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Learning Objectives - The Respiratory System

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Identify the organs forming the respiratory passageway(s) in descending order until the alveoli are reached.

The respiratory system includes the nose, nasal cavity, and paranasal sinuses; the pharynx; the larynx; the trachea; the bronchi and their smaller branches; and the lungs, which contain the terminal air sacs, or alveoli


Describe the location, structure, and function of each of the following: nose, paranasal sinuses, pharynx, and larynx.

• Nose - Jutting external portion is supported by bone and cartilage. Internal nasal cavity is divided by midline nasal septum and lined with mucosa. Roof of nasal cavity contains olfactory epithelium, which are the receptors for sense and smell. The Nose produces mucus; filters, warms, and moistens incoming air; resonance chamber for speech

• Paranasal Sinuses - Mucosa-lined, air-filled cavities in cranial bones surrounding nasal cavity. The function of the paranasal sinuses are the same as for nasal cavity; also lighten skull.

• Pharynx - Passageway connecting nasal cavity to larynx and oral cavity to esophagus. Three subdivisions: nasopharynx, oropharynx, and laryngopharynx. The pharynx serves as a passage way for food and air. The pharynx houses the tonsils which facilitates exposure of immune system to inhaled antigens

• Larynx - Connects pharynx to trachea. Has framework of cartilage and dense connective tissue. Opening (glottis) can be closed by epiglottis or vocal folds. The larynx functions to Air passageway; prevents food from entering lower respiratory tract. The larynx houses the vocal folds (true vocal cords) which produces sound for communicating.


List and describe several protective mechanisms of the respiratory system.

• Mucous and Serous glands. (Mucous cells secrete mucus, and serous cells secrete a watery fluid containing enzymes.) Each day, these glands secrete about a quart (or a liter) of mucus containing lysozyme, an antibacterial enzyme. The sticky mucus traps inspired dust, bacteria, and other debris, while lysozyme attacks and destroys bacteria chemically. The epithelial cells of the respiratory mucosa also secrete defensins, natural antibiotics that help get rid of invading microbes.

• Sneeze - The nasal mucosa is richly supplied with sensory nerve endings, and contact with irritating particles (dust, pollen, and the like) triggers a sneeze reflex. The sneeze forces air outward in a violent burst

• Air Turbulance - Nasal conchae causes air turbulence which swirls the air around forcing the non-gas particles to stick the the mucous

• Uvula - During swallowing, the soft palate and its pendulous uvula (u vu-lah; “little grape”) move superiorly an action that closes off the nasopharynx and prevents food from entering the nasal cavity.


Distinguish between conducting and respiratory zone structures.

• The bronchial tree is the site where conducting zone structures give way to respiratory zone structures. The conducting zone is made up of passageways for air to travel. These passageways branch into smaller and smaller passages until it gives way to the bronchial tree. The air pathway inferior to the larynx consists of the trachea and the main, lobar, and segmental bronchi, which branch into the smaller bronchi and bronchioles until the terminal bronchioles of the lungs are reached.

• The respiratory zone begins as the terminal bronchioles feed into respiratory bronchioles within the lung. The respiratory bronchioles lead into winding alveolar ducts, whose walls consist of diffusely arranged rings of smooth muscle cells, connective tissue fibers, and outpocketing alveoli. The alveolar ducts lead into terminal clusters of alveoli called alveolar sacs. The 300 million or so gas-filled alveoli in the lungs account for most of the lung volume and provide a tremendous surface area for gas exchange.


Describe the makeup of the respiratory membrane, and relate structure to function.
The walls of the alveoli are composed primarily of a single layer of squamous epithelial cells, called type I cells, surrounded by a flimsy basement membrane. The thinness of their walls is hard to imagine, but a sheet of tissue paper is 15 times thicker. The external surfaces of the alveoli are densely covered with a “cobweb” of pulmonary capillaries. Together, the alveolar and capillary walls and their fused basement membranes form the respiratory membrane, an air-blood barrier that has gas on one side and blood flowing past on the other
Scattered amid the type I squamous cells that form the major part of the alveolar walls are cuboidal type II cells. The type II cells secrete a fluid containing a detergent-like substance called surfactant that coats the gas exposed alveolar surfaces and they also secrete a number of antimicrobial proteins that are important elements of innate immunity.

