Download The Digestive System

Flashcard Warm-up 31
Digestive system : made of the alimentary
canal (a.k.a, the gastrointestinal tract)
and the accessory digestive organs.
The alimentary canal consists of the following organs:
Mouth, Pharynx, Esophagus, Stomach, Small intestine,
Large intestine, and Anus
Accessory digestive organs: (organs that help in the
digestive process are) : salivary glands, teeth, pancreas,
liver and gallbladder.
The Digestive System

Anatomy of the Digestive System
The organs of the digestive system can be separated into two
main groups: the alimentary canal (also called the
gastrointestinal tract) and the accessory digestive organs.
B.
The alimentary canal consists of the following organs: Mouth,
Pharynx, Esophagus, Stomach, Small intestine, Large
intestine, and Anus
1) Mouth- where the food enters the body. The hard palate
forms the anterior roof, while the soft palate forms the
posterior roof of the mouth. The muscular tongue aids in
swallowing foods.
2) Pharynx- serves as passageway for food and air. Food
movement is by alternating contractions of the muscle
layers (peristalsis).
3) Esophagus- the passageway for food only that runs from
pharynx to stomach through the diaphragm, Conducts food
by peristalsis (slow rhythmic squeezing)
Digestive System
A.
4) Stomach- located on the left side of the abdominal cavity. Acts as a
storage tank for food, a site of food breakdown, chemical
breakdown of protein begins, delivers chyme (processed food) to
the small intestine.
a)
Food enters at the cardioesophageal sphincter then enters
regions of the stomach. Food empties into the small intestine
at the pyloric sphincter. The internal folds of the stomach
mucosa are called rugae.
5) Small Intestine- The body’s major digestive organ, because nearly all
nutrient absorption from food occurs in the small intestine. This
muscular tube can extend 6-13 feet in a living person. There are
three subdivision of the small intestine:
a)
Duodenum- Attached to the stomach and curves around the
head of the pancreas
b)
Jejunum- attaches anteriorly to the duodenum
c)
d)
Ileum- extends from jejenum to the large intestine
The small intestine also contains absorptive cells called villi.
These are fingerlike projections that has a rich capillary bed
where the digested foodstuffs are absorbed.
6) Large Intestine- Larger in diameter, but shorter than the small
intestine this tube extends only 5 feet. Its major functions are to
dry out the indigestible food residue by absorbing water and to
eliminate these residues from the body as feces. Structures of the
large intestine include:
a)
Cecum – saclike first part of the large intestine
b)
Appendix- Accumulation of lymphatic tissue that sometimes
becomes inflamed (appendicitis) and hangs from the cecum
c)
Colon- includes the ascending, transverse, descending and
sigmoid regions.
d)
Rectum and the anal canal (external opening)
C. Accessory digestive organs include the salivary glands, teeth,
pancreas, liver and gallbladder.
1.
Salivary glands- contain an enzyme, salivary amylase that
begins the process of starch digestion. The saliva also helps
bind food together into a mass called a bolus which makes
chewing and swallowing easier.
2.
Teeth- aid in mastication, or chewing. This tears and grinds
the food breaking it down into smaller pieces.
3.
Pancreas- produces a wide variety of enzymes to help break
down food. The enzymes are secreted into the duodenum in
an alkaline fluid, which neutralizes the acidic chyme coming in
from the stomach. The pancreas also produces the hormones
insulin and glucagon.
4.
Liver- The largest organ in your body!! It is located under the
diaphragm more to the right side of the body. The liver is
connected to the gall bladder via the common hepatic duct.
This large organ has many metabolic and regulatory roles,
however, its digestive function is to produce bile.
Bile is a yellow to green watery solution that contains bile
salts, bile pigments (bilirubin a breakdown product of
hemoglobin), cholesterol, phospholipids, and a variety of
electrolytes. The bile salts help to emulsify fats by physically
breaking large fat globules into smaller ones.
5) Gall Bladder- a thin-walled green sac that sits in the inferior surface
of the liver. When food digestion is not occurring bile backs up
in the cystic duct and enters the gall bladder where it is stored.
If bile is stored for too long or too much water is removed, the
cholesterol it contains crystallize to form gallstones.
Digestion Animation
II. Overview of Gastrointestinal Processes
A.
Ingestion- putting the food into your mouth! Then, mechanical
digestion and chemical digestion begins. The enzyme salivary
amylase in your saliva begins to break down starches. No
food absorption occurs in the mouth. Food Propulsion- The
processes that move food to the next digestive organ.
a.
This includes swallowing, peristalsis and segmentation.
Howstuffworks "Peristalsis"
1. Peristalsis- involuntary alternating contraction and relaxation of
muscles to squeeze the food through the digestive tract. The
stomach squirts 3 ml or less of chyme into the small intestine at a
time.
2. Segmentation- single segments of the intestine alternately
contract and relax. Because active segments are separated the
food is moved forward and then backward. This mixes the food
rather than simply propelling through the tract.
