Respiratory system and structure

 Respiratory System Anatomy

• Describe the anatomy and histology of the nose, pharynx,

larynx, trachea, bronchi, and lungs.

• Identify the functions of each respiratory system structure.

The respiratory system (RES-pi-ra-toˉr-e¯) consists of the nose,

pharynx (throat), larynx (voice box), trachea (windpipe), bronchi,

and lungs . Its parts can be classified according to

either structure or function. Structurally, the respiratory system

consists of two parts: 

(1) The upper respiratory system includes the nose, nasal cavity, pharynx, and associated structures; 

(2) the lower respiratory system includes the larynx, trachea, bronchi,

and lungs. Functionally, the respiratory system also consists of

two parts. 

(1) The conducting zone consists of a series of interconnecting cavities and tubes both outside and within the lungs.

These include the nose, nasal cavity, pharynx, larynx, trachea,

bronchi, bronchioles, and terminal bronchioles; their function is

to filter, warm, and moisten air and conduct it into the lungs.

(2) The respiratory zone consists of tubes and tissues within the

lungs where gas exchange occurs. These include the respiratory

bronchioles, alveolar ducts, alveolar sacs, and alveoli and are the

main sites of gas exchange between air and blood.

 The branch of medicine that deals with the diagnosis and treat-

ment of diseases of the ears, nose, and throat (ENT) is called otorhi-

nolaryngology (oˉ--toˉ-rı¯--noˉ-lar-in-GOL-o-je¯; oto-  ear; -rhino- nose; -laryngo-  voice box; -logy  study of). A pulmonologist(pul--mo-NOL-oˉ-jist) is a specialist in the diagnosis and treatment

of diseases of the lungs.

Parts of Respiratory system

Nose

The nose is a specialized organ at the entrance of the respiratory

system that consists of a visible external portion and an internal

portion inside the skull called the nasal cavity. The external nose is

the portion of the nose visible on the face and consists of a support-

ing framework of bone and hyaline cartilage covered with muscle

and skin and lined by a mucous membrane. The frontal bone, nasal

bones, and maxillae form the bony framework of the external nose

The cartilaginous framework of the external nose

consists of several pieces of hyaline cartilage connected to each

other and certain skull bones by fibrous connective tissue. The

components of the cartilaginous framework are the septal nasal

cartilage, which forms the anterior portion of the nasal septum; the

lateral nasal cartilages inferior to the nasal bones; and the alar

cartilages (Aˉ-lar), which form a portion of the walls of the nostrils.

Because it consists of pliable hyaline cartilage, the cartilaginous

framework of the external nose is somewhat flexible. On the under-

surface of the external nose are two openings called the external

nares (NAˉ-rez; singular is naris) or nostrils.  shows the

surface anatomy of the nose.

 The interior structures of the external nose have three functions:

(1) warming, moistening, and filtering incoming air; (2) detecting

olfactory stimuli; and (3) modifying speech vibrations as they pass

through the large, hollow resonating chambers. Resonance refers to

prolonging, amplifying, or modifying a sound by vibration.

 The nasal cavity is a large space in the anterior aspect of the skull

that lies inferior to the nasal bone and superior to the oral cavity; it

is lined with muscle and mucous membrane. A vertical partition, the

nasal septum, divides the nasal cavity into right and left sides. The

anterior portion of the nasal septum consists primarily of hyaline

cartilage; the remainder is formed by the vomer, perpendicular plate

of the ethmoid, maxillae, and palatine bones .

 Anteriorly, the nasal cavity merges with the external nose, and

posteriorly it communicates with the pharynx through two open-

ings called the internal nares or choanae (koˉ-Aˉ-ne¯)  Ducts from the paranasal sinuses (which drain mucus)

and the nasolacrimal ducts (which drain tears) also open into the

nasal cavity. Recall from Chapter 7 that the paranasal sinuses are

cavities in certain cranial and facial bones lined with mucous mem-

brane that are continuous with the lining of the nasal cavity. Skull

bone, containing the paranasal sinuses are the frontal, sphenoid,

ethmoid, and maxillae. Besides producing mucus, the paranasal si-

nuses serve as resonating chambers for sound as we speak or sing.

The lateral walls of the internal nose are formed by the ethmoid,

maxillae, lacrimal, palatine, and inferior nasal conchae bones  the ethmoid bone also forms the roof. The palatine

bones and palatine processes of the maxillae, which together con-

stitute the hard palate, form the floor of the internal nose.

 The bony and cartilaginous framework of the nose help to

keep the vestibule and nasal cavity patent, that is, open or un-

obstructed. The nasal cavity is divided into a larger, inferior respiratory region and a smaller, superior olfactory region. The

respiratory region is lined with pseudostratified ciliated colum-

nar epithelium with numerous goblet cells, which is frequently

called the respiratory epithelium . The anterior

portion of the nasal cavity just inside the nostrils, called the

nasal vestibule, is surrounded by cartilage; the superior part of

the nasal cavity is surrounded by bone.

 When air enters the nostrils, it passes first through the vesti-

bule, which is lined by skin containing coarse hairs that filter out

large dust particles. Three shelves formed by projections of the

superior, middle, and inferior nasal conchae extend out of

each lateral wall of the nasal cavity. The conchae, almost reaching

the nasal septum, subdivide each side of the nasal cavity into a

series of groovelike air passageways—the superior, middle,

and inferior nasal meatuses (me¯-Aˉ-tus-e¯z -

 openings or pas-

sages; singular is meatus). Mucous membrane lines the nasal

cavity and its shelves. The arrangement of conchae and meatuses

increases surface area in the internal nose and prevents dehydra-

tion by trapping water droplets during exhalation.

