Download CRYDERS Ch22 Respiratory System

 Respiration: All living cells of body require oxygen and
produce carbon dioxide
 Respiration includes four process:
 Ventilation: Movement of air into and out of lungs
(breathing)
 External respiration: Movement of O2 from lungs to blood,
CO2 from blood to lungs
 Transport of respiratory gases: transport of O2 from lungs
to tissues via blood, CO2 from tissue to lungs via blood
 Internal respiration: movement of O2 from blood to tissues,
CO2 from tissues to blood
 Respiratory system assists in gas exchange and perform
other functions as well:
 Gas exchange: Oxygen enters blood from air and carbon
dioxide leaves blood and enter air
 Regulation of blood pH: Alter blood pH by changing
blood carbon dioxide levels
 Voice production: Movement of air past vocal folds
makes sound and speech possible
 Olfaction: Smell sensation occurs when airborne
molecules are drawn into nasal cavity
 Protection: Protect against microorganisms by preventing
entry and removing them from respiratory surfaces
 Consists of external nose, nasal cavity,
pharynx, trachea, bronchi and lungs
 Divided into upper respiratory tract and
lower respiratory tract:
 Upper Respiratory tract: nose,
pharynx and associated structures
 Lower respiratory tract: larynx,
trachea, bronchi, lungs and the tubing
within the lungs
 Nose: Consists of :
 External nose
 Nasal cavity
 External nose:
– Visible, prominent feature
of face
– Consists of nasal bones,
extensions of frontal and
maxillary bones
 Nasal cavity
– Extends from nares to conchae
– Nares (nostrils): external
openings of nasal cavity
– Conchae: Are openings into
pharynx
– Vestibule: nasal cavity
superior to nares
– The nasal cavity is
separated from the oral
cavity by the palate
– Anterior hard palate (bone)
– Posterior soft palate (muscle)
 Nasal cavity
– Nasal septum: Divides nasal
cavity into left & right parts
– Anterior part of nasal septum is
made of cartilage
– Posterior part consists of vomer
bone & perpendicular plate of
ethmoid
– Conchae: 3 bony ridges on
lateral walls of nasal cavity
– With meatuses (passageway)
between
Paranasal Sinuses
• Cavities within bones surrounding
the nasal cavity are called sinuses
• Sinuses are located in the
following bones
–
–
–
–
Frontal bone
Sphenoid bone
Ethmoid bone
Maxillary bone
• Function of the sinuses
– Lighten the skull
– Act as resonance chambers
for speech
– Produce mucus that drains
into the nasal cavity
 Passageway for air: Open even when mouth is full of food
 Cleans the air: Vestibule is lined with hair & filter air
 Nasal septum and nasal conchae increase the surface area of nasal
cavity
– Enhance air turbulence and help filter air
– Ciliated epithelial cells remove contaminated mucus
 Humidifies, warms air:
– Humidified by the high water content in the nasal cavity
– Warmed by blood flowing through mucous membrane
 Smell: Contains olfactory epithelium, sensory organ for smell
 Speech: Nasal cavity and paranasal sinuses are resonating chambers
for speech
 Pharynx (Throat): Common opening
for digestive & respiratory systems
 Receives air from nasal cavity and
food and drink from oral cavity
 Connects to nasal cavity and mouth
superiorly
– Larynx and esophagus inferiorly
 Extends from the base of the skull to
sixth cervical vertebra
 Divided into three regions:
– Nasopharynx
– Oropharynx
– Laryngopharynx
 Nasopharynx:
 Superior region behind nasal cavity,
inferior to the sphenoid, and superior to
the level of the soft palate
 Strictly an air passageway
 Closes during swallowing to prevent
food from entering the nasal cavity
 Lined with pseudostratified columnar
epithelium with goblet cells
 Mucous and debris is moved through
nasopharynx and swallowed
 Openings of two auditory tubes
 Posterior surface of nasopharynx
contains Pharyngeal tonsil (adenoid)
• Oropharynx:
• Middle region behind mouth
• Extends inferiorly from soft palate
to the epiglottis
• Oral cavity opens to oropharynx
via an archway called the fauces
• Serves as a common passageway
