Large Intestine: Bacterial Flora and Motility – Digestive System Organs (Nursing)

00:01 The large intestine is home to a large number of bacteria which help with digestion.

00:08 This is referred to the bacterial flora.

00:11 The bacterial flora consists of thousand plus different types of bacteria and the number of bacteria in our flora actually outnumber our own cells 10 to 1.

00:27 They enter from the small intestine or the anus and they colonize the colon.

00:34 The bacteria and the gut are able to undergo several metabolic processes as well that are important for human health.

00:42 First they're able to undergo fermentation which allows for the digestion or fermentation of indigestible carbohydrates and mucin.

00:53 But sometimes this can lead to the release of irritating acids and gases which happens at about 500 milliliters per day.

01:03 Also the bacteria in our large intestine are able to synthesize certain vitamins.

01:09 So for example, the synthesis of the B complex as well as some vitamin K that is needed by the liver for the production of clotting factors is produced by bacteria that are living in our large intestine.

01:25 Another very important role of these bacteria are that they keep pathogenic bacteria and check.

01:32 So sometimes we refer to the bacteria in our large intestine as the good bacteria or are pro bacteria.

01:41 The beneficial bacteria are going to outnumber and thus suppress the pathogenic bacteria because they're going to just out survive the pathogenic bacteria that don't belong.

01:53 Also our immune system destroys any bacteria that tries to breach through that mucosal barrier.

02:01 This is where the MALT of the appendix can come in handy since epithelial cells recruit dendritic cells to the mucosa to sample microbial antigens and to present those antigens to T cells in the MALT.

02:17 This then triggers the production of IgA, which is then going to restrict the microbes.

02:25 So looking at the digestive process in the large intestines, we find that residue remains in the large intestines anywhere from 12 to 24 hours.

02:36 Again, no food breakdown is actually occurring except for the breakdown by those bacteria.

02:45 Vitamins that are made by the bacteria as well as water and electrolytes are going to be absorbed in the large intestine.

02:54 And the major function of the large intestine is the propulsion of feces to the anus and as well defecation.

03:06 Movement of substances through the large intestine occurs due to haustral contractions which are the most contractions of the colon.

03:16 This is where haustria are going to sequentially contract and response to distention of the large intestine.

03:25 This slow segmenting movements are going to be occur mostly in the ascending and transverse colon of the large intestine.

03:37 Also large intestine motility can be triggered by the gastrocolic reflex, which is initiated by the presence of food in the stomach.

03:47 So if you think about it, if there's food in the stomach, we need to move whatever is in the large intestine out of the way, so that it, the food in the stomach can eventually go to the large intestine.

03:59 So that's where the gastrocolic reflex comes into play.

04:03 This is going to result in mass movements are slow very powerful peristaltic waves that are going to be activated about three to four times per day usually in response to meals.

04:18 While most of the propulsion is going to occur in the ascending and transverse colon the descending colon and the sigmoid colon are going to act as storage reservoirs for residue until the gastrocolic reflex takes over.

04:35 So then we have defecation.

04:38 Defecation involves mass movement forcing the feces toward the rectum.

04:45 Distension is going to initiate the spinal defecation reflex.

04:51 Then from there parasympathetic signals are going to stimulate contraction of that sigmoid colon as well as the rectum.

05:00 And it's going to relax that internal anal sphincter.

05:04 Recall that the internal anal sphincter is made up of smooth muscles that are under involuntary control by these parasympathetic signals.

05:15 Next you have conscious control of the external anal sphincter.

05:20 So here when during the process of defecation you have to allow for the relaxation of that second external anal sphincter in order for the feces to be released from the body.

05:35 The muscles of the rectum are going to contract in order to expel the feces.

05:41 This is assisted by a maneuver known as the valsalva's maneuver.

05:46 Recall this happens when the glottis is going to close, and the diaphragm contracts, and as well the abdominal wall muscles are also going to contract.

05:58 This leads to an increase in the intra-abdominal pressure.

06:03 As well the levator ani muscles are going to contract and this is going to cause the anal canal to be lifted superiorly, allowing for feces to leave from the body.