Chapter 15. Learning Objectives

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Chapter 15

Respiratory System

Learning Objectives

˜

Differentiate between internal and external respiration.

˜

List the secondary functions of the respiratory system.

˜

List the components of the upper respiratory tract and describe their structure and functions.

˜

List the components of the lower respiratory tract and describe their structure and functions.

˜

Describe the events that occur during inspiration and expiration.

˜

List the muscles involved in inspiration and expiration.

˜

Define the terms tidal volume, minute volume, and residual volume.

˜

Describe the processes of oxygen and carbon dioxide exchange between the alveoli and the blood.

˜

Describe the mechanical and chemical respiratory control systems.

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Respiratory System

˜ Primary Function: bring O ₂ into the body and CO ₂ out of it

Ø Respiratory system works together with the cardiovascular system

˜ Secondary functions

Ø Phonation (voice production)

Ø Regulation of body temperature

Ø Regulation of acid-base balance

Ø Sense of smell

Respiration

˜ External respiration - exchange of O ₂ and CO ₂ between the inhaled air and the blood flowing through the pulmonary capillaries

˜ Internal respiration - exchange of O ₂ and

CO ₂ between the blood in the systemic

capillaries and all the cells and tissues of

the body

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Structures of Respiratory System

Upper Respiratory Tract (outside the lungs)

˜ Nostrils

˜ Nasal passages

˜ Pharynx

˜ Larynx

˜ Trachea

Nose and Nasal Passages

˜ Nares (nostrils):

external openings of the respiratory tube

Ø Lead into the nasal passages

˜ Nasal Passages:

between the

nostrils and the

pharynx

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Nose and Nasal Passages

˜ Nasal septum:

separates the left and right nasal passage

˜ Hard and soft palates: separate the nasal

passages from the mouth.

Nose and Nasal Passages

˜ Turbinates (nasal conchae):

Ø Divide each nasal passage into 3 main passageways

Ø Thin, scroll-like bones covered with nasal epithelium

Ø Dorsal and ventral

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Nose and Nasal Passages

˜ Nasal passages lined with pseudostratified columnar epithelium

˜ Cilia project from the cell surfaces up into a layer of mucus

˜ Mucus is secreted by mucous glands and goblet cells

Nasal Passages Functions

˜ Warm, humidify, and filter inhaled air

˜ Air is warmed by blood flowing through blood vessels just beneath the nasal epithelium.

˜ Air is humidified by mucus and other fluids on the epithelial surface.

˜ Air is filtered as it passes through the winding passages produced by the turbinates.

Ø Particles do not readily pass through but

become trapped in the mucous layer; cilia

move mucus and trapped foreign material

upward to the pharynx, mouth

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Paranasal Sinuses

˜ Paranasal Sinuses:

ciliated outpouchings of the nasal passages contained within spaces in certain skull bones

˜ Most animals have two frontal sinuses and two maxillary sinuses within the frontal and maxillary bones

Pharynx

˜ Common passageway for respiratory and digestive systems

˜ Soft palate divides pharynx into the dorsal nasopharynx (respiratory passageway) and the ventral oropharynx (digestive passageway)

˜ Caudal end of pharynx opens dorsally into

the esophagus and ventrally into the larynx

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Pharynx

˜ Reflexes control actions of the muscles around the pharynx.

˜ Larynx and pharynx work together to prevent swallowing from interfering with breathing, and vice versa.

˜ Swallowing - breathing stops, opening into larynx is covered, material to be swallowed moves to rear of pharynx, esophagus opens

˜ After swallowing, larynx is reopened and breathing resumes

Larynx

˜ Short, irregular tube connecting pharynx with the trachea

˜ Composed of segments of cartilage that are connected to each other and the surrounding tissues by muscles

˜ Supported in place by the hyoid bone

˜ Cartilage components - epiglottis,

arytenoid cartilages, thyroid cartilage,

cricoid cartilage

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Larynx Cartilages

˜ Epiglottis - single, leaf-shaped; projects forward from the ventral portion of the larynx

Ø During swallowing, the epiglottis is pulled back to cover the opening of the larynx

˜ Arytenoid cartilages - paired; attachment is the site of the vocal cords

Ø Muscles adjust the tension of the vocal cords by moving the cartilages.

