Download Packet 15- Breathing

Lecture 15: Breathing
Silverthorn Chapter 17
OVERVIEW of the respiratory system
Primary functions:
1. Deliver oxygen to cells to fuel CR (review CR)
2. Remove carbon dioxide from cells (maintain pH)
Mechanisms:
1.
2.
3.
4.
Pulmonary ventilation (moving air back and forth from atmosphere into alveoli)
Gas exchange between alveoli and blood
Transport of gasses through body
Gas exchange between the blood and cells
Anatomy of the respiratory system
1. The trachea bifurcates into 2 tubes called primary bronchi. These further bifurcate into secondary and tertiary bronchi.
2. Bronchioles are the next level of branching, and these guys have no cartilage, but they do have a lot of smooth muscle.
A. When the muscles contract, you have bronchoconstriction
B. When the muscles relax, you have bronchodilation.
3. Alveoli are the terminal bubbles found at the tips of the bronchioles. Lined with simple squamous ET, this is the site of gas
exchange. (There are 22 bifurcations between the trachea and alveoli! Wow!)
The tubes are contained within the two lungs, which are not symmetrical.
1.
2.
3.
4.
Lung tissue is covered with a visceral pleura.
Thoracic cavity is covered with parietal pleura.
They are separated by the pleural cavity, which is filled with serous fluid.
Between pleura is the PLEURAL SPACE, filled with PLEURAL FLUID
A. APPLICATION: Pleurisy (Pleuritis)
i. Inflamed pleura…when layers slide by each other, there is friction and it hurts to breathe
Gas exchange takes place in alveoli
1. Alveoli are sacs made of a single layer of epithelial cells
2. Alveoli walls are surrounded by elastic proteins (ELASTIN) that enable the alveoli to resume normal volume after filling up.
A. Remember, diseases that affect elasticity are considered OBSTRUCTIVE (takes work to exhale…)
B. Ex: Emphysema
i. Alveoli are broken down, leading to less surface area for gas exchange.
ii. Elastin is destroyed, increasing energy required to exhale (Elastin is destroyed in smokers b/c activated alveolar
macrophages produce elastase, an enzyme that breaks down elastin!)
iii. Treatment? Sometimes they do a “lung volume reduction surgery” where 20-30% of the lung tissue is removed; you
have LESS air to exhale
3. 80-90% of alveoli surface is in contact with a capillary… leading to very efficient gas exchange.
4. 95% of the cells in each alveolus are type I alveolar cells, which are very thin, and are the actual site of gas exchange
5. 5% are type II alveolar cells which produce surfactant “Surface active agents” that reduce the surface tension of water!
A. Surfactant reduces the surface tension in the water lining the alveolus, making it easier to “blow up” the alveolus
i. APPLICATION: Infant respiratory distress syndrome (premature babes)
ii. Common in babes born 6 wks premature (nearly all babes born < 28 wks have it); though there also is a genetic
disorder that affects surfactant production
iii. At about 7 months (8 wks to go), ma increases CORTISOL production, which stimulates maturation of Type 2 alveolar
cells → surfactant!
iv. Lacks surfactant, so breathing takes too much work. Their bellies pull in sharply when they breathe (working so hard!)
v. Treatment: Oxygen (not too much, or causes vision problems!) via a ventilator that delivers oxygen and pressure (to
keep lungs inflated). Another option is continuous positive airway pressure (tube in nose). Sometimes surfactant drug
is given…but can cause bleeding in littlest babes…
B. Actively transport solutes OUT of the alveolar bubble…why?
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Pulmonary ventilation: Breathing
How does gas move INTO the lungs?
1. Moves DOWN its PRESSURE gradient…
Pressure gradient? (P=F/A)
vs. Concentration gradient?
(Conc = #/vol)
2. In order to get air into the lung, you must DECREASE AIR PRESSURE INSIDE THE LUNG!!! How? Boyle’s law…
A. Increase volume of chest cavity: (which WILL decrease pressure inside the chest cavity)
i. The diaphragm increases the volume of the thoracic cavity, decreasing the pressure inside the lungs (accounts for 6075% of volume change during quiet breathing)
ii. Ribs also move (due to external intercostals, which move ribs up and out…accts for 25-40% of the volume change
during quiet breathing)
B. Air rushes DOWN the pressure gradient, into the lungs (block airway, make a breathing motion with your diaphragm…can
you feel the pressure?)