The walls of the alveoli are composed primarily of a single layer of squamous epithelial cells, called type I cells, surrounded by a flimsy basement membrane. The thinness of their walls is hard to imagine, but a sheet of tissue paper is 15 times thicker. The external surfaces of the alveoli are densely covered with a “cobweb” of pulmonary capillaries. Together, the alveolar and capillary walls and their fused basement membranes form the respiratory membrane, an air-blood barrier that has gas on one side and blood flowing past on the other

Scattered amid the type I squamous cells that form the major part of the alveolar walls are cuboidal type II cells. The type II cells secrete a fluid containing a detergent-like substance called surfactant that coats the gas exposed alveolar surfaces and they also secrete a number of antimicrobial proteins that are important elements of innate immunity.


Describe the gross structure of the lungs and pleurae.

Lungs - Each cone-shaped lung is surrounded by pleurae and connected to the mediastinum by vascular and bronchial attachments, collectively called the lung root. The anterior, lateral, and posterior lung surfaces lie in close contact with the ribs and form the continuously curving costal surface. Just deep to the clavicle is the apex, the narrow superior tip of the lung. The concave, inferior surface that rests on the diaphragm is the base. The two lungs differ slightly in shape and size because the apex of the heart is slightly to the left of the median plane. The left lung is smaller than the right, and the cardiac notch—a concavity in its medial aspect—is molded to and accommodates the heart. The left lung is subdivided into superior and inferior lobes by the oblique fissure, whereas the right lung is partitioned into superior, middle, and inferior lobes by the oblique and horizontal fissures.

Pleurae - form a thin, double-layered serosa. The layer called the parietal pleura covers the thoracic wall and superior face of the diaphragm (Figure 22.10a, c). It continues around the heart and between the lungs, forming the lateral walls of the mediastinal enclosure and snugly enclosing the lung root. From here, the pleura extends as the layer called the visceral pleura to cover the external lung surface, dipping into and lining its fissures.


Explain the functional importance of the partial vacuum that exists in the intrapleural space.

Intrapulmonary pressure is the pressure in the alveoli, which rises and falls during respiration, but always eventually equalizes with atmospheric pressure.

Intrapleural pressure is the pressure in the pleural cavity. It also rises and falls during respiration, but is always about 4 mm Hg less than intrapulmonary pressure.

The amount of pleural fluid in the pleural cavity must remain minimal in order for the negative Pip to be maintained. The pleural fluid is actively pumped out of the pleural cavity into the lymphatics continuously. If it wasn’t, fluid would accumulate in the intrapleural space (remember, fluids move from high to low pressure), producing a positive pressure in the pleural cavity.

Thoracic cavity is a gas-filled box with a single entrance at the top, the tubelike trachea. The volume of this box is changeable and can be increased by enlarging all of its dimensions, thereby decreasing the gas pressure inside it. This drop in pressure causes air to rush into the box from the atmosphere, because gases always flow down their pressure gradients.


Relate Boyle’s law to the events of inspiration and expiration.

Boyle’s Law states that when the temperature is constant, the pressure of gas varies inversely with it=s volume:

P1V1 = P2V2

(where P is the pressure of gas in millimeters of mercury [mm Hg] and V is the volume of gas in mm;)
gases conform to the shape of their container (i.e. the lungs) and they always fill their container.

• therefore, in a large volume, the gas molecules will be far apart and the pressure will be low

• if the volume is reduced, the gas molecules will be compressed and the pressure will rise


Explain the relative roles of the respiratory muscles and lung elasticity in producing the volume changes that cause air to flow into and out of the lungs

• Action of the diaphragm. When the dome-shaped diaphragm contracts, it moves inferiorly and flattens out. As a result, the superior-inferior dimension (height) of the thoracic cavity increases.

