Respiratory System Part 1

exhaustedcrumΜηχανική

24 Οκτ 2013 (πριν από 3 χρόνια και 5 μήνες)

86 εμφανίσεις

respiratory

Pulmonary System

Essentials of Exercise Physiology

respiratory

Respiration


External respiration:

ventilation and exchange of
gasses in the lungs (pulmonary function).


Internal respiration
:
ventilation and exchange of
gasses in the tissues (pulmonary function).

respiratory

Functions of Respiratory System

Primary purpose of
respiratory system is:

Provide means of oxygen
exchange between external
environment and body

Provide a means of carbon
dioxide exchange between
the body and the external
environment

Exchange occurs as result:

Ventilation: mechanical

Diffusion: random movement

respiratory

Functions of Respiratory System

Respiratory system also
helps regulate acid
-
base
balance in body,
especially during
exercise.

Cl
-

+ H
+

+ NaHCO
3




NaCl + H
2
CO
3




CO
2

+ H
2
O

respiratory

Acid
-

Base Balance


Acids
-

molecules which can liberate
hydrogen ions


Bases
-

molecules which can accept hydrogen
ions


Buffer
-

resists changes in pH by either
accepting hydrogen ions or liberating them
depending upon local conditions

respiratory

Structure Pulmonary System


Right and left lungs enclosed by membranes
called pleura


Visceral pleura adheres to outer surface of
lungs


Parietal pleura adheres to thoracic wall and
diaphragm

respiratory

respiratory

Intrapleural Space


Contains fluid which
lubricates pleura


Creates a low pressure
area


pressure is below
atmospheric during
inspiration, allowing the
lungs to inflate

respiratory

Functional Zones

of Air Passages


Conducting zone


passageways leading to respiratory zone


area where no gas exchange occurs


nasal cavity, pharynx, larynx, trachea, bronchioles


Respiratory zone


where gas exchange actually occurs


alveoli

respiratory

Roles of Conducting Zone


Warms air


Mucus traps small particles


Cilia sweep particles upwards


Macrophages engulf foreign particles

respiratory

Roles of Respiratory Zone


Provides large surface area for gas exchange


600 million alveoli


Total surface area is 60


80 square meters or
about size of half a tennis court


Provides a very thin barrier for gas exchange


2 cell layers thick

respiratory

Alveoli


Type II alveolar cells secrete pulmonary
surfactant


form a monomolecular layer over alveolar
surfaces


surfactant stabilizes alveolar volume by
reducing surface tension created by moisture


respiratory

Mechanics of Ventilation


Change in thoracic cavity volume produces
corresponding change in lung volume


Increase in lung volume results in decrease in
lung pressure (Boyle’s law)


Differences in pressure pulls air into the lungs


pressure within the lungs becomes less than the
atmospheric pressure


bulk flow (from high pressure to low pressure)

respiratory

Muscles of Inspiration


Diaphragm


contracts, flattens, & moves downward up to 10 cm


enlarges & elongates chest cavity, expands volume


during quiet breathing diaphragm works alone


External intercostals,
pectoralis

minor,
sternocleidomastoid

&
scaleni


lift ribs up and outwards


during exercise, accessory muscles called into play

respiratory

Muscles of Inspiration

respiratory

Muscles of Expiration


Expiration during quiet breathing is passive
due to elastic recoil of chest cavity


Decrease in lung volume forces air out of
lungs


During exercise and voluntary
hyperventilation,


rectus
abdominus
, transverse
abdominus
: push
diaphragm up


internal intercostals: pull ribs downwards

respiratory

Total Lung Capacity


Tidal volume (V
T
)


amount either inspired or expired during normal
ventilation


Inspiratory

reserve volume


maximal volume inspired after a normal inspiration


Expiratory reserve volume


volume expired after a normal expiration


During exercise V
T
increases largely from IRV.


Residual volume


volume remaining in lungs after maximal expiration

respiratory

Lung Capacities


Total lung capacity


volume within lung after a maximal inspiration


Inspiratory

capacity


maximal volume inspired from the end of tidal
expiration


Functional residual capacity


volume in lungs after normal expiration


Vital capacity


maximal volume expired after maximal inspiration

respiratory

Dynamic Lung Volumes


Depend on volume
and

speed of air movement;
more useful in diagnosing lung disease.


FEV: Forced Expiratory Volume.
Volume that
can be forcefully expired after maximal
inspiration within given time, usually 1 sec.


MVV: Maximal Voluntary Ventilation.
Volume
of air that can be ventilated by maximal effort in
one minute. Breathe maximally for 12 (or 15)
seconds and total volume recorded, multiplied by
five (or 4).

respiratory

respiratory

Minute Ventilation


Volume of gas ventilated in one minute


equal to tidal volume times frequency


Rest in 70 kg man, 6.0 L/min = 0.5 L x 12


Maximal exercise, 120
-
175 L/m = 3
-
3.5 x 40
-
50


increases as oxygen consumption increases


closely associated with CO
2
production

ERROR

respiratory

Anatomical vs Physiological
Dead Space


Anatomical dead space


areas of conducting zone not designed for
diffusion of gases


V
T

= V
A

+ V
D


At rest, V
T

= 500 ml = 350 ml + 150 ml


Physiological dead space


areas of lung and pulmonary capillary bed which
are unable to perform gas exchange as designed

respiratory

Anatomic Dead Space

respiratory

Physiologic Dead Space


Optimal diffusion requires matching of ventilation to
perfusion: 1 ventilated alveoli/ 1 blood
perfused

alveoli


Ventilation (V) / perfusion (Q) is not equal across the
lung


Top of lung is poorly
perfused


V / Q = 3.3 at top of lung


Bottom of lung has more perfusion than ventilation


V / Q = .63 at bottom of lung


V / Q values above .5 are generally adequate

respiratory

Minute Ventilation in Exercise


Adjustments in breathing rate and depth maintain
alveolar ventilation as exercise.


Trained athletes maintain alveolar ventilation by
increasing V
T

and minimal increase rate.


Deeper breathing causes a greater percentage of
incoming “fresh” V
T

to enter alveoli.


Increasing V
T

in exercise results from encroaching
primarily on
IRV
or

ERV?


V
T

plateaus at about 60% vital capacity.

respiratory

Disruptions in Normal Breathing


Dyspnea

shortness of
breath or subjective
distress in breathing.


Hyperventilation


Hyperpnea


Valsalva maneuver
:
forced exhalation
against closed glottis.
What happens to blood
pressure?

respiratory

Gas Exchange

Fick’s Law


Diffusion occurs at a rate which is
proportional to differences in partial
pressure and the surface area available and
is inversely proportional to the thickness of
the membrane.


Diffusion rate =
(P
1

-

P
2
) area


thickness