3. Carefully examine how PRESSURE changes in the lungs…(fig 17-11)-- Start at the bottom of an exhale…
A. APPLICATION: Pneumothorax (Punctured lung: Intrapleural space loses low pressure…lung collapses)
Mechanical factors that affect pulmonary ventilation
1. Airway resistance …(Ex: Asthma)
A. 90% of the resistance in the lung comes from the trachea and bronchi, which are rigid, and cannot change diameter
B. Bronchioles have 2000x greater XS area (suggesting they are more responsible for resist.), but their diameter can change.
i. Increased diameter of bronchioles → decreased resistance to ventilation
ii. Decreased diameter of bronchioles → increased resistance to ventilation
C. Various chemicals can impact bronchiole diameter…
i. Epinephrine (sympathetic NS) binds to β2 receptors on the smooth muscle cells in bronchioles…what response?
Relaxation! Why??? Let in more air!!!
ii. ACh (parasympathetic NS) binds to muscarinic receptors on the smooth muscle cells in bronchioles…what response?
Constriction… Why? No need for more air…
D. Other substances impact bronchiole diameter…
i. CO2 is a bronchodialator…when the cells lining the bronchioles detect too much CO2, they dilate, increasing
ventilation and consequent gas exchange.
ii. Histamine is a brochoconstrictor…(Histamine is normally produced by certain WBC (basophils – mast cells) in
response to tissue damage or allergic rxn) -- Antihistamines…treat allergic rxns
iii. Albuterol- beta2 adrenergic AGONIST…
a. Stimulates the sympathetic response by increasing activity of β2 receptors…
b. Causes bronchodilation
c. (Is not recommended with beta blockers…why?)
2. Compliance (stretchiness of lung tissue)
A. Diseases that result in reduced compliance are considered RESTRICTIVE
i. Effect? It takes work to inhale…
B. Ex: Pulmonary fibrosis
i. Thickening and scarring of lung tissue
ii. Sometimes body just does it…no known cause (idiopathic)
iii. Also can be the body’s response to chronic inhalation of fine particulate matter, like asbestos…
a. Macrophages ingest the particles
b. If they can’t digest them, they trigger an inflammatory response
c. Inelastic scar tissue (collagen) is produced…
iv. Irreversible
3. Elasticity (lung’s ability to recoil after being stretched)
A. Diseases that affect elasticity are considered OBSTRUCTIVE (Takes work to exhale…) Ex: Emphysema
i. Elastin is destroyed, so air stays in the lungs, so too much energy is needed to EXHALE the air!
ii. Happens in smokers b/c activated alveolar macrophages have to work doubletime to rid lungs of the smoking crud…
iii. The macrophages produce elastase, an enzyme that breaks down elastin.
iv. Treatment? Sometimes they do a “lung volume reduction surgery” where 20-30% of the lung tissue is removed;
remaining tissue does a better job of ventilating.
B. Ex: Bronchitis (Reduced diameter of bronchi/bronchioles)
Bio 7: Human Physiology
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Spring 2014: Riggs
External Brain 15: Breathing
Study guide questions
1. What are the primary functions of the respiratory system? Explain these.
2. What are the mechanism by which the respiratory system carries out its primary functions?
3. Distinguish between external respiration and cellular respiration.
4. Describe how breathing occurs. Your answer should account for all relevant pressures and how the pressures are obtained.
5. Be able to compare the relative gas pressures in the alveoli and intrapleural space. (See fig 17-11).
6. Describe the physiology of a punctured lung (pneumothorax).
7. What are some mechanical factors that affect gas exchange?
8. Understand brochodilation and bronchoconstriction. When does each happen? What causes each in a normal, homeostatic
condition? What kinds of drugs impact the diameter of the bronchioles?
9. Compare and contrast OBSTRUCTIVE vs RESTRICTIVE lung diseases.
10.Be able to discuss the following conditions:
a. Pulmonary fibrosis
b. Bronchitis
c. Asthma
d. Emphysema
11. You should be able to explain how the syringe lung worked.
12.Describe the structure of the alveoli. Include the different cells and their ‘jobs’.
13.What is surfactant? Where is it produced? Why is it important? Relate the role surfactant plays in the alveoli to the “pepper
experiment” in lab.
14.What is elastin? What role does elastin play in a COPD like emphasema?
15.Describe the cause of breathing complications in premature infants.
Bio 7: Human Physiology
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Spring 2014: Riggs