Respiratory System
Respiration
• Pulmonary ventilation (breathing):
movement of air into and out
of the lungs
• External respiration: O2 and CO2
exchange between the lungs
and the blood
• Transport: O2 and CO2
in the blood
• Internal respiration: O2 and CO2
exchange between systemic blood
vessels and tissues
Respiratory
system
Circulatory
system
Respiratory System: Functional
Anatomy
• Major organs
– Nose, nasal cavity, and paranasal sinuses
– Pharynx
– Larynx
– Trachea
– Bronchi and their branches
– Lungs and alveoli
Nasal cavity
Nostril
Oral cavity
Pharynx
Larynx
Trachea
Carina of
trachea
Right main
(primary)
bronchus
Right lung
Left main
(primary)
bronchus
Left lung
Diaphragm
Figure 22.1
Functional Anatomy
• Respiratory zone: site of gas exchange
– Microscopic structures: respiratory bronchioles, alveolar
ducts, and alveoli
• Conducting zone: passageway to gas exchange sites
– Includes all other respiratory structures
• Respiratory muscles: diaphragm and other muscles
that promote ventilation
• Functions
– Provides an airway for respiration
– Moistens and warms the entering air
– Filters and cleans inspired air
– Serves as a resonating chamber for speech
– Houses olfactory receptors
• Mucosa
– Pseudostratified ciliated columnar epithelium
– Cilia move contaminated mucus posteriorly to
throat
Paranasal Sinuses
• In frontal, sphenoid, ethmoid, and maxillary
bones
• Lighten the skull and help to warm and
moisten the air
Pharynx
• Muscular tube that
connects to the
– Nasal cavity and
mouth superiorly
– Larynx and
esophagus
inferiorly
Nasopharynx
Oropharynx
• From the base of
Laryngopharynx
the skull to the
level of the sixth
cervical vertebra
(b) Regions of the pharynx
Larynx
• Attaches to the hyoid bone and opens into the
laryngopharynx
• Continuous with the trachea
• Functions
1. Provides an airway
2. Routes air and food into proper channels
3. Voice production
Hyaline cartilage keeps larynx and trachea open
Epiglottis: elastic cartilage; covers the larynx during
swallowing
Epiglottis
Body of hyoid bone
Thyrohyoid
membrane
Cuneiform cartilage
Corniculate cartilage
Arytenoid cartilage
Arytenoid muscles
Cricoid cartilage
Thyrohyoid membrane
Fatty pad
Vestibular fold
(false vocal cord)
Thyroid cartilage
Vocal fold
(true vocal cord)
Cricothyroid ligament
Cricotracheal ligament
Tracheal cartilages
(b) Sagittal view; anterior surface to the right
Figure 22.4b
Base of tongue
Epiglottis
Vestibular fold
(false vocal cord)
Vocal fold
(true vocal cord)
Glottis
Inner lining of trachea
Cuneiform cartilage
Corniculate cartilage
(a) Vocal folds in closed position;
closed glottis
(b) Vocal folds in open position;
open glottis
Figure 22.5
Voice Production
• Speech: intermittent release of expired air
while opening and closing the glottis
• Pitch is determined by the length and tension
of the vocal cords
• Loudness depends upon the force of air
• Chambers of pharynx, oral, nasal, and sinus
cavities amplify and enhance sound quality
• Sound is “shaped” into language by muscles of
the pharynx, tongue, soft palate, and lips
Trachea
• Windpipe
Mucosa: ciliated
pseudostratified
epithelium with goblet
cells
Rings of Hyaline Cartilage
Posterior
Mucosa
Submucosa
Esophagus
Trachealis
muscle
Lumen of
trachea
Seromucous gland
in submucosa
Hyaline cartilage
Adventitia
Anterior
(a) Cross section of the trachea and esophagus
Figure 22.6a
Conducting Zone Structures
• Trachea  right and left main (primary)
Trachea
bronchi
• Each main bronchus enters one lung
Middle lobe
of right lung
Superior lobe
of left lung
Left main
(primary)
bronchus
Lobar
(secondary)
bronchus
Segmental
(tertiary)
bronchus
Inferior lobe
of right lung
Inferior lobe
of left lung
– Right main bronchus is wider, shorter, &
more vertical than the left
Superior lobe
of right lung
Conducting Zone Structures
• From bronchi through bronchioles, structural
changes occur
– Cartilage rings give way to plates; cartilage is
absent from bronchioles
– Epithelium changes from pseudostratified
columnar to cuboidal; cilia and goblet cells
become sparse
– Relative amount of smooth muscle increases
Respiratory Zone
• Respiratory bronchioles, alveolar ducts,
alveolar sacs (clusters of alveoli)
• ~300 million alveoli account for most of the
lungs’ volume and are the main site for gas
exchange
Alveoli
Alveolar duct
Respiratory
bronchioles
Terminal
bronchiole
(a)
Alveolar duct
Alveolar
sac
Three Types of Cells found in alveoli
- Type I Cells – simple squamous cells; allow for gas diffusion
- Surfactant Cell (Type II) – produce an oily secretion; it
reduces surface tension so lungs don’t collapse
- Alveolar Macrophages –
Clear/swallow 2 million dust cells out of your lungs/hour.