for food and air
• Lined with protective stratified
squamous epithelium – abrasion
• Palatine and Lingual tonsils,
located near the fauces

Laryngopharynx

Inferior region attached to
larynx

Serves as a common
passageway for food and air

Extends from tip of
epiglottis to esophagus

And passes posterior to
larynx

Lined with moist stratified
squamous epithelium
• Located in the ant. part of throat & extend to the trachea posteriorly
• Passageway for air between pharynx and trachea
• Attaches superiorly to hyoid bone
• And consists of nine cartilages connected by muscles and ligaments
• Unpaired cartilages:
– Thyroid: largest, Adam’s apple
– Cricoid: most inferior, base of larynx
– Epiglottis: attached to thyroid cartilage
– Projects superiorly as a flap near base of tongue
– Consists of elastic rather than hyaline cartilage
• Paired Cartilages :
– Arytenoids: attached to cricoid cartilage
– Corniculate: attached to arytenoids
– Cuneiform: contained in mucous membrane, anterior to
Corniculate cartilages
• Vocal ligaments attach arytenoid cartilages to the thyroid cartilage
• True vocal cords or folds
– Composed of elastic fibers that form mucosal folds
– The medial opening between them is the glottis
– They vibrate to produce sound as air rushes up from the lungs
• False vocal cords or Vestibular folds
– Mucosal folds superior to the true vocal cords
– Have no part in sound production
 Thyroid and cricoid cartilages maintain an open
passageway for air movement
 Epiglottis and closure of vestibular folds prevent
swallowed material from moving into larynx
 Vocal folds are primary source of sound production
 The pseudostratified ciliated columnar epithelium traps
debris, and moves into pharynx, preventing their entry into
the lower respiratory tract
•
•
•
•
•
•
Trachea (wind pipe):
Is membranous tube attached to larynx
Consists of dense regular connective tissue and smooth muscle
Supported by 15-20 C-shaped hyaline cartilage rings
Absent on posterior side
Posterior surface contains elastic ligamentous membrane and bundles of
smooth muscle called the trachealis muscle
• Contracts during coughing, causes air to move inside trachea, helps expel
mucus
• Trachea:
• Inner lining of trachea contains pseudostratified ciliated
columnar epithelium with goblet cells
• Mucus traps debris, cilia push it superiorly toward larynx and
from which they enter pharynx and are swallowed
• Trachea:
• Trachea is 10-12 cm long, 12 mm diameter
• Extend from larynx to 5th thoracic vertebrae
• Divides to form
– Left and right primary bronchi
– Carina: cartilage at bifurcation
Lower Respiratory Tract
• Trachea
– Tracheal cartilages and
carina
– Lined with
pseudostratified ciliated
columnar epithelium
– Goblet cells
– Horseshoe shaped
hyaline cartilage
– Trachealis muscle
posterior
esophagus
trachealis
muscle
hyaline
cartilage
Pseudostratified
ciliated
columnar
epithelium
adventitia
Bronchial Tree
• Primary Bronchi
– Rt. Bronchus is
shorter, wider and
steeper than the left
– Same wall structure as
trachea
– Cartilage in plates in
smaller passageways
– Branch into secondary
and tertiary bronchi
(R) primary
bronchus
(L) primary
bronchus
Bronchial Tree
• Trachea  (R) and (L) primary
bronchi  secondary (lobar)
bronchi  tertiary (segmental)
bronchi  smaller bronchi 
bronchioles  terminal
(R) primary
bronchus
bronchioles  respiratory
bronchioles  alveolar duct 
alveolar sac  alveolus
(L) primary
bronchus
trachea
Bronchial Tree
• Bronchioles
– No cartilage
– No cilia or mucous
producing cells
– Epithelium changes to
simple columnar
• Terminal Bronchioles
– Simple cuboidal epithelium
– Lead into respiratory
bronchioles
terminal
bronchiole
Bronchial Tree
• Respiratory Bronchioles
alveoli
– Lead into alveolar ducts
• Alveoli
– Simple squamous epithelium
– May open into an alveolar sac
– Where gas exchange takes
place capillaries
alveolar
sac
respiratory
bronchiole
Alveoli
• Septal Cells (type II alveolar cells)
– Produce pulmonary surfactant
• Dust Cells
– Macrophages in alveoli
– Phagocytize bacteria, dirt,
