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Respiratory System


Chapter 22. Respiratory System Overview Respiratory anatomy Respiration Respiratory musculature Ventilation, lung volumes and capacities Gas exchange and transport O2 ... – PowerPoint PPT presentation

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Title: Respiratory System

Chapter 22.
  • Respiratory System

  • Respiratory anatomy
  • Respiration
  • Respiratory musculature
  • Ventilation, lung volumes and capacities
  • Gas exchange and transport
  • O2
  • CO2
  • Respiratory centers
  • Chemoreceptor reflexes
  • Respiratory Diseases

  • Is obtained from the air by diffusion across
    delicate exchange surfaces of lungs
  • Is carried to cells by the cardiovascular system
    which also returns carbon dioxide to the lungs

Functions of the Respiratory System
  • Supplies body with oxygen and get rid of carbon
  • Provides extensive gas exchange surface area
    between air and circulating blood
  • Moves air to and from exchange surfaces of lungs
  • Protects respiratory surfaces from outside
  • Produces sounds
  • Participates in olfactory sense

Components of the Respiratory System
Figure 231
Organization of the Respiratory System
  • Upper respiratory system
  • Nose, nasal cavity, sinuses, and pharynx
  • Lower respiratory system
  • Larynx, trachea, bronchi and lungs

The Respiratory Tract
  • Conducting zone
  • from nasal cavity to terminal bronchioles
  • conduits for air to reach the sites of gas
  • Respiratory zone
  • the respiratory bronchioles, alveolar ducts, and
  • sites of gas exchange

The Respiratory Epithelium
Figure 232
Respiratory Epithelia
  • Changes along respiratory tract
  • Nose, nasal cavity, nasopharynx
    pseudostratified ciliated columnar epithelium
  • Oropharynx, laryngopharynx stratified squamous
  • Trachea, bronchi pseudostratified ciliated
    columnar epithelium
  • Terminal bronchioles cuboidal epithelium
  • Respiratory bronchioles, alveoli simple
    squamous epithelium
  • Think about why each part has the lining that it
  • For example, in alveoli
  • walls must be very thin (lt 1 µm)
  • surface area must be very great (about 35 times
    the surface area of the body)
  • In lower pharynx
  • walls must be tough because food abrades them

The Respiratory Mucosa
  • Consists of
  • epithelial layer
  • areolar layer
  • Lines conducting portion of respiratory system
  • Lamina propria
  • Areolar tissue in the upper respiratory system,
    trachea, and bronchi (conducting zone)
  • Contains mucous glands that secrete onto
    epithelial surface
  • In the conducting portion of lower respiratory
    system, contains smooth muscle cells that
    encircle lumen of bronchioles

Respiratory Defense System
  • Series of filtration mechanisms removes particles
    and pathogens
  • Hairs in the nasal cavity
  • Goblet cells and mucus glands produce mucus that
    bathes exposed surfaces
  • Cilia sweep debris trapped in mucus toward the
    pharynx (mucus escalator)
  • Filtration in nasal cavity removes large
  • Alveolar macrophages engulf small particles that
    reach lungs

Upper Respiratory Tract
Figure 233
Upper Respiratory Tract
  • Nose
  • Air enters through nostrils or external nares
    into nasal vestibule
  • Nasal hairs in vestibule are the first particle
    filtration system
  • Nasal Cavity
  • Nasal septum divides nasal cavity into left and
  • Mucous secretions from paranasal sinus and tears
    clean and moisten the nasal cavity
  • Meatuses Constricted passageways in between
    conchae that produce air turbulence
  • Warm (how?) and humidify incoming air (bypassed
    by mouth breathing)
  • trap particles
  • Air flow from external nares to vestibule to
    internal nares through meatuses, then to

The Pharynx
  • A chamber shared by digestive and respiratory
    systems that extends from internal nares to the
    dual entrances to the larynx and esophagus at the
    C6 vertebrae
  • Nasopharynx
  • Superior portion of the pharynx (above the soft
    palate) contains pharyngeal tonsils epithelium?
  • Oropharynx
  • Middle portion of the pharynx, from soft palate
    to epiglottis contains palatine and lingual
    tonsils communicates with oral cavity
  • Laryngopharynx
  • Inferior portion of the pharynx, extends from
    hyoid bone to entrance to larynx and esophagus

Lower Respiratory Tract
  • Air flow from the pharynx enters the larynx,
    continues into trachea, bronchial tree,
    bronchioles, and alveoli

Anatomy of the Larynx
Figure 234
Cartilages of the Larynx
  • 3 large, unpaired cartilages form the body of the
    larynx (voice box)
  • thyroid cartilage (Adams apple)
  • hyaline cartilage
  • Forms anterior and lateral walls of larynx
  • Ligaments attach to hyoid bone, epiglottis, and
    other laryngeal cartilages
  • cricoid cartilage
  • hyaline cartilage
  • Form posterior portion of larynx
  • Ligaments attach to first tracheal cartilage
  • the epiglottis
  • elastic cartilage
  • Covers glottis during swallowing
  • Ligaments attach to thyroid cartilage and hyoid