• Action of the intercostal muscles. Contraction of the external intercostal muscles lifts the rib cage and pulls the sternum superiorly. Because the ribs curve downward as well as forward around the chest wall, the broadest lateral and anteroposterior dimensions of the rib cage are normally directed obliquely downward. But when the ribs are raised and drawn together, they swing outward, expanding the diameter of the thorax both laterally and in the anteroposterior plane. This is much like the action that occurs when a curved bucket handle is raised—it moves outward as it moves upward.


List several physical factors that influence pulmonary ventilation.

Inspiratory muscles consume energy to overcome three factors that hinder air passage and pulmonary ventilation

• Airway resistance
o increased resistance causes decreased air flow
o Occurs at larger bronchioles – smooth muscle constriction

• Alveolar surface tension
o Due to high amount of water in alveoli sides want to stick together (H bonding)
o Surfactant: contains lipids and proteins that decrease surface tension of water

• Lung compliance: distensibility of lungs


Explain and compare the various lung volumes and capacities.

• Volume
o Tidal volume (TV): amount of air that moves in and out during quiet breathing
o Inspiratory reserve volume (IRV): amount of air that can be forcibly inspired beyond TV
o Expiratory reserve volume (ERV): amount of air that can be evacuated from lungs after TV expiration
o Residual volume (RV): amount of air remaining in lungs after maximal forced expiration

• Capacity
o Vital capacity (VC): TV + IRV +ERV
o Total lung capacity (TLC): sum of all lung volumes


Define dead space.

Some inspired air never contributes to gas exchange
• Anatomical dead space: volume of the conducting zone conduits

• Alveolar dead space: alveoli that cease to act in gas exchange due to collapse or obstruction

• Total dead space: sum of above nonuseful volumes


Indicate types of information that can be gained from pulmonary function tests.

• Spirometer: instrument used to measure respiratory volumes and capacities

• Spirometry can distinguish between
o Obstructive pulmonary disease—increased airway resistance (e.g., bronchitis, emphysema)
o Restrictive disorders—reduction in total lung capacity due to structural or functional lung changes (e.g., fibrosis or TB)


State Dalton’s law of partial pressures and Henry’s law.

• Dalton’s law of partial pressures states that the total pressure exerted by a mixture of gases is the sum of the pressures exerted by each gas in the mixture.

• Henry’s law states that when a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure.


Describe how atmospheric and alveolar air differs in composition, and explain these differences.

air is composed of nitrogen (79%); oxygen (21%); carbon dioxide (0.04%) the alveoli contain much more carbon dioxide (5%) and much less oxygen (14%)
• these differences are largely due to the fact that:
o gas exchanges are occurring in the lungs B oxygen is diffusing from the alveoli into the pulmonary blood and carbon dioxide is diffusing in the opposite direction
o with each tidal inspiration, alveolar gas is actually a mixture of newly inspired air and air that remained in the respiratory pathway between breaths


Relate Dalton’s and Henry’s laws to events of external and internal respiration.

• Pulmonary Gas Exchange (External Respiration)
o oxygen enters the blood in the lungs and carbon dioxide leaves
o the movement of these gases is affected by partial pressure gradients and gas solubilities
o there is a steep gradient of PO2 across the respiratory membrane (PO2 of venous blood in the pulmonary arteries is only 40 mm Hg compared to 104 mm Hg in the alveoli), as a result, oxygen diffuses rapidly from the alveoli into the lung capillaries
o the partial pressure gradient for CO2 is much less steep (45 mm Hg in the lung capillary blood vs. 40 mm Hg in the alveoli), however, because CO2 is 20 times more soluble in plasma than oxygen is, it is exchanged at equal rates as oxygen.

• Capillary Gas Exchange in the Body Tissues (Internal Respiration)
o the partial pressure and diffusion gradients are reversed in the body tissues
o due to their metabolic activities, cells constantly use oxygen and produce equal amounts of carbon dioxide
o the PO2 in the tissues is always lower than in the systemic arterial blood (40 mm Hg to 104 mm Hg, respectively), therefore, oxygen rapidly diffuses from the blood into the tissues
o CO2 moves in the opposite direction (from tissues into the blood), along its own partial pressure gradient


Describe how oxygen is transported in the blood, and explain how oxygen loading and unloading is affected by temperature, pH, BPG, and PCO2.

