What is Digestion?
Digestion is the breakdown of complexly structured food into small and simple structured molecules which can diffuse through the plasma membrane of a cell to provide with energy.
Digestion is done physically and chemically. Chewing the food in mouth is physical digestion while the enzyme reaction inside the body is chemical digestion.
Eating complexly structured food is called holozoic nutrition.
The Digestive system:
The digestive system is found in the alimentary canal. It consists of the mouth, the gullet called esophagus, the stomach, liver, pancreas, the large intestine and small intestine.
What happens in Mouth:
Your taste buds found in the tongue decides which food is delicious. When you ingest the food(put it in your mouth) you will automatically start chewing it. This chewing action shreds the food into small pieces. The salivary glands in your mouth would secrete (squirt) saliva which has enzymes in it and help to break it down.
The tongue would roll the food over to the Pharynx. The pharynx is the area of the mouth found just above the wind pipe called the trachea and the gullet called the esophagus. The epiglottis, a flap like cartilage, expands and covers the trachea so that the food won’t accidentally fall through. This way the food reaches the gullet without the risk of being choked to death!
The esophagus or gullet is a long pipe which finds its way to the stomach. The gullet does not secrete any enzyme meaning that no digestion takes place here.
The esophagus moves the food chunks to the stomach by the help of peristalsis. Peristalsis is the movement of muscles which push the material forward in its path.
There are four layers on the gullet. The first being the serous coat which is a thin, moist and slippery membrane found on the outer side of the gullet.
The second layer is the layer of circular and longitudinal muscles which contract and relax turn by turn which helps is peristalsis.The third is the layer of blood vessels and connective tissues.The inner layer is the mucus layer which helps in ease of movement of the food mass.The gullet opens to the stomach. Here the food is further digested.
The stomach is a muscular bag found right below the diaphragm. It also has four layers just as the gullet. The mucus coat has gastric glands which squirts gastric juice through the gastric pits found the surface of the mucus coat. After digesting the food to a much smaller size the food is sent to the pyloric sphincter which leads to the small intestine.
The liver is the largest gland in the body. It is a dark red organ with 5 lobes, 3 on right and 2 on left side of the liver. The liver produces bile which is stored in Gall Bladder. The Gall Bladder secretes the bile when it contracts. The solution is secreted through the bile duct which connects to the pancreatic duct before being released in to the small intestine. Bile is alkaline and has bile pigments and bile salts. It does not digest the molecules but helps in the digestion.
The pancreas is the second biggest gland found in the body. It secretes the Pancreatic juice which has various enzymes. It reaches the small intestine through the pancreatic duct and flows to the duodenum. It also secretes insulin which helps in control of blood sugar levels.
The small intestine consists of the duodenum, the jejunum and the ileum. This organ is coiled around and is not straight. Its layer has glands on it which secretes digestive enzymes. The intestinal walls have many folds which have finger shaped structures; the villi in it and each villus (singular for villi) has micro villi. The base of the walls have passages to the intestinal glands. These intestinal glands secrete the intestinal juice which has enzymes in it. The blood vessels are involved here in transportation of various nutrients helping to maintain a stable diffusion gradient. The nutrients are completely broken down in the small intestine and are ready to diffuse. These molecules find there way through the membranes and into the cells.
No Digestion takes place here. The remaining food particles which cannot diffuse through pass through the cecum and move up the ascending colon. The water and mineral salts are absorbed by the large intestine to provide a “last minute resource”. The molecules move to the rectum and is excreted in the form of feces. This removal of feces is called egestion.
How do the Digested Food Molecules get used?
The food molecules diffuse through the villi and enter the blood vessels which transport it to other parts of body. This molecule enters a cell which is in need of energy. The molecule diffuses through and is broke down by the mitochondria. It is then stored in the andosine triphosphate (ATP) until it is further broken to collect the energy.
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