<< Chapter < Page Chapter >> Page >

Bacterial flora

Most bacteria that enter the alimentary canal are killed by lysozyme, defensins, HCl, or protein-digesting enzymes. However, trillions of bacteria live within the large intestine and are referred to as the bacterial flora    . Most of the more than 700 species of these bacteria are nonpathogenic commensal organisms that cause no harm as long as they stay in the gut lumen. In fact, many facilitate chemical digestion and absorption, and some synthesize certain vitamins, mainly biotin, pantothenic acid, and vitamin K. Some are linked to increased immune response. A refined system prevents these bacteria from crossing the mucosal barrier. First, peptidoglycan, a component of bacterial cell walls, activates the release of chemicals by the mucosa’s epithelial cells, which draft immune cells, especially dendritic cells, into the mucosa. Dendritic cells open the tight junctions between epithelial cells and extend probes into the lumen to evaluate the microbial antigens. The dendritic cells with antigens then travel to neighboring lymphoid follicles in the mucosa where T cells inspect for antigens. This process triggers an IgA-mediated response, if warranted, in the lumen that blocks the commensal organisms from infiltrating the mucosa and setting off a far greater, widespread systematic reaction.

Digestive functions of the large intestine

The residue of chyme that enters the large intestine contains few nutrients except water, which is reabsorbed as the residue lingers in the large intestine, typically for 12 to 24 hours. Thus, it may not surprise you that the large intestine can be completely removed without significantly affecting digestive functioning. For example, in severe cases of inflammatory bowel disease, the large intestine can be removed by a procedure known as a colectomy. Often, a new fecal pouch can be crafted from the small intestine and sutured to the anus, but if not, an ileostomy can be created by bringing the distal ileum through the abdominal wall, allowing the watery chyme to be collected in a bag-like adhesive appliance.

Mechanical digestion

In the large intestine, mechanical digestion begins when chyme moves from the ileum into the cecum, an activity regulated by the ileocecal sphincter. Right after you eat, peristalsis in the ileum forces chyme into the cecum. When the cecum is distended with chyme, contractions of the ileocecal sphincter strengthen. Once chyme enters the cecum, colon movements begin.

Mechanical digestion in the large intestine includes a combination of three types of movements. The presence of food residues in the colon stimulates a slow-moving haustral contraction    . This type of movement involves sluggish segmentation, primarily in the transverse and descending colons. When a haustrum is distended with chyme, its muscle contracts, pushing the residue into the next haustrum. These contractions occur about every 30 minutes, and each last about 1 minute. These movements also mix the food residue, which helps the large intestine absorb water. The second type of movement is peristalsis, which, in the large intestine, is slower than in the more proximal portions of the alimentary canal. The third type is a mass movement    . These strong waves start midway through the transverse colon and quickly force the contents toward the rectum. Mass movements usually occur three or four times per day, either while you eat or immediately afterward. Distension in the stomach and the breakdown products of digestion in the small intestine provoke the gastrocolic reflex    , which increases motility, including mass movements, in the colon. Fiber in the diet both softens the stool and increases the power of colonic contractions, optimizing the activities of the colon.

Questions & Answers

what is an inflammation
Lodrick Reply
it's a reaction from a body tissue
is the body own mechanism of fighting against disease especially infections or injuries.
which cells are responsible for bone formation?
Richard Reply
which muscles are innervated by the lateral plantar nerve?
Tinyiko Reply
what book should i read for my Msc exam (physiology)
zeleke Reply
let ask u aquiz where bones live in a body
Lowyer Reply
306 bones in a human body
Netope Reply
206 bones in a human body
there are 206 bones in human body and a baby's body has about 300 bones at birth
what is anatomy?
Nuwagaba Reply
anatomy is the study of the internal structure of a living organism
can be define as the Scientific Study Of internal structure of the body Some of this Structures are Very tiny they can only be seen by The assistance of a microscope, While other structures can be seen manipulated and Weighted
Anatomy is the scientific study of the body and the physical relationship between systems
gross anatomy is the study of the internal structure of a living organism at a visible or macroscopic level
Favour Reply
homeostasis is the steady maintenance of the internal system
study of the structure of cells,tissue using a microscope
is the study of how the human body works and relates
i cannot understand this please explain how to calculate
Sania Reply
I don't get it either
How to calculate what exactly?...
be clair
where are bones lived
name of all the bones and eg
Shantal Reply
treatment for hereditary diseases
With gene therapy, the treatment or elimination of inherited diseases or physical conditions due to these mutations could become a reality. Gene therapy involves the manipulation of genes to fight or prevent diseases. Put simply, it introduces a "good" gene into a person who has a disease caused by
Why do cardiac muscle demonstrate autorhythmicity
Olemogile Reply
cardiac muscle tissue has autorhythmicity, the unique ability to initiate a cardiac action potential at a fixed rate. spreading the impulse rapidly from cell to cell to trigger the contraction of the entire heart.
please am new here hope am welcome?😌
Okpanum Reply
you welcome
hiiiiii friends
welcome 🙏
from where are you coming mmesoma
basically I don't know how to speak in English. in India 🇮🇳 not develop English well because of this app is useful to me then if any one of you can't understand my language please excuse me I am learning now only 😉 I think all of you guys can understand my problem.I want to tell you thanks 😊 🙏
okpanum where are you coming 🤔🤔
any from kenya?
hi all, I'm jose..am new here
Kuany Reply
you are welcome
Hi everyone, am new here hope am welcomed
Oluebube Reply
Yeah Hi all,I'm Gina.....happy to meet y'all and you?
nice to meet you
hi too you , most welcome!
you are welcome ! hi too you most welcome !
hello everyone
Thanks for the welcome am in Nigeria too
what is cell division
Abduleziz Reply
cell division is just when cells multiply/divide to create two (daughter/identical) or more cells

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now

Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Anatomy & Physiology' conversation and receive update notifications?