Anatomy Review: Respiratory Structures
Graphics are used with permission of: Pearson Education Inc., publishing as Benjamin Cummings
Page 1. Introduction
• As they function, our cells use oxygen and produce carbon dioxide.
• The respiratory system brings the needed oxygen into and eliminates carbon dioxide from the body by
working closely with the cardiovascular system. • The blood transports these gases, carrying oxygen to the tissues and carbon dioxide to the lungs.
Page 2. Goals
• To review the major organs of the respiratory system.
• To examine the structures of the respiratory zone of the lungs.
• To explore the microscopic anatomy of an alveolus.
Page 3. Overview: Respiratory System Organs • Let's review the organs of the
respiratory system by following the
flow of air.
• Air enters the nose by passing
through two openings called the
external nares, or nostrils.
• Within the nose, the air passes
through the nasal cavity, and then
travels through the pharynx, a
muscular tube which carries both
food and air throughout most of its
• Air then enters the larynx.
• After passing through the larynx,
air enters the trachea, which is held
open by incomplete rings of cartilage. • The trachea divides into a right and
a left primary bronchus, which carry the air into the lungs. • Although not part of the respiratory system, the diaphragm and the intercostal muscles play important roles
• Label the diagram:
Page 4. Demonstration of Pleurae and
• Each lung is surrounded by two layers of
serous membrane known as the pleurae.
• The relationship between the pleurae and the lungs can be demonstrated by pushing a fist
into a water-filled balloon. The balloon represents the pleurae, and the fist represents the lung.
• As the fist pushes into the balloon, notice how the balloon wraps around it, and the opposite surfaces of the
balloon almost touch.
• The inner part of the balloon which wraps around the fist represents the visceral pleura. The visceral pleura is the part of the pleura which covers the surface of the lungs.
• The outer part of the balloon represents the parietal pleura, which lines the mediastinum, the diaphragm,
and the thoracic wall.
• Notice that the visceral and parietal pleurae are actually a continuation of the same membrane. • The water-filled space between the two layers represents the pleural cavity, which contains pleural fluid.
Page 5. Visceral and Parietal Pleura
• The visceral pleura and parietal pleura enclose each lung in a separate sac. The frosty layer you see here
covering the lung is the portion of the parietal pleura that lines the anterior thoracic wall.
• The visceral pleura covers the surface of the lungs and the cut edges of the parietal pleura.
• The pleural cavity is an extremely thin, slit-like space between the pleurae, separating them by a thin layer
of pleural fluid. The pleural fluid assists in breathing movements by acting as a lubricant.
• The parietal pleura lines the mediastinum, the superior surface of the diaphragm, and the inner thoracic wall.
Page 6. Bronchial Tree
• The lungs contain many branching airways
which collectively are known as the bronchial
• Air enters the lungs through the primary
bronchi, which branch into secondary bronchi,
which in turn branch into tertiary bronchi.
• The trachea and all the bronchi have
supporting cartilage which keeps the airways
• Air flows deeper into the lungs as the
tertiary bronchi branch repeatedly into smaller
bronchi, which eventually branch into
• Bronchioles lack cartilage and contain more
smooth muscle in their walls than the bronchi.
These features allow airflow regulation by altering the diameter of the bronchioles. • Bronchioles branch further into terminal bronchioles.
• The airways from the nasal cavity through the terminal bronchioles are called the conducting zone. The air
is moistened, warmed, and filtered as it flows through these passageways. • Beyond the terminal bronchioles, the air enters the respiratory zone, the region of the lung where gas exchange occurs.
• Label the diagram on the next page.
Page 7. Respiratory Zone
• Beyond the terminal bronchioles lie the structures
of the respiratory zone, where we begin to find
alveoli, tiny thin-walled sacs where gas exchange
• Respiratory bronchioles have scattered alveoli in
their walls. They lead into alveolar ducts, which are
completely lined by alveoli. These ducts end in
clusters of alveoli called alveolar sacs.
• Label the diagram on.
Page 8. Alveoli and Pulmonary Capillaries
• The pulmonary arteries carry blood which is low in oxygen
from the heart to the lungs.
• These blood vessels branch repeatedly, eventually forming
dense networks of capillaries that completely surround
• This rich blood supply allows for the efficient exchange of
oxygen and carbon dioxide between the air in the alveoli
and the blood in the pulmonary capillaries.
• Blood leaves the capillaries via the pulmonary veins, which
transports the freshly oxygenated blood out of the lungs
and back to the heart.
Page 9. Structure of an Alveolus
• Structure of the inside of an individual alveolus
shows three types of cells:
1. simple squamous epithelium
2. alveolar macrophages
3. surfactant-secreting cells
• The wall of an alveolus is primarily composed of
simple squamous epithelium, or Type I cells. Gas
exchange occurs easily across this very thin
• The alveolar macrophages, or dust cells, creep
along the inner surface of the alveoli, removing
debris and microbes.
