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Anatomy
CLIL
Second Part
Prof. Milvia Morocutti
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All the organs can be classified in two types: solid and cave or hollow organs.
Lobule
Parenchima
Secta
Lobe
Connectival
Capsule
Fig. 9a Solid organ
The former, like liver or pancreas, are formed by an outermost capsule of dense
connective tissue surrounding the entire organ, while the inside is filled with a tissue
called parenchyma.
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Fig. 9b Cave organ
Despite the diverse and specialized processes that take place in different sections of
the digestive tract, there is a fundamental consistency in the architecture of the
tubular digestive tract.
Inside cave organs like those of the G.I. tract, we can observe 3 basic concentric
layers: tunica mucosa (with submucosa); tunica muscularis; tunica serosa or
adventitia
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The animal’s alimentary canal
The animal’s alimentary canal is a long tube running from one end of its body to
the other. Food is taken into the alimentary canal by ingestion. The food you eat
usually contains some large molecules. Before they can be absorbed, they must be
broken down into small ones. This is called digestion. Before food can be of any
use to the animal, it has to get out of the alimentary canal and into the bloodstream.
This is called absorption. To be absorbed, molecules of food have to get through
the walls of the alimentary canal. They need to be quite small to be able to do this.
At the end of this process, the food which could not be digested or absorbed is
removed from the body by egestion.
Fig.10 How an animal deals with food
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food
MOUTH
Secretion of
salivary glandules
bolus
ESOPHAGUS
STOMACH
Secretion of
gastric
glandules
chimo
SMALL INTESTINE
Secretion of pancreas,
liver and enteric
glandules
LARGE
INTESTINE
Absorption only of
water and salts
chilo
The gastrointestinal tract has a
uniform general histology with some
differences
which
reflect
the
specialization in functional anatomy.
The mucosa is the innermost layer,
surrounding the lumen, or space
within the tube. This is very important
because it comes in direct contact
with the food and is responsible for
absorption and secretion.
The mucosa is highly specialized in
each organ of the G.I. tract, for
example dealing with a low pH in the
stomach, providing a multitude of
different substances in the small
intestine, and also absorbing specific
quantities of water and salts in the
large intestine (through blood
vessels). The layer of the tunica
mucosa also contains lymphatic
nodules important for the immune
function and fat absorption.
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Reflecting the varying needs of these organs, the structure of the mucosa can
consist of invaginations of secretory glands (i.e. gastric pits), or it can be
folded in order to increase surface area (i.e. villi, microvilli). These distinctive
differences in architecture especially for the epithelium (the innermost part of
the mucosa, the cell sheet in direct contact with the lumen), can be seen below
to the right in the micrographs of mouse digestive tube. The magnification of
all four images is identical and the epithelial layer is oriented toward the top.
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Mouth
Esophagus
Glandule
Stomach
Glandule
Duodenum
S
m
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l
l
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t
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s
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Large Intestine
Rectum
Serosa
Tunica
Fig. 12 digestive tissue
Submucosa
Muscularis
Mucosa
Mouth
Mechanical digestion by
teeth and tongue.
Chemical digestion by
saliva.
Esophagus
Muscle tube, takes food
down to the stomach.
Stomach
Mechanical digestion
by contraction and
relaxation of muscular
walls.
Heart
Chemical digestion by
gastric juice.
Liver
Pancreas
Bile
Gallbladder
Duodenum
Chemical digestion by bile
pancreatic
juice
Small intestine
Absorbs digested food by
villis
Large intestine
Absorbs especially water
and minerals
Rectum
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