Download Unit 7 p2

NOTES: Respiratory System (UNIT 7-part 2) – Breathing Mechanism
*Changes in the size of the thoracic cavity accompany INSPIRATION and EXPIRATION.
 INSPIRATION =
 EXPIRATION =
*ATMOSPHERIC PRESSURE (760 mmHg; the “weight” of the air) is the force that moves air into the
lungs.
*Air (gases) move from regions of
to regions of
INSPIRATION:
• if the pressure inside the lungs/alveoli decreases, atmospheric pressure will force air into the lungs
How does the pressure inside the lungs decrease???
> Diaphragm contracts (
)
> Thoracic cage moves upward and outward (
 the
)
of the thoracic cavity causes a
• as the walls of the thoracic cavity expand, they pull on the parietal pleura
(758 mmHg)
• the serous fluid in the pleural cavity holds the pleural membranes tightly together
(much like a wet microscope slide will stick to another microscope slide)
• as the parietal pleura is pulled outward, the visceral pleura follows…
•
_____!!
**for a deeper breath, the diaphragm and intercostals muscles contract with more force
EXPIRATION:
• the forces for normal exhalation come from
of tissues
• the opposite pressure and volume changes occur…pressure inside the lungs increases and forces air
out
How does the pressure inside the lungs increase???
> Diaphragm relaxes (moves upward)
> External intercostals muscles relax; thoracic cage moves downward and inward
 Lungs and thoracic cage recoil and return to their original shape
 the

of the thoracic cavity causes an
!!
(763 mmHg)
RESPIRATORY AIR VOLUMES AND CAPACITIES:
• one
= one inspiration followed by one expiration
• the amt. of air that moves in (or out) during a single respiratory cycle is the
-about 500mL
_
• even after forceful expiration, some air remains in the lungs (
)…why?
-so that lungs don’t collapse! (alveoli always stay partially inflated)
-prevents the O2 and CO2 levels from fluctuating greatly (“new” air always mixes with “old” air)
• the maximum amt. of air a person can exhale after taking the deepest possible breath is the
(4600 mL)
TOTAL LUNG CAPACITY
=
VITAL CAPACITY
+
RESIDUAL VOLUME
**all of these volumes/capacities vary with
(average is about 5800mL)
Control of Breathing / Gas Exchange and Transport
*Normal breathing is rhythmic and involuntary.
Respiratory Center:
● the respiratory center is in the brain stem (pons and medulla)
FACTORS AFFECTING BREATHING:
1) respiratory center in the brain
2) chemical concentrations (gases, ions, pH, etc.)
3) stretching of lung tissue
4) emotional state
EXAMPLES:
*when chemoreceptors in the walls of certain large arteries detect low O2 levels (or high CO2 levels),
breathing rate increases
*fear and pain typically increase the normal breathing pattern
ALVEOLAR GAS EXCHANGES
*
occurs in the alveoli.
● ALVEOLI: tiny air sacs in the lungs clustered at the ends of alveolar ducts
● Gases (O2 and CO2) diffuse from regions of
partial pressure) to regions of
● OXYGEN diffuses from
● CARBON DIOXIDE diffuses from
(and
(partial pressure)
into
into
GAS TRANSPORT IN THE BLOOD / BODY
*Blood transports gases between the lungs and body cells.
OXYGEN TRANSPORT:
● oxygen binds to the protein
in the blood (inside RBC’s)
● the resulting molecule, ______________________________, is unstable and readily releases oxygen
in regions where oxygen concentration (partial pressure of oxygen aka: PO2) is low
● more oxygen will be released from oxyhemoglobin when:
-CO2 levels in the blood increase which causes _______________________________________
CARBON DIOXIDE TRANSPORT:
● carbon dioxide may be carried:
**as a bicarbonate ion (HCO3-); MOST CO2 is in this form!
-
(different spot on molecule than where oxygen binds)
● carbon dioxide reacts with water to form carbonic acid
● carbonic acid dissociates to release hydrogen ions and bicarbonate ions:
 H+ lowers pH of blood and changes the shape of hemoglobin so that oxygen is released