The human body
1. The human body is comprised entirely of cells, the adult body has approximately 37.2 trillion cells. The major systems of the body include: integumentary system (skin, hair, nails, etc.), skeletal system (bones), nervous system (brain and nerves), cardiovascular system (heart, blood, and blood vessels), endocrine system (hormones), muscular system (muscles), respiratory system (lungs), digestive system (mouth, esophagus, stomach, etc.), reproductive system (sex organs).
2. The integumentary system involves the hair, skin, nails, and sweat glands. Hair grows approximately 1 cm a month, and the average number of hairs on the head is 120 000. Each month the body replaces the skin with entirely new cells, in a lifetime about 40 pounds of old skin cells will be shed. Your nails grow about 0.5 mm each week.
3. The skeletal system consists of 206 bones and 32 teeth. As you age, certain bones fuse together, so babies have more bones than adults, for example in the skull. Most people have 12 pairs of ribs, but some people have one rib extra, giving them 25 ribs. Your bones aren’t actually the hardest thing in your body, your tooth enamel is.
4. If you lined up all the nerve cells in the body they would stretch 965 km long. In a baby’s first year, their brain will grow three times in size. There are more neurons in the brain than stars in the Milky Way galaxy.
5. The cardiovascular system is responsible for transporting blood, nutrients, and gasses to and from the cells of the body. Sadness or emotional stress really can `break your heart´, because they cause a condition called cardiomyopathy where the heart muscle suddenly weakens and causes symptoms such as chest pain, shortness of breath, and arm aches.
6. The endocrine system is responsible for hormone secretion. Adrenaline is a powerful hormone that prepares your body for the fight or flight response, raising your heart rate and energy levels and decreasing your ability to feel pain.
7. Muscles are responsible for moving your body by contracting. One step uses 200 muscles. The strongest muscle in your body is the tongue. It takes half as long to lose muscle as it does to gain it.
8. The lungs are used for gas exchange during breathing. The average person can hold their breath for 30 to 60 seconds, but a free diver may hold their breath for 20 minutes.
9. The first step of digestion is chewing. A person produces 1-3 pints of saliva each day. An adult stomach can hold approximately 1.5 litres of material. Food stays in the stomach for 2-3 hours before moving to the small intestine. THe small intestine is about 22 feet long. To sustain a weight of 150 pounds, a person would eat 50 tonnes of food in their lifetime.
10. The male and female reproductive systems are very different. A female will ovulate 300-400 eggs in her lifetime while men produce about 500 billion sperm cells in their lives. Ancient Greeks used the same terminology for male and female reproductive parts, for example the vagina was simply an inverted, and ovaries were testes.
1. How many cells are there in the body? (37.2 trillion)
2. The endocrine system refers to which functional parts? (hormones)
3. How many hairs on the head? (120 000)
4. How long does it take to replace the body’s skin cells? (one month)
5. What is the normal number of ribs? (24 or 12 pairs)
6. Who has more bones: babies or adults? (babies)
7. The distance 965 km refers to what? (the length of all the neurons of the body lined up)
8. At what rate does the brain grow during the first year of life? (3x)
9. What three parts compose the cardiovascular system? (heart, blood, blood vessels)
10. What is cardiomyopathy? (`broken heart´ or chest pain, shortness of breath, arm aches)
11. Which system is responsible for hormone secretion? (endocrine)
12. Which hormone can reduce your ability to feel pain? (adrenaline)
13. What is the strongest muscle? (tongue)
14. How many muscles does it take to make one step? (200)
15. What is the name of the breathing system? (respiratory)
16. What is the average time a person is able to hold their breath? (30-60 seconds)
17. What is the capacity of the adult stomach? (1.5 litres)
18. How long does food stay in the stomach? (2-3 hours)
19. What is one difference between the male and female reproductive systems? (300 or 400 vs 500 billion gametes)
20. Who referred to male and female reproductive systems as the same? (Ancient Greeks)