Physiology questions

Nephron, functional unit of the kidney, the structure that actually produces urine in the process of removing waste and excess substances from the blood. There are about 1,000,000 nephrons in each human kidney.

The gut–brain axis is the biochemical signaling that takes place between the gastrointestinal tract and the central nervous system. Changes in the composition of the gut flora due to diet, drugs, or disease correlate with changes in levels of circulating cytokines, some of which can affect brain function. The gut flora also release molecules that can directly activate the vagus nerve. Around 70% of people with autism also have gastrointestinal problems, indicating that there may be a connection between autism and gut flora.

Hypocalcemia, commonly known as calcium deficiency disease, occurs when calcium levels in the blood are low. A long-term deficiency can lead to dental changes, cataracts, alterations in the brain, and osteoporosis, which causes the bones to become brittle. Otherwise symptoms may include numbness, muscle spasms, seizures, confusion, or cardiac arrest.

The term melanism refers to black pigment in the skin or its appendages. Most commonly, dark individuals become fitter to survive and reproduce in their environment as they are better camouflaged. Adaptive melanism has been shown to occur in a variety of animals, including mammals such as squirrels, many felines and canids, and coral snakes.Melanism, meaning a mutation that results in completely dark skin, does not exist in humans.