Topic 8 - Respiratory System Flashcards
(24 cards)
Nasal Cavity
Warms, moistens, filters air
Hairs + mucus trap dust
Smell receptors
Resonating chamber for speech
Pharynx (throat):
Pathway from nasal cavity to larynx/trachea
Shared with oesophagus
Epiglottis:
Flap that closes trachea when swallowing
Prevents food from entering lungs
Larynx (voice box):
Joins pharynx to trachea
Contains vocal cords → vibrate to produce sound
Trachea
Known as windpipe
Carries air to/from lungs
Supported by C-shaped cartilage rings → keeps airway open
Lined with mucous membranes + cilia
Cilia trap dust/debris and push it upwards to pharynx to be swallowed
Bronchi & Bronchioles
Bronchi:
Trachea splits into 2 primary bronchi
→ Secondary bronchi (each lung lobe)
→ Tertiary bronchi
Bronchioles:
Branch from tertiary bronchi
Made of smooth muscle (no cartilage)
End in terminal bronchioles → respiratory bronchioles
Control airflow in lungs
Contain cilia + mucus to protect lungs from contaminants
Lungs
Located in chest cavity, except mediastinum (holds heart)
Left lung: 2 lobes | Right lung: 3 lobes
Lined by pleura:
Visceral pleura (on lungs)
Parietal pleura (lines chest wall)
Pleural fluid between layers: reduces friction + keeps lungs attached to chest wall
🫧 Alveoli
Tiny air sacs (clustered at bronchiole ends)
Functional units of the lungs
Walls = 1 cell thick
Surrounded by capillary network
Site of gas exchange:
O₂ → blood
CO₂ → alveoli
Structure allows for efficient diffusion due to:
Thin wall
Large surface area
Moist surface
Close proximity to capillaries
💨 Other Structures
Ribs: Protect and form chest framework
Intercostal Muscles: Raise ribcage → increase lung volume
Diaphragm:
Separates chest from abdomen
Contracts → flattens → increases volume for inhalation
🫁 Mechanics of Breathing – Overview
Key Concept:
Diaphragm + intercostal muscles control breathing by changing lung volume, which changes air pressure, causing airflow in/out of the lungs
Ventilation
Definition: The process of moving air into (inspiration) and out of (expiration) the lungs
Air moves from high pressure to low pressure
Pressure differences drive breathing
Inspiration (Inhalation)
Goal: Increase chest cavity volume → Decrease pressure → Air flows in
Steps:
Diaphragm contracts → flattens downward
External intercostal muscles contract → rib cage lifts up & out
Pleura sticks to chest wall → lungs expand
Lung volume increases → pressure inside lungs drops
Air flows in (from high pressure outside → low pressure inside)
Used for: Normal + deep breathing
🌫️ Expiration (Exhalation)
Goal: Decrease chest cavity volume → Increase pressure → Air flows out
Steps:
Diaphragm relaxes → curves upward
Intercostal muscles relax → rib cage moves down & in
Lung volume decreases → pressure inside lungs increases
Air flows out (from high pressure inside → low pressure outside)
At rest: Passive
Forced expiration (e.g. blowing balloon): Intercostals + abdominals actively contract
What are Lungs suited for gas exchange
Large Surface Area:
- Alveoli provide a huge internal surface area (~50–80 m², ~⅓ of a tennis court).
- Hundreds of millions of alveoli increase the area for gas exchange.
Good Blood Supply:
- Each alveolus is surrounded by capillaries.
- Constant blood flow maintains a concentration gradient between alveolar air and blood (O₂ in, CO₂ out).
Thin Membrane:
- Alveolar wall is only 1 μm thick (one cell layer).
- Short diffusion distance allows gases to quickly pass into/out of blood.
Moist Membranes:
- Moisture layer helps gases dissolve before diffusing through the membrane.
Deep location in body:
- Protects the delicate lung surfaces from drying out due to evaporation.
Ventilation (airflow):
- Breathing movements refresh air in alveoli.
- Maintains oxygen/carbon dioxide concentration gradient
Gas Exchange Between Alveoli and Blood
Gas exchange between alveoli and capillaries occurs via diffusion due to concentration gradients of O₂ and CO₂.
