We all know the nose is an important organ, particularly for the sense of smell. Within the nose of mammals is a labyrinth of bones called the turbinate bones. These are covered in a thin layer of tissue in which there are areas with sensory centres and these communicate with sensory nerves (the olfactory nerves). But this is not all the nose is capable of; Here we discuss how pathology affects the biomechanics, and vice versa, within the nose…
The extra layers of tissue supported by the turbinates increases the surface area within the nose massively. As air is breathed in, it is warmed, humidified and filtered over the surface of these scrolls of tissue. Breathing through the nose can be altered to change the pathway the air takes – either to increase the amount going to the lungs, or to the sensory areas of the nose for smelling (olfaction), by sniffing.
Temperature control (thermoregulation) is important when it comes to the replication of some viruses. The cooler environment of the nose is favoured by the rhinoviruses that cause the common cold, for example. When body temperature decreases, the immune system is less able to get rid of virus infected cells . Some viruses prefer to replicate in cooler temperatures. ‘Cat flu’ (feline viral rhinotracheitis, caused by feline herpesvirus-1) infected cats can pass these viruses on to kittens, or to ill animals who are less able to control their body temperature. In fact, a fever might actually be the way the body has evolved to reduce the rate of replication of some of these viruses. Severe inflammation can destroy the turbinates, but even very mild swelling can cause the turbinate bones to breakdown and remodel.
As the air makes its journey through the nose, wind pipe, and airways of the lungs, the path splits into smaller and smaller channels. There is mucus within the nose, windpipe and larger airways within the lungs, which act to trap particles, which are sent back up to the mouth to be swallowed, sneezed or coughed out of the respiratory system. Toxic substances, which could potentially severely damage the little air sacs (alveoli) of the lungs, are diluted by repeatedly coming into contact with the mucus over the surface of all of the divisions.
The scrolled nature of the bones causes inhaled air to create a vortex, similar to the wing-tip vortex seen at the ends of wings in flight. This causes any particles to be thrown to the outside of the vortex (centrifugal). This is particularly fascinating; In order for the immune system to actually recognise foreign material or infectious agents, they have to come into contact with the immune cells. The vortex brings the particles within the inspired air into contact with the cells lining the nasal cavity.
Tumours of the nose can destroy the turbinates as they invade and grow through the nasal cavity. This gives bacteria and viruses ample opportunity to infect the damaged nose. Some tumours are particularly nasty and may even grow from the nose, through the skull and into the brain.