very informative

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Chapter 23:
The Respiratory System

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Respiratory System Anatomy
◼ Structurally
❑ Upper respiratory system
◼ Nose, pharynx and associated structures
❑ Lower respiratory system
◼ 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

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Structures of the Respiratory System

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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

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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

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Larynx
❑ Short passageway connecting laryngopharynx with trachea
❑ Composed of 9 pieces of cartilage
◼ Thyroid cartilage or Adam’s apple
◼ Cricoid cartilage hallmark 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

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Larynx

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Structures of Voice Production
❑ Mucous membrane of larynx forms
◼ Ventricular folds (false vocal cords) – superior pair
❑ Function in holding breath against pressure in thoracic
cavity
◼ Vocal folds (true vocal cords) – inferior pair
❑ 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

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Trachea
❑ Extends from larynx to superior border of T5
◼ Divides into right and left primary bronchi
❑ 4 layers
◼ Mucosa
◼ Submucosa
◼ Hyaline cartilage
◼ Adventitia
❑ 16-20 C-shaped rings of hyaline cartilage
◼ Open part faces esophagus

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Location of Trachea

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Bronchi
❑ Right and left primary bronchus goes to right lung
❑ Carina – internal ridge
◼ Most sensitive area for triggering cough reflex
❑ Divide to form bronchial tree
◼ 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

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Lungs
❑ Separated from each other by the heart and other
structures in the mediastinum
❑ Each lung enclosed by double-layered pleural membrane
◼ Parietal pleura – lines wall of thoracic cavity
◼ Visceral pleura – covers lungs themselves
❑ Pleural cavity is space between layers
◼ Pleural fluid reduces friction, produces surface tension (stick
together)
◼ Cardiac notch – heart makes left lung 10% smaller
than right

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Relationship of the Pleural Membranes to
Lungs

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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

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Microscopic Anatomy of Lobule of Lungs

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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)

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Alveolus
◼ Respiratory membrane
❑ Alveolar wall – type I and type II alveolar cells
❑ Epithelial basement membrane
❑ Capillary basement membrane
❑ Capillary endothelium
❑ Very thin – only 0.5 µm thick to allow rapid diffusion of
gases
◼ Lungs receive blood from
❑ Pulmonary artery - deoxygenated blood
❑ Bronchial arteries – oxygenated blood to perfuse muscular
walls of bronchi and bronchioles

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Components of Alveolus

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Pulmonary ventilation
◼ Respiration (gas exchange) steps
1. Pulmonary ventilation/ breathing
◼ Inhalation and exhalation
◼ Exchange of air between atmosphere and alveoli
2. External (pulmonary) respiration
◼ Exchange of gases between alveoli and blood
3. Internal (tissue) respiration
◼ Exchange of gases between systemic capillaries and
tissue cells
◼ Supplies cellular respiration (makes ATP)

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Inhalation/ inspiration
❑ Pressure inside alveoli lust become lower than
atmospheric pressure for air to flow into lungs
◼ 760 millimeters of mercury (mmHg) or 1
atmosphere (1 atm)
❑ Achieved by increasing size of lungs
◼ 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

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Boyle’s Law

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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 (intrapulmonic) pressure
drops

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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

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Airflow
◼ Air pressure differences drive airflow
◼ 3 other factors affect rate of airflow and ease of
pulmonary ventilation
❑ Surface tension of alveolar fluid
◼ Causes alveoli to assume smallest possible diameter
◼ Accounts for 2/3 of lung elastic recoil
◼ Prevents collapse of alveoli at exhalation
❑ Lung compliance
◼ 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

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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

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Spirogram of Lung Volumes and
Capacities

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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

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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

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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 are 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

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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 = 760.0 mmHg

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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)

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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
❑ 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

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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

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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
❑ 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

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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
◼ Only dissolved portion can diffuse out of blood into cells
◼ Oxygen must be able to bind and dissociate from heme

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Relationship between Hemoglobin and
Oxygen Partial Pressure
❑ Higher the PO2, More O2 combines with Hb
❑ Fully saturated – completely converted to oxyhemoglobin
❑ 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 unloaded
❑ 75% may still remain in deoxygenated blood (reserve)

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Oxygen-hemoglobin Dissociation Curve

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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

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Bohr Effect
❑ As acidity increases (pH
decreases), affinity of Hb
for O2 decreases
❑ Increasing acidity
enhances unloading
❑ 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

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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

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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

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Carbon Dioxide Transport
❑ Dissolved CO2
◼ Smallest amount, about 7%
❑ Carbamino compounds
◼ About 23% combines with amino acids including those in Hb
◼ Carbaminohemoglobin
❑ Bicarbonate ions
◼ 70% transported in plasma as HCO3
-
◼ Enzyme carbonic anhydrase forms carbonic acid (H2CO3)
which dissociates into H+ and HCO3
-

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◼ Chloride shift
❑ 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 – Cl- moves out as
moves back into RBCs
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3
-

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End of Chapter 23
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