Download Chapter 14—Respiratory System. I. The Respiratory System. a

Chapter 14—Respiratory System.
I.
II.
The Respiratory System.
a. General function: overall exchange of oxygen from the air for CO2 wastes produced in the
tissues by way of circulating blood. Fig. 14.1.
i. Breathing (ventilation): movement of oxygen rich air into the lungs and movement of
CO2 rich air out.
ii. External respiration: exchange of O2 and CO2 between the air and alveolar capillaries
(blood) in the lungs.
1. Blood entering the lungs is high in CO2 and low in O2. Blood leaving the lungs is
high in O2 and low in CO2.
iii. Gas transport: O2 is transported from the lungs to body tissues; CO2 is transported from
the body tissues to the lungs.
iv. Internal respiration: exchange of O2 and CO2 between the tissue capillaries (blood) and
the body tissues.
1. Blood entering the body tissues is high in O2 and low in CO2. Blood leaving the
tissues is high in CO2 and low in O2.
Respiratory system structures and associated functions. Fig. 14.2.
a. Nose.
i. Internally separated into 2 nasal cavities by the nasal septum.
ii. Within each nasal cavity are 3 convoluted bones: nasal conchae (pronounced kong-key).
1. Increases surface area of nasal epithelium.
iii. Nasal cavities perform the following functions:
1. Filter and cleanse the incoming air.
a. Hairs, mucus, and cilia of the pseudostratified ciliated columnar
epithelium trap some particulates that are inhaled.
i. Particles that get past the nose go all the way into the lungs, and
may be destroyed by macrophages in the lungs by phagocytosis.
1. If too many particulates enter at the same time or if the
macrophages cannot destroy the particulates; reduction in
gas exchange and infection can result.
a. Ex: chemicals in cigarette smoke.
2. Condition incoming air.
a. An extensive capillary network in the nasal tissues warms and humidifies
the incoming air.
i. Extremely cold air can kill cells in the lungs.
ii. Gasses can only diffuse into and out of the lung capillaries via a
wet membrane.
3. Olfaction. Sensory receptors for smell are located in a small region of the upper
nasal cavities.
b. Paranasal Sinuses.
i. Cavities in facial and cranial cavities that connect to the nasal cavity.
1. Help lighten these bones.
2. Help warm and humidify incoming air.
3. Serve as resonance chambers for the voice.
a. Inflammation of the sinus membranes = sinusitis. Can block the
connections between the sinuses and nasal cavity, causing pressure and
pain.
c. Pharynx (throat).
i. Common passage for food, drink, and air.
1. The openings of the 2 Eustachian (auditory) tubes are found here. These tubes
equalize air pressure in the middle ear with respect to the external ear. (The
eardrum separates these spaces).
d. Larynx (voice box). Fig. 14.5.
i. Composed of hyaline cartilage structures, connective tissues, and hyoid bone.
ii. During swallowing, the epiglottis closes off the larynx, directing food and drink into the
esophagus. (The epiglottis has a core of elastic cartilage).
1. If food becomes lodged in the larynx or trachea the Heimlich maneuver can be
used to force the blockage out. Fig. 14.6.
iii. Vocal cords.
1. Breathing and sound production.
a. The vocal cords are found near the entrance to the larynx.
b. Air passing through the glottis (the space between the vocal cords) can
cause the cords to vibrate and produce sound.
c. Varying the tension on the vocal cords (through contraction and relaxation
of muscles in the larynx) causes the glottis and vocal cords to change in
size and shape.
d. These changes cause changes in the pitch of the voice when air passes
over the vocal cords.
2. Laryngitis = vocal cords inflamed, irritated, swell, become difficult to vibrate.
e. Trachea (wind pipe) is supported by “C” rings of hyaline cartilage.
i. The open part of the “C” faces posteriorly, muscle connects the open ends of the “C”; the
esophagus is located posterior to the trachea, paralleling the trachea down the thoracic
cavity.
1. The tracheal rings of cartilage prevent the trachea from collapsing during
inhalation.
f. Bronchial tree. Fig. 14.7.
i. As the trachea descends in the thoracic cavity, there comes a point where it divides into a
pair of primary bronchi, one going to each lung. Also supported by plates of hyaline
cartilage in their walls.
ii. The primary bronchi split into several secondary bronchi, which split into many tertiary
bronchi, which split into many quaternary bronchi…
iii. Eventually, we reach the level of the bronchioles, which do not contain hyaline cartilage
in their walls. These branch into the terminal bronchioles.
