21Baby's First Breath
When a baby is inside its mother, its lungs are deflated. They’re essentially in a breathed-out half-collapsed state that’s supported by amniotic fluids. When the baby comes out, the sudden change of environment and temperature causes the body to begin its first inhalation. The lungs expand, blood flow to the lungs increases, and the fluid is absorbed. The first breath is raspy because the fluid is still there; but the lungs were never full of it, so the expanding space is filled with fresh air.
The sudden rush and overload on its senses, bright light stinging their eyes that were used to near-total darkness, the rush of sounds closing in and everything else associated with the birthing process totally tires the baby, so they sleep for nearly 24 hours afterward, misleading new parents to think they have got a really easy baby.
Traumatic experiences can make the body and brain age faster. Stress leads to higher cortisol which leads to physical aging. This process is so strong that children who experience high levels of stress like violence or trauma in infanthood/early childhood statistically start puberty earlier than their non-traumatized counterparts.
One theory posits that early puberty/aging allows for increased survival in traumatic environments. It grants not just sexual maturity but increased bone density, muscle mass, etc. which basically allows you to become an adult faster to survive.
23Antibiotic Side Effects
Indigestion, diarrhea, and other stomach issues are common side-effects of strong/broad-spectrum antibiotics because they kill nearly all of the healthy gut bacteria. Some bacteria though can escape due to a combination of factors, some are replenished from the appendix (turns out it is now thought to be a reservoir), and food. Probiotics have been found to be entirely useless in these cases.
In some extreme cases, doctors might recommend stool transplants, where a stool sample is brought in from a “stool bank” which is then transplanted into the patient via enema or an oral capsule.
Armpit sweat glands are known as apocrine sweat glands, and instead of producing just sweat, they also produce a mix of proteins and lipids. The bacteria on your skin love that stuff and eat it up, producing waste products in the process. It's those waste products that cause pungent armpit odor.
There’s a reason why we secrete these oils and proteins in the first place. Hair under our arms and between our legs acts as a dry lubricant. When it isn’t enough (during intense exercise or prolonged walking/running), these secretions help reduce the friction and damage to the skin.
Each person has a unique combination of bacteria on their skin which in turn makes them have a unique smell, kind of like an olfactory fingerprint. Humans still use it to recognize family and friends from everybody else on a subconscious level.
There’s a reason you feel tired by just traveling in a vehicle and doing nothing else. There is lots of data on the “stressors of flight” (many of these stressors are also present in automobiles). As the vehicle moves, the sway and direction change causes you to make micro-adjustments to keep yourself upright. These micro-movements cause your muscles to be continuously working (even if you don't realize it).
Studies done by the US Airforce reports that consistent exposure to aircraft vibrations can lead to fatigue and an increased chance of health problems.
26Skin Tensile Strength
Human skin is amazingly resilient and has a shockingly high tensile strength, which is roughly 27 MPa (MegaPascals), whereas High-Density Polyethylene (milk jug plastic) is only around 15 MPa and ABS (LEGO plastic) is only about 50% stronger at 40 MPa. When someone gets big rapidly like during puberty, muscle growth, or pregnancy; the skin won’t tear but this will only result in stretch marks.
Estrogen alone is not solely responsible for breast development and size. It is a complex interaction between genetics and several different hormones which includes steroid hormones, estrogen and progesterone, growth hormone, insulin-like growth factor 1, and prolactin.
The best (but not the only) predictor of your breast size will be your other female relatives. Having high estrogen, just like having high testosterone, is not even necessarily a good thing. It’s associated with an increased risk of depression, anxiety, hair loss, thyroid disease, heart attack, stroke, blood clots, breast cancer, and ovarian cancer. It also doesn’t make you more likely to conceive as it causes decreased sex drive and irregular periods.
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Children tend to be more sensitive to bitterness, which is apparent in foods like broccoli and Brussels sprouts. This is an evolved defense mechanism because poisons are often bitter-tasting. As we grow, we learn which foods are poisonous and which aren't, so we don't need the same sensitivity and through evolutionary pressure, we lose the sensitivity over time.
When you complete a quick, strenuous exercise, some excess hemoglobin is released from your blood cells into the lungs due to increased heart rate and the resulting increased blood pressure, which is then carried to your mouth during an exhale. Hemoglobin is made up of iron. This is why you get a metallic blood-like taste when you thoroughly exhaust yourself.
30Viruses & Autoimmunity
Some viruses are structured in a way that when antibodies necessary to disable them are activated, they also become harmful to the human body itself. Many forms of kidney failure in the young are triggered by the immune reaction to streptococcus. Many forms of type I juvenile diabetes are thought to be caused by the body’s immune response to a viral infection. This is in fact the mechanism presumed for a number of autoimmune diseases that appear to be precipitated by a viral illness.