The Respiratory System 2 Chapter 15

The Lower Respiratory Tract Contains the trachea, bronchi, bronchioles, and alveoli Structurally similar throughout Tubes made of hyaline cartilage, smooth muscle, and connective tissue dense with elastic protein fibers Lined with ciliated mucous membrane (PSCC epithelial tissue) to protect from foreign particles

Mucous is produced by goblet cells The cilia beat synchronously to “sweep” mucous toward pharynx where it is usually swallowed This system is called the mucociliary transport system Digestive processes destroy microbes

Trachea Extends from larynx to bronchi Approx. 4 inches long and 1 inch wide Located anterior to esophagus Walls supported by rings of cartilage that are open in the back to accommodate expansion of esophagus when swallowing (shaped like “C”) The rings prevent closure of main air passage

Bronchial Tree Main branches of “bronchial tree” are called “bronchi” Extend toward right and left lungs; left branches at sharper angle than right—inhaled particles usually end up in right lung Branch off into progressively smaller tubes called bronchioles; amount of cartilage decreases as tubes get smaller Terminate in alveolar ducts which lead to alveoli

Alveoli Tiny air sacs where gases are exchanged Average adult has between 300 and 500 million alveoli Comprise a surface area of approximately 70 square meters Massive surface area necessary to support metabolism Walls of alveoli are only 0.5 micrometers thick; diameter is approx. 10 micrometers

Walls are made of a single layer of simple squamous epithelial tissue Alveoli must remain moist to dissolve gases At this microscopic scale, the force from surface tension holding the walls of alveoli together are significant (this force arises from the polarity of water molecules) A surfactant is produced to allow alveoli to re-inflate easily following expiration

Lungs Made of the many branches of tubes that form the bronchial tree, the alveoli and capillaries, along with supportive tissues Lungs are soft, spongy, and cone-shaped Occupy most of the thoracic cavity, from the diaphragm to just above the clavicles Blood vessels mirror the pathway of the bronchial tree beginning from the medial surface of each lung; convergence called a root

Serous Membranes Two layers of serous membranes surround each lung, collectively called the pleurae Animation: The Pleural Membranes Outer layer is called parietal pleura; lines the thoracic wall and mediastinum; links with layer from opposite lung to form a ligament that supports each lung from its root

The visceral pleura is attached firmly to the surface of each lung Between the two layers is a potential space called the pleural cavity Contains a thin film of fluid produced by serous cells Acts as a lubricant between the two membranes as lungs expand and contract during breathing

Divisions of Lungs Each lung is divided into smaller compartments Right lung has 3 lobes; left has two Lines of division called fissures Each lobe is divided into segments Within each segment are numerous lobules, each of which receives a single bronchiole, an arteriole, a venule, and a lymphatic vessel Lobules contain alveolar ducts, their alveoli and capillaries

Mechanics of Breathing Pulmonary ventilation relies heavily upon Boyle’s Law (pressure is inversely proportional to volume at a constant temperature)

Recall that the pressure of a gas is the result of collisions between atoms and molecules with the walls of its container An expansion of the thoracic cavity causes an increase in the volume of the space within and the gases inside decrease in pressure This creates a pressure gradient between the inside of the lungs and the atmosphere

Air rushes into the lungs following this gradient This is how your lungs fill with air when you inhale To exhale, the volume of the thoracic cavity is decreased, resulting in an increase in pressure which forces the air out

Expansion and Contraction of the Thoracic Cavity The thoracic cage is formed by the ribs, sternum, and clavicles Muscles responsible for the movement of these bones are primarily the diaphragm and intercostal muscles To a lesser extent, the pectoralis minor and abdominal muscles play a role

Recall that there are no muscles attached directly to the surface of the lungs Surface tension from serous fluid between the layers of the plurae holds the outer surface of the lungs to the inner surface of the thoracic cavities

Inspiration For inspiration, or breathing in, the diaphragm (pulls down toward the abdominal cavity) and external intercostals contract (pull each inferior rib up) For a deep breath, the pectoralis minor can assist with further lifting of the ribs

For normal expiration, or breathing out, these same muscles relax On a forced expiration, the abdominal muscles and internal intercostals contract to further shrink the cavity These muscular movements are stimulated by the respiratory center found in the pons and medulla Expiration

Respiratory Volumes The amounts of gases that need exchanged vary according to how much energy is required to meet the body’s immediate needs This need is determined by the several areas of the autonomic nervous system which monitor things like the amount of carbon dioxide in the blood and the degree of stretch in the bronchial tree

TypeDefinitionAverage Volume tidal volumeamount of air moving into or out of lungs during quiet breathing 500 ml inspiratory reserve volume maximum amount of air that can be inhaled forcibly over the tidal volume 3100 ml expiratory reserve volume maximum amount of air that can be exhaled forcibly over the tidal volume 1200 ml residual volumeamount of air remaining in the lungs following a forced expiration 1200 ml vital capacitythe total amount of exchangeable air, determined by the sum of the tidal volume, inspiratory reserve volume, and expiratory reserve volume 4800 ml total lung capacity the total amount of air contained in the fully inflated respiratory system, determined by the sum of the vital capacity and the residual volume 6000 ml