Small Cartilages of the Larynx
  • 3 pairs of small hyaline cartilages
  • arytenoid cartilages
  • corniculate cartilages
  • cuneiform cartilages
  • Corniculate and arytenoid cartilages function in
    opening and closing the glottis and the
    production of sound

Larynx Functions
  • To provide a patent airway
  • To function in voice production
  • To act as a switching mechanism to route air and
    food into the proper channels
  • Thyroid and cricoid cartilages support and
    protect the glottis and the entrance to trachea
  • During swallowing the larynx is elevated and the
    epiglottis folds back over glottis prevents entry
    of food and liquids into respiratory tract

Sphincter Functions of Larynx
  • The larynx is closed during coughing, sneezing,
    and Valsalvas maneuver
  • Valsalvas maneuver
  • Air is temporarily held in the lower respiratory
    tract by closing the glottis
  • Causes intra-abdominal pressure to rise when
    abdominal muscles contract
  • Helps to empty the rectum
  • Acts as a splint to stabilize the trunk when
    lifting heavy loads
  • Glottis also closed (covered) by epiglottis
    during swallowing

The Glottis
Figure 235
Sound Production
  • Air passing through glottis
  • vibrates vocal folds and produces sound waves
  • Sound is varied by
  • tension on vocal folds
  • voluntary muscles position cartilages

Anatomy of the Trachea
Figure 236
The Trachea
  • Extends from the cricoid cartilage into
    mediastinum where it branches into right and left
  • Has mucosa, submucosa which contains mucous
    glands, and adventitia
  • Adventita made up of 1520 C-shaped tracheal
    cartilages (hyaline) strengthen and protect
  • Ends of each tracheal cartilage are connected by
    an elastic ligament and trachealis muscle where
    trachea contacts esophagus. Why?

The Primary Bronchi
  • Right and left primary bronchi are separated by
    an internal ridge (the carina)
  • Right primary bronchus
  • larger in diameter than the left
  • descends at a steeper angle

The Bronchial Tree
  • Formed by the primary bronchi and their branches
  • Each primary bronchus (R and L) branches into
    secondary bronchi, each supplying one lobe of the
    lungs (5 total)
  • Secondary Bronchi Branch to form tertiary bronchi
  • Each tertiary bronchus branches into multiple
  • Bronchioles branch into terminal bronchioles
  • 1 tertiary bronchus forms about 6500 terminal

Bronchial Tree
Figure 239
Bronchial Structure
  • The walls of primary, secondary, and tertiary
  • contain progressively less cartilage and more
    smooth muscle, increasing muscular effects on
    airway constriction and resistance
  • Bronchioles
  • Consist of cuboidal epithelium
  • Lack cartilage support and mucus-producing cells
    and are dominated by a complete layer of circular
    smooth muscle

Autonomic Control
  • Regulates smooth muscle
  • controls diameter of bronchioles
  • controls airflow and resistance in lungs
  • Bronchodilation of bronchial airways
  • Caused by sympathetic ANS activation
  • Reduces resistance
  • Bronchoconstriction
  • Caused by parasympathetic ANS activation or
  • histamine release (allergic reactions)

The Bronchioles
Figure 2310
Conducting Zones
Figure 22.7
Figure 237
The Lungs
  • Left and right lungs in left and right pleural
  • The base
  • inferior portion of each lung rests on superior
    surface of diaphragm
  • Hilus
  • Where pulmonary nerves, blood vessels, and
    lymphatics enter lung
  • Anchored in meshwork of connective tissue

Lung Anatomy
  • Lungs have lobes separated by deep fissures
  • Right lung is wider and is displaced upward by
    liver. Has 3 lobes
  • superior, middle, and inferior
  • separated by horizontal and oblique fissures
  • Left lung is longer is displaced leftward by the
    heart forming the cardiac notch. Has 2 lobes
  • superior and inferior
  • separated by an oblique fissure

Relationship between Lungs and Heart
Figure 238
Respiratory Zone
  • Each terminal bronchiole branches to form several
    respiratory bronchioles, where gas exchange takes
    place (Exchange Surfaces)
  • Respiratory bronchioles lead to alveolar ducts,
    then to terminal clusters of alveolar sacs
    composed of alveoli
  • Approximately 300 million alveoli
  • Account for most of the lungs volume
  • Provide tremendous surface area for gas exchange

Respiratory Zone
  • Alveoli Are air-filled pockets within the lungs
    where all gas exchange takes place
  • Alveolar epithelium is a very delicate, simple
    squamous epithelium
  • Contains scattered and specialized cells
  • Lines exchange surfaces of alveoli

