Respiratory System

 

1.            Describe the 4 distinct processes of respiration.

The major function of the respiratory system is to supply the body with oxygen and dispose of carbon dioxide. The four processes of respiration:

a.            pulmonary ventilation – air must move in and out of the lungs (ventilation or breathing)

b.            external respiration – gas exchange between the blood and alveoli (air sacs of the lung).

c.            transport of respiratory gases – to and from the lungs and tissue cells of the body.

d.         internal respiration – at systemic capillaries, gas exchange occurs between blood and tissue cells.

 

2.            Identify the organs forming the respiratory passages from nose to alveoli. Distinguish between conducting and respiratory zones.

 

Organs of the respiratory system: nose, pharynx, larynx, trachea, bronchi, alveoli

 

Respiratory zone – actual site of gas exchange, composed of respiratory bronchioles, alveolar ducts, and alveoli.

 

Conducting zone – dead air space; all other respiratory passageways; the conducting zone organs purify, humidify, and warm incoming air so that air reaching the lungs has fewer irritants.

 

3.            Describe the functions of the nose, pharyngeal regions, larynx, and trachea.

Nose – provides an airway for respiration, moistens and warms entering air, filters inspired air and cleanses it of foreign matter, serves as a resonating chamber for speech, and houses olfactory receptors. The hairs of the nose filter particles from the air. The remainder of the nasal cavity is lined with mucus membranes that produce mucus containing lysozyme, so that the mucus can trap and kill bacteria. Ciliated cells move contaminated mucus back toward the throat. Blood vessels near the surface of the nasal mucosa warms incoming air.

 

Pharynx – connects the nasal cavity and mouth to the larynx and esophagus. Common pathway for food and air. Three regions – nasopharynx, oropharynx, and laryngopharynx.

Nasopharynx – only an air passage; uvula prevents food from entering it during swallowing.

Oropharynx – posterior to the mouth, passageway for food and air.

Laryngopharynx – passageway for food and air. Directly posterior to the epiglottis and extends to the larynx, then becomes continuous with esophagus.

 

Larynx (voice box) – functions to provide an open airway, acts as a switching mechanism to route air and food, and houses vocal cords which produce speech. The epiglottis is the switching mechanism. When air is flowing into the larynx, the free edge projects upward. During swallowing the larynx is pulled superiorly and the epiglottis covers the larynx, routing food or fluids into the esophagus.

 

Trachea – descends from the larynx and divides inferiorly into two primary bronchi. Cells have cilia which propel mucus loaded with debris upward toward the pharynx. Smoking destroys these cilia and then the only way to prevent mucus from accumulating in the lungs is coughing.

 

4.            Describe the structure and function of the bronchial tree.

Right and left bronchi enter the lungs at the hilus. Once inside the lungs, each primary bronchus subdivides into secondary bronchi. This branching continues for a total of 23 orders of branching. Each branch gets smaller, until the smallest passageways are found which are called bronchioles.

 

5.            Describe how the structure of the respiratory membrane allows efficient gas exchange.

The respiratory zone begins as the terminal bronchioles feed into the respiratory bronchioles. The respiratory bronchioles branch into alveolar sacs and alveoli where the bulk of gas exchange occurs. The walls of the alveoli are composed of a single layer of epithelium. The alveolar and capillary walls form the respiratory membrane which has gas on one side and blood flowing past on the others. Gas exchange occurs readily by simple diffusion. Efficient gas exchange requires a moist membrane. Some alveolar cells produce surfactant, a fluid that coats gas-exposed surfaces and reduces surface tension. Alveolar macrophages provide defense against inhaled dust, bacteria, and other foreign particles.

 

6.            Describe the structure and function of the lungs and pleural coverings.

Each lung is suspended in its own pleural cavity and rests on the muscular diaphragm. The medial surface has a hilus (indentation) where the bronchi enter. Because of the shape and location of the heart, the lungs differ in size and shape. The left lung is smaller with 2 lobes, the right has 3 lobes. Lungs are mostly air spaces and connective tissue. The lung contains the air sacs where oxygen diffuses from air sacs into the blood vessels and waste carbon dioxide diffuses from the blood vessels into the air sacs. Each lung exists in a pleural cavity, a serous membrane compartment which prevents friction damage as the lungs expand and contract during breathing. The visceral pleura is the membrane fused to the outer surface of the lung; the parietal pleura is the membrane which lines the body wall. Between the two membranes in the pleural fluid.

