12BIC - Unit 6: Gas Exchange

Primary gas exchange organs

Lungs, which are closely connected to the circulatory system.

Pulmonary ventilation warming

The process where air is warmed to body temperature as it passes through the cavity during inhalation.

Thoracic cavity location

The area inside the chest, surrounded by the rib-cage and diaphragm, where the lungs are located.

Pleural membranes

Two layers lining the thoracic cavity that secrete pleural fluid to reduce friction during breathing.

Pleural fluid surface tension

Attaches the lungs to the ribs, allowing the lungs to move sequentially with the movement of the ribs.

Trachea function

Funnels air into and out of the lungs.

Trachea cartilage

C-shaped, flexible rings that keep the airway open, prevent collapse when air pressure drops, and allow compression when food is swallowed.

Trachea dimensions

Boasts a diameter of approximately 1.8cm.

Trachea lining tissues

Made of muscle and lined with ciliated epithelium and goblet cells to prevent bacteria and dirt from entering the lungs.

Bronchi

The divisions of the trachea; larger bronchi start with cartilage rings which later become cartilage blocks.

Bronchioles

Branching divisions of the bronchi which, for exam purposes, have no cartilage.

Terminal bronchioles

Airways with a 1mm diameter (~48,000 present) containing no cartilage or goblet cells, but possessing smooth muscles and cilia.

Respiratory bronchioles

Airways with a 0.5mm diameter (~300,000 present) containing no cartilage, goblet cells, or smooth muscles, and only a few cilia.

Alveolar ducts and sacs

Structures found at the ends of bronchioles; each duct contains about 100 alveolar sacs, and each sac contains about 30 alveoli.

Alveoli wall structure

Folded and extremely thin (one flat squamous cell thick) to increase surface area and reduce diffusion distance.

Alveoli composition

Contains elastic fibres and collagen which allow them to stretch and recoil to expel air.

Alveolar elasticity function

Helps to maintain a steep concentration gradient during the ventilation cycle.

Ventilation cause

Breathing movements that occur due to pressure changes within the thorax.

Inspiration energy requirement

An active process requiring energy, whereas expiration is mostly passive.

Inspiration mechanism

The diaphragm and external intercostal muscles contract, increasing thoracic cavity volume, dropping pressure, and drawing air in.

Antagonistic muscle pairs in breathing

The internal intercostal muscles act antagonistically to the external intercostal muscles.

Diffusion

The net movement of particles down a concentration gradient.

Rapid gas exchange requirement

Requires a steep concentration gradient, which is actively maintained by continuous breathing and constant blood flow.

Direction of lung gas exchange

Oxygen diffuses from the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli.

Cartilage function

Provides structural support to the trachea and bronchi, keeping the airways open (patent) and preventing them from collapsing when air pressure drops during inhalation.

Cilia function

Hair-like projections on epithelial cells that beat synchronized in a wave-like motion to move trapped mucus, dirt, and pathogens upward and outward away from the lungs toward the throat.

Goblet cells function

Synthesize and secrete mucus onto the airway surface to trap inhaled dust, pollen, bacteria, and other foreign pathogens.

Mucous glands function

Found deeper in the tissue wall of larger airways, they work alongside goblet cells to produce additional mucus to keep the lining moist and trap inhaled particles.

Smooth muscle function

Regulates the diameter of the airways (especially bronchioles) by contracting or relaxing, which controls the volume and rate of airflow into the alveoli.

Elastic fibres function

Found in the walls of the alveoli and airways; they stretch to accommodate air during inhalation and recoil passively during exhalation to help force air out of the lungs.