UNIT 6

What is the main function of the lungs?

To enable gas exchange—oxygen in, carbon dioxide out—through respiration.

How many lobes does each lung have

The right lung has 3 lobes; the left lung has 2.

Why does the left lung have fewer lobes than the right?

To make space for the heart.

What are bronchi?

Branches of the trachea that deliver air to each lung lobe.

What are alveoli?

Tiny air sacs where oxygen enters the blood and carbon dioxide exits

What surrounds the alveoli and helps with gas exchange?

Capillaries.

What is respiration?

The gas exchange of oxygen and carbon dioxide in the alveoli.

What are two diseases that can affect the lungs?

Emphysema and pneumonia.

What are some causes of lung diseases?

Tobacco smoke and infectious organisms

What is the most important function of the lungs?

Gas exchange—O₂ enters the blood, CO₂ exits it by simple diffusion.

How do the lungs regulate blood pH?

By altering CO₂ levels in the blood faster than the kidneys can.

Why are lungs important for speech?

Air must pass over the vocal cords for sound to be produced.

How do lungs protect the body from illness?

They have a strong host defense system against particles like dust, bacteria, and viruses.

What happens to small blood clots in the lungs?

They are trapped and dissolved in lung capillaries to avoid blood flow disruption

What enzyme in the lungs helps regulate blood pressure?

ACE (angiotensin-converting enzyme), which converts angiotensin I to II.

Where is ACE highly concentrated in the lungs?

In the walls of the lung capillaries.

Where are the lungs located in the body?

In the thoracic cavity, beneath the ribs.

What muscle separates the thoracic and abdominal cavities?

The diaphragm.

What does the diaphragm do during breathing?

It contracts and relaxes to help us inhale and exhale.

What other muscles help with breathing?

The intercostal muscles between the ribs.

How many lobes does the right lung have?

Three.

: How many lobes does the left lung have?

Two.

What is the largest airway in the respiratory system?

: The trachea.

Why is the left lung smaller than the right?

Because the heart sits slightly to the left between the lungs.

What are the two functional zones of the lungs?

The conducting zone and the respiratory zone.

What is the main function of the respiratory zone?

Gas exchange.

What happens to airway size as you go deeper into the lungs?

Airways branch and become progressively smaller, like blood vessels do.

Which zone includes the alveoli where gas exchange occurs?

The respiratory zone.

Which zone includes airways that just move air but don't exchange gases?

The conducting zone.

What is the largest airway in the respiratory system?

The trachea.

What are the branches that follow the trachea?

Primary bronchi → secondary bronchi → tertiary bronchi → bronchioles.

Where does the conducting zone end?

At the terminal bronchioles.

What is the function of the conducting zone?

To conduct air to the respiratory zone and protect from inhaled particles.

What structures help move trapped particles out of the lungs?

Cilia on ciliated bronchial epithelial cells.

What traps dust and microbes in the conducting zone?

Mucus on top of the epithelial cells.

What happens to the cilia of smokers?

They beat uncoordinatedly, making it harder to clear mucus and increasing infection risk.

Where does gas exchange occur in the lungs?

In the respiratory zone, specifically in the alveoli.

What is the main function of the respiratory zone in the lungs?

The respiratory zone is responsible for gas exchange.

What structures must air reach for gas exchange to occur in the lungs?

Air must reach the alveoli for gas exchange to happen.

What structures make up most of the respiratory zone?

The alveoli make up the majority of the respiratory zone.

Where does gas exchange occur in the lungs?

Only in the respiratory zone, not in the conducting zone.

What is the first airway of the respiratory zone?

The respiratory bronchiole.

What is the last airway of the conducting zone?

The terminal bronchiole.

How can you distinguish a respiratory bronchiole from a terminal bronchiole?

The respiratory bronchiole has the odd alveolus attached; the terminal bronchiole does not.

What do respiratory bronchioles branch into?

Alveolar ducts.

What do alveolar ducts lead into?

Alveolar sacs.

What is an alveolar sac?

A cluster of alveoli, similar to a cluster of grapes.

What is each individual air sac in the alveolar sac called?

An alveolus.

What surrounds each alveolus externally?

A network of blood vessels (capillaries).

What fills the inside of each alveolus?

: Air.

What is the purpose of wrapping alveoli in capillaries?

To allow oxygen to move into the blood and CO₂ to move out of the blood.

What must gases pass through to be exchanged between alveoli and blood?

The alveolar wall and the capillary wall.

What is the structure called where gas exchange occurs between blood and alveoli?

The blood-gas barrier.

What forms the blood-gas barrier?

One alveolar cell and one capillary cell (2-cell thickness).

Why is the blood-gas barrier extremely thin?

