Ch 15 Respiratory System

Essentials of Anatomy and Physiology, Seventh Edition
Valerie C. Scanlon and Tina Sanders
Copyright © F.A. Davis Company 2015
Chapter 15
The Respiratory System

The respiratory system moves air into and out of the lungs. The
lungs are the site of exchange of O2 and CO2.
The functioning of the respiratory system depends directly on
the proper functioning of the circulatory system.
Divisions
Upper respiratory tract—the parts outside the chest cavity:
Lower respiratory tract—the parts within the chest cavity:

Nose and Nasal Cavities
The nose is made of bone and cartilage covered with skin.
Entry of dust is blocked—
The two nasal cavities are within the skull, separated by the
nasal septum.
Nasal mucosa: ciliated epithelium
Functions:
Question: Can you name the bones that form the nasal septum and those that
increase the surface area of the nasal mucosa?

Answer
The nasal septum is formed by the vomer and the
perpendicular plate of the ethmoid bone.
The surface area of the nasal mucosa is increased by the
scroll-shaped conchae.

Nasal Cavities (continued)
Olfactory receptors—in the upper nasal cavities:
Paranasal sinuses: in the frontal, sphenoid, and ethmoid bones,
and the maxillae.
Functions:

Pharynx—posterior to the nasal and oral cavities
Nasopharynx—a passageway for air only; above the level of
the soft palate
Function of soft palate:
Eustachian tubes—
Adenoid—on the posterior wall:

Pharynx (continued)
Oropharynx—a passageway for air or food; behind the oral cavity
Palatine tonsils—
Laryngopharynx—a passageway for air or food
Opens anteriorly:
Opens posteriorly:

Larynx—the voice box, and the airway between the
pharynx and trachea
Made of nine cartilages; lined with ciliated epithelium
The thyroid cartilage is the largest.
Epiglottis—the uppermost cartilage
Function:
The vocal cords are lateral to the glottis.
Exhaled air vibrates the vocal cords—
Cranial nerves for speech—

Trachea—the airway from the larynx to the primary
bronchi
Structure: 16 to 20 C-shaped cartilages in the wall
Lined with ciliated epithelium—
Bronchial tree—from the trachea to the alveoli
Primary bronchi:
Secondary bronchi:
Bronchioles:

Lungs—on either side of the heart, from the diaphragm below
to the level of the clavicles
Hilus—an indentation on the medial side of a lung; site of entry
for:
Pleural membranes—the serous membranes of the thoracic
cavity
Parietal pleura:
Visceral pleura:
Serous fluid:

Alveoli—the sites of gas exchange
Alveolar type I cells: simple squamous epithelium—
Pulmonary capillaries surround the alveoli—
Elastic connective tissue is between the alveoli—
Lining each alveolus is a thin layer of tissue fluid—
Alveolar type II cells produce pulmonary surfactant to
decrease the surface tension within—

Mechanism of Breathing
Ventilation—the movement of air into and out of the lungs
Ventilation takes place because of pressure changes:
Atmospheric pressure—
Intrapleural pressure—
Intrapulmonic pressure—
Question: Name the respiratory muscles, and state the location of the CNS
respiratory centers.

Answer
The respiratory muscles are the diaphragm and the external
and internal intercostal muscles.
The CNS respiratory centers are located in the medulla and
pons.

Inhalation (inspiration)
From the medulla:
Motor impulses to the diaphragm:
Motor impulses to the external intercostal muscles:
The chest cavity is expanded and expands the pleural
membranes, which expand the lungs.
Intrapulmonic pressure decreases—

Exhalation (expiration)
Motor impulses from the medulla decrease—
The chest cavity becomes smaller—
The elastic lungs recoil—
Intrapulmonic pressure increases—
Forced exhalation:
Contraction of internal intercostal muscles—
Contraction of abdominal muscles—

Pulmonary Volumes
Tidal volume—the amount of air in one normal inhalation
and exhalation; about 500 mL
Inspiratory reserve—
Expiratory reserve—
Vital capacity—
Forced expiratory volume—

Pulmonary Volumes (continued)
Minute respiratory volume—
Average range of respirations per minute: 12 to 20
Residual air—remains in the lungs even after the most
forceful exhalation:
Importance:

Pulmonary Volumes (continued)
Alveolar ventilation—the air that reaches the alveoli for gas
exchange; depends on normal thoracic and lung
compliance (expansibility)
Anatomic dead space—air in the respiratory passages at
the end of inhalation (normal)
Physiological dead space—the volume of nonfunctional
alveoli (caused by anything that decreases compliance);
decreases gas exchange
Question: Name a pulmonary disease that would decrease lung compliance.

Answer
Pulmonary diseases that decrease lung compliance include
pneumonia, emphysema, and tuberculosis.

