The Respiratory system

• Pulmonary ventilation – Chp 16

• Respiration

Outline

• Overview of the respiratory system

• Anatomy

• Forces for pulmonary ventilation

• Factors affecting pulmonary ventilation

• Clinical significance of respiratory volumes and air flows

Outline

• Overview of the respiratory system

• Anatomy

• Forces for pulmonary ventilation

• Factors affecting pulmonary ventilation

• Clinical significance of respiratory volumes and air flows

Overview

• Respiration = gas exchange -- Occurs at the levels of the lungs and tissues (external respiration) and cell (internal or cellular respiration).

• External respiration: - Pulmonary ventilation:

movement of air in and out of the lungs

- Gas exchange in the alveoli- Gas transport in the blood- Gas exchanges between

blood and tissues

Outline

• Overview of the respiratory system

• Anatomy

• Forces for pulmonary ventilation

• Factors affecting pulmonary ventilation

• Clinical significance of respiratory volumes and air flows

Airways

Airways

• Upper airways: - nose to pharynx

• Lower airways:- Conducting airway:

larynx bronchioles

- Respiratory airway:alveoli

Due to the wall structure of the airway: one cell layer (SSE) allows for gas exchange

Conducting airways

• Presence of cartilage in the wall, from larynx to small bronchi prevents airway collapse.

• Goblet cells secreted mucus. Ciliated cells help move the mucus out of the airway.

• Presence of smooth muscle fibers in the bronchioles (but no cartilage)

• Volume of the conducting airway: 150 ml

Respiratory airway: Alveoli

• Alveolar wall is formed by simple squamous epithelium = type I cells (SSE) gas exchange

• Respiratory membrane: membrane separating alveolus from blood capillary.

• Large surface area from the numerous alveoli better gas exchange

• Presence of elastic fibers between alveoli

Blood supply to the lungs

Alveolar structure

• Type I cells gas exchange

• Type II cells secrete surfactant (lipoproteins) decrease surface tension allowing for easier alveoli inflation

• Surfactants start to be secreted by the 7th month of pregnancy risk of lung disease in premature babies

• Presence of macrophages in alveoli

Structure of the thoracic cavity

The pleura

• Formed by 2 layers: the parietal and visceral pleura

• Roles: - prevents friction of the lungs against the rib cage (due to the thin layer of liquid present in the pleural space)- maintains lung expansion: due to the negative pressure within the pleural space

What is negative pressure? What is its importance?

Pleura and negative pressure

• Pneumothorax: lung collapse due to air entering in the pleural cavity

• (not to be confused with atelectasy alveoli collapse)

Outline

• Overview of the respiratory system

• Anatomy

• Forces for pulmonary ventilation

• Factors affecting pulmonary ventilation

• Clinical significance of respiratory volumes and air flows

Mechanics of breathing

• Boyle’s law: The pressure of a gas in a closed container is inversely proportional to the volume of the container.

• Air flow in the lungs is driven by the differences in pressure between the atmosphere and the alveoli

• P.atm is constant changes in P.alv drive ventilation

Inspiration and expiration

• Inspiration: chest wall expands due to muscle contraction (diaphragm and/or other muscles)

Pressure in alveoli ↓ air moves toward alveoli

• Expiration: passive process muscle relax chest wall return to resting state alveoli become compressed ↑ alveolar pressure move moves out

Ventilation

Outline

• Overview of the respiratory system

• Anatomy

• Forces for pulmonary ventilation

• Factors affecting pulmonary ventilation

• Clinical significance of respiratory volumes and air flows

Factors affecting pulmonary ventilation

• 1- Lung compliance: ease with which lungs can be stretched- Compliance is a measure of the elasticity of lung tissue and the alveolar surface tension

• 2- Airway resistance: to changes in airway radius (↓radius ↑resistance)

Pathology

• lung disease resulting in stiffness of tissue

• no or ↓ surfactant

• Asthma• Airway obstruction• COPD

Outline

• Overview of the respiratory system

• Anatomy

• Forces for pulmonary ventilation

• Forces affecting pulmonary ventilation

• Clinical significance of respiratory volumes and air flows

Lung volumes

Pulmonary function tests

• Can help distinguish between obstructive pulmonary disease and restrictive pulmonary disease

- Obstructive disease: obstruction in bronchi-bronchioles severely restricts the speed and amount of air movement

- Damage to lung tissue prevents full lung expansion and recoil

Anatomical dead space

• Anatomical dead space: space within the conductive airway, about 150 ml.

• What will happen to a person who has a tidal volume of 150 ml due to lung disease?

• What can be done to help the person?