22 Chapter Study Guide
Caryn p3
1. Many animals are capable of exchanging gases from environments humans would find inhospitable.
Some birds can stand the cold and low oxygen concentrations of altitudes of 20,00030,000 feet.
They have more efficient lungs, hemoglobin with a very high affinity for oxygen, a larger number of
capillaries, and muscle proteins that hold oxygen.
2. People born in and adapted to high altitudes have relatively large lungs and hearts, more red blood
cells, and elevated hemoglobin concentrations. A short period of conditioning will help those living
in lower altitudes acclimate to higher altitudes. Faster heart rate and larger capillary diameter are
replaced over time with deeper and more rapid rates of breathing, more capillaries, and higher
numbers of red blood cells and levels of hemoglobin.
I.
MechanismsofGasExchange
- There are three steps to gas exchange:
1. Breathing involves inhaling O2 and exhaling CO2
2. The transport of gases involves diffusion into and transport by hemoglobin in the red blood cells of
the circulatory system.
3. Blood supplies every cell with O2 and picks up waste CO2.
- The portion of an animal where gas exchange with the environment takes place is called the
respiratory surface. Respiratory surfaces vary among animal groups. However, what all respiratory
surfaces have in common is that they must be moist, thin, and extensive. Gases must be dissolved in
water before they can diffuse across a body surface.
- There are four types of respiratory:
1.
Earthworms and other skin breathers must live in moist environments to keep their skin moist.
Small size or flatness provides the high ratio of respiratory surface to body volume required for
efficient gas exchange between environment and cells
2. Gills have evolved in most aquatic animals to increase the respiratory surface. They generally
project from the body surface.
3. A system of branching tubes is used by insects and is called a trachealsystem. These branched tubes
bring external gases directly to the inner cells without the aid of the circulatory system.
4. Lungs are found in the majority of terrestrial vertebrates. They are composed of branched tubes
ending in tiny internal sacs lined with a moist epithelium. Gases are carried between the lungs and
body cells by the circulatory system.
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However, the concentration of O2 is only 35% of its concentration in air, and the warmer and
saltier the water, the less O2 it can carry. Consequently, gills must be very efficient to extract O 2
from water.
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Energy is expended as a fish covers its gill surfaces with water by inhaling water with its opercula
closed and mouth opened, and exhaling the water across the gills with its mouth closed and
opercula opened. The process of increasing contact of the surface area with oxygen is called
ventilation regardless of if its a fish, bird, or any other animal.
- Countercurrentexchange is a general principle of transfer found in many animal systems. Countercurrent
exchange is the transfer of a substance from a fluid flowing in one direction to another fluid moving
in the opposite direction.
. Air contains much more O2 than an equal volume of water, and air is easier to move than water. Thus,
terrestrial animals expend less energy in ventilating their respiratory surfaces.
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Tracheae in an insect branch throughout the body, conveying air directly to body cells. Included in
the system are tracheal air sacs that work like bellows when muscles around them alternately
contract and relax, moving air out and in. Water is conserved and respiratory surfaces remain moist
because only the narrowest tubes, the tracheoles, contain fluid. It is across the tracheoles that gas
exchange occurs.
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Since lungs are restricted to one part of the body, unlike tracheae, the circulatory system must be
involved in transporting the gases to and from cells. body Amphibians supplement their lungs with
skin breathing, but all other terrestrial vertebrates (and aquatic reptiles and mammals) have efficient
lungs only.
The human respiratory system is in the chest cavity and is bounded at the bottom by the diaphragm.
The human respiratory system includes:
1. The nasal cavity (filters, warms, humidifies, and samples odors of incoming air).
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2. The pharynx (controls the passage of air through the mouth region and into the larynx)
3. A branched system of tubes (tracheae and bronchi) that lead into the lungs.
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Exhaling through the vocalcords of the larynx produces sounds. High-pitched sounds are produced
by tightening the vocal cords, which will vibrate rapidly when air passes over them. Conversely,
low-pitched sounds are made with relaxed vocal cords.
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Breathing is the inhalation of air followed by exhalation of air. During inhalation, the rib cage
expands, the rib muscles and diaphragm contract, and the chest expands. The lungs also increase in
size. These changes reduce the air pressure within the alveoli, and air moves in as a result of the
higher pressure outside. This is called negativepressurebreathing. During exhalation, both the rib
muscles and diaphragm relax, decreasing the volume of the rib cage and forcing air out.
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Although breathing can be consciously controlled, most of the time automatic control centers in our
brain regulate our breathing movements. Breathingcontrolcenters are located in the lower parts
of the brainstem, the pons and the medulla oblongata. About 1014 times a minute, nerves from
those areas signal the diaphragm and rib muscles to contract.
II. TransportofGasesintheBody
The human circulatory system functions in gas transport. One side of the heart pumps O 2-poor,
CO2-rich blood from the body to the lungs, and the other side of the heart pumps O 2-rich, CO2-poor
blood from the lungs to the rest of the body.
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Every gas in a mixture accounts for a portion (that gass partialpressure) of the mixtures total
pressure. At each location (lungs and tissues), gases are exchanged as they diffuse along their own
partial pressure gradient.
O2 is not very soluble in water. Hemoglobin in red blood cells has a much higher affinity for O2
than water. Hemoglobin consists of four polypeptide chains (of two types); each chain is attached to
a heme group with an iron atom in its center. Each iron atom can carry one O 2 molecule
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Hemoglobin not only transports oxygen, but also carries CO2 and can help buffer harmful pH
changes in the blood. Within red blood cells, CO2 reacts with water to form carbonic acid (H2CO3).
This breaks into acidic hydrogen ions and basic bicarbonate ions more quickly in red blood cells
under the control of an enzyme (carbonic anhydrase). Hemoglobin picks up most of the hydrogen
ions and allows most of the bicarbonate to diffuse back into the plasma. This provides a buffer in the
blood that will react with any hydrogen ions that are picked up elsewhere.
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When blood flows through the lungs, the process is reversed. Hydrogen ions are given up by the
hemoglobin, reacting with the bicarbonate (HCO32) ions to form carbonic acid. This is then
converted back into CO2, and the CO2 diffuses from the blood to the air. The fetus lies within a
watery bath of amniotic fluid. Its lungs are filled with this fluid.
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Capillaries from the fetal blood supply (through the umbilical cord) mix with capillaries of the uterus
in the placenta. A fetus also has a different type of hemoglobin from the mother. This fetal
hemoglobin has a higher affinity for oxygen than normal adult hemoglobin, thus enhancing the
transfer of O2 from mother to fetus. When the baby is born and placental transfer stops, CO 2
concentration in the blood increases, lowering the pH and stimulating the breathing center, causing
the baby to take its first breath.