The document provides an overview of the human digestive system, including its main components and functions. It describes the mouth, esophagus, stomach, small intestine, large intestine, liver, pancreas, and gallbladder. The digestive system begins with ingestion and breaks down food, absorbs nutrients, and eliminates waste to sustain the body. Key functions include mechanical and chemical breakdown of food, absorption of nutrients into bloodstream, and removal of undigested waste.

1. The Digestive System
(Also called Gastrointestinal or
Alimentary system)

2. Food We Eat - Healthy

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6. Bottlefeeding

7. Breastfeeding

8. Unhealthy Food

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16. Animals We Eat

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25. Animals We are Eaten by

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32. Being Food

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34. Functions
The digestive system begins with the mouth or
the oral (buccal) cavity, where food enters the
body, and terminates at the anus where solid
waste materials leave the body. The functions
of the digestive system are threefold.
1. It prepares food for absorption
2. It absorbs food into the bloodstream
3. It eliminates solid waste materials

35. Preparation of Food for Absorption
The ingested food is in a form that cannot reach the cells because of its
inability to pass through the intestinal mucosa into the
bloodstream. Therefore, the consumed food must be prepared for
absorption.
Digestive enzymes are are substances that speed up chemical reactions
and help in the breakdown (digestion) of complex nutrients:
a) Complex proteins are digested to simpler amino acids;
b) Complex sugars are reduced to simpler sugars, such as glucose;
c) Large fat molecules are broked down to fatty acids and
triglycerides.
Thus, we can define digestion as a complete process of changing the
chemical and physical composition of food in order to facilitate
assimilation of the nourishing ingredients of food by the cells of
the body.

36. Absorption of Food into the
Bloodstream
The digested food must be absorbed into the
bloodstream by passing through the walls of the small
intestine. Within the cells, nutrients are catabolized
(burned) in the presence of oxygen to release energy
stored in the food. Amino acid nutrients are used to
anabolize (build) large protein molecules which are
needed for growth and development of cells. Fatty
acids and triglycerides are also absorbed through the
walls of the small intestine but enter lymphatic vessels
rather than blood vessels. These digested fats
eventtually enter the bloodstream as lymph vessels
join blood vessels in the upper chest region.

37. Elimination of Solid Waste Materials
The third function of the digestive system is to
eliminate solid waste materials that cannot be
absorbed into the bloodstream. These waste
materials are called feces (stools). They are
concentrated in the large intestine and finally
pass out of the body through the anus. This
process is called defecation.

38. Anatomy of the Digestive System

39. The Oral Cavity (Mouth)
The digestive system is composed of the gastrointestinal
tract and accessory digestive organs. The gastrointestinal
tract begins at the oral cavity or mouth. Digestion begins in
the mouth, where chemical and mechanical digestion
occurs. Saliva or spit, produced by the salivary glands
(located under the tongue and near the lower jaw), is
released into the mouth. Saliva begins to break down the
food, moistening it and making it easier to swallow. A
digestive enzyme (called amylase) in the saliva begins to
break down the carbohydrates (starches and sugars). One
of the most important functions of the mouth is chewing.
Chewing allows food to be mashed into a soft mass that is
easier to swallow and digest later.

40. Mouth

41. Tongue

42. Tongue
The structures within the oral cavity are cheeks or
bucca and the tongue and its muscles, which
extend across the floor of the mouth. The main
functions of the tongue are manipulation of food
during chewing process, deglutition or
swallowing, speech production, and
determination of taste. The surface of the tongue
has rough elevations; these elevations are taste
buds. The sense organs are called papillae and
are capable of perceiving a variety of flavors
found in food, such as
bitterness, sweetness, saltiness and sourness.

43. Teeth

44. Teeth
Types of teeth
• The functions of teeth vary, depending on their
individual shape and size and their location in the
jaws. The three basic food processing functions
of the teeth are cutting, holding or grasping, and
grinding.
• Incisors are single-rooted teeth with a relatively
sharp thin edge referred to as the incisal edge.
Located in the front of the mouth, they are
designed to cut food without the application of
heavy forces. Central (front teeth) and lateral
(distal to the centrals) teeth are incisors

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• Canines, also known as cuspids, are located at
the corner of the arch. They are designed for
cutting and tearing foods, which require the
application of force.
• Premolars are a cross between canines and
molars. An older term for premolar is
bicuspid. The pointed cusps hold and grind
the food. They have a broader surface for
chewing food. There are two sets of
premolars in the permanent dentition and NO
premolars in the primary dentition.

