Lesson 2 The Digestive system -Functions of Digestive system -Digestion -Types of Digestion -Enzymes -The role of Enzymes in Digestion -Organs of Digestive system -The Mouth -the Esophagus -Peristalsis -The Stomach -Chyme -the Small Intestine -Villi -the Large intestine -Bacteria and Digestion -the Digestive system and Homeostasis -Common Ailments and Disorders of the Digestive system

1. The Digestive
System
Grade 7 Biology
Prepared and Presented By:
Lerma P. Pendon

2. FUNCTIONS OF THE
DIGESTIVE SYSTEM
There are 4 main steps of digestion in the human
body:
1. Ingestion is the act of eating or putting food in your
mouth.
2. Digestion is the mechanical and chemical breakdown
of food into small particles and molecules that your body
can absorb and use.
3. Absorption occurs when the cells of the digestive
system take in small molecules of digested food.
4. Elimination or excretion is the removal of
undigested food and other wastes from your body.

3. TYPES OF DIGESTION
There are 2 types of digestion:
1. Mechanical Digestion
- food is physically broken into smaller pieces.
- digestion happens when you chew, mash, and
grind food with your teeth and tongue.
2. Chemical Digestion
- chemical reactions break down pieces of food
into small molecules.

4. ENZYMES
• Chemical digestion cannot occur without substances called
enzymes.
• Enzymes are proteins that help break down larger molecules into
smaller molecules.
• Enzymes also speed up or catalyze the rate of chemical reactions.
• Without enzymes, some chemical reactions would be too slow or
would not occur at all.

5. The Role of Enzymes in Digestion
• Amylase helps break down
carbohydrates into sugars or glucose. It
is produced by the salivary glands and
pancreas.
• Pepsin helps break down proteins. It is
produced in our stomach.
• Lipase helps break down fats. It is
produced in the pancreas, mouth, and
stomach.

7. ORGANS OF THE DIGESTIVE SYSTEM
• Two Parts of the Digestive System:
1. Digestive Tract
- it extends from the mouth to the anus.
- the mouth and anus are the two openings of the digestive tract.
2. Accessory Organs
- organs that help the body break down and absorb food.
- these organs include the tongue, salivary glands, liver, gallbladder, and pancreas.

8. Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large Intestine
Rectum
Anus
• The digestive tract is made up of:

9. Mouth
• The teeth mechanically break down food into
small pieces.
• Tongue mixes food with saliva (contains amylase,
which helps break down starch).
• The mouth is responsible for mastication.
Mastication is the process of chewing. Also
known as mechanical digestion.
• Bolus is the product mechanical digestion.

10. Pharynx
• Also called the throat.
• Pharynx is the portion of the digestive tract that receives
the food from your mouth.
• Its muscular walls function in the process of
swallowing, and it serves as a pathway for the
movement of food from the mouth to the esophagus.
• Epiglottis is a flap-like structure at the back of the
throat that closes the windpipe over the trachea
preventing food from entering it.

11. Esophagus
• A muscular tube that connects the mouth to the
stomach. Approximately 10 inches long.
• It moves the food from the throat to the stomach
using muscle movement called peristalsis.
• Peristalsis is a wavelike contraction from the
esophagus to the large intestine.
• At the inferior end of the esophagus is a muscular
ring called cardio-esophageal sphincter.
• The function of this sphincter is to close the end of
the esophagus and prevent the backflow of food
from the stomach to the esophagus.

12. Stomach
• A large and hollow organ, located on the left side of the
abdominal cavity.
• This major organ acts as temporary storage for food so that
the body has time to digest large meals properly.
• The stomach contains an acidic fluid called gastric juice. The
gastric juice makes the stomach acidic.
• It mixes food with digestive juices that contain enzymes such as
lipase to break down proteins and lipids, the process is called
chemical digestion.
• The product of chemical digestion is called Chyme.
• Chyme is a watery liquid that passes from the stomach to the
small intestine, consisting of gastric juices and partly digested
food.

13. Small Intestine
• It is a long, thin tube connected to the stomach. It
measures about 2.5 cm long.
• 3 Parts of the Small Intestine:
• Duodenum – chemical digestion of proteins,
carbohydrates, nucleic acids, and fats takes place.
• Jejunum - breaking down and absorbing
nutrients from food.
• Ileum - most water and nutrients are absorbed.
• The folds of the small intestine are covered with
fingerlike projections called villi.

