Transcript Gas Exchange notes

Gas Exchange
TOPIC 6.4 AND H6 GAS EXCHANGE
Overview: Gas exchange
 Gas exchange makes it possible animals to put to
work the food molecules the digestive system
provides.
 3 phases of gas exchange:
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1. Breathing
2. Transport of gases
3. Exchange of O2 and CO2
Overview: 3 phases of gas exchange
1.
Breathing
When an animal breathes, a large, moist internal surface is
exposed to air.
O2 diffuses across the cells lining the lungs and into surrounding
blood vessels.
Simultaneously, CO2 diffuses out of the blood and into the lungs,
released from the body when exhaling occurs.
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2.
3.
2.
Transport of gases
The O2 that has diffused into the blood attaches to hemoglobin in
red blood cells and is carried from the lungs to the body’s tissues.
The CO2 is also transported in blood from the tissues back to the
lungs.
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3.
Exchange of O2 and CO2
Body cells take up O2 from the blood and release CO2 to the blood.
O2 is required for cells to obtain energy from the food molecules
the body has digested and absorbed (cell respiration!)
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2.
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Our body needs O2 to function as the final electron acceptor in ETC to
produce ATP
Respiratory Surface
• Respiratory surface is the part of an animal where
gases are exchanged with the environment
• Made up of living cells, whose plasma membranes
must be wet to function properly
• Surface area must be extensive enough to take up
sufficient O2 for every cell in the body and to dispose
of all waste CO2
• Must also be thin and moist enough to allow CO2 to
diffuse rapidly into the circulatory system or body
tissues and allow CO2 to diffuse out.
Respiratory Surface
 Humans have lungs, which are internal sacs lined
with epithelium
 Inner surfaces of the lungs branch extensively,
forming a large respiratory surface.
 Gases are carried between the lungs and the body
cells by the circulatory system.
Respiratory Structures
• Lungs are located in the chest cavity, which is
bounded at the bottom by a sheet of muscle called
the diaphragm.
1. Air usually enters our respiratory system through
the nostrils.
–
Air is filtered by hairs and warmed, humidified, and sampled
for odors
We can also draw in air through the mouth
–
Does not allow the air to be processed by the nasal cavity.
Respiratory Structures
2. From the nasal cavity or mouth, air passes to the pharynx,
where the paths for air and food cross.
*the air passage in the pharynx is always open for
breathing except when we swallow
3. From the pharynx, air is inhaled into the larynx (voice
box)
*when we exhale, the outgoing air rushes by
a
pair of vocal cords in the larynx, and we can
produce sounds by voluntarily tensing muscles in
the
voice box, stretching the cords and making
them
vibrate.
*we produce high-pitched sounds when our
vocal cords are tense and therefore vibrating
very fast.
*when the cords are less tense, they vibrate
slowly and produce low-pitched sounds
Respiratory Structures
4. From the larynx, inhaled air passes toward the
lungs through the trachea, or windpipe.
*rings of cartilage maintain the shape of the
trachea, much as metal rings keep the hose of a
vacuum cleaner from collapsing.
5. The trachea forks into two bronchi (singular,
bronchus), one leading to each lung.
*within the lung, the bronchus branches repeatedly
into finer and finer tubes called bronchioles.
Respiratory Structures
6.Bronchioles dead-end in grape-like clusters of air sacs
called alveoli
*each of our lungs contains millions of these tiny sacs
*the inner surface of each alveolus is lined with a thin
layer of epithelial cells that form the respiratory surface.
*The O2 in inhaled air dissolves in a film of moisture on
the epithelial cells
*It then diffuses across the epithelium and into a web of
blood capillaries that surrounds each alveolus.
*The CO2 diffuses the opposite way—from the capillaries,
across the epithelium of the alveolus, into the air space of
the alveolus, and finally out in the exhaled air.
Structure of alveoli
Respiratory Structures
 The trachea and major branches are lined by a moist
epithelium covered by cilia and a thin film of mucus.
