Respiratory system:
anatomy & physiology
Kaiu Prikk
2009 autumn
The respiratory system: TWO LUNGS,
CONDUCTING AIRWAYS
Upper airways:
nose, mouth, larynx, pharynx
Lower airways:
trachea, right & left main bronchi, secondary
bronchi, bronchioles, alveoli
Basic functions of respiratory system:
1. Air distributor
2. A gas exchanger O2, CO2, warming and
humidifying
3. Acid-base balance
4. Phonation
5. Pulmonary defence & metabolism
Respiration is an important homeostatic
mechanism
Defense Mechanisms of respiratory system
The average person (moderately active) during the
daytime breathes about 20,000 liters air/ 24 hours
•small particles < 3 to 5 microns in diameter
penetrate to the deep lung.
Lung defence mechanisms:
1. Structural protection: hears in the nose, cilia in the
upper and lower airways (trap and remove foregin
bodies form airways)
2. Mucosal lining fluid upper and lower airways:
warms and humidifies air
3. Irritant receptors in the nose and airways
(recognize injurious agenst  sneeze or cough
reflex
4. Immune protection: respiratory tract mucosa and
macropahges in alveoli
Pulmonary ventilation & Control of Breathing
Respiratory rate at rest is 15/per minute
Pulmonary ventilation is the exchange of air between the
atmosphere and the lungs.
Breathing process:
-automatic
-controlled subconsciously by the respiratory center at the
base of the brain.
People control their breathing for example during speech,
singing, or voluntary breath holding.
For example: an increased concentration of carbon dioxide is the strongest
stimulus to breathe more deeply and more frequently.
Conversely, when the carbon dioxide concentration in the blood is low, the brain
decreases the frequency and depth of breaths
Respiratory Centers
1. The primary respiratory center: medulla
Function: stimulation of basic inspiration for about 3
seconds and then basic expiration for about 2 seconds (5
sec/breath= 12 breaths/min).
2. Secondary respiratory center:
pons contains 1) the pneumotaxic respiratory center; 2) the
apneustic respiratory center.
Function: Secondary respiratory center: modifies the basic
respiratory rate
The pneumotaxic respiratory center inhibits inspiratory time
and increases breaths per minute.
The apneustic respiratory center has not been clearly
defined, (is postulated to prolong inspiratory time and
reduces breaths per minute).
Respiratory centers in the brain stem
Respiration:
1. External respiration is gas exchange between the lung
alveoli and the blood of the pulmonary circulation. This
process depends on: 1) gas partial pressure differences; 2)
the integrity of lung membranes, 3) blood flow in and out of
the lungs.
2. Internal respiration is the exchange of gas between the
blood and the cells of the body.
This process generally depends on the same factors as
external respiration
Movement of gases between the alveoli, blood and cells depends on the partial
pressure difference of a gas across these regions.
According to the Law of Diffusion, gases always move from a region of high partial
pressure to a region of low partial pressure. If your lungs have a higher gas
pressure than your blood, then the gas will move into your blood and visa versa
Respiration:
1. Quiet
A.Quiet inspiration:
The diaphragm contracts:  causes an increase in
volume of the thorax and the lungs  which causes a
decrease in pressure of the thorax and lungs  air to enter
the lungs, moving down its pressure gradient.
B. Quiet expiration: The diaphragm relaxes  The
elasticity of the muscle tissue and of the lung stroma causes
recoil  returns the lungs to their volume before inspiration
 the reduced volume causes the pressure in the lungs to
increase  air leaves the lungs due to the pressure
gradient.
.
2. Forced
A. Forced inspiration: Other muscles aid in the increase in thoracic
and lung volumes.
The scalenes - pull up on the first and second ribs.
The sternocleidomastoid muscles pull up on the clavicle and
sternum.
The pectoralis minor pulls forward on the ribs.
The external intercostals are especially important because they
spread the ribs apart, thus increasing thoracic volume. It's these
muscles whose contraction produces the "costal breathing" during
rapid respirations
B. Forced Expiration: The muscles aid in reducing the volume of the
thorax and lungs:
The internal intercostals - these compress the ribs together
The abdominus rectus and abdominal obliques: internal
obliques, external obliques- these muscles push the diaphragm up
by compressing the abdomen.
