42_2 Flashcards

1
Q

gas exchange

A

Gas

exchange is the uptake of molecular O2 from the environment and the discharge of CO2 to the environment.

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2
Q

partial pressure

A

the atmosphere is 21% O2 by volume, the partial pressure of O2 is 0.21*760, or about
160 mm Hg. This value is called the partial pressure of O2 (abbreviated PO2) because it is the part of atmospheric pressure
contributed by O2

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3
Q

partial pressures in dissolved gases

A

Partial pressures also apply to gases dissolved in a liquid,
such as water. When water is exposed to air, an equilibrium is
reached in which the partial pressure of each gas in the water
equals the partial pressure of that gas in the air.
- However, the concentrations of gas in
the air and water differ substantially because gases is much less
soluble in water than in air

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4
Q

gas exchange w/ air as the respiratory medium

A

As already noted, O2 is plentiful in air, making
up about 21% of Earth’s atmosphere by volume. Compared
to water, air is much less dense and less viscous, so it is easier
to move and to force through small passageways. As a result,
breathing air is relatively easy and need not be particularly efficient. Humans, for example, extract only about 25% of the
O2 in inhaled air

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5
Q

gas exchange w/ water as the respiratory medium

A
  • Gas exchange with water as the respiratory medium is much more demanding.
  • The amount of O2 dissolved in a
    given volume of water varies but is always less than in an
    equivalent volume of air: the concentration in many marine and freshwater habitats is roughly 40 times less than in air. The warmer
    and saltier the water is, the less dissolved O2 it can hold.
  • Water’s lower O2 content, greater density, and greater viscosity mean that aquatic animals such as fishes and lobsters
    must expend considerable energy to carry out gas exchange.
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6
Q

respiratory surfaces

A
  • Like all living cells, the cells that carry
    out gas exchange have a plasma membrane that must be in
    contact with an aqueous solution. Respiratory surfaces are
    therefore always moist and tend to be large and thin.
  • The general body surface of most animals lacks sufficient
    area to exchange gases for the whole organism. The evolutionary solution to this limitation is a respiratory organ that
    is extensively folded or branched. Gills, tracheae, and
    lungs are three such organs.
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7
Q

movement of gases across respiratory surfaces

A
  • The movement of O2 and CO2 across moist respiratory
    surfaces takes place entirely by diffusion.
  • The rate of diffusion is proportional to the surface area across which it occurs
    and inversely proportional to the square of the distance
    through which molecules must move. In other words, gas exchange is fast when the area for diffusion is large and the
    path for diffusion is short. As a result, respiratory surfaces
    tend to be large and thin.
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8
Q

gills

A

Gills are outfoldings of the body surface that are suspended
in the water. Regardless of their
distribution, gills often have a total surface area much greater
than that of the rest of the body’s exterior

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9
Q

ventilation

A
  • Movement of the respiratory medium over the respiratory surface, a process called ventilation, maintains the
    partial pressure gradients of O2 and CO2 across the gill that are necessary for gas exchange.
  • To promote ventilation,
    most gill-bearing animals either move their gills through
    the water or move water over their gills.
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10
Q

why are gills are generally unsuitable for an animal living on land?

A
  • An expansive surface of wet membrane exposed directly to air
    currents in the environment would lose too much water by
    evaporation.
  • Furthermore, the gills would collapse as their fine
    filaments, no longer supported by water, stuck together.
  • In most
    terrestrial animals, respiratory surfaces are enclosed within the
    body, exposed to the atmosphere only through narrow tubes.
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11
Q

efficiency of countercurrent exchange mechanisms

A
  • Countercurrent exchange mechanisms are remarkably efficient. In the fish gill, more than 80% of the O2 dissolved in
    the water is removed as it passes over the respiratory surface.
  • In other settings, countercurrent exchange contributes to
    temperature regulation and to the functioning of the mammalian kidney.
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12
Q

countercurrent exchange

A

The arrangement of capillaries in a fish gill allows for
countercurrent exchange, the exchange of a substance
or heat between two fluids flowing in opposite directions. In
a fish gill, this process maximizes gas exchange efficiency.
- Because blood flows in the direction opposite to that of water
passing over the gills, at each point in its travel blood is less
saturated with O2 than the water it meets.

