungs are mostly air spaces. The balance of the lung tissue, its stroma, is mainly elastic connective tissue that allows the lungs to stretch and recoil (spring back) as we breathe. Thus, in spite of their relatively large size, the lungs weigh only about 2½ pounds, and they are soft and spongy.
What is the structure and function of the respiratory membrane, and how does gas exchange occur?
The walls of the alveoli are composed largely of a single, thin layer of simple squamous epithelial cells. The thinness of their walls is hard to imagine, but a sheet of tissue paper is much thicker. Alveolar pores connect neighboring air sacs and provide alternative routes for air to reach alveoli whose feeder bronchioles have been clogged by mucus or otherwise blocked. The external surfaces of the alveoli are covered with a “cobweb” of pulmonary capillaries. Together, the alveolar and capillary walls, their fused basement membranes, and occasional elastic fibers construct the respiratory membrane (air-blood barrier) (Figure 13.6). The respiratory membrane has gas (air) flowing past on one side and blood flowing past on the other. Gas exchange occurs by simple diffusion through the respiratory membrane—oxygen passes from the alveolar air into the capillary blood, and carbon dioxide leaves the blood to enter the alveoli (Figure 13.6). The total gas exchange surface provided by the alveolar walls of a healthy man is estimated to be 50 to 70 square meters, or approximately 40 times greater than the surface area of his skin!
What role do alveolar macrophages and surfactant-secreting cells play in the respiratory system?
The final line of defense for the respiratory system is in the alveoli. Remarkably efficient alveolar macrophages, sometimes called “dust cells,” wander in and out of the alveoli picking up bacteria, carbon particles, and other debris. Also scattered amid the epithelial cells that form most of the alveolar walls are cuboidal surfactant-secreting cells, which look very different from the squamous epithelial cells. These cells produce a lipid (fat) molecule called surfactant, which coats the gas-exposed alveolar surfaces and is very important in lung function (as described in Section