 As inhaled air whirls around the conchae and meatuses, it is

warmed by blood in the capillaries. Mucus secreted by the goblet

cells moistens the air and traps dust particles. Drainage from the

nasolacrimal ducts also helps moisten the air, and is sometimes

assisted by secretions from the paranasal sinuses. The cilia move

the mucus and trapped dust particles toward the pharynx, at which

point they can be swallowed or spit out, thus removing the parti-

cles from the respiratory tract.

 The olfactory receptor cells, supporting cells, and basal cells

lie in the respiratory region, which is near the superior nasal con-

chae and adjacent septum. These cells make up the olfactory epi-

thelium. It contains cilia but no goblet cells.

Pharynx

The pharynx (FAR-inks), or throat, is a funnel-shaped tube about

13 cm (5 in.) long that starts at the internal nares and extends to

the level of the cricoid cartilage, the most inferior cartilage of the

larynx (voice box) . The pharynx lies just pos-

terior to the nasal and oral cavities, superior to the larynx, and just

anterior to the cervical vertebrae. Its wall is composed of skeletal

muscles and is lined with a mucous membrane. Relaxed skeletal

muscles help keep the pharynx patent. Contraction of the skeletal

muscles assists in deglutition (swallowing). The pharynx func-

tions as a passageway for air and food, provides a resonating

chamber for speech sounds, and houses the tonsils, which partici-

pate in immunological reactions against foreign invaders.

 The pharynx can be divided into three anatomical regions:

(1) nasopharynx, (2) oropharynx, and (3) laryngopharynx. (See

the lower orientation diagram in  The muscles of

the entire pharynx are arranged in two layers, an outer circular

layer and an inner longitudinal layer.

 The superior portion of the pharynx, called the nasophar-

ynx, lies posterior to the nasal cavity and extends to the soft

palate. The soft palate, which forms the posterior portion of the

roof of the mouth, is an arch-shaped muscular partition between

the nasopharynx and oropharynx that is lined by mucous mem-

brane. There are five openings in its wall: two internal nares,

two openings that lead into the auditory (pharyngotympanic)

tubes (commonly known as the eustachian tubes), and the open-

ing into the oropharynx. The posterior wall also contains the pha-

ryngeal tonsil (fa-RIN-je-al), or adenoid. Through the internal

nares, the nasopharynx receives air from the nasal cavity along

with packages of dust-laden mucus. The nasopharynx is lined

with pseudostratified ciliated columnar epithelium, and the cilia

move the mucus down toward the most inferior part of the phar-

ynx. The nasopharynx also exchanges small amounts of air with

the auditory tubes to equalize air pressure between the middle ear

and the atmosphere.

 The intermediate portion of the pharynx, the oropharynx, lies

posterior to the oral cavity and extends from the soft palate infe-

riorly to the level of the hyoid bone. It has only one opening into

it, the fauces (FAW-se¯z  throat), the opening from the mouth.

This portion of the pharynx has both respiratory and digestive

functions, serving as a common passageway for air, food, and

drink. Because the oropharynx is subject to abrasion by food par-

ticles, it is lined with nonkeratinized stratified squamous epithe-

lium. Two pairs of tonsils, the palatine and lingual tonsils, are

found in the oropharynx.

 The inferior portion of the pharynx, the laryngopharynx (la-

RING-goˉ-far-ingks), or hypopharynx, begins at the level of the

hyoid bone. At its inferior end it opens into the esophagus (food

tube) posteriorly and the larynx (voice box) anteriorly. Like the

oropharynx, the laryngopharynx is both a respiratory and a diges-

tive pathway and is lined by nonkeratinized stratified squamous

epithelium.

Larynx

The larynx (LAR-ingks), or voice box, is a short passageway that

connects the laryngopharynx with the trachea. It lies in the mid-

line of the neck anterior to the esophagus and the fourth through

sixth cervical vertebrae (C4–C6).

 The wall of the larynx is composed of nine pieces of cartilage

(Figure 23.4). Three occur singly (thyroid cartilage, epiglottis,

and cricoid cartilage), and three occur in pairs (arytenoid, cunei-

form, and corniculate cartilages). Of the paired cartilages, the

arytenoid cartilages are the most important because they influ-

ence changes in position and tension of the vocal folds (true vocal

cords for speech). The extrinsic muscles of the larynx connect

the cartilages to other structures in the throat; the intrinsic mus-

cles connect the cartilages to one another. The cavity of the

larynx is the space that extends from the entrance into the larynx

down to the inferior border of the cricoid cartilage (described

shortly). The portion of the cavity of the larynx above the ves-

tibular folds (false vocal cords) is called the laryngeal vestibule.

The portion of the cavity of the larynx below the vocal folds is

called the infraglottic cavity (infra- = below) (Figure 23.4d).

 The thyroid cartilage (Adam’s apple) consists of two fused

plates of hyaline cartilage that form the anterior wall of the lar-

ynx and give it a triangular shape. It is present in both males and

females but is usually larger in males due to the influence of

male sex hormones on its growth during puberty. The ligament

that connects the thyroid cartilage to the hyoid bone is called the

thyrohyoid membrane.