Alveolar Organization
Figure 2311
Alveolar Organization
  • Respiratory bronchioles are connected to alveoli
    along alveolar ducts
  • Alveolar ducts end at alveolar sacs common
    chambers connected to many individual alveoli
  • Each individual alveolus has an extensive network
    of capillaries and is surrounded by elastic fibers

Alveolar Epithelium
  • Consists of simple squamous epithelium (Type I
  • Patrolled by alveolar macrophages, also called
    dust cells
  • Contains septal cells (Type II cells) that
    produce surfactant
  • oily secretion containing phospholipids and
  • coats alveolar surfaces and reduces surface

Alevolar problems
  • Respiratory Distress difficult respiration
  • Can occur when septal cells do not produce enough
  • leads to alveolar collapse
  • Pneumonia inflammation of the lung tissue
  • causes fluid to leak into alveoli
  • compromises function of respiratory membrane

Respiratory Membrane
  • The thin membrane of alveoli where gas exchange
    takes place. Consists of
  • Squamous epithelial lining of alveolus
  • Endothelial cells lining an adjacent capillary
  • Fused basal laminae between alveolar and
    endothelial cells
  • Diffusion across respiratory membrane is very
    rapid because distance is small and gases (O2 and
    CO2) are lipid soluble

Blood Supply to Respiratory Surfaces
  • Pulmonary arteries branch into arterioles
    supplying alveoli with deox. blood
  • a capillary network surrounds each alveolus as
    part of the respiratory membrane
  • blood from alveolar capillaries passes through
    pulmonary venules and veins, then returns to left
    atrium with ox. blood

Blood Supply to the Lungs Proper
  • Bronchial arteries provide systemic circulation
    bringing oxygen and nutrients to tissues of
    conducting passageways of lung
  • Arise from aorta and enter the lungs at the hilus
  • Supply all lung tissue except the alveoli
  • Venous blood bypasses the systemic circuit and
    just flows into pulmonary veins
  • Blood Pressure in the pulmonary circuit is low
    (30 mm Hg)
  • Pulmonary vessels are easily blocked by blood
    clots, fat, or air bubbles, causing pulmonary

Pleural Cavities and Membranes
  • 2 pleural cavities are separated by the
  • Each pleural cavity holds a lung and is lined
    with a serous membrane the pleura
  • Consists of 2 layers
  • parietal pleura
  • visceral pleura
  • Pleural fluid a serous transudate that
    lubricates space between 2 layers

  • Refers to 4 integrated processes
  • Pulmonary ventilation moving air into and out
    of the lungs (provides alveolar ventilation)
  • External respiration gas exchange between the
    lungs and the blood
  • Transport transport of oxygen and carbon
    dioxide between the lungs and tissues
  • Internal respiration gas exchange between
    systemic blood vessels and tissues

Gas Pressure and Volume
Figure 2313
Boyles Law
  • Defines the relationship between gas pressure and
  • P 1/V
  • Or
  • P1V1 P2V2
  • In a contained gas
  • external pressure forces molecules closer
  • movement of gas molecules exerts pressure on

Pulmonary Ventilation
Respiration Pressure Gradients
Figure 2314
  • Air flows from area of higher pressure to area of
    lower pressure (its the pressure difference, or
    gradient, that matters)
  • Volume of thoracic cavity changes (expansion or
    contraction of diaphragm or rib cage) creates
    changes in pressure
  • A Respiratory Cycle Consists of
  • an inspiration (inhalation)
  • an expiration (exhalation)

Lung Compliance
  • An indicator of expandability
  • Low compliance requires greater force to expand
  • High compliance requires less force
  • Kind of like capacitance
  • Affected by
  • Connective-tissue structure of the lungs
  • Level of surfactant production
  • Mobility of the thoracic cage

Pressure Relationships
Figure 22.12
Gas Pressure
  • Normal atmospheric pressure (Patm) 1 atm (or
    760 mm Hg) at sea level
  • Intrapulmonary Pressure (intra-alveolar pressure)
    is measured relative to Patm
  • In relaxed breathing, the difference between Patm
    and intrapulmonary pressure is small only -1 mm
    Hg on inhalation or 1 mm Hg on expiration
  • Max range from -30 mm Hg to 100 mm Hg)

Intrapleural Pressure
  • Pressure in space between parietal and visceral
  • Actually a potential space because serous fluid
    welds the two layers together (like a wet glass
    on a coaster)
  • Remains below Patm throughout respiratory cycle
    due to
  • Elasticity of lungs causes them to assume
    smallest possible size
  • Surface tension of alveolar fluid draws alveoli
    to their smallest possible size
  • These forces are resisted by the bond between the
    layers of pleura so there is always a negative
    pressure trying to pull the lungs into a smaller
  • If lungs were allowed to collapse completely,
    based on their elastic content they would only be
    about 5 of their normal resting volume