• The alveolus also contains scattered surfactant-
secreting, or Type II, cells.
Page 10. Role of Surfactant
• The inside surface of the alveolus is lined with alveolar fluid. • The water in the fluid creates a surface tension. Surface tension is due to the strong attraction between water molecules at the surface of a liquid, which draws the water molecules closer together. • As seen here, this force pulls the alveolus inward and reduces its size. If an alveolus were lined with pure water, it would collapse.
• Surfactant, which is a mixture of phospholipids and lipoproteins, lowers the surface tension of the fluid by
interfering with the attraction between the water molecules, preventing alveolar collapse.
• Without surfactant, alveoli would have to be completely reinflated between breaths, which would take an
enormous amount of energy.
Page 11. Structure of the Respiratory Membrane
• The wall of an alveolus and the wall of a capillary form the respiratory membrane, where gas exchange
• The respiratory membrane is made up of two layers of simple squamous epithelium and their basement
membranes. This membrane is extremely thin, averaging 0.5 micrometers in width. • Notice also that in many regions of the membrane there is no interstitial fluid. This is because pulmonary
blood pressure is so low that little fluid filters out of the capillaries into the interstitial space. Oxygen and carbon dioxide can diffuse easily across this thin respiratory membrane.
• Label the diagram:
Page 12. Review: Respiratory
Page 13. Summary
• The respiratory system consists of the nose, pharynx, larynx, trachea, bronchi, and lungs.
• The visceral pleura covers the surface of the lungs. The parietal pleura covers the mediastinum and the diaphragm, and lines the thoracic wall.
• The lungs contain the bronchial tree, the branching airways from the primary
bronchi through the terminal bronchioles. • The respiratory zone of the lungs is the region containing alveoli, tiny thin-walled sacs where gas
• Oxygen and carbon dioxide diffuse between the alveoli and the pulmonary capillaries across the very thin
Page 1. Introduction
• The blood transports oxygen and carbon dioxide between the lungs and other tissues
throughout the body.
• These gases are carried in several different forms:
1. dissolved in the plasma
2. chemically combined with hemoglobin 3. converted into a different molecule
Page 2. Goals
• To explore how oxygen is transported in the blood. • To explore how carbon dioxide is transported in the blood.
• To understand the effect of variables, such as P and P, on oxygen and carbon OCO22
Page 3. Oxygen Transport
• Transport of oxygen during external respiration:
• With its low solubility, only approximately 1.5% of the oxygenis transported dissolved
• The remaining 98.5% diffuses into red blood cells and chemically combines with
• Label this diagram:
Page 4. Hemoglobin
• Within each red blood cell, there are
approximately 250 million hemoglobin
• Each hemoglobin molecule consists of:
1. A globin portion composed of 4 polypeptide
2. Four iron-containing pigments called heme
• Each hemoglobin molecule can transport up
to 4 oxygen molecules because each iron atom
can bind one oxygen molecule.
• When 4 oxygen molecules are bound to hemoglobin, it is 100% saturated; when there are fewer, it is partially saturated.
• Oxygen binding occurs in response to the high partial pressure of oxygen in the lungs. • When hemoglobin binds with oxygen, it is called oxyhemoglobin.
• When one oxygen binds to hemoglobin, the other oxygen molecules bind more readily. This is called cooperative binding. Hemoglobin's affinity for oxygen increases as its saturation increases.
• Label this diagram:
Page 5. Oxyhemoglobin and
• The formation of oxyhemoglobin occurs
as a reversible reaction, and is written
as in this chemical equation:
• In reversible reactions, the direction depends on the quantity of products and
• In the lungs, where the partial pressure of oxygen is high, the reaction proceeds to the
right, forming oxyhemoglobin.
• In organs throughout the body where the partial pressure of oxygen is low, the reaction
reverses, proceeding to the left. Oxyhemoglobin releases oxygen, forming
deoxyhemoglobin, which is also called reduced hemoglobin.
• Notice that the affinity of hemoglobin for oxygen decreases as its saturation decreases.
Page 6. Oxygen-Hemoglobin Dissociation Curve
• The degree of hemoglobin saturation is determined by the partial pressure of oxygen,
which varies in different organs throughout the body.
• When these values are graphed, they produce the oxygen-hemoglobin dissociation
curve. Notice that the axes on the graph are: partial pressure of oxygen and percent
saturation of hemoglobin.
