hi let's talk about the functions of the digestive system in terms of the GI or
digestive system there are two major functions the first is to serve as a pathway for fluid and
nutrients so we would bring materials in through the mouth the oral cavity through the pharynx down
the esophagus into the stomach through the small intestines eventually through the large intestines
the rectum and then out the anus the the goal here is to absorb these fluids and nutrients
from the lumen or the central portion of the tube of the gut into the body which would be
into the cardiovascular and lymphatic systems the other basic function or major function of
the GI system is to help modulate the immune system locally with respect to the surface of
the gut tube in terms of the fluid and nutrient pathways there are six basic processes that are
going to modulate these materials the first being ingestion now a typical human is going to take
in about 3 to 4 liters of water and somewhere between 2 to 3,000 calories per day of course
this is going to vary with respect to activity level general metabolism and diet goals but on
average 3 to 4 liters of water and 2 to 3,000 calories daily so this comes in through the
mouth typically and your GI system is then going to secrete its own fluid into the lumen and so
we go from the process of ingestion to secretion there's also the mixing and the propulsion of the
materials within the lumen and so the the goal here is to bring as much of the the contents
of the ingested materials into contact with the various chemicals and materials secreted by the
GI system this is greatly enhanced through the processes of mixing and propulsion there are
layers of smooth muscle that are embedded within the walls of the digestive system some of this
smooth muscle is arranged in longitudinal layers and as it contracts it's responsible for the inch
wise movement of peristalsis and some of those layers of smooth muscle are arranged in circular
fibers and that's responsible for segmentation contractions which can either move materials
forward or backwards depending on how that smooth muscle is contracted now there are also processes
of digestion occurring and this can occur at the physical level such as teeth acting upon
materials that are ingested the smooth muscle sort of churning those materials with the the
digestive secretions or at the chemical level we could have various enzymes and acids mixed
with very large particulate matter to help break that down into smaller portions that may be then
absorbed by the lining of the GI system and this process of absorption moves materials from the
lumen of the GI so if we were to conceptualize the gut tube like so if the ingested materials
are here that space is actually outside of the body and we want to move those materials
inside the body so into the capillaries whether they be cardiovascular capillaries or lymphatic
capillaries so that we can then move that material up to the liver for processing and send it out to
the rest of the body any materials which are within the lumen of the GI tract that are not
absorbed are then dehydrated down not totally but largely and turned into feces which are
then defecated from the rectum through the anal canal out the anus and outside of the body now
there's also an immune component to the digestive system you can think of the the digestive system
or the GI tract as a physical barrier between the outside or the stuff that's within the lumen in
the inside of the body that space has a remarkably large surface area so from the mouth down through
into the the anal canal there's approximately 32 square meters of surface area that's roughly twice
the size of a parking space and throughout the wall is embedded a lot of lymphoid or lymphatic
tissue that hosts lymphocytes and various other cells that are capable of defending
the body from any pathogenic material or anything that might mean the body harm now one of the the
latest hot topics of that the GI system is that of the microbiome now within the GI t
we have the microbiota the microbiota references all of the bacteria or fungi or protozoans that
live within the lumen of the gastrointestinal tract now the microbiome are the sum total of
all of the genomes of those living creatures and what's significant here is many of these living
organisms especially the bacteria are beneficial to the human so they form this micro ecological
community that contains genes which are capable of metabolizing substance is synthesizing vitamins
and communicating with the body's own immune system so to greatly enhance metabolism to help
maintain a healthy gut and a healthy body and this is a this is a greatly underappreciated service
that that's performed by the the microbiota for people so as we'll see throughout the
discussions that we'll have regarding the anatomy of the digestive system I want you
to to pull forward these ideas of ingestion and secretion and absorption and elimination
and where these processes are occurring as we as we discussed the anatomy thank you