P and V Changes with Inhalation and Exhalation
Figure 2315
The Respiratory Pump
  • Cyclical changes in intrapleural pressure operate
    the respiratory pump which aids in venous return
    to heart

Lung Collapse
  • Injury to the chest wall can cause pneumothorax
    when air is allowed to enter the pleural space.
  • Caused by equalization of the intrapleural
    pressure with the intrapulmonary pressure (the
    bond between lung and pleura breaks)
  • Causes atelectasis (a collapsed lung)

The Respiratory Muscles
Figure 2316a, b
Respiratory Muscles
  • Inhalation always active
  • Diaphragm contraction flattens it, expanding the
    thorax and drawing air into lungs, accounts for
    75 of normal air movement
  • External intercostal muscles assist inhalation
    by elevating ribs, accounts for 25 of normal air
  • Exhalation normally passive
  • Relaxation of diaphragm decreases thoracic volume
  • Gravity causes rib cage to descend
  • Elastic fibers in lungs and muscles cause elastic
  • All serve to raise intrapulmonary pressure to

Muscles of Active Exhalation
  • Internal intercostals actively depress the ribs
  • Abdominal muscles compress the abdomen, forcing
    diaphragm upward
  • Both serve to greatly decrease the thoracic
    volume, thus increasing the pressure ? more air
    leaves (and does so faster)

Resistance in Respiratory Passageways
  • As airway resistance rises, breathing movements
    become more strenuous
  • Severely constricted or obstructed bronchioles
  • Can prevent life-sustaining ventilation
  • Can occur during acute asthma attacks which stops
  • Epinephrine release via the sympathetic nervous
    system dilates bronchioles and reduces air

Figure 22.15
Modes of Breathing
  • Quiet Breathing (Eupnea) involves active
    inhalation and passive exhalation
  • Diaphragmatic breathing or deep breathing
  • is dominated by diaphragm
  • Costal breathing or shallow breathing
  • is dominated by ribcage movements
  • usually occurs due to conscious effort or
    abdominal/thoracic obstructions (e.g. pregnancy)
  • Forced Breathing (hyperpnea) involves active
    inhalation and exhalation
  • Both assisted by accessory muscles

Respiratory Rates and Volumes
  • Respiratory system adapts to changing oxygen
    demands by varying
  • the number of breaths per minute (respiratory
  • the volume of air moved per breath (tidal volume)
  • Both can be modulated
  • Minute Volume (measures pulmonary ventilation)
    respiratory rate ? tidal volume
  • kind of like CO HR x SV)
  • Both RR and TV can be modulated

Dead Space
  • Only a part of respiratory minute volume reaches
    alveolar exchange surfaces
  • Volume of air remaining in conducting passages is
    anatomic dead space

Alveolar Ventilation
  • Alveolar ventilation is the amount of air
    reaching alveoli each minute respiratory rate ?
    (Tidal Volume - anatomic dead space)
  • for a given respiratory rate
  • increasing tidal volume increases alveolar
    ventilation rate
  • for a given tidal volume
  • increasing respiratory rate increases alveolar
  • Alveoli contain less O2, more CO2 than
    atmospheric air because inhaled air mixes with
    exhaled air

Mammalian Respiratory System poor design?
  • Inhaled air mixes with exhaled air
  • Lots of dead space in the system
  • These are the results of a bi-directional, blind
    ended ventilation system what if water entered
    and left your sink through the same spout?
  • Birds, fish have unidirectional circuits so fresh
    and stale air never mix

Respiratory Volumes and Capacities
Figure 2317
Lung Volumes
  • Resting tidal volume
  • Expiratory reserve volume (ERV)
  • Residual volume
  • minimal volume (in a collapsed lung)
  • Inspiratory reserve volume (IRV)

Calculated Respiratory Capacities
  • Inspiratory capacity
  • tidal volume IRV
  • Functional residual capacity (FRC)
  • ERV residual volume
  • Vital capacity
  • ERV tidal volume IRV
  • Total lung capacity
  • vital capacity residual volume

Gas Exchange
  • Occurs between blood and alveolar air across the
    respiratory membrane
  • Depends on
  • partial pressures of the gases
  • diffusion of molecules between gas and liquid in
    response to concentration or pressure gradients

The Gas Laws
  • Rate of diffusion depends on physical principles,
    or gas laws
  • Boyles law P 1/V
  • Daltons law each gas contributes to the total
    pressure in proportion to its number of molecules
  • Henrys Law at a given temperature, the amount
    of a gas in solution is proportional to partial
    pressure of that gas

