Human Physiology Week 10 - Respiratory (Week 10 Study Guide)

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Questions and Answers

What is the primary method of oxygen transport in the blood?

Converted to carbonic acid

Bound to myoglobin

Bound to hemoglobin (correct)

Dissolved in plasma

Which of the following statements about carbon dioxide transport is accurate?

Carbon dioxide is mainly dissolved in the plasma.

Bound to hemoglobin constitutes approximately 20% of carbon dioxide transport.

Carbon dioxide is primarily transported as carbonic acid.

Bicarbonate accounts for roughly 70% of carbon dioxide transport. (correct)

What limitation of pulse oximetry can lead to misinterpretation in patients with low hemoglobin levels?

It does not indicate what is bound to hemoglobin. (correct)

It measures carbon dioxide saturation instead of oxygen.

It shows the total volume of blood present.

It can accurately quantify the amount of hemoglobin in blood.

Which statement accurately describes the role of central chemoreceptors in regulating ventilation?

They are the major controller stimulated by increased hydrogen ions and carbon dioxide. Signup and view all the answers

What significant factor can affect the accuracy of pulse oximeter readings?

Skin pigmentation levels. Signup and view all the answers

Which statement accurately describes the distribution of cartilage and smooth muscle in the respiratory system?

Trachea contains the most cartilage, while bronchioles have none. Signup and view all the answers

What contributes to the greatest resistance in airflow within the respiratory tract?

The bronchioles because they can constrict and lack cartilage. Signup and view all the answers

How does expiration affect airway resistance?

Airway resistance increases due to airway compression. Signup and view all the answers

Which factor primarily causes bronchoconstriction?

Parasympathetic release of Acetylcholine. Signup and view all the answers

Which of the following is NOT a mechanism that increases airway resistance in disease states?

Muscle relaxation in bronchial smooth muscle. Signup and view all the answers

What is the role of bronchodilators in managing airway resistance?

They decrease smooth muscle contraction. Signup and view all the answers

Which factor is associated with decreased lung compliance?

Chronic inflammation and presence of scar tissue. Signup and view all the answers

What is the effect of stiffer lung tissue on lung function?

Requires more effort to inflate the lungs Signup and view all the answers

How is partial pressure of oxygen in the blood described?

It denotes only the oxygen dissolved in plasma Signup and view all the answers

What happens to oxygen diffusion from the alveoli during high altitude?

It decreases due to reduced gas concentration gradient Signup and view all the answers

What is one consequence of increased distance between the alveoli and capillaries during gas exchange?

Decreased rate of diffusion Signup and view all the answers

Which of the following describes the concept of 'dead space' in respiration?

Air that does not reach the area of gas exchange Signup and view all the answers

What changes occur to pulmonary blood flow during exercise?

It increases and decreases resistance Signup and view all the answers

What is the primary problem caused by a pulmonary embolism?

Inadequate blood perfusion to alveoli Signup and view all the answers

What does FiO2 represent in a clinical context?

Fraction of oxygen in the inhaled air Signup and view all the answers

What happens to the partial pressure of carbon dioxide (PACO2) in the alveoli when blood flow is inadequate?

It increases due to accumulation from blood Signup and view all the answers

What physiological condition is indicated by the presence of anatomic dead space?

Sections of the respiratory tract with non-exchangeable air Signup and view all the answers

Study Notes

Airway Anatomy

Cartilage decreases distally; most cartilage is in the trachea, no cartilage in the bronchioles
Smooth muscle is present where cartilage is absent
Bronchioles are almost entirely smooth muscle, except respiratory bronchioles

Airway Resistance

Bronchioles have the greatest resistance due to the presence of smooth muscle, allowing for bronchoconstriction, while lacking cartilage for structural support.

Ventilation and Airway Resistance

Inspiration decreases airway resistance as lung inflation pulls tissue apart and opens airways.
Expiration increases airway resistance due to compression of airway during lung deflation.
High airway resistance causes turbulent airflow, resulting in wheezing.

Factors Influencing Bronchoconstriction and Bronchodilation

Sympathetic nervous system (neuroepinephrine and epinephrine) causes bronchodilation.
Parasympathetic nervous system (acetylcholine) causes bronchoconstriction.

