The human digestive system is essentially a continuous tube, which is open at both
Therefore, the lumen (cavity) connects directly with the surrounding environment.
Along with the ingested food, almost anything can pass through the mouth into the digestive system.
The digestive tract is open to the surrounding environment also at the other end, the anus.
Page 2 The Reticuloendothelial System
Since a variety of toxic materials and/or microorganisms may be included with ingested foods, special protective mechanisms are associated with the human digestive system.
Such protective mechanisms are said to belong to the reticuloendothelial system.
This term refers to the association of such mechanisms with a particular layer of epithelial cells.
Page 3 Lymphoid Tissues
The lymphoid tissues are a primary component of the reticuloendothelial system.
The lymphocyte is an important type of white blood cell that is also found in the interspaces of lymphoid (or lymphatic) tissues.
Lymphocytes signal other types of white blood cells to phagocytize (engulf) foreign materials found within
The lymphoid tissues are particularly important in individuals from birth until about 15 years of age.
The mass of lymphoid tissue found in the body of a 12-year-old is about twice the mass found in a full-grown adult.
Between 6 and 15 years of age, the immune system of the blood becomes the primary protector of the body from disease.
Page 5 Tonsils
Tonsils are aggregates of lymphoid tissue found at the beginning of the pharynx.
There are three pairs of tonsils. Together, they form a ring of lymphoid tissue at the beginning of the pharynx.
This ring, called Waldeyer's ring, completely surrounds the entrance to the pharynx from both the mouth (digestive entrance) and the nose and nasal chambers (respiratory entrance).
In the upper recess of the pharynx is the pair of pharyngeal tonsils (commonly known as the adenoids).
On either side, below the soft palate, are the palatine tonsils.
These are the tonsils that one sees most frequently in small children.
The lingual tonsils are on the back of the root of the tongue.
Page 7 “Tonsils” of the Small Intestines
Lymphoid aggregates of varying size are found in the walls of the small intestines.
In the ileum portion, in particular, these aggregates are large enough to be easily observed and are called Peyer's patches.
These might be considered "tonsils" of the small intestines.
Page 8 “Tonsils” of the Large Intestine
At the beginning of the large intestine, at the inferior end of the cecum, is a structure known as the vermiform appendix.
Since the vermiform appendix is actually a collection of lymphoid tissue, it should be considered the "tonsil" of the large intestine.
Page 9 Kupffer’s Cells
As we have seen, blood from the absorptive areas of the gut tract is collected and delivered to the liver by the hepatic venous portal system.
As this blood passes through the sinusoids (channels) of the liver, it is acted upon by cells called Kupffer's
These cells line the sinusoids.
Since Kupffer's cells remove harmful substances from the blood, they are considered to be part of the reticuloendothelial system.