Because thin cells maximize gas exchange

How thin is the blood-gas barrier?

1/50,000th the thickness of a millimeter.

What fills the inside of each alveolus?

Air.

What wraps around the outside of each alveolus?

Pulmonary capillaries.

What is the path of blood to the alveolar capillaries?

Right ventricle → pulmonary arteries → pulmonary arterioles → pulmonary capillaries.

What is the role of the pulmonary capillaries?

Oxygen enters the blood and carbon dioxide leaves the blood.

What is the blood-gas barrier?

The thin barrier that separates alveolar air from blood in surrounding capillaries.

What is the function of the blood-gas barrier?

Allows oxygen to enter the blood and CO₂ to leave the blood for exhalation.

What forms the blood-gas barrier?

A type I epithelial cell and a capillary endothelial cell.

What is the main role of Type I epithelial cells?

They form most of the alveolar wall and enable gas exchange due to their thin squamous shape.

Why are type I epithelial cells ideal for gas exchange?

They are very thin (squamous), which allows easy diffusion of gases.

What do type II epithelial cells do?

They produce surfactant, a substance essential for lung function.

Are type II epithelial cells abundant in the alveolar wall?

No, there are few of them, but they still contribute to the wall.

What is surfactant?

A substance produced by type II epithelial cells that helps the lungs function normally.

What is the function of alveolar macrophages?

They roam the alveoli, removing bacteria, viruses, and debris via endocytosis.

What are the two functional zones of the lung?

The conducting zone (no gas exchange) and the respiratory zone (gas exchange occurs).

Where does gas exchange take place in the lungs?

In the respiratory zone, specifically the alveoli.

What happens if you take very shallow breaths?

Air may only reach the conducting zone, so no gas exchange occurs.

What is alveolar ventilation?

The movement of air into the alveoli for gas exchange.

How do breathing patterns affect gas exchange?

Poor or shallow breathing reduces alveolar ventilation, leading to poor gas exchange

Why is it important for air to reach the alveoli?

Because gas exchange only occurs in the respiratory zone, which includes the alveoli.

What is alveolar ventilation (VA)?

The amount of air per minute that reaches the alveoli and participates in gas exchange.

What is pulmonary ventilation (VE)?

The total amount of air entering the lungs per minute; VE = Tidal Volume (VT) × Respiratory Rate (RR).

What is anatomical dead space (VD)?

The volume of air that remains in the conducting zone and does not participate in gas exchange.

How is anatomical dead space estimated?

About 1 mL per pound of body weight. A 150 lb person has ~150 mL of dead space per breath.

How is alveolar ventilation (VA) calculated?

VA = (VT – VD) × RR, where VT = tidal volume and VD = dead space.

What happens with shallow, rapid breathing?

Most air stays in the dead space, so alveolar ventilation is low despite high pulmonary ventilation.

What happens with deep, slow breathing?

More air reaches the alveoli, so alveolar ventilation is high, even if total ventilation stays the same

What surrounds the lungs and helps prevent them from collapsing?

Two thin, flexible pleural membranes.

Why are pleural membranes important in breathing?

They help maintain pressures that keep the lungs inflated.

What are the muscles between the ribs called?

Intercostal muscles.

What is the diaphragm's role in the thoracic cavity?

It's a key breathing muscle forming the base of the cavity.

What are the two pleural membranes?

Parietal pleura (attached to diaphragm and rib cage) and visceral pleura (attached to lungs).

What does "visceral" in "visceral pleura" refer to?

Organs or guts—so it's the membrane touching the lungs.

What fills the space between the pleural membranes?

A small amount of fluid for lubrication.

What is the name of the space between the pleural membranes?

Intrapleural space.

Why is the fluid in the intrapleural space important?


It allows the membranes to slide smoothly and prevents pain during breathing.

Does each lung have its own set of pleural membranes?


Yes, both lungs are encased in separate pleural membranes.

What is Boyle's Law?

Boyle's Law states that pressure and volume are inversely related: if volume increases, pressure decreases, and vice versa.

How does Boyle’s Law apply to breathing?

Breathing involves changing lung volume to create pressure differences that allow air to flow in or out.

What happens to pressure when you squeeze a balloon?

The volume decreases and pressure increases, which can cause it to burst.

What direction does air flow based on pressure?

From high pressure to low pressure.

What is intrapulmonary pressure?

The pressure of air inside the lungs.

What is atmospheric pressure considered to be in this course?

760 mmHg.

to inhale, how must intrapulmonary pressure compare to atmospheric pressure?

Intrapulmonary pressure must be lower than atmospheric pressure.

What must happen to thoracic cavity volume to inhale?

It must increase to lower intrapulmonary pressure.