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Respiratory System

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Title: Respiratory System


1
Chapter 23
  • Respiratory System

2
Respiration
  • Ventilation Movement of air into and out of
    lungs
  • External respiration Gas exchange between air in
    lungs and blood
  • Transport of oxygen and carbon dioxide in the
    blood
  • Internal respiration Gas exchange between the
    blood and tissues

3
Respiratory System Functions
  • Gas exchange Oxygen enters blood and carbon
    dioxide leaves
  • Regulation of blood pH Altered by changing blood
    carbon dioxide levels (increase CO2 decrease
    pH)
  • Voice production Movement of air past vocal
    folds makes sound and speech
  • Olfaction Smell occurs when airborne molecules
    are drawn into nasal cavity
  • Protection Against microorganisms by preventing
    entry and removing them from respiratory surfaces.

4
Respiratory System Divisions
  • Upper tract nose, pharynx and associated
    structures
  • Lower tract larynx, trachea, bronchi, lungs and
    the tubing within the lungs

5
Nose (Nasus) and Nasal Cavities
  • External nose (visible part includes hyaline
    cartilage plates nasal bones )
  • Nasal cavity
  • From nares (nostrils) to choanae (openings into
    the pharynx)
  • Vestibule just inside nares lined with
    stratified squamous epithelium continuous with
    skin
  • Hard palate floor of nasal cavity separates
    nasal cavity from oral cavity covered by mucous
    membrane
  • Nasal septum partition dividing cavity. Anterior
    cartilage posterior vomer and perpendicular
    plate of ethmoid (divides nasal cavity into right
    left parts)
  • Choanae bony ridges on lateral walls with
    meatuses (passageways) between. Openings to
    paranasal sinuses and to nasolacrimal duct

6
Functions of Nasal Cavity
  • Passageway for air (open even if mouth full of
    food)
  • Cleans the air vestibule lined with hair this
    traps particles / mucous membrane consists of
    pseudostratified ciliated columnar epithelium
    with goblet cells (mucus)
  • Humidifies( moisture from mucous membranes from
    excess tears that drains into nasal cavity
    through nasolacrimal duct), warms air ( warm
    blood flowing through mucous membranes - this
    prevents damage to respiratory passages caused by
    cold air)
  • Smell superior part of nasal cavity consists of
    olfactory epithelium (sensory receptors)
  • Along with paranasal sinuses are resonating
    chambers for speech

7
Pharynx
  • Common opening for digestive and respiratory
    systems (connected to respiratory at larynx to
    digestive at esophagus)
  • Three regions
  • Nasopharynx
  • a. Pseudostratified columnar epithelium with
    goblet cells.
  • b. Mucous and debris from nasal cavity is
    swallowed.
  • c. Openings of Eustachian (auditory) tubes air
    that passes through them to equalize air pressure
    between atmosphere middle ear.
  • d. Floor is soft palate (separates nasopharynx
    from oropharynx), uvula is posterior extension of
    the soft palate prevents swallowed materials
    from entering nasopharynx nasal cavity
  • Oropharynx shared with digestive system (extends
    from soft palate to epiglottis). Lined with moist
    stratified squamous epithelium air, food,
    drink passes through.
  • Laryngopharynx epiglottis to esophagus. Lined
    with moist stratified squamous epithelium food
    drink pass through here to esophagus (very
    little air passes /
  • too much air gas)

8
Larynx
9
Larynx - base of tongue to trachea / passageway
for air
  • Unpaired cartilages
  • Thyroid largest, Adams apple
  • Cricoid most inferior, base of larynx (other
    cartilages rest here)
  • Epiglottis attached to thyroid and has a flap
    near base of tongue. Elastic rather than hyaline
    cartilage
  • Paired
  • Arytenoids attached to cricoid
  • Corniculate attached to arytenoids
  • Cuneiform contained in mucous membrane
  • Ligaments extend from arytenoids to thyroid
    cartilage
  • Vestibular folds or false vocal folds
  • True vocal cords or vocal folds sound
    production. Opening between is glottis -
    laryngitis is an inflammation of mucosal
    epithelium of vocal folds