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13
Q

countercurrent exchange and partial pressure

A
  • As blood enters a gill capillary, it encounters water that is
    completing its passage through the gill. Depleted of much of
    its dissolved O2, this water nevertheless has a higher PO2 (partial pressure of O2) than
    the incoming blood, and O2 transfer takes place.
  • As the blood
    continues its passage, its PO2 steadily increases, but so does
    that of the water it encounters, since each successive position in the blood’s travel corresponds to an earlier position in the
    water’s passage over the gills.
  • Thus, a partial pressure gradient
    favoring the diffusion of O2 from water to blood exists along
    the entire length of the capillary.
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14
Q

tracheal system

A
  • Although the most familiar respiratory structure among terrestrial animals is the lung, the most common is actually the
    tracheal system of insects.
  • Made up of air tubes that
    branch throughout the body, this system is one variation on
    the theme of an internal respiratory surface.
  • The largest tubes, called tracheae, open to the outside.
  • The finest branches extend close to the surface of nearly
    every cell, where gas is exchanged by diffusion across the
    moist epithelium that lines the tips of the tracheal branches.
  • Because the tracheal system brings air
    within a very short distance of virtually every body cell in an
    insect, it can transport O2 and CO2 without the participation
    of the animal’s open circulatory system.
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15
Q

lungs

A
  • Unlike tracheal systems, which branch throughout the insect body, lungs are localized respiratory organs.
  • Representing an infolding of the body surface, they are typically
    subdivided into numerous pockets.
  • Because the respiratory
    surface of a lung is not in direct contact with all other parts
    of the body, the gap must be bridged by the circulatory system, which transports gases between the lungs and the rest
    of the body.
  • Lungs have evolved in organisms with open circulatory systems, such as spiders and land snails, as well
    as in vertebrates.
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16
Q

larynx

A

When food is swallowed, the larynx (the
upper part of the respiratory tract) moves upward and tips the
epiglottis over the glottis (the opening of the trachea, or
windpipe). This allows food to go down the esophagus to the
stomach (see Figure 41.11). The rest of the time, the glottis is
open, enabling breathing

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17
Q

respiration: air entering

A
  • Air enters through the nostrils and is then filtered by hairs,
    warmed, humidified, and sampled for odors as it flows
    through a maze of spaces in the nasal cavity.
  • The nasal cavity
    leads to the pharynx, an intersection where the paths for air
    and food cross. The glottis is open, and from the larynx, air passes into the trachea. Cartilage reinforcing the walls of both the larynx and the trachea keeps this
    part of the airway open.
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18
Q

vocal cords

A
  • Within the larynx of most mammals, exhaled air rushes by a pair of elastic bands of muscle called
    vocal folds, or, in humans, vocal cords.
  • Sounds are produced
    when muscles in the larynx are tensed, stretching the cords so
    they vibrate.
  • High-pitched sounds result from tightly
    stretched cords vibrating rapidly; low-pitched sounds come
    from less tense cords vibrating slowly.
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19
Q

bronchi

A

The trachea branches into two bronchi (singular,
bronchus), one leading to each lung. Within the lung, the
bronchi branch repeatedly into finer and finer tubes called
bronchioles
- The entire system of air ducts has the appearance of an inverted tree, the trunk being the trachea.

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20
Q

mucus escalator

A

The epithelium lining the major branches of this respiratory tree is
covered by cilia and a thin film of mucus.
- The mucus traps
dust, pollen, and other particulate contaminants, and
- the
beating cilia move the mucus upward to the pharynx, where
it can be swallowed into the esophagus.
- This process, sometimes referred to as the “mucus escalator,” plays a crucial role
in cleansing the respiratory system

