Chapter 23:
The Respiratory System
Copyright 2009, John Wiley & Sons, Inc.
Respiratory System Anatomy

Structurally

Upper respiratory system


Lower respiratory system


Nose, pharynx and associated structures
Larynx, trachea, bronchi and lungs
Functionally

Conducting zone – conducts air to lungs


Nose, pharynx, larynx, trachea, bronchi, bronchioles and
terminal bronchioles
Respiratory zone – main site of gas exchange

Respiratory bronchioles, alveolar ducts, alveolar sacs, and
alveoli
Copyright 2009, John Wiley & Sons, Inc.
Structures
of the
Respiratory
System
23_02a
Nose


External nose – portion visible on face
Internal nose – large cavity beyond nasal
vestibule




Internal nares or choanae
Ducts from paranasal sinuses and nasolacrimal
ducts open into internal nose
Nasal cavity divided by nasal septum
Nasal conchae subdivide cavity into meatuses


Increase surface are and prevents dehydration
Olfactory receptors in olfactory epithelium
Copyright 2009, John Wiley & Sons, Inc.
Pharynx



Starts at internal nares and extends to cricoid cartilage of
larynx
Contraction of skeletal muscles assists in deglutition
Functions




Passageway for air and food
Resonating chamber
Houses tonsils
3 anatomical regions



Nasopharynx
Oropharynx
Laryngopharynx
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Larynx






Short passageway connecting laryngopharynx with
trachea
Composed of 9 pieces of cartilage
 Thyroid cartilage or Adam’s apple
 Cricoid cartilage landmark for tracheotomy
Epiglottis closes off glottis during swallowing
Glottis – pair of folds of mucous membranes, vocal
folds (true vocal cords, and rima glottidis (space)
Cilia in upper respiratory tract move mucous and
trapped particles down toward pharynx
Cilia in lower respiratory tract move them up toward
pharynx
Copyright 2009, John Wiley & Sons, Inc.
Covering and Lining Epithelium
Copyright 2009, John Wiley & Sons, Inc.
Larynx
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Structures of Voice Production

Mucous membrane of larynx forms

Ventricular folds (false vocal cords) – superior pair


Vocal folds (true vocal cords) – inferior pair




Function in holding breath against pressure in thoracic
cavity
Muscle contraction pulls elastic ligaments which stretch
vocal folds out into airway
Vibrate and produce sound with air
Folds can move apart or together, elongate or shorten,
tighter or looser
Androgens make folds thicker and longer – slower
vibration and lower pitch
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Trachea

Extends from larynx to superior border of T5


4 layers





Divides into right and left primary bronchi
Mucosa
Submucosa
Hyaline cartilage
Adventitia
16-20 C-shaped rings of hyaline cartilage

Open part faces esophagus
Copyright 2009, John Wiley & Sons, Inc.
Location of Trachea
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Bronchi


Right and left primary bronchus
Carina – internal ridge


Divide to form bronchial tree


Most sensitive area for triggering cough reflex
Secondary lobar bronchi (one for each lobe), tertiary
(segmental) bronchi, bronchioles, terminal bronchioles
Structural changes with branching



Mucous membrane changes
Incomplete rings become plates and then disappear
As cartilage decreases, smooth muscle increases


Sympathetic ANS – relaxation / dilation
Parasympathetic ANS – contraction / constriction
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Lungs


Separated from each other by the heart and other
structures in the mediastinum
Each lung enclosed by double-layered pleural membrane



Pleural cavity is space between layers


Parietal pleura – lines wall of thoracic cavity
Visceral pleura – covers lungs themselves
Pleural fluid reduces friction, produces surface tension (stick
together)
Cardiac notch – heart makes left lung 10% smaller
than right
Copyright 2009, John Wiley & Sons, Inc.
Relationship of the Pleural Membranes to
Lungs
Copyright 2009, John Wiley & Sons, Inc.
Anatomy of Lungs

Lobes – each lung divides by 1 or 2 fissures




Each lobe receives it own secondary (lobar) bronchus that
branch into tertiary (segmental) bronchi
Lobules wrapped in elastic connective tissue and
contains a lymphatic vessel, arteriole, venule and
branch from terminal bronchiole
Terminal bronchioles branch into respiratory
bronchioles which divide into alveolar ducts
About 25 orders of branching
Copyright 2009, John Wiley & Sons, Inc.
Alveoli



Cup-shaped outpouching
Alveolar sac – 2 or more alveoli sharing a
common opening
2 types of alveolar epithelial cells