10
Functions of Larynx
  • Maintain an open passageway for air movement
    thyroid and cricoid cartilages
  • Epiglottis and vestibular folds prevent swallowed
    material from moving into larynx during
    swallowing, epiglottis covers the opening of
    larynx so, food liquid slide over epiglottis
    toward esophagus. Also, closure of vestibular
    folds can also prevent the passage of air----when
    person holds breath.
  • Vocal folds are primary source of sound
    production. Greater the amplitude of vibration,
    louder the sound (force of air moving past vocal
    cords determines amplitude). - Frequency of
    vibration determines pitch. Also, length of
    vibrating segments of vocal folds
    affect-------ex when only anterior parts of
    folds vibrate, higher pitched tones are produced
    when longer sections of vibrate, lower tones
    result.
  • - Arytenoid cartilages and skeletal muscles
    determine length of vocal folds and also
    abduct the folds when not speaking (only
    breathing) to pull them out of the way making
    glottis larger (allows greater movement of air).
  • The pseudostratified ciliated columnar epithelium
    (lines larynx) traps debris, preventing their
    entry into the lower respiratory tract.

11
Vocal Folds
12
Trachea - windpipe
  • Membranous tube of dense regular connective
    tissue and smooth muscle supported by 15-20
    hyaline cartilage C-shaped rings (protects
    maintains open passageway for air) . Posterior
    surface is devoid of cartilage contains elastic
    ligamentous membrane and bundles of smooth muscle
    called the trachealis.
  • Contracts during coughing-----this causes air
    to move more rapidly through trachea, which helps
    expel mucus foreign
    objects.
  • Inner lining pseudostratified ciliated columnar
    epithelium with goblet cells. Mucus traps debris,
    cilia push it superiorly toward larynx and
    pharynx.
  • Divides to form
  • Left and right primary bronchi (each extends to a
    lung)
  • Carina cartilage at bifurcation (forms ridge).
    Membrane of carina especially sensitive to
    irritation and inhaled objects initiate the cough
    reflex

13
Tracheobronchial Tree and Conducting Zone
  • Trachea to terminal bronchioles which is ciliated
    for removal of debris.
  • Trachea divides into two primary bronchi. (right
    is larger in diameter more in line with trachea
    than left)
  • Primary bronchi divide into secondary (lobar)
    bronchi (one/lobe) which then divide into
    tertiary (segmental) bronchi.
  • Bronchopulmonary segments defined by tertiary
    bronchi.
  • Tertiary bronchi further subdivide into smaller
    and smaller bronchi then into
    bronchioles (less than 1 mm in diameter), then
    finally into terminal bronchioles.
  • Cartilage holds tube system open smooth muscle
    controls tube diameter-----
  • ex during exercise, diameter increases,
    decreases resistance to airflow, increases volume
    of air moved
  • during asthma attack, diameter decreases,
    increases resistance to airflow, decreases volume
    of air flow
  • As tubes become smaller, amount of cartilage
    decreases, amount of smooth muscle
    increases------ex terminal bronchioles have no
    cartilage only have smooth muscle.

14
Respiratory Zone Respiratory Bronchioles to
Alveoli
  • Respiratory zone site for gas exchange
  • Respiratory bronchioles branch from terminal
    bronchioles. Respiratory bronchioles have very
    few alveoli (small, air filled chambers where gas
    exchange between air blood takes place). Give
    rise to alveolar ducts which have more alveoli.
    Alveolar ducts end as alveolar sacs that have 2
    or 3 alveoli at their terminus.
  • Tissue surrounding alveoli contains elastic
    fibers (alveoli expand during inspiration
    recoil during expiration)
  • No cilia, but debris removed by macrophages.
    Macrophages then move into nearby lymphatics or
    into terminal bronchioles.

