I’m like, super super excited for today because the small intestine is the most complex part of the alimentary canal. Today we’ll only be focusing on the small intestine!
Anyways, moving on…
The Small Intestine->
The small intestine kinda looks like an unravelled brain, come to think of it. It’s typically 2 meters long in adults, which is about as tall as Michael Jordan…
The small intestine can be divided into 3 parts- the duodenum, the jejenum, and the ileum. The inside of the intestine is covered in thousands of little projections called villi, which are responsible for absorbing nutrients from our food!
Before we begin, lemme just clear some stuff up. The yellow thing in the above is the pancreas. The little green pouch is the gallbladder. Only the peach-ish tube thingy is the duodenum. Even though the pancreas, gallbladder and liver aren’t a part of the alimentary canal, they play an essential role in digestion!
Okay, so food passes directly into the duodenum from the stomach. But, remember that the stomach is filled with hydrochloric acid? To dilute the acidic nature of the chyme, it’s mixed with an agent called sodium hydrogencarbonate [Well, that’s a mouthful.] Sodium hydrogencarbonate is an alkaline substance, so it reduces the acidity of the chyme.
The chyme is also doused with bile and pancreatic juice. Bile helps breakdown fatty items in a process known as emulsification. It’s made by the liver and stored in the gallbladder. Pancreatic juice is [obviously] made by the pancreas, and contains 3 enzymes. These are: trypsin, pancreatic amylase and lipase. Together, these 3 enzymes help to digest starch, fats and proteins!
Right, this guy isn’t half as complex as the duodenum. The food just moves further. However, there are 4 enzymes at work here! These are- peptidase, sucrase, maltase and lactase. Peptidase further digests proteins into amino acids. Sucrase digests sucrose, maltase digests maltose, and lactase digests lactose!
PS. People who are lactose intolerant can’t digest the sugar lactose because the enzyme lactase isn’t present, or isn’t in enough quantity! This can give them tummyaches and the like
The ileum is the last part of the small intestine, and the least complicated. Nothing really happens here- there’s no enzymes, or anything! The nutrients are simply absorbed from the food. More on that below!
Yes, that’s what they look like. They’re basically a weird little forest of nutrient absorbing bald trees… xD! A single villi would be called a villus.
Anyway, these villi help bring nutrients from the food into the blood and the lymph. The final products of digestion are- glycerol and fatty acids [from fats], amino acids [from proteins] and glucose and other monomers [from carbohydrates]. Amino acids and simple sugars diffuse into the capillaries present in the villi. These capillaries empty into the hepatic portal vein, which goes to the liver! The fatty acids and glycerol, however, drain into another fluid called the lymph.
Yeah, that’s it for today. I do hope it wasn’t an info overload…
Thanks for reading!