chapter 23 Respiratory System

major functions of respiratory system

supply body with O2 for cellular respiration and dispose of CO2, a waste product of cellular respiration.

The respiratory system provides the means

•for gas exchange

•Consists of respiratory passageways in head, neck, and trunk, and the lungs

respiration

Respiration (exchange of gases between atmosphere and body's cells) involves four processes

respiratory system consists of

pulmonary ventilation and pulmonary gas exchange

pulmonary ventilation (breathing)

: movement of air into and out of lungs (movement of gases between atmosphere and alveoli)

Pulmonary Gas Exchange

•(External respiration): exchange of O2 and CO2 between lungs (alveoli) and blood

circulatory system consists of

gas transport and tissue gas exchange

Gas Transport

transport of gases in blood between lungs and systemic cells

Tissue Gas Exchange

(Internal respiration): exchange of O2 and CO2 between systemic blood vessels and tissues (the systemic cells)

air passageway

•Air moves between atmosphere and alveoli as we breathe

Site for exchange of oxygen and carbon dioxide

•Oxygen diffuses from alveoli into blood

•Carbon dioxide diffuses from blood into alveoli

Detection of odors

•Olfactory receptors in superior nasal cavity

Sound Production

•Air moves across vocal cords of the larynx (voice box)

•Vocal cords vibrate, producing sound

upper respiratory tract

Nose, nasal cavity, pharynx, larynx

lower respiratory tract

Trachea, bronchi, bronchioles, alveolar ducts, alveoli

Structures of the conducting zone

•transport air

•Nose to terminal bronchioles (Nose, pharynx, larynx, trachea, most bronchioles)

•Cleanse, humidify, and warm incoming air

Structures of the respiratory zone

•participate in gas exchange

•Respiratory bronchioles, alveolar ducts, alveoli

Mucosa

= mucous membrane: respiratory lining

Respiratory epithelium

•Becomes thinner from the nasal cavity to the alveoli

•Starts out as pseudostratified ciliated columnar - Changes to simple ciliated columnar - Changes to simple cuboidal - Changes to simple squamous

•Exceptions: stratified squamous found in high abrasion areas - oropharynx, laryngopharynx, vocal cords, superior portion of larynx

mucous secretions

•Produced from secretions of Goblet cells of epithelial lining. Mucous and serous glands of the lamina propria

nose

first conducting structure for inhaled air

nasal cavity

from nostrils to choanae

Choanae

(posterior nasal apertures) - paired openings that lead to pharynx

nasal septum

divides left and right sides

The Nasal conchae

•Three paired, scroll-like, mucosa-covered, bony projections on lateral walls (Superior, middle, and inferior nasal conchae) protrude medially.

•Also called turbinate bones - Produce turbulence in inhaled air

•Partition the nasal cavity into separate passages - nasal meatus

•Increase mucosal area

nasal cavity parts

nasal vestibule, olfactory region, respiratory region

nasal vestibule

nasal cavity superior to nostrils

Lined with hairs that filter coarse particles from inspired air

olfactory region

Olfactory mucosa: Odor detection.

respiratory region

•Respiratory mucosa: pseudostratified ciliated columnar epithelium that contains goblet cells and rests on lamina propria that contains many seromucous nasal glands

•Serous cells secrete watery fluid containing enzymes

•Ciliated cells sweep contaminated mucus towards throat

•Inspired air is warmed by plexuses of capillaries and veins

•Has an extensive vascular network

•Nasal mucosa contains many sensory nerve endings that can cause sneezing to force particles out of cavity

nosebleeds

•(epistaxis) common due to large numbers of superficial vessels

nasolacrimal ducts

•Drain lacrimal secretions from eye surfaces to nasal cavity

Nasal cavity conditions the air (warms, cleanses, and humidifies)

•Air turbulence created by conchae enhances all three processes

Functions of the nose

•Provides an airway for respiration

•Moistens and warms entering air - Moist environment humidifies and air is warmed by extensive blood vessels

•Filters and cleans inspired air - Mucus traps dust, microbes, and foreign material

•Serves as resonating chamber for speech

•Houses olfactory receptors

paranasal sinuses

•spaces within skull bones

•Named for specific bone in which they are housed

•Lighten skull, Secrete mucus, Help to warm and moisten air

•Lined by pseudostratified ciliated columnar epithelium

•Mucus swept into pharynx and swallowed

superior to inferior paranasal sinuses

•Frontal sinuses

•Ethmoidal sinuses

•Sphenoidal sinuses posterior to ethmoidal sinuses

•Maxillary sinuses

nasopharynx

•passageway for air, pseudostratified columnar epithelium.

•Soft palate and uvula close nasopharynx during swallowing

•Pharyngeal tonsils (adenoids)

•Eustachian tubes (auditory tubes) drain and equalize pressure in middle ear

oropharynx

•Passageway for food and air from level of soft palate to epiglottis (closes off airway)

•stratified squamous epithelium

•Palatine and lingual tonsil

laryngopharynx

•Passageway for food and air

•Extends to larynx, continuous with esophagus

•stratified squamous epithelium

Larynx

voice box

•Opens into laryngopharynx and is continuous with the trachea.

