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Contents
1. Chapter 1. An Introduction to the Human Body
1. 1.0 Introduction
2. 1.1 How Structure Determines Function
3. 1.2 Structural Organization of the Human Body
4. 1.3 Homeostasis
5. 1.4 Anatomical Terminology
6. 1.5 Medical Imaging
2. Chapter 2. The Chemical Level of Organization
1. 2.0 Introduction
2. 2.1 Elements and Atoms: The Building Blocks of Matter
3. 2.2 Chemical Bonds
4. 2.3 Chemical Reactions
5. 2.4 Inorganic Compounds Essential to Human Functioning
6. 2.5 Organic Compounds Essential to Human Functioning
3. Chapter 3. The Cellular Level of Organization
1. 3.0 Introduction
2. 3.1 The Cell Membrane
3. 3.2 The Cytoplasm and Cellular Organelles
4. 3.3 The Nucleus and DNA Replication
5. 3.4 Protein Synthesis
6. 3.5 Cell Growth and Division
7. 3.6 Cellular Differentiation
4. Chapter 4. The Tissue Level of Organization
1. 4.0 Introduction
2. 4.1 Types of Tissues
3. 4.2 Epithelial Tissue
4. 4.3 Connective Tissue Supports and Protects
5. 4.4 Muscle Tissue
6. 4.5 Nervous Tissue
7. 4.6 Tissue Injury and Aging
5. Chapter 5. The Integumentary System
1. 5.0 Introduction
2. 5.1 Layers of the Skin
3. 5.2 Accessory Structures of the Skin
4. 5.3 Functions of the Integumentary System
5. 5.4 Diseases, Disorders, and Injuries of the Integumentary System
6. Chapter 6. Bone Tissue and the Skeletal System
1. 6.0 Introduction
2. 6.1 The Functions of the Skeletal System
3. 6.2 Bone Classification
4. 6.3 Bone Structure
5. 6.4 Bone Formation and Development
6. 6.5 Fractures: Bone Repair
7. 6.6 Exercise, Nutrition, Hormones, and Bone Tissue
8. 6.7 Calcium Homeostasis: Interactions of the Skeletal System and Other Organ Systems
7. Chapter 7. Axial Skeleton
1. 7.0 Introduction
2. 7.1 Divisions of the Skeletal System
3. 7.2 Bone Markings
4. 7.3 The Skull
5. 7.4 The Vertebral Column
6. 7.5 The Thoracic Cage
7. 7.6 Embryonic Development of the Axial Skeleton
8. Chapter 8. The Appendicular Skeleton
1. 8.0 Introduction
2. 8.1 The Pectoral Girdle
3. 8.2 Bones of the Upper Limb
4. 8.3 The Pelvic Girdle and Pelvis
5. 8.4 Bones of the Lower Limb
6. 8.5 Development of the Appendicular Skeleton
9. Chapter 9. Joints
1. 9.0 Introduction
2. 9.1 Classification of Joints
3. 9.2 Fibrous Joints
4. 9.3 Cartilaginous Joints
5. 9.4 Synovial Joints
6. 9.5 Types of Body Movements
7. 9.6 Anatomy of Selected Synovial Joints
8. 9.7 Development of Joints
10.
Chapter 10. Muscle Tissue
1. 10.0 Introduction
2. 10.1 Overview of Muscle Tissues
3. 10.2 Skeletal Muscle
4. 10.3 Muscle Fiber Excitation, Contraction, and Relaxation
5. 10.4 Nervous System Control of Muscle Tension
6. 10.5 Types of Muscle Fibers
7. 10.6 Exercise and Muscle Performance
8. 10.7 Smooth Muscle Tissue
9. 10.8 Development and Regeneration of Muscle Tissue
11.
Chapter 11. The Muscular System
1. 11.0 Introduction
2. 11.1 Describe the roles of agonists, antagonists and synergists
3. 11.2 Explain the organization of muscle fascicles and their role in generating force
4. 11.3 Explain the criteria used to name skeletal muscles
5. 11.4 Axial Muscles of the Head Neck and Back
6. 11.5 Axial muscles of the abdominal wall and thorax
7. 11.6 Muscles of the Pectoral Girdle and Upper Limbs
8. 11.7 Appendicular Muscles of the Pelvic Girdle and Lower Limbs
12.
Chapter 12. The Nervous System and Nervous Tissue
1. 12.0 Introduction
2. 12.1 Structure and Function of the Nervous System
3. 12.2 Nervous Tissue
4. 12.3 The Function of Nervous Tissue
5. 12.4 Communication Between Neurons
6. 12.5 The Action Potential
13.