14. • The villi contain blood
vessels.
• Nutrients in the small
intestine diffused into the
blood cells through these
blood vessels.
• Then, your circulatory
system passes them on to
other parts of your body to
store or use.
Villi (villus, singular)

15. The Pancreas, Liver
and Gallbladder
• The pancreas and the liver produce substances
that enter the small intestine and help with
chemical digestion.
• The pancreas produces an enzyme called
amylase that helps break down carbohydrates
and a substance that neutralizes stomach acid.
• The liver produces a substance called bile.
Bile makes it easier to digest fats.
• The gallbladder stores bile until it is needed in
the small intestine.

16. Large Intestine
• It is a long, thick tube about 1.5 meters
long, it is much shorter than the small
intestine.
• Materials that pass through the large
intestine are the waste products of
digestion.
• The waste products become more solid
as excess water is absorbed. It is where
the feces are formed.
• Large intestine is also called the
“Colon”.

17. Rectum
• Peristalsis continues to force the remaining
semisolid waste material into the last section of
the large intestine called the rectum.
• The final straight portion of the large intestine,
approximately 6 inches long.
• The rectum is a continuation of the large
intestine and connects to the anus.
• For temporary storage of feces.
• To expel solid and gaseous waste from the
gastrointestinal tract.
• Anal Sphincter – prevents the release of
feces/wastes.

18. Anus
• The anus is the last part of the digestive tract. It is a 2-inch-
long canal consisting of the pelvic floor muscles and the two
anal sphincters (internal and external).
• The lining of the upper anus is specialized to detect rectal
contents. It lets you know whether the contents are liquid,
gas, or solid.
• The internal sphincter is always tight, except when stool enters
the rectum. It prevents us from pooping involuntarily when
we are asleep or otherwise unaware of the presence of stool.
• When we get an urge to go to the bathroom, we rely on our
external sphincter to hold the stool until reaching a toilet, where
it then relaxes to release the feces or wastes.

19. Bacteria and
Digestion
• It's perfectly normal for poop to have an unpleasant
odor. The smell comes from bacteria in the colon
that help break down digested food.
• Some bacteria have an important role in the
digestive system.
• The large intestine absorbs water and contains many
symbiotic bacteria that aid in the breaking down of
wastes to extract some small amounts of nutrients.
• Some bacteria digest food and produce important
vitamins and amino acids.
• Bacteria in the intestines are essential for proper
digestion.

20. The Digestive System and Homeostasis
• Homeostasis is the balance our body maintains to function properly.
• Recall that nutrients from the food are absorbed in the small intestine.
• The digestive system must be functioning properly for this absorption to occur.
• These nutrients are necessary for other body systems to maintain homeostasis.
• For example, the blood in the circulatory system absorbs the products of digestion.
The blood carries the nutrients to all other body systems providing them with
materials that contain energy.

21. Common Ailments and
Disorders of the Digestive
System
• Gastroesophageal reflux
disease (GERD) is a
condition in which the
acid from the stomach
enters the esophagus this
is also referred to as
heartburn.

22. Common Ailments
and Disorders of the
Digestive System
• Gastritis or ulcer is a sore or
inflammation in the lining of
the stomach that is mostly
caused by the bacteria,
Helicobacter pylori.
• It causes pain and discomfort
in the lower part of the
stomach.
• It could be an acute or
chronic condition.

23. Common Ailments
and Disorders of the
Digestive System
• Diarrhea is not a disease, but a
symptom characterized by the frequent
passage of stools.
• It may be caused by contaminated food
and water or an intestinal disorder like
the irritation of the colon.
• If you have diarrhea, you must drink a
lot of water to replenish the water that
has been lost by the body.

24. Common Ailments
and Disorders of the
Digestive System
• Indigestion is a type of
discomfort felt along the
upper part of the
abdomen.
• This happens when a
person eats too much or
too quickly.
• It can be avoided by
eating slowly and regularly.

25. Common Ailments and Disorders of
the Digestive System
• Flatulence is caused by a buildup of gas in the
abdomen when you eat quickly and swallow
large chunks of food without properly chewing
it.
• Stress can also aggravate flatulence which can
cause discomfort and belching.

26. Common Ailments and Disorders of the
Digestive System
• Constipation is when you cannot move your
bowels regularly and have difficulty moving
them out. You are constipated.
• This can be remedied by ensuring regular bowel
movement, drinking enough water during the
day, and eating a lot of fibrous foods which
serve as a broom that cleans the digestive tube.