Transcript body surface, gills, or lungs

Gas Exchange
Chapter 44
Learning Objectives
• Define Physiological Respiration, Ventilation and
Perfusion
• Diagram the human respiratory tract and explain
functions of the organs
• Define Tidal Volume, Vital Capacity and Residual
Volume
• Compare and contrast negative and positive pressure
breathing
• Describe how breathing is both a conscious and
subconscious effort
• Describe the physiological gradient that allows for CO2
and O2 diffusion within the body
• Define COPD and health impact
Physiological Respiration
• Process by which animals exchange O2
and CO2 with the environment
Cellular respiration
Physiological respiration
Respiratory
surface
(body
surface,
gills, or
lungs)
Mitochondrion
Circulatory
system
Respiratory
medium
(air or water)
Fig. 44.1, p. 998
Breathing (Gas Exchange)
• Two primary operating features of gas
exchange
– The respiratory medium, either air or water
– The respiratory surface, a wetted epithelium
over which gas exchange takes place
Respiratory Surfaces
• In some invertebrates, the skin is the
respiratory surface
• In other invertebrates and all vertebrates,
gills or lungs are the primary respiratory
surfaces
Gas Exchange
• Simple diffusion of molecules drives
exchange of gases across the respiratory
surface
– From regions of higher concentration to
regions of lower concentration
• Area of respiratory surface determines
total quantity of gases exchanged by
diffusion
Maximizing Gas Exchange
Concentration gradients of O2 and CO2
across respiratory surfaces are kept at
optimal levels by ventilation and perfusion
Ventilation: Movement of respiratory media
over the external respiratory surface
Perfusion: Movement of circulatory fluid over
the internal respiratory surface
Air Breathers
• Air is high in O2 content
– Allows air-breathers to maintain higher
metabolic levels than water breathers
• Air has lower density and viscosity than
water
– Allows air breathers to ventilate respiratory
surfaces with relatively little energy
Insects: Tracheal System
• Insects breathe by a tracheal system
– Air-conducting tubes (trachea) lead from the
body surface (through spiracles) and branch
to all body cells
• Gas exchange takes place in fluid-filled
tips at ends of branches
Lungs (Air Breathers)
• Invaginations of the body surface
– Allow air to become saturated with water
before it reaches the respiratory surface
– Reduce water loss by evaporation
Lung Ventilation
• Positive pressure breathing
– Air is forced into lungs by muscle contractions
• (Frogs do this)
• Negative pressure breathing
– Muscle contractions expand lungs, lowering
air pressure inside
– Allows air to be pulled into the lungs
Mammalian Respiratory System
• Air enters the respiratory system through
the nose and mouth and passes through
the pharynx, larynx, and trachea
• Trachea divides into two bronchi leading to
lungs
• Within lungs, bronchi branch into
bronchioles, leading into alveoli surrounded
by networks of blood capillaries
Nasal passages
Chamber in which air is moistened,
warmed, and filtered and in which
sounds resonate
Pharynx (throat)
Airway connecting nasal passages and
mouth with larynx; enhances sounds;
also connects with esophagus
Epiglottis
Closes off larynx during swallowing
Larynx (voice box)
Airway where sound is produced;
closed off during swallowing
Trachea (windpipe)
Airway connecting larynx with two
bronchi that lead into the lungs
Lung
Lobed, elastic organ of breathing
exchanges gases between
internal environment and
outside air
Bronchi
Increasingly branched
airways leading to alveoli
of lung tissue
Mouth
Supplemental airway
Pleura
Double-layered membrane that
separates lungs from the wall of
the thoracic cavity; fluid between
its two layers lubricates breathing
movements
Intercostal muscles
Skeletal muscles between ribs that
contract to fill and empty lungs
Diaphragm
Muscle sheet between the chest
cavity and abdominal cavity that
contracts to fill lungs
Alveoli
(sectioned)
Bronchiole
Alveoli
Alveoli
Pulmonary capillaries Fig. 44.8, p. 1004
Ventilation: Mammals
• Negative pressure mechanism
• Air is exhaled passively
– Relaxation of diaphragm and external
intercostal muscles between ribs
– Elastic recoil of lungs (pleural membranes)
• Deep and rapid breathing
– Forceful expulsion of air driven by contraction
of internal intercostal muscles
Internal
intercostal
muscles
Inward
bulk flow
of air
Outward
bulk flow
of air
External
intercostal
muscles
Diaphragm
Inhalation.
Diaphragm contracts
and moves down. The
external intercostal
muscles contract and
lift rib cage upward
and outward. The
lung volume expands.
Exhalation during
breathing or rest.
Diaphragm and
external intercostal
muscles return to
the resting
positions. Rib cage
moves down.
Lungs recoil
passively.
