Digestive System
Digestive System
Structures involved in digestive
system
• The digestive system of mammals
consists of the following:
-(mouth, oral cavity, pharynx, esophagus,
stomach, small intestine, large intestine,
rectum, anus)
-also includes other associated
structures/organs/glands (salivary
glands, gall bladder, liver, pancreas).
Function of Digestive System
• Digestion is the process of breaking
down food into molecules small
enough for the body to absorb.
Oral Cavity
• hard palate: has ridges; separates the oral
cavity from the nasal cavities
• soft palate: soft because there is no bone
underneath (nasopharynx lies above it)
• pharynx: (throat) common passageway for
digestive and respiratory system
• esophagus: tube connecting oral cavity to
stomach.
• glottis: the opening to the larynx (a.k.a.
voicebox which leads to trachea/windpipe)
• epiglottis: the flap that covers the glottis during
swallowing
Oral Cavity Diagram
uvula
Oral Cavity
• Purpose of teeth is to grind food &
increase the surface area.
• Papillae (tiny bumps) on the tongue
contain taste buds.
• Like all young mammals, fetal pigs have
milk teeth (baby teeth) that are later
replaced by permanent teeth.
Oral Cavity
• Salivary glands produce
large amounts of saliva
(>1 l/day in humans).
• Saliva contains:
• water for moistening food
• Mucus for lubricating food and binding it
into a bolus (ball of mush)
• salivary amylase to start the breakdown of
starch
How is food swallowed?
• Food moves to the pharynx, (throat)
which in humans, leads to both the
trachea and the esophagus.
• While food is being swallowed, the
epiglottis blocks the trachea and the
uvula blocks off the nose.
• Then food reaches the esophagus,(tube
that connects the pharynx to the stomach)
(throat)
uvula
Oral Cavity of Pig
Stomach
• The stomach has several muscle layers
surround the stomach, serving to churn
food.
• The stomach can expand to hold about 2 L
of food (= 1/2 gal). It contains acid to
digest food (ph = 2) and enzymes to
breakdown protein.
Stomach diagram
Sphincters
• The cardiac sphincter closes off the top
end of the stomach and the pyloric
sphincter closes off the bottom
Small Intestine and accessory
organs
•
•
•
Small intestine has a length of about 6 m. A lot of
digestion happens here. S. int. secretes enzymes
and pancreas/gall bladder dump enzymes into
duodenum to continue digestion.
Liver- The largest internal organ of the body.
Makes bile, which aids in the digestion of fat.
Detoxifies poisons like alcohol. Stores extra
glucose in the form of glycogen.
Gall Bladder- Sack on the bottom of one of the
liver lobes. Stores bile until it is ready to move into
the duodenum.
Pancreas- Makes digestive enzymes that are
dumped into duodenum of the small intestine.
Makes the hormone, insulin, which regulates the
amount of sugar in the blood.
Small Intestine
• SECTIONS OF THE SMALL INSTESTINE
• Duodenum- The first part of the small intestine
which has ducts (tubes) leading into it from the
liver/gall bladder and pancreas. Bile and
pancreatic enzymes are mixed with food here.
• Jejuno-ileum- All the small intestine except for
the duodenum. Digestion of food is completed
here and nutrients are absorbed through its
walls into the blood stream.
• Caecum-a pouch off the digestive tract between
the small intestine and the colon. Produces
enzymes that digest cellulose. (is the appendix
in humans)
Lower digestive tract of the pig
Lower digestive tract of pig
Large Intestine
• The large intestine or colon functions to
re-absorb water.
• Bacteria live here like Escherichia coli (E.
coli) which produce gases as they ferment
their food.
• Occasionally, some of this gas is released.
As these bacteria digest/ferment left-over
food, they secrete beneficial chemicals
such as vitamin K, Vitamin B, and some
amino acids, and are our main source of
some of these nutrients.
Sections of Large Intestine
•
•
Spiral colon-spiraled part of the large
intestine. Absorbs water, vitamins, and
minerals from the food and moves them
into the bloodstream.
Descending colon- The part of the
large intestine leading from the spiral
colon down to the rectum. Same
function as the spiral colon.
Large Intestine Diagram
Rectum
• The rectum is the end of the large intestine and
functions for storage of the feces, the wastes of
the digestive tract, until these are eliminated.
• The external opening at the end of the rectum is
called the anus. The anus has two sphincters,
one voluntary and one involuntary. The pressure
of the feces on the involuntary sphincter causes
the urge to defecate and the voluntary sphincter
controls whether a person defecates or not.
Rectum of digestive tract of the
pig