Study "Cell Biology", a flashcard deck on FORKSAI.
Define pathogenicity and virulence, and explain how they relate to a microbe's ability to cause disease.
Pathogenicity is the ability of a microbe to cause disease by overcoming the host's defenses. Virulence, on the other hand, is the degree of pathogenicity. A microbe must first be pathogenic to cause disease, and its virulence determines how severe or likely that disease will be.
What are the primary portals of entry for pathogens into the human body?
The primary portals of entry for pathogens are mucous membranes, the skin, and the parenteral route. Mucous membranes include the respiratory, gastrointestinal, and genitourinary tracts, as well as the conjunctiva. The skin acts as a barrier, but some microbes can enter through openings or even bore through intact skin. The parenteral route involves direct deposition into tissues when barriers are penetrated.
How does the gastrointestinal tract serve as a portal of entry for pathogens, and what challenges do these microbes face?
The gastrointestinal tract serves as a portal of entry through contaminated food, water, or fingers. Most microbes entering this route are destroyed by stomach acid and digestive enzymes. However, those that survive can cause diseases like polio, hepatitis A, and typhoid fever, and can be eliminated via feces, leading to further transmission.
Explain the concept of a 'preferred portal of entry' for pathogens.
A preferred portal of entry refers to the specific avenue through which a pathogen must gain access to the host to cause disease. If a pathogen enters the body through a different portal than its preferred one, it might not be able to establish an infection or cause illness. This specificity is crucial for the pathogen's ability to overcome host defenses and initiate disease.
In what situations would the parenteral route be the primary portal of entry for a pathogen?
The parenteral route becomes the primary portal of entry when microorganisms are deposited directly into tissues, bypassing natural barriers like skin or mucous membranes. This can occur through punctures, injections, bites, cuts, wounds, surgical procedures, or even the splitting of skin or mucous membranes due to swelling or drying. Examples include HIV, hepatitis viruses, and bacteria causing tetanus or gangrene.
Why is the respiratory tract considered the easiest portal of entry for many microbes?
The respiratory tract is considered the easiest portal of entry because microbes can be readily inhaled into the nose or mouth within drops of moisture. This direct access to a large surface area of mucous membranes makes it a common entry point for a wide range of diseases, including the common cold, pneumonia, tuberculosis, influenza, and measles.
Distinguish between ID50 and LD50, and explain what each measures.
ID50 stands for the infectious dose for 50% of a sample population, and it measures the virulence of a microbe by indicating how many organisms are needed to cause infection in half of the exposed individuals. LD50, or lethal dose for 50% of a sample population, measures the potency of a toxin or pathogen by indicating the amount required to kill half of the exposed individuals. Both are indicators of pathogenicity, but ID50 focuses on infection while LD50 focuses on mortality.
How does the number of invading microbes influence the likelihood of disease?
The number of invading microbes significantly influences the likelihood of disease. If only a few microbes enter the body, the host's defenses are likely to overcome them. However, if a large number of microbes gain entry, the chances of disease increase dramatically because the host's immune system can become overwhelmed, allowing the pathogens to establish an infection.
Describe how the genitourinary tract serves as a portal of entry for pathogens.
The genitourinary tract serves as a portal of entry primarily for diseases contracted sexually. Some microbes causing sexually transmitted infections (STIs) can penetrate an unbroken mucous membrane in this tract. Other pathogens, however, require a pre-existing cut or abrasion to gain entry. Examples of diseases transmitted this way include HIV infection, genital warts, chlamydia, human herpesvirus-2, syphilis, and gonorrhea.
Explain how some microbes can cause disease without directly damaging host tissue.
Some microbes do not cause disease by directly damaging host tissue. Instead, the disease is a result of the accumulation of microbial waste products within the host. These waste products can be toxic or disrupt normal physiological processes, leading to the symptoms and pathology associated with the infection, even if the microbes themselves aren't directly destroying cells.