UNIT 5 - CHAPTER 19: RESPIRATORY SYSTEM
LEARNING OUTCOMES:
19.1
Introduction
1.
19.2
Why We Breathe
2.
19.3
19.4
19.5
19.6
19.7
19.8
Identify the general functions of the respiratory system.
Explain why respiration is necessary for cellular survival.
Organs of the Respiratory System
3.
Name and describe the locations of the organs of the respiratory system.
4.
Describe the functions of each organ of the respiratory system.
Breathing Mechanism
5.
Explain how inspiration and expiration are accomplished.
6.
Describe each of the respiratory air volumes and capacities.
7.
Show how alveolar ventilation rate is calculated.
8.
List several nonrespiratory air movements, and explain how each occurs.
Control of Breathing
9.
Locate the respiratory areas, and explain control of normal breathing.
10.
Discuss how various factors affect breathing.
Alveolar Gas Exchanges
11.
Describe the structure and function of the respiratory membrane.
12.
Explain the importance of partial pressure in diffusion of gases.
Gas Transport
13.
Explain how the blood transports oxygen and carbon dioxide.
14.
Describe gas exchange in the pulmonary and systemic circuits.
Life-Span Changes
15.
Describe the effects of aging on the respiratory system.
19-1
UNIT 5 - CHAPTER 19: RESPIRATORY SYSTEM
19.1
INTRODUCTION
A. The respiratory system consists of passageways that filter incoming air and ultimately
transport it into the microscopic air sacs where gases are exchanged.
B. The entire process of exchanging gases between the atmosphere and body cells is
called respiration.
C. Respiration includes 5 parts:
1.
Ventilation* = breathing
2.
External respiration* = air into lungs gas exchange (O2 load/ CO2
unload) air out
3.
Transport of respiratory gases = gases in blood transported from lungs
to body cells and back to lungs
4.
Internal respiration = exchange of gases at body capillaries (O2
unload/CO2 load).
5.
Cellular respiration (CR) = use of oxygen by cells to produce energy
(production of CO2).
*
Only these two portions are accomplished by respiratory system organs.
19.2
WHY WE BREATH
Respiration is necessary because of cellular respiration, the process by which animal cells
use oxygen to release energy from nutrients we eat. The metabolic waste gas, carbon
dioxide is produced during CR, and it must be transported to the lungs to be expelled.
19.3
ORGANS OF THE RESPIRATORY SYSTEM
See Fig 19.1, page 736.
A. Upper Respiratory Organs (UROs):
1.
2.
3.
See Fig 19.2, page 736.
The UROs are lined with mucous membranes.
See Fig 19.3, page 737.
a.
Epithelium over connective tissue (ET/CT) with many goblet cells
(mucus).
b.
Specifically, pseudostratified columnar ET in the trachea.
o
The mucus functions to trap debris.
o
The cilia beat the debris to the pharynx to be swallowed
and destroyed by digestive enzymes.
o
This tissue also serves to warm and moisten incoming air.
Nose (external nares or nostrils)
a.
bone and cartilage with internal hairs
b.
traps large particles (i.e. filters air)
Nasal cavity (separated by nasal septum)
a.
bone and cartilage lined with mucous membranes
b.
warms and moistens incoming air
c.
olfactory reception
d.
resonating chambers for speech
19-2
UNIT 5 - CHAPTER 19: RESPIRATORY SYSTEM
19.3
ORGANS OF THE RESPIRATORY SYSTEM
A.
B.
Upper Respiratory Organs (UROs)
4.
Nasal conchae (within nasal cavity)
See Fig 19.2, page 736.
a.
superior, middle, and inferior
b.
divide nasal cavity into a series of groove-like passageways
c.
lined by mucous membranes
d.
increase turbulence of incoming air (to better warm, moisten, and
filter).
5.
(Paranasal) Sinuses Fig 19.4, page 737.
a.
within four skull bones (frontal, ethmoid, sphenoid, maxillary)
b.
drain into nasal cavity
c.
lined with mucous membranes
d.
reduce weight of skull
e.
resonating chambers for speech
6.
Pharynx (or throat)
See Fig 19.2, page 736.
a.
wall of skeletal muscle lines with mucous membranes
b.
passageway for air and food
c.
resonant chamber for speech sounds
d.
three parts:
a. nasopharynx (uppermost, behind nasal cavity)
b. oropharynx (middle, behind oral cavity)
c. laryngopharynx (lowest)
Lower Respiratory Organs
1.
Larynx (or voice box) See Fig 19.5, page 739 and Fig 19.6, page 740.
a.
Anatomy (Nine pieces of cartilage; all hyaline except elastic
cartilage of epiglottis).
a.
b.
c.
d.
e.
f.
g.
h.
Thyroid cartilage (Adam's apple)
Epiglottis closes off the airway during swallowing.
two pairs of vocal folds (false over true vocal cords)
Glottis = triangular slit opening between two pairs of
vocal cords.
Cricoid cartilage = ring of hyaline cartilage attached to
first ring of trachea site of tracheotomy.
arytenoid cartilages
corniculate cartilages
cuneiform cartilages
19-3
UNIT 5 - CHAPTER 19: RESPIRATORY SYSTEM
19.3
ORGANS OF THE RESPIRATORY SYSTEM
B.
Lower Respiratory Organs:
1.
Larynx (or voice box)
b.
See Fig 19.7, page 740.
Voice production
Mucous membranes form two pairs of folds.
o
o
o
upper ventricular folds (false vocal cords)
lower vocal folds (true vocal cords)
Triangular space between them = glottis.

