what are the requirements needed to apply to uni in the uk from canada? are ap’s needed? what about ib? (im aiming for ucl/cambridge and a major in a biological science/medicine)

Answer:

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Based on the information provided, the most likely title for Helena's research paper would be "The Unique Characteristics of the Puumala Virus and Its Potential Usefulness in Hantavirus Research."

The Puumala virus is a type of hantavirus that is primarily found in Europe and is transmitted to humans through contact with the urine and droppings of infected rodents. Compared to other hantavirus strains, the Puumala virus causes a milder form of disease known as nephropathia epidemica. However, the unique genetic makeup of the Puumala virus may hold important clues for scientists studying hantaviruses in general.

Therefore, Helena's research paper is likely to focus on the unique characteristics of the Puumala virus, and how this knowledge can be useful to scientists who study hantaviruses.

When ventricular relaxation begins, the semilunar valves close, creating the “dup” sound. It has a duration of 0.1 seconds with a fundamental frequency of 50 cycles per second. Compared to “lub,” it is louder, sharper, higher pitched, and shorter in length. Thus, option B is correct.

This noise is caused by the heart's blood-flow control valves closing. The mitral and tricuspid valves close, which causes the first noise (the lub) to be heard.

The aortic and pulmonary valves close when the blood has been forced out of the heart, which causes the subsequent sound (the dub) to occur.

Two distinct sounds that are audible with a stethoscope are produced during each heart cycle. Whereas the second heart sound (dubb) is connected to the closure of the semilunar valves, the first heart sound (lubb) is connected to the closing of the tricuspid and bicuspid valves.

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ANSWR:The partial pressure of oxygen and carbon dioxide in blood changes as you hold your breath. Oxygen is used up by metabolic processes, reducing its partial pressure, and carbon dioxide is produced, raising its partial pressure.

The partial pressure of oxygen and carbon dioxide in blood changes as you hold your breath. Oxygen is used up by metabolic processes, reducing its partial pressure, and carbon dioxide is produced, raising its partial pressure. One might think that there are mechanisms to detect these concentrations, and give rise to the impulse to breathe if oxygen gets too low and/or carbon dioxide gets too high.

Early research pointed to the partial pressure of CO2 being the crucial variable. Back in the day before intrusive institutional review boards, studies such as the following (Schneider, 1930) could take place. Hook some people up to a tube, and, without their knowledge, switch the gas they receive from the tube to pure nitrogen. When such subjects inhale from the tube and exhale into the room, their oxygen is going down but carbon dioxide levels are staying relatively constant. Do people experience the panic of imminent asphyxiation? As Schneider (1930) writes: “The sensations experienced during an acute anoxemia, such as result from nitrogen breathing, are not distinctly unpleasant; in fact they are quite like those of nitrous-oxide anesthesia…” Subjects in this study had to be observed and monitored for cues that they were about to pass out – “cyanosis, mask-like facial expression, pupil dilation, eye convergence, falling systolic pressure.” Results such as these point to the idea that it’s the buildup of CO2, rather than the lack of oxygen, that gives rise to the impulse to breathe.

Having said that, Parkes (2006) reviews evidence that shows that it’s more complicated than this, and there could be multiple systems at work here. The fact that the system seems to work on CO2 levels rather than O2 is interesting, of course, but it seems reasonable to think that under normal circumstances – in worlds without tanks of pure nitrogen about – these two are likely to vary systematically with one another, so either could work.

In modern environments, all things are, of course, not always equal, and here enters the vignette by Kean. He discusses how NASA decided to use nitrogen in simulators subsequent to the horrible fire during training for the Apollo missions in 1967 in which three astronauts were killed. Using nitrogen rather than pure oxygen on the ground is useful insofar as it reduces the chance of fires, but its use had a side effect. In one case, five men entered a compartment filled with nitrogen and collapsed. There was no oxygen to breathe, but, like the subjects in Schneider’s study, they simply passed out; two of them died. As Downey remarks, linking this to his interest, diving, the fact that the urge to breathe seems to be triggered by high CO2 levels “may also be the reason that free diving participants pass out with some frequency; they run low on oxygen before carbon dioxide levels get high enough to prompt breathing.” In short, again quoting Downy: “When you breath hold, you are not so much ‘running out of air’ as you are fighting powerful impulses to breathe when you don’t really need the oxygen yet.”

So, anyway, this is all pretty neat. There’s an adaptive problem, which is to replenish oxygen, which is necessary for normal metabolic processes. One part of the solution to the problem seems to be – but, again, only a part, as Parkes indicates – a sensory system designed to measure CO2 and motivate breathing when this level gets high, which is, under normal circumstances, related to when levels of O2 are low. As this level rises, the phenomenological urge to breathe is produced, motivating appropriate action. This urge can be offset, for a time, but only for a time, and this limit seems to have to do with the increasing chance of damage due to lack of oxygen. Again, it’s complex, but still, we seem to be building toward a satisfying account of these systems.

An alternative view is that because breathing is “automatic,” and “overriding” automatic processes “depletes” the “self’s” “resources,” it gets harder and harder over time. This theoretical approach has the virtue of not “resorting” to any sort of functional explanation/storytelling.

When a person holds their breath, the levels of oxygen (O2) in their blood start to decrease, while the levels of carbon dioxide (CO2) start to increase. This triggers a response in the brain, specifically in the respiratory center located in the medulla oblongata, which controls breathing.

What is suffocation?

Suffocation is a condition in which an individual's oxygen supply is cut off or reduced, leading to difficulty breathing or even death.

When someone suffocates to death, it means that they have experienced oxygen deprivation for a prolonged period, leading to irreversible tissue damage and, ultimately, death.

Suffocation can occur due to various reasons, including choking, strangulation, smothering, or inhaling toxic fumes or gases.

The brain sends a signal to the diaphragm and other respiratory muscles to contract, causing a person to involuntarily take a breath.

This involuntary response is known as the "breaking point," and it occurs when the levels of CO2 in the blood become too high, causing the brain to override the voluntary control of breathing.

At this point, the person will take a breath even if they are trying to hold it. This is why a person cannot suffocate to death from holding their breath.

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