Digestive Process
B. Food Breakdown: Mechanical digestion is mixing of food in the
mouth by the tongue, churning of food in the stomach, and
segmentation in the small intestine. This prepares the food for
chemical digestion.
1. Activities of the stomach- secreting gastric juice through
sight, smell or taste of food. Two to three liters or gastric juice are
produced a day. Hydrochloric acid is also released in the stomach.
C. Food Breakdown: Chemical Digestion- Enzymes break down food
products into their building blocks. Enzymes are located in saliva,
stomach, and the pancreas releases enzymes into the intestines
that help break down the food. The pancreas enzymes are
totally responsible for fat digestion with the enzyme lipase.
1. Carbohydrates are broken into monosaccharides (simple
sugars).
2. Proteins are broken down into amino acids.
3. Lipids are broken down into fatty acids and glycerol.
a) Absorption- The small intestine is the main site
where food is absorbed into the blood or lymph. The
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III. Activities occurring through the digestive tract
Digestion animation
A.
Activities occurring in the mouth, Pharynx, and esophagus
1. Once food is placed in the mouth the physical
breakdown begins by chewing. Salivary amylase also
contributes to the breakdown of starches and to moisten the
food to make swallowing and digestion an easier process.
2. Swallowing or deglutition is aided by the tongue, soft
palate, pharynx and esophagus. Once the bolus is forced
into the pharynx by the tongue we no longer have conscious
control and are into the realm of our reflex activity.
3. The epiglottis closes off the trachea to ensure we do not
choke on our food.
4. Food is moved down through the esophagus through
peristaltic contractions.
B. Activities in the Stomach
1.
The food then reaches the stomach passing through the
cardioesophageal sphincter. As the food enters the stomach the
walls begins to stretch and the secretion of gastric juices begins.
In addition, the presence of food and falling pH levels in the
stomach stimulate the stomach cells to secrete the hormone
gastrin, prodding the stomach to produce more of the proteindigesting enzymes, mucus and hydrochloric acid. 2 to 3 liters of
gastric juice are secreted everyday.
a. Occasionally the cardioesophageal sphincter fails to close
tightly and gastric juice backs up in the esophagus. This is
commonly called heartburn. If the acids in the stomach begin
digesting the stomach itself this is called an ulcer.
2. The stomach works to compress and pummel the food breaking it
apart physically. The chemical digestion of proteins also begins
in the stomach using enzymes called pepsin.
Flashcard Warm-up
 Location
of carbohydrate, protein, and
lipid breakdown by enzymes
 Use
your notes and book to write down
enzyme names and the location where
they are breaking down the food that we
eat
3.
C.
Once the food is well mixed a rippling peristalsis begins in the
lower half of the stomach. The pylorus holds about 30 mL of
chyme, and each contraction squirts only 3 mL through the pyloric
sphincter into the small intestine. The emptying of the stomach
takes about 4 hours after a well-balanced meal, and 6 after a high
fat meal to empty.
Activities of the small intestine
1. Once food reaches the small intestine it is only partially
digested. Carbohydrate and protein digestion has begun but no
fat has been digested at this point. The journey through the small
intestine will take about 3 to 6 hours to complete. Food will be
moved through the small intestine using peristaltic contractions
and segmented movements to mix the chyme and propel through.
2. The microvilli of the small intestine have important enzymes,
known as brush border enzymes that break down double sugars
into simple sugars and complete protein digestion.
Pancreatic juices are also enzyme rich and delivered to the small
intestine to complete the digestion of starch, protein, and are
totally responsible for fat digestion using lipases, and digest
nucleic acids. The pancreatic juice also contains bicarbonate
which neutralizes the acidity of the chyme.
4. The two hormones that regulate the release of pancreatic juice into
the small intestine are secretin and cholecystokinin.
5. Bile also plays a role in fat digestion but is not an enzyme. It acts to
emulsify or help break down large fat globules.
6.
Absorption of some water and end products then occurs
throughout the passage through the small intestine through the
villi. At the end of the ileum all that remains is the indigestible
3.
food materials and large amounts of bacteria.
D. Activities of the Large Intestine
1. The food enters the large intestine through the ileocecal
valve. When the residue is delivered here it still has another 12-24
hours to spend there.
2. The “resident” bacteria then metabolize some of the
remaining nutrients and release gases.
3. Water is absorbed from the residue.
4. Peristalsis and mass movements (slow-moving powerful
contractile waves that move over the colon three to four times a day)
are the two propulsive movements occurring in the large intestine.
Bulk, or fiber, increases the strength of colon contractions softening
the stool and allowing the colon to function properly.
5. Watery stools or diarrhea results when food passes through
the large intestine before water can be absorbed. If food remains in
the large intestine for extended periods too much water is absorbed
and the stool becomes difficult to pass. This is called constipation,
usually due to low fiber diets, “failing to heed the call”, and laxative
abuse.