• In the lungs, the partial pressure of oxygen is approximately 100 millimeters of
mercury. At this partial pressure, hemoglobin has a high affinity for oxygen, and is
• In the tissues of other organs, a typical partial pressure of oxygen is 40 millimeters of
mercury. Here, hemoglobin has a lower affinity for oxygen and releases some but not
all of its oxygen to the tissues. When hemoglobin leaves the tissues it is still 75%
• Label this graph as you proceed through this page:
• Notice that the oxygen-hemoglobin
dissociation curve is an S-shaped
curve, with a nearly flat slope at high
P's and a steep slope at low P's. OO22
Page 7. Hemoglobin Saturation at High
• A closer look at the flat region of the
oxygen-hemoglobin dissociation curve
between 80 and 100 millimeters of
• In the lungs at sea level, a typical P O2
is 100 millimeters of mercury. At this
P, hemoglobin is 98% saturated. O2
• In the lungs of a hiker at higher elevations or a person with particular
cardiopulmonary diseases, the P may be 80 millimeters of mercury. At this P, OO22
hemoglobin is 95% saturated.
• Notice that even though the P differs by 20 millimeters of mercury there is almost O2
no difference in hemoglobin saturation. This means that although the P in the O2
lungs may decline below typical sea level values, hemoglobin still has a high affinity
for oxygen and remains almost fully saturated.
Page 8. Hemoglobin Saturation at Low P's O2
• A closer look at the steep region of the graph between 20 and 40 millimeters of
• A P of 40 millimeters of mercury is typical in resting organs. O2
• At 40 millimeters of mercury, hemoglobin has a lower affinity for oxygen and is 75%
• In vigorously contracting muscles, would you expect the P is lower than in resting O2
muscle because an actively contracting muscle uses more oxygen, so it has a lower
P than a resting muscle, typically 20 millimeters of mercury. At this P, OO22
hemoglobin is only 35% saturated.
• As the Pdecreases, hemoglobin releases much more oxygen to the tissues. This O2
allows the body to closely match oxygen unloading by hemoglobin to oxygen
utilization by the tissues.
• Fill in the blanks on the graph with the appropriate letters below:
a. Corresponds to the partial pressure of oxygen in the
lungs at a high altitude.
b. Corresponds to the partial pressure of oxygen in the
tissues at rest.
c. Corresponds to the partial pressure of oxygen in the
lungs at a low altitude.
d. Corresponds to the partial pressure of oxygen in
e. Corresponds to the percent saturation of hemoglobin
in the lungs at a high altitude.
f. Corresponds to the percent saturation of hemoglobin
in the tissues at rest.
g. Corresponds to the percent saturation of hemoglobin
in the lungs at a low altitude.
h. Corresponds to the percent saturation of hemoglobin
in active tissues.
Page 9. Factors Altering Hemoglobin Saturation
• Factors which alter hemoglobin saturation:
3. P CO2
4. BPG (2,3-biphosphoglycerate)
• All of these factors, together or individually, play a role during exercise. • During vigorous exercise, contracting muscles produce more metabolic acids, such as
lactic acid, which lower the pH, more heat, and more carbon dioxide. In addition,
higher temperature and lower P increase the production of BPG by the red blood O2
• These conditions decrease hemoglobin's affinity for oxygen, releasing more oxygen to
the active muscle cells.
• Let's look at a typical P of active muscle, 20 millimeters of mercury. At a normal O2
blood pH, hemoglobin releases 65% of its oxygen to the muscle cells, and remains
35% saturated. However, as the muscle cells release lactic acid, the pH decreases
and hemoglobin releases 75% of its oxygen, leaving it 25% saturated. • When pH decreases, the curve shifts to the right. This represents increased oxygen
unloading compared to normal blood pH. A similar shift to the right occurs in
response to increased temperature, P, or BPG. CO2
• Label this graph:
Page 10. Predict the Effect of Decreased Temperature
• Label this graph:
• If body tissues are chilled, their hemoglobin saturation changes.
• At decreased temperatures, hemoglobin's affinity for oxygen is higher, so hemoglobin
releases less oxygen to less active tissues. Represented graphically, the curve shifts to
• A similar shift to the left occurs in response to increased pH, decreased P, and CO2
Page 11. COTransport 2
• Carbon dioxide transport:
• Carbon dioxide is produced by cells throughout the
• It diffuses out of the cells and into the systemic
capillaries, where approximately 7% is transported
dissolved in plasma.
• The remaining carbon dioxide diffuses into the red
blood cells. Within the red blood cells,
approximately 23% chemically combines with
hemoglobin, and 70% is converted to bicarbonate
ions, which are then transported in the plasma.
• Fill in this diagram:
Page 12. CO Transport: Carbaminohemoglobin (Tissues) 2
• Of the total carbon dioxide in the blood, 23% binds to the
globin portion of the hemoglobin molecule to form
carbaminohemoglobin, as written in this equation:
• Carbaminohemoglobin forms in regions of high P, as CO2
blood flows through the systemic capillaries in the
Page 13. CO Transport: Carbaminohemoglobin (Lungs) 2
• The formation of carbaminohemoglobin is reversible.