Exchange of Gases—O2 and CO2
External respiration—exchange of gases between the air in
the alveoli and the blood in the pulmonary capillaries
Internal respiration—exchange of gases between the blood
in the systemic capillaries and the tissue fluid (cells)
Inhaled air: 21% O2 and 0.04% CO2
Exhaled air: 16% O2 and 4.5% CO2

Exchange of Gases (continued) (see Table 15–1)
Diffusion of O2 and CO2 in the body occurs because of
pressure gradients.
Each gas has a partial pressure (P) in each site and will
diffuse from an area of higher pressure to an area of lower
pressure.

Exchange of Gases (continued)
External respiration:
PO2 in the air in the alveoli is high.
PO2 in the blood in the pulmonary capillaries is low.
Therefore, oxygen diffuses:
PCO2 in the air in the alveoli is low.
PCO2 in the blood in the pulmonary capillaries is high.
Therefore, carbon dioxide diffuses:

Exchange of Gases (continued)
Internal respiration:
PO2 in the blood in the systemic capillaries is high.
PO2 in the tissue fluid is low.
Therefore, oxygen diffuses:
PCO2 in the blood in the systemic capillaries is low.
PCO2 in the tissue fluid is high.
Therefore, carbon dioxide diffuses:

Transport of Gases in the Blood
Oxygen—most is carried by red blood cells
The protein:
The mineral:
The O2–Hb bond is formed where PO2 is high.
In tissues, Hb releases O2.
Important factors: Low PO2
High CO2
High temperature

Transport of Gases in the Blood (continued)
Oxygen saturation of hemoglobin (SaO2) in systemic arteries
averages 95% to 97%.
In systemic veins—
Some oxygen is dissolved in blood plasma, but not enough to
sustain life.

Carbon dioxide—some (about 20%) is dissolved in blood
plasma or carried by hemoglobin.
Most CO2 is carried in plasma in the form of bicarbonate
ions: HCO3
–
.
In the tissues, CO2 enters the blood and diffuses into RBCs.
The enzyme carbonic anhydrase catalyzes the reaction:
CO2 + H2O 
Question: What is the product of this reaction?

Answer
CO2 + H2O  H2CO3 (carbonic acid)

Carbonic acid dissociates:
H2CO3  H+
+ HCO3
–
The bicarbonate ions diffuse out of the RBCs into the plasma.
Hemoglobin buffers the H+
ions that remain in the RBCs.
In the lungs, the reactions are reversed—

Regulation of Respiration – two types of
mechanisms: nervous and chemical
Nervous regulation:
Medulla –
Impulses to the respiratory muscles:
As the lungs inflate, baroreceptors detect the stretching –
Impulses to respiratory muscles decrease:
Forceful exhalations –

Regulation of Respiration (continued)
Pons—has two respiratory centers that work with those of
the medulla:
Apneustic center—
Pneumotaxic center—
Hypothalamus—
Cerebral cortex—

Respiratory reflexes:
Coughing—
Sneezing—
Question: Where are the CNS centers for these reflexes?

Answer
The centers for the respiratory reflexes are in the medulla.

Chemical regulation—the effect of blood pH and blood
levels of O2 and CO2
Chemoreceptors—in the carotid and aortic bodies and in
the medulla
Decreased blood oxygen (hypoxemia)—
Response: increased respiration
Purpose:
Question: Can you name the sensory nerves for the carotid and aortic bodies?

Answer
The vagus nerves are sensory for the aortic body.
The glossopharyngeal nerves are sensory for the carotid
bodies.

Increased blood CO2 (hypercapnia)—
Response: increased respiration
Purpose:
The major regulator of breathing is CO2, because increased
CO2 lowers blood pH.
Oxygen may become a regulator—

Respiration and Acid–Base Balance
The respiratory system may be a cause of a pH imbalance, or
it may help correct a pH imbalance created by another
cause.
Respiratory acidosis—occurs when the rate or efficiency of
respiration decreases:
Examples:

Respiration and Acid–Base Balance (continued)
Respiratory alkalosis—occurs when the rate of respiration
increases:
Examples:

Respiration and Acid–Base Balance (continued)
Respiratory compensation for a metabolic acidosis—
Respiratory compensation for a metabolic alkalosis—

Wrap-Up Question
Name the part or aspect of the respiratory system described.
1. Lines the thoracic cavity
2. Site of inhalation and exhalation centers
3. pH change that might accompany pneumonia
4. Protein and mineral that carry O2
5. The tissue that keeps airways open
6. Blocks the larynx during swallowing
7. Form in which CO2 is carried in the blood
8. Term for one normal breath

Answers
1. Lines the thoracic cavity—parietal pleura
2. Site of inhalation and exhalation centers—medulla
3. pH change that might accompany pneumonia—respiratory
acidosis
4. Protein and mineral that carry O2—hemoglobin and iron
5. The tissue that keeps airways open—cartilage
6. Blocks the larynx during swallowing—epiglottis
7. Form in which CO2 is carried in the blood—bicarbonate
ions in plasma
8. Term for one normal breath—tidal volume

Ch 15 Respiratory System

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