Airway Resistance in Disease States

Muscle contraction: Bronchoconstriction (acute or chronic).
Inflammation: Presence of blood and edema in airway walls.
Blockages in airway lumen: Mucus, tumors, foreign objects.

Reducing Airway Resistance

Bronchodilators: Activate β-adrenergic receptors for bronchodilation.
Inhaled steroids: Reduce inflammation.

Decreased Lung Compliance

Causes: Chronic inflammation and scar tissue.
Effects:
- Increased effort to inflate lungs, leading to increased metabolic rate.
- Incomplete lung inflation, potentially impacting gas exchange.
- Reduced recoil during expiration, possibly requiring active expiration, which increases metabolic rate.

Partial Pressure

Blood gases are measured in terms of partial pressure, reflecting the amount of dissolved gas in the blood.
Partial pressure is calculated as the product of atmospheric pressure and the percentage of a given gas in the atmosphere.

Partial Pressure Abbreviations

Air:
- PO2: Partial pressure of oxygen in the air we breathe in (about 160mmHg at sea level).
- FO2: Fraction of oxygen in the air (about 21% regardless of elevation).
- FiO2: Fraction of oxygen in the air we breathe in (21% for normal air).
Body:
- PAO2: Alveolar partial pressure of oxygen (about 100-105mmHg at sea level).
- PaO2: Systemic arterial partial pressure of oxygen (about 100mmHg at sea level).
- PvO2: Systemic venous partial pressure of oxygen (about 40mmHg at rest, decreases during exercise).

Gas Exchange

Gases move from high partial pressure to low partial pressure.
- Oxygen moves from alveolus to blood.
- Carbon dioxide moves from blood to alveolus.
Oxygen transport:
- Any fluid in lungs.
- Alveolar epithelium.
- Epithelial basement membrane.
- Interstitial space.
- Capillary basement membrane.
- Capillary endothelial membrane.

Factors Limiting Gas Exchange

Reduced gas concentration gradient:
- High altitude, reduced PO2.
- Pulmonary pathology, difficulty exchanging air.
Reduced surface area of membrane:
- Fluid or mucus in alveoli.
- Reduced number of active alveoli
- Reduced total surface area, e.g. emphysema.
Increased distance between alveoli and capillary:
- Fluid or mucus in alveoli.
- Fluid in interstitium.
- Scar tissue

Ventilation-Perfusion Matching

For gas exchange, both ventilation and perfusion must be adequate.
- Ventilation: Air in the alveolus.
- Perfusion: Blood flow through the capillary.

Pulmonary Blood Flow During Exercise

Increased by more than four times during exercise.
Increases number of open capillaries.
Distends open capillaries, both decreasing vascular resistance.

Dead Space

Air that never reaches the area of gas exchange.
Removed first, creating difficulties in removing expiratory gases from the alveoli.

Anatomical vs. Physiological Dead Space

Anatomical dead space: Areas of the respiratory tract where gas exchange cannot occur.
Physiological dead space: Alveoli with incomplete perfusion for gas exchange.

Pulmonary Embolism

Blood clots in the pulmonary vessels, potentially leading to:
- Blocked perfusion of alveoli, preventing gas exchange.
- Increased pulmonary vascular resistance, increasing workload on the right ventricle.

Oxygen Transport in Blood

Bound to hemoglobin (97%).
Dissolved (3%).

Carbon Dioxide Transport in Blood

Bicarbonate (most, ~70%).
Bound to hemoglobin (95% during exercise).

Pulse Oximetry Limitations

Only measures the percentage of saturated hemoglobin, not overall hemoglobin levels.
Does not differentiate between oxygen and other molecules bound to hemoglobin, e.g. carbon monoxide.
Affected by skin pigmentation, leading to potential overestimation of saturation level.

Blood Gases in Regulation of Ventilation

Increased carbon dioxide levels in blood stimulate ventilation.
Central chemoreceptors in the medulla are the major controllers, stimulated by increased hydrogen ions and carbon dioxide.
Peripheral chemoreceptors in the carotid bodies and aortic play a minor role, being stimulated by decreased PaO2.

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