Respiratory System Review

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Respiratory System Review

    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

    in breathing.

    • Label the diagram:

    Page 4. Demonstration of Pleurae and

    the Lungs

    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

    each alveolus.

    • 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

    System Structures

    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

    exchange occurs.

    • Oxygen and carbon dioxide diffuse between the alveoli and the pulmonary capillaries across the very thin

    respiratory membrane.

    Gas Transport

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

    dioxide transport.

Page 3. Oxygen Transport

    • Transport of oxygen during external respiration:

    With its low solubility, only approximately 1.5% of the oxygenis transported dissolved

    in plasma.

    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

    reactants present.

    • 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

    98% saturated.

    • 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

    P's O2

    • 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

    active tissues.

    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:

    1. pH

    2. temperature

    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

    the left.

    • A similar shift to the left occurs in response to increased pH, decreased P, and CO2

    decreased BPG.

    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

    the plasma.

    • 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

    Haldane effect.

    • 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

    this diagram:

    • 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

    blood pH.

    • 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.

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