Module 5 (Respiratory System )

Describe the structure and function of the respiratory system and its components.

The functions of the reparatory system is the breath, gas exchange, smell and regulate blood pH.

It is divided into the upper and lower respiratory tract.

What consist of the Upper respiratory tract

• Nasal cavity

• Pharynx

• Larynx

Nasal cavity (Structure and function)

• On the lateral wall of the nasal cavity there is the nasal conchae (superior, middle, inferior) that increases surface area and creates turbulence allowing the air to stay in the cavity for longer

• Divided by the Nasal septum (cartilage at the front and bone at the back) separating the nose into the left and right nasal cavity

Function

• Filters air

• Warms inhaled air

• Humidifies air

• Traps particles in mucus

Pharynx (Structure and function)

A muscular tube behind the nasal and oral cavities divided into:

• Nasopharynx (Pseudostratified ciliated columnar - Filters, warms, and humidifies air)

• Oropharynx (Nonkeratinized stratified squamous - Protects against abrasion from food)

• Laryngopharynx (Nonkeratinized stratified squamous - Protects against abrasion from food)

Function

• Passageway for air

• Assists swallowing

• Protects respiratory tract

Walls lined with mucosa

Larynx (Structure and function)

Structure

• Cartilaginous structure connecting pharynx to trachea

• What connects the pharynx and the trachea

Function

• Maintains open airway

• Produces sound (voice)

• Prevents food entering airway during swallowing

What consist of the Lower Respiratory Tract

Trachea

Bronchi and Bronchioles

Alveoli

Trachea

Structure

• Flexible and slightly rigid tube within the mediastinum

• Bifurcates (splits in two) into the primary bronchi

Functions:

• Conducts air to and from the lungs.

Bronchi and Bronchioles

Bronchi - continues to bifurcate from primary to secondary and then to tertiary bronchi

Bronchioles - From tertiary it turns into bronchioles (smaller branches of bronchi), then terminal, respiratory and finally alveolar ducts.

Function

• Conduct air throughout lungs

Alveoli

Structure

• Tiny air sacs

• Functional units of the lungs

• Made of:

  • Type I and Type II alveolar cells

Function

• Site of gas exchange

• O₂ diffuses into blood

• CO₂ diffuses out of blood

Pleura and Pleural cavities

Structure

• Visceral pleura - inner layer, covers lungs

• Parietal pleura - outer layer, lines thoracic wall

NOTE: both pleura’s are the same one layer just wrapper around like an elastic band

Between them is the pleural cavity containing pleural fluid.

Function

• Reduces friction during breathing

• Maintains negative pressure to keep lungs expanded

Lungs lobes and fissures

• Right lung has 3 lobes (Superior, Middle, Inferior), separated by the horizontal and oblique fissure

• Left lung has 2 lobes (Superior, Inferior), separated by the oblique fissure

Intercostal Muscles

Function

• External intercostals assist inspiration

• Internal intercostals assist forced expiration

Diaphragm

Function

Primary muscle of inspiration.

• Contracts → thoracic cavity volume increases, air enters the lungs

Alveolar Pressure Changes (Inhalation + Exhalation)

• Inhalation: Diaphragm contracts, flattening, increasing the lung volume thus reducing the pressure making the air move in

• Exhalation: Diaphragm and intercostals relax causing the lungs to recoil back elastically, decreased volume moving the air out

Quiet breathing

Two types:

Diaphragmatic (deep) breathing

• Inhale: diaphragm contracts → thoracic cavity expands

• Exhale: diaphragm relaxes (passive)

Costal (shallow) breathing

• Inhale: external intercostals contract as well as the diaphragm → ribs rise → thoracic cavity expands

• Exhale: muscles relax (passive)

Fast-forced breathing

Inhalation:

• Engages both the external intercostal muscles (elevate the rib cage) and diaphragm (make the lungs bigger)

Exhalation:

• Internal intercostals (lower rib cage) and Abdominal muscles contract to reduce thoracic volume

Negative Pressure System (Interpleural Pressure)

Lungs want to recoil inward and the chest want to spring outward, creating a slight vacuum

• Always less than atmospheric pressure

Air moves into the lungs when intrapulmonary pressure falls below atmospheric pressure. Air moves out when intrapulmonary pressure rises above atmospheric pressure.