 Cilia and mucus serve as the system’s cleaning
elements:
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Mucus traps dust, pollen, and other contaminants
Beating cilia move the mucus upward to the pharynx, where it
is usually swallowed.
Respiratory Structures
Breathing
 Breathing is the alternation of inhalation and
exhalation.
 This ventilation of our lungs maintains high O2
and low CO2 concentrations at the respiratory
surface.
 We breathe by pulling air into the lungs, and then
pushing it back out.
Breathing: Inhalation
 During inhalation:
 Both the rib cage and chest cavity expand, and the lungs follow
suit.
 Ribs move upward and the rib cage expands as muscles
between the ribs contract.
 At the same time, the diaphragm contracts, moving downward
and expanding the chest cavity as it goes
 Increase in volume of the lungs lowers the air pressure in the
alveoli to less than atmospheric pressure
 Negative pressure breathing
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Air rushes through the nostrils into the alveoli from a region of
higher pressure to one of lower pressure.
Breathing: Exhalation
 During exhalation:
 Rib muscles and diaphragm both relax, decreasing the volume
of the rib cage and the chest cavity and forcing air out of the
lungs.
 The diaphragm curves upward into the chest cavity
 Decrease in volume of the lungs increases the air pressure in
the alveoli to be greater than atmospheric pressure
Breathing
 Each year, a human adult may take between 4 million and
10 million breaths.
 Volume of air is about 500 mL when we breathe quietly
 Vital capacity
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Maximum volume of air that we can inhale and exhale
during forced breathing.
Averages about 3.4 L and 4.8 L for college-age females and
males (women tend to have smaller rib cages and lungs)
Lungs actually hold more air than the vital capacity
Because the alveoli do not completely collapse, a residual
volume of “dead” air remains in the lungs even after we
exhale
As lungs lose resilience with age or as result of disease
(emphysema), the residual volume increases at the
expense of vital capicity.
Negative Pressure Breathing
Breathing Control Centers
 Although we can voluntarily hold our breath, most of
the time, it is controlled by automatic control centers
in our brain to regulate our breathing movements.
 Automatic control is essential; it ensures
coordination between the respiratory and circulatory
systems and the body’s metabolic needs for gas
exchange.
Breathing Control Centers
 Breathing control centers
 Located in parts of the brain called the pons and medulla
oblongata
 Nerves from the medulla’s control center signal the diaphragm
and rib muscles to contract, making us inhale.
 Nerves send out signals that result in about 10 to 14 inhalations
per minute when we are at rest
 Between inhalations, the muscles relax and we exhale.
 Control center in pons smooths out the basic rhythm of
breathing set by the medulla.
Breathing control centers
 Adjusting our breathing rate in response to the body’s
needs:
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Medulla’s control center monitors the CO2 level of the blood and
regulates breathing rate in response.
Its main cues about CO2 concentration come form slight changes in
the pH of the blood and in the fluid bathing the brain (cerebrospinal
fluid)
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pH decreases when CO2 in blood increases
When we exercise vigorously:
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our metabolism speeds up and our body cells generate more CO2 as a
waster product.
Co2 goes into the blood, where it reacts with water to form carbonic acid,
lowering the pH of the blood and cerebrospinal fluid slightly
The medulla senses this drop and its b.c.c. increases the breathing rate and
depth.
More CO2 is eliminated in the exhaled air, and the pH returns to normal.
Breathing Control Centers
 Hyperventilating
 Excessively taking rapid, deep breaths
 Action of your b.c.c. that is hard on your body
 Deep, rapid breathing purges blood of so much CO2 that the
control center temporarily ceases to send signals to the rib
muscles and diaphragm
 Breathing stops until the CO2 levels increases enough to
switch the breathing center back on.
Breathing Control Centers
 B.C.C. responds directly to CO2 levels, but it usually
does not respond directly to oxygen levels.
 Since the same process that consumes O2, cell
respiration, also produces CO2, a rise in CO2 (drop
in pH) is generally a good indication of a drop in
blood oxygen.
