The anthrax toxin is the reason for its virulence. The toxin’s mode of action has been studied in mice (the nature of the disease is similar in humans and mice).
Study results are demonstrated in the following graphs:
Graph no 1:
The effect of time on average heart rate in mice, after injection of the toxin.
Graph no. 2:
The effect of time on mean blood pressure in mice, after a toxin injection.
The anthrax bacteria do not damage the heart’s muscle directly, but cause the accumulation of fluid blood around the heart. This results in pressure on the heart, a situation termed cardiac tamponade, as you can see in the following picture:
 Medical Encyclopedia > Cardiac tamponade
| In a postmortem surgery of a person who died of anthrax, an accumulation of fluids was found between the heart and the heart’s surrounding membrane (pericardium). Can this situation explain the decrease in mean blood pressure and mean heart rate indicated by the graphs? |
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Arterial blood pressure is the force that blood flow activates in the arteries, and it is the result, among other things, of the stoke intensity. If there are fluids around the heart's membrane , the heart's ability to expand and contract is damaged, resulting in a decrease in the pumped blood pressure. This is why we see a continuous decrease in mean blood pressure.
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| During the disease there is an elevation in the respiratory rate, in both humans and mice. In addition, during the autopsy they found a large accumulation of fluids in the lungs, and parts of the lung cells were damaged.
How can you explain the elevation in respiratory rate in humans and mice in light of the autopsy finding?
In your answer, please consider the mechanism by which respiratory rate is controlled. |
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The accumulation of fluid and the damage to the cells minimize the active surface in the lungs, which means that there is less gas exchange. The resulting increase in the concentration of carbon dioxide (CO2, in the blood) acts as a stimulus to the breathing action, increasing respiration/ventilation to supply more oxygen and release excess CO2.
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| Based on your knowledge of the respiratory system, explain why an infection in that system is fatal.
Specify two characteristics that separate a spore from the active bacteria. |
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The spore is resilient to extreme environmental conditions while the active bacteria are limited by certain environmental criteria (such as pH, temperature, moisture, etc.).
Spore characteristics:
The spore does not reproduce
The spore is enclosed within a thick envelope
The spore has a low metabolism
Specify two factors that can signal the spore to become an active bacterium:
Change in temperature
Change in pH value
Conditions under which the envelope undergoes lysis/dismantling (chemical/physical):
Change in moisture (water)
Passage through an animal’s stomach
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