chapter 26 physiology of the digestive system

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Chapter 26: Anatomy of the Respiratory System

Anatomy & Physiology


Structural Plan of the Respiratory System

Structure determined by respiratory system functions of air distributor and gas exchanger—supplying oxygen and removing carbon dioxide from cells (Figure 26-1)

Alveoli—sacs that serve as gas exchangers; all other parts of respiratory system serve as air distributors

The respiratory system also warms, filters, and humidifies air

Respiratory organs involved in speech, homeostasis of body pH, and olfaction

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Structural Plan of the Respiratory System

The respiratory system is divided into two structural divisions

Upper respiratory tract—the organs are located outside the thorax and consist of the nose, nasopharynx, oropharynx, laryngopharynx, and larynx

Lower respiratory tract—the organs are located within the thorax and consist of the trachea, the bronchial tree, and the lungs

Accessory structures include the oral cavity, rib cage, and diaphragm

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Upper Respiratory Tract Nose

Structure of the nose—external portion consists of a bony and cartilaginous frame covered by skin containing sebaceous glands

The two nasal bones meet and are surrounded by the frontal bone to form the root

The nose is surrounded by the maxilla (Figure 26-2)

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Upper Respiratory Tract Nose (cont)

Internal portion of the nose (nasal cavity) lies over the roof of the mouth, separated by the palatine bones

Cleft palate—condition in which the palatine bones fail to unite completely and only partially separate the nose and the mouth, thereby producing difficulty swallowing

Cribriform plate—separates the roof of the nose from the cranial cavity

Septum—separates the nasal cavity into right and left cavities; it consists of four structures: the perpendicular plate of the ethmoid bone, the vomer bone, the vomeronasal cartilages, and the septal nasal cartilage

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Each nasal cavity is divided into three passageways: superior, middle, and inferior meatuses (Figure 26-3)

Anterior (external) nares—external openings to the nasal cavities; open into the vestibule

Sequence of airflow through the nose into the pharynx—anterior nares to the vestibule to all three meatuses simultaneously and then to the posterior (internal) nares

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Nasal mucosa Air passes over respiratory

mucosa, which contains a rich blood supply (Figure 26-4)

Olfactory epithelium—special sensory membrane containing many olfactory nerve cells and a rich lymphatic plexus

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Paranasal sinuses Four pairs of air-containing

spaces that open or drain into the nasal cavity

Each is lined with respiratory mucosa (Figure 26-5)

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Functions of the nose Provides a passageway for air

traveling to and from the lungs Filters the air, aids speech, and

makes possible the sense of smell

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Upper Respiratory Tract Pharynx (throat)

Structure of pharynx Tubelike structure extending from

the base of the skull to the esophagus

Made of muscle and divided into three parts (Figure 26-3)—nasopharynx, oropharynx, and laryngopharynx

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Upper Respiratory Tract Pharynx (cont)

Pharyngeal tonsils

• Located in the nasopharynx•Called adenoids when they become

enlarged Oropharynx contains two pair of organs—the

palatine tonsils (most commonly removed in tonsillectomy) and the lingual tonsils (rarely removed)

Functions of the pharynx—pathway for the respiratory and digestive tracts

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Upper Respiratory Tract Larynx (Figures 26-6 and 26-7)

Location of larynx—positioned between the root of the tongue and the upper end of the trachea

Structure of larynx

•Consists of cartilages attached to each other by muscle • Lined by a ciliated mucous membrane,

which forms two pairs of folds (Figure 26-8)— vestibular folds (false vocal folds) and vocal folds

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Upper Respiratory Tract Larynx (cont)

Cartilages (framework) of the larynx—formed by nine cartilages

• Single laryngeal cartilages—the three largest cartilages: the thyroid cartilage, the epiglottis, and the cricoid cartilages• Paired laryngeal cartilages—three

pairs of smaller cartilages: the arytenoid, the corniculate, and the cuneiform cartilages

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Upper Respiratory Tract Larynx (cont)

Muscles of the larynx Intrinsic muscles both insert and

originate within the larynx Extrinsic muscles insert in the

larynx but originate on some other structure

Functions of the larynx—forms part of the airway to the lungs and produces the voice

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Lower Respiratory Tract Trachea—often called “windpipe” (Figure 26-10)

Structure of trachea Extends from the larynx to the primary bronchi Wall composed of (outer) adventitia, (middle)

smooth muscle and C-shaped cartilage rings, (inner) respiratory mucosa; posterior wall is very elastic (Figure 26-11)

Incomplete rings and posterior elasticity allows esophagus to expand into trachea during swallowing

Functions of trachea—furnishes part of the open airway to the lungs; obstruction causes death

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Lower Respiratory Tract Bronchi and alveoli

Structure of bronchi Lower end of the trachea divides into

two primary bronchi, one on the right and one on the left

Primary bronchi enter the lung and divide into secondary bronchi, which branch into bronchioles and eventually divide into alveolar ducts and alveoli

23 levels of branching (Figure 26-12)

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Lower Respiratory Tract Bronchi and alveoli (cont)

Structure of alveoli—the primary gas exchange structures

Respiratory membrane—the barrier between which gases are exchanged by alveolar air and blood (Figure 26-15)

Respiratory membrane consists of the alveolar epithelium, the capillary endothelium, and their joined basement membranes

Surfactant—a component of the fluid coating the respiratory membrane that reduces surface tension; produced by type II cells

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Lower Respiratory Tract Bronchi and alveoli (cont)

Functions of bronchi and alveoli Distribute air to the lung’s interior;

23 levels of branching are optimal for oxygen transfer to the blood

Mucus blanket cleans the airways as it is moved upward by the ciliary escalator

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Lower Respiratory Tract Lungs

Structure of the lungs—cone-shaped organs extending from the diaphragm to above the clavicles (Figure 26-17)

Hilum—slit on the lung’s medial surface where the primary bronchi and pulmonary blood vessels enter

Base—the inferior surface of the lung that rests on the diaphragm

Costal surface—lies against the ribs

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Lower Respiratory Tract Structure of the lungs (cont)

Left lung is divided into two lobes—superior and inferior

Right lung is divided into three lobes—superior, middle, and inferior

Lobes are further divided into functional units—bronchopulmonary segments

Ten segments in the right lung Eight segments in the left lung

Functions of the lungs—air distribution and gas exchange

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Lower Respiratory Tract Thorax (Figure 26-18)

Structure of the thoracic cavity—three divisions divided by the pleura

Pleural divisions—the part occupied by the lungs

Mediastinum—part occupied by the esophagus, trachea, large blood vessels, and heart

Functions of the thorax—brings about inspiration and expiration

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Cycle of Life: Respiratory System Respiration may be affected by

developmental defects, age-related structural changes, or loss of function throughout the life cycle

Age-related changes affect lung capacity, make ventilation difficult, or reduce the oxygen- or carbon dioxide–carrying capacity of blood

Respiratory efficiency is reduced in old age as a result of changes in ribs, respiratory muscles, and hemoglobin levels

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chapter 26 physiology of the digestive system

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