foreign particles
• Respiratory Membrane=
– Squamous alveoli epithelium +
alveolar basement membrane +
endothelium of capillary walls
– Gas on one side, blood on
other
– Gas diffuses easily
 Trachea divides into two
primary bronchi
 Primary bronchi divide into
secondary bronchi (one/lobe)
 Right lung - 3 lobes
 Left lung – 2 lobes
 Sec. bronchi then divide into
tertiary bronchi
 Tertiary bronchi subdivide into
smaller and smaller bronchi then
into bronchioles (less than 1 mm
in diameter), then finally into
terminal bronchioles
 Approx. 16 generations of
branching occur from trachea to
terminal bronchioles
• As conducting tubes become smaller, structure of their
walls changes:
– Cartilage support structures change:
– Main bronchi are supported by C-shaped cartilage
– In lobar bronchi, C-shaped cartilages are replaced with
cartilage plates
– As bronchi becomes smaller, amount of cartilage
decreases, amount of smooth muscle increases
– smooth muscle controls tube diameter, change the
volume of air moving through them
– Epithelium types change:
– Bronchi are lined with pseudostratified ciliated
columnar epithelium
– Larger Bronchioles are lined with ciliated simple
columnar epithelium
– Terminal bronchioles – ciliated simple cuboidal
epithelium
– Trachea to terminal bronchioles are ciliated for removal
of debris, Traps debris and moves it to larynx
Respiratory Zone:
Respiratory Bronchioles to Alveoli
 Respiratory zone: site for gas exchange
– Respiratory bronchioles branch
from terminal bronchioles
– Respiratory bronchioles give rise to
alveolar ducts
– Alveolar ducts end as alveolar sacs
composed of alveoli
– Alveoli – are small air-filled
chambers where gas exchange
between air and blood takes place
• Approximately 300 million alveoli:
– Occupy most of the lungs’ volume
– Provide tremendous surface area for
gas exchange
• Alveoli: Elastic fibers surround the
alveoli
• Allow alveoli to expand during
inspiration
• Recoil during expiration
• Alveolar ducts and alveoli consist of
simple squamous epithelium
• Epithelium is not ciliated, but debris
from air is removed by
macrophages
• Wall of Alveoli is very thin
• Two types of cell forms the wall
Type I pneumocytes: Thin squamous
epithelial cells
– forms 90% of surface of alveolus
– Gas exchange between alveolar air
and blood takes place through these
cells
Type II pneumocytes: Round to cubeshaped secretory cells. Produce
surfactant (mixture of lipoprotein
molecules)
– Makes easier for alveoli to expand
during inspiration
• Gas exchange takes place between air and
blood in respiratory membrane of lungs
• Formed by alveolar walls and pulmonary
capillaries
•
Respiratory membrane is very thin for
diffusion of gases. Consists of:
– Thin layer of fluid lining the alveolus with
surfactant
– Alveolar epithelium composed of simple
squamous epithelium
– Basement membrane of the alveolar
epithelium
– Thin interstitial space
– Basement membrane of the capillary
endothelium
– Capillary endothelium composed of
simple squamous epithelium
• Two lungs: Principal organs of respiration
– Base sits on diaphragm, apex at the top
– Hilus on medial surface where bronchi and blood vessels enter or exit the
lung
– Right lung: three lobes. Lobes separated by fissures
– Left lung: Two lobes
• Divisions
– Lobes (supplied by secondary bronchi)
– Lobes are subdivided into bronchopulmonary segments
– (supplied by tertiary bronchi), separated by connective tissues
– R. Lung – 10 bronchopulmonary segments
– L. Lung – 9 Broncho pulmonary segments
– Broncho pulmonary segments are subdivided into lobules (supplied by
bronchioles)
• Thoracic wall consists of 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
• Diaphragm and other skeletal muscles associated with thoracic wall
are responsible for respiration
• Inspiration: Muscles of inspiration
include diaphragm, external
intercostals, pectoralis minor,
scalenes
• Diaphragm: dome-shaped
• Quiet inspiration: Contraction of
diaphragm
– accounts for 2/3 of increase in
size of thoracic volume.