Type I alveolar cells – form nearly continuous lining,
more numerous than type II, main site of gas exchange
Type II alveolar cells (septal cells) – free surfaces
contain microvilli, secrete alveolar fluid (surfactant
reduces tendency to collapse)
Copyright 2009, John Wiley & Sons, Inc.
Microscopic Anatomy of Lobule of Lungs
Alveolus

Respiratory membrane






Alveolar wall – type I and type II alveolar cells
Epithelial basement membrane
Capillary basement membrane
Capillary endothelium (layer of SE)
Very thin – only 0.5 µm thick to allow rapid diffusion of
gases
Lungs receive blood from
1.
2.
Pulmonary artery - deoxygenated blood
Bronchial arteries – oxygenated blood to perfuse the
muscular walls of bronchi and bronchioles
Copyright 2009, John Wiley & Sons, Inc.
Components
of Alveolus
Copyright 2009, John Wiley & Sons, Inc.
Pulmonary ventilation

Respiration (gas exchange) steps
1.
Pulmonary ventilation / breathing


2.
External (pulmonary) respiration

3.
Inhalation and exhalation
Exchange of air between atmosphere and alveoli
Exchange of gases between alveoli and blood
Internal (tissue) respiration


Exchange of gases between systemic capillaries and
tissue cells
Supplies cellular respiration (makes ATP)
Copyright 2009, John Wiley & Sons, Inc.
Inhalation/inspiration

Pressure inside alveoli must become lower than
atmospheric pressure for air to flow into lungs


Achieved by increasing size of lungs


760 millimeters of mercury (mmHg) or 1
atmosphere (1 atm)
Boyle’s Law – pressure of a gas in a closed
container is inversely proportional to the volume of
the container
Inhalation – lungs must expand, increasing lung
volume, decreasing pressure below atmospheric
pressure
Copyright 2009, John Wiley & Sons, Inc.
Boyle’s Law
Copyright 2009, John Wiley & Sons, Inc.
Inhalation

Inhalation is active – Contraction of
 Diaphragm – most important muscle of inhalation



Flattens, lowering dome when contracted
Responsible for 75% of air entering lungs during normal quiet
breathing
External intercostals


Contraction elevates ribs
25% of air entering lungs during normal quiet breathing
Accessory muscles for deep, forceful inhalation
When thorax expands, parietal and visceral pleurae adhere
tightly due to subatmospheric pressure and surface tension –
pulled along with expanding thorax
As lung volume increases, alveolar pressure drops



Copyright 2009, John Wiley & Sons, Inc.
Exhalation/expiration


Pressure in lungs greater than atmospheric pressure
Normally passive – muscle relax instead of contract




Based on elastic-recoil of chest wall and lungs from elastic
fibers and surface tension of alveolar fluid
Diaphragm relaxes and become dome shaped
External intercostals relax and ribs drop down
Exhalation only active during forceful breathing
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Airflow


Air pressure differences drive airflow
3 other factors affect rate of airflow and ease of
pulmonary ventilation

Surface tension of alveolar fluid




Lung compliance



Causes alveoli to assume smallest possible diameter
Accounts for 2/3 of lung elastic recoil
Prevents collapse of alveoli at exhalation
High compliance means lungs and chest wall expand easily
Related to elasticity and surface tension
Airway resistance


Larger diameter airway has less resistance
Regulated by diameter of bronchioles & smooth muscle tone
Copyright 2009, John Wiley & Sons, Inc.
Lung volumes and capacities




Minute ventilation (MV) = total volume of air
inhaled and exhaled each minute
Normal healthy adult averages 12 breaths
per minute
moving about 500 ml of air in and out of lungs
(tidal volume)
MV = 12 breaths/min x 500 ml/ breath
= 6 liters/ min
Copyright 2009, John Wiley & Sons, Inc.
Lung Volumes





Only about 70% of tidal volume reaches respiratory
zone
Other 30% remains in conducting zone
Anatomic (respiratory) dead space – conducting
airways with air that does not undergo respiratory
gas exchange
Alveolar ventilation rate – volume of air per minute
that actually reaches respiratory zone
Inspiratory reserve volume – taking a very deep
breath
Copyright 2009, John Wiley & Sons, Inc.
Lung Volumes




Expiratory reserve volume – inhale normally
and exhale forcefully
Residual volume – air remaining after
expiratory reserve volume exhaled
Vital capacity = inspiratory reserve volume +
tidal volume + expiratory reserve volume
Total lung capacity = vital capacity + residual
volume
Copyright 2009, John Wiley & Sons, Inc.
Spirogram of Lung Volumes and Capacities
Exchange of Oxygen and Carbon
Dioxide

