Before I start I just want to clarify that many of you who are reading this might consider this content to be rudimentary and I do agree with you. Since this is my first EVER post I thought it would a good idea to start off with something so basic. Additionally this topic is also one of my all time favorites. I don't really know why. But it just is. And I happen to remember this effortlessly even though I learned this back in 8th grade. Don't worry I will post more extensive content later on. I will however, appreciate any suggestions on a topic that you find interesting. Something that would be beneficial for everyone. Thank You.
Since we are going to talk about digestion I believe it will be useful for you to know what the alimentary canal is. The alimentary canal is a protracted tube running through the body. The interior portion of the alimentary canal is lined with layers of cells called the epithelium. New cells are produced simultaneously in order to replace the old cells, which might have been worn down by the movement of food. There are also cells present in the lining which produce a slimy liquid called mucus. Mucus helps in lubricating the lining and protects the lining from being attacked by digestive enzymes present in the canal. The alimentary canal is made up longitudinal and circular muscles. A series of contraction along the alimentary canal helps to push the food in front. This process is called peristalsis.
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| A diagram of peristalsis |
Many might not realize this but digestion actually starts the moment you take in food into your mouth. Munch! Munch! Chewing your food (the only good part) is how everything starts. The chewed food is mixed with saliva. Salivary amylase, the enzyme present in saliva helps in breaking down starch to maltose. For the food to enter the esophagus-the tube that transports food to the stomach-it has to pass the windpipe. Gosh! The windpipe? How come we don't choke when we eat? When we swallow, our tongue presses upward and back against the mouth. This as a result forces the bolus to the back of our mouth. A soft palate closes the nasal cavity. The top of the windpipe is circumscribed by the larynx cartilage. This cartilage is pulled upwards so that the glottis:the opening of the windpipe lies under the tongue. A flap of cartilage called the epiglottis prevents food from going down the windpipe instead of the esophagus.
Say hello to the stomach! Stomach is used to store food which then ends up getting turned to liquid in order to be released to remaining portion of the alimentary canals. The glands in the stomach produce gastric juice containing protease, an enzyme responsible for breaking down protein into soluble compounds known as peptides. The stomach lining also manufactures HCl, a strong acid that helps pepsin to work at its best level. Wait a minute. There's acid in my stomach?! How come I am not...dead?! Remember the mucus lining I mentioned earlier? Damage to the stomach wall by acid is prevented by the mucus. The acid also kills any bacteria that might have present in your food. Bacteria in your food? Ugh! Where on earth do you get your pizza from?! Just kidding.
After spending some time in the stomach, the liquid products of digestion enters the small intestine through the duodenum: the first part of the small intestine. Pancreatic juice from the pancreas and bile from the liver are poured into the duodenum to act on the food present over there. In case you were wondering, the pancreas is a digestive gland sited below the stomach. It is responsible for making numerous enzymes which in turn can act on all classes of food. Pancreatic amylase attacks starch and converts it to maltose. Lipase breaks down fats to fatty acids and glycerol. The pancreatic juice also contains sodium hydrogen-carbonate, an alkali which partly neutralizes the acid which was present from before. In contrast bile is a green fluid made by the liver. Bile is stored in the gall bladder which is later delivered to the duodenum through the bile duct. The green pigment is a result of the breakdown of hemoglobin in the liver. Bile salts present in bile helps in emulsifying fats.
You might be wondering "Do the enzymes get digested too?" The simple answer is no. The complicated answer? Well, the proteases released earlier are in inactive state. pepsin is produced as pepsinogen and doesn't become active until it encounters HCl in the stomach. Similarly, trypsin, one of the proteases secreted from pancreas is released as trypsyinogen and is later activated by the enzyme enterokinase. In this manner the body ensures that the enzymes do not get digested. Additionally the secretion of liquids is controlled by hormones released by the body.
