An example of positive feedback is the hormone that causes childbirth (when babies are born.) The hormone that causes this is oxytocin. This hormone is made by the pituitary gland. When the baby starts coming out, it stretches the muscle in the cervix (the bottom of the uterus). Nerves in the cervix send a message to the pituitary. This message makes the pituitary release more oxytocin. The oxytocin then causes the muscles of the uterus to contract, or squeeze. This causes more stretching in the cervix. This stretching then tells the pituitary to make even more oxytocin. So levels of oxytocin keep rising until the squeezing or contractions of the uterus force the baby out.
There are clear distinctions between hormones and neurotransmitters:
Most hormones start a cellular response by binding to cell membranes or receptors inside the cell. A cell may have several different receptor types that recognize the same hormone but activate different signal transduction pathways, or a cell may have several different receptors that recognize different hormones and activate the same biochemical pathway.
Hormones are defined functionally, not structurally. They may have various chemical structures. Hormones occur in multicellular organisms (plants, animals, fungi, brown algae and red algae). These compounds occur also in unicellular organisms, and may act as signalling molecules,
Peptide hormones are hormones with a short chain of amino acids.
Testosterone
Testosterone is an androgen sex hormone. A hormone is one that is made from cholesterol. A sex hormone is one that regulates sexual changes in the body. An androgen is the male type of sex hormone.
The testicles of men make lots of testosterone. Ovaries and adrenal glands make testosterone too. But they make much less than the testicles do. So men have much higher testosterone levels than women. The process takes place during the ages of puberty for both males and females
Testosterone has two different kinds of effects. One effect is anabolic. This effect causes growth of muscle and bone. The other effect of testosterone is androgenic. These effects make the body look male. This includes the effects that boys have at puberty: growing a beard, making the penis and testicles bigger, and making the voice deeper.
Patio
A patio is a paved area in a garden often used for barbeques or relaxing outside.
Cholera
Cholera is an infectious disease caused by the bacterium "Vibrio cholerae". It infects the small intestine.
There are many types (strains) of the "Vibrio cholera" bacteria. Some of them cause more serious illnesses than others. Because of this, some people who get cholera have no symptoms; others have symptoms that are not very bad, and others have very bad symptoms.
The most common symptom is large amounts of watery diarrhea. In the worst cases, diarrhea can be so bad that people can die in a few hours from dehydration.
Cholera is a very old disease. Writings about cholera (written in Sanskrit) have been found from the 5th century BC. Throughout history, there have been many outbreaks and epidemics of cholera.
Cholera still affects many people throughout the world. Estimates from 2010 say that between 3 million and 5 million people get cholera every year, and 58,000–130,000 people die from the disease every year. Today, cholera is considered a pandemic. However, it is most common in developing countries, especially in children.
People usually get cholera by eating food or drinking water that is unclean. When people have cholera, they have a lot of diarrhea, and the cholera bacteria stays alive in their feces. In developing countries, often there is not good sanitation. Cholera can spread if this diarrhea gets into water that other people use. For example, if sewage (human waste) gets into a river, people can get cholera if they:
Cholera is very rarely spread directly from person to person.
Cholera's main symptoms are bad diarrhea and vomiting clear fluid. These symptoms usually start suddenly. They start half a day to five days after the person gets infected. (This is called cholera's "incubation period".)
If they do not get treatment, about half of people with serious cholera die. People with bad cholera may have so much diarrhea that they do not have enough water and electrolytes (salts) left in their bodies to survive. Cholera has been nicknamed the "blue death" because a person dying of cholera may lose so many body fluids that their skin turns bluish-gray.
Other symptoms may include:
If people with cholera get good, quick medical treatment, less than 1% die from the disease. However, if cholera is not treated, at least half of people with the disease (50% to 60%) die.
Some strains of the "Vibrio cholera" bacteria have different genes than others, which make them more dangerous. These more dangerous strains of cholera bacteria caused the 2010 epidemic in Haiti and the 2004 outbreak in India. A person who gets these strains of cholera can die within two hours of getting sick. This means there is very little time to get the person treated.
There are antibiotics for cholera. There are various treatments which can help. For example:
There is a cholera vaccine that can be taken by mouth. It provides some protection from cholera for about six months.
People can also do some other things to prevent cholera. For example:
Governments could stop outbreaks or epidemics from happening by improving sanitation. For example, cholera is very uncommon in developed countries because they have good sanitation and because they add chemicals to their water to kill germs. Even after people start to get cholera, it is possible for governments to stop the disease from spreading, though:
Cholera probably started in the Indian subcontinent. As early as the 5th century BC, people in the Ganges River delta area wrote about cholera. The disease first spread to Russia in 1817 by trade routes (over both land and sea). Later, cholera spread to the rest of Europe, and from Europe to North America and the rest of the world.
Seven cholera pandemics have happened in the past 200 years. The latest started in Indonesia in 1961. There have also been many serious outbreaks. The worst outbreak in recent history happened in Haiti after the earthquake there in 2010. Between October 2010 and August 2015, more than 700,000 Haitians got cholera, and over 9,000 died. The outbreak was caused by a United Nations base where Nepalese soldiers were living. The soldiers would dump human waste into the Artibonite River, which many Haitians used for drinking, cooking, and bathing.
Cholera was common in the 19th century. It has killed tens of millions of people. Just in Russia, between 1847 and 1851, more than one million people died of cholera. During the second pandemic, which lasted from 18271835, the disease killed 150,000 Americans. Between 1900 and 1920, in India, up to eight million people died of cholera.
in 1854, an English doctor named John Snow was the first person to realize that contaminated water caused cholera.
The English engineer Joseph Bazalgette solved the problem for London in the middle of the 19th century. He invented the system for cleaning foul water, a system which is still used world-wide. Cholera has come back to the world because cities have hugely increased populations, and the treatment of sewage has overrun the facilities. It was the British who built most of the world's sewage plants, and until about 1950 they were able to work well unless they were damaged by warfare. Later governments did not invest money in their infrastructure, which meant the increased population eventually caused cholera to return.
Cholera is not the only problem with water supply. Blooms of red algae occur from time to time in hot weather, and they have to be killed off. Emergency control is got by adding chlorine to the water supply. This works, but makes the water rather distasteful.