Ø Arytenoid cartilages and the vocal cords form the boundaries of the glottis.

Larynx Functions

Voice Production

˜ Vocal cords - two connective tissue bands attached to the arytenoid cartilages

Ø Stretched across lumen of larynx parallel to each other

˜ Vocal cords vibrate as air passes over them.

˜ Muscles attached to the arytenoid cartilages control the tension of the vocal cords.

Ø Complete relaxation opens the glottis wide; no sound

Ø Lessening the tension produces lower-pitched sounds

Ø Tightening the tension produces higher-pitched sounds

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Larynx Function

Prevention of foreign material being inhaled

Ø During swallowing, muscle contractions pull the larynx forward and fold the epiglottis back over its opening.

˜ Control airflow to and from the lungs

Ø Small adjustments in the size of the glottis aid movement of air.

Trachea

˜ Short, wide tube

˜ Extends from the larynx into the thorax

˜ Divides into the two main bronchi that enter the lungs

Ø Bifurcation of the trachea

˜ Composed of fibrous tissue and smooth muscle held open by hyaline cartilage rings

˜ Lined with ciliated epithelium

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Trachea

˜ C-shaped rings of hyaline cartilage

˜ Open part of

tracheal rings face dorsally

˜ Gap between the ends of each ring bridged by smooth muscle

Structures of Respiratory System

Lower Respiratory Tract

˜ Bronchi

˜ Bronchioles

˜ Alveolar ducts

˜ Alveoli

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Bronchial Tree

˜ Each bronchus divides into smaller bronchi, which divide into even smaller bronchi, and then tiny bronchioles

˜ Bronchioles

subdivide into

alveolar ducts

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Bronchial Tree

˜ Alveolar ducts end in groups of alveoli

˜ Arranged like bunches of grapes

˜ Alveolar sacs:

groups of alveoli

Bronchial Tree

˜ Autonomic nervous system controls smooth muscle fibers in wall of bronchial tree

˜ Bronchodilation - bronchial smooth muscle relaxes

Ø Aids respiratory effort during intense physical activity

˜ Bronchoconstriction - bronchial smooth muscle partially contracts

Ø Reduces size of the air passage

Ø Irritants in inhaled air can cause

bronchoconstriction

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Alveoli

˜ Site of external respiration

˜ Tiny, thin-walled sacs of simple squamous epithelium

˜ Surrounded by networks of capillaries

˜ Lined with fluid that

contains surfactant

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Lungs

˜ Each lung has a base, an apex, and a convex lateral

surface.

˜ Base is in caudal part of thoracic cavity

Ø Lies directly on cranial surface of diaphragm

˜ Apex lies in cranial portion of thoracic cavity

Lungs

˜ Convex lateral surface lies against inner surface of the thoracic wall

˜ Mediastinum -

area between the

lungs

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Lungs

˜ Lungs are divided into lobes (in most species)

Ø Pattern varies with species

˜ Lobes are distinguished by the major branches of the bronchi

˜ Hilus - small, well-defined area on medial side of lung

Ø Site where air, blood, lymph, and nerves enter and leave the lung

Pulmonary Circulation

˜ Deoxygenated blood enters the lungs from right ventricle of heart through the

pulmonary artery

Ø Pulmonary artery splits into left and right pulmonary arteries that enter the two lungs

Ø Pulmonary arterioles enter capillary networks around the alveoli

˜ Oxygenated blood returns to the left side

of heart in the pulmonary veins.

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Thoracic Cavity

˜ Bound by thoracic vertebrae dorsally, ribs & intercostal muscles laterally, the sternum ventrally

˜ Mediastinum – area between lungs

Ø Contains heart, trachea, esophagus, blood vessels, nerves, lymphatic structures

Pleura

˜ Thin membrane that lines thoracic cavity and covers organs and structures in the thorax

Ø Visceral layer covers thoracic organs and structures

Ø Parietal layer lines the cavity

˜ Space between the two pleural layers is filled with a small amount of pleural fluid

Ø Helps ensure that surfaces of organs slide

smoothly along the lining of the thorax during

breathing

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Diaphragm

˜ Thin, dome-shaped skeletal muscle sheet

˜ Forms caudal boundary of thorax

˜ Important respiratory muscle

Ø Flattens when it contracts

Ø Enlarges volume of the thorax and aids inspiration

Process of Respiration

˜ Pressure within the thorax is negative with respect to atmospheric pressure.

