31Reduced Immunity in Old Age
The thymus is an important immunological gland located in your upper chest that produces T cells. These are important white blood cells of the immune system. This gland begins to deteriorate after you hit puberty, though it doesn't fully degrade until old age at which point it essentially becomes non-existent. This is the reason why with aging it becomes harder to heal from illnesses and why young kids tend to bounce back faster after illnesses.
Basically, our immune system starts to shut down as we get older because we’re simply not meant to live so long. There's no biological reason to live very long, just sentimental reason.
When you have a “gut feeling” it’s the subconscious part of your brain triggering a mild fight or flight response. This happens when the always watching and listening subconscious part of your brain notices something that the conscious part of the brain was too distracted to notice. The hypothalamus then signals your adrenal glands to release adrenaline to give your body some extra strength, so that you can either run faster or fight harder.
Among other things, adrenaline will cause your bowels to contract and your blood vessels to expand. This is what that stomach sensation basically is and why some people will literally sh*t themselves during a high-stress situation.
It is also worthwhile to point out that the gut feeling can be sometimes completely wrong and you can see extreme examples of this in people with anxiety disorders, who experience way more “false positive” alarms.
Humans are insanely good at seeing patterns. We see patterns in things we're not even supposed to, and we do it all the time. It's why we can see animals in clouds and faces of dead celebrities in malformed potato chips.
It's not just visual patterns we’re good at. One really interesting example of this is the ‘red flag’ phenomenon, where you just get a bad feeling about someone, even if you haven’t actually seen them do anything that warrants caution. In many cases, this red flag turns out to be right all along. That’s the pattern recognition in our brains going off. There may have been just something about the person that set off your internal alarms. Perhaps maybe you’ve subconsciously noticed similar expressions, speech patterns, behaviors, etc. in people who did actually turn out to be bad in the past. Your brain keeps extensive records of that sort of thing whether you're aware of it or not.
34Unconscious Decision Making
Contrary to what most of us would like to believe, decision-making may be a process handled to a large extent by unconscious mental activity. A team of scientists has unraveled how the brain actually unconsciously prepares our decisions. Many processes in the brain occur automatically and without the involvement of our consciousness. This prevents our minds from being overloaded by simple routine tasks.
The need for resistance training for muscle growth is mostly a human trait. With appropriate genes, simply growing muscle without the training is not only possible, but takes fewer calories, so it is much more efficient and preferable by other species.
Exercise for the sake of exercise burns up a lot of calories which in other animals is best preserved for acquiring food, reproducing, etc. Humans engage in muscle building as a result of our societal evolution from that of hunter-gatherers where we were just like other animals of today. Division of labor has made food acquisition the least of our worries. So, we now have dedicated plenty of time and resources to working out to impress people (or most likely ourselves).
In countries with poor access to clean water, a lot of people suffer from water-borne diseases, and this leads to substantial morbidity and mortality, especially in young children. Healthy adults, however, in these countries have higher resistance to some pathogens compared to people who grew up in countries that have easy access to clean water, which explains traveler’s diarrhea.
37Preventing Tooth Decay
Bacteria floating around in your mouth by and themselves are not strong enough to get through your enamel (hardest outer layer of the tooth), but when bacteria are left around long enough they begin to stick together to form a biofilm. This starts as a soft biofilm called plaque. Brushing your teeth or scraping it will remove this soft biofilm without much effort. In left untouched, this soft plaque begins to strengthen and hardens into tartar.
Tarter is solid and no matter how hard you brush, it will not come off. That’s why dentists scrape it off with special instruments. This is the reason why tooth decay can’t be prevented just chemically (mouthwash), it has to be addressed mechanically (brushing/flossing). Mouthwash is not a rip-off though, it’s just more supplemental. For an average person, fluoride mouthwash is best unless your dentist says otherwise.
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Cancer cells are the result of mutations that disable the mechanisms that keep cell growth in check. Those mutations come from incorrect repairs to cell DNA, and those errors happen more frequently the more repairs take place. If the body is forced to do repairs often and faster (e.g. for smokers), it will make more mistakes.
The human body already has a number of ways to deal with cancer though. Cancer cells are produced in the body all the time but those cells have mechanisms in place to kill themselves if they become cancerous or they are obliterated by the immune system. It needs to get past both of those things and start reproducing out of control to become an issue.
39Post-Workout Delayed Soreness
Any intense activity that you are not used to can cause delayed onset muscle soreness. It does not hurt right after a workout but hurts usually a day later when you move the affected muscle. The current scientific consensus is that your nerves are actually responsible for this. Intense activity results in microscopic damage to the muscles, which is not intense enough to cause pain right away. The repair process of this damage involves some inflammation and immune cells, so to call them the muscle produces some signal chemicals and molecules that initiate repair. This also makes the neurons that innervate the muscles to become more sensitive to movement.
This does not happen that fast though (it takes time to make new proteins). Thus you are not sore right away because it’s not the neurons sensing damage but them becoming more sensitive to movement. This makes you move your muscles a bit less so that they can heal.
40Bladder Control in Kids
During the first three years of human life, bladder storage capacity increases disproportionately relative to body surface area. By four years of age, most children void five to six times per day. Development of bladder control appears to be a progressive maturation whereby the child first becomes aware of bladder filling, then develops the ability to suppress voiding involuntarily, and, finally, learns to coordinate muscles necessary to void voluntarily.
These skills usually are achieved, at least during the day, by approximately four years of age. Nighttime bladder control is achieved months to years after daytime control but is not expected until five to seven years of age.