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RESPIRATORY PHYSIOLOGY
Anatomy and Physiology
Pulmonary Ventilation- breathing

Boyle’s Law- volume of a gas caries
inversely with pressure at a constant
temperature
Defines the relationship between gas
pressure and volume
– volume decrease  pressure increases
– Volume increase  pressure decreases
Respiration

What is respiration?
– External respiration – exchange of O2 and
CO2 between respiratory surfaces and the
blood (breathing)
– Internal respiration – exchange of O2 and
CO2 between the blood and cells
– Cellular respiration – process by which
cells use O2 to produce ATP
The Respiratory Muscles
Figure 23–16c, d
Inspiration

Expansion of thorax
(increased volume)
leads to decreased
intrapleural
pressure, causing
air to move inside
the lung
3 Muscle Groups of Inhalation
1.
Diaphragm:
– contraction draws air into lungs
– 75% of normal air movement
2.
External intracostal muscles:
– assist inhalation
– 25% of normal air movement
3.
Accessory muscles assist in elevating
ribs:
–
–
–
–
sternocleidomastoid
serratus anterior
pectoralis minor
scalene muscles
1.
2.
3.
Contraction of diaphragm
Contraction of external intercostals
Contraction of sternocleidomastoid, pectoralis
minor, serratus ventralis/ant.
Expiration

Inspiratory muscles
relax, causing
decrease in size of
thorax and increase
in intrapleural
press., releasing air.
Factors Influencing Pulmonary
Ventilation

Airway resistance: friction/drag
– Diameter of airways

Alveolar surface tension  shrinks alveoli
– Surfactant: detergent-like film of lipids and proteins
that reduces surface tension
– IRDS: Infant respiratory distress syndrome

Lung compliance: ease by which the lungs can
be expanded
– Reduced in fibrosis
– Blocking smaller pathways  pneumonia and
bronchitis
Pulmonary Volumes (1-4)
1. Tidal volume (TV)- volume of air exhaled normally
after typical inspiration. ~500 ml
2. Expiratory Reserve Volume (ERV)- largest
additional volume of air that one can forcibly expire
after expiring tidal air. ~1000-1200 ml
3. Inspiratory Reserve Volume (ERV)- amount of air
that can be forcibly inspired over and above normal
inspiration ~2100-3200 ml
4. Residual Volume (RV)- amount of air that cannot be
forcibly expired ~ 1200 ml
Pulmonary Volumes
5. Vital Capacity (VC)= IRV + TV + ERV

The largest volume of air that an individual
can move in and out of the lungs.

Determined by measuring the largest
possible expiration after the largest possible
inspiration.

In general, larger people have larger VC.
Lung Volumes: Spirometry
Review Lung & Breathing Volumes
What’s going on here?
C. Exchange of Gases in the Lungs
1.
2.
3.
4.
Gases move both ways
Oxygen enters blood
from the alveolar air
from an area of higher to
lower concentration
Carbon dioxide move
from the blood into the
alveoli in the same way
This 2 way exchange
converts deoxygenated
blood to oxygenated
blood
External Respiration
Exchange of O2 and CO2 between
alveoli and blood
 Partial pressure of O2 higher in alveoli
than blood so O2 diffuses into blood
 Partial pressure of CO2 higher in blood
than alveoli, so CO2 moves into alveoli
in opposite direction and gets exhaled
out

Form meets functions
Internal Respiration





Exchange of O2 and CO2 between blood
and tissues
Pressure of O2 higher in blood than
tissues so O2 gets release into tissues.
Pressure of CO2 higher in tissue than in
blood so CO2 diffused in opposite
direction into blood.
CO2 Is a waste product
O2 Is used in cellular respiration
D. How Blood Transports Gases
Large volumes of gases can be
transported by binding to proteins
rather than dissolving in plasma
Hemoglobin in red blood cells is a
quaternary protein with 2 alpha
and 2 beta chains associated with
iron-containing heme groups.


–
–
O2 can combine with Fe
CO2 can combine with the alpha and
beta chains
How Blood Transports Gases

Carbon dioxide
– 70% as bicarbonate ion (HCO3-) dissolved in plasma
– 23% bound to hemoglobin
– 7% as CO2 dissolved in plasma

Oxygen
– 99% bound to hemoglobin
– 1% as O2 dissolved in plasma

Carbon monoxide poisoning occurs because
CO binds to hemoglobin more readily than O2
Hamburger's phenomenon  Chloride Shift
E. Regulation of Breathing
1. Respiratory centers- in brainstem;
control nerves that affect breathing
muscles
1. medullary rhythmic center with inspiratory and
expiratory centers
2. apneustic center in the pons
3. pneumontaxic center in the pons
Control of Breathing
Regulated by 4 factors:
1. changes in concentration of O2 and CO2
 increase CO2 sends message to increase
breathing frequency and breath more
deeply
2. changes in blood pH
3. arterial blood pressure
4. Cerebral cortex
nervous control - natural flight response
triggers increased rate of breathing
Control of Breathing

Breathing is regulated by the rhythmicity
center in the medulla of brain
rhytmicity
center

Medulla stimulates inspiratory muscles
(diaphragm & external intercostal muscles)
Control of Breathing

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The most important
factor affecting the
rhythmicity center is CO2
 in arterial CO2 causes
 in acidity of
cerebrospinal fluid (CSF)
 in CSF acidity is
detected by pH sensors
in medulla
medulla  rate and
depth of breathing
Why does breathing rate increase
during exercise?
 CO2
levels increase
 Blood becomes acidic
 Aorta sends signals to brain
 Brain stimulates diaphragm to
contract more rapidly
 Therefore, you take in more O2
and release more CO2
Respiratory System at Birth
1.
Before birth:
– pulmonary vessels are collapsed
– lungs contain no air
2.
During delivery:
– placental connection is lost
– blood PO falls
2
– PCO rises
2
3.
At birth:
– newborn overcomes force of surface
tension to inflate bronchial tree and alveoli
and take first breath
Respiratory System at Birth
4.
Large drop in pressure at first breath:
– pulls blood into pulmonary circulation
– closing foramen ovale and ductus
arteriosus
– redirecting fetal blood circulation patterns
5.
Subsequent breaths:
– fully inflate alveoli
3 Effects of Aging on the Respiratory
System
1.
Elastic tissues deteriorate:
– reducing lung compliance
– lowering vital capacity
2.
Arthritic changes:
– restrict chest movements
– limit respiratory minute volume
3.
Emphysema:
– affects individuals over age 50
– depending on exposure to respiratory
irritants (e.g., cigarette smoke)
Respiratory Performance and Age
Figure 23–28