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The Respiratory System
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Breath of Fresh Air
• Anatomy of respiratory system
• Ventilation
• Gas exchange and transport
Respiratory System
• What are some functions of the respiratory
system?
• Respiration as a process
– Ventilation
– External and internal respiration
– Cellular respiration
Anatomy
• Principal organs
– Nose, pharynx, larynx, trachea, bronchi, and lungs
• Conducting division
– Function only in airflow
• Respiratory division
– Function in gas exchange
Organs of Respiratory System
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Nasal
cavity
Posterior
nasal
aperture
Hard
palate
Soft palate
Epiglottis
Nostril
Pharynx
Larynx
Esophagus
Trachea
Left lung
Right lung
Left main
bronchus
Lobar
bronchus
Segmental
bronchus
Pleural
cavity
Pleura
(cut)
Diaphragm
Figure 22.1
The Nose
• Functions
– Warms, cleanses, and humidifies inhaled air
– Detects odors
– Resonating chamber for voice
• Nose extends from nostrils (nares), to a pair of posterior
openings called the posterior nasal apertures (choanae)
• Facial part is shaped by bone and hyaline cartilage
– superior half nasal bones and maxillae
– inferior half lateral and alar cartilages
– ala nasi – flared portion at the lower end of nose shaped by alar
cartilages and dense connective tissue
Anatomy of Nasal Region
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Nasal bone
Lateral cartilage
Septal nasal
cartilage
Minor alar
cartilages
Major alar
cartilages
Dense connective
tissue
(b)
Figure 22.2b
© The McGraw-Hill Companies/Joe DeGrandis, photographer
Nasal Cavity
• Nasal fossae – right and left halves of nasal
cavity
– Divided by nasal septum
• Composed of bone and cartilage
– Perpendicular plate
– Vomer
– Septal cartilage
– Roof and floor
• Ethmoid and sphenoid
• Hard palate
Nasal Cavity
• Vestibule – dilated chamber inside the nares
– Stratified squamus epithelium
– Vibrissae
• Nasal Conchae (turbinates) – superior, middle, inferior
– Meatus
• Cleanses, warms, and humidifies air
• Epithelium of nasal cavity
– Ciliated pseudostratified columnar with goblet cells
• Olfactory
– cilia immobile
• Respiratory
– cilia mobile
• Erectile tissue – venous plexus in inferior concha
– Allows one side of the nasal cavity to recover from drying out by restricting
airflow in that side
– Changes sides once or twice per hour
Upper Respiratory Tract
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Tongue
Lower lip
Meatuses:
Superior
Middle
Inferior
Sphenoid sinus
Posterior nasal
aperture
Pharyngeal
tonsil
Auditory
tube
Soft palate
Uvula
Palatine tonsil
Lingual tonsil
Mandible
Epiglottis
Frontal
sinus
Nasal conchae:
Superior
Middle
Inferior
Vestibule
Guard hairs
Naris (nostril)
Hard palate
Upper lip
Vestibular fold
Vocal cord
Larynx
Trachea
Esophagus
(b)
Figure 22.3b
Pharynx
• Pharynx (throat) – a muscular funnel extending about 13 cm (5 in.) from the
choanae to the larynx
• Three regions
– Nasopharynx
•
•
•
•
Posterior to nasal apertures and above soft palate
Receives auditory tubes and contains pharyngeal tonsil
90 downward turn traps large particles (>10m)
Passes only air, lined by pseudostratified columnar epithelium
– Oropharynx
• Space between soft palate and epiglottis
• Contains palatine tonsils
– Laryngopharynx
• Epiglottis to cricoid cartilage
• Esophagus begins at that point
