exhalation Flashcards
(8 cards)
volume,preasure,air gas
Breathing, or pulmonary ventilation, is a mechanical process that depends on volume changes occurring in the thoracic cavity. Keep this rule in mind about the mechanics of breathing: Volume changes lead to pressure changes, which lead to the flow of gases to equalize the pressure.
collisions boyles law
A gas, like a liquid, always conforms to the shape of its container. However, unlike a liquid, a gas fills its container. Consider a container with a large volume of gas. The gas molecules will be far apart, and the pressure (created by the gas molecules colliding with one another and the container walls) will be low. Assuming the same amount of gas were in a smaller container, the gas molecules would be closer together, and the pressure would be higher than it was in the larger container.
Concept Link
inspiration
Inspiration (Inhalation) – Summary:
Muscle Contraction:
Diaphragm contracts and moves downward → increases the height (superior-inferior dimension) of the thoracic cavity.
External intercostal muscles contract → lifts the rib cage and pushes the sternum forward → increases the width (lateral) and depth (anteroposterior) of the thoracic cavity.
Thoracic Cavity Expansion:
Overall increase in thoracic volume.
Lung Expansion:
Lungs adhere to thoracic walls via pleural fluid surface tension, so they stretch with the cavity.
Intrapulmonary volume increases (space inside the lungs expands).
Pressure Changes:
As volume increases, intrapulmonary pressure drops (below atmospheric pressure).
This creates a partial vacuum.
Air Flow:
Air flows into the lungs from outside, down the pressure gradient.
Continues until intrapulmonary pressure = atmospheric pressure.
expiration
Expiration (Exhalation) – Key Points:
🔹 1. It’s Passive (in healthy people):
Unlike inhalation, no muscles actively push the air out.
It happens because of the natural elasticity (springiness) of the lungs and thoracic cage.
🔹 2. What Happens During Expiration:
Inspiratory muscles relax:
Diaphragm moves upward (back to its dome shape).
Rib cage drops as external intercostals relax.
This makes the thoracic cavity get smaller in all directions:
Vertical (top to bottom)
Lateral (side to side)
Anteroposterior (front to back)
Because the chest cavity shrinks, the lungs also recoil (spring back to smaller size).
This decreases intrapulmonary volume (space inside the lungs).
🔹 3. Pressure Rises Inside the Lungs:
The same amount of air is now in a smaller space → gas molecules get crowded.
So, intrapulmonary pressure increases (now higher than atmospheric pressure).
🔹 4. Air Flows Out:
Because the pressure inside the lungs is now greater than outside, air flows out naturally (down the pressure gradient) until it equalizes with outside pressure.
🧠 TL;DR:
Expiration is passive.
Muscles relax, lungs recoil, volume decreases, pressure increases, and air flows out.
expiration
Expiration (Exhalation) – Key Points:
🔹 1. It’s Passive (in healthy people):
Unlike inhalation, no muscles actively push the air out.
It happens because of the natural elasticity (springiness) of the lungs and thoracic cage.
🔹 2. What Happens During Expiration:
Inspiratory muscles relax:
Diaphragm moves upward (back to its dome shape).
Rib cage drops as external intercostals relax.
This makes the thoracic cavity get smaller in all directions:
Vertical (top to bottom)
Lateral (side to side)
Anteroposterior (front to back)
Because the chest cavity shrinks, the lungs also recoil (spring back to smaller size).
This decreases intrapulmonary volume (space inside the lungs).
🔹 3. Pressure Rises Inside the Lungs:
The same amount of air is now in a smaller space → gas molecules get crowded.
So, intrapulmonary pressure increases (now higher than atmospheric pressure).
🔹 4. Air Flows Out:
Because the pressure inside the lungs is now greater than outside, air flows out naturally (down the pressure gradient) until it equalizes with outside pressure.
🧠 TL;DR:
Expiration is passive.
Muscles relax, lungs recoil, volume decreases, pressure increases, and air flows out.
inner intercostals and abdomin raising upwards during forceful breathing
What normally happens during expiration:
Passive process → happens naturally due to lung recoil.
No muscle effort needed in healthy people at rest.
❗ But in conditions like asthma, bronchitis, or pneumonia:
Airways are narrowed or blocked by:
Bronchospasms (tight bronchioles) → asthma
Mucus or fluid → chronic bronchitis, pneumonia
Air gets trapped, and it becomes harder to push it out.
So now the body has to force expiration using extra muscles.
💪 Forced Expiration – How It Works:
1. Internal Intercostal Muscles
These are the opposite of external intercostals.
They pull the ribs down and inward, which shrinks the chest cavity more than usual.
- Abdominal Muscles
Muscles like the rectus abdominis and obliques contract.
They push abdominal organs upward, which:
Pushes the diaphragm up
Further shrinks thoracic volume
Increases pressure inside lungs
Forces air out harder and faster
intrepleural preausure
Normally the pressure within the pleural space, the intrapleural pressure, is always negative (meaning it is lower than the pressure inside the lungs). This is the major factor preventing lung collapse. If for any reason the intrapleural pressure becomes equal to the atmospheric pressure, the lungs immediately recoil and collapse.
Homeostatic Imbalance 13.7
atelacasis
What Is Atelectasis?
Atelectasis = Lung collapse
When a lung (or part of it) collapses, it can’t inflate properly, so it becomes useless for ventilation (no air in, no gas exchange).
💥 How Does It Happen?
There are two main causes mentioned:
- Air enters from outside (trauma):
Example: A stab wound or injury allows air to enter the pleural space from outside the body.
The pleural space is supposed to be airtight with negative pressure.
If air gets in, it breaks the suction holding the lung to the chest wall.
- Air enters from inside (ruptured visceral pleura):
The visceral pleura (the membrane covering the lung) ruptures, allowing air to leak from the lung into the pleural space.
Both situations allow air to enter the pleural cavity, which leads to a:
❗ Pneumothorax (air in the pleural space):
The air in the pleural cavity causes pressure on the lung, pushing it inward.
The lung detaches from the chest wall and collapses.
This disrupts the surface tension (fluid bond) that normally keeps the lung expanded.
🛠️ How Is It Treated?
➤ Chest tube:
A chest tube is inserted to suck the air out of the pleural space.
This restores negative pressure in the pleural cavity.
Once the air is removed, the lung can reinflate and function normally again.
🧠 Simple Analogy:
Think of the lungs like a balloon stuck to the inside of a jar with water (pleural fluid) keeping them stuck:
If air leaks into the jar, the balloon detaches and collapses.
To fix it, you have to suck the air out of the jar (chest tube), so the balloon can stick to the wall again and re-inflate.
📌 Summary:
Term Meaning
Atelectasis Lung collapse (can’t ventilate)
Pneumothorax Air in pleural space causing lung to collapse
Causes Chest injury or ruptured visceral pleura
Fix Chest tube removes air, lung reinflates