2.
Trachea (windpipe)
a.
b.
Sound originates from vibration of the vocal folds,
but other structures (pharynx, mouth, nasal cavity,
and paranasal sinuses) convert that sound into
recognizable speech.
See Fig 19.8, page 741.
Location = mediastinum anterior to esophagus extends from larynx
to T5
Structure:
o
o
o
o
16-20 incomplete rings of hyaline cartilage = C-rings
Rings are completed by trachealis muscle and elastic CT
facing esophagus.
See Fig 19.9, page 741.
lined by mucous membranes (pseudostratified columnar
ET)
See Fig 19.10, page 741.
Carina = point where trachea divides into right & left
primary bronchi.
c.
Function = support against collapse continue to warm, moisten &
filter air.
*
*
See Fig 19.11, page 741, Tracheostomy.
See box on page 742 re: George Washington dying from
epiglottitis. A tracheostomy may have saved his life.
19-4
UNIT 5 - CHAPTER 19: RESPIRATORY SYSTEM
19.3
ORGANS OF THE RESPIRATORY SYSTEM
B.
Lower Respiratory Organs: See Fig 19.12, page 742.
3.
Bronchial Tree consists of branched airways leading from the trachea to
microscopic air sacs in the lungs. See Fig 19.12, page 742 and Fig 19.14,
page 743.
a.
Branches of the Bronchial Tree:
o
Right and left main (primary) bronchi lead into each
lung and then branch into
o
Lobar (secondary) bronchi, which branch to each lobe
and then branch into
o
Segmental (tertiary) bronchi which each serve one of 810 lobules (bronchopulmonary segment), that divide into
o
Intralobular bronchioles which branch several times into
tubes called
o
Terminal bronchioles (50-80 terminal bronchioles occupy
a lung lobule), which branch into 2 or more
o
Respiratory bronchioles which subdivide into several (211)…
o
Alveolar ducts that lead to
o
Alveolar sacs and
o
Alveoli.
b.
Structure of the Respiratory Tubes:
o
Each bronchus is similar to trachea with C-shaped plates
rather than rings.
o
As branching continues within lungs to terminal
bronchiole:
1.
Epithelium changes from ciliated pseudostratified
columnar epithelium with goblet cells to nonciliated simple columnar epithelium with scarce
goblet cells
2.
Cartilage decreases
3.
Smooth muscle with elastic fibers scattered
within increases.
o
Respiratory bronchioles are lined by simple cuboidal
epithelium
o
Alveoli are simply a layer of simple squamous epithelium
with no mucous lining.
b.
Functions of the Respiratory Tubes and Alveoli:
o
The branches of the bronchial tree continue to warm, filter,
and moisten incoming air and deliver it to alveoli.
o
The alveoli provide a large surface area of thin cells
through which gas exchange occurs.
*
The lungs contain more than 300 million alveoli = SA of
70m2 for gas exchange at one time!
*
See box on page 744 re: artificial respiration and extracorporeal
membrane oxygenation.
19-5
UNIT 5 - CHAPTER 19: RESPIRATORY SYSTEM
19.3
ORGANS OF THE RESPIRATORY SYSTEM:
B.
Lower Respiratory Organs
5.
Lungs
a.
b.
c.
See Fig 19.19, page 745.
Location = thoracic cavity; separated by mediastinum
Description:
o
paired, cone-shape organs enclosed by diaphragm and
thoracic cage.
o
surrounded by pleural (serous) membranes: See Fig
19.20, page 746.