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Figure 22.3c
• Oropharynx and laryngopharynx pass air, food, and drink, lined by stratified
squamous epithelium
Larynx
•
Cartilaginous chamber about 4 cm long
•
Functions
– Keep food and drink out of airway
•
•
Epiglottis
Vestibular folds (internal folds on each side of larynx)
– Production of sound
•
•
Vocal folds (second pair of internal folds on each side of larynx)
Framework composed of nine cartilages
– First three solitary and large
•
•
•
Epiglotic - spoon-shaped supportive plate
Thyroid – large shield-shaped, laryngeal prominence
Cricoid – connects larynx to trachea, ring-like
– Second three smaller and paired
•
•
•
•
Corniculate – attached to arytenoid superiorly
Arytenoid – posterior to thyroid
Cuneiform – Supports soft tissues between arytenoids and epiglottis
Fibrous ligaments – bind cartilages of larynx together and to adjacent structures
– Extrinsic – thyrohyoid and cricotracheal
– Intrinsic – 2 pairs of vestibular and vocal ligaments
Views of Larynx
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Epiglottis
Epiglottis
Hyoid bone
Hyoid bone
Epiglottic cartilage
Thyrohyoid ligament
Fat pad
Thyroid cartilage
Thyroid cartilage
Laryngeal prominence
Cuneiform cartilage
Corniculate cartilage
Arytenoid cartilage
Vestibular fold
Cricoid cartilage
Vocal cord
Cricotracheal
ligament
Arytenoid cartilage
Arytenoid muscle
Cricoid cartilage
Trachea
(a) Anterior
Tracheal cartilage
(b) Posterior
Figure 22.4 a-c
(c) Median
Muscles of Larynx
Intrinsic
• Operate vocal cords
• Pull on corniculate and
arytenoid cartilage
– Pivot and abduct or adduct
vocal cords
– Air forced through adducted
vocal cords causes them to
vibrate
• Produces sound
Extrinsic
• Infrahyoid group
• Connect larynx to hyoid
• Elevate larynx during
swallowing
Lower Respiratory Tract
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Mucus
Larynx
Thyroid
cartilage
Mucociliary
escalator
Particles
of debris
Cricoid
cartilage
Epithelium:
Goblet cell
Ciliated cell
Mucous gland
Trachea
Cartilage
Chondrocytes
(b)
Carina
Trachealis
muscle
Lobar
bronchi
Hyaline
cartilage ring
Main
bronchi
Lumen
Mucosa
Segmental
bronchi
Mucous gland
Perichondrium
(a)
Figure 22.7 a-c
(c)
Trachea
• Windpipe, rigid tube about 12 cm in length and 2.5 cm
diameter
– Anterior to esophgus
– Supported by C-shaped rings
• Trachealis muscle spans opening in rings
• Inner lining
– Ciliated pseudostratified columnar epithelium
– Mucociliary escalator
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• Carina – internal median ridge in lowermost tracheal
cartilage
Lungs
• Right lung
– Three lobes divided by
horizontal and oblique fissures
• Left lung
– Two lobes divided by oblique
fissure
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• Pleurae
– Visceral
– Parietal
– Pleural cavity
• Pleural fluid
(b) Mediastinal surface, right lung
The Bronchial Tree
•
Right main bronchus (primary)
•
Left main bronchus
•
Superior, middle, inferior lobar
bronchi (secondary)
•
Superior and inferior lobar bronchi
•
Segmental bronchi, 8
•
Bronchioles
– Pulmonary lobules
•
Terminal bronchioles
•
Terminal bronchioles
•
Respiratory bronchioles
•
Respiratory bronchioles
•
Alveolar ducts
•
Alveolar ducts
•
Alveolar sacs
•
Alveolar sacs
•
Segmental bronchi (tertiary), 10
– Bronchopulmonary segment
•
Bronchioles
– atrium
– atrium
Alveoli
• ~ 150 million sacs for gas exchange
– Why so many?
