Human body in numbers
1. The total length of capillaries in the human body has been estimated at 96 000 km.
2. The velocity of blood in the aorta averages 0,32 m/s.
3. In humans the thyroid gland has a supply of the hormone, sufficient for 3 moths.
4. Every B lymphocyte is covered by 150 000 molecules of IgM (receptors for specific antigens).
5. During the process of terminal differentiation and selection, T lymphocytes undergo numerous mitoses, but nevertheless more than 95% of them die by apoptosis.
6. Both testes combined contain about 1000 seminiferous tubules - the total length of which has been estimated at 0,5 km.
7. It takes 64 days to produce a spermatozoon from a spermatogonium.
8. An average ejaculate (3 ml) contains 200 - 300 million spermatozoa. A man with less than 20 million spermatozoa per ml of ejaculate is considered sterile.
9. A female newborn has 400 000 ova (egg cells). In her lifetime only about 450 of these will mature; others undergo atresion.
10. Fertilization of the oocyte happens in the oviduct. Once fertilized, the oocyte (now called a zygote) begins cell division and is transported to the uterus. Its journey lasts 5 days.
11. In the brain neurons typically connect to at least a thousand other neurons.
12. There are about 100 million cells in the nervous system.
13. Most synapses impinging on neurons are located in dendrite spines, which occur in vast numbers: they are estimated to be on the order of 10^14 for the human cerebral cortex.
14. Some nerves can propagate messages at speeds up to 100 m/s.
15. The longest axon in the body is about 100 cm long.
2 Comments:
13. Is this the same as the number of nerve cells in the brain (the cells that helps us to think and all that)? I thought a human starts his life with around 10^11 of such brain cells. Each day 10^5 of those cells pass away. This is how one by default losses 1% of his brain cells in 30 years. By an alcoholic this happens much faster. The number of his brain cells can fall even ten times faster. This means that instead of 30 years it takes an alcoholic only 3: to become 1% dumber. Alcoholism is one of the saddest things there are and it is in no way worthy of a man.
No, that is the number of "contacts" between the cells in the cortex of the brain, which is only one layer of the brain. They are the cells that help us think, they are the centre of consciousness and the abilities of thinking, reflecting and learning.
The capacity of the human brain to adapt is amazing, because even at the rate the cells are dying, the functions of the brain are not severely compromised. Also, there are several types of cells in the nervous tissues, and not every cell death is the same as the other.
Alcoholism indeed is sad, but as to its effect on the brain no universal conclusion can be made. It depends on the person and also on the amount one drinks.
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