Food is broken down by the teeth and mixed with saliva with the help of salivary glands. It contains salivary amylase which breakdown the carbohydrate into smaller pieces. The mixture of food and saliva is called bolus. The bolus is pushed into throat and into the esophagus The esophageal lumen is flexible and allows different size of bolus to transfer from mouth to the stomach. The outer muscle layer of esophagus is responsible for peristalsis, which is the bolus can transport to the stomach from the mouth even if the person is standing on his head. Peristalsis is the contraction and relaxation of the esophageal lumen to transfer the bolus into the stomach. The stomach has outer longitudinal muscle layer, middle circular muscle fibre and inner oblique muscle layer; covered by the rugae of mucosa. The stomach wall contains gastric gland which produce the mucosa to protect the stomach from the gastric acid. On seeing or smelling the food, the stomach expand and produce gastric juice. 1-2 liter of gastric juice is produced daily. Since the esophagus does not contain the protective mucosal layer, the esophagus and the stomach is separated by the sphincter. The sphincter relaxes when the bolus is pushed from the esophagus to the stomach and contracts to prevent the gastric acid and the bolus to move upward to the esophagus. Through gastric juice and stomach movement which occur approximately every 20 seconds, the individual bolus is converted into semi fluid partly digested food called chyme. The pyloric sphincter open only few millimeters so that the large particles remain inside the stomach and the chyme enters the first section of small intestine that is duodenum. The duodenum and jejunum have circular folds to increase the contact surface with the food. It is covered with small finger like projection called villi, which is 1 milli meter long. The villus has both blood capillaries and lymphatic capillaries called lacteal. The nutrients are absorbed by the villi and transported to the blood capillaries The small intestine and large intestine is separated by ileocecal valve. The chyme enters the large intestine via the ileocecal valve. The large intestine does not have villi but it has 100 billion bacteria responsible for various processes such as production of vitamins and digestion of fibre. These bacteria are important part of immune system by killing harmful germs. Through peristalsis, the chyme is moved from the ascending colon to the transverse colon and to the descending colon. Water is removed from the chyme on its way through large intestine and mucus is added for the better excretion of waste. The substance that cannot be absorbed by the small intestine and large intestine is collected in rectum and excreted via anus.

1. Digestive system
Vasugi . M
vaisuvasu07@gmail.com

2. Mouth
Food is broken down by the teeth and mixed with saliva with the help of salivary glands. It
contains salivary amylase which breakdown the carbohydrate into smaller pieces. The
mixture of food and saliva is called bolus. The bolus is pushed into throat and into the
esophagus

3. Esophagus
The esophageal lumen is flexible and allows different size of bolus to transfer from mouth
to the stomach. The outer muscle layer of esophagus is responsible for peristalsis, which is
the bolus can transport to the stomach from the mouth even if the person is standing on his
head. Peristalsis is the contraction and relaxation of the esophageal lumen to transfer the
bolus into the stomach.

4. Stomach
The stomach is divided into,
Ø Cardia
Ø Fundus
Ø Body
Ø Pyloric antrum
Ø Pyloric canal

5. The stomach has outer longitudinal muscle layer, middle circular muscle fibre and inner
oblique muscle layer; covered by the rugae of mucosa. The stomach wall contains gastric
gland which produce the mucosa to protect the stomach from the gastric acid. On seeing or
smelling the food, the stomach expand and produce gastric juice.
1-2 liter of gastric juice is produced daily. Since the esophagus does not contain the
protective mucosal layer, the esophagus and the stomach is separated by the sphincter. The
sphincter relaxes when the bolus is pushed from the esophagus to the stomach and
contracts to prevent the gastric acid and the bolus to move upward to the esophagus.

6. The gastric juice consists of, HCL, Pepsin, Intrinsic factor, Lipase
● HCL kills the bacteria in the food. It also converts the pepsinogen produced by the
gastric gland to pepsin
● Pepsin helps the breakdown of protein
● Intrinsic factor is combined to the vitamin b12 for its absorption in the small intestine
(vitamin b12 is responsible for the nerve and blood cells healthy and also helps making
DNA)
● Lipase breakdown the triglycerides into diglycerides and a free fatty acid. The effective
digestion of triglycerides takes place in the small intestine

7. Through gastric juice and stomach movement which occur approximately every 20
seconds, the individual bolus is converted into semi fluid partly digested food called
chyme. The pyloric sphincter open only few millimeters so that the large particles remain
inside the stomach and the chyme enters the first section of small intestine that is
duodenum.

8. Small intestine
Bile and pancreatic secretion enters the duodenum via ampulla of vater and mix with
the chyme. The bile secreted by liver and stored in gallbladder. The pancreatic secretions have
digestive proenzymes and enzymes. Pancreatic juice contains sodium hydrogen carbonate, the
hydrogen carbonate alter the ph of the chyme and brings an optimum ph level of 7 or 8.
Through enterokinase released by duodenal wall, the proenzyme, trypsinogen is converted to
trypsin, which is responsible for the protein breakdown and activation of other trypsinogen.
o Alpha amylase converts the glucose into maltose and isomaltose
o Pancreatic lipase breaks the triglyceride into 2 free fatty acids since the bile can breakdown
the fat in to tiny droplets, it is known as emulsification.

9. The small intestine is divided into
· Duodenum
· Jejunum
· Ileum

10. The duodenum and jejunum have circular folds to increase the contact surface with the
food. It is covered with small finger like projection called villi, which is 1 milli meter long.
The villus has both blood capillaries and lymphatic capillaries called lacteal. The nutrients
are absorbed by the villi and transported to the blood capillaries.
 Glucose does not require carrier and it can be transported free in the blood stream
 Iron requires a carrier protein, transferrin
 Lipid is transported by chylomicron, which is a lipoprotein. The triglycerides are
enclosed inside the lipoprotein. The chylomicron and triglyceride is transported via
the lacteal of the villi.
Each villus has many microvilli which absorbs the nutrients and transfer inside it.

11. The last part of small intestine is the ileum, which does not have circular folds and
responsible for the absorption of electrolyte such as calcium for the formation of bones,
teeth and hair. It responsible for the absorption of trace elements such as; zinc for sperm
production and immune system, vitamin b12 for the formation and maturation of RBC.
The remaining bile salts are transferred back to the liver via the blood stream.
The chyme is mixed by segmentation contraction
The small intestine and large intestine is separated by ileocecal valve. The chyme enters
the large intestine via the ileocecal valve.

12. Large intestine
The large intestine does not have villi but it has 100 billion bacteria responsible
for various processes such as production of vitamins and digestion of fibre. These bacteria
are important part of immune system by killing harmful germs. Through peristalsis, the
chyme is moved from the ascending colon to the transverse colon and to the descending
colon. Water is removed from the chyme on its way through large intestine and mucus is
added for the better excretion of waste. The substance that cannot be absorbed by the small
intestine and large intestine is collected in rectum and excreted via anus.

13. Thank you