– Other muscles also increase
thoracic volume by elevating ribs
– Pressure decreases
– Air flows in
• Expiration: muscles that depress the ribs and sternum: such as
abdominal muscles and internal intercostals
• Quiet expiration: relaxation of diaphragm and external intercostals
with contraction of abdominal muscles
• Causes decrease in thoracic volume
 Each lung is surrounded by
pleural cavity formed by the
pleural membranes Filled
with pleural fluid
 Visceral pleura: covers the
surface of lung
 Parietal pleura: covers the
internal thoracic wall
 Pleural fluid: acts as a lubricant and helps hold the two
membranes close together (adhesion).
• Two sources of blood to lungs:
– Two blood flow routes to the lungs exist:
– Pulmonary artery brings deoxygenated blood to lungs from right side of
heart to be oxygenated
– After oxygenated, Blood leaves from lung via the pulmonary veins and
returns to the left side of the heart
– Oxygenated blood flows from thoracic aorta through bronchial arteries
to capillaries
– Oxygenated blood travels to the tissues of the bronchi
– Part of this now deoxygenated blood exits through the bronchial veins
to the azygous venous system
Lymphatic Supply
• Two lymphatic supplies: superficial and deep lymphatic
vessels. Exit from hilus
– Superficial lymphatic vessels : drain lymph from superficial lung tissue
& visceral pleura
– Deep lymphatic vessels: drain lymph from bronchi and associated
connective tissues
– No lymphatics vessels are present in the walls of alveoli
• Breathing, or pulmonary ventilation, consists of two phases
– Inspiration – air flows into the lungs
– Expiration – gases exit the lungs
• Air moves from area of higher pressure to area of lower
pressure
F = P1 - P2
R
• F = airflow (ml/min.) in a tube
•
•
•
P1 = pressure at one point
P2 = pressure at point two
R = resistance to airflow
• For eg. During inspiration, air pressure is greater outside the body than in
alveoli
• And air flows through trachea and bronchi to alveoli
 Boyle’s Law: P = k/V
 P = gas pressure
 V = volume
 k = constant at a given temperature
 Pressure in a container, such as thoracic cavity or alveolus
is inversely proportional to volume
 When volume increases, pressure decreases
 When volume decreases, pressure increases
• Movement of air into and out of lungs results from
changes in thoracic volume which changes alveolar
volume
• Changes in alveolar volume produce changes in
alveolar pressure
• If barometric air pressure (atmospheric air pressure) is
greater than alveolar pressure
(PB – Palv), then air flows into the alveoli
• End of expiration:
•PB = Palv
• no movement of air into or out of lung
• During Inspiration:
• Diaphragm contracts, & increases
thoracic volume
• lungs expand, & increases alveolar
volume & decreases alveolar pressure
• PB is more than Palv
• Air flows into lungs
• End of Inspiration:
• Palv = PB
• No air movement takes place
• During expiration:
• Diaphragm relaxes, thoracic volume
decreases
• Results in decreased alveolar volume
& increased alveolar pressure
• Palv is greater than PB
• Air moves out of the lungs
 Two factors can change alveolar volume
 Lung Recoil
 Pleural Pressure




Lung Recoil
Is decrease in size of an expanded lung
Lung size decreases as alveoli size decreases
Alveoli decreases in size for two reasons:
– Elastic recoil: caused by elastic fibers in the alveolar walls
– Surface tension: surface tension of film of fluid that lines the
–
–
–
–
alveoli
surface tension occurs between water and air at the boundary
polar water molecules have great attraction for each other than air
tends to form water droplet
Causes alveoli to collapse
Surfactant: Reduces tendency of lungs to collapse
by reducing surface tension
Surfactant is a mixture of lipoprotein molecules
produced by type II pneumocytes
 Forms layer over the surface of the fluid and reduce
surface tension
Infant Respiratory distress syndrome (hyaline
membrane disease): Common in infants with
gestation age of less than 7 months.
