Respiratory Physiology Review

Lung Functions• Gas exchange– Moves O2 into blood

– Removes CO2 from blood

• Blood storage• Regulate vasoconstricting substances– Bradykinin– Angiotensin II– Heparin

Conducting Airways• Move air into lungs• Warm and

humidify air• Trap inhaled

particles

Respiratory Airways

• Bronchioles

• Alveoli

• Gas is exchanged with the blood

Membranes and Cavities

• Parietal pleura• Visceral pleura• Pleural space (between

pleurae)• Mediastinum

Question Which serous membrane lines the thoracic

cavity?a. Visceral pleurab. Parietal pleurac. Visceral mediastinumd. Parietal mediastinum

Answer b. Parietal pleuraRationale: 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 Muscles• Diaphragm• Accessory muscles of inhalation– External intercostals– Scalene– Sternocleidomastoid

• Accessory muscles of exhalation– Internal intercostals– Abdominal muscles

Question Tell whether the following statement is true or

false.During inhalation, the diaphragm contracts and

flattens.

Answer TrueRationale: 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.

Compliance• How easily lungs can be inflated depends on:

– Elastin and collagen fibers

– Water content

– Surface tension

Surfactant Reduces Surface Tension

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 Volumes• Tidal volume

• Inspiratory reserve

• Expiratory reserve

• Residual volume

Lung Capacities• Vital capacity

• Inspiratory capacity

• Functional residual capacity

• Total lung capacity

Dynamic Lung Function• Forced vital capacity

• Forced expiratory volume

• FEV1.0

• Minute volume

• Maximum voluntary ventilation

Question Which measure of lung function indicates the

total amount of air that the lungs can hold?a. Tidal volumeb. Functional residual capacityc. Vital capacityd. Total lung capacity

Answer d. Total lung capacity Rationale: 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 Exchange

• Oxygen moves from alveolar air into blood

• Carbon dioxide moves from blood into alveolar air

Ventilation and PerfusionScenario:

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 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 Tell whether the following statement is true or

false.Ventilation–perfusion mismatch results in

hypoxia.

Answer TrueRationale: 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—Oxygen• Dissolved oxygen = PaO2 or PO2

– Normal value >80 mm Hg

• Oxygen bound to hemoglobin = oxyhemoglobin

– Normal value 95% to 97% saturation

Hemoglobin Holds Four Oxygen Molecules

O2O2

O2

• How saturated is this molecule of hemoglobin?

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

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 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.)• 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?

Oxygen Affinity• How tightly the

hemoglobin holds onto the oxygen

• Which of these hemoglobin samples has the highest oxygen affinity?

• Which will release the most oxygen to the tissues?

AB

C

Blood 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

Tell whether the following statement is true or false.

The relationship between PCO2 and pH is direct.

Answer FalseRationale: 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 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

Scenario• You 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?