Composition of Air
  • Nitrogen (N2) 78.6
  • Oxygen (O2) 20.9
  • Water vapor (H2O) 0.5
  • Carbon dioxide (CO2) 0.04
  • Atmospheric pressure produced by air molecules
    bumping into each other 760 mmHg
  • Partial Pressure the pressure contributed by
    each gas in the atmosphere
  • Daltons Law says PO2 .209 x 760 160mmHg

Normal Partial Pressures
  • In pulmonary vein plasma (after visiting lungs)
  • PCO2 40 mm Hg
  • PO2 100 mm Hg
  • PN2 573 mm Hg

Mixing in Pulmonary Veins
  • Oxygenated blood mixes with deoxygenated blood
    from conducting passageways that bypasses
    systemic circuit
  • Remember the bronchial arteries? There are no
    bronchial veins these venules join the
    pulmonary veins that otherwise have oxygenated
  • Lowers the PO2 of blood entering systemic circuit
    (about 95 mm Hg)

Henrys Law
Figure 2318
Henrys Law
  • When gas under pressure comes in contact with
    liquid, gas dissolves in liquid until equilibrium
    is reached
  • At a given temperature, the amount of a gas in
    solution is proportional to partial pressure of
    that gas
  • The amount of a gas that dissolves in solution
    (at given partial pressure and temperature) also
    depends on the solubility of that gas in that
    particular liquid CO2 is very soluble, O2 is
    less soluble, N2 has very low solubility

Overview of Pressures in the Body
  • PO2 (atmosphere) 160 mm Hg
  • PO2 (lungs) 100 mm Hg 104
  • PO2 (left atrium) 95 mm Hg
  • PO2 (resting tissue) 40 mm Hg
  • PO2 (active tissue) 15 mm Hg
  • PCO2 (lungs) 40 mm Hg
  • PCO2 (tissue) 45 mm Hg

Diffusion and the Respiratory Membrane
  • Direction and rate of diffusion of gases across
    the respiratory membrane are determined by
  • partial pressures and solubilities
  • matching of alveolar ventilation and pulmonary
    blood perfusion (gotta have enough busses)

Efficiency of Gas Exchange
  • Due to
  • substantial differences in partial pressure
    across the respiratory membrane
  • distances involved in gas exchange are small
  • O2 and CO2 are lipid soluble
  • total surface area is large
  • blood flow and air flow are coordinated

Respiratory Processes and Partial Pressure
Figure 2319
O2 and CO2
  • Blood arriving in pulmonary arteries has low PO2
    and high PCO2
  • The concentration gradient causes O2 to enter
    blood and CO2 to leave blood
  • Blood leaving heart has high PO2 and lowPCO2
  • Interstitial Fluid has low PO2 40 mm Hg and
    high PCO2 45 mm Hg
  • Concentration gradient in peripheral capillaries
    is opposite of lungs so CO2 diffuses into blood
    and O2 to enter tissue
  • Although carbon dioxide has a lower partial
    pressure gradient (only 5mmHg)
  • It is 20 times more soluble in plasma than oxygen
  • It diffuses in equal amounts with oxygen

Gas Pickup and Delivery
  • Red Blood Cells (RBCs) transport O2 to, and CO2
    from, peripheral tissues
  • Remove O2 and CO2 from plasma, allowing gases to
    diffuse into blood
  • Hb carries almost all O2, while only a little CO2
    is carried by Hb

Oxygen Transport
  • O2 binds to iron ions in hemoglobin (Hb)
    molecules in a reversible reaction
  • Each RBC can bind a billion molecules of O2
  • Hemoglobin Saturation the percentage of heme
    units in a hemoglobin molecule that contain bound

Respiration Oxygen and Carbon Dioxide Transport
Environmental Factors Affecting Hemoglobin
  • PO2 of blood
  • Blood pH
  • Temperature
  • Metabolic activity within RBCs

Respiration Hemoglobin
Respiration Percent O2 Saturation of Hemoglobin
Hemoglobin Saturation Curve
Figure 2320 (Navigator)
Oxyhemoglobin Saturation Curve
  • Graph relates the saturation of hemoglobin to
    partial pressure of oxygen
  • Higher PO2 results in greater Hb saturation
  • Is a curve rather than a straight line because Hb
    changes shape each time a molecule of O2 is
    bound. Each O2 bound makes next O2 binding easier

Oxygen Reserves
  • Notice that even at PO2 40 mm Hg, Oxygen
    saturation is at 75. Thus, each Hb molecule
    still has 3 oxygens bound to it. This reserve is
    needed when tissue becomes active and PO2drops to
    15 mm Hg

Carbon Monoxide Poisoning
  • CO from burning fuels
  • Binds irreversibly to hemoglobin and takes the
    place of O2

pH, Temperature, and Hemoglobin Saturation
Figure 2321
Hemoglobin Saturation Curve
  • When pH drops or temperature rises
  • more oxygen is released
  • curve shift to right
  • When pH rises or temperature drops
  • less oxygen is released
  • curve shifts to left