• Cells types
– Squamous alveolar cells (type I)
• 95% of surface, thinness allows rapid
gas exchange
– Great alveolar cells (type II)
• Repair alveolar epithelium
• Secrete surfactant
– Alveolar macrophages (dust cells)
• Phagocytize dust particles, bacteria,
debris
• Respiratory membrane
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Ventilation
• Respiratory cycle
– Inspiration
– Expiration
• Respiratory muscles
– Diaphragm
– Intercostals
– Accessory muscles of respiration
• Sternocleidomastoids, scalenes, pectoralis muscles, serratus
anterior, erector spinae
Respiratory Muscles
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Inspiration
Sternocleidomastoid
(elevates sternum)
Scalenes
(fix or elevate ribs 1–2)
External intercostals
(elevate ribs 2–12,
widen thoracic cavity)
Pectoralis minor (cut)
(elevates ribs 3–5)
Forced expiration
Internal intercostals,
interosseous part
(depress ribs 1–11,
narrow thoracic cavity)
Internal intercostals,
intercartilaginous part
(aid in elevating ribs)
Diaphragm
(ascends and
reduces depth
of thoracic cavity)
Diaphragm
(descends and
increases depth
of thoracic cavity)
Rectus abdominis
(depresses lower ribs,
pushes diaphragm upward
by compressing
abdominal organs)
External abdominal oblique
(same effects as
rectus abdominis)
Figure 22.13
Neural Control of Breathing
• Conscious and sub-conscious control
• Three pairs of respiratory centers in reticular formation of
medulla and pons
– Ventral respiratory group (VRG)
• Inspiratory (I) neurons
• Expiratory (E) neurons
– Dorsal respiratory group (DRG)
• External influence of VRG
• Integrating center
– Central and peripheral chemoreceptors, stretch receptors, irritant receptors
– Pontine respiratory group
• Integrates input from higher brain centers
• Influences VRG and DRG
• Modifies breathing to sleep, emotional responses, exercise, other
special circumstances
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Key
Inputs to respiratory
centers of medulla
Outputs to spinal centers
and respiratory muscles
Output from
hypothalamus,
limbic system, and
higher brain centers
Respiratory
Control Centers
Pons
Pontine respiratory
group (PRG)
Dorsal respiratory
group (DRG)
Central chemoreceptors
Glossopharyngeal n.
Ventral respiratory
group (VRG)
Vagus n.
Medulla oblongata
Intercostal
nn.
Spinal integrating
centers
Phrenic n.
Diaphragm and intercostal muscles
Figure 22.14
Accessory muscles
of respiration
Taking a Breath
• Inspiration
– Boyle’s law
• Pressure of a gas inversely proportional to its volume at constant
temp.
– Charles’s law
• Volume of a gas directly proportional to its temperature at constant
pressure
• Expiration
– Passive process, elastic recoil of thoracic cage
• Resistance to airflow
– Diameter of bronchioles
– Pulmonary compliance
– Surface tension of alveoli
Measurements of Ventilation
•
Spirometer
•
Dead space
– Approx. 150 ml of air remain in conductive division
– Alveolar ventilation rate (AVR) – volume of air used in gas exchange X breaths/min
•
Tidal volume (TV) – one cycle of quite breathing, about 500 ml
•
Inspiratory reserve volume (IRV) – amount that can be inhaled beyond TV
inhalation, 3000 ml
•
Expiratory reserve volume (ERV) – amount that can be forcefully exhaled beyond
TV exhalation, 1200 ml
•
Residual volume (RV) – volume of air that remains even after maximal expiration,
1300 ml
Lung Volumes and Capacities
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6,000
Maximum possible inspiration
5,000
Lung volume (mL)
4,000
Inspiratory
reserve volume
Vital capacity
Inspiratory
capacity
Tidal
volume
3,000
Total lung capacity
Expiratory
reserve volume
2,000
1,000
0
Maximum voluntary