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21
Q

alveoli

A
  • Gas exchange in mammals occurs in alveoli, air sacs clustered at the tips of the
    tiniest bronchioles.
  • Human lungs contain millions of alveoli,
    which together have a surface area of about 100 m2, 50 times that of the skin.
  • Oxygen in the air entering the alveoli dissolves in the moist film lining their inner surfaces and rapidly diffuses across the epithelium into a web of capillaries
    that surrounds each alveolus.
  • Net diffusion of carbon dioxide
    occurs in the opposite direction, from the capillaries across
    the epithelium of the alveolus and into the air space
22
Q

alveoli contamination

A
  • Lacking cilia or significant air currents to remove particles
    from their surface, alveoli are highly susceptible to contamination.
  • White blood cells patrol alveoli, engulfing foreign
    particles. However, if too much particulate matter reaches the
    alveoli, the defenses can be overwhelmed, leading to inflammation and irreversible damage.
  • For example, particulates
    from cigarette smoke that enter alveoli can cause a permanent reduction in lung capacity.
  • For coal miners, inhalation
    of large amounts of coal dust can lead to silicosis, a disabling,
    irreversible, and sometimes fatal lung disease.
23
Q

Given their tiny diameter (about

0.25 mm), why don’t alveoli collapse under high surface tension?

A
  • The film of liquid that lines alveoli is subject to surface tension, an attractive force that acts to minimize the surface area
    of a liquid
  • Researchers reasoned that alveoli must be coated with
    a material that reduces surface tension. In 1955, biophysicist Richard Pattle obtained experimental evidence
    for such a material, now called a surfactant, for surfaceactive agent.
24
Q