Volume and Pressure changes during inspiration and expiration?

Inspiration:

• Thoracic volume ↑

• Lung volume ↑

• Intrapulmonary pressure ↓

• Air flows in

Expiration:

• Thoracic volume ↓

• Lung volume ↓

• Intrapulmonary pressure ↑

• Air flows out

Note: Intrapleural pressure may drop further if the lungs are inflated even more, increasing more air intake.

What factors affect inspiration and expiration?

• Airway resistance

  • Increased by bronchoconstriction/dilation, mucus, or fluid

  • Makes breathing more difficult

• Alveolar surface tension

  • Tends to collapse alveoli as water pulls attracts it to one another

  • Surfactant reduces surface tension and makes inflation easier

• Lung compliance

  • How easy you can stretch the lungs

  • High compliance = easier breathing

  • Low compliance = harder breathing

• Elastic recoil

  • Natural tendency of lungs to recoil after inflation

  • Helps passive expiration

What is Partial Pressure

Mixture of gasses in the air, each gas creates its own share of pressure.

PO2 or PCO2

How does PO₂ change throughout the respiratory system and body?

160 → 104 (Air → Alveoli)

• The air is mixed with the residual air already in lungs as well as being diluted by water particles

104 → 100 (Alveoli → Blood)

• O₂ diffuses into blood

• Blood becomes oxygenated

100 → 40 (Blood → Tissues)

• Cells continuously use O₂ for respiration

• O₂ diffuses from blood into tissues (doesn’t completely empty out)

How does PCO₂ change throughout the respiratory system and body?

0.3 → 40 (Air → Alveoli)

• CO₂ from blood enters alveoli

40 → 40 (Alveoli → Blood )

• 40 is left in order to maintain this acid-base balance

40 → 45 (Blood → Tissues)

• Cells produce CO₂ during cellular respiration

45 → 40 (Blood → Alveoli)

• CO₂ diffuses into alveoli and is exhaled

How are oxygen and carbon dioxide carried in the blood?

Oxygen

• 98.5% bound to hemoglobin (Hb)

• 1.5% dissolved in plasma

Carbon Dioxide

• 70% as bicarbonate ions (HCO₃⁻)

• 23% bound to hemoglobin

• 7% dissolved in plasma

What are the plateau and steep regions of the oxyhemoglobin dissociation curve?

• Plateau region (lungs): Large changes in PO₂ cause small changes in Hb saturation (acts as a safety feature to ensure oxygen is received throughout the body) → Hb binds O₂ strongly and remains highly saturated.

• Steep region (tissues): Small decreases in PO₂ cause large decreases in Hb saturation → Hb releases O₂ easily.

Link to CO₂:
↑ CO₂ (and H⁺) in tissues reduces Hb's affinity for O₂, making O₂ unload even more easily where it is needed. This results in the CO₂ then being picked up by Hb, while the O₂ is unloaded

Ventilation

Movement of air in and out of the body

Arterial partial pressure of Oxygen

• Located in the carotid and aortic bodies.

• Detect ↓ PaO₂, ↑ PaCO₂, and ↓ pH.

• Important when blood O₂ levels become low.

  • Many neural tissue becomes less active except for this, peripheral chemoreceptors becomes more active with less oxygen

• Stimulates the medullar for increased ventilation.

A lifesaving mechanism

Arterial partial pressure of Carbon Dioxide

• Located in the medulla (brainstem).

• Detect ↑ PaCO₂ indirectly through ↑ H⁺ in the CSF.

• When CO₂ rises → ventilation increases through the central chemoreceptors (detected through the low pH).

Main regulator of normal breathing.

Changes in arterial pH

• Blood H⁺ increases

• Peripheral chemoreceptors detect the increased H⁺ (low pH) directly

• Ventilation increases, removing CO2

Caused by increase in CO2