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