 Not enough surfactant produced
 Cortisol is given to pregnant women – stimulate
surfactant synthesis
 Pleural pressure (Ppl) is the pressure in
the pleural cavity
 When pleural pressure is less than
(negative pleural pressure) alveolar
pressure, alveoli expand
 eg. Balloon expands when outside
pressure is less than inside pressure
 Pneumothorax is an opening between
pleural cavity
 caused from penetrating trauma by knife,
bullet, broken rib etc.
 Pleural pressure increases & equal to
barometric air pressure
 Alveoli do not expand, lungs collapses
 symptoms: chest pain, shortness of breath
• In respiratory physiology, small pressure
is expressed in cm of H2O. Pressure of 1
cm H2O is .74 mm Hg
• Changes during Inspiration:
• At the end of normal expiration, pleural
pressure is – 5cm H2O and alveolar
pressure = barometric pressure (0 cm H2O)
• During inspiration, pleural pressure
decreases to -8 cm H2O , thoracic cavity
volume increases, lungs expand, increased
lung recoil, alveolar volume increases, Palv
is less than PB, air flows into lungs
• By the end of inspiration Palv = PB
• Changes during Expiration:
• Pleural pressure increases, thoracic volume
decreases , decreased lung recoil
• Alveolar volume decreases, Palv is more than
PB, air flows out of lung
• As air flows out of lung Palv = PB
 Compliance: Is a 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)
– Increased resistance to airflow caused by airway obstruction
(asthma, bronchitis, lung cancer)
– Deformities of the thoracic wall that reduce the ability of the
thoracic volume to increase (scoliosis)
 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 (1100 mL at rest)
 Residual volume: volume still remaining in respiratory
passages and lungs after most forceful expiration (1200 mL)
• The sum of two or more pulmonary volumes
• Inspiratory capacity: tidal volume plus inspiratory
reserve volume (approx. 3500 ml at rest)
• Functional residual capacity: expiratory reserve volume
plus residual volume (approx. 2300 ml at rest)
• Vital capacity: sum of inspiratory reserve volume, tidal
volume, and expiratory reserve volume (approx. 4600 ml)
• Total lung capacity: sum of inspiratory and expiratory
reserve volumes plus tidal volume and residual volume
(approx. 5800 ml)
Lung Volumes, and Lung Capacities
• Minute ventilation: total air moved into and out of respiratory
system each minute
• = tidal volume X respiratory rate
• Respiratory rate (respiratory frequency): number of breaths
taken per minute
• Tidal volume = 500 ml
• Respiratory rate = 12 breaths/min
• Minute ventilation = 6 L/min
• Dead space: Part of respiratory system where gas exchange does
not takes place
• Anatomic dead space: Measures approx. 150 ml.
• Formed by nasal cavity, pharynx, larynx, trachea, bronchi,
bronchioles, and terminal bronchioles
• Physiological dead space: anatomic dead space plus the volume
of any alveoli in which gas exchange is less than normal.