Fig. 44.9, p. 1005
Measuring Lung Ventilation
• Tidal volume
– Amount of air moved in and out of lungs
during an inhalation and exhalation
• Vital capacity
– Total volume of air a person can inhale and
exhale by breathing as deeply as possible
• Residual volume
– Air remaining in the lungs after as much air as
possible is exhaled
Control of Breathing
• Control mechanisms
– Local chemical controls
– Regulation centers in the brain stem
• Control functions
– Match rate of air and blood flow in lungs
– Link rate and depth of breathing to body’s
requirements for O2 uptake and CO2 release
Interneurons Regulate
Breathing
• Basic rhythm of breathing
– Produced by interneurons in the medulla
• When more rapid breathing is required
– Other interneurons in the medulla reinforce
inhalation, produce forceful exhalation
• Fine-tuned breathing
– Two interneuron groups in the pons stimulate
or inhibit the inhalation center in the medulla
Blood Gas Control
Sensory receptors in medulla detect
changes in levels of O2 and CO2 in blood
and body fluids (aortic and carotid, too)
• Control centers in medulla and pons adjust
rate and depth of breathing to compensate
for changes in blood gases
O2 Transport
• O2 diffuses from alveolar air into blood
– Partial pressure of O2 is higher in alveolar air
than in blood in capillary networks
surrounding alveoli
• Most O2 entering the blood combines with
hemoglobin inside erythrocytes
Dry
inhaled air
Moist
exhaled air
160 0.04
120
Pulmonary
arteries
40 46
100 40
Alveolar sacs
27
Alveolar sacs O2 Pulmonary
100 40
veins
40
O2
46
CO2
Capillaries
entering
lungs
CO2
100 40
O2
CO2
Start of
veins in
body
tissues
40
Start of
capillaries
in body
tissues
46
40
46
Cell
100 40
Cells of body tissues
Less than 40
More than 46
100 40
O2 CO2
Capillaries
entering
tissues
Fig. 44.11, p. 1008
Hemoglobin and Oxygen
• One hemoglobin molecule can combine
with four O2 molecules
• Large quantities of O2 combined with
hemoglobin maintain a large partial
pressure gradient between O2 in alveolar
air and in blood
Oxygen saturation (%)
a. Hemoglobin saturation level in lungs
Saturation
level in
lungs
Hemoglobin
O2
Body tissues PO2
(mm Hg)
Alveoli
In the alveoli, in which the PO2 is about 100 mm Hg and the
pH is 7.4, most hemoglobin molecules are 100% saturated,
meaning that almost all have bound four O2 molecules.
Fig. 44.12a, p. 1009
O2 Diffuses into Body Cells
• O2 concentration in interstitial fluid and
body cells is lower than in blood plasma
• O2 diffuses from blood into interstitial fluid,
and from interstitial fluid into body cells
CO2 Transfer: Body Tissues
• Partial pressure of CO2 is higher in tissues
than in blood
– About 10% of CO2 dissolves in blood plasma
– 70% is converted into H+ and HCO3(bicarbonate) ions
– 20% combines with hemoglobin
a. Body tissues
Body cells
CO2
–
HCO3 +
H+
Slow
CO2 + H2O
Capillary
wall
Erythrocyte
CO2 + H2O
CO2
Fast
Hemoglobin
HCO3– + H+
Capillary
In body tissues, some of the
CO2 released into the blood
combines with water in the
blood plasma to form HCO3–
and H+. However, most
of the CO2 diffuses into
erythrocytes, where some
combines directly with
hemoglobin and some
combines with water to
form HCO3– and H+. The H+
formed by this reaction
combines with hemoglobin;
the HCO3– is transported out
of erythrocytes to add to the
HCO3– in the blood plasma.
Fig. 44.13a, p. 1009
b. Lungs
–
HCO3 +
Slow
H+
CO2 + H2O
HCO3– + H+
Hemoglobin
Fast
CO2 + H2O
Alveolar
air
CO2
CO2
Capillary
wall
CO2
Alveolar
wall
In the lungs, the reactions
are reversed. Some of the
HCO3– in the blood plasma
combines with H+ to form
CO2 and water. However,
most of the HCO3– is
transported into
erythrocytes, where it
combines with H+ released
from hemoglobin to form
CO2 and water. CO2 is
released from hemoglobin.
The CO2 diffuses from the
erythrocytes and, with the
CO2 in the blood plasma,
diffuses from the blood into
the alveolar air.
Fig. 44.13b, p. 1009
44.5 Respiration at High
Altitudes and
in Ocean Depths
• High altitudes reduce the PO2 of air
entering the lungs
• Diving mammals are adapted to survive
the high partial pressures of gases at
extreme depths
High Altitudes: PO2 Decreases
• When mammals move to high altitudes,
the number of red cells and amount of
hemoglobin per cell increase
• These changes are reversed if the animals
return to lower altitudes
Adaptations to High Altitudes
• Humans living at higher altitudes from birth
develop more alveoli and capillary
networks in the lungs
• Some mammals and birds adapted to high
altitudes have forms of hemoglobin with
greater O2 affinity
– Allows saturation at lower PO2
Deep-Diving Marine Mammals
• Blood (compared to other mammals)
– Contains more red blood cells
– Has higher hemoglobin content
– Greater blood volume per unit of body weight
• Muscles contain more myoglobin
– Allows more O2 to be stored in muscle tissues
Adaptations for Deep-Diving
• During a dive
– Heartbeat slows
– Circulation is reduced to all parts of the body
except the brain
COPD
•
•
•
•
•
Chronic Obstructive Pulmonary Disorder
Number 4 leading cause of Death in US
24 million adults affected
Causes include tobacco use and asthma
Asthma- Percent of noninstitutionalized
adults who currently have asthma: 7.3%
• Percent of children who currently have
asthma: 9.4%