bio 120

1. Digestive System
Chapter 8
Sierra Lewis

2. Digestive system
 The digestive system begins breaking down food
through mechanical and chemical digestion. After
digested molecules are absorbed into the body
and enter the blood stream. Any food not
digested is eliminated as solid waste.

3. Stomach
 The stomach is an organ of digestion. It has a
saclike shape and is located between the
esophagus and the intestines. The human
stomach is a muscular, elastic, pear-shaped bag,
lying crosswise in the abdominal cavity beneath
the diaphragm. It changes size and shape
according to is position of the body and the
amount of food inside. The stomach is about 12
inches (30.5 cm) long and is 6 inches. (15.2 cm)
wide at its widest point. The stomach's capacity is
about 1 qt (0.94 liters) in an adult.

4. Stomach cont….
 Food enters the stomach from the esophagus. The
connection between the stomach and the esophagus
is called the cardiac sphincter. Once the food enters
the stomach, gastric juices are used to break down
the food. Some substances are absorbed muscle
lining of the stomach. The stomach is composed of
five layers. Starting from the inside and working our
way out, the innermost layer is called the mucosa.
Stomach acid and digestive juices are made in the
mucosa layer. The next layer is called the
submucosa. The submucosa is surrounded by the
muscularis, a layer of muscle that moves and mixes
the stomach contents. The next two layers, the
subserosa and the serosa are the wrapping for the

5. Pancreas
 The pancreas is a glandular organ that secretes
digestive enzymes and hormones. In humans, the
pancreas is a yellowish organ about 7 inches
(17.8 cm) long and 1.5 inches. (3.8 cm) wide. The
pancreas lies beneath the stomach and is
connected to the small intestine at the duodenum

6. Pancreas cont….
 The pancreas contains enzyme producing cells
that secrete two hormones. The two hormones
are insulin and glucagon. Insulin and glucagon
are secreted directly into the bloodstream, and
together, they regulate the level of glucose in the
blood. The pancreas produces the body's most
important enzymes. The enzymes are designed
to digest foods and break down starches. If the
pancreas is not working properly to neutralize
chyme and break down proteins, fats and starch,
starvation may occur.

7. liver
 The liver is the largest glandular organ of the
body. It weighs about 3 lb (1.36 kg). It is reddish
brown in color and is divided into four lobes of
unequal size and shape. The liver lies on the right
side of the abdominal cavity beneath the
diaphragm. Liver tissue is composed of
thousands of lobules, and each lobule is made up
of hepatic cells, the basic metabolic cells of the
liver.

8. Liver cont…
 The liver has many functions. Some of the
functions are: to produce substances that break
down fats, convert glucose to glycogen, produce
urea (the main substance of urine), make certain
amino acids. The liver is also responsible for
producing cholesterol. It produces about 80% of
the cholesterol in your body.

9. The small intestine
 The small intestine is the portal for absorption of
virtually all nutrients into blood. Accomplishing
this transport entails breaking down large
supramolecular aggregates into small molecules
that can be transported across the epithelium. By
the time ingesta reaches the small intestine,
foodstuffs have been mechanically broken down
and reduced to a liquid by mastication and
grinding in the stomach. The final stages of
digestion occur on the surface of the small
intestinal epithelium.