• Emphysema and physiological dead space:
• Alveolar walls degenerate – patients with emphysema
• small alveoli combine – forms large alveoli
• Forms alveoli with large volume and less surface area
• less gas exchange
• increases physiological dead space
• Alveolar ventilation (VA): volume of air available for gas
exchange/minute
VA = f (VT – VD), f = respiratory rate
VT = tidal volume, VD = dead space
 Ventilation supplies atmospheric air to alveoli
 Diffusion of gases between alveoli and blood in pulmonary
capillaries takes place
 Physical Principles of Gas Exchange:
 Dalton’s Law of Partial Pressures
 Total pressure exerted by a mixture of gases is the sum of the
pressures exerted independently by each gas in the mixture
 Pressure exerted by each type of gas in a mixture is Partial
pressure of that gas
Basic Properties of Gases: Henry’s Law
• When a mixture of gases is in contact with a liquid, each gas
will dissolve in the liquid in proportion to its partial pressure
• The amount of gas that will dissolve in a liquid also depends
upon its solubility
Conc. of dissolved gas = Pressure of gas x solubility coefficient
– Carbon dioxide is the most soluble
– Oxygen is 1/20th as soluble as carbon dioxide
– Nitrogen is practically insoluble in plasma

Diffusion of gases through the respiratory membrane
depends upon:
 Membrane thickness: The thicker, the lower the
diffusion rate
 Inflammation of lung tissues such as tuberculosis,
pneumonia cause fluid accumulation around alveoli
 Diffusion coefficient of gas: Is a measure of how
easily a gas diffuses through a liquid or tissue
 CO2 is 20 times more diffusible than O2
 Surface area. Diseases like lung cancer reduce
available surface area
 Small decrease in surface area affect gas exchange
 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
 Increase alveolar ventilation increase partial gradient
for O2 and CO2, increase gas exchange
Relationship Between Alveolar Ventilation and
Pulmonary Capillary Perfusion
 Increased ventilation or increased pulmonary capillary blood
flow increases gas exchange
– Low PO2 causes arterioles to constrict & reduce blood flow
– & reroutes blood to higher PO2 area of alveoli
– where oxygen pickup is more efficient
– High PO2 causes arterioles to dilate, increase blood flow into
pulmonary capillaries
– In other tissues of the body, low PO2 causes arterioles to
dilate to deliver more blood to the tissues
Oxygen Diffusion Gradients
– Oxygen moves from alveoli into blood
– Because partial pressure oxygen (PO2)
of alveoli is 104 mm Hg
– & pulmonary capillary is 40 mm Hg
– O2 diffuse from higher to lower
pressure gradient
– And reaches in equilibrium state in less
than .25 sec
– PO2 at venous end decreases because
of mixing with deoxygenated blood
– Then oxygen moves from tissue
capillaries into the tissues
Carbon Dioxide Diffusion Gradients
– CO2 moves from tissues
into tissue capillaries
– Because PCO2 in tissue is
46 mm Hg and tissue
capillaries is 40 mmHg
– Reaches equilibrium at
venous end of capillaries,
PCO2 is 45 mm Hg
– Moves from pulmonary
capillaries into the alveoli
• Hemoglobin and Oxygen Transport
• Molecular oxygen is carried in the blood in two ways:
– 98.5% O2 bound to Hb within red blood cells
– 1.5% O2 Dissolved in plasma
• Each Hb molecule binds four oxygen atoms
• The hemoglobin-oxygen combination is called oxyhemoglobin (HbO2)
• Hemoglobin that has released oxygen is called reduced hemoglobin (HHb),
or deoxyhemoglobin
Lungs
HbO2 + H+
HHb + O2
Tissues
• Saturated hemoglobin: when all four hemes of the molecule
are bound to oxygen