The Bohr Effect
  • The effect of decreased pH on hemoglobin
    saturation curve
  • Caused by CO2
  • CO2 diffuses into RBC
  • an enzyme, called carbonic anhydrase, catalyzes
    reaction with H2O
  • produces carbonic acid (H2CO3)
  • Carbonic acid (H2CO3)
  • dissociates into hydrogen ion (H) and
    bicarbonate ion (HCO3)
  • Hydrogen ions diffuse out of RBC, lowering pH

Hemoglobin and pH
2,3-biphosphoglycerate (BPG)
  • RBCs generate ATP by glycolysis, forming lactic
    acid and BPG
  • BPG directly affects O2 binding and release more
    BPG, more oxygen released
  • There is always some BPG around to lower the
    affinity of Hb for O2 (without it, hemoglobin
    will not release oxygen)
  • BPG levels rise
  • when pH increases
  • when stimulated by certain hormones

Fetal and Adult Hemoglobin
Figure 2322
Fetal and Adult Hemoglobin
  • At the same PO2
  • fetal Hb binds more O2 than adult Hb, which
    allows fetus to take O2 from maternal blood

  • Hemoglobin in RBCs
  • carries most blood oxygen
  • releases it in response to low O2 partial
    pressure in surrounding plasma
  • If PO2 increases, hemoglobin binds oxygen
  • If PO2 decreases, hemoglobin releases oxygen
  • At a given PO2 hemoglobin will release additional
    oxygen if pH decreases or temperature increases

Carbon Dioxide Transport
Figure 2323 (Navigator)
CO2 Transport
  • CO2 is generated as a byproduct of aerobic
    metabolism (cellular respiration)
  • Takes three routes in blood
  • converted to carbonic acid
  • bound to protein portion of hemoglobin
  • dissolved in plasma

CO2 in the Blood Stream
  • 70 is transported as carbonic acid (H2CO3) which
    dissociates into H and bicarbonate (HCO3-)
  • Bicarbonate ions move into plasma by a
    countertransport exchange mechanism that takes in
    Cl- ions without using ATP (the chloride shift)
  • At the lungs, these processes are reversed
  • Bicarbonate ions move into the RBCs and bind with
    hydrogen ions to form carbonic acid
  • Carbonic acid is then split by carbonic anhydrase
    to release carbon dioxide and water
  • Carbon dioxide then diffuses from the blood into
    the alveoli, then is breathed out

CO2 inside RBCs
  • CO2 H2O H2CO3
  • (Enzyme carbonic anhydrase)
  • H2CO3 H HCO3-

CO2 in the Blood Stream
  • 20 - 23 is bound to amino groups of globular
    proteins in Hb molecule forming
  • 7 - 10 is transported as CO2 dissolved in plasma

  • CO2 travels in the bloodstream primarily as
    bicarbonate ions, which form through dissociation
    of carbonic acid produced by carbonic anhydrase
    in RBCs
  • Lesser amounts of CO2 are bound to Hb and even
    fewer molecules are dissolved in plasma

Summary Gas Transport
Figure 2324
Influence of Carbon Dioxide on Blood pH
  • The carbonic acidbicarbonate buffer system
    resists blood pH changes
  • If hydrogen ion concentrations in blood begin to
    rise, excess H is removed by combining with
  • If hydrogen ion concentrations begin to drop,
    carbonic acid dissociates, releasing H
  • Changes in respiratory rate can also
  • Alter blood pH
  • Provide a fast-acting system to adjust pH when it
    is disturbed by metabolic factors

Control of Respiration
  • Ventilation the amount of gas reaching the
  • Perfusion the blood flow reaching the alveoli
  • Ventilation and perfusion must be tightly
    regulated for efficient gas exchange
  • Gas diffusion at both peripheral and alveolar
    capillaries maintain balance by
  • changes in blood flow and oxygen delivery
  • changes in depth and rate of respiration

Regulation of O2 Transport
  • Rising PCO2 levels in tissues relaxes smooth
    muscle in arterioles and capillaries, increasing
    blood flow there (autoregulation)
  • Coordination of lung perfusion (blood) and
    alveolar ventilation (air)
  • blood flow is shifted to the capillaries serving
    alveoli with high PO2 and low PCO2 (opposite of
  • PCO2 levels control bronchoconstriction and
    bronchodilation high PCO2 causes bronchodilation
    (just like with blood in the tissues)

Ventilation-Perfusion Coupling
  • In tissue high CO2 causes vasodilation, in lungs,
    high CO2 causes vasoconstiction (Why?)
  • In lungs high CO2 causes bronchodilation (Why?)
    while low CO2 causes constriction
  • ? Blood goes to alveoli with low CO2 , air goes
    to alveoli with high CO2