1. Up to this point, the epithelium of the respiratory tract has been a pseudostratified
ciliated columnar epithelium. Fig. 14.4.
iv. Terminal bronchioles give rise to the respiratory bronchioles, which have a simple
squamous epithelium; this is the first location within the lungs where gas exchange can
occur.
v. Respiratory bronchioles give rise to alveolar ducts, which then become alveolar sacs with
alveoli, all of which also have a simple squamous epithelium. The vast majority of gas
exchange in the lungs occurs in alveoli. Fig. 14.8.
1. Each lung has about 300 million alveoli, with a total surface area of about 70-80
meters square!
vi. To facilitate gas exchange and to keep the alveoli from collapsing, special lung cells
produce a compound called surfactant.
1. Surfactant is composed of special phospholipids that reduce the surface tension of
water.
a. Surfactant production begins during the 8th month of pregnancy;
premature babies often have respiratory distress syndrome because the
alveoli collapse.
III.
IV.
V.
i. Artificial surfactants are administered and ventilators are used to
prevent death.
Mechanism of Breathing. Fig. 14.9.
a. Respiratory cycle = breathing—ventilates the respiratory surfaces of the lungs. There are two
parts to the cycle:
i. Inspiration—when you inhale a breath of air.
ii. Expiration—when you exhale a breath of air.
b. Inspiration occurs due to the contraction of the diaphragm, external intercostal muscles, and
some neck muscles. [Discuss significance, pleural coverings, volume changes, pressure
gradients, etc.].
c. Expiration—passively occurs as the inspiratory muscles relax. Expiration may actively occur
when the abdominal muscles and internal intercostals muscles contract.
d. Lung volumes (in a healthy adult male). Fig. 14.10.
i. Tidal Volume (TV)—normal, relaxed breathing. About 500 ml.
ii. Inspiratory Reserve Volume (IRV)—additional air volume that may be forcefully
inhaled. About 3100 ml.
iii. Expiratory Reserve Volume (ERV)—additional air volume that may be forcefully
exhaled. About 1200 ml.
iv. Vital Capacity (VC)—ERV + TV + IRV. About 4800 ml.
v. Residual Volume—volume of air that still remains in the lungs after a maximal forced
expiration. About 1200 ml. [Talk about importance—lungs won’t collapse, gas
exchange always occurring].
vi. Total Lung Capacity = Residual Volume + VC. About 6000 ml.
vii. Anatomical dead space = 150 ml.
Transport of Gasses between the Lungs and the Cells.
a. Gas exchange occurs when oxygen and CO2 diffuse down their concentration gradients; when
discussing gasses = pressure gradient. Normal atmospheric pressure at sea level is 760 mm Hg.
b. Components of air:
i. 78% nitrogen.
ii. 21% oxygen.
iii. 0.04% CO2.
iv. 0.96% other gasses.
c. Each gas only exerts a portion of the total atmospheric pressure; therefore, each gas is said to
exert a “partial pressure.”
d. For gas exchange to occur the respiratory surface of the lungs must be moist; this is so gasses can
dissolve into the fluid bathing the alveoli and diffuse across & into the blood.
e. Surface area and pressure gradients greatly affect the rate and amount of gas that may cross the
respiratory surface.
Gas exchange in alveoli and in body tissues. Fig. 14.11.
a. Each alveolus is a simple squamous epithelium covered with a thin layer of pulmonary
surfactant. This fluid keeps the alveoli moist so the gasses can dissolve and diffuse; it also
reduces surface tension so the alveoli and lungs don’t collapse.
b. Between the alveolus and capillary, there is a thin layer of interstitial fluid that the gasses also
diffuse across.
c. When fresh air enters the lungs, it has relatively little CO2 and plenty of oxygen within it.
d. Blood entering the lung capillaries from the pulmonary circuit has relatively little oxygen and
high concentrations of CO2.
e. Therefore, oxygen diffuses into the blood plasma and into the RBC’s, while CO2 diffuses out of
the blood and into the lungs to be blown off during expiration.
f. Up to four oxygen molecules can form a weak bond with hemoglobin (Hb) to form
oxyhemoglobin.
g. Generally, the higher the partial pressure of oxygen, the more oxygen will be picked up by Hb.
h. Hb will release oxygen in tissues where the partial pressure of oxygen is lower than in the blood.