expiration
Residual
volume
Functional residual
capacity
Spirometry
• Restrictive disorders
– Reduce pulmonary compliance
– Appear as a reduced vital capacity
• Obstructive disorders
– Blockage or narrowing of airway
– More difficult to inhale/exhale given amount of air
– Measure by forced expiratory volume (FEV)
• Percentage of vital capacity that can be exhaled in a given
time interval
– 75-85% in 1 second for healthy adult
Gas Exchange
• Involves oxygen and carbon dioxide
• Composition of air
– 78.6% N2, 20.9% O2, .04% CO2, 0.5% H2O
• Dalton’s law – total atmospheric pressure is sum of
partial pressures of individual gases
• Composition of gases will vary depending on where air
is in the respiratory tract
– Inhaled air differs from alveolar air differs from exhaled air
Driving Force Behind Alveolar
Exchange
• Diffusion down concentration gradient
– Have to consider that we are going from air to water
• Henry’s law – for a given temperature, at the air-water
interface the amount of gas that dissolves in the water
is determined by its solubility in water and its partial
pressure in air
• Erythrocytes load O2 and unload CO2
• Efficiency of exchange may be affected by:
– Pressure gradients, solubility, membrane thickness
and area, ventilation-perfusion coupling
Gas Transport
• Oxygen binds to hemoglobin (98.5%)
– Oxyhemoglobin (HbO2)
• Carbon dioxide
– Carbonic acid (90%)
– Carbamino compounds (carbaminohemoglobin,
HbCO2)
– Dissolved gases
Systemic Gas Exchange
• Systemic gas exchange - the unloading of O2 and loading of CO2 at
the systemic capillaries
• CO2 loading
– CO2 diffuses into the blood
– carbonic anhydrase in RBC catalyzes
• CO2 + H2O  H2CO3  HCO3- + H+
– chloride shift
• keeps reaction proceeding, exchanges HCO3- for Cl• H+ binds to hemoglobin
• O2 unloading
– H+ binding to HbO2 reduces its affinity for O2
• tends to make hemoglobin release oxygen
• HbO2 arrives at systemic capillaries 97% saturated, leaves 75%
saturated –
– venous reserve – oxygen remaining in the blood after it passes through the
capillary beds
– Utilization coefficient – given up 22% of its oxygen load
Systemic Gas Exchange
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Respiring tissue
Capillary blood
7%
Dissolved CO2 gas
CO2
CO2 + plasma protein
Carbamino compounds
23%
CO2
HbCO2
CO2 + Hb
70%
CO2
CO2 + H2O
CAH
H2CO3
Chloride shift
Cl–
HCO3– + H+
98.5%
O2
1.5%
O2
HbO2+ H+
O2 + HHb
Dissolved O2 gas
Figure 22.24
Key
Hb
Hemoglobin
HbCO2
HbO2
HHb
CAH
Carbaminohemoglobin
Oxyhemoglobin
Deoxyhemoglobin
Carbonic anhydrase
Alveolar Gas Exchange
• Reactions that occur in the lungs are reverse of
systemic gas exchange
• CO2 unloading
– As Hb loads O2 its affinity for H+ decreases, H+
dissociates from Hb and bind with HCO3• CO2 + H2O  H2CO3  HCO3- + H+
– Reverse chloride shift
• HCO3- diffuses back into RBC in exchange for Cl-,
free CO2 generated diffuses into alveolus to be
exhaled
Alveolar Gas Exchange
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Alveolar air
Respiratory membrane
Capillary blood
7%
CO2
Dissolved CO2 gas
Carbamino compounds
CO2 + plasma protein
23%
CO2
70%
CO2
CO2 + H2O
CAH
Chloride shift
Cl-
HbCO2
CO2 + Hb
H2 CO3
HCO3- + H+
98.5%
O2
O2 + HHb
HbO2 + H+
1.5%
O2
Dissolved O2 gas
Key
Hb
Figure 22.25
HbCO2
HbO2
HHb
CAH
Hemoglobin
Carbaminohemoglobin
Oxyhemoglobin
Deoxyhemoglobin
Carbonic anhydrase
Concentration Gradients of Gases
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Expired air
Inspired air
PO2 116 mm Hg
PCO2 32 mm Hg
PO2 159 mm Hg
PCO2 0.3 mm Hg
Alveolar
gas exchange
Alveolar air
O2 loading
PO2 104 mm Hg
CO2 unloading
PCO2 40 mm Hg
CO2
Gas transport
O2
Pulmonary circuit
O2 carried