15
The Respiratory Membrane
  • Three types of cells in membrane.
  • Type I pneumocytes. Thin squamous epithelial
    cells, form 90 of surface of alveolus. Gas
    exchange.
  • Type II pneumocytes. Round to cube-shaped
    secretory cells. Produce surfactant (makes it
    easier for alveoli to expand during inspiration).
  • Dust cells (phagocytes)
  • Layers of the respiratory membrane
  • Thin layer of fluid lining the alveolus
  • Alveolar epithelium (simple squamous epithelium
  • Basement membrane of the alveolar epithelium
  • Thin interstitial space
  • Basement membrane of the capillary endothelium
  • C apillary endothelium composed of simple
    squamous epithelium
  • Tissue surrounding alveoli contains elastic
    fibers that contribute to recoil.

16
Lungs
  • Two lungs Principal organs of respiration
  • Base sits on diaphragm, apex at the top, hilus
    (hilum) on medial surface where bronchi and blood
    vessels enter the lung. All the structures in
    hilus called root of the lung.
  • Right lung three lobes. Lobes separated by
    fissures (deep prominent)
  • Left lung Two lobes
  • Right lung is larger heavier than left
  • Divisions
  • Lobes (supplied by secondary bronchi), each lobe
    is subdivided into bronchopulmonary segments
    (supplied by tertiary bronchi and separated from
    one another by connective tissue partitions),
    bronchopulmonary segments are subdivided into
    lobules (supplied by bronchioles and separated by
    incomplete partitions).
  • Note 9 bronchopulmonary segments present in left
    lung 10 present right lung
  • Note Individual diseased bronchopulmonary
    segments can be surgically removed, leaving the
    rest of lung intact, because major blood
    vessels bronchi do not cross connective tissue
    partitions.

17
Thoracic Wall and Muscles of Respiration
18
Thoracic Wall
  • Thoracic vertebrae, ribs, costal cartilages,
    sternum and associated muscles
  • Thoracic cavity space enclosed by thoracic wall
    and diaphragm
  • Diaphragm separates thoracic cavity from
    abdominal cavity

19
Inspiration and Expiration
  • Inspiration diaphragm, external intercostals,
    pectoralis minor, scalenes
  • Diaphragm dome-shaped with base of dome attached
    to inner circumference of inferior thoracic cage.
    Central tendon top of dome which is a flat sheet
    of connective tissue.
  • Quiet inspiration accounts for 2/3 of increase
    in size of thoracic volume. Inferior movement of
    central tendon and flattening of dome. Abdominal
    muscles relax
  • Other muscles elevate ribs and costal cartilages
    allow lateral rib movement
  • Expiration muscles that depress the ribs and
    sternum such as the abdominal muscles and
    internal intercostals.
  • Quiet expiration relaxation of diaphragm and
    external intercostals with contraction of
    abdominal muscles
  • Labored breathing all inspiratory muscles are
    active and contract more forcefully. Expiration
    is rapid

20
Effect of Rib and Sternum
21
Pleura
  • Pleural cavity surrounds each lung and is formed
    by the pleural membranes. Filled with pleural
    fluid.
  • Visceral pleura adherent to lung. Simple
    squamous epithelium, serous.
  • Parietal pleura adherent to internal thoracic
    wall.
  • Pleural fluid acts as a lubricant and helps hold
    the two membranes close together (adhesion).
  • Mediastinum central region, contains contents of
    thoracic cavity except for lungs.

