pulmonary ventilation

What is the pathway of air through the respiratory system

Nasal cavity → pharynx → glottis → trachea → bronchi → bronchioles → alveolar ducts → alveoli

What is the function of the glottis

Separates swallowing (digestive) from breathing (respiratory)

What structural features does the trachea have

Rigid tube with cartilage rings and smooth muscle

What is the difference between bronchi and bronchioles?

Bronchi = larger airways; bronchioles = smaller airways lined with smooth muscle

What lines the bronchioles and why

Epithelium (not endothelium) because airways are exposed to the external environment

What are alveoli

Tiny epithelial pouches where gas exchange occurs (~50–100 µm diameter)

What are the two layers of pleura

Visceral pleura (on lung) and parietal pleura (on chest wall)

What is the function of pleural fluid

To reduce friction during lung expansion and contraction, and to create surface tension that helps keep the lungs inflated.

How is pulmonary circulation different from systemic circulation

Pulmonary arteries carry O₂-poor blood; pulmonary veins carry O₂-rich blood

Why are lungs heavily vascularized

To facilitate gas exchange and provide oxygen to the blood.

Where does gas exchange occur

Alveoli

What layers separate air from blood in alveoli

The alveolar and capillary walls, consisting of a thin epithelial layer and a basement membrane, ensure efficient gas exchange between air and blood.

How many cell membranes separate air from RBC interior

5 membranes

Why is the gas exchange barrier so thin

Minimizes diffusion distance faster gas exchange

What is tidal volume (TV)

The amount of air inhaled or exhaled during normal breathing. It typically measures about 500 mL in adults.

What is inspiratory reserve volume

(IRV) is the maximum amount of air that can be inhaled after a normal inhalation, typically around 3000 mL in adults.

What is expiratory reserve volume (ERV)

The maximum amount of air that can be exhaled after a normal exhalation, typically around 1200 mL in adults.

What is vital capacity (VC)

Vital capacity is the maximum amount of air that can be exhaled after a maximum inhalation, typically around 4800 mL in adults.

What is residual volume (RV)?

Residual volume is the amount of air that remains in the lungs after a maximum exhalation, typically around 1200 mL in adults.

Why does residual volume exist

Residual volume prevents lung collapse and maintains gas exchange between breaths.

What is normal respiratory rate

Normal respiratory rate is the number of breaths taken per minute, typically ranging from 12 to 20 breaths in a healthy adult.

What is ventilation rate at rest

amount of air breathed in and out per minute, usually around 6 to 10 liters.

What is the most important concept about alveoli

They are the primary site for gas exchange in the lungs.

Is breathing done by pushing air into lungs

No — lungs are pulled open by negative pressure

What determines lung expansion

Pressure difference between inside and outside (transpulmonary pressure)

What happens to diaphragm during inhalation

Contracts and moves downward

What happens to rib cage during inhalation

It expands and moves upward, increasing thoracic volume.

What happens to pleural pressure during inhalation

Becomes more negative

What happens to lungs during inhalation

Expand due to increased transpulmonary pressure

What happens during quiet exhalation

Diaphragm relaxes lungs recoil

What muscles are used in forced exhalation

The internal intercostal muscles and abdominal muscles contract to push air out of the lungs forcibly.

What do abdominal muscles do during forced exhalation

Contract to assist in pushing air out of the lungs.

Define transpulmonary pressure

It is the difference between the alveolar pressure and the intrapleural pressure, which helps keep the lungs inflated.

What happens when transpulmonary pressure increases

Lungs expand (inhalation)

What is alveolar pressure usually near?

Atmospheric (≈ 0)

What is pleural pressure normally

slightly negative compared to atmospheric pressure.

Why is pleural pressure negative?

Keeps lungs pulled open

Why isn’t alveolar pressure always exactly atmospheric?

Airflow requires a pressure gradient → slight deviations above/below atmospheric

What happens to lung volume as pleural pressure becomes more negative

Lung volume increases, leading to greater capacity for air as the negative pleural pressure allows the lungs to expand more easily.

What is hysteresis

A phenomenon in which the lung volume does not follow the same path during inflation and deflation, caused by elastic properties of lung tissue and surfactant effects.

What does hysteresis indicate about the lung?

Hysteresis indicates that the lung volume during inflation is not the same as during deflation, reflecting the biomechanical properties and energy losses that occur in lung tissue and the presence of surfactant.

What are the two forces that cause lung collapse

The two forces that cause lung collapse are elastic recoil of the lung tissue and surface tension in the alveoli. These forces work against the expansion of the lungs, promoting collapse.

What creates elastic forces?

Collagen and elastin in lung tissue

What causes surface tension

Hydrogen bonding between water molecules

Why does surface tension pull inward

The surface tension pulls inward due to the cohesive forces between water molecules, which creates tension on the air-water interface, reducing the alveoli's ability to expand.

Where does surface tension act in lungs

Surface tension acts at the air-water interface in the alveoli of the lungs, helping to maintain their structure and facilitate gas exchange.

What is the Law of Laplace for alveoli

P = 2T / r

What happens when alveolar radius decreases

When the alveolar radius decreases, the pressure within the alveoli increases according to the Law of Laplace, which can cause the alveoli to collapse if the surface tension is not reduced.

What is surfactant

Mixture of phospholipids and proteins

What does surfactant do

Decreases surface tension (~5× reduction)

Why is surfactant necessary

Prevents alveolar collapse and reduces breathing effort

How is surfactant structured?

Hydrophilic heads toward water, hydrophobic tails toward air

What causes RDS in premature babies

Lack of surfactant

When does surfactant production begin

26 weeks gestation

Why is breathing difficult in RDS

High surface tension → alveoli collapse easily → high effort to open

What happens to collapsing pressure in RDS

Increases significantly

What are symptoms of RDS

Dyspnea, tachypnea, cyanosis, grunting

How is RDS treated?

Treatment involves supplemental oxygen, mechanical ventilation, and administration of surfactant to reduce surface tension.