Transcript Presentation Title - York Technical College

Chapter 24 – Respiratory
Physiology
Dr. Kim Wilson
Respiratory Physiology
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Definition: complex, coordinated processes
that help maintain homeostasis
Primary goal of respiration = adequate and
efficient regulation of gas exchange
between blood cells and under changing
conditions
Supplies O2 and removes CO2 from body
cells
Respiratory system is composed of an
integrated set of regulated processed
including:
– 1. External respiration
• Pulmonary ventilation (breathing)
• Pulmonary gas exchange
– 2. Transport of gases by the blood
– 3. Internal respiration
• Systemic tissue gas exchange
• Cellular respiration
– 4. Regulation of respiration
Pulmonary Ventilation
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Def: respiratory cycle (ventilation,
“breathing”)
– Inspiration: movement of air into the
lungs
– Expiration: movement of air out of the
lungs
Primary principle of ventilation
– The pulmonary ventilation mechanism
must establish two gas pressure
gradients
• Inspiration – one in which the
pressure within the alveoli of the
lungs is lower than atmospheric
pressure
• Expiration - one in which the
pressure in the alveoli of the lungs is
higher than atmospheric pressure
Pulmonary Ventilation:
Mechanism
– Pressure gradients are established
by changes in the size of the
thoracic cavity
• How? By contraction and
relaxation of muscles
• Based on principle of Boyle’s
law: the volume of gas varies
inversely with pressure at a
constant temperature
• Ventilation is often modeled
by balloon in a jar 
Video Time!
• Pulmonary ventilation video (Interactive Physiology)
Respiratory Cycle
– Air moves into the lungs
when alveolar pressure
drops below atmospheric
pressure
– Contraction of the
diaphragm produces
inspiration 
– Diaphragm contracts and
the thoracic cavity
becomes larger 
– Expansion of the thorax
results in decreased
intrapleural pressure,
leading to decreased
alveolar pressure (Boyle’s
law)
Respiration Video
• Mammalian Respiration:
http://www.mhhe.com/biosci/genbio/elearning/raven6/reso
urces53.mhtml
Mechanism of Inspiration
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STRUCTURAL CHANGES
Diaphragm:
– Contraction - moves
down; increases the size
of the thoracic cavity
from top to bottom
– Relaxation - moves back
up to original position
External Intercostals:
– Contraction - elevate
the ribs; increases the
size of the thoracic
cavity from front to
back and from side to
side
– Relaxation - depress the
ribs
Summary of What Happens
During Inspiration
• 1. Diaphragm and external intercostals contract
• 2. Sternocleidomastoid, pectoralis minor, and serratus anterior muscles
contract
• 3. Volume of thorax increases
• 4. Intrapleural (intrathoracic) and intraalveolar pressure decrease
• 5. Intrathoracic pressure is less than atmospheric pressure
• 6. Air moves into lungs
• 7. Compliance is the ability of the lungs and thorax to stretch
Pulmonary Ventilation:
Expiration
– Process begins when
the inspiratory muscles
are relaxed, which
decreases the size of
the thorax
• Increasing thoracic
volume increases
the intrapleural
pressure and thus
increases alveolar
pressure above the
atmospheric
pressure
• Air moves out of
the lungs when
alveolar pressure
exceeds the
atmospheric
pressure
Summary of What Happens
During Expiration
• 1. Inspiratory muscles relax
• 2. Thorax decreases in size
• 3. Intrathoracic pressure increases
• 4. Intrathoracic pressure is greater than atmospheric pressure
• 5. Air moves out of lungs
• 6. Elastic recoil
• 7. Transpulmonary pressure
Inspiration vs. Expiration
(Summary)
Pressure Changes During
Respiration
• Intrapleural pressure = the pressure between parietal and visceral pleura
• The difference between intrapleural pressure and alveolar pressure is
called transpulmonary pressure
• Intrapleural pressure is ALWAYS less then alveolar pressure and
atmospheric pressure
• Difference in pressure = Pip - Pa
– Inspiration – pressure (Pip) begins at 758 mm Hg
– Expiration – pressure (Pip) begins at 754 mm Hg
– The moment that alveolar pressure decreases from atmospheric level
(drop of 1-3 mm Hg), a pressure gradient forms.