22
Blood and Lymphatic Supply
  • Two sources of blood to lungs Pulmonary
    Bronchial
  • Pulmonary artery brings deoxygenated blood to
    lungs from right side of heart to be oxygenated
    in capillary beds that surround the alveoli.
    Blood leaves via the pulmonary veins and returns
    to the left side of the heart.
  • Bronchial arteries provide oxygenated systemic
    blood to lung tissue. They arise from the aorta
    run along the branching bronchi. Part of this now
    deoxygenated blood exits through the bronchial
    veins to the azygous (drains chest muscles) part
    merges with blood of alveolar capillaries and
    returns to left side of heart.
  • Blood going to left side of heart via pulmonary
    veins carries primarily oxygenated blood, but
    also some deoxygenated blood from the supply of
    the walls of the conducting and respiratory zone.
  • Two lymphatic supplies superficial and deep
    lymphatic vessels. Exit from hilus
  • Superficial drain superficial lung tissue and
    visceral pleura
  • Deep drain bronchi and associated C.T.
  • No lymphatics drain alveoli
  • Phagocytic cells within lungs phagocytize carbon
    particles other debris from inspired air move
    them to lymphatic vessels
  • Older people smokers lungs appear gray to black
    because accumulation of these particles
  • Cancer cells from lungs can spread to other parts
    of body through lymphatic vessels.

23
Ventilation
  • Movement of air into and out of lungs
  • Air moves from area of higher pressure to area of
    lower pressure (requires a pressure gradient)
  • If barometric pressure (atmospheric pressure) is
    greater than alveolar pressure, then air flows
    into the alveoli.
  • Boyles Law P k/V, where P gas pressure,
  • V volume, k constant at a given temperature
  • If diaphragm contracts, then size of alveoli
    increases. Remember P is inversely proportionate
    to V so as V gets larger (when diaphragm
    contracts), then P in alveoli gets smaller.

24
Alveolar Pressure Changes (Note Barometric air
pressure is always assigned a value of
zero)
25
Changing Alveolar Volume Lung Recoil( Lung
recoil changes in pleural pressure cause
changes in alveolar volume which results in
changes in pressure )
  • Causes alveoli to collapse resulting from
  • Elastic recoil elastic fibers in the alveolar
    walls
  • Surface tension film of fluid lines the alveoli.
    Where water interfaces with air, polar water
    molecules have great attraction for each other
    with a net pull in toward other water molecules.
    Tends to make alveoli collapse.
  • (attracted molecules of fluid surface tension
    draws alveoli to their smallest possible
    dimension)
  • Surfactant Reduces tendency of lungs to collapse
    by reducing surface tension. Produced by type II
    pneumocytes.
  • Respiratory distress syndrome (hyaline membrane
    disease). Common in infants with gestation age
    of less than 7 months. Not enough surfactant
    produced.

26
Pleural Pressure ( pressure in pleural cavity)
  • Negative pressure can cause alveoli to expand
  • Alveoli expand when pleural pressure is low
    enough to overcome lung recoil
  • Pneumothorax is an opening between pleural cavity
    and air that causes an increase of pleural
    pressure (air gets into pleural cavity by an
    opening in the thoracic wall or lung---------can
    be caused by penetrating trauma ex knife,
    bullet, broken rib or by non-penetrating trauma
    ex blow to chest, medical procedure (inserting
    catheter to withdraw pleural fluid), infections.
  • Causes part or all of the lung to collapse.

27
Normal Breathing Cycle (Inspiration pleural
pressure decreases alveolar volume increases
alveolar pressure decreases below barometric
pressure air flow into lungs.
28
Compliance
  • Measure of the ease with which lungs and thorax
    expand
  • The greater the compliance, the easier it is for
    a change in pressure to cause expansion
  • A lower-than-normal compliance means the lungs
    and thorax are harder to expand
  • Conditions that decrease compliance
  • Pulmonary fibrosis deposition of inelastic
    fibers in lung (emphysema)
  • Pulmonary edema (the alveoli fill with fluid
    instead of air, preventing oxygen from
    being absorbed into your bloodstream)
  • Respiratory distress syndrome
  • Increased resistance to airflow caused by airway
    obstruction (asthma, bronchitis, lung cancer)
  • Deformities of the thoracic wall (kyphosis
    (hunchback), scoliosis)