Ventilation-Perfusion Coupling
in alveoli
Reduced alveolar ventilation excessive perfusion
Reduced alveolar ventilation reduced perfusion
Pulmonary arterioles serving these
alveoli constrict
in alveoli
Enhanced alveolar ventilation inadequate
Enhanced alveolar ventilation enhanced perfusion
Pulmonary arterioles serving these alveoli dilate
Figure 22.19
The Respiratory Rhythmicity Centers
  • Respiratory rhythmicity centers in medulla set
    the pace of respiration
  • Can be divided into 2 groups
  • dorsal respiratory group (DRG)
  • Inspiratory center
  • Functions in quiet breathing (sets the pace) and
    forced breathing
  • Dormant during expiration
  • ventral respiratory group (VRG)
  • Inspiratory and expiratory center
  • Functions only in forced breathing

Quiet Breathing
  • Brief activity in the DRG stimulates inspiratory
  • After 2 seconds, DRG neurons become inactive,
    allowing passive exhalation
  • Note that VRG is not involved

Forced Breathing
  • Increased activity in DRG
  • stimulates VRG to become active
  • which activates accessory inspiratory muscles
  • After inhalation
  • expiratory center neurons stimulate active

Forced Breathing
Quiet Breathing
Figure 2325b
Centers of the Pons
  • Paired nuclei that adjust output of respiratory
    rhythmicity centers
  • regulating respiratory rate and depth of
  • Pons centers
  • Influence and modify activity of the medullary
  • Smooth out inspiration and expiration transitions
    and vice versa
  • The pontine respiratory group (PRG)
    continuously inhibits the inspiration center

Respiratory Centers and Reflex Controls
Figure 2326
Sensory Modifiers of Respiratory Center Activities
  • Chemoreceptors are sensitive to
  • PCO2, PO2, or pH of blood or cerebrospinal fluid
  • Baroreceptors in aortic or carotid sinuses
  • sensitive to changes in blood pressure
  • Stretch receptors respond to changes in lung
  • Irritating physical or chemical stimuli in nasal
    cavity, larynx, or bronchial tree promote airway

Chemoreceptor Reflexes
  • Respiratory centers are strongly influenced by
    chemoreceptor input from
  • carotid bodies (cranial nerve IX)
  • aortic bodies (cranial nerve X)
  • receptors in medulla that monitor cerebrospinal
  • All react more strongly to changes in pH and
    PCO2, to a lesser extent to changes in PO2
  • So in general, CO2 levels, rather than O2 levels,
    are primary drivers of respiratory activity
  • At rest, it is the H ion concentration in brain
    CSF (which is a proxy measure of CO2 levels)

Chemoreceptors and oxygen
  • Arterial oxygen levels are monitored by the
    aortic and carotid bodies
  • Substantial drops in arterial PO2 (to 60 mm Hg)
    are needed before oxygen levels become a major
    stimulus for increased ventilation
  • If carbon dioxide is not removed (e.g., as in
    emphysema and chronic bronchitis), chemoreceptors
    become unresponsive to PCO2 chemical stimuli
  • In such cases, PO2 levels become the principal
    respiratory stimulus (hypoxic drive)

Chemoreceptor Responses to PCO2
Figure 2327
Effect of Breathing on Ventilation
  • Breathing faster and deeper gets rid of more CO2
    , takes in more O2
  • Breathing more slowly and shallowly allows CO2 to
    build up, less O2 comes in

Chemoreceptor Stimulation
  • Leads to increased depth and rate of respiration
  • Is subject to adaptation decreased sensitivity
    due to chronic stimulation

Changes in Arterial PCO2
  • Hypercapnia an increase in arterial PCO2
  • Stimulates chemoreceptors in the medulla
    oblongata to restore homeostasis by increasing
    breathing rate
  • Hypocapnia a decrease in arterial PCO2
  • Inhibits chemoreceptors, breathing rate decreases

Ventilation Issues
  • Hypoventilation
  • A common cause of hypercapnia
  • Abnormally low respiration rate allows CO2
    build-up in blood, should result in increased RR
  • Hyperventilation
  • Excessive ventilation
  • Results in abnormally low PCO2 (hypocapnia)
  • Stimulates chemoreceptors to decrease respiratory
  • Treatment? Why?

