1. Chapter 16
Respiratory System

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Introduction
The respiratory system consists of tubes that filter incoming air and transport it into the microscopic alveoli where gases are exchanged.
The entire process of exchanging gases between the atmosphere and body cells is called respiration and consists of the following: ventilation, gas exchange between blood and lungs, gas transport in the bloodstream, gas exchange between the blood and body cells, and cellular respiration.

3. Organs of the Respiratory System
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Organs of the Respiratory System
A. The organs of the respiratory tract can be divided into two groups: the upper respiratory tract (nose, nasal cavity, sinuses, and pharynx), and the lower respiratory tract (larynx, trachea, bronchial tree, and lungs).

4. Fig16.01 Front alsinus Nasal cavity Soft palate Hard palate Pharynx
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Front
alsinus
Nasal
cavity
Soft palate
Hard
palate
Pharynx
Nostril
Epiglottis
Oral
cavity
Esophagus
Larynx
Trachea
Bronchus
Right lung
Left lung

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B. Nose
1. The nose, supported by bone and cartilage, provides an entrance for air in which air is filtered by coarse hairs inside the nostrils.

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C. Nasal Cavity
1. The nasal cavity is a space posterior to the nose that is divided medially by the nasal septum.
2. Nasal conchae divide the cavity into passageways that are lined with mucous membrane, and help increase the surface area available to warm and filter incoming air.

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3. Particles trapped in the mucus are carried to the pharynx by ciliary action, swallowed, and carried to the stomach where gastric juice destroys any microorganisms in the mucus.

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D. Paranasal Sinuses
1. Sinuses are air-filled spaces within the maxillary, frontal, ethmoid, and sphenoid bones of the skull.
2. These spaces open to the nasal cavity and are lined with mucus membrane that is continuous with that lining the nasal cavity.
3. The sinuses reduce the weight of the skull and serve as a resonant chamber to affect the quality of the voice.

9. 1. The pharynx is a common passageway for air and food.
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E. Pharynx
1. The pharynx is a common passageway for air and food.
2. The pharynx aids in producing sounds for speech.

10. Fig16.02 Superior Middle Frontal sinus Inferior Sphenoidal sinus
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Superior
Middle
Nasal
conchae
Frontal sinus
Inferior
Sphenoidal sinus
Nostril
Pharyngeal tonsil
Hard palate
Nasopharynx
Opening of
auditory tube
Uvula
Palatine tonsil
Tongue
Oropharynx
Lingual tonsil
Epiglottis
Hyoid bone
Laryngopharynx
Larynx
Esophagus
Trachea

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F. Larynx
1. The larynx is an enlargement in the airway superior to the trachea and inferior to the pharynx.
2. It helps keep particles from entering the trachea and also houses the vocal cords.
3. The larynx is composed of a framework of muscles and cartilage (thyroid, cricoid and epiglottic) bound by elastic tissue.

12. Fig16.04 Epiglottic cartilage Hyoid bone Thyroid cartilage
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Epiglottic cartilage
Hyoid bone
Thyroid cartilage
Cricoid cartilage
Trachea
(a)
Hyoid bone
Epiglottic cartilage
Thyroid cartilage
Cricoid cartilage
Trachea
(b)

13. a. The upper pair is the false vocal cords.
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4. Inside the larynx, two pairs of folds of muscle and connective tissue covered with mucous membrane make up the vocal cords.
a. The upper pair is the false vocal cords.
b. The lower pair is the true vocal cords.
c. Changing tension on the vocal cords controls pitch, while increasing the loudness depends upon increasing the force of air vibrating the vocal cords.

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5. During normal breathing, the vocal cords are relaxed and the glottis is a triangular slit.
6. During swallowing, the false vocal cords and epiglottis close off the glottis.

15. Posterior portion of tongue False vocal cord True vocal cord Glottis
Fig16.05ab
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Posterior portion
of tongue
False vocal
cord
True vocal
cord
Glottis
(a)
Epiglottis
Glottis
Inner lining
of trachea
(b)

16. (c) Fig16.05c ©CNRI/PhotoTake
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(c)
©CNRI/PhotoTake

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G. Trachea
1. The trachea extends downward anterior to the esophagus and into the thoracic cavity, where it splits into right and left bronchi.
2. The inner wall of the trachea is lined with ciliated mucous membrane with many goblet cells that serve to trap incoming particles.
3. The tracheal wall is supported by incomplete cartilaginous rings.

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H. Bronchial Tree
1. The bronchial tree consists of branched tubes leading from the trachea to the alveoli.
2. The bronchial tree begins with the two main (primary) bronchi, each leading to a lung.

19. then alveolar sacs which terminate in alveoli.
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3. The branches of the bronchial tree from the trachea are right and left primary bronchi; these further subdivide until bronchioles give rise to alveolar ducts ,
then alveolar sacs which terminate in alveoli.
4. It is through the thin epithelial cells of the alveoli that gas exchange between the blood and air occurs.

