Transcript Chapter 23

Chapter 23
Respiratory System
23-1
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
23-2
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.
23-3
Respiratory System Divisions
• Upper tract: nose,
pharynx and
associated structures
• Lower tract: larynx,
trachea, bronchi, lungs
and the tubing within
the lungs
23-4
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
23-5
Functions of Nasal Cavity:
• Passageway for air
• Cleans the air
(open even if mouth full of food)
[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
• Along with paranasal sinuses are
resonating chambers for speech
[superior part of nasal cavity consists of olfactory epithelium (sensory receptors)]
23-6
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 / 23-7
too much air = gas)
Larynx
23-8
Larynx -
base of tongue to trachea / passageway for air
• Unpaired cartilages
– Thyroid: largest, Adam’s 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
23-9
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.
23-10
Vocal Folds
23-11
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
23-12
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.
23-13
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.
23-14
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 cubeshaped 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.
23-15
•
•
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.
23-16
Thoracic Wall
and Muscles of Respiration
23-17
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
23-18
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
23-19
Effect of Rib and Sternum
23-20
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.
23-21
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.
23-22
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.
• Boyle’s 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.
23-23
Alveolar Pressure Changes: (Note: Barometric air pressure is
always assigned a value of zero)
23-24
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.
23-25
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.
23-26
Normal Breathing Cycle: (Inspiration: pleural pressure decreases =
alveolar volume increases = alveolar pressure decreases below barometric pressure = air flow into lungs.
23-27
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)
23-28
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
23-29
expiration (1200 mL)
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.
23-30
Spirometer, Lung Volumes, and
Lung Capacities
23-31
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)
23-32
VT = tidal volume
VD = dead space
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%)
– Dalton’s 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)
– Henry’s 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
23-33
than O2 )
Physical Principles of Gas Exchange
•
Diffusion of gases through the respiratory membrane
depends upon three things
1. Membrane thickness. The thicker, the lower the
diffusion rate (diseases can cause an increase in thickness)
2. 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
3. Surface area. Diseases like emphysema and lung
cancer reduce available surface area
4. 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
23-34
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.
23-35
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
• Carbon dioxide
– Moves from tissues
into tissue capillaries
– Moves from
pulmonary capillaries
into the alveoli
(because blood from pulmonary
capillaries mixes with
deoxygenated blood from
bronchial veins)
– Oxygen moves from
tissue capillaries into the
tissues
23-36
Gas Exchange
23-37
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.
23-38
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
23-39
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.
23-40
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.
23-41
Shifting the Curve
23-42
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
23-43
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
23-44
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)
23-45
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 of23-46
the brain & by input from peripherally located receptors.
Rhythmic Ventilation
• 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)
• 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
23-47
Modifying Respiration
23-48
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
23-49
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
23-50
does the chemosensitive area of medulla
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
23-51
Regulation of Blood pH and Gases
23-52
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
23-53
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,
23-54
lactic acid produced by skeletal muscles
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
23-55
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
23-56
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
23-57