Monday, June 11, 2012

Physiology of the nose, nasal fossae

  • A. Physiology of the nose
The nasal fossae perform a series of functions associated with each other, which include:
  • Respiratory function: This transports air to the tracheobronchial tree. This is its function par excellence.
  • Sensory function:  This conveys the odorous particles towards the olfactory mucosa.
  • Defensive function:  This protects against agents from the environment, which stimulate the nasal mucosa leading to reflex responses, the most important one being the sneeze reflex.
  • Phonatory function.

Physiology of the nasal mucosa: glandular secretion function

The nasal mucosa is coated by a layer of mucus, a permeable barrier between the mucosa and inspired air and the centre of all its metabolic exchanges.

The mucous lining is comprised fundamentally of water and mucus.
The mucus is secreted by the goblet cells and the mucosal glands. 
The water comes from the serous glands through secretion and the epithelial cells through transudation, but is also accumulated through the condensation of water vapour from the inspired air.

Nasal secretion is called rhinorrhea and is a common symptom in all nasal conditions. Rhinorrhea comes from the glands of the nasal mucosa and the transudate of blood serum.
Physiological function of nasal secretion:
Humidification of inspired air as it passes through the fossae and maintenance of the moisture needed for the cilia to work properly.
Heating of inspired air on evaporating. Effect of heat regulation: the evaporation process, which heats inspired air, in turn cools the blood of the nasal mucosa.
Filtering of inspired air
Bacteriostatic or bactericidal action of nasal secretion.

Composition of the mucus:
Composition: 95% water, 3% organic elements and 2% minerals.Amount secreted: 0.1 to 0.3 ml/kg/day. A normal individual secretes 1.0 l/day.
Mucus is hypertonic with regard to plasma and presents an osmotic pressure of about 0.314 osmoles. Its ion composition does not change with time. It is comprised mainly of:
Proteins: Mucin, a glycoproteinthatrepresents 60% of the total amount of the mucus proteins and whose amount depends on the viscosity of the nasal mucus, and of albumin, which comes in its entirety from plasma serum through transudation. The nasal mucus proteins have a marked circadian variation, which is four times higher at night than during the day.
Water and mineral salts: The moisturizing of the mucus is indispensable for ciliary functioning. A large part of the water contained in the mucus evaporates with inspiration and is only recovered partially through condensation during expiration. To compensate for this liquid loss, the mucosa exchanges liquids with mucus, generally through the basal membrane.

Mucus properties:
Physical properties  The nasal mucus has a viscosity that changes with the degree of moisturisation and mucin content.  Its pH has night-day time variations.  It has buffer power: This is its most characteristic physical property. Acid or alkaline solutions are normalised at a pH of 7 in a few minutes.

Biological properties
It is an important water reservoir.
It participates in the defence against infectious agents through its antimicrobial action. 
The proteolytic enzymes such as lysozyme and other enzymatic action proteins (lactoferrin, LDH and certain proteases) may support this specific defence system.

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