RDS

A
  • Pattle proposed that the absence of surfactant might cause respiratory distress syndrome (RDS), a
    disease common among preterm infants born 6 weeks or
    more before their due dates.
  • In the late 1950s, Mary Ellen Avery carried out the first experiment linking RDS to a surfactant deficiency
  • Subsequent studies revealed that surfactant contains a mixture
    of phospholipids and proteins and typically appears in the
    lungs after 33 weeks of development. (full-term: 38wk) Artificial surfactants are
    now used routinely to treat early preterm infants.
25
positive pressure breatrhing
- An amphibian such as a frog ventilates its lungs by positive pressure breathing, inflating the lungs with forced airflow. - During the first stage of inhalation, muscles lower the floor of an amphibian’s oral cavity, drawing in air through its nostrils. - Next, with the nostrils and mouth closed, the floor of the oral cavity rises, forcing air down the trachea. - During exhalation, air is forced back out by the elastic recoil of the lungs and by compression of the muscular body wall.
26
Two features of ventilation in birds make it highly efficient:
First, when birds breathe, they pass air over the gas exchange surface in only one direction. Second, incoming fresh air does not mix with air that has already carried out gas exchange.
27
How a Bird Breathes
- To bring fresh air to their lungs, birds use eight or nine air sacs situated on either side of the lungs. The air sacs do not function directly in gas exchange but act as bellows that keep air flowing through the lungs. - Instead of alveoli, which are dead ends, the sites of gas exchange in bird lungs are tiny channels called parabronchi. Passage of air through the entire system—lungs and air sacs—requires two cycles of inhalation and exhalation.
28
negative pressure breathing
- Unlike amphibians and birds, mammals employ negative pressure breathing—pulling, rather than pushing, air into their lungs. - Using muscle contraction to actively expand the thoracic cavity, mammals lower air pressure in their lungs below that of the air outside their body. Because gas flows from a region of higher pressure to a region of lower pressure, air rushes through the nostrils and mouth and down the breathing tubes to the alveoli. - During exhalation, the muscles controlling the thoracic cavity relax, and the volume of the cavity is reduced. The increased air pressure in the alveoli forces air up the breathing tubes and out of the body. - Thus, inhalation is always active and requires work, whereas exhalation is usually passive.
29
diaphragm
Expanding the thoracic cavity during inhalation involves the animal’s rib muscles and the diaphragm, a sheet of skeletal muscle that forms the bottom wall of the cavity. - Contracting the rib muscles expands the rib cage, the front wall of the thoracic cavity, by pulling the ribs upward and the sternum outward. - At the same time, the diaphragm contracts, expanding the thoracic cavity downward.
30
lungs' double membrane
- Within the thoracic cavity, a double membrane surrounds the lungs. - The inner layer of this membrane adheres to the outside of the lungs, and - the outer layer adheres to the wall of the thoracic cavity. - A thin space filled with fluid separates the two layers. Surface tension in the fluid causes the two layers to stick together like two plates of glass separated by a film of water: The layers can slide smoothly past each other, but they cannot be pulled apart easily. - Consequently, the volume of the thoracic cavity and the volume of the lungs change in unison.
31
heightened activity level and breathing
- Depending on activity level, additional muscles may be recruited to aid breathing. - The rib muscles and diaphragm are sufficient to change lung volume when a mammal is at rest. - During exercise, other muscles of the neck, back, and chest increase the volume of the thoracic cavity by raising the rib cage. - The result is a piston-like pumping motion that pushes and pulls on the diaphragm, further increasing the volume of air moved in and out of the lungs.
32
tidal volume
The volume of air inhaled and exhaled with each breath is | called tidal volume. It averages about 500 mL in resting humans.
33
vital capacity
The tidal volume during maximal inhalation and exhalation is the vital capacity, which is about 3.4 L and 4.8 L for college-age women and men, respectively.
34
residual volume
The air that remains after a forced exhalation is called the residual volume. As we age, our lungs lose their resilience, and residual volume increases at the expense of vital capacity.
35
Because the lungs in mammals do not completely empty | with each breath,
Because the lungs in mammals do not completely empty with each breath, and because inhalation occurs through the same airways as exhalation, each inhalation mixes fresh air with oxygen-depleted residual air. - As a result, the maximum PO2 in alveoli is always considerably less than in the atmosphere. - The maximum PO2 in lungs is also less for mammals than for birds, which renew the air in their lungs with every exhalation. - This is one reason mammals function less well than birds at high altitude.
36
what part of nervous system controls breathing?
- The neurons mainly responsible for regulating breathing are in the medulla oblongata, near the base of the brain. - Neural circuits in the medulla form a breathing control center that establishes the breathing rhythm. - When you breathe deeply, a negative-feedback mechanism prevents the lungs from overexpanding: During inhalation, sensors that detect stretching of the lung tissue send nerve impulses to the control circuits in the medulla, inhibiting further inhalation. - The pons, a part of the brain next to the medulla, also regulates breathing, although its exact role remains an open question. The pons may act in the regulatory circuit with the medulla or modulate the output of that circuit
37
pH and regulation of breathing
