recap vemt

Recap of the Respiratory System

Presentation by: Leanne Adair

Overview of the Respiratory System

The respiratory system is essential for gas exchange.
Functions of the respiratory system:
- Allows oxygen to enter the body.
- Facilitates the expulsion of carbon dioxide.

Anatomy of the Respiratory System

The respiratory system is divided into two main parts:
1. Upper Respiratory System:
- Composed of:
  - Nose
  - Nasal cavities
  - Sinuses
  - Pharynx
  - Part of the larynx
- Functions:
  - Air Filtration: Filters out particles and pathogens.
  - Humidification: Adds moisture to inhaled air.
  - Warming: Heats air to body temperature before reaching the lungs.
  - Conducting Air: Provides a clear airway for air to enter and exit the lungs.
- Clinical Relevance:
  - Common infections here include:
    - Colds
    - Sinusitis
    - Laryngitis
  - Symptoms are typically milder.
1. Lower Respiratory System:
- Composed of:
  - Lower larynx
  - Trachea
  - Bronchi
  - Bronchioles
  - Alveoli
  - Lungs
- Tracheobronchial Tree:
  - Branches approximately 23 times, leading to the alveoli where gas exchange occurs.
  - Gas exchange begins after branch 17-19; the first 16 branches are for air conduction only.
- Main Function:
  - Gas Exchange: Responsible for exchanging oxygen and carbon dioxide between air and blood in alveoli.
  - Conducting Air: Conducts air to and from the lungs.
- Clinical Relevance:
  - Infections here tend to be more severe, including conditions such as:
    - Pneumonia
    - Bronchitis
    - Bronchiolitis
  - Common symptoms include:
    - Coughing
    - Shortness of breath
    - Chest pain
- The Conducting Zone includes nose to terminal bronchioles where anatomical dead space exists.

Key Structures

Trachea:
- The windpipe conducting air into the lungs.
Bronchi:
- Two main bronchi branch from the trachea into each lung.
Bronchioles:
- Smaller airways leading to alveolar ducts and alveoli.
Alveoli:
- Tiny air sacs where gas exchange occurs; large surface area for efficient diffusion.

Physiology of Gaseous Exchange

Gas exchange in the lungs is critical for allowing oxygen to enter the bloodstream while removing carbon dioxide.
Primary Locations for Gas Exchange:
1. External Respiration:
- Involves exchange of gases between alveoli and blood in pulmonary capillaries.
- Mechanism:
  - Oxygen diffuses into blood; carbon dioxide diffuses out to be exhaled.
1. Internal Respiration:
- Occurs at the tissue level where oxygen is delivered to cells, and carbon dioxide is collected from them.

Mechanisms Driving Gaseous Exchange

Diffusion:
- Involves concentration gradients.
- Oxygen in alveoli diffuses into blood in pulmonary capillaries while carbon dioxide moves from blood to alveoli.
- This process is passive.
Surface Area:
- Alveolar Structure and thin membranes enhance gas exchange efficiency.
Ventilation and Perfusion Matching:
- Ventilation: Movement of air into and out of the lungs.
  - Adequate ventilation ensures fresh oxygen reaches alveoli and carbon dioxide is expelled.
- Perfusion: The flow of blood through pulmonary capillaries.
  - Proper matching of ventilation and perfusion is essential for optimal gas exchange.
  - Inadequate matching can lead to reduced oxygenation or inefficient carbon dioxide removal.
Partial Pressure Gradients:
- Determines diffusion direction and rate based on partial pressures of oxygen and carbon dioxide in alveoli and blood.
- Higher partial pressure of oxygen in alveoli than in deoxygenated blood drives oxygen into the blood.
- Higher carbon dioxide levels in blood promote diffusion into alveoli.

Mechanics of Respiration

Breathing involves two phases: inhalation and exhalation.
Inhalation:
- Diaphragm contracts and moves downward, increasing thoracic volume.
- Intercostal muscles lift the ribs upward and outward.
- This creates negative pressure in the thoracic cavity, drawing air into the lungs.
Exhalation:
- Diaphragm relaxes and moves upward; intercostal muscles relax.
- Elastic recoil of lung tissues decreases thoracic volume, pushing air out.
- This process is passive at rest but can become active during forceful exhalation with abdominal muscle contraction.