Type II Cell
Macrophage
Red blood
cell
Nucleus of type I
(squamous
epithelial) cell
Alveolar pores
Capillary
O2
Capillary
CO2
Alveolus
Alveolus
Type I cell
of alveolar wall
Macrophage
Endothelial cell nucleus
Alveolar
epithelium
Fused basement
membranes of the
Respiratory alveolar epithelium
membrane and the capillary
Red blood cell
endothelium
Alveoli (gas-filled in capillary
Type II (surfactantCapillary
air spaces)
secreting) cell
endothelium
(c) Detailed anatomy of the respiratory membrane
Figure 22.9c
Right lung
Right
superior
lobe (3
segments)
Left lung
Left superior
lobe
(4 segments)
Right
middle
lobe (2
segments)
Right
inferior lobe (5 segments)
Left inferior
lobe (5 segments)
Figure 22.11
Blood Supply
• Pulmonary circulation (low pressure, high
volume)
– Pulmonary arteries deliver systemic venous blood
• Branch profusely, along with bronchi
• Feed into the pulmonary capillary networks
– Pulmonary veins carry oxygenated blood from
respiratory zones to the heart
Blood Supply
• Systemic circulation (high pressure, low volume)
– Bronchial arteries provide oxygenated blood to lung
tissue
• Arise from aorta and enter the lungs
• Supply all lung tissue except the alveoli
– Pulmonary veins carry most venous blood back to the
heart
Mechanics of Breathing
• Pulmonary ventilation consists of two phases
1. Inspiration: gases flow into the lungs
2. Expiration: gases exit the lungs
Caused by changes between atmospheric gas
pressure (14.7 psi) and gas pressure in the lungs
Atmospheric pressure
Movement of air always flows
from higher gas pressure to
lower gas pressure
Thoracic wall
756
760
Lung
Diaphragm
Intrapleural
pressure
756 mm Hg
(–4 mm Hg)
Intrapulmonary
pressure 760 mm Hg
(0 mm Hg)
Figure 22.12
Pulmonary Ventilation
• Inspiration and expiration
• Mechanical processes that depend on volume
changes in the thoracic cavity
– Volume changes  pressure changes
– Pressure changes  gases flow to equalize
pressure
Boyle’s Law
• The relationship between the pressure and
volume of a gas
• Used to explain the mechanics of breathing
• Under constant temperature, Pressure (P)
varies inversely with volume (V):
P1V1 = P2V2 P=1/V
• Lungs can change volume, so air pressure in
lungs will also change
Inspiration
• An active process
– Inspiratory muscles contract
– Lungs are stretched and volume increases
– Air pressure in lungs drops
– Air flows into the lungs
Sequence of events
Changes in anteriorposterior and superiorinferior dimensions
Changes in lateral
dimensions
(superior view)
1 Inspiratory muscles
contract (diaphragm
descends; rib cage rises).
2 Thoracic cavity volume
increases.
Ribs are elevated
and sternum flares
as external
intercostals
contract.
3 Lungs are stretched;
External
intercostals
contract.
intrapulmonary volume
increases.
4 Intrapulmonary pressure
drops.
5 Air (gases) flows into
lungs down its pressure
gradient until intrapulmonary
pressure is 0 (equal to
atmospheric pressure).
Diaphragm
moves inferiorly
during contraction.
Figure 22.13 (1 of 2)
Expiration
• Quiet expiration is normally a passive process
–
–
–
–
–
Inspiratory muscles relax
Thoracic cavity volume decreases
Elastic lungs recoil and volume inside lungs decreases
Pressure inside lungs increases
Air flows out of the lungs
• Note: forced expiration is an active process: it uses
abdominal and internal intercostal muscles
Sequence
of events
Changes in anteriorposterior and superiorinferior dimensions
Changes in
lateral dimensions
(superior view)
1 Inspiratory muscles
relax (diaphragm rises; rib
cage descends due to
recoil of costal cartilages).
2 Thoracic cavity volume
Ribs and sternum
are depressed
as external
intercostals
relax.
decreases.
3 Elastic lungs recoil
External
intercostals
relax.
passively; intrapulmonary
volume decreases.
4 Intrapulmonary pres-
sure rises.
5 Air (gases) flows out of
Lungs.
Diaphragm
moves
superiorly
as it relaxes.
Figure 22.13 (2 of 2)
Lung Volumes
Tidal volume
Inspiratory reserve volume
Expiratory reserve volume
Vital Capacity
Residual Volume
Total Lung Capacity
Tidal volume – normal breath in and out
Vital Capacity – total amount of air you can forcefully
inspire and expire in one respiratory cycle
Physical Factors Influencing Pulmonary
Ventilation
• Inspiratory muscles consume energy to
overcome three factors that hinder air
passage and pulmonary ventilation
1. Airway resistance
2. Lung compliance
3. Lung Elasticity
Airway Resistance
• As airway resistance rises, breathing
movements become more strenuous
• Severely constricting or obstruction of
bronchioles
– Can prevent life-sustaining ventilation
– Can occur during acute asthma attacks and stop
ventilation
• Epinephrine dilates bronchioles and reduces
air resistance
Air Resistance
• Friction in the respiratory passageways,
decreases the flow of gases.
• I.e. Asthma attack, constriction of bronchiole
tubes
• Accumulation of mucus (infections)
• Cystic Fibrosis - mutation on chromosome #7
where lungs produce too much mucus
– Leads to poor gas exchange since mucus blocks
diffusion of gases.
Lung Compliance
• The ease at which lungs stretch
• Decrease in Lung compliance occurs when:
– Smaller passageways are blocked
• Diminished by
– Nonelastic scar tissue (fibrosis)
– Reduced production of surfactant
– Decreased flexibility of the thoracic cage
Lung Elasticity
• The lungs’ ability to
recoil
• I.e. Emphysema
– Air sacs enlarge and
lose their elasticity;
lungs remain over
inflated