 

7.            Describe inspiration and expiration. Note the functional importance of the negative pressure in the intrapleural space.

Breathing consists of inspiration (air flow into lungs) and expiration (air flow out of lungs). Atmospheric pressure at sea level is 760 mm Hg. The intrapulmonary pressure within the alveoli of the lungs always equalizes itself with the atmospheric pressure outside the body. The pressure within the pleural cavity (intrapleural pressure) also fluctuates with breathing phases. However, the intrapleural pressure is always 4 mm Hg less than the pressure in the alveoli, so it is said to be negative relative to both the intrapulmonary and atmospheric pressures. The negative intrapleural pressure helps keep the lungs from collapsing during expiration.

 

The negative intrapleural pressure results from two groups of factors:

1.         Those that hold the lungs to the thorax wall.

            a.            The adhesive force (surface tension) created by the pleural fluid in the pleural cavity.

            b.            The positive pressure within the lungs (equal to atmospheric pressure).

c.         The atmospheric pressure acting externally on the thorax (always greater than that in the intrapleural space.

2.         Those that act to pull lungs away from the thorax wall.

            a.            The natural recoil tendency of the lungs.

            b.            The surface tension of fluid film in the alveoli, which constantly draws the alveoli to their

                        smallest possible size.

 

8.            Describe several physical factors that influence pulmonary ventilation.

Pulmonary ventilation is a mechanical process that depends on volume changes occurring in the thoracic cavity. Volume changes lead to pressure changes, which leads to the flow of gases to equalize the pressure.

Inspiration – Contraction of the diaphragm causes the volume of the thoracic cavity to enlarge. This temporarily decreases the gas pressure within the lungs. Air rushes in to equalize the intrapulmonary pressure with atmospheric pressure. Inspiration depends on the action of the diaphragm.

Expiration – Quiet expiration is a passive process that just depends on the natural elasticity of the lungs. Thus the pressure in the lungs is temporarily increased as the tissue recoils, causing gas to flow out of the lungs. Forced expiration uses abdominal wall muscles.

 

9.         Define surfactant and describe its role in gas exchange in the alveoli.

At any gas-liquid boundary, the molecules of liquid are more strongly attracted to each other than to the gas. This unequal attraction produces a state of tension at the liquid surface called surface tension which draws the liquid molecules more closely together and reduces contact with the gas molecules. The liquid film coating the alveolar walls acts to reduce alveoli to the smallest size. The alveolar film contains surfactant which is a detergent-like substance which interferes with the cohesiveness of water molecules. As a result, surface tension is reduced and less energy is needed to overcome surface tension forces to expand the lungs and discourage alveolar collapse.

 

10.        Define the following respiratory terms.

Tidal volume – amount of air that moves into and out of the lungs with each breath during normal quiet breathing.

Inspiratory reserve volume – amount of air that can be forcibly inspired beyond tidal volume.

Expiratory reserve volume – amount of air that can be evacuated from the lungs after a tidal expiration.

Vital capacity – total amount of exchangeable air.

 

11.            Describe the factors that influence gas exchange.

a.            Pressure gradients – The partial pressure of oxygen in pulmonary blood is only 40 mm Hg as opposed to 104 mm Hg in the alveoli. Oxygen then diffuses rapidly from alveoli to the blood. Carbon dioxide moves in the opposite direction along a less steep concentration gradient. Opposite pressure differences in the tissues cause oxygen to diffuse from the blood to the tissue cells and carbon dioxide to diffuse from the tissue cells to the blood.

b.            Structural characteristics of respiratory membrane – Thin tissue with a great surface area allows efficient gas exchange.

c.            Matching ventilation with perfusion – Poor ventilation causes pulmonary capillaries in that area to constrict. Good ventilation causes pulmonary capillaries in that area to dilate to maximize the amount of gas exchange that can occur.