- In regulating breathing, the medulla uses the pH of the surrounding tissue fluid as an indicator of blood CO2 concentration. - The reason pH can be used in this way is that blood CO2 is the main determinant of the pH of cerebrospinal fluid, the fluid surrounding the brain and spinal cord. - Carbon dioxide diffuses from the blood to the cerebrospinal fluid, where it reacts with water and forms carbonic acid (H2CO3). The H2CO3 can then dissociate into a bicarbonate ion (HCO3-) and a hydrogen ion (H+): CO2 + H2O <=> H2CO3 <=> HCO3- + H+
38
pH and exercise
Increased metabolic activity, such as occurs during exercise, lowers pH by increasing the concentration of CO2 in the blood. - Sensors in blood vessels and the medulla detect this pH change. - In response, the medulla’s control circuits increase the depth and rate of breathing. Both remain high until the excess CO2 is eliminated in exhaled air and pH returns to a normal value.
39
gas exchange at alveolar capillaries
- Blood flowing through the alveolar capillaries has a lower PO2 and a higher PCO2 than the air in the alveoli. - As a result, CO2 diffuses down its partial pressure gradient from the blood to the air in the alveoli. - Meanwhile, O2 in the air dissolves in the fluid that coats the alveolar epithelium and diffuses into the blood. - By the time the blood leaves the lungs in the pulmonary veins, its PO2 has been raised and its PCO2 has been lowered. After returning to the heart, this blood is pumped through the systemic circuit.
40
gas exchange at tissue capillaries
- In the tissue capillaries, gradients of partial pressure favor the diffusion of O2 out of the blood and CO2 into the blood. - These gradients exist because cellular respiration in the mitochondria of cells near each capillary removes O2 from and adds CO2 to the surrounding interstitial fluid. - After the blood unloads O2 and loads CO2, it is returned to the heart and pumped to the lungs again.
41
respiratory pigments
- The low solubility of O2 in water (and thus in blood) poses a problem for animals that rely on the circulatory system to deliver O2 - Respiratory pigments circulate with the blood or hemolymph and are often contained within specialized cells - greatly increase the amount of O2 that can be carried in the circulatory fluid - distinct color; protein bound to metal
42
hemocyanin
respiratory pigment One example is the blue pigment hemocyanin, which has copper as its oxygen-binding component and is found in arthropods and many molluscs.
43
hemoglobin
The respiratory pigment of almost all vertebrates and many invertebrates is hemoglobin. In vertebrates, it is contained in the erythrocytes.
44
hemoglobin structure
``` - Vertebrate hemoglobin consists of four subunits (polypeptide chains), each with a cofactor called a heme group that has an iron atom at its center. - Each iron atom binds one molecule of O2; hence, a single hemoglobin molecule can carry four molecules of O2. ```
45
hemoglobin reversible binding
- Like all respiratory pigments, hemoglobin binds O2 reversibly, loading O2 in the lungs or gills and unloading it in other parts of the body. - This process depends on cooperativity between the hemoglobin subunits. - When O2 binds to one subunit, the others change shape slightly, increasing their affinity for O2. - When four O2 molecules are bound and one subunit unloads its O2, the other three subunits more readily unload O2, as an associated shape change lowers their affinity for O2.
46
dissociation curve for hemoglobin
- Cooperativity in O2 binding and release is evident in the dissociation curve for hemoglobin. - Over the range of PO2 where the dissociation curve has a steep slope, even a slight change in PO2 causes hemoglobin to load or unload a substantial amount of O2. - Notice that the steep part of the curve corresponds to the range of PO2 found in body tissues. - When cells in a particular location begin working harder—during exercise, for instance—PO2 dips in their vicinity as the O2 is consumed in cellular respiration. Because of the effect of subunit cooperativity, a slight drop in PO2 causes a relatively large increase in the amount of O2 the blood unloads.
47
bohr shift
- The production of CO2 during cellular respiration promotes the unloading of O2 by hemoglobin in active tissues. - As we have seen, CO2 reacts with water, forming carbonic acid, which lowers the pH of its surroundings. Low pH, in turn, decreases the affinity of hemoglobin for O2, an effect called the Bohr shift. - Thus, where CO2 production is greater, hemoglobin releases more O2, which can then be used to support more cellular respiration.
48
hemoglobin and CO2
- hemoglobin helps transport CO2 and assists in buffering the blood—that is, preventing harmful changes in pH. - Only about 7% of the CO2 released by respiring cells is transported in solution in blood plasma. - Another 23% binds to the amino ends of the hemoglobin polypeptide chains, and - about 70% is transported in the blood in the form of bicarbonate ions (HCO3-).
49
how is bicarbonate formed in the blood
- carbon dioxide from respiring cells diffuses into the blood plasma and then into erythrocytes. There the CO2 reacts with water (assisted by the enzyme carbonic anhydrase) and forms H2CO3, which dissociates into H+ and HCO3-. - Most of the H+ binds to hemoglobin and other proteins, minimizing the change in blood pH. - The HCO3- diffuses into the plasma.
50
conversion of bicarbonate to CO2
``` - When blood flows through the lungs, the relative partial pressures of CO2 favor the diffusion of CO2 out of the blood. - As CO2 diffuses into alveoli, the amount of CO2 in the blood decreases. This decrease shifts the chemical equilibrium in favor of the conversion of HCO3- to CO2, enabling further net diffusion of CO2 into alveoli. - Overall, the PCO2 gradient is sufficient to reduce PCO2 by roughly 15% during passage of blood through the lungs. ```
51
adaptation of diving mammals
ability to store large amounts of O2. | - Compared with humans, the Weddell seal can store about 2x as much O2 and 2x the blood per kilogram of body mass
52
myoglobin
Diving mammals also have a high concentration of an oxygen-storing protein called myoglobin in their muscles. The Weddell seal can store about 25% of its O2 in muscle, compared with only 13% in humans