29
Pulmonary Volumes and Capacities
  • Spirometry measures volumes of air that move
    into and out of respiratory system. Uses a
    spirometer
  • Tidal volume amount of air inspired or expired
    with each breath. At rest 500 mL
  • Inspiratory reserve volume amount that can be
    inspired forcefully after inspiration of the
    tidal volume (3000 mL at rest)
  • Expiratory reserve volume amount that can be
    forcefully expired after expiration of the tidal
    volume (100 mL at rest)
  • Residual volume volume still remaining in
    respiratory passages and lungs after most
    forceful expiration (1200 mL)

30
Pulmonary Capacities
  • The sum of two or more pulmonary volumes
  • Inspiratory capacity tidal volume plus
    inspiratory reserve volume
  • Functional residual capacity expiratory reserve
    volume plus residual volume
  • Vital capacity sum of inspiratory reserve
    volume, tidal volume, and expiratory reserve
    volume
  • Total lung capacity sum of inspiratory and
    expiratory reserve volumes plus tidal volume and
    residual volume.
  • Factors such as sex, age, body size, and
    physical conditioning cause variations in
    respiration capacities from one individual to
    another. Ex males, younger people, thin people,
    tall people, athletes------------have greater
    vital capacities.

31
Spirometer, Lung Volumes, and Lung Capacities
32
Minute Ventilation and Alveolar Ventilation
  • Minute ventilation total air moved into and out
    of respiratory system each minute tidal volume X
    respiratory rate
  • Respiratory rate (respiratory frequency) (f)
    number of breaths taken per minute
  • Anatomic dead space formed by nasal cavity,
    pharynx, larynx, trachea, bronchi, bronchioles,
    and terminal bronchioles (part of respiratory
    system where gas exchange does NOT take place)
  • Physiological dead space anatomic dead space
    plus the volume of any alveoli in which gas
    exchange is less than normal. (these are
    nonfunctional alveoli--------few exist in healthy
    individual)
  • Alveolar ventilation (VA) volume of air
    available for gas exchange/minute VA f ( VT
    VD)
  • VT tidal volume VD dead space

33
Physical Principles of Gas Exchange
  • Partial pressure
  • The pressure exerted by each type of gas in a
    mixture
  • ex atmospheric pressure 760 mmHg
  • (contains nitrogen 79 oxygen 21)
  • Daltons law in a mixture of gases, the
    percentage of each gas is proportionate to its
    partial pressure
  • N2 79 79/100 0.79 ----?partial pressure
    0.79 x 760 mmHg 600mmHg
  • partial pressure is denoted----? PN2
  • Water vapor pressure pressure exerted by gaseous
    water in a mixture of gases (water evaporated
    into air)
  • Air in the respiratory system contains humidity
    because of mucus lining system
  • Diffusion of gases through liquids (gas molecules
    move from air into liquid, or from a liquid into
    air, because of partial pressure gradient----ex
    partial pressure of gas in the air is greater
    than in the liquid, movement of gas molecules
    into the liquid)
  • Henrys Law Concentration of a gas in a liquid
    is determined by its partial pressure and its
    solubility coefficient (solubility coefficient is
    a measure of how easily the gas dissolves in the
    liquid. Ex solubility coefficient for oxygen is
    0.024 carbon dioxide is 0.57-----?CO2 is 24
    times more soluble than O2 )

34
Physical Principles of Gas Exchange
  • Diffusion of gases through the respiratory
    membrane depends upon three things
  • Membrane thickness. The thicker, the lower the
    diffusion rate (diseases can cause an increase in
    thickness)
  • Diffusion coefficient of gas (measure of how
    easily a gas diffuses through a liquid or
    tissue). This takes into account the solubility
    of the gases size of gas molecules (molecular
    weight). CO2 is 20 times more diffusible than O2
  • Surface area. Diseases like emphysema and lung
    cancer reduce available surface area
  • Partial pressure differences. Gas moves from area
    of higher partial pressure to area of lower
    partial pressure. Normally, partial pressure of
    oxygen is higher in alveoli than in blood.
    Opposite is usually true for carbon dioxide

