Download The Digestive System

The Digestive System
T. Zack Crawford
Function of
the Digestive
System
• To break down
large food
molecules into
smaller ones the
body can use
such as
proteins,
carbohydrates,
fats, vitamins
and minerals
Components of the Digestive System –
The Mouth
• The mouth is the first portion of the digestive
system where food enters the body.
• It contains the cavity between the lips and the
pharynx where food can be broken down
physically by a crushing force from the jaw and
teeth and chemically by saliva.
• Salivary glands will secrete saliva into the mouth
which will break down the food with chemical
enzymes wile simultaneously cleaning the mouth.
• The tongue will form the food into a ball-shaped
bolus for swallowing.
The Pharynx and Esophagus
• The pharynx is the part of the neck and throat
behind the mouth and nasal cavity where both air
and food pass.
• Located in the pharynx, the epiglottis closes over
the trachea while food is swallowed to prevent
asphyxiation.
• The esophagus is the muscular tube connecting
the pharynx and stomach as the only pathway for
the food. The bolus remains in the esophagus for
only about 7 seconds.
The Stomach
• The stomach is the muscular pouch which stores
and breaks down the food both physically by
churning and chemically by enzymes such as
pepsin.
• Gastric acid provides an optimal pH for the
reaction with pepsin, along with killing any
microorganisms digested with the food, and
denaturing proteins.
• After leaving the stomach, the food is now in a
semi-liquid form known as chyme.
The Small Intestine
• After leaving the stomach via the pyloric
sphincter, the chyme enters the small intestine,
about 6 meters of tubing folded thousands of
times to fit in al small amount of volume.
• Inside this tubing, there are millions of small
finger-like projections called villi. These are
important for increasing the surface area inside
the intestines for absorption of molecules.
The Small Intestine
• The small intestine is split into three parts.
• The duodenum is the first section of the small
intestine where secretions from the liver and
pancreas are received and chemical digestion
occurs.
• The next two sections, the jejunum and the ileum
are similar in most ways. The ileum is paler in
color, thinner in diameter, and contains a large
number of cells of the immune system, such as
lymphocytes.
The Large Intestine
• After leaving the small intestine, the
remaining food material enters the large
intestine where it is retained over time for its
fermentation by gut bacteria. Some of this
leftover material may be broken down and
absorbed before being hardened and
concentrated into feces.
• The large intestine is a 1.5 meter tube
surrounding the small intestine in an upside
down “U” shape.
The Large Intestine and Anus
• The large intestine is split into 5 parts.
• The first three of these parts are the ascending,
transverse, and descending colon, which are named
after the direction in which the remaining material
flows.
• The sigmoid colon lies directly above the rectum,
within the pelvis.
• The rectum is the final, straight portion of the large
intestine where feces will be stored before defecation.
• The feces will be held within the rectum by the anal
sphincter.
Accessory Digestive Organs
• The Liver creates bile to break down fats and
detoxifies the blood.
• The Gallbladder is a small sack hanging from
the liver which stores bile created by the liver.
• The Pancreas is a long organ, behind the
stomach, that produces insulin and also
enzymes that assist in digestion within the
small intestine.
The Breakdown of Nutrients (Proteins)
• Proteins are digested into polypeptides within
the stomach and duodenum by three
enzymes. Pepsin within the stomach, along
with trypsin and chymotrypsin from the
pancreas.
• The resulting polypeptides will be broken into
amino acids by exopeptidases and
dipeptidases found in the small intestine.
The Breakdown of Nutrients
(Fats and Carbohydrates)
• Fats are broken down into fatty acids by lingual
liptase in saliva, pancreatic liptase, and bile.
• Salivary and pancreatic amylase break down
carbohydrates from polysaccharides to simple
sugars such as glucose and maltose to be
absorbed in the small intestine.
• Also, lactase and sucrase break down lactose and
sucrose (respectively) so that they may be
absorbed by the small intestine.
Physical vs. Chemical Digestion
Digestive Disorders – Lactose intolerance
• Lactose intolerance is the inability to make lactase, and
sub sequentially break down lactose, found in milk, into
glucose and galactose.
• Symptoms include bloating, cramps, flatulence, diarrhea,
nausea, and vomiting after consumption of lactose.
Severity generally increases with an increase in
consumption.
• The disorder is prevalent in approximately half of the
adult population.
• The only real treatment for this disorder is to avoid
consumption of lactose, especially in high concentration.
Try to avoid dairy products, especially with lactose
additives such as low-fat milk.
Digestive Disorders
Gastroesopageal Reflux Disease(GERD)
• GERD refers to transient or permanent damage caused by
stomach acid flowing into the esophagus, usually caused by
abnormal relaxation of the lower esophageal sphincter (LES)
above the stomach or a hiatus hernia (a protrusion of the
upper part of the stomach into the thorax via a weakness in
the diaphragm)
• Symptoms include heartburn, vomiting, and trouble
swallowing
• GERD could be prevalent in up to 20% of the western
population
• GERD can be prevented or treated by eating smaller, less
acidic meals, losing weight, or elevating your upper body.
• As a last resort, GERD can be suppressed by a surgery known
as Nissen fundoplication where the LES is strengthened by
wrapping the upper part of the stomach around it.
Bibliography
http://en.wikipedia.org/wiki/Digestive_system
http://science.nationalgeographic.com/science/health-and-humanbody/human-body/digestive-system-article/
http://en.wikipedia.org/wiki/Human_mouth
http://upload.wikimedia.org/wikipedia/commons/c/c5/Digestive_syst
em_diagram_edit.svg
http://en.wikipedia.org/wiki/Jejunum and
http://en.wikipedia.org/wiki/Ileum
http://en.wikipedia.org/wiki/Sphincters
http://en.wikipedia.org/wiki/Lactose_intolerance
http://en.wikipedia.org/wiki/Gastroesophageal_reflux_disease
All accessed on 1/21/13