•Three functions of larynx:

•Air passageway - Provides patent (open)

airway due to cartilage

•Prevents ingested materials from entering

respiratory tract. Routes air and food into

proper channels - via epiglottis

•Voice production - via vocal cords and

glottis

- Vocal folds vibrate during expiration

Sound Production

vocal cord vibration

•Air is forced past vocal cords during expiration

range

•voice determined by length, thickness of vocal cords

•Males have longer and thicker folds, and so deeper voices

•Folds increase in length with growth, deepening range

pitch

•(frequency) determined by tension on vocal cords

•Increased tension = folds vibrate more = higher pitch

Loudness

•depends on force of air passing across vocal cords

More air = louder sound

lower respiratory system

•Includes conducting pathways from trachea to terminal bronchioles

•Includes structures involved in gas exchange: respiratory bronchioles, alveolar ducts, and alveoli

lower respiratory system broken into two zones

conducting and respiratory zone

conducting zone

•conduits that transport gas to and from gas exchange sites

•Includes all other respiratory structures

•Cleanses, warms, and humidifies air

respiratory zone

•site of gas exchange

•Consists of microscopic structures such as respiratory bronchioles, alveolar ducts, and alveoli

Trachea

windpipe

•Epithelium is ciliated and produces mucus

•Posterior branching into 2 main bronchi

tracheal cartilage

•support anterior and lateral walls

•C-shaped rings of hyaline cartilages

•Ensure trachea is always open

tracheal wall inner to outer

•Mucosa: pseudostratified ciliated columnar epithelium and lamina propria

•Submucosa: areolar connective tissue with blood vessels, nerves, serous and mucous glands, lymphatic tissue

•Tracheal cartilage

•Adventitia: elastic connective tissue

histology of the bronchial tree

•Main bronchi are supported by incomplete rings of hyaline cartilage (keep them open)

•Wall support (cartilage) lessens as bronchi divide

•Bronchioles have no cartilage but have proportionally thicker layer of smooth muscle

•Muscle contraction narrows bronchiole diameter

Bronchoconstriction

•less air through bronchial tree (less entry of potentially harmful substances)

•Muscle relaxation increases bronchiole diameter

Bronchodilation

more air through the bronchial tree

respiratory zone structures

•Respiratory zone begins where terminal bronchioles feed into respiratory bronchioles, which lead into alveolar ducts and finally into alveolar sacs (saccules)

•Alveolar sacs contain clusters of alveoli

•Each lung contains 300-400 million alveoli which make up most of the lung volume

•Sites of actual gas exchange

respiratory epithelium

•Respiratory bronchioles lined with simple cuboidal epithelium

•Alveoli and alveolar ducts lined by simple squamous

•Thinness facilitates gas exchange

Alveolar pores: openings providing collateral ventilation

•Surrounded by pulmonary capillaries

respiratory membrane

•Blood/air barrier that consists of alveolar & capillary walls and their fused basement membranes

Very thin (~0.5 mm); allows gas exchange across membrane by simple diffusion

alveolar walls consist of:

1.Single layer of squamous epithelium - alveolar type I cells

2.Scattered cuboidal alveolar type II cells secrete surfactant and antimicrobial proteins. Coats inside of alveolus and opposes collapse during expiration

3. Alveolar macrophages (dust cells) keep alveolar surfaces sterile

respiratory membrane 2

•Thin barrier (0.5 microns) separating air in alveoli and blood in pulmonary capillaries made of fused basement membrane of:

•Alveolar epithelium and its basement membrane

•Capillary epithelium and its basement membrane

•Oxygen diffuses from alveolus into capillaries - Erythrocytes become oxygenated

•Carbon dioxide diffuses from blood to alveolus - Expired to external environment

pulmonary circulation 2

replenishes O2, eliminates CO2

pulmonary arteries

•deliver blood from heart to lungs for oxygenation

•Branch profusely to feed into pulmonary capillary networks

pulmonary veins

•carry oxygenated blood from respiratory zones back to heart

•Low-pressure, high-volume system

bronchial circulation

•Bronchial arteries provide oxygenated blood to lung tissue

•Arise from aorta and enter lungs at hilum

•Part of systemic circulation, so are high pressure, low volume

•Supply all lung tissue except alveoli

•Bronchial veins anastomose with pulmonary veins

- Pulmonary veins carry most venous blood back to heart

Pleurae

thin, double-layered serosal membrane that divides thoracic cavity into two pleural compartments and mediastinum

parietal pleura

•membrane on thoracic wall, superior face of diaphragm, around heart, and between lungs

visceral pleura

membrane on external lung surface

pleural fluid

•fills slit like pleural cavity between two pleurae

•Provides lubrication and surface tension that assists in expansion and recoil of lungs

respiration 4 processes

pulmonary ventilation, pulmonary gas exchange, gas transport, and tissue gas exchange.