Baroreceptor Reflexes
  • Carotid and aortic baroreceptor stimulation
    affects both blood pressure and respiratory
  • When blood pressure falls
  • respiration increases
  • When blood pressure increases
  • respiration decreases

Breathing and Heart Rate
  • Your ventilation and perfusion must be
    coordinated, otherwise the circulatory and
    respiratory systems not efficient.
  • Examples
  • Increase HR but not RR no more O2 coming in
    than before so blood cant deliver it to tissues
  • Increase RR but not HR O2 is coming in more
    quickly but it cant get to the tissues
  • Also, if BP falls, RR and HR rise and vice versa

The HeringBreuer Reflexes
  • 2 baroreceptor reflexes involved in forced
  • inflation reflex
  • Caused by stretch receptor in lungs
  • prevents lung overexpansion
  • deflation reflex
  • inhibits expiratory centers and stimulates
    inspiratory centers during lung deflation so
    inspiration can start again

Changes in Respiratory System at Birth
  • Before birth pulmonary vessels are collapsed and
    lungs contain no air
  • During delivery blood PO2 falls, PCO2 rises
  • At birth newborn overcomes force of surface
    tension to inflate bronchial tree and alveoli and
    take first breath
  • Large drop in pressure at first breath pulls
    blood into pulmonary circulation, closing foramen
    ovale and ductus arteriosus redirecting fetal
    blood circulation patterns
  • Subsequent breaths fully inflate alveoli

Respiratory Disorders
  • Restrictive disorders lung cancer, fibrosis,
  • Fibrosis decreases compliance
  • harder to inhale
  • Obstructive disorders emphysema, asthma,
    bronchitis (COPD)
  • Loss of elasticity increases compliance
  • Harder to exhale (FRC increased)

COPD Chronic Obstructive Pulmonary Disease
  • Includes emphysema, chronic bronchitis, asthma.
    Often, both emphysema and bronchitis are present
    but in differing proportions
  • Symptoms
  • difficult to exhale
  • May have barrel chests due to trapped air in
  • dyspnea (shortness of breath) accompanied by
    wheezing, and a persistent cough with sputum

COPD - Emphysema
  • Loss of elastic tissue in the lung alveoli lead
    to their enlargement and degeneration of the
    respiratory membrane leaving large holes behind
  • Suffers are called pink puffers because they
    are thin, usually maintain good oxygen
    saturation, and breathe through pursed lips
  • Caused by smoking or (rarely) by alpha1
    anti-trypsin deficiency this is a congenital
    lack of the gene for alpha1 antitrypsin which
    normally protects alveoli from enzyme neutrophil
    elastase without it, elastase eats away the
    elastic fibers

COPD - Chronic Bronchitis
  • Inflammation of airways causes narrowing of
    bronchioles and a buildup of mucus, both of which
    restrict air flow
  • During exhalation, airways collapse (why not
    during inhalation?)
  • These patients are often called blue bloaters
    because they have low oxygen saturation
    (cyanosis), and often have systemic edema
    secondary to vasoconstriction and right-sided
    heart failure
  • Adaptation of the chemoreceptors occurs
    especially in the ones sensitive to CO2
  • Thus, their only drive to breathe is provided by
    low O2 levels! This is why they are always blue.
    DO NOT GIVE THESE PATIENTS O2 ! They will stop
    breathing totally.

  • Altitude sickness low pressure leads to hypoxia,
    can cause cerebral and pulmonary edema
  • Normal response to acute high altitude exposure
  • Increased ventilation 2-3 L/min higher than at
    sea level due to Increased RR and tidal volume
  • Increased HR
  • Substantial decline in PO2 stimulates peripheral
  • Chemoreceptors become more responsive to PCO2
  • Over time
  • Increased hematocrit
  • Increased BPG causes a right shift in Hb making
    it easier to offload oxygen at the tissues

Lung fluid
  • Pleural effusion fluid buildup in pleural
    cavity/space (kind of like pericarditis)
  • Pulmonary edema fills exchange surfaces

Cystic Fibrosis
  • Recessive genetic disease caused by simple
    mutation in both copies of the gene for a
    chloride transporter.
  • Without it, Cl- cannot be pumped onto the lung
    surface, Na doesnt follow and neither does
  • Sticky mucus builds up inside lungs and
    infections are common. Often fatal before age 30

  • Decompression sickness the bends, nitrogen
    bubbles exit the blood, enter the tissues
    painful and dangerous
  • Shallow water blackout hyperventilation leads to
    artificially reduced CO2, allows you to hold your
    breath to the point of passing out

  • Hole in pleural membrane causes lung collapse
  • Non-tension pneumothorax a hole through both
    lung and pleural membrane breaks tension between
    the pleura, lung elasticity causes it to pull
    away from the chest wall
  • Tension pneumothorax a hole in the lung allows
    air to escape into the pleural space with each
    breath, further raising in the intrapleural
    pressure and collapsing the lung

(No Transcript)
  • Sudden infant death syndrome
  • Disrupts normal respiratory reflex pattern
  • May result from connection problems between
    pacemaker complex and respiratory centers
  • See extra credit options

Lung cancer
  • 50 die within one year of diagnosis
  • Only 20 or so survive 5 years
  • Around 90 of cases are due exclusively to smoking
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