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Anatomy - Small Intestine (small bowel)
• Stomach empties into the small intestine
• Extends from
to Large Intestine
• The acidic digestive juices released from the stomach create a
mixture that is released into the small intestine
• Unlike the large intestine, the small intestine normally remains bacteria-free
• Long, coiled looped tube with
long
[thumb]
diameter and up to 8 m
• Fills lower
of abdominal cavity & is attached by a thin membrane
called mesentery [ serves several functions: attaches and supports SI preventing loops
from tangling; carries blood and lymph vessels which supply O2 and remove nutrients]
Small Intestine
• The
of digestion and absorption processes occur in this
area of the digestive tract.
• There is a layer of the intestine that contains a rich supply of
in order to provide the blood an opportunity
to pick up the digested substances
• Resulting nutrient molecules absorbed into circulatory system &
delivered to cells of the body
Villi in the Small Intestine
- The inside wall of the SI
has millions of projections
called
on which
are located
-
Small Intestine
• The small intestine releases about
of fluid a day to produce digestive juices
• Many mucus producing glands called
are located in the
• These glands release secretions that
the small intestine from the acidic
the
stomach releases.
• These glands do not function well during times of stress
.
Absorption of Nutrients
C6H12O6 and aas (
cells of the intestinal wall to the blood stream by
Fig. 6.22
Fig. 6.23
)move through the
Absorption of Nutrients
Glycerol and fatty acid molecules
into the cells of the
intestinal wall where they are resynthesized into fats, coated with
proteins, and move into lymph vessels for eventual transport into the
bloodstream.
Fig. 6.24
Peristalsis
Fig. 6.15
Small Intestine
• The small intestine is made up of three sections:
• Duodenum:
• is about
• receives food from
(stored in gall bladder), and
from the pancreas
• some absorption occurs here
• Jejunum
• is about 2 m long -
• Ileum
• is about 3 m long - mainly absorbtion
• connects to the first part of the LI(
)
long
,
from liver
Small Intestine
• Intestinal Enzymes:
• Intestinal
lining has an important
exocrine function
• The cells in this lining produce many important enzymes that
do the majority of the chemical digestion
• The intestinal enzymes are needed to break nutrients into
their smallest chemical components so they can be absorbed
into the
• Large Molecules- such as most proteins, polysaccharides and
disaccharides are too large to move into the blood stream
• They must first be broken down in the small intestine by the
intestinal enzymes
Intestinal Hormones
• The lining of the duodenum produces an important digestive
hormone called
.
• Increased acidity in the small intestine or nervous activity
causes the release of secretin by the lining of the small
intestine
• The release of secretin into the blood stream causes the nearby
pancreas to step up the production of
juices to
acidic materials that the stomach is beginning to release
Pancreas
• As food moves from the stomach to the small
intestine, soaked in
and pepsin.
• When acids enter the small intestine, a chemical
called
is converted into
.
• Secretin is absorbed into the
and carried to the
, where it
signals the release of a solution containing
• Bicarbonate ions are released by the pancreas and
carried to the small intestine where they
the HCl in gastric juices and raise the pH from about
2.5 to 9.0.
• The basic pH
1. HCl enters the
2. HCl stimulates the conversion of
from the stomach
into secretin
3. Secretin is absorbed into the blood vessels
4. Secretin is carried by the
into the pancreas
5. Here secretin acts as a
release of pancreatic fluids.
, stimulating the
6. The bicarbonate ions released by the pancreas, neutralize the HCl from the stomach. The
neutralization of acid protects the lining of the duodenum
Pancreatic Secretions
• Pancreatic secretions also contain enzymes that promote the breakdown of
the three major components of food
1. Protein: Trypsinogen
- Once trypsinogen reaches the
small intestine, an enzyme called
enterokinase converts the inactive
trypsinogen into trypsin, which acts
on partially digested proteins.
- Trypsin breaks down long-chain
polypeptides into shorter peptide chains.
Pancreatic Secretions
• Erepsin: Released from the pancreas and small intestine
-Complete protein digestion by breaking the bonds between short chain
peptides, releasing individual amino acids
2. Carbohydrates: Amylase
- Continue digestion of carbohydrates which began in the mouth
- Carbohydrates are further broken down by disaccharides from the small
intestine
Pancreatic Secretions
3) Lipids: Lipases
2 Types:
1) Pancreatic Lipase: the most common breaks
down fats into
2) Phospholipase: acts on
Liver and Gallbladder
• The liver continually produces a fluid called
• Bile contains
.
, which help with fat (lipid) digestion.
• When the stomach is empty, bile is stored and concentrated by the
Liver and Gallbladder
1. Fats enter the duodenum (small intestine) and stimulates the release of the
hormone
2. CKK is carried by the
to the gallbladder.
3. CKK stimulates the gallbladder to release
4. Once inside the small intestine the bile salts
large fat globules (
5. Increase surface area 
breakdown fats
(breakdown)
)
further
Liver and Gallbladder
• Bile also contains pigments.
• The liver breaks down
from
stores the products in the gallbladder for removal (poo is brown because of
hemoglobin breakdown)
• Liver stores
and vitamins A, B12 , and D
• The liver is also important in
body.
- Harmful chemicals are made
the blood and
* One of the more
and
many substances in the
and can be dissolved in
.
Liver and Gallbladder Problems
• Cholesterol, an
component of bile. Acts as
a
for the salt crystals found
in bile.
- The
and form larger
crystals called
.
-Gallstones can
the
,
impairing fat digestion and causing pain.
- Any obstruction of the bile duct or accelerated destruction of
RBC can cause
 turns skim and other
tissues yellow
Large Intestine (Colon)
• About 1.5 m long and has a diameter of 7 cm
• Receives
digestion (material unable to pass into bloodstream)
• H2O, Na+ and other minerals are absorbed at the LI as
is formed
• If absorption process is interfered with diarrhea results
[mortality from infant diarrhea, still the main cause if death in infants in many countries,
principally caused by dehydration]
of
Large Intestine
• The large intestine is made up of three distinct sections:
• Transverse colon:
• Ascending colon
• Descending colon
• These colons are designed to go up, across and then down
so that materials move slowly through this area of the GI
tract, which allows for sufficient time to
Large Intestine
• There is an important one-way valve called the
valve that
fecal contents from the colon into the small intestine
• There are
control the
the body.
one-way valve called
• The last of these two sphincters is called the
and is controlled
.
or
that
out of
Large Intestine
• The colon contains a rich supply of
for
the
of water into the blood stream.
• However, there is no villi or microvilli in the large intestine or
enzymatic production; therefore no digestion occurs.
• The main function of the large intestine is to
and to slow the progress of material through
the digestive process.
• The colon also
solids slide through the intestinal tubing
to help
Large Intestine
• LI harbours
bacteria
• break down minerals for which we lack enzymes to digest
• synthesize a.a. and vitamins some of which are absorbed into the
bloodstream
• This organ does not experience continuous peristalsis like the SI
 several times per day it experiences
contractions which move its contents a short distance
• The area of the large intestine that
until they are ready to be released is called the
Four Functions of the Large Intestine
1.
2.
3.
4.
Absorbs water, minerals and salts
Decomposes left-over organic material with the
help of resident bacteria
Produces vitamin B, vitamin K and folic acid
(needed for blood cell production)
Stores and eliminates solid wastes and feces
when appropriate
Anatomy - Anus
• Sphincter
which ends the GI tract
• When the rectum is distended & full, nerve endings in the
walls (stretch receptors) send a message to the
indicating that it is time to void the feces
• The bulk of feces consists of
cells) and
indigestible materials
(mostly dead
along with other
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