visceral pleura covers surfaces of lung

parietal pleura lines the thoracic cavity

pleural cavity filled with thin layer serous fluid.
*
Pleural fluid has a very high surface
tension that allows the two membranes to
act as one.
Gross Anatomy:
o
Each lung is divided into lobes by fissures:

Larger right lung has 3 lobes.

Left lung has 2 lobes.
o
Each lobe:

receives a secondary bronchus

is divided into lobules (bronchopulmonary segment)
o
Each lobule: See Fig 19.14, page 743.

is wrapped in elastic connective tissue

contains a lymphatic vessel, an arteriole, a venule,
and a branch from a terminal bronchiole.
*
See box on page 744 re: bronchoscopy.
*
See Table 19.1, page 746: Parts of the Respiratory System.
*
See Clinical Application 19.2 page 747, Lung Irritants.
19-6
UNIT 5 - CHAPTER 19: RESPIRATORY SYSTEM
19.4
BREATHING MECHANISM (ventilation)
A.
Introduction:
Recall that the function of the respiratory system is to supply cells with oxygen
and remove carbon dioxide. The breathing mechanism is called ventilation.
B.
Ventilation involves two actions, inspiration and expiration.
1.
Inspiration (inhalation) = breathing air in.
a.
*
Force necessary is atmospheric pressure.
Fig 19.21, page 748.
o
When the diaphragm is at rest, it is curved upward.

The air pressure outside the lungs is equal to the air
pressure inside the lungs (1 atm or 760 mm Hg).

The thoracic cavity has a given size and volume.
o
During inspiration:
See Fig 19.23, page 749.

The diaphragm muscle pushes downward.

The size of thoracic cavity increases.

The pressure in the thoracic cavity decreases (758
mm Hg) (Boyles' Law).

The air pressure inside the thoracic cavity (lungs) is
less than the atmospheric pressure and therefore air
rushes into lungs to equalize the pressure gradient.
o
Pleural Membranes aid in inspiration:
See Fig 19.20, page 746.

Serous fluid between membranes primarily contains
water.

The water in the serous fluid has great surface
tension and therefore,

Membranes move together.
1.
Thoracic cage expands.
2.
Parietal pleura expand.
3.
Visceral pleura expand.
4.
Lungs expand.
o
Contraction of the external intercostal muscles also aid
inspiration.

Maximal inspiration is aided by contraction of the
sternocleidomastoid and pectoralis minor muscles.
See Major Events of Inspiration, Table 19.2, page 749.
19-7
UNIT 5 - CHAPTER 19: RESPIRATORY SYSTEM
19.4
BREATHING MECHANISM
A.
Ventilation
2.
Expiration = breathing out depends on two factors. See Fig 19.25, page 751.
a.
elastic recoil of tissues that were stretched during inspiration (i.e.
tissues bouncing back to shape).
b.
the inward pull of surface tension due to the alveolar fluid
c.
Maximal Expiration is aided by contraction of abdominal wall
and posterior interior intercostal muscles.
*
See Major Events of Expiration, Table 19.3, page 750.
3.
Atelectasis (Collapsed Lung)
a.
At the end of an expiration, the alveoli tend to recoil inward and
collapse on themselves.
b.
Surfactant (mixture of phospholipid & proteins) produced by
Type II Alveolar cells decreases the surface tension in the lungs.
c.
As the alveoli become smaller during expiration, the surfactant
overcomes the pressure differential and allows the alveoli to
remain inflated.
*
Respiratory Distress Syndrome (RDS) in premature newborns
(collapsed lungs) occurs due to the lack of surfactant in the alveoli.
See box on page 749.
*
See box on page 750 re: pneumothorax.
4.
Respiratory Air Volumes and Capacities See Fig 19.26, page 751.
a.
are measured by a spirometer. See Fig 19.27, page 752.
o
One inspiration plus the following expiration is called a
respiratory cycle. Tidal Volume = amount (volume) of air
that enters the lungs during normal inspiration and leaves
the lungs during normal expiration; approximately 500 ml.
o
Inspiratory Reserve Volume (IRV) = the amount of air
the can be forcibly inhaled after a normal tidal inspiration;
approximately 3000 ml.
o
Expiratory Reserve Volume (ERV) = the amount of air
that can be forcibly exhaled after a normal tidal expiration;
approximately 1100 ml.
o
Residual Volume (RV) = amount of air that always
remains in lungs; approximately 1200 ml.
o
Vital Capacity (VC) = the maximum amount of air that
can be exhaled after a maximum inhalation.

