Infections of the respiratory tract

Question 1

Upper Respiratory System

Answer 1

With every breath we inhale several microorganisms; therefore, the upper respiratory system is a major portal of entry for pathogens. In fact, respiratory system infections are the most common type of infection and among the most damaging. Some pathogens that enter via the respiratory route can infect other parts of the body, causing such diseases as measles, mumps and rubella.

Defenses include coarse hairs in the nose that filter large dust particles and the lining mucous membrane that secretes mucus and contains cilia. At the junction of the nose and throat lie masses of lymphoid tissue, the tonsils, which contribute immunity to certain infections. Because of the close connections between the ear, nose and throat, infections often spread from one region to another.

Ears, nose and throat = disgusting buggy mess!!

A number of potentially pathogenic microorganisms are part of the normal microbiota in the upper respiratory system. However, they usually do not cause illness because the predominant microorganisms of the normal microbiota suppress their growth by competing with them for nutrients and producing inhibitory substances.

Infections include:

Strep throat
Diptheria
Otitis media
Common cold

Question 2

Lower Respiratory System

Answer 2

By contrast the lower respiratory tract is nearly sterile – although the trachea may contain a few bacteria, because of the normally efficient functioning of the ciliary escalator in the bronchial tubes.
A ciliated mucous membrane lines the lower respiratory tract down to the smaller bronchial tubes and helps prevent microorganisms from reaching the lungs. Particles trapped in the larynx, trachea, and larger bronchial tubes are moved up toward the throat by a ciliary action called the ciliary escalator. If microorganisms actually reach the lungs, phagocytic cells called alveolar macrophages usually locate, infest, and destroy most of them. IgA antibodies in such secretions as respiratory mucus, saliva, and tears also help protect mucosal surfaces from pathogens.

Many of the same bacteria and viruses that infect the upper respiratory system can also affect the lower respiratory system. As the bronchi become involved, bronchitis or bronchiolitis develops. A sever complication of bronchitis is pneumonia, in which the pulmonary alveoli become involved.

Question 3

Whooping Cough

Answer 3

B. pertussis is a severe disease!
The bacteria have specific adhesins that allow it to attach to the ciliated respiratory mucosa
It multiplies in epithelial cells
The organism produces several toxins which increase respiratory secretions and mucus production and induce an inflammatory response
“Tracheal cytotoxin” is a cell wall component that appears to kill tracheal epitheial cells, thereby partially immobilising the muciliary escalator and causing an accumulation of mucus in the airway

Question 4

GAS and Rheumatic Fever

Answer 4

Acute Rheumatic Fever may follow a Group A Streptococcus (GAS) pharyngeal infection leading to autoimmune inflammatory lesions of the heart (carditis), joints (arthritis), subcutaneous tissues (nodules), and CNS (chorea, tics). Although acute in nature, GAS reinfections can trigger recurrent ARF and lead to chronic rheumatic heart disease (RHD) evidenced by mitral or aortic valve damage, cardiac enlargement, and heart failure. The image shows an example of aortic stenosis representative of RHD where the normally three distinct leaflets of the aortic valve (center) have thickened and fused into two. The result is a defective, leaky valve that, if not replaced, can lead to heart failure.