pulmonary ventilation 2

.movement of gases between atmosphere and alveoli

pulmonary gas exchange

exchange of gases between alveoli and blood

Gas Transport

.transport of gases in blood between lungs and systemic cells

tissue gas exchange

exchange of respiratory gases between the blood and the systemic cells

pulmonary ventilation (breathing)

air movement between atmosphere and alveoli

two cyclic phases of pulmonary ventilation

•Inspiration brings air into the lungs (inhalation)

•Expiration forces air out of the lungs (exhalation)

Quiet Breathing (Eupnea)

rhythmic breathing at rest

Forced breathing

•vigorous breathing

•Autonomic nuclei in brainstem regulate breathing activity

•Skeletal muscles contract and relax changing thorax volume

Volume changes result in

•changes in pressure gradient between lungs and atmosphere

•Air moves down its pressure gradient

•Air enters lung during inspiration; exits during expiration

volume changes in thoracic cavity

Thoracic volume changes vertically, laterally, and anterior-posteriorly

Vertical changes result from diaphragm movement

•Flattens (by moving inferiorly) when contracted

•When relaxed, returns to original position, vertical dimensions decrease

•For relaxed breathing: only small movements required

•For forced expiration: abdominal muscle contraction causes larger movement of diaphragm superiorly

Boyle's gas law

•Relationship of volume and pressure

•At constant temperature, pressure (P) of a gas decreases if volume (V) of the container increases, and vice versa

•P1V1 = P2V2

•Inverse relationship between gas pressure and volume

•An air pressure gradient exists when force per unit area is greater in one place than another

•If the two places are interconnected, air flows from high to low pressure until pressure is equal

Intrapulmonary and Intrapleural Pressure Relationships

Importance: the difference in the pressures keeps lungs inflated, however if they become equal, the lungs will collapse - transpulmonary pressure must be maintained!!!

atmospheric pressure

pressure of air in environment

•Changes with altitude - Increased altitude = "thinner air" = lower pressure

•Sea level value is 760 mm Hg = 14.7 lbs per square inch = 1 atm

intrapulmonary pressure

pressure (intra-alveolar pressure): : pressure in alveoli

•Fluctuates with breathing - May be higher, lower, or equal to atmospheric pressure

•Is equal to atmospheric pressure at end of inspiration and expiration

intrapleural pressure

pressure pressure in pleural cavity

•Fluctuates with breathing

•Is lower than intrapulmonary pressure (keeps lungs inflated)

•About 4 mm Hg lower than intrapulmonary pressure between breaths

transpulmonary pressure

•Pressure that keeps lung spaces open

•Keeps lungs from collapsing

•Greater transpulmonary pressure, the larger the lungs will be

•Lungs will collapse if:

•Pip = Ppul or

•Pip = Patm

•Negative Pip must be maintained to keep lungs inflated

quiet inspiration

•Diaphragm and external intercostals contract increasing thoracic volume

•Intrapleural volume increases, so intrapleural pressure decreases

Lungs pulled by pleurae

•so lung volume increases and intrapulmonary pressure decreases

Because intrapulmonary pressure is less than atmospheric pressure

•air flows in until these pressures are equal

•Typically, 0.5 L flows in as tidal volume

Quiet expiration

Diaphragm and external intercostals relax decreasing thoracic volume

•Pleural cavity volume decreases, so intrapleural pressure increases

Elastic recoil pulls lungs inward

so alveolar volume decreases and intrapulmonary pressure increases

Since intrapulmonary pressure is greater than atmospheric pressure

•air flows out until these pressures are equal

About 0.5 L of air leaves the lung

neural respiratory control

respiratory center of the brain

Medulla Respiratory Centers

ventral respiratory group and dorsal respiratory group

Ventral Respiratory Group (VRG)

•Generates breathing rhythm - Sets eupnea: normal respiratory rate and rhythm (12-15 breaths/minute)

•Stimulates ventilation muscles - via phrenic (diaphragm) and intercostal nerves (external intercostals)

Dorsal Respiratory Group (DRG)

•Integration of incoming signals

•VRG communication

Pontine Respiratory Centers

•also known as pneumotaxic center

•Talks to medulla about incoming information

•Fine-tunes breathing rhythms - Pontine respiratory center facilitates smooth transitions between inspiration and expiration

•Brainstem neurons influence respiratory muscles - VRG neurons synapse with lower motor neurons of skeletal muscles in spinal cord

•Axons innervating diaphragm travel in phrenic nerves

•Axons innervating intercostal muscles travel in intercostal nerves

central chemoreceptors

in medulla monitor pH of CSF

•CSF pH changes are caused by changes in blood PCO2

peripheral chemoreceptors

are in aortic and carotid bodies

•Stimulated by changes in H+ or respiratory gases in blood

•Monitor PCO2

•Most potent and most closely monitored (in brain)

•Brain CO2 inc, and pH dec

•inc depth and rate of ventilation to inc pH

•Apnea: breathing cessation that may occur when PCO2 levels drop abnormally low