A Level Life and Health Sciences CCEA

Respiratory System

Structure and Components of the Respiratory System

• The respiratory system consists primarily of the lungs, the trachea, bronchi, bronchioles, and alveoli.
• The primary function of this system is to facilitate the exchange of oxygen and carbon dioxide between the blood and the atmospheric air.
• The respiratory system can be divided into the upper and lower respiratory tracts. The upper tract includes the nose, nasal cavity, mouth, throat (pharynx), and voice box (larynx). The lower tract comprises of the trachea, bronchi, bronchioles, and lungs.
• The diaphragm, a large dome-shaped muscle located at the base of the lungs, plays a crucial role in breathing.

Gas Exchange in the Alveoli

• Alveoli, the small sac-like structures at the end of the bronchioles, are where the exchange of gases occurs.
• The alveoli walls are made up of a single layer of flattened epithelial cells, allowing for a very thin barrier (respiratory membrane) for gas exchange.
• Oxygen diffuses across the alveolar and capillary walls, binding to haemoglobin in red blood cells, to be transported around the body. Carbon dioxide, a waste product, diffuses from the blood and into the alveoli, to be expelled from the body.

Breathing Mechanism

• During inspiration (inhaling), the diaphragm contracts and flattens, causing a decrease in pressure within the thoracic cavity and forcing air into the lungs.
• During expiration (exhaling), the diaphragm relaxes and resumes its dome-like shape. This increases the pressure in the chest cavity, forcing air out of the lungs.
• The rib muscles (intercostal muscles) assist in increasing or decreasing chest cavity volume.

Regulation of Breathing

• Breathing is primarily regulated by the nervous system via the respiratory centers in the medulla oblongata and pons in the brain stem.
• Elevated levels of carbon dioxide in the blood (hypercapnia) is the main trigger for increased breathing rate, but low levels of oxygen (hypoxia) can also stimulate breathing, albeit to a lesser extent.
• The chemoreceptor cells in the aortic and carotid bodies are responsible for detecting changes in the levels of these gases.

Diseases and Disorders of the Respiratory System

• Asthma is a chronic inflammatory condition that narrows airways causing shortness of breath, wheezing, and coughing.
• Chronic obstructive pulmonary disease (COPD) is a group of diseases, including chronic bronchitis and emphysema, that block air flow and cause breathing problems.
• Pneumonia is an infection that inflames the air sacs in one or both lungs, which may fill with fluid or pus.
• Exposure to harmful substances such as cigarette smoke and air pollutants can damage the respiratory system and contribute to respiratory diseases.