 Thus, by responding to lowered pH, the b.c.c. also
controls blood O2 level.
Breathing Control Centers
 Secondary control over breathing is exerted by sensors
in the aorta and carotid arteries that monitor
concentrations of O2 and CO2.
 When O2 level in the blood is severely depressed, these
sensors signal the control center via nerves to increase the
rate and depth of breathing.
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May occur at high altitudes, where the air is thin that we
cannot get enough O2 by breathing normally.
 B.C.C. respond to a variety of nervous and chemical signals
to keep the breathing rate and depth in tune with the
changing demands of the body.
 Breathing rate must be coordinated with the circulatory
system.
Transport of Gases
 Heart pumps oxygen-poor blood to the alveolar
capillaries in the lungs .
 Gases are exchanged between air in the alveolar
spaces and blood in the alveolar capillaries.
 Blood leaves the alveolar capillaries, having lost CO2
and gained O2
 Oxygen-rich blood returns to the heart and is
pumped out to body tissues.
Transport of gases
 Exchange of gases between capillaries and cells
around them occurs by the diffusion of gases down
gradients of pressure.
 A mixture of gases, such as air, exerts prsessure.
 Each kind of gas in a mixture accounts for a portion,
called the partial pressure, of the mixture’s total
pressure.
 Molecules of each kind of gas will diffuse down a
gradient of its own partial pressure independent of
other gases.
Transport of gases
 For example,
 O2 moves from oxygen-rich blood through the interstitial fluid
and into tissue cells because it diffuses from a region of higher
partial pressure to a region of lower partial pressure.
 The tissue cells maintain this gradient as they consume O2 in
cell respiration.
 CO2 produced as a waste product of cellular respiration
diffuses down its own partial-pressure gradient out of the cells
and into the capillaries.
 Diffusion also accounts for gas exchange in the alveoli
Transport of gases
 Oxygen is not very soluble in water, and most of the
O2 in blood is carried by hemoglobin in the red
blood cells.
 A hemoglobin molecule consists of four
polypeptide chains.
 Attached to each polypeptide chain is a chemical
group called a heme, at the center of which is an
iron atom.
 Each iron atom can carry one O2 molecule; every
hemoglobin can carry up to four oxygen molecules.
Transport of gases
 Hemoglobin loads up with O2 in the lungs and
transports it to the body tissues.
 At the tissues, hemoglobin unloads O2, depending in
the needs of the cells
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(partial pressure of O2 in the tissue reflects how much O2 the
cells are using)
 Hemoglobin also helps blood transport CO2 and
assists in buffering the blood
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(preventing harmful changes in pH)
Transport of gases
 Hemoglobin also helps blood transport CO2 and
assists in buffering the blood
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Helps to prevent harmful changes in pH
When CO2 leaves a tissue cell, it diffuses through the interstitial
fluid, across the wall of a capillary, and into the blood fluid (plasma)
Most of the CO2 enters the rbc’s where some of it combines with
hemoglobin
Rest reacts with water molecules, forming carbonic acid (H2CO3)
with the help of an enzyme (carbonic anhydrase) on the rbc’s
H2CO3 then breaks apart into H+ and HCO3Hemoglobin binds most of the H+, minimizing change in blood pH
HCO3- diffuses into the plasma, where they are carried to the lungs
Transport of Gases
 Hemoglobin also helps blood transport CO2 and
assists in buffering the blood (continued)
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Process is reversed as blood flows through capillaries in the
lungs.
Carbonic acid forms when bicarbonate combines with H+
Carbonic acid is then converted back to CO2 and water
Finally, the CO2 diffuses from the blood into the alveoli and
out of the body in exhaled air.
Transport of Gases
 Oxygen dissociation curves
 important tool for understanding how our blood carries and
releases oxygen
 relates oxygen saturation (SO2) and partial pressure of oxygen
in the blood (PO2)
 is determined by what is called "hemoglobin's affinity for
oxygen"; that is, how readily hemoglobin acquires and releases
oxygen molecules into the fluid that surrounds it
Transport of gases
 Bohr shift
 a property of hemoglobin which states that at lower pH (more
acidic environment), hemoglobin will bind to oxygen with less
affinity.