20. Fig16.07 Larynx Trachea Right superior (upper) lobe Left superior
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Larynx
Trachea
Right superior (upper) lobe
Left superior
(upper) lobe
Right main (primary)
bronchus
Lobar (secondary)
bronchus
Segmental (tertiary)
bronchus
Terminal bronchiole
Right inferior (lower) lobe
Left inferior
(lower) lobe
Right middle lobe
Respiratory bronchiole
Alveolar duct
Alveolus

21. Fig16.08 Blood flow Pulmonary venule Blood flow
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Blood flow
Pulmonary
venule
Blood flow
Intralobular bronchiole
Pulmonary
arteriole
Smooth muscle
Blood flow
Alveolus
Pulmonary
artery
Capillary network on
surface of alveolus
Pulmonary
vein T
Terminal
bronchiole
Respiratory
bronchiole
Alveolar
duct
Alveolar
sac
Alveoli

22. 2. The bronchus and large blood vessels enter each lung.
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I. Lungs
1. The right and left soft, spongy, cone- shaped lungs are separated medially by the mediastinum and are enclosed by the diaphragm and thoracic cage.
2. The bronchus and large blood vessels enter each lung.

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3. A layer of serous membrane, the visceral pleura, folds back to form the parietal pleura.
4. The visceral pleura is attached to the lung, and the parietal pleura lines the thoracic cavity; serous fluid lubricates the pleural cavity between these two membranes.

24. 5. The right lung has three lobes, the left has two.
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5. The right lung has three lobes, the left has two.
6. Each lobe is composed of lobules that contain air passages, alveoli, nerves, blood vessels, lymphatic vessels, and connective tissues.

25. Fig16.11 Right lung Left lung Plane of section Heart Visceral pleura
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Right lung
Left lung
Plane of
section
Heart
Visceral
pleura
Pericardial
cavity
Parietal
pleura
Pericardium
Pleura
Right pleural
cavity
Left pleural
cavity

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Breathing Mechanism
A. Ventilation (breathing), the movement of air in and out of the lungs, is composed of inspiration and expiration.
B. Inspiration
1. Atmospheric pressure is the force that moves air into the lungs.
2. When pressure on the inside of the lungs decreases, higher pressure air flows in from the outside.

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3. Air pressure inside the lungs is decreased by increasing the size of the thoracic cavity; due to surface tension between the two layers of pleura, the lungs follow with the chest wall and expand.
4. Muscles involved in expanding the thoracic cavity include the diaphragm and the external intercostal muscles.

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5. As the lungs expand in size, surfactant keeps the alveoli from sticking to each other so they do not collapse when internal air pressure is low.

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C. Expiration
1. The forces of expiration are due to the elastic recoil of lung and muscle tissues and from the surface tension within the alveoli.
2. Forced expiration is aided by thoracic and abdominal wall muscles that compress the abdomen against the diaphragm.

30. Fig16.12 Atmospheric pressure (760 mm Hg) Intra-alveolar pressure
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Atmospheric pressure
(760 mm Hg)
Intra-alveolar
pressure
(760 mm Hg)
Intra-alveolar
pressure
(758 mm Hg)
Diaphragm
(a)
(b)

31. D. Respiratory Air Volumes and Capacities
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D. Respiratory Air Volumes and Capacities
1. The measurement of different air volumes is called spirometry, and it describes four distinct respiratory volumes.
2. One inspiration followed by expiration is called a respiratory cycle; the amount of air that enters or leaves the lungs during one respiratory cycle is the tidal volume.

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3. During forced inspiration, an additional volume, the inspiratory reserve volume, can be inhaled into the lungs. IRV + TV gives us the inspiratory capacity.
4. During a maximal forced expiration, an expiratory reserve volume can be exhaled, but there remains a residual volume in the lungs. Adding the two together gives us the functional reserve capacity.

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5. Vital capacity is the tidal volume plus inspiratory reserve and expiratory reserve volumes combined.
6. Vital capacity plus residual volume is the total lung capacity.
7. Anatomic dead space is air remaining in the bronchial tree.

34. Lung volume in milliliters (mL)
Fig16.15
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6,000
5,000
Vital
capacity
Inspiratory
reserve volume
Inspiratory
capacity
4,000
Total lung
capacity
Lung volume in milliliters (mL)
3,000
2,000
Tidal
volume
Functional
residual
capacity
1,000
Expiratory
reserve volume
Residual
volume

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Control of Breathing
Normal breathing is a rhythmic, involuntary act even though the muscles are under voluntary control.
B. Respiratory Areas
1. Groups of neurons in the brain stem comprise the respiratory areas, which controls breathing by causing inspiration and expiration and by adjusting the rate and depth of breathing.

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3. The medullary rhythmicity center includes two groups of neurons: the dorsal respiratory group and the ventral respiratory group.
a. The dorsal respiratory group is responsible for the basic rhythm of breathing.
b. The ventral respiratory group is active when more forceful breathing is required.
4. Neurons in the pons form the pontine respiratory group. They may contribute to the rhythm of breathing by limiting inspiration.

