g. Antibody (Ab) Production. Antibodies are an important defense mechanism
against infection and invasion of body tissues by bacteria. They are formed in the
plasma cells found in lymphoid tissue. The liver contains a very large amount of
lymphoid tissue, lymph nodes, and lymph. Damage may severely impair the immune
process of the body.
1-16. THE PANCREAS
The other accessory organ important to the gastrointestinal tract is the pancreas.
The pancreas functions as both an endocrine and exocrine gland and it is the exocrine
portion that is concerned with digestion. The pancreas secretes lipases and proteases
that are responsible for the digestion of fats and proteins in the small intestine. The
endocrine portion of the pancreas is composed of groups of cells scattered throughout
the pancreas called the Islets of Langerhans. There are alpha and beta cells in the
pancreas. These alpha and beta cells have specific functions. The alpha cells secrete
glucagon, a hormone which promotes the breakdown of glycogen and sugar stores and
causes their release into the bloodstream. The beta cells secrete insulin, a hormone
which promotes the movement of glucose from the bloodstream into the cells and the
subsequent oxidation of the glucose. The release of insulin promotes a lowering of
blood sugar. Diabetics have insulin deficiency and hence have unusually high blood
sugar levels that "spill over" into the urine.
Section VIII. ABSORPTION AND METABOLISM IN THE DIGESTIVE SYSTEM
1-17. INTRODUCTION
Once foodstuffs are taken into the body and have passed through the
gastrointestinal tract, their end products are either stored or used by our cells for
energy. The only substance that can be used by our body cells for the purpose of
obtaining energy is glucose. Our bodies can obtain glucose directly from the absorption
and digestion of carbohydrates or from the production of glucose from other substances
(if necessary).
1-18. THE DIGESTION OF CARBOHYDRATES
a. The digestion of carbohydrates begins in the mouth by the enzyme alpha-
amylase or ptyalin, which is found in saliva. The process of turning complex
carbohydrates (starches) into simple disaccharide units thus begins in the mouth. The
mouth is very important in the digestion of carbohydrates--food is chewed, mixed with
saliva, and swallowed. This occurs within a very short period of time, which allows for
only about five percent of the starch to split. As the bolus moves on to the stomach, the
low pH of the stomach prevents further action by salivary amylase. Hence, very little
further digestion of carbohydrates occurs in the stomach.
b. After the carbohydrates pass into the small intestine, their digestion is
completed. In the small intestine, pancreatic amylase acts on the remaining starch and
MD0807
1-10