35
Relationship Between Alveolar Ventilation and
Pulmonary Capillary Perfusion
  • Increased ventilation or increased pulmonary
    capillary blood flow increases gas exchange
  • Shunted blood blood that is not completely
    oxygenated
  • Physiologic shunt is deoxygenated blood returning
    from lungs. Two sources
  • Blood returning from bronchi bronchioles
  • Blood from capillaries around alveoli
  • 1 - 2 of cardiac output makes up the
    physiological shunt
  • Regional distribution of blood flow determined
    primarily by gravity, but can also be determined
    by alveolar PO2.
  • Low PO2 causes arterioles to constrict so that
    blood is shunted to a region of the lung where
    the alveoli are better ventilated. Ex when
    bronchus becomes partially blocked
  • In other tissues of the body, low PO2 causes
    arterioles to dilate to deliver more blood to the
    tissues.

36
Oxygen and Carbon Dioxide Diffusion Gradients
  • Oxygen
  • Moves from alveoli into blood. Blood is almost
    completely saturated with oxygen when it leaves
    the capillary
  • PO2 in blood decreases because of mixing with
    deoxygenated blood (because blood from pulmonary
    capillaries mixes with deoxygenated blood from
    bronchial veins)
  • Oxygen moves from tissue capillaries into the
    tissues
  • Carbon dioxide
  • Moves from tissues into tissue capillaries
  • Moves from pulmonary capillaries into the alveoli

37
Gas Exchange
38
Hemoglobin and Oxygen Transport
  • Oxygen is transported by hemoglobin (98.5) and
    is dissolved in plasma (1.5)
  • Oxygen-hemoglobin dissociation curve describes
    the percentage of hemoglobin saturated with
    oxygen at any given PO2
  • Oxygen-hemoglobin dissociation curve at rest
    shows that hemoglobin is almost completely
    saturated when PO2 is 80 mm Hg or above. At
    lower partial pressures, the hemoglobin releases
    oxygen.
  • Thus, as tissues use more oxygen, hemoglobin
    releases more oxygen
  • to those tissues.

39
Bohr Effect
  • Effect of pH on oxygen-hemoglobin dissociation
    curve as pH of blood declines, amount of oxygen
    bound to hemoglobin at any given PO2 also
    declines
  • Occurs because decreased pH yields increase in H
    that combines with hemoglobin changing its
    shape and oxygen cannot bind to hemoglobin

40
Effects of CO2 and Temperature
  • Increase in PCO2 causes decrease in p H
  • Carbonic anhydrase causes CO2 and water to
    combine reversibly and form H2CO3 (carbonic
    acid) which ionizes to H and HCO3-
    (bicarbonate ion)
  • Increase temperature decreases tendency for
    oxygen to remain bound to hemoglobin, so as
    metabolism goes up, more oxygen is released to
    the tissues.

41
Effect of BPG
  • 2,3-bisphosphoglycerate (BPG) released by RBCs
    as they break down glucose for energy
  • Binds to hemoglobin and increases release of
    oxygen (reduces its affinity for oxygen)
  • Ex High altitudes decrease barometric
    pressure partial pressure of oxygen in alveoli
    decreased saturation of blood with oxygen in
    pulmonary capillaries decreased less oxygen in
    blood to be delivered to tissues
  • BPG helps increase oxygen delivery to tissues
    because increased levels of BPG increase the
    release of oxygen in tissues.