Dalton’s Law
 Each gas in a mixture of gases exerts its own
pressure as if no other gases were present
 Pressure of a specific gas is partial pressure Px
 Total pressure is the sum of all the partial pressures
 Atmospheric pressure (760 mmHg) = PN2 + PO2 + PH2O
+ PCO2 + Pother gases
 Each gas diffuses across a permeable membrane
from the area where its partial pressure is greater to
the area where its partial pressure is less
 The greater the difference, the faster the rate of
diffusion
Copyright 2009, John Wiley & Sons, Inc.
Partial Pressures of Gases in Inhaled Air
PN2
=0.786
x 760mm Hg
= 597.4 mmHg
PO2
=0.209
x 760mm Hg
= 158.8 mmHg
PH2O
=0.004
x 760mm Hg
= 3.0 mmHg
PCO2
=0.0004 x 760mm Hg
= 0.3 mmHg
Pother gases
=0.0006 x 760mm Hg
= 0.5 mmHg
TOTAL
Copyright 2009, John Wiley & Sons, Inc.
= 760.0 mmHg
Henry’s law




Quantity of a gas that will dissolve in a liquid is
proportional to the partial pressures of the gas
and its solubility
Higher partial pressure of a gas over a liquid and
higher solubility, more of the gas will stay in
solution
Much more CO2 is dissolved in blood than O2
because CO2 is 24 times more soluble!
Even though the air we breathe is mostly N2, very
little dissolves in blood due to low solubility

Decompression sickness (bends)
Copyright 2009, John Wiley & Sons, Inc.
External Respiration in Lungs


Oxygen
 Oxygen diffuses from alveolar air (PO2 105 mmHg??) into blood
of pulmonary capillaries (PO2 40 mmHg)
 Diffusion continues until PO2 of pulmonary capillary blood
matches PO2 of alveolar air, i.e., equilibrium
 Small amount of mixing with blood from conducting portion of
respiratory system drops PO2 of blood in pulmonary veins to 100
mmHg
Carbon dioxide
 Carbon dioxide diffuses from deoxygenated blood in pulmonary
capillaries (PCO2 45 mmHg) into alveolar air (PCO2 40 mmHg??)
 Continues until of PCO2 blood reaches 40 mmHg
Copyright 2009, John Wiley & Sons, Inc.
Internal Respiration




Internal respiration – in tissues throughout body
Oxygen
 Oxygen diffuses from systemic capillary blood (PO2 100 mmHg)
into tissue cells (PO2 40 mmHg) – cells constantly use oxygen to
make ATP
 Blood drops to 40 mmHg by the time blood exits the systemic
capillaries
Carbon dioxide
 Carbon dioxide diffuses from tissue cells (PCO2 45 mmHg) into
systemic capillaries (PCO2 40 mmHg) – cells constantly make
carbon dioxide
 PCO2 blood reaches 45 mmHg
At rest, only about 25% of the available oxygen is used
 Deoxygenated blood would retain 75% of its oxygen capacity
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Rate of Pulmonary and Systemic Gas Exchange

Depends on

Partial pressures of gases




Alveolar PO2 must be higher than blood PO2 for diffusion to
occur – problem with increasing altitude
Surface area available for gas exchange 750 ft2
Diffusion distance
Molecular weight and solubility of gases

O2 has a lower molecular weight and should diffuse faster
than CO2 except for its low solubility - when diffusion is slow,
hypoxia occurs before hypercapnia
Copyright 2009, John Wiley & Sons, Inc.
Transport of Oxygen and Carbon Dioxide

Oxygen transport


Only about 1.5% dissolved in plasma
98.5% bound to hemoglobin in red blood cells

Heme portion of hemoglobin contains 4 iron atoms –
each can bind one O2 molecule



Oxyhemoglobin
Key- only dissolved portion can diffuse out of blood into
(tissue) cells
Oxygen must be able to bind and then dissociate from
heme
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Relationship between Hemoglobin and
Oxygen Partial Pressure




Higher the PO2, More O2 combines with Hb
Fully saturated – completely converted to oxyhemoglobin
The percent saturation expresses average saturation of
hemoglobin with oxygen
Oxygen-hemoglobin dissociation curve


In pulmonary capillaries, O2 loads onto Hb
In tissues, O2 is not held and is unloaded