37. Fig16.16
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Midbrain
Fourth
ventricle
Pontine respiratory
group
Pons
Medulla oblongata
Ventral respiratory group
Dorsal respiratory group
Medullary
respiratory
center
Internal (expiratory)
intercostal muscles
External (inspiratory)
intercostal muscles
Diaphragm

38. C. Factors Affecting Breathing
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C. Factors Affecting Breathing
1. Chemicals, lung tissue stretching, and emotional state affect breathing.
2. Chemosensitive areas (central chemoreceptors) are associated with the respiratory center and are sensitive to changes in the blood concentration of carbon dioxide and hydrogen ions.

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a. If either carbon dioxide or hydrogen ion concentrations rise, the central chemoreceptors signal the respiratory center, and breathing rate increases.

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3. Peripheral chemoreceptors in carotid bodies and aortic bodies sense changes in blood oxygen concentration, transmit impulses to the respiratory center, and breathing rate and tidal volume increase.
4. An inflation reflex, triggered by stretch receptors in the visceral pleura, bronchioles, and alveoli, helps to prevent overinflation of the lungs during forceful breathing.
5. Hyperventilation lowers the amount of carbon dioxide in the blood.

41. Alveolar Gas Exchanges
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Alveolar Gas Exchanges
A. The alveoli are the only sites of gas exchange between the atmosphere and the blood.
B. Alveoli
1. The alveoli are tiny sacs clustered at the distal ends of the alveolar ducts.

42. C. Respiratory Membrane
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C. Respiratory Membrane
1. The respiratory membrane consists of the epithelial cells of the alveolus, the endothelial cells of the capillary, and the two fused basement membranes of these layers.
2. Gas exchange occurs across this respiratory membrane.

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D. Diffusion Across the Respiratory Membrane 1. Gases diffuse from areas of higher pressure to areas of lower pressure.
2. In a mixture of gases, each gas accounts for a portion of the total pressure; the amount of pressure each gas exerts is equal to its partial pressure.

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3. When the partial pressure of oxygen is higher in the alveolar air than it is in the capillary blood, oxygen will diffuse into the blood.
4. When the partial pressure of carbon dioxide is greater in the blood than in the alveolar air, carbon dioxide will diffuse out of the blood and into the alveolus.
5. A number of factors favor increased diffusion; more surface area, shorter distance, greater solubility of gases, and a steeper partial pressure gradient.

45. Alveolus Diffusion of O2 Alveolar wall PCO2 = 40 mm Hg PO2 = 104 mm Hg
Fig16.20
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Alveolus
Diffusion of O2
Alveolar
wall
PCO2 = 40 mm Hg
PO2 = 104 mm Hg
PCO2 = 45 mm Hg
PO2 = 40 mm Hg
Diffusion of O2
Blood flow
(from body
tissues)
Blood flow
(to body
tissues)
Capillary
PCO2 = 40 mm Hg
PO2 = 104 mm Hg

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Gas Transport
A. Gases are transported in association with molecules in the blood or dissolved in the plasma.
B. Oxygen Transport
1. Over 98% of oxygen is carried in the blood bound to hemoglobin of red blood cells, producing oxyhemoglobin.
2. Oxyhemoglobin is unstable in areas where the concentration of oxygen is low, and gives up its oxygen molecules in those areas.

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3. More oxygen is released as the blood concentration of carbon dioxide increases, as the blood becomes more acidic, and as blood temperature increases.
4. A deficiency of oxygen reaching the tissues is called hypoxia and has a variety of causes.

48. Fig16.21 Alveolus Blood PO2 = 95 mm Hg Capillary Hemoglobin molecules
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Alveolus
Blood
PO2 = 95 mm Hg
Capillary
Hemoglobin
molecules
Blood
PO2 = 40 mm Hg
Alveolar
wall
Oxygen
molecules
Blood flow
(to lungs)
Oxyhemoglobin
molecule
Diffusion
of oxygen
Blood flow
(from body
tissues)
Tissue cells
Tissue
PO2 = 40 mm Hg
Diffusion
of oxygen
Hemoglobin
molecules
(a)
(b)

49. C. Carbon Dioxide Transport
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C. Carbon Dioxide Transport
1. Carbon dioxide may be transported dissolved in blood plasma, as carbaminohemoglobin, or as bicarbonate ions.
2. Most carbon dioxide is transported in the form of bicarbonate.

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3. When carbon dioxide reacts with water in the plasma, carbonic acid is formed slowly, but instead much of the carbon dioxide enters red blood cells, where the enzyme carbonic anhydrase speeds this reaction.
4. The resulting carbonic acid dissociates immediately, releasing bicarbonate and hydrogen ions.
5. Carbaminohemoglobin also releases its carbon dioxide which diffuses out of the blood into the alveolar air.

51. Fig16.22 Tissue cell Tissue PCO2 = 40 mm Hg Cellular CO2 CO2 dissolved
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Tissue cell
Tissue
PCO2 = 40 mm Hg
Cellular CO2
CO2 dissolved
in plasma
CO2 + H2O
CO2 combined with
hemoglobin to form
carbaminohemoglobin
H2CO3
PCO2 = 40 mm Hg
PCO2 = 45 mm Hg
HCO3− + H+
Blood
flow from
systemic
arteriole
Blood
flow to
systemic
venule
H+ combines
with hemoglobin
HCO3−
Plasma
Red blood cell
Capillary wall