 Since carbon dioxide is in direct equilibrium with the
concentration of protons in the blood, increasing blood carbon
dioxide levels leads to a decrease in pH, which ultimately leads
to a decrease in affinity for oxygen by hemoglobin.
 promotes the dissociation of oxygen from hemoglobin to the
tissue, allowing the tissue to obtain enough oxygen to meet its
demands
Transport of gases
 Bohr Shift: Oxygen Dissociation curve
 shifts to the right when carbon dioxide or hydrogen ion
concentration is increased.
 This facilitates increased oxygen dumping.
 This mechanism allows for the body to adapt the problem of
supplying more oxygen to tissues that need it the most.
 When muscles are undergoing strenuous activity, they generate
CO2 and lactic acid as products of cellular respiration and
lactic acid fermentation.
 In fact, muscles generate lactic acid so quickly that pH of the
blood passing through the muscles will drop to around 7.2. As
lactic acid releases its protons, pH decreases, which causes
hemoglobin to release ~10% more oxygen
This shifting of the curve to the RIGHT from these
4 factors is referred to as the Bohr effect.
Breathing Challenges
 Asthma
 an inflammatory disorder of the airways, which causes attacks
of wheezing, shortness of breath, chest tightness, and coughing
 When an asthma attack occurs, the muscles surrounding the
airways become tight and the lining of the air passages swell.
This reduces the amount of air that can pass by, and can lead to
wheezing sounds.
 Excess mucus is also produced, further contributing to airflow
restriction, making it difficult for oxygen to get through to the
alveoli and into the bloodstream.
 Asthma attacks can last minutes to days and can become
dangerous if the airflow becomes severely restricted.
Breathing Challenges
 High altitudes
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The percentage of oxygen in the air at two miles (3.2 km.) is the same as at
sea level (21%). However, the air pressure is 30% lower at the higher altitude
because the atmosphere is less dense--that is, the air molecules are farther
apart
At high altitudes, the lower air pressure makes it more difficult for oxygen to
enter our vascular systems. The result is hypoxia, or oxygen deprivation.
Hypoxia usually begins with the inability to do normal physical activities,
such as climbing a short flight of stairs without fatigue.
Other early symptoms of "high altitude sickness" include a lack of appetite,
distorted vision, and difficulty with memorizing and thinking clearly.
In serious cases, pneumonia-like symptoms (pulmonary edema) and an
abnormal accumulation of fluid around the brain (cerebral edema) develop,
leading to death within a few days if there is not a return to normal air
pressure levels. There is also an increased risk of heart failure due to the
added stress placed on the lungs, heart, and arteries at high altitudes.
Breathing challenges
 High Altitudes: Body response
 When we travel to high altitudes, our bodies initially develop
inefficient physiological responses.
There is an increase in breathing and heart rate to as much as
double even while resting.
 Pulse rate and blood pressure go up sharply as our hearts pump
harder to get more oxygen to the cells.
 These are stressful changes, especially for people with weak hearts.
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Breathing challenges
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High Altitudes: Body response
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Later, a more efficient response normally develops as
acclimatization takes place.
 More red blood cells and capillaries are produced to carry more
oxygen. T
 the lungs increase in size to facilitate the osmosis of oxygen and
carbon dioxide.
 There is also an increase in the vascular network of muscles
which enhances the transfer of gases.
Breathing Challenges
On returning to sea level after successful acclimatization to high
altitude, the body usually has more red blood cells and greater lung
expansion capability than needed.
 Since this provides athletes in endurance sports with a
competitive advantage, the U.S. maintains an Olympic training
center in the mountains of Colorado.
 Several other nations also train their athletes at high altitude for
this reason. However, the physiological changes that result in
increased fitness are short term at low altitude. In a matter of
weeks, the body returns to a normal fitness level.
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