VC = TV + IRV + ERV = approximately 4600 ml.
o
Inspiratory Capacity = total amount of air that can be
inspired after a tidal expiration.

IC = TV + IRV
o
Functional Residual Capacity = amount of air left in the
lungs after a tidal expiration.

FRC = ERV + RV
o
Total Lung Capacity = VC + RV; approximately 6 L.
*
See Respiratory Air Volumes and Capacities, Table 19.4, page 752.
19-8
UNIT 5 - CHAPTER 19: RESPIRATORY SYSTEM
19.4
BREATHING MECHANISM
B.
Ventilation
5.
Alveolar Ventilation
a.
Minute Ventilation (MV) = TV X RR (respiratory rate)
o
Amount of air that enters and exits respiratory system in
one minute
o
About 6000mL
b.
Anatomic dead space (ADS) = air space in respiratory
passageways not involved in gas exchange; approximately 150mL.
c.
Alveolar ventilation = the actual amount of air involved in gas
exchange.
o
AV = (TV – ADS) X RR
o
AV = (500mL – 150mL) X 12 breaths per minute
o
AV = 350mL X 12 b/m
o
AV = 4200mL
6.
Non-Respiratory Air Movements
Table 19.5, page 753.
Modified respiratory movements occur in addition to normal breathing;
usually the result of reflexes.
a.
b.
c.
d.
e.
*
19.5
Cough = sends blast of air through and clears lower respiratory
tract. See box on page 752 re: triggering of cough reflex.
Sneeze = forcefully expels air through nose & mouth
Laugh =
a deep breath released in a series of short convulsive
expirations
Hiccup = spasmodic contraction of diaphragm
Yawn =
deep inspiration through open mouth (ventilates
alveoli).
See Clinical Application 19.3, page 754, Respiratory Disorders that
Decrease Ventilation: Bronchial Asthma and Emphysema.
CONTROL OF BREATHING
A.
Normal breathing = rhythmic and involuntary.
B.
Respiratory Areas = Nervous Control
1.
located in pons and medulla of brain stem
a.
See Fig 19.28, page 753.
2.
Medullary Rhythmicity Area
a.
composed of ventral respiratory group which controls the basic
rhythm of breathing
b.
dorsal respiratory group which controls forceful breathing.
3.
Pontine Respiratory Group (formerly called the Pneumotaxic area)
and apneustic area is located in the pons.
a.
controls rate of breathing
b.
can influence breathing rhythm by inhibiting medulla
*
See Fig 19.29, page 755 for Summary of Nervous Control of Breathing
*
See box on page 755 re: Sleep Apnea.
19-9
UNIT 5 - CHAPTER 19: RESPIRATORY SYSTEM
19.5
CONTROL OF BREATHING
C.
Factors Affecting Breathing
See Fig 19.30, page 756.
1.
The partial pressure of a gas is determined by the concentration of that
gas in a mixture of gases (i.e. air). Discussed in greater detail on next
page.
2.
Chemicals, lung tissue stretching, and emotional state affect
breathing.
3.
Chemosensitive areas (central chemoreceptors) are associated with the
respiratory center:
a.
CO2 combines with water to form carbonic acid, which in turn,
releases hydrogen ions in cerebrospinal fluid (CSF).
b.
Stimulation of these areas increases alveolar ventilation.
4.
Peripheral Chemoreceptors located in carotid bodies and aortic
bodies (in certain arteries)
a.
Sense low oxygen levels
b.
When this occurs, alveolar ventilation increases.
5.
Stretching of lung tissue triggers an inflation reflex.
a.
This reflex reduces the duration of inspiratory movements.
b.
This prevents overinflation of lungs during forceful breathing.
6.
Hyperventilation decreases CO2 levels, but this is dangerous when
associated with breath holding during underwater swimming.
a.
rapid, shallow breathing increases O2 level