Chapter 13. The Peripheral Nervous System
1. 13.0 Introduction
2. 13.1 Sensory Receptors
3. 13.2 Ganglia and Nerves
4. 13.3 Spinal and Cranial Nerves
5. 13.4 Relationship of the PNS to the Spinal Cord of the CNS
6. 13.5 Ventral Horn Output and Reflexes
7. 13.6 Testing the Spinal Nerves (Sensory and Motor Exams)
8. 13.7 The Cranial Nerve Exam
14.
Chapter 14. The Central Nervous System
1. 14.0 Introduction
2. 14.1 Embryonic Development
3. 14.2 Blood Flow the meninges and Cerebrospinal Fluid Production and Circulation
4. 14.3 The Brain and Spinal Cord
5. 14.4 The Spinal Cord
6. 14.5 Sensory and Motor Pathways
15.
Chapter 15. The Special Senses
1. 15.0 Introduction
2. 15.1 Taste
3. 15.2 Smell
4. 15.3 Hearing
5. 15.4 Equilibrium
6. 15.5 Vision
16.
Chapter 16. The Autonomic Nervous System
1. 16.0 Introduction
2. 16.1 Divisions of the Autonomic Nervous System
3. 16.2 Autonomic Reflexes and Homeostasis
4. 16.3 Central Control
5. 16.4 Drugs that Affect the Autonomic System
17.
Chapter 17. The Endocrine System
1. 17.0 Introduction
2. 17.1 An Overview of the Endocrine System
3. 17.2 Hormones
4. 17.3 The Pituitary Gland and Hypothalamus
5. 17.4 The Thyroid Gland
6. 17.5 The Parathyroid Glands
7. 17.6 The Adrenal Glands
8. 17.7 The Pineal Gland
9. 17.8 Gonadal and Placental Hormones
18.
10.
17.9 The Pancreas
11.
17.10 Organs with Secondary Endocrine Functions
12.
17.11 Development and Aging of the Endocrine System
Chapter 18. The Cardiovascular System: Blood
1. 18.0 Introduction
2. 18.1 Functions of Blood
3. 18.2 Production of the Formed Elements
4. 18.3 Erythrocytes
5. 18.4 Leukocytes and Platelets
6. 18.5 Hemostasis
7. 18.6 Blood Typing
19.
Chapter 19. The Cardiovascular System: The Heart
1. 19.0 Introduction
2. 19.1 Heart Anatomy
3. 19.2 Cardiac Muscle and Electrical Activity
4. 19.3 Cardiac Cycle
5. 19.4 Cardiac Physiology
6. 19.5 Development of the Heart
20.
Chapter 20. The Cardiovascular System: Blood Vessels and Circulation
1. 20.0 Introduction
2. 20.1 Structure and Function of Blood Vessels
3. 20.2 Blood Flow, Blood Pressure, and Resistance
4. 20.3 Capillary Exchange
5. 20.4 Homeostatic Regulation of the Vascular System
6. 20.5 Circulatory Pathways
7. 20.6 Development of Blood Vessels and Fetal Circulation
21.
Chapter 21. The Lymphatic and Immune System
1. 21.0 Introduction
2. 21.1 Anatomy of the Lymphatic and Immune Systems
3. 21.2 Barrier Defenses and the Innate Immune Response
4. 21.3 The Adaptive Immune Response: T lymphocytes and Their Functional Types
5. 21.4 The Adaptive Immune Response: B-lymphocytes and Antibodies
6. 21.5 The Immune Response against Pathogens
7. 21.6 Diseases Associated with Depressed or Overactive Immune Responses
8. 21.7 Transplantation and Cancer Immunology
22.
Chapter 22. The Respiratory System
1. 22.0 Introduction
2. 22.1 Organs and Structures of the Respiratory System
3. 22.2 The Lungs
4. 22.3 The Process of Breathing
5. 22.4 Gas Exchange
6. 22.5 Transport of Gases
7. 22.6 Modifications in Respiratory Functions
8. 22.7 Embryonic Development of the Respiratory System
23.
Chapter 23. The Digestive System
1. 23.0 Introduction
2. 23.1 Overview of the Digestive System
3. 23.2 Digestive System Processes and Regulation
4. 23.3 The Mouth, Pharynx, and Esophagus
5. 23.4 The Stomach
6. 23.5 Accessory Organs in Digestion: The Liver, Pancreas, and Gallbladder
7. 23.6 The Small and Large Intestines
8. 23.7 Chemical Digestion and Absorption: A Closer Look
24.
