Simple sugars and amino acids are absorbed into the blood capillaries. Most of
the fatty acids and glycerol are absorbed into the lymphatic capillaries. (para 6-19b)
The blood capillaries absorbing substances from the digestive tract join to form
the hepatic portal venous system. A venous portal system begins in capillaries, which
join to form veins, which in turn end in another group of capillaries. The hepatic portal
vein carries blood from the absorptive area of the digestive system to the liver.
In the liver, excess materials are removed and stored. For example, some
glucose is stored as glycogen. Toxic materials are degraded. Microorganisms are
removed. The "treated" blood is then routed from the liver to the heart and then
Lipid materials are stored as fat throughout the body so that they will be available
The lumen of the digestive system connects directly with the surrounding
environment. For this reason, special protective mechanisms are associated with the
human digestive system. Such mechanisms belong to the reticuloendothelial system.
A primary component of the reticuloendothelial system are the lymphoid tissues.
An important type of cell found within these tissues is the lymphocyte. These cells
signal other types of white blood cells to phagocytize foreign materials. These tissues
are more important in the child.
The aggregate of lymphoid tissue at the beginning of the pharynx are called
Peyer's patches might be considered the "tonsils" of the small intestine.
At the beginning of the large intestine, at the inferior end of the cecum, is the
vermiform appendix, which might be considered the "tonsil" of the large intestines.
Lining the sinusoids of the liver and removing harmful substances from the blood
are Kupffer's cells. These cells are also considered to be part of the reticuloendothelial
During nursing, the initial secretion of the mammary glands is called colostrum.
Although this secretion lacks nutrients, it is loaded with antibodies. These provide the
infant with its primary protection for the first 6 months of life.
Later, if the infant has an upper respiratory infection, the mammary gland will
produce the appropriate antibodies. This is due to a reflux of fluid into the milk ducts of