Chapter 23
The Respiratory System
Conducting division
Respiratory division
Respiratory system


Functions to allow the exchange of O2 rich air from the
atmosphere with the O2 poor air in lungs and the blowing off
of CO2 in the process.
Broken down into 2 zones:




“Conducting zone” structures: nose, nasal cavity, pharynx, larynx,
trachea and bronchioles.
“Respiratory zone” structures: alveolar ducts, alveoli and alveolar
sacs where gaseous exchange occurs across the capillary endothelium.
Upper respiratory tract – extends from nares through the
larynx.
Lower respiratory tract – extends from larynx to alveolar sacs.
Respiratory System

Defined: Includes the nose, nasal cavity, pharynx,
larynx, trachea and lungs.

Respiratoy tree showing extensive branching
Conducting division


These structures serve for the exchange of air only
(i.e. ventilation).
No respiration occurs until the air reaches the
respiratory structures (i.e. terminal brochioles, alveoli,
etc.) in the respiratory zone.
Nose and external nares




External nose: covered by skin, it is the only part of
the respiratory system exposed to the outside.
External nares (nostrils) are openings from the
outside into upper respiratory tract.
Nasal cavity a) warms air; b) moistens air, and c)
filters out large particulates before they reach the
pharynx.
Also serves for olfaction and as a resonating
chamber for voice
Nose
The Pharynx: “Throat”

Defined: posterior part of nasal cavity and oral cavity



Consists of 3 divisions:
nasopharynx - posterior nasal cavity, past internal
nares; air passage way from nasal cavity to
oropharynx
oropharynx – passageway for air and food; extends
from soft palate down to epiglottis
laryngopharynx –passageway for air only, extends
from epiglottis to larynx
Nasal and oropharynx
The Larynx: the “voice box”




a.- opening into trachea from laryngopharynx
b.- diverts air and food in correct directions
c.- houses vocal cords
9 cartilages total (you are responsible for knowing the 4 below)




Thyroid cartilage “Adams apple”
Cricoid cartilage completely encircles upper trachea
Arytenoid cartilage
Epiglottis – made of elastic cartilage acts as a flap valve
to close glottis during swallowing.
The Larynx “voice box”
1. thyroid cartilage – “Adams apple” made of hyaline
cartilage.
- largest of the laryngeal cartilages
2. cricoid cartilage – hyaline cartilage
- inferior to thyroid cartilage.
3. arytenoid cartilage – hyaline cartilage
- true vocal cords are attached to these
and they rotate laterally to tighten vocal
cords for speech.
4. epiglottis – made of elastic cartilage
- hood over glottic opening and deflects food
and liquids away from glottis.
Glottis is the opening into the trachea.
Larynx “voice box”
vocal folds/”true” vocal cords
The Trachea: “windpipe”







Cartilaginous tube going from larynx to hilus of lungs.
 basic tissue structure
mucosa – lined with pseudostratified ciliated columnar
epithelium- cilia are part of mucociliary escalator
mechanism.
Submucos - contains goblet mucous glands
Tracheal cartilage – 16-20 “C” shaped rings of hyaline
cartilage.
adventitia – fibrous CT attached to perichondrium of rings.
trachealis muscle joins end of “C”rings on posterior
opening
Bifurcates at “carina” into left and right primary bronchus.
The Trachea: “windpipe”

Cilia and goblets cells with microvilli in trachea
Bronchial tree
Conducting division:
R/L Primary Bronchi – right mainstem bronchus comes
off 1st and is more vertical, as a result foreign objects
getting into trachea are more likely to enter right
mainstem bronchus.
 Secondary Bronchi – lobar bronchi
- right side – three secondary bronchii
-left side – two secondary bronchi
Tertiary Bronchi – segmental bronchi
-divide repeatedly into smaller and smaller bronchi
Bronchioles – air passages < 1 mm in diameter
Terminal Bronchioles – air passages < .5 mm in
diameter
Respiratory division

Is found only in the lungs beginning at terminal
bronchioles

Includes terminal bronchioles, alveolar ducts, alveoli
and alveolar sacs where gaseous exchange occurs
across the capillary endothelium.

Allows the exchange of respiratory gases (O2 &CO2)
from alveolar space into blood and to be bound to
Hgb in RBC’s
The LUNGS
Respiratory division

defined by the presence of alveoli
 respiratory bronchioles – give rise to alveolar ducts
 alveolar ducts – walls consist of rings of smooth
muscle
 alveolar sacs – terminal clusters of alveoli
 alveoli – ~300 million and account for greatest
protion of lung volume and a large surface area for
air exchange
Respiratory division
Respiratory division anatomy
Alveolar sac cell types

type I cells – alveolar cells; squamous cells that cover
95% of alveolar surface where gas exchange occurs.

type II cells – alveolar septal cells comprise other 5%
of alveolar cells and produce “surfactant” that keeps
alveoli from collapsing and sticking together.

alveolar macrophages – dust cells; most numerous of
alveolar cells. Housekeepers of the alveoli.
Alveolar sac anatomy
Pleural membranes

Serous Membranes: similar to pericardium and
consists of:
 visceral pleura – closely adhered to lung
tissue proper.
 parietal pleura – lines the thoracic cavity.
 pleural fluid/space – clear plasma ultrafiltrate
that fills pleural cavity and reduces friction
when lungs inflate and deflate.
Lung anatomy
Occupy greatest portion of
thoracic cavity. Weigh ~ 0.6 #’s
Left lung- 2 lobes
Right lung- 3 lobes
Lobes made up of lobules, which
are smallest division of lungs.
Bronchi and vessels enter lungs at
hilus.
Base rests on diaphragm
Apex is top of lung
Lung tissue is primarily of elastic
connective tissue.
Blood supply to lung tissue is via
bronchial vessels off of aorta.
Bronchopulmonary segments
Muscles involved in breathing


Most important muscle is diaphragm and it descends
as we inhale.
Next most important are the external and internal
intercostal muscles which help to elevate the ribs in a
“bucket handle” motion.
Accessory muscles include: Inhalation- serratus anterior,
sternocleidomastoid, scalenes pectoralis minor.
 Exhalation- rectus abdominis, external obliques,
transversus thoracis

Muscles involved in breathing
Thoracic cavity changes
Neural control of respiration

Normal breathing occurs automatically but are
regulated by 3 reflex mechanisms. [Mechanoreceptors (vol
and abp), chemoreceptors (pH, pCO2, & pO2) and Protective reflexes
(injury or irritants to respiratory tract)]

Three pairs of regulatory centers exist in the reticular
formation of the pons and medulla.
The respiratory rhythmicity center regulates rate and depth
 The apneustic center causes strong sustained inspiration
 The pneumotaxic center inhibits the apneustic center
stopping inspiration


The latter two centers modify the pace and rhythm of respiration
based on information from higher centers (cortex, limbic system
and hypothlamus)
Neural control of respiration