Chapter 24. Metabolism and Nutrition
1. 24.0 Introduction
2. 24.1 Overview of Metabolic Reactions
3. 24.2 Carbohydrate Metabolism
4. 24.3 Lipid Metabolism
5. 24.4 Protein Metabolism
6. 24.5 Metabolic States of the Body
7. 24.6 Energy and Heat Balance
8. 24.7 Nutrition and Diet
25.
Chapter 25. The Urinary System
1. 25.0 Introduction
2. 25.1 Internal and External Anatomy of the Kidney
3. 25.2 Microscopic Anatomy of the Kidney: Anatomy of the Nephron
4. 25.3 Physiology of Urine Formation: Overview
5. 25.4 Physiology of Urine Formation: Glomerular Filtration
6. 25.5 Physiology of Urine Formation: Tubular Reabsorption and Secretion
7. 25.6 Physiology of Urine Formation: Medullary Concentration Gradient
8. 25.7 Physiology of Urine Formation: Regulation of Fluid Volume and Composition
9. 25.8 Urine Transport and Elimination
10.
26.
25.9 The Urinary System and Homeostasis
Chapter 26. Fluid, Electrolyte, and Acid-Base Balance
1. 26.0 Introduction
2. 26.1 Body Fluids and Fluid Compartments
3. 26.2 Water Balance
4. 26.3 Electrolyte Balance
5. 26.4 Acid-Base Balance
6. 26.5 Disorders of Acid-Base Balance
27.
Chapter 27. The Sexual Systems
1. 27.0 Introduction
2. 27.1 Anatomy of Sexual Systems
3. 27.2 Development of Sexual Anatomy
4. 27.3 Physiology of the Female Sexual System
5. 27.4 Physiology of the Male Sexual System
6. 27.5 Physiology of Arousal and Orgasm
28.
Chapter 28. Development and Inheritance
1. 28.0 Introduction
2. 28.1 Fertilization
3. 28.2 Embryonic Development
4. 28.3 Fetal Development
5. 28.4 Maternal Changes During Pregnancy, Labor, and Birth
6. 28.5 Adjustments of the Infant at Birth and Postnatal Stages
7. 28.6 Lactation
8. 28.7 Patterns of Inheritance
29.
Creative Commons License
30.
Recommended Citations
31.
Versioning
Anatomy & Physiology
22.2 The Lungs
Learning Objectives
By the end of this section, you will be able to:




Describe the overall function of the lung
Summarize the blood flow pattern associated with the lungs
Outline the anatomy of the blood supply to the lungs
Describe the pleura of the lungs and their function
A major organ of the respiratory system, each lung houses structures of both the conducting and
respiratory zones. The main function of the lungs is to perform the exchange of oxygen and carbon
dioxide with air from the atmosphere. To this end, the lungs exchange respiratory gases across a very
large epithelial surface area—about 70 square meters—that is highly permeable to gases.
Gross Anatomy of the Lungs
The lungs are pyramid-shaped, paired organs that are connected to the trachea by the right and left
bronchi; on the inferior surface, the lungs are bordered by the diaphragm. The diaphragm is the flat,
dome-shaped muscle located at the base of the lungs and thoracic cavity. The lungs are enclosed by the
pleurae, which are attached to the mediastinum. The right lung is shorter and wider than the left lung,
and the left lung occupies a smaller volume than the right. The cardiac notch is an indentation on the
surface of the left lung, and it allows space for the heart (Figure 22.2.1). The apex of the lung is the
superior region, whereas the base is the opposite region near the diaphragm. The costal surface of the
lung borders the ribs. The mediastinal surface faces the midline.
Figure 22.2.1 Gross Anatomy of
the Lungs.
Each lung is composed of smaller units called lobes. Fissures separate these lobes from each other. The
right lung consists of three lobes: the superior, middle, and inferior lobes. The left lung consists of two
lobes: the superior and inferior lobes. A bronchopulmonary segment is a division of a lobe, and each
lobe houses multiple bronchopulmonary segments. Each segment receives air from its own tertiary
bronchus and is supplied with blood by its own artery. Some diseases of the lungs typically affect one
or more bronchopulmonary segments, and in some cases, the diseased segments can be surgically
removed with little influence on neighboring segments. A pulmonary lobule is a subdivision formed as
the bronchi branch into bronchioles. Each lobule receives its own large bronchiole that has multiple
branches. An interlobular septum is a wall, composed of connective tissue, which separates lobules
from one another.
