So, our mouth contains salivary enzymes which
can partially digest carbohydrates. After the food passes through the oesophagus, it
gets stored in the stomach where further digestions take place. Now, proteins get digested into
polypeptides and peptides. So, in the stomach, proteins get digested. Now, for a proper healthy
body, our body needs nutrition. So, we need to absorb all the nutrients such as glucose,
amino acids, fats and glycerol from the food so that we can utilize these nutrients for
a proper healthy body. So, food gets broken down in the stomach but even these food molecules
are big enough to be absorbed by our body. These food molecules need to further broken
down. So, food that gets digested in the stomach comes out of the stomach and enters into a
22 feet long small intestine. So, food that comes out of the stomach enters the small
intestine. Now, the starting portion of the small intestine is known as duodenum. See,
this portion which is a U-shaped structure is known as duodenum. Duo means two and den
means ten. So, this duodenum is 12 fingers in diameter and hence it is named as duodenum.
So, carbohydrates get partially digested in the mouth. Proteins like meat, they get partially
digested in the stomach and fats like cheese have not yet been digested in our body but
for all the food and all the nutrients to get absorbed in the body, it needs to be completely
digested. So, it is the task of the small intestine to completely digest the food. So,
three enzymes are secreted by an organ known as the pancreas and the three enzymes can
be abbreviated as TAL. T-A-L, TAL so that you can remember it better during the examinations.
So, pancreas secretes TAL. T for trypsin, A for amylase and L for lipase. So, trypsin
breaks down or digests any undigested or incompletely digested proteins and polypeptides into smaller
peptides and amino acids. Amylase breaks down starch which is a polysaccharide into a monosaccharide
like glucose. And lipase converts or digests fats into fatty acids and glycerol. Now, these
molecules are small enough to be absorbed and utilized by our body. Now, the tripsin
which was secreted by the pancreas is not secreted in its active form. It is secreted
as trypsinogen which is an inactive enzyme. So, this inactive enzyme needs to be activated.
So, an enzyme known as enterokinase is secreted by the duodenum which converts this inactive
trypsinogen in active trypsin and the trypsin is responsible for the breakdown or for the
digestion of proteins. Now, amylase can only digest starch partially, i.e., starch is a
polysaccharide. Now, amylase can digest this polysaccharide to disaccharides like maltose
but what after that? Disaccharides are big enough to be not absorbed by the body. It
needs to be further broken down so that our body can absorb it. So, the duodenum secretes
three enzymes, known as the maltase, lactase and sucrase. Now, maltase breaks down maltose
into monosaccharide like glucose. Similarly, lactase breaks down lactose which is a disaccharide
and is present in milk into monosaccharide like glucose and galactose. Similarly, sucrose,
which is present in sugarcanes and is a disaccharide can be broken down by the enzyme known as
sucrase into glucose and fructose both of which are monosaccharide and can be absorbed
by the body. So, the pancreas secretes the three enzymes which can digest proteins, carbohydrates
and fats. Now, in case 1, we see that the enzymes can digest polysaccharides into monosaccharide
like glucose. In case 2, we see that the enzymes can further break down proteins into smaller
molecules known as amino acids. And in the third case, we see that this enzyme breaks
down fats into smaller molecules of fatty acids and glycerol. Now, for these three enzymes
or all the enzymes that are secreted from the duodenum as well as the pancreas, it requires
a basic medium. But, the stomach had a very acidic environment. So, the chyme coming out
of the stomach was also acidic in nature. So, to convert the acidic nature of the chyme
coming out of the stomach, liver secretes sodium bicarbonate which is a base and this
converts the acidic medium of the chyme into a basic medium so that all these enzymes secreted
by the duodenum as well as the pancreas can perform. Now, notice that this secretion is
yellow in colour. Now, this is because, along with sodium bicarbonate, liver secretes bile
and bile consists of two molecules known as bilirubin and biliverdin. So, what are the
functions of these two molecules? Well, these two molecules help break down bigger molecules
of fat into smaller molecules of fat and this process of breaking down of bigger molecules
of fat into smaller molecules of fat is known as emulsification. Now, after big molecules
of fat gets broken down to the small molecules of fat by the bile, lipase which is secreted
by the pancreas further acts on these small molecules of fat and breaks it down into glycerol
and the fatty acids which can be then absorbed by the body. So, glucose, amino acids and
fat molecules are now small in size and can be absorbed by the body. Now, see glucose
and amino acids get absorbed by the blood vessels present in these structures of the
small intestine but the fat molecules are absorbed by the lymph ducts present inside
these structures. So, these structures, pipe like structures that are present inside the
small intestine is known as the villi. These finger like structures are known as villi.
They are finger like in shape. Now, glucose and amino acids get absorbed in these blood
vessels and so these blood vessels are sugar and protein transporters but the fat molecules
get absorbed by this lymph duct that is present inside the villi. So, this lymph duct is known
as the fat transporter. These villi or finger like structures are mostly present in the
ileum which is the latter portion of the small intestine. Now, the former portion of the
small intestine is known as the jejunum. It is empty and so it helps in the transportation
of the digested food in the small intestine so that it can be absorbed by the villi present
in the ileum. So, the small intestine consists of three parts – the U-shaped portion which
is known as the duodenum, digestion takes place in duodenum because of the enzymes secreted
by the pancreas and the duodenum, jejunum which is this portion of the small intestine
helps in the transport of the digested food and ileum which is the latter portion of the
small intestine helps in the absorption of all the nutrients from the food.

9 thoughts on “Small Intestine

  1. 22 feet long small intestine πŸ˜ΉπŸ˜ΉπŸ€”πŸ€”πŸ˜‚πŸ˜‚πŸ€πŸ€πŸ˜¨πŸ˜¨πŸ˜±πŸ˜±

  2. Is pancreas a part of small intestine because in this video you are talking about small intestine but at the same time you're telling about the enzymes of the pancreas? Please reply soon I've an exam tomorrow

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