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• Molars are much larger than premolars. The
molars have more cusps than other teeth that
are used to chew or grind up food. There are
two sets of molars in the primary dentition
and three sets of molars in the permanent
dentition.

47. Tooth

48. Tooth Structure
Teeth are covered by hard enamel, which gives
them a white and smooth appearance. The
enamel is the hardest substance in the body.
Beneath the enamel is the main structure of the
tooth, the dentin. It is yellowish and is composed
of bony tissue which is softer than enamel.
Dentin is surrounded by a thin layer of modified
bone called cementum. In the innermost part of
the tooth is the pulp, a soft, delicate layer, which
stores the nerves and blood vessels of the tooth.
The teeth are embedded in pink fleshy tissue
known as gums, or gingiva.

49. Tooth_2

50. Other Structures
• Some of the other structures located within the
mouth are the hard and soft palates. The hard
palate lies in the anterrior portion of the roof of
the mouth, while the soft palate lies in its
posterior portion. The soft palate forms a
partition between the mouth and nasopharynx
and is continuous with the hard palate. Rugae are
the irregular ridges in the mucous membrane
covering the anterior portion of the hard palate.
The entire buccal cavity, like the rest of the
digesttive tract, is lined with mucous membrane.

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• After the food is chewed, it is formed into a
round, sticky mass called a bolus. The bolus is
pushed by the tongue from the mouth into
the pharynx. Its downward movement is
guided into the pharynx or throat by the
soft, fleshy V-shaped tissue hanging from the
soft palate, which is called uvula. Uvula also
functions to aid in speech production.

52. Pharynx
The pharynx is a muscular tube which serves as a
common passageway for air from the nasal cavity
to the larynx (voicebox), as well as for food going
from the mouth to the esophagus. The pharynx is
divided into three major sections:
1. The nasopharynx (the throat behind the nose)
2. The oropharynx (the throat behind the moouth)
3. The laryngopharynx (the throat above the
larynx)

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• The laryngopharynx is further divided into two
tubes; one which leads to the lungs, called the
trachea (wind pipe), and one which leads to
the stomach, called the esophagus. A small
flap of tissue, the epiglottis, covers the
trachea. The main function of the epiglottis is
to prevent food from entering the
trachea, thus allowing all food to be
channeled to the stomach through the
esophagus

54. Esophagus

55. Esophagus
• Anatomically and functionally, the esophagus is
the least complex section of the digestive tract.
Its role in digestion is simple: to convey boluses
of food from the pharynx to the stomach. The
esophagus begins as an extension of the pharynx
in the back of the oral cavity. It then courses
down the neck next to the trachea, through the
thoracic cavity, and penetrates the diaphragm to
connect with the stomach in the abdominal
cavity. It uses rhythmic, wave-like muscle
movements (called peristalsis) to force food from
the throat into the stomach.

56. Stomach
The stomach, which is attached to the end of the
esophagus by way of the cardiac sphincter, is a stretchy
sack shaped like the letter J. It is located in the
abdominal cavity directly below the diaphragm. It has
three important jobs:
1. To store the food we have eaten
2. To break down the food into a creamy mixture
3. To slowly empty that creamy mixture into the small
intestine

57. Stomach

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The stomach is like a mixer, churning and
mashing together all the small balls of food
that came down the esophagus into smaller
and smaller pieces. It does this with help from
the strong muscles in the walls of the stomach
and gastric juices that also come from the
stomach's walls. These juices contain enzymes
and hydrochloric acid.

59. Stomach_2

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Pepsin breaks down protein, rennin curdles
milk, while hydrochloric acid kills bacteria that
might be in the eaten food. The creamy
mixture (digested food) which is emptied into
the small intestine through the pyloric
sphincter is called chyme. The sphincter is
designed to open partially so that large
particles are kept in the stomach for further
mixing and breaking down.