Haemoglobin and Gas Transport

Haemoglobin is crucial for gas transport in blood, mainly for oxygen, but also for carbon dioxide and nitric oxide.
Oxygen Transport:
- Oxygen Binding:
- Haemoglobin binds to oxygen and transports it from lungs to tissues.
- Each haemoglobin molecule has four subunits; each binds one oxygen molecule.
- A single haemoglobin protein can carry up to four oxygen molecules.
- Cooperative Binding:
- Exhibits cooperative binding, ensuring efficient oxygen loading in lungs where oxygen concentration is high.
- In the lungs, oxygen binds to haemoglobin (loading), then haemoglobin delivers oxygen to metabolizing tissues for ATP production.
- Factors affecting Loading/Unloading:
- Binding and release of oxygen depend on pH, carbon dioxide levels, and the presence of 2,3-bisphosphoglyceric acid (2,3-BPG).
- In tissues with low pH, high carbon dioxide and BPG, oxygen is released from haemoglobin.

Carbon Dioxide Transport

Binding and Transport:
- Haemoglobin transports carbon dioxide from body tissues back to lungs.
- About 10% of carbon dioxide is transported via binding to haemoglobin, forming carbaminohaemoglobin.
- Reversible Binding:
- The binding of carbon dioxide to haemoglobin is reversible.
- In lungs, low partial pressure of carbon dioxide allows it to dissociate from haemoglobin and be expelled.

Nitric Oxide Transport

Nitric Oxide Binding:
- Haemoglobin also transports nitric oxide, which binds to thiol groups in globin chains.
- Nitric oxide helps expand blood vessels and increase blood flow.

Factors Influencing Haemoglobin Affinity for Oxygen

Partial Pressure of Carbon Dioxide (PCO2):
- Higher PCO2 decreases haemoglobin's affinity for oxygen, shifting the oxygen dissociation curve to the right.
- Conversely, lower PCO2 increases affinity, shifting the curve to the left.
pH:
- Lower pH (acidity) decreases haemoglobin's affinity for oxygen, shifting curve to the right.
- Higher pH (alkalinity) increases affinity, shifting curve to the left.
Temperature:
- Increased temperature decreases affinity, shifting curve to the right.
- Decreased temperature increases affinity, shifting curve to the left.
2,3-Diphosphoglycerate (2,3-DPG):
- Higher concentrations decrease affinity, shifting the curve to the right.
- Increased 2,3-DPG occurs in response to hypoxia or erythropoietin.
- Lower concentrations increase affinity and shift the curve to the left.

The Oxyhaemoglobin Dissociation Curve (ODC)

The ODC depicts how haemoglobin in blood picks up oxygen in lungs and releases it into tissues.
Shape of the Curve:
- The curve is sigmoidal due to positive cooperativity.
- Each haemoglobin molecule has four subunits; first oxygen binding changes Hb shape, facilitating subsequent bindings.
Plateau of the Curve:
- At high partial pressure of oxygen (PO₂ > 80 mmHg), the curve plateaus, ensuring near-100% saturation despite slight PO₂ drops.
Steep Part of the Curve:
- In metabolizing tissues, lower PO₂ (around 40 mmHg) means small drops lead to large releases of oxygen from Hb.
Shifting the Curve:
- The Bohr Effect indicates Hb affinity for oxygen changes based on the local environment.
Right Shift (Decreased Affinity):
- Causes include lower pH, higher PCO₂, increased temperature, and higher 2,3-DPG.
- Hb releases oxygen more readily to tissues under distress.
Left Shift (Increased Affinity):
- Causes include higher pH, lower PCO₂, and decreased temperature.
- Hb binds oxygen more tightly, occurring in cooler, less acidic lung environments.

Pulmonary Circulation

Pulmonary circulation absorbs blood between the heart and lungs.
Pulmonary Artery: Carries deoxygenated blood from the right ventricle to the lungs.
Capillary Network: Surrounds alveoli for gas exchange; oxygen enters, carbon dioxide exits into alveolar spaces.
Pulmonary Veins: Return oxygenated blood to the left atrium of the heart for distribution throughout the body.