75% may still remain in deoxygenated blood (reserve)
Copyright 2009, John Wiley & Sons, Inc.
Oxygenhemoglobin
Dissociation
Curve
Copyright 2009, John Wiley & Sons, Inc.
Hemoglobin and Oxygen


Other factors affecting affinity of Hemoglobin
for oxygen
Each makes sense if you keep in mind that
metabolically active tissues need O2, and
produce acids, CO2, and heat; as wastes



Acidity
PCO2
Temperature
Copyright 2009, John Wiley & Sons, Inc.
Bohr Effect




As acidity increases (pH ___________), affinity of
Hb for O2 decreases
Increasing acidity
enhances unloading of
O2
Shifts curve to right
PCO2
 Also shifts curve to right
 As PCO2 rises, Hb unloads
oxygen more easily
 Low blood pH can result
from high PCO2
Copyright 2009, John Wiley & Sons, Inc.
Temperature Changes
Within limits, as
temperature
increases, more
oxygen is released
from Hb
 During hypothermia,
more oxygen remains
bound
2,3-bisphosphoglycerate
 BPG formed by red
blood cells during
glycolysis
 Helps unload oxygen
by binding with Hb


Copyright 2009, John Wiley & Sons, Inc.
Fetal and Maternal Hemoglobin



Fetal hemoglobin has a
higher affinity for
oxygen than adult
hemoglobin
Hb-F can carry up to
30% more oxygen
Maternal blood’s
oxygen readily
transferred to fetal
blood
Copyright 2009, John Wiley & Sons, Inc.
Carbon Dioxide Transport

Dissolved CO2


Carbamino compounds



Smallest amount, about 7%
About 23% combines with amino acids including those in Hb
Carbaminohemoglobin
Bicarbonate ions


70% transported in plasma as HCO3Enzyme carbonic anhydrase forms carbonic acid (H2CO3)
which dissociates into H+ and HCO3-
Copyright 2009, John Wiley & Sons, Inc.
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3
Chloride shift (exchange of “–” ions)




HCO3- accumulates inside RBCs as they pick up
carbon dioxide
Some diffuses out into plasma
To balance the loss of negative ions, chloride (Cl-)
moves into RBCs from plasma
Reverse happens in lungs
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Respiratory Rhythm
Control
Respiratory Center

1.
2.
3.
3 clusters of neurons
Medullary rhythmicity area of medulla
oblongata
Pneumotaxic area in pons
Apneustic area in pons
Medullary Rhythmicity Area






Inspiratory area
Establishes basic rhythm
Impulses sent muscles contract for inhalation
No impulse, muscles relax for exhalation
Expiratory area inactive during normal, quiet
breathing
In forceful breathing the inspiratory area
activates expiratory area
Pneumotaxic Area


Located in upper pons
Helps turn off inspiratory area


Prevents overfilling of lungs
Increased breathing rate
Apneustic Area


Located in lower pons
Activates inspiratory area


Prolonged inspiration
Overridden by activity of pneumotaxic area
Regulation of the
respiratory center
Influences that Modify Respiration

Cortical Influences

Voluntary control up to a point
Protective mechanism
Limited by PCO2 and H+ increase




Hypothalamus and limbic system
Altered respiration results from emotional
changes
Influences that Modify Respiration

Chemoreceptors - sensory neurons respond
to changes in chemical levels

Central chemoreceptors
Located in or near medulla oblongata in CNS
Sense changes in H+ and PCO2 in CSF


Influences that Modify Respiration




Peripheral chemoreceptors
Located in wall of left and right common
carotid arteries
Part of PNS
Sense changes in PO2, H+ and PCO2 in blood
Influences that Modify Respiration







Hypercapnia
Increase in PCO2 of arterial blood
Stimulates inspiratory center
Hyperventilation
Hypocapnia
Arterial PCO2 < 40 mmHg
Inspiratory area sets moderate pace
Influences that Modify Respiration




Proprioceptor
Monitor movement of joints and muscles
Inflation reflex
Baroreceptors – stretch-sensitive receptors in
walls of bronchi and bronchioles
Copyright 2009, John Wiley & Sons, Inc.
Influences that Modify Respiration








Limbic system stimulation
Temperature
Increase in temperature increases breathing
rate
Decrease in temperature decreases
breathing rate (temporary apnea)
Pain
Stretching of anal sphincter muscle
Irritation of airways
Blood pressure
Lung
Copyright 2009, John Wiley & Sons, Inc.
Lung
Copyright 2009, John Wiley & Sons, Inc.
Trachea c.s.
Copyright 2009, John Wiley & Sons, Inc.
Trachea l.s.