Ø Pulls lungs tight out against the thoracic wall

Ø Lungs follow passively as movements of the thoracic wall and diaphragm alternately enlarge and reduce the volume of the thorax.

Ø Negative intrathoracic pressure helps draw

blood through veins and into the atria

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Inspiration

˜ Process of drawing air into lungs (inhalation)

˜ Results from enlargement of the volume of the thoracic cavity by the inspiratory

muscles

˜ Main inspiratory muscles: diaphragm and external intercostal muscles

Ø External intercostal muscles located in the

external portion of the intercostal spaces

(between ribs)

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Expiration

˜ Process of pushing air out of lungs (exhalation)

˜ Results from decrease in size of thoracic cavity

˜ Main expiratory muscles: internal intercostal muscles and abdominal muscles

Ø Internal intercostal muscles located between the ribs, deep to the external intercostal muscles

˜ Contraction of abdominal muscles pushes

abdominal organs against the diaphragm and

pushes diaphragm back into its full dome shape.

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Respiratory Volumes

˜ Tidal volume - volume of air inspired and expired during one breath

Ø Varies according to the body's needs

˜ Minute volume - volume of air inspired and expired during 1 minute of breathing

˜ Residual volume - volume of air remaining

in the lungs after maximum expiration

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Alveolar Gas Exchange

˜ Simple diffusion of gas molecules according to concentration gradient

˜ O ₂ diffuses from the alveolar air into the blood of the alveolar capillary

˜ CO ₂ diffuses from the blood into the

alveolus

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Partial Pressure of Gases

˜ Pressure of each individual gas in a mixture of gases

˜ Example:

Ø Atmospheric air ~ 21% O ₂

Ø Total atmospheric pressure ~ 760 mm of mercury (Hg)

Ø Partial pressure of oxygen (PO ₂ ) in atmosphere:

21% × 760 mm Hg = 159.6 mm Hg

˜ Partial pressures of O 2 and CO 2 in the blood of

alveolar capillaries is determined by the partial

pressures of O ₂ and CO ₂ in alveolar air

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Respiratory Center

˜ Area in the medulla oblongata of the brain stem

˜ Controls respiratory muscle contractions

Ø Directs timing and strength of contraction

˜ Individual control centers - inspiration, expiration, breath holding

˜ Can be consciously controlled for brief

periods

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Mechanical Control System

˜ Stretch receptors in the lungs set limits on routine resting inspiration and expiration.

˜ Respiratory center sends out nerve impulses when lungs inflate to a certain point

Ø Stops muscle contractions that produce inspiration and starts contractions to produce expiration

˜ Another set of nerve impulses sent when lungs deflate sufficiently

Ø Stops expiration and starts the process of

inspiration again

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Chemical Control System

˜ Adjusts the normal rhythmic breathing pattern produced by the mechanical control system

˜ Chemical receptors in carotid artery and aorta monitor blood CO ₂ , pH, and O ₂

Chemical Control System

˜ Blood level of CO ₂ and blood pH are usually linked

˜ Increased CO ₂ in blood and decreased blood pH triggers respiratory center to increase rate and depth of respiration

˜ Decreased CO ₂ in blood increases blood

pH; increased blood pH level triggers

respiratory center to decrease rate and

depth of respiration

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Clinical Applications

˜ Sinusitis

˜ Endotracheal Intubation

˜ Roaring in Horses

˜ Aspiration Pneumonia

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Clinical Applications

˜ Tracheal Collapse

˜ Asthma

˜ Respiratory Tract Infections

˜ Pneumothorax and Lung Collapse

Clinical Applications

˜ Coughs, Sneezes, Yawns, Sighs, and

Hiccups

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