61. Small and Large Intestines

62. Small Intestine (small bowel)
Most digestion and absorption of food occurs
in the small intestine. The small intestine is a
narrow, twisting tube that occupies most of
the lower abdomen between the stomach and
the beginning of the large intestine. It extends
about 20 feet in length. The small intestine
consists of 3 parts: the duodenum (the C-
shaped part), the jejunum (the coiled
midsection), and the ileum (the last section).

63. Intestines

64. Duodenum - Pancreas

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• The small intestine has 2 important functions.
First, the digestive process is completed here
by enzymes and other substances made by
intestinal cells, the pancreas, and the liver.
Glands in the intestine walls secrete enzymes
that breakdown starches and sugars. The
pancreas secretes enzymes into the small
intestine that help breakdown
carbohydrates, fats, and proteins.

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The liver produces bile, which is stored in the
gallbladder. Bile helps to make fat molecules
(which otherwise are not soluble in water)
soluble, so they can be absorbed by the body.
Second, the small intestine absorbs the
nutrients from the digestive process. The
inner wall of the small intestine is covered by
millions of tiny fingerlike projections called
villi.

67. Villi

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• The villi are covered with even tinier
projections called microvilli. The combination
of villi and microvilli increase the surface area
of the small intestine greatly, allowing
absorption of nutrients to occur. Undigested
material travels next to the large intestine.

69. Large Intestine

70. The Large Intestine
• The large intestine forms an upside down U
over the coiled small intestine. It begins at the
lower right-hand side of the body and ends on
the lower left-hand side. The large intestine is
about 5-6 feet long. It has 3 parts: the
cecum, the colon, and the rectum. The cecum
is a pouch at the beginning of the large
intestine.

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This area allows food to pass from the small
intestine to the large intestine. The colon is
where fluids and salts are absorbed and extends
from the cecum to the rectum. The large intestine
consists of the following sections:
cecum, ascending colon, transverse
colon, descending colon, sigmoid
colon, rectum, anal cana, and anus.
The last part of the large intestine is the
rectum, which is where feces (waste material) are
stored before leaving the body through the anus.

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• The main job of the large intestine is to
remove water and salts (electrolytes) from the
undigested material and to form solid wastes
that can be excreted. Bacteria in the large
intestine help to break down the undigested
materials. The remaining contents of the large
intestine are moved toward the
rectum, where feces are stored until they
leave the body through the anus as a bowel
movement.

73. Liver
• The liver is the largest gland, and the largest solid
organ in the body, weighing some 1.8 kg in men and
1.3 kg in women. It holds approximately 13% (about
one pint or 0.57 liter) of our total blood supply at any
given moment and is estimated to have over 500
functions. The liver is dark reddish brown in color and
is divided into two main lobes (the much larger right
and the smaller left) which are further subdivided into
approximately 100,000 small lobes, or lobules. It is
located beneath the diaphragm in the right upper
quadrant (RUQ) of the abdominal cavity.

74. Liver

75. Some of the Liver`s Functions
• processing digested food from the intestine
• controlling levels of fats, amino acids and glucose in the blood
• combating infections in the body
• clearing the blood of particles and infections including bacteria
• neutralizing and destroying drugs and toxins
• manufacturing bile
• storing iron, vitamins and other essential chemicals
• breaking down food and turning it into energy
• manufacturing, breaking down and regulating numerous hormones
including sex hormones
• making enzymes and proteins which are responsible for most chemical
reactions in the body, for example those involved in blood clotting and
repair of damaged tissues (e.g. prothrombin, fibrinogen).

76. Pancreas
• The pancreas is both an endocrine gland
(producing several important
hormones, including insulin, glucagon, and
somatostatin), as well as an exocrine
gland, secreting pancreatic juice containing
digestive enzymes that pass to the small
intestine. These enzymes help in the further
breakdown of the carbohydrates, protein, and
fat in the chyme.

78. Gallbladder
• The gallbladder is a pear-shaped sac, usually
stained dark green by the bile it contains. It is
located in the hollow underside of the liver. Its
duct, the cystic duct, joins the hepatic duct
from the liver to form the common bile
duct, which enters the duodenum. The
gallbladder receives bile from the liver and
then concentrates and stores it. It secretes bile
when the small intestine is stimulated by the
entrance of fats.

79. Gallbladder

80. Finished