Respiratory patients are some of our most challenging cases to care for as nurses. There are a huge variety of different respiratory diseases, affecting different areas in the respiratory tract. Many cases present as acute emergencies and require rapid assessment and emergency nursing care.

These cases provide us with a fantastic opportunity to use our skills - but in order to effectively nurse these patients, we need to understand the common respiratory conditions seen and the structure and function of each area of the respiratory tract.

In the first post in our respiratory series, we’re going to be chatting all about the different areas within the respiratory system, and what they do.

The respiratory system starts at the nose and ends in the alveoli. It is a large system spanning the upper and lower airways, and also includes the mediastinum and pleural space. Its primary function is the delivery of oxygen to the lungs, where it is exchanged with carbon dioxide.

The upper airways

The upper airway includes all the structures cranial to the trachea – including the nose, sinus, pharynx and larynx. 

The nose permits olfaction, provides thermoregulation in hyperthermic patients, and filters particulate matter during inhalation. In the nasal cavities, the air is warmed and humidified as it passes over the turbinate bones (thin, delicate folds of bone covered in mucous membranes). The larynx protects the lower airway from aspiration of food/water and produces the voice.

The pharynx is part of both the respiratory and digestive systems and is located between the base of the skull and the second cervical vertebra. It connects the oral cavity to the nose, airway and oesophagus, and is separated into the nasopharynx, oropharynx and laryngeal pharynx.

The larynx is a cartilaginous structure that sits on the floor of the pharynx where it divides into the trachea and oesophagus. The larynx contains the epiglottis, a fold of cartilage that functions to protect the lower airway from aspiration of food/water. The vocal and vestibular folds also sit within the larynx, and as such, it is responsible for producing the voice.

The lower airways

The lower airways include the trachea, carina, bronchi and bronchioles. The trachea bifurcates at the carina into the left and right principal bronchi (or mainstem bronchi); these then divide into lobar bronchi, which each supply a lung lobe. Lobar bronchi branch into smaller and smaller segmental and subsegmental bronchi, before ending in a terminal bronchus which has an attached alveolar sac. 

Each alveolar sac is lined with a membrane that is one cell thick and surrounded by capillaries. This allows gaseous exchange to take place. Here, oxygen (and inhalant anaesthesia where applicable) diffuses across the alveolar membrane and is taken up into the bloodstream in the alveolar capillaries. Carbon dioxide (and other waste gases) are also released from the alveolar capillaries into the lungs for exhalation.

The trachea and bronchi are formed of rings of cartilage and smooth muscle. These serve to keep the trachea/bronchi open, allowing the passage of air through them. The lower airways are lined with ciliated epithelial cells and Goblet cells; Goblet cells produce mucous to moisten inhaled air and trap inhaled particles, and ciliated epithelial cells move the mucous layer towards the pharynx where it is coughed out or swallowed.

The mediastinum

The mediastinum is the central compartment of the thoracic cavity - essentially the bit between the lungs! It is made up of a number of structures and is surrounded by connective tissue. These structures include the heart, oesophagus, trachea, thymus, thoracic duct, phrenic and cardiac nerves, and central thoracic lymph nodes. 

The pleural space

The pleura are serous membranes that coat the lungs and line the thoracic cavity. They allow the lungs to move during respiration without friction against the heart or the thoracic wall. 

The pleural space is a potential space between the thoracic wall and the lungs. Within this space a very small amount of pleural fluid is normally present; this lubricates the pleural surface this normally contains a very small amount of pleural fluid which lubricates the pleural surface.

What does the respiratory system do?

As we know, the major function of the respiratory system is just that - respiration. The delivery of air (and therefore oxygen) to the alveoli, where it diffuses into the bloodstream. But, did you know the respiratory system is responsible for a ton of other functions, including:

• Regulating acid/base balance

• Metabolism of certain substances

• Filtering of emboli

So now you’ve had a refresher on the different structures within the respiratory system, and their functions. Next time you have a respiratory patient come in, take a second and think about the area of the respiratory tract affected and its function, and how that relates to the signs you’re seeing!

What respiratory diseases do you see commonly in practice? Let me know below!

References

1. Merrill, L. 2012. Small Animal Internal Medicine for Veterinary Technicians and Nurses. Iowa: Wiley-Blackwell.

2. Tonozzi, C. 2021. The Respiratory System in Animals. MSD Veterinary Manual. Available from: https://www.msdvetmanual.com/respiratory-system/respiratory-system-introduction/the-respiratory-system-in-animals

3. WikiVet, 2017. Pharynx - Anatomy & Physiology. WikiVet. Available from: https://en.wikivet.net/Pharynx_-_Anatomy_%26_Physiology