Defence Mechanisms

• Nasal secretion has bactericidal and viricidal properties.
• Micro-organisms can cause disease by accessing the tissues of the host and multiplying, or by multiplying in food and producing toxins.
• Mucus flows backwards to the nasopharynx and may be swallowed.
• Modes of transmission of infection include transplacental, ingestion of contaminated food/water, inoculation, direct skin contact, and spread by droplets and dust.
• The skin has mechanical strength due to layers of epithelial cells, a tough outer layer of keratin, and a distinct basement membrane.
• The skin can decontaminate itself by desquamation of surface squames and the presence of resident flora that produce antibiotic substances and compete with other organisms for essential foodstuffs.
• The mechanical barrier is weakest at the Gingival Margin, which has a thin epithelium and is easily traumatised.
• The Tonsillar Crypts have a very thin epithelium and are prone to infection, especially when the general body defences are impaired.
• Saliva plays a crucial role in keeping the mouth clean by trapping organisms and removing particles from the mucosa.
• The resident flora in the body includes alpha haemolytic streptococci, Borrelia Vincenti, Actinomyces organisms, yeast, and various Bacteroidaceae.
• Many strains of alpha haemolytic streptococci produce hydrogen peroxide, which plays a role in the decontaminating mechanism.
• Saliva inhibits pathogens, possibly due to its lysozymes or mucus content.
• IgA produced by the salivary glands is important for defense.
• The stomach guards the intestines and vomiting removes chemicals and bacterial irritants.
• Irritation of the intestine usually causes diarrhea, which helps expel organisms during an established infection.
• Blinking prevents large particles from contaminating the eye and ensures that the conjunctiva and cornea are always covered by a thin layer of lacrimal secretion.
• Tears wash away irritants and contain lysozyme, which kills some organisms and inhibits the growth of others.
• The nose and nasopharynx play a role in defense mechanisms, but specific information is not provided in the text.
• The epithelium of the respiratory tract does not provide an adequate barrier against local infection.
• Sneezing helps to expel irritants from the respiratory tract.
• Below the larynx, the respiratory tract should normally be sterile.
• The mucosa of the respiratory tract is frequently infected by the influenza virus.
• The cough reflex expels irritants but may also disseminate organisms within the lung.
• Mucous secretion protects epithelial cells and allows cilia to move it as a continuous sheet.
• Obstruction to the mucous sheet impairs respiratory tract defenses and can lead to infection.
• Macrophages in bronchioles and alveoli phagocytose and kill bacteria.
• Organism fate depends on the immunity of the host and the virulence of the organism.
• Possible outcomes include rapid destruction, temporary growth followed by destruction, or symbiotic state within the host.
• The severity of infection depends on the intrinsic nature of the organism and its virulence.
• Virulence can manifest in two ways: the ability of the organism to spread throughout the tissues and the ability to cause tissue damage.
• Exotoxins are potent chemical substances produced by bacteria that cause tissue damage and are circulated to distant tissues.
• Endotoxins are derived from the cells of the organisms and are usually of low potency, causing non-specific actions on the tissues.
• Inflammation is the body's response to tissue damage.
• Inflammation can be caused by various factors, including physical trauma, pathogens, toxins, and immune responses.
• Most pathogenic organisms cause tissue damage, leading to inflammation.
• Immune responses often result in tissue damage and are commonly associated with inflammation.