This document provides an overview of the human digestive system and the process of digestion. It discusses the main parts of the digestive system including the mouth, stomach, liver, pancreas, small intestine and large intestine. It describes the role of each organ in further breaking down food through mechanical and chemical digestion. Key enzymes and fluids involved in digestion at each stage are also outlined, such as saliva in the mouth, gastric juices in the stomach, bile from the liver and pancreatic juices. The small intestine is highlighted as the primary site of nutrient absorption into the bloodstream.

1. SCIENCES
BIOLOGY
LIFE PROCESSES - DIGESTION
By,
D. Sesharanjith,
X Topaz,
Shree Niketan Patasala.
BIBLIOGRAPHY : www.learnnext.com
Google images
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2. TOPICS TO BE DISCUSSED:
 Life processes
 Nutrition in human beings
 Human alimentary canal
 Buccal cavity
 Stomach
 Liver
 Pancreas
 Small intestine
 Large intestine
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3. LIFE PROCESSES
 The word life processes means the processes take place
in the human body which are needed for the existence of
life on Earth.
 Four main life processes are as follows:
1. Nutrition
2. Respiration
3. Transportation
4. Excretion
 In this ppt, we will see about Nutrition in human beings.
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4. NUTRITION IN HUMAN BEINGS
 The nutrition in human beings takes place through
human digestive system.
 Digestion: The process of breaking down complex food
substances into simple molecules is called as digestion.
 Digestive system in human beings consists of alimentary
canal and digestive glands.
1. Alimentary canal is made up of mouth, pharynx,
oesophagus, stomach, intestine, rectum and anus.
2. The digestive glands are the salivary glands, the gastric
glands, the liver, the pancreas and the intestinal glands.
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6. BUCCAL CAVITY
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 Digestion in buccal cavity is brought about by three pairs
of salivary glands opening into the oral cavity.
1. Salivary glands include submaxillary, sublingual and
parotid glands.
2. Amylase, a digestive enzyme in saliva, breaks down the
starch in food into simpler sugar.
3. Saliva also prevents tooth decay due to the presence of
amylase, lysozyme and minerals.
 Peristalsis includes a series of muscular contractions in
the oesophagus that push food forward to the stomach.

7. STOMACH
 The stomach is divided into three compartments namely
cardiac, fundus and pylorus.
 The junction of oesophagus and stomach is guarded by
valve which does not allow the food to travel in
backward direction.
1. In the stomach, food is mixed with the gastric juices
secreted by the gastric glands.
2. Gastric juice is a combination of hydrochloric acid,
enzymes like pepsin, lipase and mucus.
3. Partially digested food in stomach becomes acidic and
is known as chyme.
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8. LIVER
 Liver is the largest gland in our body.
 The liver secretes a yellowish green watery fluid called
bile.
 It is temporarily stored in a sac called the gall bladder.
 Bile plays an important role in the digestion of fats.
 Bile is sent into duodenum through a narrow tube-like
structure called the bile duct.
 Bile breaks the larger fat molecules into tiny droplets,
thereby increasing their surface area, which helps in the
digestion of fats easily.
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9.  Bile is a dark green alkaline fluid secreted by liver.
 It comprises of water, bile salts, bile pigments, fats and
inorganic salts.
 Bile comprises of yellow pigment bilirubin which
oxidizes to form green pigment biliverdin only when it
enters the intestine.
1. Bile makes the food alkaline for the action of
pancreatic and intestinal enzymes in the small intestine.
2. Bile brings about emulsification of fats which are later
digested by intestinal lipases.
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10. PANCREAS
 Pancreas is the mixed gland. It acts as a both endocrine
and exocrine gland.
 The pancreas secretes the pancreatic juice that helps to
digest carbohydrates, proteins and fats.
 The pancreatic juice converts carbohydrates into simple
sugars and glucose, proteins into amino acids, and the
lipids into fatty acids and glycerol.
 The exocrine part of pancreas secretes pancreatic juice
which includes trypsin and lipase that help break down
proteins and fats.
 Liver and pancreas open into intestine through hepato-
pancreatic duct to throw their secretions for further
digestion of food. 10

11. SMALL INTESTINE
 Small intestine is made up of three regions namely
duodenum, jejunum and ileum.
 Acidic chyme from the stomach is received by the
duodenum for further digestion.
 Duodenum receives bile from the liver. Bile provides an
alkaline environment for many enzymes to get active.
 It also reduces the acidity of chyme. Bile plays an
important role in the digestion of fats.
 Duodenum also receives pancreatic secretions which
help in the digestion of food.
 Pancreas secretes the pancreatic juice that helps to digest
carbohydrates, proteins and fats.
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12.  Duodenum also secretes some enzymes on its own. Cells
lining the inner lining of intestine secrete enzyme rich
intestinal juice.
 Intestinal juice comprises of many enzymes like
enterokinase, invertase, maltase and lipase.
 The intestinal enzymes act upon partially digested
proteins, carbohydrates and fats.
 All these substances bring about digestion of food in the
duodenum.
 The inner walls of small intestine are thrown into many
folds which have millions of small finger like projections
called villi.
 The intestinal enzymes such as invertase, maltase and
lipase act upon partially digested proteins, carbohydrates
and fats. 12

13.  Proteins, carbohydrates and fats are simplified into
amino acids, glucose, fatty acids and glycerol in a liquid
medium known as chyme.
 Specific structures called as villi in the small intestine
increase its surface area to ensure efficient and rapid
absorption of nutrients.
 Villi increase the surface area for digestion as well as
absorption of digested food by eight times.
 Blood capillaries in the villi absorb nutrients and
transport the food to all the cells in the body.
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14. LARGE INTESTINE
 The large intestine comprises caecum, appendix, colon,
rectum and anus.
 The large intestine absorbs water from undigested food
and forms solid waste.
 The rectum stores the solid excreta until it is ready to be
excreted from the digestive system through anus.
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