Lung Diseases | TB - Tuberculosis | A Level Biology Revision Notes скачать в хорошем качестве

Lung Diseases | TB - Tuberculosis | A Level Biology Revision Notes

Lung Diseases | TB - Tuberculosis | A Level Biology Revision Notes 1. Know that pulmonary TB is a communicable, infectious disease, caused by the bacterium mycobacterium tuberculosis. 2. Describe how TB is transmitted. 3. Explain how the immune system responds to TB infection. 4. Understand how TB affects ventilation rate. 5. Understand that Secondary TB infections are major contributor to mortality rates in immune supressed patients (e.g. AIDS patients). Tuberculosis (TB) is an infectious disease caused by the pathogenic (disease causing) bacterium mycobacterium tuberculosis. Typically, infection arises as a result of droplet transmission – whereby an infected individual expels the bacteria whilst coughing, hence, TB is a communicable disease. Remember communicable disease are those that are transmitted from person to person, as opposed to a non-communicable disease such as, Asthma or Cancer for example). Upon inhalation a healthy individual normally fights off infection, as their macrophages (phagocytes) are activated – If bacterial numbers are low, macrophages deal with the bacterium with relative ease… However, if the bacteria are not destroyed by the immune system (and the microbial load (number of bacteria) is quite high), it is, in fact the Phagocytes that offer a refuge for the infectious agent! Here’s what happens... 1. The TB bacteria are inhaled (droplet transmission). 2. The bacteria reach the Alveoli in the lungs. 3. Cell mediated immune response enlists the Phagocytes which engulf the infectious bacterium – but often, the bacteria survive! 4. More macrophages (phagocytes) arrive at the infection site (activated by cytokines which have been released from macrophages at the infection site), [Cytokine - a protein released in response to bacterial infection]. These phagocytes (macrophages) engulf and surround the bacteria. 5. After a few weeks, the macrophages begin to die, releasing the bacteria, which lead to the development of a walled off lesion, a “hard lump” known as a tubercle [which actually means “lump”]. The bacteria can lay dormant here for years. 6. However, when the bacteria divide (binary fission) the lesion (this Tubercle) begins to enlarge and causes rupturing of the alveolus and bronchiole wall - the disease is now highly contagious. The bacteria are able to enter the bronchiole where they are coughed up and transmitted via droplets expelled into the air. So we know how TB is transmitted and we know how the immune system responds… But what effect does this infectious disease have upon an infected individual? Well, firstly, we’ll take a look at the common symptoms – i.e. Persistent cough (usually including the coughing up of blood and mucus), accompanied by chest pains, fatigue and of course shortness of breath… From those symptoms and of course what we know about the transmission and immune response its now easy to understand how TB affects ventilation rate. For example, the bacteria have caused the alveoli / bronchioles to rupture, the damage caused to the gas exchange surfaces has caused a decrease in tidal volume. The damage caused also results in the formation of scar tissues (fibrosis), which reduces Tidal volume even more! Now, since Tidal volume has decreased due to the effects of the disease, the infected individual is not able to inhale oxygen as efficiently. Hence the “shortness of breath” … So, Ventilation rate increases, i.e. the affected person breathes quicker in order to try and take in more oxygen. What we have just outlined here is a primary infection caused by the TB bacterium. It is important to recognise here that despite TB having one of the highest mortality rates of the infectious (communicable) diseases, healthy individuals are typically able to combat this bacterial pathogen with relative ease… So, why are mortality rates so high? TB is an opportunistic microorganism and commonly presents as a secondary infection in patients with a suppressed immune system, e.g. AIDS patients, the elderly, children, the malnourished, etc. And that brings us to the end of this revision session looking at the key points of TB. The important points to take from all this are... 1 ) be able to Describe the transmission and course of infection of pulmonary tuberculosis. 2) know that TB reduces tidal volume (and give reasons why)… and 3 understand that TB is a major contributor to mortality rates in immunosuppressed individuals… Visit the Website (www.learnbiology.net) where you can you can join up and download revision notes and accompanying lesson booklets with knowledge check and exam style questions with answers! If you are learning (or teaching) A Level biology then this is a great place to get loads of subject knowledge and resources. #ALevelbiology #Learnbiologynet #Biology