• In the lungs, which have a lower P, carbon CO2
dioxidedissociates from carbaminohemoglobin,
diffuses into the alveoli, and is exhaled.
Page 14. COTransport: Bicarbonate Ions (Tissues) 2
• Of the total carbon dioxide in the blood, 70% is converted into bicarbonate ions within the
red blood cells, in a sequence of reversible reactions. The bicarbonate ions then enter
• In regions with high P, carbon dioxide enters the red blood cell and combines with CO2
water to form carbonic acid. This reaction is catalyzed by the enzyme carbonic
anhydrase. The same reaction occurs in the plasma, but without the enzyme it is very
• Carbonic acid dissociates into hydrogen ions and bicarbonate ions. The hydrogen ions
produced in this reaction are buffered by binding to
hemoglobin. This is written as HHb.
• In order to maintain electrical neutrality, bicarbonate
ions diffuse out of the red blood cell and chloride ions
diffuse in. This is called the chloride shift.
• Within the plasma, bicarbonate ions act as a buffer and
play an important role in blood pH control.
• Label this diagram to show what happens at the tissues:
Page 15. COTransport: Bicarbonate Ions (Lungs) 2
• In the lungs, carbon dioxidediffuses out of the plasma and into the alveoli. This lowers
the P in the blood, causing the chemical reactions to reverse and proceed to the left. CO2
• In the lungs, the bicarbonate ions diffuse back into the red blood cell, and the chloride
ions diffuse out of the red blood cell. Recall that this
is called the chloride shift.
• The hydrogen ions are released from hemoglobin, and
combine with the bicarbonate ion to form carbonic
• Carbonic acid breaks down into carbon dioxide and
water. This reverse reaction is also catalyzed by the
enzyme carbonic anhydrase.
• Label this diagram:
Page 16. Summary: OLoadingand CO Unloading in the Lungs 2 2
• Summary of external respiration in the lungs.
• Although we will look at the processes step by step, they actually occur simultaneously.
• Remember, gases always follow their partial pressure gradients.
• As you go through the steps, place the numbers that correspond with the steps in the
blanks on this diagram:
• During external respiration, a small amount of oxygen (1) remains dissolved in the plasma.
However, the majority of the oxygen (2) continues into the red blood cells, where it
combines with deoxyhemoglobin (3) to form oxyhemoglobin (4), releasing a hydrogen ion
• When hemoglobin is saturated with oxygen, its affinity for carbon dioxide decreases. Any
carbon dioxide combined with hemoglobin (6) dissociates and diffuses out of the red
blood cell (7), through the plasma and into the alveoli. In other words, oxygen loading
facilitates carbon dioxide unloading from hemoglobin. This interaction is called the
• The hydrogen ion released from hemoglobin combines with a bicarbonate ion (8), which
diffuses into the red blood cell from the plasma in exchange for a chloride ion (9). Recall
that this exchange is the chloride shift. The reaction between hydrogen and bicarbonate
ions forms carbonic acid (10).
• Carbonic acid then breaks down into water and carbon dioxide (11), catalyzed by the
enzyme carbonic anhydrase. The water produced by this reaction may leave the red
blood cell, or remain as part of the cytoplasm. The carbon dioxide diffuses out of the red
blood cell (12) into the plasma and then into the alveoli. The small amount of carbon
dioxide transported in the plasma diffuses into the alveoli (13).
Page 17. Summary: OUnloading and CO Loading 2 2
in the Tissues
Summary of internal respiration in the tissues.
• As you go through the steps, place the numbers
that correspond with the steps in the blanks on
• During internal respiration, a small amount of
carbon dioxide (1) remains dissolved in the
plasma, but most of the carbon dioxide (2)
continues into the red blood cells where much of
it combines with water to form carbonic acid (3)
or combines with hemoglobin to form
carbaminohemoglobin (11). This reaction is
catalyzed by carbonic anhydrase. The carbonic acid then dissociates into hydrogen and
bicarbonate ions (4).
• During the chloride shift, bicarbonate ions (5) diffuse out of the red blood cell in exchange
for chloride ions (6). Bicarbonate ions act as buffers within the plasma, controlling
• Within the red blood cell, hydrogen ions (7) are buffered by hemoglobin (8). When
hemoglobin binds hydrogen ions, it has a lower affinity for oxygen. As a result, oxygen
(9) dissociates from hemoglobin, diffuses out of the red blood cell and into the tissues.
The interaction between hemoglobin's affinity for oxygen and its affinity for hydrogen
ions is called the Bohr effect. By forming hydrogen ions, carbon dioxide loading
facilitates oxygen unloading.
• The small amount of oxygen transported in the dissolved state (10) also diffuses out of the
plasma and into the tissue cells.