42
Shifting the Curve
43
Transport of Carbon Dioxide
  • Carbon dioxide is transported as bicarbonate ions
    (70) in combination with blood proteins (23
    primarily alpha beta globin chains of
    hemoglobin) and in solution with plasma (7)
  • Hemoglobin that has released oxygen binds more
    readily to carbon dioxide than hemoglobin that
    has oxygen bound to it ( Haldane effect)
  • In tissue capillaries, carbon dioxide combines
    with water inside RBCs to form carbonic acid
    which dissociates to form bicarbonate ions and
    hydrogen ions

44
Carbon Dioxide Transport and Chloride Movement
  • (a) Tissue capillaries as C O2 enters red blood
    cells, reacts with water to form bicarbonate and
    hydrogen ions. C hloride ions enter the RB C
    and bicarbonate ions leave chloride shift. H
    ydrogen ions combine with hemoglobin. (pH of RBC
    does not decrease bec. hemoglobin is a buffer )
    Lowering the concentration of bicarbonate and
    hydrogen ions inside red blood cells promotes the
    conversion of C O2 to bicarbonate ion.
  • (b) Pulmonary capillaries C O2 leaves red blood
    cells, resulting in the formation of additional
    C O2 from carbonic acid. The bicarbonate ions are
    exchanged for chloride ions, and the hydrogen
    ions are released from hemoglobin.
  • Increased plasma carbon dioxide lowers blood p H.
    The respiratory system regulates blood p H by
    regulating plasma carbon dioxide levels

45
Respiratory Areas in the Brainstem
  • Medullary respiratory center
  • Dorsal groups stimulate the diaphragm
  • Ventral groups stimulate the intercostal and
    abdominal muscles
  • This section is especially sensitive during
    infancy, and the neurons can be destroyed if the
    infant is dropped and/or shaken violently. The
    result can be death due to "shaken baby syndrome
  • Pontine (pneumotaxic) respiratory group
  • Involved with switching between inspiration and
    expiration (fine tunes the breathing
    pattern-----there is a connection with medullary
    resp. center but precise function unknown)

46
Rhythmic Ventilation
  • Starting inspiration
  • Medullary respiratory center neurons are
    continuously active
  • Center receives stimulation from receptors (that
    monitor blood gas levels) and simulation from
    parts of brain concerned with voluntary
    respiratory movements and emotion
  • Combined input from all sources causes action
    potentials to stimulate respiratory muscles
  • Increasing inspiration
  • More and more neurons are activated (to stimulate
    respiratory muscles)
  • Stopping inspiration
  • Neurons stimulating the muscles of respiration
    also stimulate the neurons in the medullary
    respiratory center that are responsible stopping
    inspiration. They also receive input from
    pontine group and stretch receptors in lungs.
    Inhibitory neurons activated and relaxation of
    respiratory muscles results in expiration.
  • Note although the medullary neurons establish
    the basic rate depth of breathing, their
    activities can be influenced by input from other
    parts of the brain by input from peripherally
    located receptors.

47
Rhythmic Ventilation
  • Chemical control
  • Carbon dioxide is major regulator, but indirectly
    through p H change
  • Increase or decrease in pH can stimulate
    chemo-sensitive area, causing a greater rate and
    depth of respiration
  • Oxygen levels in blood affect respiration when a
    50 or greater decrease from normal levels exists
  • CO2.
  • Hypercapnia too much CO2
  • Hypocapnia lower than normal CO2
  • Apnea. Cessation of breathing. Can be conscious
    decision, but eventually PCO2 levels increase to
    point that respiratory center overrides
  • Hyperventilation. Causes decrease in blood PCO2
    level, which causes respiratory alkalosis (high
    blood pH). Fainting, leads to changes in the
    nervous system fires and leads to the paresthesia
    (pins needles)
  • Cerebral (cerebral cortex)and limbic system.
    Respiration can be voluntarily controlled and
    modified by emotions (ex strong emotions can
    cause hyperventilation or produce the sobs
    gasps of crying)