• Partially saturated hemoglobin: when one to three hemes are
bound to oxygen
• The rate that hemoglobin binds and releases oxygen is regulated
by:
– PO2, temperature, blood pH, PCO2, and the concentration of
BPG (an organic chemical)
• Effect of PO2
• Hemoglobin saturation plotted against PO2
produces a oxygen-hemoglobin dissociation
curve
• At 104 mm Hg PO2, Hb is 98% saturated
• 98% saturated arterial blood contains 20 ml
oxygen per 100 ml blood (20 vol %)
• Decrease in PO2 has small effect on Hb
saturation
• Hb saturation curve shows that:
• Hemoglobin is almost completely saturated
at a PO2 of 70 mm Hg
• Oxygen loading and delivery to tissue is
adequate when PO2 is below normal levels
Hemoglobin Saturation Curve
• Only 20–25% of bound oxygen is
unloaded during one systemic
circulation
• Hb of venous blood is still 75%
saturated with O2 after one systemic
circulation
• If oxygen levels in tissues drop
(vigorous exercise):
– More oxygen dissociates from
hemoglobin and is used by cells
Bohr Effect
• Effect of pH on oxygen-hemoglobin dissociation
curve – Bohr effect
• As pH of blood declines, amount of oxygen bound to
hemoglobin also declines
• Because decreased pH yields increase in H+
• H+ combines with protein part of hemoglobin and change
its shape and oxygen cannot bind to hemoglobin
• Increase in blood pH – increase in hemoglobin`s ability to
bind oxygen
Effects of CO2 and Temperature
• Increase in PCO2 causes decrease in pH
• Carbonic anhydrase causes CO2 and water to combine
reversibly and form carbonic acid (H2CO3) which ionizes
to H+ and HCO3CO2 + H2O carbonic anhydrase H2CO3
H+ + HCO3-
• Increase temperature: decreases tendency for oxygen to
remain bound to hemoglobin
• As metabolism goes up, temp. rises, more oxygen is
released to the tissues from Hb
• Less metabolism, low temp., less O2 is released from Hb
Effect of BPG
• 2,3-bisphosphoglycerate (BPG): released
by RBCs as they break down glucose for
energy
• Binds to hemoglobin
• And reduces affinity for oxygen
• and increases release of oxygen
Shifting the Curve
• In tissues - When Hb affinity for oxygen decreases – O2-Hb
dissociation curve shifted to right and releases more oxygen
• eg. pH decrease, PCO2 increase, temp. increase – curve shifts to Right
• But in the lungs, the curve shifts to left because of lower CO2 level,
lower temp.
• Hb affinity for oxygen increases and saturated easily
Fetal Hemoglobin
• Fetal hemoglobin is very efficient at picking up oxygen from maternal
hemoglobin for several reasons:
• Concentration of fetal hemoglobin is 50% greater than concentration of
maternal hemoglobin
• Oxygen-hemoglobin dissociation of fetal hemoglobin is left of maternal; i.e.,
fetal hemoglobin can hold more oxygen than maternal Hb
• Movement of carbon dioxide out of fetal blood causes the fetal oxygenhemoglobin dissociation curve to shift to the left
• Simultaneously, movement of carbon dioxide into mother’s blood causes
maternal oxygen-hemoglobin dissociation curve to shift to the right
• Carbon dioxide is transported in the blood in three forms
– Dissolved in plasma – 7 to 10%
– Chemically bound to hemoglobin – 23% is carried in RBCs
as carbaminohemoglobin
– Bicarbonate ion in plasma – 70% is transported as
bicarbonate (HCO3–)
Transport and Exchange of Carbon Dioxide
• CO2 exchange in Tissues:
• CO2 diffuses from tissues to plasma and then to
•
•
•
•
•
•
•
•
•
blood
In RBCs – CO2 reacts with water – form carbonic
acid
Carbonic acid dissociates & form bicarbonate ion
and H+
Bicarbonate quickly diffuses out from RBCs into
the plasma
Removing bicarbonate ion from RBCs promotes
CO2 transport