The work of breathing is done by the diaphragm, intercostal muscles, the muscles
in the neck, and the abdominal muscles.
When the diaphragm contracts and moves lower, the chest cavity enlarges,
reducing the pressure outside the lungs. To equalize the pressure, air enters the
lungs.
When the diaphragm relaxes and moves back up, the elasticity of the lungs and
chest wall pushes air out of the lungs
Muscles of inspiration and expiration
Gas exchange
Air movement into and out of the lungs results:
1) differences in pressure brought about by changes in lung
volume.
Inspiration: intrapulmonary pressue < atmospheric presssue
Changes in lung volume occur due to muscle contractions in
the thorax and diaphragm
Ventilation is influenced by the physical properties
of the lungs:
• compliance
• elasticity
• surface tension
Compliance: the tendency of the lungs to expand, is
due to the pulling action exerted by the pleural
membranes.
Expansion is also facilitated by the action of
surfactant in preventing the collapse of the alveoli.
Surface tension: action of surfactant
Elasticity or recoil: is the process by which the lungs
return to their original or resting volume.
Elasticity is due to the elastic stroma of the lungs and
the series elastic elements of the respiratory muscles,
particularly the diaphragm.
Ventilation - Inspiration
Ventilation - Expiration
Alveolus and gas exchange
Respiratory regulation:
Normal values
exchange rates of O2 and CO2 at the tissues and in the
lungs must be equal:
•High pCO2 levels increase O2 dissociation in peripheral
tissues
•Low pO2 causes alveolar capillaries to constrict & send
blood to lobules with high pO2
•High pCO2 levels cause bronchodilation to occur
increasing airflow, reverse
Changes in depth and rate of respiration are regulated by
brain centers
Normal Blood Gases
Arterial
pH 7.35 - 7.45
PaO2 80 to 100 mm Hg (The partial pressure of oxygen that is
dissolved in arterial blood)
PaCO2 35-45 mm Hg (The amount of carbon dioxide dissolved
in arterial blood. Measured. Partial pressure of arterial CO2.)
SaO2 95% to 100% (The arterial oxygen saturation)
B.E. –2 to +2 mEq/lite
(The base excess indicates the
amount of excess or insufficient level of bicarbonate in the system. A
base excess > +3 = metabolic alkalosis a base excess < -3 = metabolic
acidosis
HCO3 22 to 26 mEq/liter (21–28 mEq/L) The calculated
value of the amount of bicarbonate in the bloodstream
Hypoventilation: the state in which a reduced
amount of air enters the alveoli in the lungs
resulting in decreased levels of oxygen and
increased levels of carbon dioxide in the blood.
Hypoventilation can be due to breathing that is
too shallow (hypopnea) or too slow (bradypnea) or
to diminished lung function.
Hyperventilation: is excessive ventilation of the lungs, beyond
what is required to achieve normal arterial blood gases
For example: Rapid or deep breathing in infection, bleeding, or
heart attack
Hyperventilation:
-has little effect on arterial pO2
- no effect on oxygen saturation
- main effect is to lower pCO2 and produce a respiratory
alkalosis and secondary hypocalcaemia
Causes of hyperventilation:
1. Disordered blood chemistry with normal homeostatic
response to stimulate the brain's respiratory centre, increasing
rate and depth of breathing.
2. Voluntary and conscious act.
3. Psychological response to anxiety or stress, with little
awareness.
Dyspnea: Difficult breathing; shortness of breath.
Dyspnea is a sign of serious disease of the airway,
lungs, or heart.
(Resting) Tidal Volume (TV): This is the volume of air taken into the lungs
when you inhale. Tidal volume increases with exercise or activity.
Residual Volume (RV): is the volume of air left in the lungs at the end of
maximal expiration (ie. the volume of air which you cannot voluntarily
exhale from your lungs).
Vital Capacity (VC): is the volume of air expelled from the lungs during a
maximal forced expiration strating after a maximal forced inspiration.
Total Lung Capacity (TLC): The residual volume (air you cannot expire)
+ vital capacity (total volume available for use) = total lung capacity.