The small intestine contains the ileum. Almost all of the absorption of the digested food takes place here in the ileum. It is efficient in absorbing nutrients for numerous reasons. Some of which include a large absorbing surface, an internal surface filled with villi and the epithelium lining which is known for its thinness. Each villus also has a dense network of capillaries. Amino acids and glucose travel into the epithelial cells and then through the walls of the capillaries in the villus and finally into the bloodstream. The capillaries join to form the vein, which in turn forms the hepatic portal vein. This vein carries all the blood from the intestine to the liver. When the products are released from the liver, they enter into the bloodstream. Sometimes fatty acids and glycerol are combined to form fats again in the epithelium. These fats then travel to the lacteal and eventually flows into the lymphatic system, which makes a network throughout the body and gradually empties the stored fat to the bloodstream to be absorbed by cells. The absorption of the food molecules aren't just done through diffusion but it is also done using active transport. Amino acids, sugars and ions of mineral salts are absorbed through the process of active transport.
The content travelling to the large intestine generally consist of water, cellulose and vegetable fiber, mucus and innumerable dead cells. Despite the lack of any presence of enzymes, with the help of bacteria in colon, the large intestine digests some of the fiber to be used as fatty acids. Some of the bile salts are also absorbed and returned to the liver. In addition the colon also absorbs much of the water from the undigested residues. This step is important because if the colon doesn't absorb the water then the body would have to suffer from dehydration. After spending some hours inside your body the unwanted materials in your pizza is excreted from body in the form of feces. The journey is finally over!
Here are the links of some cool sites which I used for my post:
http://www.biologyguide.net/
http://www.mrothery.co.uk/
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| A diagram explaining how food travels down the esophagus to the stomach |
After spending some time in the stomach, the liquid products of digestion enters the small intestine through the duodenum: the first part of the small intestine. Pancreatic juice from the pancreas and bile from the liver are poured into the duodenum to act on the food present over there. In case you were wondering, the pancreas is a digestive gland sited below the stomach. It is responsible for making numerous enzymes which in turn can act on all classes of food. Pancreatic amylase attacks starch and converts it to maltose. Lipase breaks down fats to fatty acids and glycerol. The pancreatic juice also contains sodium hydrogen-carbonate, an alkali which partly neutralizes the acid which was present from before. In contrast bile is a green fluid made by the liver. Bile is stored in the gall bladder which is later delivered to the duodenum through the bile duct. The green pigment is a result of the breakdown of hemoglobin in the liver. Bile salts present in bile helps in emulsifying fats.
 |
| A diagram of the stomach, liver, pancreas and their respective parts |
You might be wondering "Do the enzymes get digested too?" The simple answer is no. The complicated answer? Well, the proteases released earlier are in inactive state. pepsin is produced as pepsinogen and doesn't become active until it encounters HCl in the stomach. Similarly, trypsin, one of the proteases secreted from pancreas is released as trypsyinogen and is later activated by the enzyme enterokinase. In this manner the body ensures that the enzymes do not get digested. Additionally the secretion of liquids is controlled by hormones released by the body.
The small intestine contains the ileum. Almost all of the absorption of the digested food takes place here in the ileum. It is efficient in absorbing nutrients for numerous reasons. Some of which include a large absorbing surface, an internal surface filled with villi and the epithelium lining which is known for its thinness. Each villus also has a dense network of capillaries. Amino acids and glucose travel into the epithelial cells and then through the walls of the capillaries in the villus and finally into the bloodstream. The capillaries join to form the vein, which in turn forms the hepatic portal vein. This vein carries all the blood from the intestine to the liver. When the products are released from the liver, they enter into the bloodstream. Sometimes fatty acids and glycerol are combined to form fats again in the epithelium. These fats then travel to the lacteal and eventually flows into the lymphatic system, which makes a network throughout the body and gradually empties the stored fat to the bloodstream to be absorbed by cells. The absorption of the food molecules aren't just done through diffusion but it is also done using active transport. Amino acids, sugars and ions of mineral salts are absorbed through the process of active transport.
 |
| A diagram of villus |
The content travelling to the large intestine generally consist of water, cellulose and vegetable fiber, mucus and innumerable dead cells. Despite the lack of any presence of enzymes, with the help of bacteria in colon, the large intestine digests some of the fiber to be used as fatty acids. Some of the bile salts are also absorbed and returned to the liver. In addition the colon also absorbs much of the water from the undigested residues. This step is important because if the colon doesn't absorb the water then the body would have to suffer from dehydration. After spending some hours inside your body the unwanted materials in your pizza is excreted from body in the form of feces. The journey is finally over!
Here are the links of some cool sites which I used for my post:
http://www.biologyguide.net/
http://www.mrothery.co.uk/
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