This Study Guide Key has additional answers to questions that you did not have
to complete but all you answer are available here.
I. Aids to Understanding Words
alveoli – small cavity
cric – ring
epi – upon
hemo – blood
1. Ventilation –movement of air in and out of the lungs.
2. Gas Exchange – the exchange of gases between the blood and the
air in the lungs.
3. Gas Transport – the process of transporting blood to and from the
lungs to and from body cells.
4. Cellular respiration – the process of oxygen utilization and carbon
dioxide production at the cellular level.
III. Organs of the Respiratory System
A. Drawing to label.
B. Mucus entraps dust
The sinuses lighten the skull and provide vocal resonance.
The mucous membrane warms and humidifies air entering the nose.
The cilia provide movement to the mucus layer.
C. The sinuses are air filled cavities located within the maxillary, frontal,
ethmoid, and sphenoid bones.
D. The pharynx is behind the oral cavity. It links the nasal cavity and the
E. 1. Drawing to label.
2. The structure of the larynx that helps close the glottis during
swallowing is the epiglottis.
3. The structures of the larynx that produce sound are the vocal
F. The trachea is a hollow tube that is flexible and extends downward in
front of the esophagus into the thoracic cavity. The inner wall of the
trachea is composed of ciliated mucous membrane whose function is
to move entrapped particles upward to the pharynx.
G. 1. Drawing to label.
2. The alveoli of the lung increase the surface area available for gas
exchange and present a surface across which gas can diffuse.
H. 1. The right lung has three lobes; the left lung has two lobes.
2. The pleural cavity is formed when the parietal pleura folds back
over the visceral pleura that cover the surface of the lung. This
creates a potential space which is filled with pleural fluid.
IV. Breathing Mechanisms
A. 1. During inspiration, it is the atmospheric pressure that moves air into
the lungs. Atmospheric pressure at sea level is 760 millimeters of
pressure. If the pressure in the lungs is reduced below 760 mm of
mercury, air will be forced into the lungs. A number of events
create just this situation.
Pressure and volume are inversely related; as one increases the
other decreases. When the diaphragm contracts, it moves
downward. When the intercostals muscle contract, they pull the
ribs up. These actions increase the anterior/posterior size as well
as the superior/inferior size of the chest. These actions decrease
the pressure in the thoracic cavity allowing atmospheric pressure to
push air into the lungs.
2. The fluid in the pleural cavity creates surface tension between the
two pleural membranes. The effect of this is to pull the visceral
pleura along with the parietal pleural as the chest wall expands and
contracts. Surface tension in the alveoli is the result of moisture in
the small sacs which can create a force to pull the walls of the
alveoli together. This would not support gas exchange.
3. Surfactant is a fluid synthesized by the alveoli which overcomes the
attraction created by surface tension.
B. Expiration is essentially a passive process. As the diaphragm and
intercostal muscles relax, the size of the chest cavity, increasing the
pressure, and forcing air out of the lungs.
C. 1-h; 2-d; 3-e; 4-f; 5-g; 6-b; 7-c; 8-a
D. A neonate’s first breath is his most difficult one because this breath
must overcome the force of surface tension in opening alveoli that
have never been filled with air. Without sufficient surfactant, the
neonate may not be able to overcome surface tension and inflate the
V. Control of Breathing
A. Neural – the respiratory center in the brain stem control both
inspiration and expiration.
Muscular – The muscles of respiration are the intercostals muscles and
the diaphragm, and the muscles of the abdominal wall. These muscles
contract with varying degrees of strength and with various degrees of
Skeletal – Normal respiration depends upon an intact rib cage upon
which the muscles of respiration can act.
Pulmonary – the pulmonary structures involved in breathing are the
structures of the bronchial tree, the bronchioles, and the alveoli.
B. The respiratory center of the central nervous system is a complex
network of neurons located in the brain stem, primarily in the medulla
and the pons. There are two centers of special interest: the
rhythmicity center in the medulla and the pneumotaxic center of the
pons. The medullary rhythmicity center includes two groups of
neurons that extend the length of the medulla oblongata. These
groups are the dorsal respiratory group and the ventral respiratory
group. The dorsal group controls the basic rhythm of inspiration
sending motor impulses to the diaphragm and other respiratory
muscles to contract. These impulses are not sent during expiration.
The ventral group is active only when more forceful respiratory activity
is needed. These neurons generate impulses that result in both
forceful inspiration and expiration.
The neurons in the pneumotaxic group control the rate of respiration by
inhibiting the impulses of the dorsal respiratory group.
C. Various chemical factors influence the rate and depth of respiration.
There are chemoreceptors in the medulla oblongata that respond to
changes in the cerebrospinal fluid concentration of carbon dioxide and
hydrogen ions. Low oxygen content in the blood is detected by
sensors in the walls of the carotid arteries and the aorta. Oxygen
concentration must be extremely low to stimulate these receptors.
Oxygen plays a very small role in the regulation of respiration.
An inflation reflex senses the pressure within the lung tissue and
prevents over inflation by regulation of the depth of respiration.
VI. Alveolar Gas Exchange
A. The wall of an alveolus consists of an inner lining of simple squamous
epithelium and a dense network of capillaries. These capillaries are
also lined with simple squamous epithelium. Thin, fused basement
membranes separate the two layers and make up the respiratory
membrane. Gas exchange is accomplished across this membrane.
B. 1. The pressure of gas determines the direction in which it will move
and the rate at which it will move. Since the concentration of
oxygen (or its partial pressure) is greatest in the alveoli, oxygen will
move out of the alveoli and into the capillary.
2. In a mixture of gases, each gas contributes to the total pressure of
the gases and is known as its partial pressure. For instance, the
air of the atmosphere is a mixture of gases: oxygen is 21% of the
mixture. Its partial pressure is calculated by multiplying 0.21 and
760 mm Hg (atmospheric pressure at sea level) to find its partial
pressure of 160 mm of Hg.
3. The mixture of gases returning to the alveoli of the lungs has lost
some of its oxygen to the cells of the body and has therefore a
lower partial pressure of oxygen than the air in the lungs. Oxygen
will therefore move into the capillary blood in the lungs.
VII. Gas Transport
A. 1. Gases dissolve in the plasma of blood and oxygen then combines
with the hemoglobin of red blood cells for transportation to cells of
2. Oxygen is released at the cell because the partial pressure of
oxygen in the cells is less than that in the blood. Oxygen
dissociates from the hemoglobin molecule and crosses the cell
membrane. Carbon dioxide, obeying the law of partial pressure,
moves out of the cell land into the plasma of the capillary blood.
B. carbon monoxide
C. 1. A variety of mechanisms are used to carry carbon dioxide away
from cells. Up to 7% of carbon dioxide can be transported
dissolved in plasma. The partial pressure of carbon dioxide
determines the amount of carbon dioxide that is carried in this
manner. Carbon dioxide can bind to the amino groups of the globin
portion of hemoglobin. It does not compete with the oxygen for
binding sites. The most important mechanism of carbon dioxide is
in the formation of bicarbonate ions. The gas reacts with water to
carbonic acid catalyzed by carbonic anhydrase. This molecule
dissociates to form hydrogen ions and bicarbonate ions.
2. Carbon dioxide is lost in the lung because its concentration or
partial pressure is greater than its concentration or partial pressure
in the air in the alveoli.