Science

• Across the whole planet, humans eat on average between one and 2.7 kilograms of food a day
• That's over 365 kilograms a year per person, and more than 28,800 kilograms over the course of a lifetime
• Every last scrap of food makes its way through the digestive system
• Digestive system


  • Comprised of ten organs covering nine meters
  • Contains over 20 specialized cell types
  • One of the most diverse and complicated systems in the human body
• Digestive system


  Continuously works in unison to transform the raw materials of food into the nutrients and energy that keep you alive
• Main components of the digestive system

  • Gastrointestinal tract
  • Pancreas, gallbladder, and liver
  • Body's enzymes, hormones, nerves, and blood
  • Mesentery
• Gastrointestinal tract


  • A twisting channel that transports food
  • Has an internal surface area of between 30 and 40 square meters, enough to cover half a badminton court
• Pancreas, gallbladder, and liver


  • Break down food using an array of special juices
• Body's enzymes, hormones, nerves, and blood


  • Work together to break down food, modulate the digestive process, and deliver its final products
• Mesentery


  • A large stretch of tissue that supports and positions all digestive organs in the abdomen, enabling them to do their jobs
• Digestive process


  1. Anticipation of food triggers saliva production

  2. Chewing and saliva turn food into a moist lump called the bolus

  3. Peristalsis propels the bolus into the stomach

  4. Stomach walls break down the bolus into chunks

  5. Hormones trigger release of acids and enzymes to dissolve and break down food

  6. Bile, pancreatic and intestinal juices break down fats, proteins and carbohydrates in the small intestine

  7. Villi in the small intestine absorb the molecules into the bloodstream

  8. Leftover fiber, water and dead cells make it to the large intestine where most fluid is drained out

  9. Remaining soft mass is squeezed into the rectum and expelled as stool through the anus
• The digestive process typically lasts between 30 and 40 hours
• If you could take a look inside this person riding the skateboard you would see an amazing team of different body systems working together
• Body systems


  • Integumentary system
  • Skeletal system
  • Muscular system
  • Urinary system
  • Respiratory system
  • Digestive system
  • Endocrine system
  • Reproductive system
  • Lymphatic system
  • Nervous system
  • Circulatory system
• Integumentary system


  Consists of our skin, which acts as a barrier, prevents water loss, regulates temperature, and allows us to touch our surroundings
• Skeletal system


  • Made up of bones, ligaments, tendons, and joints
  • Helps with movement and protection
• Muscular system


  • Responsible for movement inside and out of the body
  • Three major types: skeletal, smooth, and cardiac
• Urinary system


  Filters blood through the kidneys to filter out waste and produce urine
• Respiratory system


  Exchanges oxygen and carbon dioxide between the atmosphere and the blood
• Digestive system


  • Breaks down food so nutrients can be absorbed by the body
  • Has three main functions: ingest food, break food down, and eliminate what can't be digested
• Endocrine system


  Sends chemical messages (hormones) throughout the body
• Reproductive system


  Responsible for producing offspring
• Lymphatic system


  • Includes organs and cells that filter lymph and blood, and destroy foreign microorganisms
  • Lymph is the fluid that leaks out of the capillaries and circulates among the tissue cells before being collected by lymphatic vessels and returned to the veins
• Nervous system


  • Sends electrical signals throughout the body
  • Composed of the central nervous system (brain and spinal cord) and the peripheral nervous system (nerves that branch out from the brain and spinal cord)
• Circulatory system


  • Pumps blood throughout the body
  • Consists of the heart, veins that carry blood to the heart, arteries that carry blood away from the heart, and capillaries that connect the veins and arteries
• Excretory system


  System made up of the urinary system and the sweat glands
• Excretion


  Removal of toxic substances that are present in our body which could be harmful if they remain
• Urinary system


  • Responsible for collecting waste that the body doesn't need
  • Kidneys filter waste from the blood
  • Urine is made up of the waste substances that the kidneys have eliminated from the blood
  • Urine contains a very high water percentage (95%)
  • Urine travels from the kidneys through tubes called ureters to the bladder
  • Bladder stores urine until it is expelled outside the body through the urethra
• Sweat glands


  • Located under the skin
  • Responsible for expelling sweat to cleanse the body's blood
  • Sweat is 99% water, 1% salts and other substances
  • Sweating helps regulate body temperature
• When we're hot or exercise

  Our body generates sweat to expel through pores on the skin
• The excretory system expels two types of toxic waste substances: urine and sweat
• If someone gave me a penny every time one of my cells died, I'd be a millionaire in less than 30 seconds
• Most of the cells should have died by now, but the body has a way of replacing hard-working cells so we can live much longer on average than they do
• Cell cycle


  A process by which cells grow and divide to create new cells, typically with the goal of replacing cells that are worn out or damaged
• Cell cycle


  1. Cells are born from the division of other cells

  2. Those cells divide and create more new cells
• Cell cycle


  • It is a cycle because this process is constantly repeating itself to keep you healthy
• Phases of the cell cycle

  1. G1 (first gap phase)

  2. S phase (DNA synthesis)

  3. G2 (second gap phase)

  4. M phase (mitosis)
• G1 phase


  Cells grow and prepare to divide
• S phase


  Cells synthesize an identical copy of their DNA
• G2 phase


  Cells continue to grow and make final preparations to divide