The chloride shift – to counterbalance the charge,
Cl– move from the plasma into the RBCs
H+ combines with Hb and releases O2 – Bohr
effect
O2 diffuses from RBCs to plasma to tissues
CO2 combines with Hb
Smaller the amount of O2 bound to Hb, greater the
amount of CO2 bind to Hb – Haldane effect
Transport and Exchange of Carbon Dioxide
• Gas exchange in Lungs:
•
•
•
•
•
•
•
•
•
•
•
At the lungs, these processes are reversed
CO2 diffuses from RBCs – plasma – alveoli
As CO2 levels in RBCs decreases
In presence of carbonic anhydrase Carbonic acid
is converted into CO2 & H2O
In response, Bicarbonate ion combines with H+
and forms Carbonic acid
As HCO3- and H+ conc. decreases, HCO3diffuses in RBCs and Cl- diffuses out
O2 diffuses – plasma - RBCs
O2 binds to Hb – releases H+
Release of H+ increases Hb affinity for oxygen
CO2 releases from Hb
Diffuses out of RBCs – plasma- alveoli
Hb binds to O2, releases
more CO2 – Halden effect
Influence of Carbon Dioxide on Blood pH
• The carbonic acid–bicarbonate buffer system resists blood pH
changes
• If hydrogen ion concentrations in blood begin to rise, excess
H+ is removed by combining with HCO3–
• If hydrogen ion concentrations begin to drop, carbonic acid
dissociates, releasing H+
CO2 + H2O carbonic anhydrase H2CO3
H + + HCO3-
 Basic rhythm of ventilation is controlled
by neurons within medulla oblongata in
brain
 Medullary respiratory center:
Consists of
– Two Dorsal respiratory groups
stimulate contraction of diaphragm
– Ventral groups stimulate the
intercostal and abdominal muscles
• Pontine (pneumotaxic center)
respiratory group:
– collection of neurons in pons
– Involved with switching between
inspiration and expiration
– fine-tuning the breathing pattern
Rhythmic Ventilation
• Starting inspiration
– Medullary respiratory center neurons are continuously active
– Center receives stimulation from receptors that monitor blood gas levels,
blood temp., movement of muscles and joints
– Combined input from all sources causes action potentials to stimulate
respiratory muscles
• Increasing inspiration
– Once inspiration begins, More and more neurons are activated
• Stopping inspiration
– Neurons stimulating muscles of respiration also responsible for stopping
inspiration
– Receive input from pontine group and stretch receptors in lungs
– Inhibitory neurons activated and relaxation of respiratory muscles
results in expiration
Chemical Control of Ventilation
•
Respiratory system maintains blood oxygen, CO2 conc.
Blood pH within normal range
• Chemoreceptors:
• Are specialized neurons that respond to changes in
chemicals in solution
– Central chemoreceptors: Located in chemo sensitive
area of the medulla oblongata; and connected to
respiratory center
– Peripheral chemoreceptors: Found in carotid and
aortic bodies. Connected to respiratory center by cranial
nerves IX and X
Chemical Control of Ventilation
• Effect of pH: chemo sensitive area of medulla
oblongata and carotid and aortic bodies respond to
blood pH changes
– Chemo sensitive areas respond indirectly through
changes in carbon dioxide
– Carotid and aortic bodies respond directly to pH
changes
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
– Hypercapnia: greater-than-normal amount of carbon
dioxide
– Hypocapnia: lower-than-normal amount of carbon
dioxide
• Chemo sensitive area in medulla oblongata and
Carotid and aortic bodies respond to changes in
CO2 level
• Vital capacity and maximum minute ventilation decreases
• Residual volume and dead space increase
• Ability to remove mucus from respiratory passageways
decreases
• Gas exchange across respiratory membrane is reduced