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Respiratory System
The Mechanics of Breathing
Breathing….
• --also called VENTILATION
• --movement of air outside the body
into the bronchial tree and alveoli
--Involves Inspiration and Expiration
Inhalation/Inspiration
– active process (muscle contraction)
• Diaphragm contracts (pulls lungs down)
• External intercostal muscles contract (pulls rib cage up
and out).
• This increases the size of the thoracic cavity (and lungs)
causing a drop in pressure inside the lungs
• (Boyle’s Law = volume pressure)
At sea level, air pressure is 760 mm Hg. The change in size
of the lungs causes the pressure inside to drop to about
758 mm Hg.
• Outside air rushes in to equalize the difference in
pressure.
Forced Inhalation
- active process (muscle contraction)
• – taking a deeper breath
• – requires stronger contraction of normal inspiratory
muscles (diaphragm and external intercostals)
• --plus help of the pectoralis minor and
sternocleidomastoid (SCM) muscle.
Exhalation/Expiration
- elastic recoil
– passive process (no muscle contraction)
• Muscles relax
• tissues return to their normal shape and size
• decrease size of the thoracic cavity (and lungs)
• increase pressure inside and forcing air out
Forced Expiration
• - active process (muscle contraction)
• Contraction of internal intercostal muscles (pulls
rib cage down)
• -- abdominal muscles (pull sternum down and
squeeze abdominal cavity
• – this forces more air out than normal
Review….
• Why does air naturally move into the lungs ? Hint: mmHg
• What happens when we inhale?
When we force inhalation, what muscles help with that?
What happens when we exhale?
Gas Exchange
• Ventilation (inhalation and exhalation) brings air into the
lungs
• Air contains oxygen, which diffuses from inside the
alveoli into adjacent capillaries (both made of simple
squamous epithelium).
• Carbon dioxide diffuses in the opposite direction.
• If you go up in elevation, the outside air pressure is less,
so inhaled oxygen does not diffuse into the blood as
easily.
• Pressure of inhaled air is not enough by itself to inflate
the individual alveoli of the lungs, which contain a very
small amount of fluid.
• Fluid would normally cause the alveoli walls to stick
together (b/c of surface tension)
• Body creates a chemical called surfactant, which disrupts
surface tension inside alveoli, preventing them from
sticking together.
• Surfactant - not made until the 7th month of fetal life,
therefore if born prematurely, alveoli will stick together
and baby cannot breathe. This is RDS (Resp. Distress
Syndrome).
• Baby is put on a ventilator and given artificial surfactant
as long as needed
Transport of Gases
Oxygen
• 98% - transported bound to the hemoglobin of a RBC
(oxyhemoglobin)
• 2% - dissolved in plasma
To stimulate the RBC to give up its oxygen to the tissues :
• increase in body temp.
• increase in breathing rate (hyperventilation)
• increase in CO2 concentration
These three things are associated with exercise:
• an increase in CO2 concentration results in blood
that is more acidic (lower pH).
• To counter this, a person will hyperventilate –
the rapid breathing is a way to help stimulate
removal of CO2 from the blood
• therefore lower the blood’s acidity (or raise the
blood’s pH)
Carbon Dioxide
• 23% - transported bound to the hemoglobin of a RBC
(carbaminohemoglobin)
• 7% - dissolved in plasma
• 70% - transported as a bicarbonate ion so it doesn’t
adversely affect the pH of the blood
• it must undergo a chemical change from carbon dioxide
to bicarb. ions
CO2 + H2O
H2CO3
H+
carbon +
dioxide
carbonic acid
hydrogen + bicarbonate
ions
ions
water
+ HCO3 -
carbonic anhydrase – enzyme that comes from RBC is the catalyst that speeds up the reaction
this reaction is reversible – bicarbonate ions must change back to carbon dioxide when upon arrival at the
lungs in order to be exhaled as a gas
Review
• What type of tissue is found in the capillaries and alveoli?
• What molecule on the RBCs does oxygen and carbon dioxide
attach to?
• What is that molecule called with Oxygen? With Carbon
Dioxide?
• What could lead to the alveoli sticking together? How is that
prevented? What substance is produced by the alveoli?
Review….
• How much oxygen is transported by the RBCs?
• How much carbon dioxide is tranported by RBCs?
• What does CO2 do to your blood pH? What is its effect on
breathing?
Composition of Air
• Air is made up of a mixture of gases
• Nitrogen= 79%, Oxygen = 21% and CO2 = .03%
• Air pressure is 760 mmHg of which each of the gases
contribute to that total.
• Ex: .21[760]= 160 mmHg partial pressure of O2
Nervous System Control
• Portions of your Spinal
Cord control your
breathing.
pH sends impulse to
Resp center which
causes in breathing
*CO2
• Medulla Oblongata
• Pons
Respiratory Volumes…
• SPIROMETRY- measurement of air volume in and out of the
lungs
•
• Tidal volume – least affected by missing all/part of a lung
• – since lungs are only filled to about half capacity after normal
inhalation, air can be compressed to make up for missing part
of lung.
•
• Other resp. volumes that require forced inhalation to
measure (vital capacity, inspiratory reserve) cannot be made
up for with missing all/part of a lung.