Inspiratory Reserve Volume (IRV): Total lung capacity minus the volume
of air in the lung at the end of a normal inspiration.
Expiratory Reserve Volume (ERV): .is the volume of gas that is expelled
from the lungs during a maximal forced expiration that strats at the end of
normal tidal expiration
Functional Residual Capacity: is the total volume of air
left in the lungs at the conclusion of normal, resting
expiration. This value includes the expiratory reserve
volume plus the residual volume (ERV + RV).
Forced Expiratory Volume 1 (FEV1): the volume of air
that can be expired during the first second of expiration in a
vital capacity determination.... generally about 80% of VC.
Forced Expiratory Volume 1 (%) or FEV1(%):
FEV1/VC, expressed as %, normal value >70%
expressed as a percentage
ratio
PEF - peak expiratory flow rate - the peak flow rate during
expiration
Lung function tests or PFTs
-evaluate how well your lungs work.
1.
2.
3.
4.
5.
6.
7.
Spirometry
Diffusion test
Body plethysmography
Inhalation challenge tests
Cardiopulmonary exercise test
Six-minute walk test
A peak flor meter or PEF (A home lung function test
uses a peak flow meter)
8. Blood Gas analysis
.
Spirometry:
-is the first lung function test done.
- detect the presence of lung disease.
Spirometry is recommended as the “Gold Standard” for
diagnosis of obstructive lung disease by: National Lung Health
Education Program (NLHEP); National Heart, Lung and Blood Institute (NHLBI);
World Health Organization (WHO)
The lung function values measured with spirometry are:
Forced vital capacity (FVC). This measures the amount of air you can exhale
with force after you inhale as deeply as possible.
Forced expiratory volume (FEV). This measures the amount of air you can
exhale with force in one breath. The amount of air you exhale may be measured
at 1 second (FEV1), 2 seconds (FEV2), or 3 seconds (FEV3). FEV1 divided by
FVC can also be determined.
Forced expiratory flow 25% to 75%. This measures the air flow halfway through
an exhale (FVC).
Peak expiratory flow (PEF). This measures how quickly you can exhale. It is
usually measured at the same time as your forced vital capacity (FVC).
Slow vital capacity (SVC). This measures the amount of air you can slowly
exhale after you inhale as deeply as possible
Spirogram
Pred
Act1
%Soll
VC IN (L)
2,94
2,17
73,8
FVC (L)
2,96
1,99
67,3
FEV1 (L)
2,52
1,40
55,3
FEV1 % VC MAX (%)
79,41
64,20
80,8
PEF (L/S)
6,27
4,76
75,9
Body plethysmography :
To measure total lung capacity (TLC), RV, airway
resistance
Diffusion test or transfer test: measures how well your
lungs transfer a small amount of carbon monoxide (CO)
into the blood. Diffusing capacity provides an estimate of
how well a gas is able to move from your lungs into your
blood.
Atrerial blood gases analysis: to determine the amount
of oxygen and carbon dioxide in your bloodstream.
Cardiopulmonary exercise testing
-
is a non-invasive and objective method of evaluating both cardiac and
pulmonary function
Airway obstruction & restriction
Airway obstruction
Forced expiratory volume (FEV1) Lower with higher FEV2 and FEV3
FEV1 divided by FVC
Lower < 70%
Forced expiratory flow 25% to
75%
Lower
Peak expiratory flow (PEF)
Lower
Total lung capacity (TLC) (VT)
Normal or higher
Slow vital capacity (SVC)
Normal or lower
Functional residual capacity
(FRC)
Higher
Residual volume (RV)
Higher
Expiratory reserve volume (ERV) Normal or lower
RV divided by TLC ratio
Higher
Airway restriction
Forced vital capacity (FVC)
Lower than predicted value
Forced expiratory volume (FEV1) Normal or lower with higher FEV2 and FEV3
FEV1 divided by FVC
Normal or higher
Forced expiratory flow 25% to
75%
Normal or lower
Peak expiratory flow (PEF)
Normal or higher
Total lung capacity (TLC) (VT)
Lower
Slow vital capacity (SVC)
Lower