SMALL INTESTINE
1. ANATOMY
The length of the human small
intestine after its separation from
the mesentery is 6 to 8 meters.
*
In life because of muscle tone in
the wall of the intestines
the length is about 3 meters. The
mucosal surface provides a
larger area for absorption surface.
*
The surface of the mucosa shows finger like villi of 1 mm
height and each villi shows a brush border of microvilli (Fig.
18.1) further increases the area
of contact with the contents
and thus the absorption surface.
*
The mucosa also
secretes 3 litres
of alkaline succus
entericus.
The
small intesinte receives its blood supply from the superior
mesenteric artery a branch of the
abdominal aorta.
Absorption
The
absorbing surface of the small bowel is over 20c m2 as a result of
folds, villi, and microvilli which provide increased surface area. Absorption
can occur either actively or passively. The active form is transcellular,
carrier mediated, and energy dependent. Passive absorption can occur through
the tight junctions between cells, a process referred to as paracellular
diffusion. Passive diffusion also can occur transcellularly by diffusion,
concentration gradient, or convection.
1.1 LYMPHATICS
The
peyer's patches are the
equivalent of lymph nodes and are
aggregation of lymphoid tissues of the sub-mucosa of the
small
intestine. They
are more in number in the ileum but
are also
present in the jejunum. The lymphatic drainage from these areas
passes
into lymphnodes placed
closed to the
wall of the
intestine. The next group are placed further away in the
arcades
of
mesenteric and 3rd set are
around the superior
mesenteric
arcades. These finally drain into the cisterna
chyli. This is
the major route of absorbed fats
(lipids) in to the circulation
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