Chapter 13:
The Respiratory System
• Gas exchanges between the blood and
– Occurs in the alveoli of the lungs
• Passageways to the lungs purify,
humidify, and warm the incoming air
The Nose
• Only externally visible part of the
respiratory system
• Air enters the nose through the
external nostrils (nares)
• Interior of the nose consists of a nasal
cavity divided by a nasal septum
Inside the nasal cavity:
• Olfactory receptors in mucosa on superior
surface for sense of smell
• Respiratory mucosa everywhere else
produces sticky mucus
– Moisten air
– Trap incoming foreign particles
• Cilia = tiny hair-like structures that move
contaminated mucus towards the pharynx
where it is swallowed and digested by
stomach juices
• Projections called conchae on lateral walls
– Increase surface area & air turbulence
Figure 13.2
• The nasal cavity is separated from
the oral cavity by the palate
– Anterior part = hard palate (bone)
– Posterior part = soft palate (muscle)
Paranasal Sinuses
• Cavities within bones surrounding the
nasal cavity
• Located in the following bones:
– Frontal
– Sphenoid
– Ethmoid
– Maxillary
• Functions:
– Lighten the skull
– Act as resonance chambers for speech
– Produce mucus
Pharynx (Throat)
• Muscular passage from nasal cavity to
• Three regions from superior to
– Nasopharynx
– Oropharynx
– Laryngopharynx
• Passageways for air and food
• Pharyngotympanic tubes that drain
middle ear open into the nasopharynx
– Ear infections may follow sore throat
• Tonsils:
– Pharyngeal tonsil (adenoids) in the
– Palatine tonsils in the oropharynx
– Lingual tonsils at the base of the tongue
Figure 13.2
Larynx (Voice Box)
• Function:
– Routes air and food into proper channels
– Plays a role in speech
• Structure:
– Eight rigid hyaline cartilages
• Thyroid cartilage is largest = Adam’s apple
– Epiglottis =spoon-shaped flap of elastic cartilage
• Rises to covers larynx when you swallow so that liquid
and food go to the esophagus instead of airway
– Vocal folds (aka true vocal cords)
• Vibrate with expelled air to create sound
– Glottis = opening between vocal cords
Anterior View of Larynx
Posterior View of Larynx
Upper Respiratory Tract: Larynx
Figure 13.2
Trachea (Windpipe)
• 4 inch long tube that connects larynx
with bronchi
• Walls are reinforced with C-shaped
hyaline cartilage
• Lined with ciliated mucosa
– Beat continuously in the opposite
direction of incoming air
– Expel mucus loaded with dust and other
debris away from lungs
Trachea (Windpipe)
Figure 13.3a
Trachea (Windpipe)
The yellow structures are cilia. The orange structures
are goblet cells that secrete mucus and have microvilli.
Figure 13.3b
Main (Primary) Bronchi
• Formed by division of the trachea
• Right bronchus is wider, shorter, and
straighter than left
– More common site for inhaled objects to
get stuck
• Subdivide into smaller and smaller
Main Bronchi
Figure 13.1
• Occupy most of the thoracic cavity
– Heart occupies central portion called
• Apex (superior part) is near the clavicle
• Base (inferior part) rests on the
• Each lung is divided into lobes by fissures
– Left lung has two lobes
– Right lung has three lobes
Figure 13.4a
• Covering of lungs:
– Serosa covers the outer surface of the lungs
• Pulmonary (visceral) pleura covers the lung surface
• Parietal pleura lines the walls of the thoracic cavity
– Pleural fluid fills the area between layers of
pleura to allow gliding = less friction
Bronchial (Respiratory) Tree
• All but the smallest of these
passageways have reinforcing cartilage
in their walls
• Largest to smallest:
– Primary bronchi
– Secondary bronchi
– Tertiary bronchi
– Bronchioles
– Terminal bronchioles
Respiratory Zone
• Structures from largest to smallest:
Respiratory bronchioles
Alveolar ducts
Alveolar sacs
Alveoli (air sacs) – 40x more surface area than skin
• Site of gas exchange = alveoli only
Respiratory Membrane
(Air-Blood Barrier)
• Walls of alveoli are thin squamous epithelial
layer (much thinner than tissue paper!)
• Alveolar pores connect neighboring air sacs
incase mucus blocks other paths
• Pulmonary capillaries cover external surfaces of
• One side of membrane is air and the other side
is blood flowing past
• Also has:
– Alveolar macrophages (“dust cells”) that remove
bacteria and debri
– Cuboidal cells that make surfactant (prevent alveoli
from collapsing)
Respiratory Membrane (Air-Blood
Figure 13.6 (1 of 2)
Respiratory Membrane (Air-Blood
Figure 13.6 (2 of 2)