Forensic Pathology for Police - Brainshare Public Online Library

Specific Organ Systems 111
water content. It is within the large intestine that most of the residual water is reabsorbed
into the bloodstream. What remains are soft, formed stools which contain
abundant bacteria intermixed with other waste.
Bacteria and other microbial organisms that are normally present on or reside
within the human body, without causing illness, are referred to as normal microbial
“flora.” Many of these are “commensal” organisms, where both the host (human)
and micro-organism receive a benefit from the mutual existence. For example, certain
GI bacteria are involved in the production of vitamins that are subsequently
absorbed into the blood stream.
Each specific portion of the GI tract has a distinct gross and microscopic appearance
(Disc Images 6.19, 6.20, 6.21, 6.22, 6.23). The oral cavity, tongue, portions of
the larynx, and the esophagus are lined by stratified squamous epithelium, similar
in appearance to epidermis, but without keratinization. The stomach, small intestine,
and large intestine are lined by columnar (tall) epithelium and have various
other specialized cells. For instance, the stomach also has parietal cells, which are
responsible for producing hydrochloric acid. The walls of each also contain smooth
muscle cells which allow for peristalsis to propel the food substance along its way.
As with all organ systems, blood vessels flow to and from each part of the GI system,
and lymphatic vessels and lymph nodes provide for drainage and filtering of
excess extracellular fluid. The major arteries supplying blood to the GI tract include
the celiac artery, the superior mesenteric artery, and the inferior mesenteric artery.
Each arises from the abdominal aorta.
The liver and pancreas play a very important role in the digestive process. With
regard to the liver, bile salts are produced which aid in the digestion of fats (please
refer to the hepatobiliary section for more information about bile). The pancreas has
two functional components which are designated as the exocrine pancreas and the
endocrine pancreas. The endocrine pancreas is described further in the endocrine
system below. The exocrine pancreas, which makes up the bulk of the pancreatic
tissue, involves the production and excretion of digestive enzymes that aid in
food digestion. Some of these enzymes include amylase (involved in carbohydrate
digestion), lipase (involved in fat digestion), and various proteases (involved in the
digestion of proteins). After nutrients are absorbed across the small intestine walls
and into the blood stream, the blood from the intestines empties into the portal vein,
which drains directly into the liver.
Hepatobiliary System
The hepatobiliary system essentially encompasses the liver, the gallbladder, and the
ducts that drain the liver and gallbladder (the biliary ducts). The liver is a large organ
that resides primarily within the upper right side of the peritoneal cavity, just under
the diaphragm (Fig. 6.22 and Disc Image 6.24). The liver can be considered the
metabolic workhorse of the body because it is within the liver that many very important
metabolic activities and processes occur. As we learned from the discussion of
the GI system, all nutrients absorbed within the small intestine travel via the portal