b.
breathing into paper bag rich in CO2 normalizes gas concentrations
*
See box on page 756 re: hyperventilation.
*
See Table 19.6, page 757: Factors that Influence Breathing
1.
Stretch of Tissues: Inflation Reflex – prevent over inflation
2.
Low plasma oxygen (↓O2)
3.
High plasma carbon dioxide (↑CO2)
a.
See box on page 755 re: stimulation of rate and rhythm of
breathing by increasing [CO2] in air.
b.
See box on page 756 re: patients with COPD adapting to high
[CO2].
4.
High CSF hydrogen ion concentration (↑ CSF H+)
5.
Others: temperature, pain, and irritation of airways.
*
*
See Clinical Application 19.4, page 757, Exercise and Breathing.
See box on page 759 re: hyperoxia (i.e. exposure to high concentrations of
oxygen).
19-10
UNIT 5 - CHAPTER 19: RESPIRATORY SYSTEM
19.6
ALVEOLAR GAS EXCHANGES
A.
Alveoli : See Fig 19.15, page 744, Fig 19.18, page 745, Fig 19.32 and Fig 19.33,
page 758.
1.
2.
B.
Respiratory (Alveolar-Capillary) Membrane See Fig 19.33, page 758.
1.
2.
3.
C.
microscopic air sacs
wall consists of two types of epithelial cells and macrophages
a.
Type I Alveolar cells form a continuous simple squamous lining
of the alveolar wall.
b.
Type II Alveolar cells interrupt above lining and secrete
surfactant:
o
complex mixture = detergent
o
lowers surface tension and prevents alveolar collapse.
c.
Alveolar pores, tiny openings in some alveoli may permit air to
pass easily from one alveolus to another.
d.
Alveolar Macrophages remove dust particles and other debris
from alveolar spaces.
Tissue components:
a.
simple squamous epithelium of alveolus
o
basement membrane of alveolus
b.
endothelium of the lung capillary
o
basement membrane of lung capillary
Structure = thin (0.5 um in thickness).
Function = allows for rapid diffusion of gases (from [high] to [low]
and/or high pressure to low pressure) = External Respiration
Diffusion through the Respiratory Membrane (External Respiration)
1,
2.
3.
4.
5.
External Respiration is the exchange of oxygen and carbon dioxide
between the alveoli and lung blood capillaries.
The pressure of gas determines the rate at which it will diffuse from region
to region (Dalton's Law).
Air is a mixture of gases:
a.
78% Nitrogen
b.
21% Oxygen
c.
.04% Carbon Dioxide
In a mixture of gases, the amount of pressure that each gas creates =
partial pressure.
In air that reaches the alveoli:
a.
O2 = 21% PO2 = 104 mm Hg
b.
CO2 = .04% PCO2 = 40 mm Hg
19-11
UNIT 5 - CHAPTER 19: RESPIRATORY SYSTEM
19.6
ALVEOLAR GAS EXCHANGES
C.
Diffusion through the Respiratory Membrane (External Respiration)
6.
A gas diffuses from where it’s at high partial pressure to where it’s at
low partial pressure.
Alveolus
PCO2 = 40 mm Hg
PO2 = 104 mm Hg
↑
↓
__________________________________________________________________
↑
↓
PCO2 = 45 mm Hg
PO2 = 40 mm Hg
Capillary
Therefore, CO2 flows from lung capillary to the alveolus and
O2 flows from alveolus to the lung capillary.
D.
The rate of diffusion of gases also depends on a number of factors, including the
following:
2.
gas exchange surface area
3.
diffusion distance
4.
breathing rate and depth.
*
See Clinical Application 19.5, page 760, Effects of High Altitude.
*
See Clinical Application 19.6, page 761, Disorders that Impair Gas Exchange:
Pneumonia, Tuberculosis, and Acute Respiratory Distress Syndrome.
(E.
Internal Respiration – FYI)
1.
Definition = the exchange of oxygen and carbon dioxide between tissue