Blood Supply and Nervous Innervation of the
Lungs
The blood supply of the lungs plays an important role in gas exchange and serves as a transport system
for gases throughout the body. In addition, innervation by the both the parasympathetic and
sympathetic nervous systems provides an important level of control through dilation and constriction of
the airway.
Blood Supply
The major function of the lungs is to perform gas exchange, which requires blood from the pulmonary
circulation. This blood supply contains deoxygenated blood and travels to the lungs where
erythrocytes, also known as red blood cells, pick up oxygen to be transported to tissues throughout the
body. The pulmonary artery is an artery that arises from the pulmonary trunk and carries
deoxygenated, arterial blood to the alveoli. The pulmonary artery branches multiple times as it follows
the bronchi, and each branch becomes progressively smaller in diameter. One arteriole and an
accompanying venule supply and drain one pulmonary lobule. As they near the alveoli, the pulmonary
arteries become the pulmonary capillary network. The pulmonary capillary network consists of tiny
vessels with very thin walls that lack smooth muscle fibers. The capillaries branch and follow the
bronchioles and structure of the alveoli. It is at this point that the capillary wall meets the alveolar wall,
creating the respiratory membrane. Once the blood is oxygenated, it drains from the alveoli by way of
multiple pulmonary veins, which exit the lungs through the hilum.
Nervous Innervation
Dilation and constriction of the airway are achieved through nervous control by the parasympathetic
and sympathetic nervous systems. The parasympathetic system causes bronchoconstriction, whereas
the sympathetic nervous system stimulates bronchodilation. Reflexes such as coughing, and the ability
of the lungs to regulate oxygen and carbon dioxide levels, also result from this autonomic nervous
system control. Sensory nerve fibers arise from the vagus nerve, and from the second to fifth thoracic
ganglia. The pulmonary plexus is a region on the lung root formed by the entrance of the nerves at the
hilum. The nerves then follow the bronchi in the lungs and branch to innervate muscle fibers, glands,
and blood vessels.
Pleura of the Lungs
Each lung is enclosed within a cavity that is surrounded by the pleura. The pleura (plural = pleurae) is a
serous membrane that surrounds the lung. The right and left pleurae, which enclose the right and left
lungs, respectively, are separated by the mediastinum. The pleurae consist of two layers. The visceral
pleura is the layer that is superficial to the lungs, and extends into and lines the lung fissures (Figure
22.2.2). In contrast, the parietal pleura is the outer layer that connects to the thoracic wall, the
mediastinum, and the diaphragm. The visceral and parietal pleurae connect to each other at the hilum.
The pleural cavity is the space between the visceral and parietal layers.
Figure 22.2.2 Parietal
and Visceral Pleurae of the Lungs.
The pleurae perform two major functions: They produce pleural fluid and create cavities that separate
the major organs. Pleural fluid is secreted by mesothelial cells from both pleural layers and acts to
lubricate their surfaces. This lubrication reduces friction between the two layers to prevent trauma
during breathing, and creates surface tension that helps maintain the position of the lungs against the
thoracic wall. This adhesive characteristic of the pleural fluid causes the lungs to enlarge when the
thoracic wall expands during ventilation, allowing the lungs to fill with air. The pleurae also create a
division between major organs that prevents interference due to the movement of the organs, while
preventing the spread of infection.
Everyday Connection – The Effects of Second-Hand Tobacco Smoke
The burning of a tobacco cigarette creates multiple chemical compounds that are released through
mainstream smoke, which is inhaled by the smoker, and through sidestream smoke, which is the smoke
that is given off by the burning cigarette. Second-hand smoke, which is a combination of sidestream
smoke and the mainstream smoke that is exhaled by the smoker, has been demonstrated by numerous
scientific studies to cause disease. At least 40 chemicals in sidestream smoke have been identified that
negatively impact human health, leading to the development of cancer or other conditions, such as
immune system dysfunction, liver toxicity, cardiac arrhythmias, pulmonary edema, and neurological
dysfunction. Furthermore, second-hand smoke has been found to harbor at least 250 compounds that
are known to be toxic, carcinogenic, or both. Some major classes of carcinogens in second-hand smoke
are polyaromatic hydrocarbons (PAHs), N-nitrosamines, aromatic amines, formaldehyde, and
acetaldehyde.
