Chapter021

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins


Chapter 21

Control of Respiratory Function

Chapter 21

Control of Respiratory Function


Lung FunctionsLung Functions• Gas exchange

– Moves O2 into blood

– Removes CO2 from blood

• Blood storage

• Regulate vasoconstricting substances

– Bradykinin

– Angiotensin II

– Heparin


Conducting AirwaysConducting Airways

• Move air into lungs

• Warm and humidify air

• Trap inhaled particles



Respiratory Airways

Respiratory Airways

• Bronchioles

• Alveoli

• Gas is exchanged with the blood


Question Question

Which serous membrane lines the thoracic cavity?

a. Viscera pleura

b. Parietal pleura

c. Visceral mediastinum

d. Parietal mediastinum


Answer Answer

b. Parietal pleura

The organs and walls of the thoracic and abdominal cavities are covered with serous membranes. Visceral membranes cover the organ; parietal membranes line the cavity walls. The two membranes and the space between them allow for ease of movement.

The thoracic cavity is lined by parietal pleura; the lungs are covered by visceral pleura.


Respiratory MusclesRespiratory Muscles

• Diaphragm

• Accessory muscles of inhalation

– External intercostals

– Scalene

– Sternocleidomastoid

• Accessory muscles of exhalation

– Internal intercostals

– Abdominal muscles


Question Question

Tell whether the following statement is true or false:

During inhalation, the diaphragm contracts and flattens.


Answer Answer

True

The diaphragm is the main muscle of inhalation/inspiration. During inhalation, the diaphragm contracts and flattens (it moves downward in order to accommodate the volume of air you are taking in, allowing space for the lungs to expand).

During exhalation, the diaphragm relaxes and moves back up.


ComplianceCompliance

• How easily lungs can be inflated depends on:

– Elastin and collagen fibers

– Water content

– Surface tension


Scenario:Scenario:

• A man’s lungs were damaged during a fire

• He developed severe respiratory distress

• The doctor said smoke inhalation had caused an inflammation of his alveoli

• The damage had also destroyed some of his surfactant

Question:

• What had happened to his lung compliance?

• Why was he given positive-pressure ventilation?


Lung VolumesLung Volumes

• Tidal volume

• Inspiratory reserve

• Expiratory reserve

• Residual volume


Lung CapacitiesLung Capacities

• Vital capacity

• Inspiratory capacity

• Functional residual capacity

• Total lung capacity


Dynamic Lung FunctionDynamic Lung Function

• Forced vital capacity

• Forced expiratory volume

• FEV1.0

• Minute volume

• Maximum voluntary ventilation


Question Question

Which measure of lung function indicates the total amount of air that the lungs can hold?

a. Tidal volume

b. Functional residual capacity

c. Vital capacity

d. Total lung capacity


Answer Answer

d. Total lung capacity is the maximum amount of air that the lungs can hold—everything (volume-wise) at the end of a maximal inhalation (the deepest breath one can possibly take). Normal TLC is approximately 6 L.


Gas ExchangeGas Exchange

• Oxygen moves from alveolar air into blood

• Carbon dioxide moves from blood into alveolar air


Ventilation and PerfusionVentilation and Perfusion

Scenario:

A child has inhaled a peanut, blocking her left primary bronchus.

Question:

• How will the ventilation in her two lungs change?

• How will the composition of the air in her two lungs differ?

• Which lung should she send more blood to?

• How should her body alter perfusion of the lungs?


Ventilation-Perfusion MismatchingVentilation-Perfusion Mismatching

• Blood goes to parts of the lung that do not have oxygen to give it

• Blood does not go to parts of the lung that have oxygen


Question Question


Ventilation-perfusion mismatch results in hypoxia.


Answer Answer

True

In either case (ventilation without perfusion or perfusion without ventilation) oxygen is not picked up by the capillaries and delivered to the tissues. The result of decreased oxygen at the tissue level is termed hypoxia.


Blood Gases—OxygenBlood Gases—Oxygen

• Dissolved oxygen = PaO2 or PO2

– Normal value >80 mm Hg

• Oxygen bound to hemoglobin = oxyhemoglobin

– Normal value 95% to 97% saturation


Hemoglobin Holds 4 Oxygen MoleculesHemoglobin Holds 4 Oxygen Molecules

• How saturated is this molecule of hemoglobin?

• How could a person have a hemoglobin saturation of 95%?


Oxygen Capacity Oxygen Capacity

• Amount of oxygen the blood can hold

• What is the oxygen capacity of normal blood?

• What is the oxygen capacity of anemic blood?


Oxygen ReleaseOxygen Release

• If the blood released half of its oxygen to the tissues …

– How much oxygen would the normal tissues receive?

– How much would the anemic person's tissues receive?


Oxygen Release (cont.)Oxygen Release (cont.)

• Most body tissues have a PO2 of 40-60 mm Hg

• How much oxygen does the normal blood release at a PO2 of 40 mm Hg?

• The anemic blood?


Blood Gases—Carbon DioxideBlood Gases—Carbon Dioxide

• Dissolved carbon dioxide = PaCO2 or PCO2

– Normal value 35–45 mm Hg

• Carbon dioxide bound to hemoglobin = carbaminohemoglobin

• Carbonic acid bicarbonate ion and H+

• When you exhale you remove CO2 from your blood and also decrease the amount of carbonic acid, raising your blood pH


Question Question


The relationship between PCO2 and pH is direct.


Answer Answer

False

The relationship is indirect. As PCO2 levels rise, the amount of carbonic acid in the blood increases, making the pH more acidic (decreasing it).


Respiratory centers

pneumotaxic apneustic

stops inspiration; begins exhalation

lungs deflate

stretch receptors note decreased lung

volume

begins inspiration

lungs inflate

stretch receptors note increased lung

volume


Chemoreceptors Can Adjust Respiration RateChemoreceptors Can Adjust Respiration Rate

• Central chemoreceptors

– Measure PCO2 and pH in cerebrospinal fluid

– Increase respiration when PCO2 increases or pH decreases

• Peripheral chemoreceptors

– Measure PO2 in arterial blood

– Increase respiration when PO2 <60 mm Hg


ScenarioScenarioYou are caring for a COPD client…

• He has chronically high PCO2

• He is being given low-flow oxygen and complains all the time that he “needs more air,” so you turn up his oxygen.

Question:

• When you check on him later, he is unconscious and not breathing. What happened?

Chapter021

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