capillaries and tissue cells.
2.
In tissue cell:
In tissue cap:
pCO2 = 45 pO2 = 40
pCO2 = 40 pO2 = 95.
See Figure 19.37b, page 762.
3.
Therefore, oxygen moves from the tissue cap into the tissue cell and
carbon dioxide moves from the tissue cell into the tissue capillary.
19-12
UNIT 5 - CHAPTER 19: RESPIRATORY SYSTEM
19.7
GAS TRANSPORT
A.
B.
Oxygen Transport
1.
Oxygen binds with hemoglobin (Hb) in red blood cells to form
oxyhemoglobin.
a.
Hemoglobin is completely saturated (with 4 oxygen molecules) at
normal systemic arterial pO2. See Fig 19.36, page 762.
2.
A weak bond is formed so oxygen can be delivered (released) to tissues
when needed (i.e. internal respiration). See Fig 19.37, page 762.
3.
The release of oxygen from hemoglobin depends on several factors:
a.
high blood [CO2]
b.
low blood pH (acidity)
c.
high blood temperature
d.
See oxyhemoglobin dissociation curves on page 763.
*
See box on page 762 re: Carbon Monoxide (CO) poisoning. CO binds
hemoglobin more efficiently than oxygen does. If the hemoglobin (that is
supposed to bind with oxygen) is bound to CO, much less Hb is available
to bind and transport oxygen to the tissues Hypoxia results.
Carbon Dioxide Transport (CO2) See Fig 19.41 page 763.
1.
CO2 is transported in 3 forms:
a.
dissolved CO2=
7%
b.
carbaminohemoglobin= 23%
c.
bicarbonate ions=
70%
2.
In tissues, CO2 is produced by cellular respiration.
a.
Much of this CO2 diffuses into red blood cells, which have an
enzyme called carbonic anhydrase, which speeds the reaction
between CO2 and H2O forming H2CO3 (Carbonic acid).
Carbonic
Anhydrase
o
CO2 +
H2O 
H2CO3
b.
Carbonic acid dissociates almost immediately releasing H+ and
bicarbonate ion (HCO3-): See Fig 19.41, page 763.
o
H2CO3
→
H+
+
HCO3 -
c.
3.
*
As the bicarbonate ions leave the red blood cells and enter the
plasma, chloride ions with negative charges are electrically
repelled, and they move from the plasma into the red blood cells.
This exchange maintains the ionic balance between the red blood
cells and the plasma. It is termed the chloride shift. See Fig
19.42, page 764.
The reaction is reversed in lungs and CO2 is expelled during expiration.
See Fig 19.43, page 764.
See Table 19.7, page 765, Gases Transported in Blood.
19-13
UNIT 5 - CHAPTER 19: RESPIRATORY SYSTEM
19.8
LIFE SPAN CHANGES
A.
B.
C.
D.
The lungs, respiratory passageways, and alveoli undergo aging-related changes
exacerbated by exposure to pollutants, smoke, etc., increasing the risk of
developing respiratory illnesses.
Loss of cilia, thickening of mucus, and impaired macrophages increases the risk
of infection as one ages.
Breathing becomes more difficult as one ages due to:
1.
calcified cartilage
2.
skeletal changes
3.
altered posture
4.
replacement of bronchiole smooth muscle by fibrous connective tissue.
Vital Capacity decreases with age.
1.
The lungs contain a greater proportion of “stale” air.
2.
Alveoli coalesce and become shallower, slowing gas exchange.
OTHER INTERESTING TOPICS:
A.
B.
C.
Danger! Secondhand Smoke. See introduction on page 735.
Deviated Septum. See box on page 736.
The Effects of Cigarette Smoking on the Respiratory System.
Application 19.2, page 738.
See Clinical
INNERCONNECTIONS OF THE RESPIRATORY SYSTEM. See page 766.
CHAPTER SUMMARY – see pages 767-769.
CHAPTER ASSESSMENTS – see pages 769-670.
INTEGRATIVE ASSESSMENTS/ CRITICAL THINKING – see page 770.
19-14