It will also be more likely to release oxygen when temperature rises and/or pH falls.
CO2 Transport and Bicarbonate Ions.
a. CO2 is a waste product of aerobic cellular respiration.
b. Active tissues have higher CO2 concentrations than the blood within capillaries passing through
those tissues.
c. Therefore, CO2 moves out of the tissues and into the capillaries by diffusion; blood then
transports the CO2 to the lungs in one of three ways:
i. About 7-10% of CO2 stays dissolved in the plasma.
ii. About 20-23% of CO2 binds to Hb to form carbaminohemoglobin.
iii. About 70% of CO2 is transported in the plasma as bicarbonate (HCO3-):
VI.
CO2  Red blood cell + H2O ↔ H2CO3 ↔ HCO3- + H+ 
(contains enzyme
(carbonic
↓
carbonic anhydrase)
acid)
Diffuses
out of RBC
and back into
the plasma.
VII.
Some H+ binds to Hb,
which acts as a buffer.
d. These reactions reverse in the alveoli, where the partial pressure of CO2 is less than in the
capillaries. CO2  alveolar sacs  exhaled.
Respiratory Centers in the Brain. Fig. 14.12.
a. The area of the brain from which nerve impulses are sent to respiratory muscles is located in the
respiratory center. It consists of the medullary rhythmicity area (inspiratory and expiratory
areas), the pneumotaxic area, and the apneustic area.
b. Medullary Rhythmicity Area.
i. The function of the medullary rhythmicity area (in the medulla oblongata) is to control
the basic rhythm of respiration.
ii. Normally, inspiration lasts 2 seconds and expiration lasts 3 seconds.
c. Pneumotaxic Area.
i. The pneumotaxic area in the upper pons helps coordinate the transition between
inspiration and expiration. Inhibitory impulses from this area turn off the inspiratory area
before the lungs become too full.
d. Apneustic Area.
i. The apneustic area in the lower pons sends stimulatory impulses to the inspiratory area
that activate it and prolong inspiration, inhibiting expiration.
e. Regulation of the Respiratory Center.
i. Influences of the cerebral cortex:
1. Cortical influences allow conscious control of respiration that may be needed to
avoid inhaling noxious gasses or water.
2. Breath holding is limited by the overriding stimuli of increased [H+] and [CO2] on
the inspiratory area.
3. Levels of CO2 (especially) and oxygen (to a much lesser degree) in the blood are
closely monitored by the nervous system:
a. As CO2 levels change in the blood, the pH of cerebrospinal fluid changes,
and receptors on the surface of the medulla oblongata detect this.
i. This leads to an adjustment in the rate and depth of breathing to
adjust the CO2 levels. (Negative feedback loop).
b. Sensory receptors called the carotid and aortic bodies detect changes in
pH, CO2, and oxygen levels in the blood.
VIII.
i. This information is sent to the brain, and the ventilation rate is
adjusted accordingly.
ii. Figure 14.13 summarizes these events.
4. Increased CO2 levels in the blood also cause the bronchioles to dilate, enhancing
air flow.
5. Decreased CO2 levels in the blood causes the bronchioles to constrict.
6. Lung capillaries also adjust their diameters in response to oxygen and CO2
concentrations in the blood.
a. If there is too much air flow relative to blood flow, vessels dilate to allow
more blood through.
b. If there is not enough air flow relative to blood flow, vessels constrict.
Respiratory Disorders.
a. Effects of cigarette smoke on the respiratory system. Fig. 14.14 and 14.15.
b. You will not be tested on the rest of the material in this section. However, it is interesting
because each of us has suffered through some of the discussed ailments…
Study suggestions for this chapter: In the textbook at the end of the chapter, the sections entitled 1)
Highlighting the Concepts, 2) Recognizing Key Terms, and 3) Reviewing the Concepts are all good for you to
gauge your comprehension and focus your study efforts.