The human body is a marvel of design. It houses many complex systems that are uniquely independent in function, yet interdependently related in purpose. More than 100 trillion cells, 206 bones,600 muscles and 22 internal organs work together to keep us alive. One of the 10 major organ systems is the digestive system.
Without the digestive system, the body will be deprived of the basic nutrients: protein, carbohydrates and fats. Without carbs, you will lack energy. Without glucose (the only food for the many brain cells), you won’t have mind power. Without protein, your cells cannot repair and grow. Without fat, there would be no hormones, cholesterol and many vital cells in your body. And the list does not stop here – what about fibers, vitamins and minerals?
The Digestive System
The digestive system works hand-in-hand with the nerves, which control the muscles, signaling them when and to what degree to contract as food moves through the digestive tract. These contractions – known as peristalsis – push food down the alimentary canal right up to the final evacuation of waste from the body.
1) Mouth
Food digestion starts here. Chewing triggers the release of saliva, which contains the enzyme ptyalin (PRONOUNCED ty-u-lin). Saliva is slightly acidic (pH 5.6-6.9)to help kill harmful pathogens in food.
Enzyme: Ptyalin.
Source: Salivary glands.
Action: Mainly digests starch (carbohydrates) into maltose (simple sugar).
2) Stomach
The stomach is very acidic(pH 1-3) due to the presence of hydrochloric acid (also known as gastric juice). This acid kills most bacteria and other pathogens in food. The food which is now mixed with acid is known as chyme (PRONOUNCED kime). The stomach ends with a valve known as the pyloric sphincter (PRONOUNCED PIE-lore-ik SFINK-ter), which regulates the release of food from the stomach into the small intestine.
Enzyme: Pepsin.
Source: Cells lining the stomach.
Action: Digests most protein in food
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Enzyme: Rennin (also known as chymosin).
Source: Cells lining the stomach.
Action: Coagulates milk protein into casein.
3) Small intenstine
The small intestine (about 6-8 m long) is the final stop in food digestion. Here, most foods are broken down into basic nutritional units small enough to pass through the intestine’s cell membranes. It takes about four hours to complete the entire digestive process. What remains is liquid waste, which is transported to the colon (large intestine)
Enzyme: Amylase.
Source: Pancreas.
Action: Digests carbohydrates into maltose.
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Enzyme: Trypsin.
Source: Pancreas.
Action: Digests protein into peptides.
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Enzyme: Peptidase.
Source: Intestinal lining.
Action: Digests peptides into amino acids.
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Enzyme: Lactase.
Source: Intestinal lining.
Action: Break down milk sugar into lactose.
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Enzyme: Maltase.
Source: Intestinal lining.
Action: Break down maltose into glucose.
4) Colon
The colon (large intestine) is about 1.5 m long and is the final stop to absorb the remaining minerals before waste is excreted from the body. The colon also absorbs water from liquid waste to make it solid (stool).
5) Rectum
Stool is then delivered by means of peristalsis for storage in the rectum.
6) Anus
This is the opening where waste finally leaves the body.