Tobacco and second-hand smoke are considered to be carcinogenic. Exposure to second-hand smoke
can cause lung cancer in individuals who are not tobacco users themselves. It is estimated that the risk
of developing lung cancer is increased by up to 30 percent in nonsmokers who live with an individual
who smokes in the house, as compared to nonsmokers who are not regularly exposed to second-hand
smoke. Children are especially affected by second-hand smoke. Children who live with an individual
who smokes inside the home have a larger number of lower respiratory infections, which are associated
with hospitalizations, and higher risk of sudden infant death syndrome (SIDS). Second-hand smoke in
the home has also been linked to a greater number of ear infections in children, as well as worsening
symptoms of asthma.
Chapter Review
The lungs are the major organs of the respiratory system and are responsible for performing gas
exchange. The lungs are paired and separated into lobes; The left lung consists of two lobes, whereas
the right lung consists of three lobes. Blood circulation is very important, as blood is required to
transport oxygen from the lungs to other tissues throughout the body. The function of the pulmonary
circulation is to aid in gas exchange. The pulmonary artery provides deoxygenated blood to the
capillaries that form respiratory membranes with the alveoli, and the pulmonary veins return newly
oxygenated blood to the heart for further transport throughout the body. The lungs are innervated by the
parasympathetic and sympathetic nervous systems, which coordinate the bronchodilation and
bronchoconstriction of the airways. The lungs are enclosed by the pleura, a membrane that is composed
of visceral and parietal pleural layers. The space between these two layers is called the pleural cavity.
The mesothelial cells of the pleural membrane create pleural fluid, which serves as both a lubricant (to
reduce friction during breathing) and as an adhesive to adhere the lungs to the thoracic wall (to
facilitate movement of the lungs during ventilation).
Review Questions
Critical Thinking Questions
1. Compare and contrast the right and left lungs.
2. Why are the pleurae not damaged during normal breathing?
Glossary
bronchoconstriction
decrease in the size of the bronchiole due to contraction of the muscular wall
bronchodilation
increase in the size of the bronchiole due to contraction of the muscular wall
cardiac notch
indentation on the surface of the left lung that allows space for the heart
hilum
concave structure on the mediastinal surface of the lungs where blood vessels, lymphatic vessels,
nerves, and a bronchus enter the lung
lung
organ of the respiratory system that performs gas exchange
parietal pleura
outermost layer of the pleura that connects to the thoracic wall, mediastinum, and diaphragm
pleural cavity
space between the visceral and parietal pleurae
pleural fluid
substance that acts as a lubricant for the visceral and parietal layers of the pleura during the
movement of breathing
pulmonary artery
artery that arises from the pulmonary trunk and carries deoxygenated, arterial blood to the alveoli
pulmonary plexus
network of autonomic nervous system fibers found near the hilum of the lung
visceral pleura
innermost layer of the pleura that is superficial to the lungs and extends into the lung fissures
Solutions
Answers for Critical Thinking Questions
1. The right and left lungs differ in size and shape to accommodate other organs that encroach on
the thoracic region. The right lung consists of three lobes and is shorter than the left lung, due to
the position of the liver underneath it. The left lung consist of two lobes and is longer and
narrower than the right lung. The left lung has a concave region on the mediastinal surface
called the cardiac notch that allows space for the heart.
2. There is a cavity, called the pleural cavity, between the parietal and visceral layers of the pleura.
Mesothelial cells produce and secrete pleural fluid into the pleural cavity that acts as a lubricant.
Therefore, as you breathe, the pleural fluid prevents the two layers of the pleura from rubbing
against each other and causing damage due to friction.
This work, Anatomy & Physiology, is adapted from Anatomy & Physiology by OpenStax, licensed
under CC BY. This edition, with revised content and artwork, is licensed under CC BY-SA except
where otherwise noted.
Images, from Anatomy & Physiology by OpenStax, are licensed under CC BY except where otherwise
noted.
Access the original for free at https://openstax.org/books/anatomy-and-physiology/pages/1introduction.
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Previous: 22.1 Organs and Structures of the Respiratory System
Next: 22.3 The Process of Breathing
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License
Anatomy & Physiology Copyright © 2019 by Lindsay M. Biga, Staci Bronson, Sierra Dawson, Amy
Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham,
Kristen Oja, Devon Quick, Jon Runyeon, OSU OERU, and OpenStax is licensed under a Creative
Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.
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