48
Modifying Respiration
49
Chemical Control of Ventilation
  • Chemoreceptors specialized neurons that respond
    to changes in chemicals in solution
  • Central chemoreceptors chemosensitive area of
    the medulla oblongata connected to respiratory
    center
  • Peripheral chemoreceptors carotid and aortic
    bodies. Connected to respiratory center by
    cranial nerves IX and X (9 10)
  • Effect of pH chemosensitive area of medulla
    oblongata and carotid and aortic bodies respond
    to blood pH changes
  • Chemosensitive areas respond indirectly through
    changes in carbon dioxide
  • Carotid and aortic bodies respond directly to p H
    changes

50
Chemical Control of Ventilation
  • Effect of carbon dioxide small change in carbon
    dioxide in blood triggers a large increase in
    rate and depth of respiration
  • - ex an increase PCO2 of 5 mm Hg causes an
    increase in ventilation of 100.
  • Hypercapnia greater-than-normal amount of carbon
    dioxide
  • Hypocapnia lower-than-normal amount of carbon
    dioxide
  • Chemosensitive area in medulla oblongata is more
    important for regulation of PCO2 and pH than the
    carotid aortic bodies (responsible for 15 -
    20 of response)
  • During intense exercise, carotid aortic bodies
    respond more rapidly to changes in blood pH than
    does the chemosensitive area of medulla

51
Chemical Control of Ventilation
  • Effect of oxygen carotid and aortic body
    chemoreceptors respond to decreased PO2 by
    increased stimulation of respiratory center to
    keep it active despite decreasing oxygen levels
    (50 or greater decrease----------bec. of
    oxygen-hemoglobin dissociation curve-------at any
    PO2 above 80 mm Hg nearly all of hemoglobin is
    saturated with oxygen)
  • Hypoxia decrease in oxygen levels below normal
    values

52
Regulation of Blood pH and Gases
53
Hering-Breuer Reflex
  • Limits the degree of inspiration and prevents
    overinflation of the lungs
  • Depends on stretch receptors in the walls of
    bronchi bronchioles of the lung.
  • It is an inhibitory influence on the respiratory
    center results in expiration. (as expiration
    proceeds, stretch receptors no longer stimulated)
  • Infants
  • Reflex plays a role in regulating basic rhythm of
    breathing and preventing overinflation of lungs
  • Adults
  • Reflex important only when tidal volume large as
    in exercise

54
Effect of Exercise on Ventilation
  • Ventilation increases abruptly
  • At onset of exercise
  • Movement of limbs has strong influence (body
    movements stimulate proprioceptors in joints of
    the limbs)
  • Learned component (after a period of training,
    the brain learns to match ventilation with the
    intensity of exercise)
  • Ventilation increases gradually
  • After immediate increase, gradual increase occurs
    (4-6 minutes it levels off)
  • Anaerobic threshold highest level of exercise
    without causing significant change in blood pH.
    If exercise intensity is high enough to exceeded
    anaerobic threshold, lactic acid produced by
    skeletal muscles

55
Other Modifications of Ventilation
  • Activation of touch, thermal and pain receptors
    affect respiratory center
  • Sneeze reflex (initiated by irritants in the
    nasal cavity), cough reflex (initiated by
    irritants in the lungs)
  • Increase in body temperature yields increase in
    ventilation

56
Respiratory Adaptations to Exercise
  • Athletic training
  • Vital capacity increases slightly residual
    volume decreases slightly
  • At maximal exercise, tidal volume and minute
    ventilation increases
  • Gas exchange between alveoli and blood increases
    at maximal exercise
  • Alveolar ventilation increases
  • Increased cardiovascular efficiency leads to
    greater blood flow through the lungs

57
Effects of Aging
  • Vital capacity and maximum minute ventilation
    decrease (these changes are related to weakening
    of respiratory muscles decreased compliance of
    thoracic cage caused by stiffening of cartilage
    ribs)
  • Residual volume and dead space increase
  • Ability to remove mucus from respiratory
    passageways decreases
  • Gas exchange across respiratory membrane is
    reduced
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