– Table 24-1, pg. 805 shows pressure changes
• Terms:
– Compliance: ability of the lungs and thorax to stretch
– Elastic recoil: tendency of pulmonary tissues to return to a smaller size
after having been stretched; occurs passively during expiration
Rhythm of Ventilation
Pulmonary Volumes
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The volume of air in the lungs must be
normal so normal exchange of oxygen
and carbon dioxide can occur
Spirometer: instrument used to
measure the volume of air exhanged in
breathing
– Tidal volume (TV): amount of air
exhaled after normal inspiration
– Expiratory reserve volume (ERV):
largest volume of additional air that
can be forcibly exhaled (1.0 to 1.2 L
is normal ERV)
– Inspiratory reserve volume (IRV):
amount of air that can be forcibly
inhaled after normal inspiration
(normal IRV is 3.3 L)
– Residual volume: amount of air
that cannot be forcibly exhaled (1.2
L)
Pulmonary
Capacities
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Def: the sum of two or more pulmonary
“volumes”
Vital capacity (VC) = IRV + TV + ERV
VC represents the largest volume of air an
individual can move in and out of the lungs
VC depends on many factors:
– Size of thoracic cavity
– Posture (large VC when standing than lying
down)
– Excess fluids in pleural cavity
– Diseases: Ex. Emphysema causes increased RV
Clinical diagnosis of lung disorders is often based
on inspiratory capacity (IC)
IC = TV + IRV
Functional residual capacity (FRC) = the amount of
air left in the lungs at the end of normal expiration
Total lung capacity (TLC) = total volume of air a
lung can hold
Pulmonary Capacities cont.
– Anatomical dead space: air in passageways that do not participate in
gas exchange
• Only this volume of air takes part in the exchange of gases
between air and blood
• “dead air” because does not descend into any alveoli and can’t
take part in gas exchange
– Physiological dead space: anatomic dead space plus the volume of
any nonfunctioning alveoli (as in pulmonary disease)
– Alveoli must be properly ventilated for adequate gas exchange
• Chronic obstructive pulmonary disease (COPD): some alveoli are
not able to function in gas exchange (“dead space”)
Pulmonary Air Flow
• DEF: rates of air flow into and out of the pulmonary airways
• Spirometry can be used to determine the rate of pulmonary
ventilation or total minute volume
– Total minute volume: volume moved per minute (ml/min)
– Spirometry can also be used to determine:
• Forced expiratory volume (FEV) or forced vital capacity (FVC):
volume of air expired per second during forced expiration (as a
percentage of VC) (Figure 24-12)
• Flow-volume loop: graph that shows flow (vertically) and volume
(horizontally), with the top of the loop representing expiratory
flow volume and the bottom of the loop representing inspiratory
flow volume relations (Figure 24-13)
Pulmonary Gas Exchange
• Dalton’s law provides insight into
understanding of gas exchange
• Partial pressure of gases: pressure
exerted by a gas in a mixture of gases
or a liquid
– Law of partial pressures (Dalton’s
law): the partial pressure of a gas
in a mixture of gases is directly
related to the concentration of
that gas in the mixture and to the
total pressure of the mixture
– Partial pressure = P
– Arterial blood PO2 and PCO2 =
alveolar PO2 and PCO2
Exchange of Gases in the Lungs
• Takes place between alveolar
air and blood flowing through
lung capillaries
– Four factors determine
the amount of oxygen
that diffuses into blood
1. The oxygen pressure
gradient between
alveolar air and blood
2. The total functional
surface area of the
respiratory
membrane
3. The respiratory
minute volume
4. Alveolar ventilation
Exchange of Gases in the
Lungs
• STRUCTURAL FACTORS that
facilitate oxygen diffusion
from the alveolar air to the
blood
• The walls of the alveoli and
capillaries form only a very
thin barrier for gases to
cross.
• The alveolar and capillary
surfaces are large.
• The blood is distributed
through the capillaries in a
thin layer so that each red
blood cell comes close to
alveolar air.