from alveoli
to systemic
tissues
CO2 carried
from systemic
tissues to
alveoli
Deoxygenated
blood
Oxygenated blood
PO2 95 mm Hg
PCO2 40 mm Hg
PO2 40 mm Hg
PCO2 46 mm Hg
Systemic circuit
Systemic
gas exchange
CO2
O2
O2 unloading
CO2 loading
Tissue fluid
PO2 40 mm Hg
PCO2 46 mm Hg
Figure 22.19
Adjustment to the Metabolic Needs of
Individual Tissues
• Hemoglobin unloads O2 to match metabolic needs of different states of activity
of the tissues
• Four factors that adjust the rate of oxygen unloading
– ambient PO2
•
active tissue has  PO2 ; O2 is released from Hb
– temperature
•
active tissue has  temp; promotes O2 unloading
– Bohr effect
•
active tissue has  CO2, which lowers pH of blood ; promoting O2 unloading
– bisphosphoglycerate (BPG)
•
RBCs produce BPG which binds to Hb; O2 is unloaded
• Haldane effect – rate of CO2 loading is also adjusted to varying needs of the tissues, low
level of oxyhemoglobin enables the blood to transport more CO2
•  body temp (fever), thyroxine, growth hormone, testosterone, and epinephrine all raise
BPG and cause O2 unloading
•  metabolic rate requires  oxygen
Blood Gases and the
Respiratory Rhythm
• Rate and depth of breathing adjust to maintain levels
of:
– pH
7.35 – 7.45
– PCO2
40 mm Hg
– PO2
95 mm Hg
• Brainstem respiratory centers receive input from central and
peripheral chemoreceptors that monitor the composition of
blood and CSF
• Most potent stimulus for breathing is pH, followed by CO2, and
least significant is O2
Hydrogen Ions
• Acidosis – blood pH lower than 7.35
• Alkalosis – blood pH higher than 7.45
• Hypocapnia – PCO2 less than 37 mm Hg (normal 37
– 43 mm Hg)
• most common cause of alkalosis
• Hypercapnia – PCO2 greater than 43 mm Hg
• most common cause of acidosis
Effects of Hydrogen Ions
•
Respiratory acidosis and respiratory alkalosis – pH imbalances resulting from a
mismatch between the rate of pulmonary ventilation and the rate of CO2
production
•
Hyperventilation is a corrective homeostatic response to acidosis
– “blowing off ” CO2 faster than the body produces it
– pushes reaction to the left
CO2 (expired) + H2O  H2CO3  HCO3- +  H+
– reduces H+ (reduces acid) raises blood pH towards normal
•
Hypoventilation is a corrective homeostatic response to alkalosis
–
–
–
–
allows CO2 to accumulate in the body fluids faster than we exhale it
shifts reaction to the right
CO2 + H2O  H2CO3  HCO3- + H+
raising the H+ concentration, lowering pH to normal
Effects of Oxygen
• PO2 usually has little effect on respiration
• Chronic hypoxemia, PO2 less than 60 mm Hg, can
significantly stimulate ventilation
– Hypoxic drive – respiration driven more by low PO2 than by
CO2 or pH
– Emphysema, pneumonia
– High elevations after several days
Respiration and Exercise
• Causes of increased respiration during exercise
1.
When the brain sends motor commands to the muscles
•
Also sends this information to the respiratory centers
•
Increase pulmonary ventilation in anticipation of the needs of the
exercising muscles
2. Exercise stimulates proprioceptors of the muscles and joints
•
Transmit excitatory signals to the brainstem respiratory centers
•
Increase breathing because they are informed that the muscles have
been told to move or are actually moving
•
Increase in pulmonary ventilation keeps blood gas values at their normal
levels in spite of the elevated O2 consumption and CO2 generation by the
muscles
Effect of Smoking
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Tumors
(a) Healthy lung, mediastinal surface
(b) Smoker's lung with carcinoma
a: © The McGraw-Hill Companies/Dennis Strete, photographer; b: Biophoto Associates/Photo Researchers, Inc.
Figure 22.27 a-b