Path of Blood to the Lungs from the Body
Pulmonary arteries bring deoxygenated blood from the body to the lungs.
This blood has:
- Low oxygen (used up by body cells)
- High carbon dioxide (produced by respiration)
Gas Movement at the Alveoli
Oxygen diffuses:
From the high concentration in alveolar air (20.95%)
➡️ To the low concentration in blood (15.80% in expired air)
Carbon dioxide diffuses:
From the high concentration in blood (4.30% in expired air)
➡️ To the low concentration in alveolar air (0.04%)
These gases dissolve in the moisture layer inside alveoli before diffusing.
Structural Adaptations for Gas Exchange
Alveolus wall is 1 cell thick
Capillary wall is also 1 cell thick
Thin walls + large surface area + moisture = efficient diffusion
To keep diffusion happening in the blood/alveoli, the gradient must be maintained by…
Constant blood flow through capillaries:
New, low-oxygen, high-CO₂ blood constantly arrives.
This ensures oxygen is continually absorbed and carbon dioxide removed.
Constant ventilation (breathing):
Air low in O₂ and high in CO₂ is exhaled.
Replaced by fresh air (high O₂, low CO₂).
Keeps the alveolar gas concentration ideal for diffusion.
Expired Air vs. Inspired Air
Inspired air is the air we breathe in, while expired air is the air we breathe out. Gas exchange in the alveoli changes the composition of Air.
Oxygen Gas:
- Inspired Air: 20.95%
- Expired Air: 15.80%
- The change is caused as it is used by body cells
Carbon Dioxide:
- Inspired Air: 0.04%
- Expired Air: 4.30%
- Change is because its a waste product from respiration
Why The Difference:
- Oxygen diffuses from alveoli to blood → lower in expired air
- Carbon dioxide diffuses from blood to alveoli → higher in expired air
- Gases dissolve in alveolar moisture layer before diffusion
Emphysema - Cause, Effect on Lungs/Alveoli, Summary
Cause: Long-term exposure to airborne irritants (e.g. tobacco smoke, dust, pollution).
Effect on Alveoli:
- Alveoli walls break down and join, forming larger but fewer alveoli → reduced surface area for gas exchange.
- Alveoli lose elasticity, replaced by fibrous tissue.
Impact on Lungs:
- Lungs stay inflated, can’t recoil passively → breathing becomes difficult and forced.
Symptoms: Difficulty exhaling, shortness of breath.
Irreversible: No cure; damage is progressive and permanent.
Lung Cancer - Cause, Effect on Airways, Outcome
Cause:
- Uncontrolled cell division forming tumors.
- Strongly linked to tobacco smoke and asbestos exposure.
Effect on Airways:
- Tumors grow in air passages → block airflow.
- Smoke irritates mucous membrane → excess mucus produced.
Outcome:
- Tumors disrupt normal breathing.
- Mucus build-up and inflammation may rupture alveoli.
- May lead to emphysema or spread to other body parts.
Risk:
- Smokers who work with asbestos have 20–90× higher risk.
Lung Infections - Causes, Pneumonia, Tuberculosis (TB)
Causes: Bacteria, viruses, fungi (e.g., pneumonia, tuberculosis).
Pneumonia:
- Alveoli fill with fluid and mucus → less air and less gas exchange.
- Common symptoms: chest pain, fever, difficulty breathing.
Tuberculosis (TB):
- Caused by Mycobacterium tuberculosis.
- Spread by droplets (coughing, sneezing).
- Prevented through hygiene: cover mouth, handwashing.
Asthma - Cause, Triggers, Effect on Gas Exchange
Cause: Narrowing of airways due to:
- Smooth muscle contraction
- Inflammation of airway lining
- Mucus build-up
Triggers:
- Allergens (dust, pollen, smoke), cold air, exercise, stress, infections.
Effect on Gas Exchange:
- Airway narrows → less air movement → reduced oxygen intake.
During Attack:
- Bronchioles spasm suddenly, lining swells, mucus increases.
- Leads to wheezing, shortness of breath, coughing.
