Anatomy of the Respiratory System

Macroscopic Anatomy

-Respiratory system extends from the nose/nasal cavity → lungs → alveoli.

Right lung = 3 lobes

• Superior

• Middle

• Inferio

Left lung = 2 lobes

• Superior

• Inferior

Macroscopic Anatomy

-Main Function: gas exchange (O2 and CO2)

-Ventilation (movement of air)

Microscopic Anatomy (Histology)

-The bronchial tree is made of progressively smaller tubes that carry air toward the alveoli.

-Bronchi

• Larger airways

• Contain cartilage

-Bronchioles

• Smaller airways

• Do not contain cartilage

-Alveoli

• Tiny air sacs at the ends of bronchioles

• Important location for gas exchange

• Only 2 cell linings separate air from blood.

• Type II alveolar cells produce surfactant

Ventilation

Ventilation = movement of air into and out of the lungs. (inspiration and expiration)

• Controlled by interaction between:

  • Respiratory muscles

  • Ribcage

  • Pleura

Inspiration

• Usually an active process.

• Diaphragm and other respiratory muscles contract. Pulls parietal pleura which pulls visceral pleura

• This expands the lungs.

• Lung pressure decreases.

• Air moves into the lungs.

Expiration

• Can be passive or active.

• When respiratory muscles relax:

  • Ribcage returns toward its normal position.

  • Thoracic volume decreases.

  • Air is pushed out.

• During forced expiration, abdominal and other muscles can contract to help push air out.

⭐ Easy way to remember:

Inspiration → volume ↑ → pressure ↓ → air IN

Expiration → volume ↓ → pressure ↑ → air OUT

Gas Exchange

• One major function of the respiratory system is gas exchange.

• The body needs to:

  • Get rid of CO₂ produced by tissues.

  • Bring O₂ into the body/cells.

• Gas exchange can be affected by:

  • Air composition

  • Membrane area

  • Membrane thickness

  • Gas solubility

Gas exchange

How gases are transported

CO₂

• 5% dissolved in plasma

• 25% bound to hemoglobin

• 70% as bicarbonate

O₂

• 2% dissolved in plasma

• 98% bound to hemoglobin

-Difussion of gasses is passive