How Blood Transports Gases
• Oxygen and carbon dioxide are transported as solutes and as
parts of molecules of certain chemical compounds
• One gas molecules are bound to other molecules, their
plasma concentration decreases allowing for more gas
diffusion into plasma
– Enables large amounts of gases to be transported
Hemoglobin (Hb)
• Review of Hemoglobin (Hb)
– Composed of four polypeptide chains (two alpha chains, two beta
chains), each with an iron-containing heme group
– CO2 can bind to amino acids in the chains, and oxygen can bind to iron
in the heme groups
Transport of Oxygen
– Oxygen is transported as
oxyhemogloblin (oxygen and
hemoglobin)
– Hb increases the oxygencarrying capacity of blood
– Oxygen is transported as a
solute (dissolved)
– Oxygenated blood contains
approximately 0.3 ml of
dissolved O2 per 100 ml of
blood
Transport of CO2
• Transport of carbon dioxide
– A small amount of CO2 dissolves
in plasma and is transported as
a solute (10%)
– Less than one fourth of blood
CO2 combines with NH2 (amine)
groups of Hb and other proteins
to form carbaminohemoglobin
(20%)
– CO2’s association with Hb is
accelerated by an increase in
blood PCO2
– More than two thirds of the CO2
is carried in plasma as
bicarbonate ions (70%)
CO2 Transport in the Blood
Video Time!
• Gas transport!
Systemic Gas Exchange
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WHERE? In tissues takes place between
arterial blood flowing through tissue
capillaries and cells
– 02 diffuses from alveolar air ---> blood
in lung caps
– C02 diffuses from blood in lung caps --->
alveolar air
– How?
• Oxygen diffuses out of arterial
blood because the oxygen pressure
gradient favors its outward
diffusion
• As dissolved oxygen diffuses out of
arterial blood, blood PO2
decreases, which accelerates
oxyhemoglobin dissociation to
release more oxygen to plasma for
diffusion to cells
Transport of Gases
• What determines whether hemoglobin prefers to carry O2 or CO2?
• If blood PO2 is increased  Hemoglobin carries O2
– (increased blood PO2 increases the assoc. between
hemoglobin and O2)
• If blood PCO2 is increased  Hemoglobin carries CO2
– (increased blood PCO2 increases the assoc. between
hemoglobin and CO2)
Systemic Gas Exchange
• CO2 exchange between tissues and
blood takes place in the opposite
direction from oxygen exchange
– Bohr effect: increased PCO2
decreases the affinity between
oxygen and Hb (Figure 24-29)
– Haldane effect: increased CO2
loading caused by a decrease in
PO2
Video Time!
• Gas Exchange
Regulation of Pulmonary
Function
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Respiratory control centers: the
main integrators controlling the
nerves that affect the inspiratory
and expiratory muscles are
located in the brainstem
– Medullary rhythmicity
center: generates the basic
rhythm of the respiratory
cycle
• Consists of two
interconnected control
centers
– Inspiratory center
stimulates
inspiration
– Expiratory center
stimulates
expiration
Regulation of Pulmonary
Function (cont.)
– The basic breathing rhythm
can be altered by different
inputs to the medullary
rhythmicity center
• Input from the
apneustic center in the
pons stimulates the
inspiratory center to
increase the length and
depth of inspiration
• Pneumotaxic center in
the pons inhibits the
apneustic center and
inspiratory center to
prevent overinflation of
the lungs
Image source:
http://www.physioweb.org/respiration/control_breath.html
Video Time
• “Control of Respiration”
Factors that Influence
Breathing
• Sensors from the nervous system provide feedback to the
medullary rhythmicity center
– Changes in the PO2, PCO2, and pH of arterial blood influence the
medullary rhythmicity area
• PCO2 acts on central chemoreceptors in the medulla—if it increases, the
result is faster breathing; if it decreases, the result is slower breathing
• A decrease in blood pH stimulates peripheral chemoreceptors in the
carotid and aortic bodies and, even more so, stimulates the central
chemoreceptors (because they are surrounded by unbuffered fluid)
• Arterial blood PO2 presumably has little influence if it stays above a
certain level
REGULATION OF PULMONARY
FUNCTION (cont.)
– Arterial blood pressure controls breathing
through the respiratory pressoreflex
mechanism
– Hering-Breuer reflexes help control
respirations by regulating depth of
respirations and the volume of tidal air
– Cerebral cortex influences breathing by
increasing or decreasing the rate and
strength of respirations
• Ventilation and perfusion (Figure 24-33)
– Alveolar ventilation: air flow to the alveoli
– Alveolar perfusion: blood flow to the alveoli
– Efficiency of gas exchange can be maintained
by limited ability to match perfusion to
ventilation (e.g., vasoconstricting arterioles
that supply poorly ventilated alveoli and
allow full blood flow to well-ventilated
alveoli)
Putting it all Together
• Respiratory system -- provides O2 for, and removes CO2 from, body cells
• Circulatory system--gas exchange
• Nervous system--respiratory regulation
• Muscular system--flow of air
• Skeletal system--expansion and contraction of thorax
• Immune system--protection of respiratory system