RS02 - Respiratory Overview and Lung Volumes

What are the functions of the respiratory system?

• Exchange of gases between the atmosphere and blood

• Regulation of extracellular pH levels (coordinates with renal system)

• Protection from inhaled pathogens (epithelial defense mechanisms)

• Vocalization by moving air past vocal cords

What is cellular respiration?

Utilization of oxygen for energy at the cellular level.

How do single-celled organisms receive oxygen for respiration?

• O2 moves into the cell from the atmostphere via diffusion

• Concentration is reduced surrounding the cell

• Cilia mix the air in the surroundings to keep O2 concentration high

How do multicellular organisms receive oxygen for respiration?

Via external respiration and convection (gas exchange). Ensures delivery of O2 to individual cells of the organism through the blood.

What are the processes of external respiration?

1. Ventilation: exchange of air between atmosphere and lungs

2. Exchange of O2 and CO2 between lungs and blood

3. Transport of O2 and CO2 by blood

4. Exchange of gases between blood and cells

What are the two main zones of the respiratory system?

Conducting zone (150 mL) and respiratory zone (3000 mL)

What structures make up the conducting zone?

Made up of upper airways, trachea, bronchi, and bronchioles

What are the functions of the conducting zone?

• Brings air into the lungs.

• Lined with ciliated epithelium

• Warm and humidify air

• Trap particles before they get to alveoli

What is the function of the respiratory zone?

It is the site of gas exchange between inhaled air and blood via alveoli.

What physical characteristics change as you go from the conducting zone to the respiratory zone?

• Less cartilage

• Increased elastic fibers for stretch

• Increased smooth muscles for contraction

What kind of epithelium is in the upper airways?

Ciliated epithelium with a thick overlying mucus layer with a saline layer underneath.

What is the purpose of mucus and cilia in the upper airways?

Mucus traps inhaled particles, and cilia move mucus upward and out of the lungs (mucociliary escalator).

What happens to mucus removed by the mucociliary escalator?

It is expelled or swallowed.

What effect does cigarette smoke have on cilia?

It paralyzes the cilia.

How is saline secreted into the conducting zone lumen?

• Cl⁻ enters cell via Na-2Cl-K channel

• Cl⁻ exits into lumen through CFTR channel

• Na⁺ and H₂O follow paracellularly

CFTR = Cystic Fibrosis Transmembrane Conductance Regulator

What happens in cystic fibrosis regarding saline secretion?

CFTR mutations impair saline secretion, making mucus thick and impairing mucociliary clearance.

What are alveoli?

Air-filled sacs at the ends of respiratory bronchioles that serve as the site of gas exchange.

Why are alveoli variable in size?

They stretch due to increased air pressure and recoil due to elastin and collagen fibers.

What surrounds alveoli?

Capillaries, occupying about 80–90% of the space between alveoli.

Which cells make up ~95% of the alveolar surface?

Type 1 pneumocytes (Type 1 alveolar cells).

What is the function of Type 1 alveolar cells?

They are very thin epithelial cells that allow efficient diffusion of gases.

What is the function of Type 2 alveolar cells?

They secrete surfactant.

What is the role of alveolar macrophages?

They remove inspired foreign material.

Why must the distance between airspace and capillary lumen be small?

To allow efficient gas exchange.

Why do type 1 alveolar cells have similar thickness to capillary endothelium?

Allows for efficient diffusion of gases.

Why must gases move into a liquid layer before entering blood?

Because a fluid layer covers the inside surface of alveoli.

What does Dalton’s Law state regarding partial pressures?

The pressure of an individual gas in a mixture depends on its percentage within the mixture.

What do PO₂ and PCO₂ represent?

Partial pressures of oxygen and carbon dioxide.

How do gases equilibrate between air and the alveolar liquid layer?

Gas concentration in liquid is directly proportional to its partial pressure and depends on solubility.

Why do physiologists use partial pressure when referring to gases in liquid?

Because partial pressure determines dissolved gas concentration.

Which gas is more soluble in water, CO₂ or O₂?

CO₂ is more soluble than O₂. Therefore, the concentration of CO2 in blood will be much closer to the concentration in air at the same partial pressure (compared to O2).

What cells secrete surfactant?

Type 2 alveolar cells.

What is surfactant made of?

A lipid-protein mixture, primarily dipalmitoyl phosphatidylcholine (DPPC) and apoproteins.

What stimulates surfactant secretion?

Deep breaths.

How does surfactant reduce surface tension?

It decreases pressure in small alveoli and prevents them from collapsing into larger ones.

How does surfactant equalize pressure between alveoli of different sizes?

Surfactant concentration is higher in small alveoli and becomes diluted as alveoli expand, allowing smaller alveoli to expand faster and slowing expansion as they enlarge.

What cells absorb excess fluid in alveoli?

Type 2 pneumocytes.

Why does fluid naturally accumulate in alveoli?

Due to hydrostatic pressure pushing fluid out of pulmonary capillaries.

How is fluid removed from alveoli?

It is reabsorbed via ENaC channels in Type II cells; anions and water follow.

How can cytokines cause alveolar flooding?

By altering ion channels and tight junctions, reducing salt and water reabsorption and allowing excess fluid into alveoli.

What conditions can result from alveolar flooding due to cytokines?

• Acute lung injury, infection, or inflammation

• Pulmonary edema

• Acute respiratory distress syndrome (ARDS)

What is a spirometer?

A machine that measures the volume changes of the lungs during inspiration and expiration.

What is tidal volume (VT)?

The amount of air inhaled and exhaled in one normal breath.

• Small, rythmic peaks on spirometer

What is expiratory reserve volume (ERV)?

The extra air that can be exhaled with maximum effort after a normal breath.

What is inspiratory reserve volume (IRV)?

The extra air that can be inhaled with maximum effort after a normal breath.

What is residual volume (RV)?

The air remaining in lungs after maximal expiration; keeps alveoli inflated and cannot be measured by spirometry.

What are lung capacities determined by?

Combinations of two or more lung volumes.

What is functional residual capacity (FRC)?

ERV + RV; The amount of air remaining after normal tidal expiration.

What is inspiratory capacity (IC)?

VT + IRV; The amount of air inhaled after tidal expiration.

What is vital capacity (VC)?

VT + IRV + ERV; The maximum exhalation amount after maximal inspiration.

What is total lung capacity (TLC)?

Sum of all four lung volumes; the maximum air lungs can contain.

What is forced vital capacity (FVC)?

The amount of air that can be forcibly exhaled after maximal inspiration.

What is forced expiratory volume (FEV₁)?

The amount of air that is exhaled in the first second of FVC; normally ~80% of FVC in a healthy individual.

What is the normal FEV₁/FVC ratio?

0.8

How does obstructive lung disease affect FEV₁/FVC?

The ratio is reduced (e.g., asthma, emphysema, chronic bronchitis).

How does restrictive lung disease affect FEV₁/FVC?

Both values decrease but the ratio increases (e.g., fibrosis).