• Molecular oxygen is carried in blood in two ways:
o bound to hemoglobin within red blood cells 98%
o dissolved in plasma 1.5%

• As O2 loads, the affinity of Hb for it increases making O2 loading very efficient. Opposite also occurs

• A Hb molecule is saturated when all four hemes have O2 bonded
Temperature: ↑causes Hb affinity to ↓. Oxygen unloads.
Blood pH: ↓ (acidosis) = ↓ Hb affinity
Pco2: ↑ = ↓ Hb affinity


Describe carbon dioxide transport in the blood.

• CO2 is transported in the blood in three forms
o 7 to 10% dissolved in plasma
o 20% bound to globin (aminos) of hemoglobin(carbaminohemoglobin)
o 70% transported as bicarbonate ions (HCO3–) in plasma

• As plasma oxygen pressure ↓ and Hb saturation ↓ more carbon dioxide is loaded from tissues and carried in blood to lungs for release


Describe the neural controls of respiration.

• Involves neurons in the reticular formation of the medulla and pons

• The neural centers maintain rythmic breathing at about 12-15 BPM (normal resting rate)


Compare and contrast the influences of arterial pH, arterial partial pressures of oxygen and carbon dioxide, lung reflexes, volition, and emotions on respiratory rate and depth.

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Compare and contrast the hyperpnea of exercise with hyperventilation.

• During vigorous exercise, deeper and more vigorous respirations, called hyperpnea, ensure that tissue demands for oxygen are met.

• Three neural factors contribute to the change in respiration: psychic stimuli, cortical stimulation of skeletal muscles and respiratory centers, and excitatory impulses to the respiratory areas from active muscles, tendons, and joints.


Describe the process and effects of acclimatization to high altitude.

• Acute mountain sickness (AMS) may result from a rapid transition from sea level to altitudes above 8000 feet.

• A long-term change from sea level to high altitudes results in acclimatization of the body, including an increase in ventilation rate, lower than normal hemoglobin saturation, and increased production of erythropoietin.


Compare the causes and consequences of chronic bronchitis, emphysema, asthma, tuberculosis, and lung cancer.

• Emphysema is characterized by permanently enlarged alveoli and deterioration of alveolar walls.

• Chronic bronchitis results in excessive mucus production, as well as inflammation and fibrosis of the lower respiratory mucosa.

• Asthma is characterized by coughing, dyspnea, wheezing, and chest tightness, brought on by active inflammation of the airways

• Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis and spread by coughing and inhalation

• Lung Cancer
o In both sexes, lung cancer is the most common type of malignancy, and is strongly correlated with smoking.
o Squamous cell carcinoma arises in the epithelium of the bronchi, and tends to form masses that hollow out and bleed.
o Adenocarcinoma originates in peripheral lung areas as nodules that develop from bronchial glands and alveolar cells.
o Small cell carcinoma contains lymphocyte-like cells that form clusters within the mediastinum and rapidly metastasize.


Trace the embryonic development of the respiratory system.

• By the fourth week of development, the olfactory placodes are present and give rise to olfactory pits that form the nasal cavities

• The nasal cavity extends posteriorly to join the foregut, which gives rise to an outpocketing that becomes the pharyngeal mucosa. Mesoderm forms the walls of the respiratory passageways and stroma of the lungs


Describe normal changes that occur in the respiratory system from infancy to old age.

• As a fetus, the lungs are filled with fluid, and vascular shunts are present that divert blood away from the lungs; at birth, the fluid drains away, and rising plasma PCO2 stimulates respiratory centers

• Respiratory rate is highest in newborns, and gradually declines to adulthood; in old age, respiratory rate increases again

• As we age, the thoracic wall becomes more rigid, the lungs lose elasticity, and the amount of oxygen we can use during aerobic respiration decreases

• The number of mucus glands and blood flow in the nasal mucosa decline with age, as does ciliary action of the mucosa, and macrophage activity

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