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Ravela Da Cruz

Large Intestine Study Guide

🗻 Big Picture: The large intestine is a crucial piece of the digestive system that we use to excrete waste from our bodies. It is formed by 4 major organs–the cecum, colon, rectum, and anal canal–that help us absorb water and convert food to fecal matter.

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Introduction

Everybody does it, nobody wants to talk about it 💩. While the entire digestive system contributes to the process, one organ does most of the dirty work—the large intestine. Let’s learn about its structure, function, and some of the common illnesses and conditions that affect your digestive system.

Lesson Objectives

  • Understand the structure of the large intestine and the functions of all of its parts.
  • Understand the functions of the large intestine.
  • Learn about common diseases and conditions that affect the large intestine.

The Large Intestine

The Large Intestine is the final portion of the digestive tract. Contrary to its name, the large intestine is actually shorter than the small intestine—1.5 meters in length compared to 6 (or about 5 feet to 20). It is lined with a thin tissue called mucosa, and unlike the small intestine, it contains no villi to absorb nutrients, nor does it secrete digestive enzymes.

The large intestine begins at the endpoint of the ileum of the small intestine and terminates at the anus. Once the small intestine has absorbed the majority of the nutrients and water from your food, it moves down the digestive tract into the large intestine where the remaining water is absorbed and feces are formed. Apart from making and storing fecal matter, the large intestine also harbors a vast and diverse microbiome crucial for our survival.

The large intestine is divided into 4 main parts: the cecum, the colon, the rectum, and the anal canal. Each portion serves a different purpose in the process of digestion. Let’s learn about them below!

Large Intestine

Source


Structure of The Large Intestine

Cecum: The cecum is the starting point of the long intestine, connecting from the ileum of the small intestine to the appendix.

  • The cecum’s primary functions are the absorption of electrolytes and fluids and the temporary storage of chyme.

  • The appendix, also known as the vermiform appendix, is a muscular sac attached to the cecum. Its structure is long and tubelike, somewhat resembling a worm. The appendix helps maintain gut immunity by protecting good bacteria in your intestinal microbiome.

The Colon Is the section of the large intestine between the cecum and the rectum.

  • Its key function is fluid and electrolyte absorption.

  • It’s composed of four sections–the ascending colon, transverse colon, descending colon, and sigmoid colon.

  • Saccules called haustra help move food through the colon, and are what give it its segmented appearance.

  • Microbiota in the colon produce energy through a process known as fermentation, where carbohydrates and fatty acids that were not absorbed by the small intestine are broken down and converted to cellular ATP.

The Rectum is found in the lower part of the large intestine between the sigmoid colon and the anal canal.

  • The rectum has multiple bends and a distinctive S-shape.

  • Its primary function is to store fecal matter and push it out of your anus during a bowel movement.

The Anal Canal, the final segment of the gastrointestinal tract, is a tube found at the end of your rectum, measuring about 4 cm (about 1.5 inches) in length.

  • It’s surrounded by a group of smooth muscles known as the external anal sphincter that control the release of waste from your body.

  • The primary function of the anal canal is to control defecation.


Functions of the Large Intestine

The large intestine has four main functions: peristalsis, bacterial digestion, absorption, and defecation.

  • Peristalsis is the rhythmic contraction of the muscles of the intestine that create waves of movement, pushing the contents of the canal forward.

  • Bacterial digestion is the breakdown of waste materials by bacteria that populate the large intestine. When fermenting indigestible material, the bacteria release a variety of gases (basically, this is where 💨 are made). Not only does bacterial digestion form gases, it also produces vitamin K and a variety of B vitamins.

  • Absorption in the large intestine involves the absorption of water, vitamins B and K, and electrolytes such as sodium, chloride, and bicarbonate.

  • Defecation occurs when a large amount of excrement enters the rectum. A defecation reflex is triggered which causes the internal anal sphincter to open. Feces will be expelled from the anus unless the external anal sphincter is actively closed.


Common Illnesses of the Digestive Tract

Diverticulosis

Diverticulosis is an asymptomatic, diagnosable condition in which the colon develops several sac-like protrusions called diverticula. When one or more of these sacs become inflamed, symptoms emerge, and we call the condition diverticulitis. Symptoms of diverticulitis can include stomach discomfort, nausea, vomiting, and a low-grade fever.

Diverticulosis is caused by some non-controllable factors such as age, sex, and genetics. Controllable risk factors include obesity, smoking, a lack of exercise, a high-fat low-fiber diet, and certain medications.

Crohn’s Disease

Crohn’s disease is a chronic inflammatory bowel illness with no known cause that can affect any portion of the digestive system, most commonly the terminal ileum and colon. Inflammation of the bowels causes symptoms such as fever, stomach discomfort, diarrhea, and weight loss. Crohn’s disease can be identified by an endoscopic and radiographic examination of the abdomen, and is generally treated with immunosuppressive medications.


💡 Summary

  • The large intestine is divided into 4 main parts: the cecum, colon, rectum, and anal canal.

  • The cecum connects the small intestine and the colon. Its primary functions are the absorption of electrolytes and fluids and the temporary storage of chyme.

  • The cecum also connects to the appendix, an organ designed to protect good bacteria in your gut.

  • The colon connects the cecum and the rectum. Its primary function is fluid and electrolyte absorption.

  • The rectum connects the colon to the anal canal. Its primary function is to store and push out fecal matter during a bowel movement.

  • The anal canal is the final segment of the large intestine. Its primary function is to control defecation.

  • The four key functions of the large intestine are peristalsis, bacterial digestion, absorption, and defecation.

  • Common diseases and conditions of the large intestine include diverticulosis/diverticulitis and Crohn’s disease.


🧐 FAQs

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Sources

  1. Large intestine (colon). https://medlineplus.gov/ency/imagepages/19220.htm. Accessed on 25 Nov, 2021.

  2. Large Intestine. https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/13.37/primary/lesson/large-intestine-bio/. Accessed on 25 Nov, 2021.

  3. The Anatomy of the Colon (Large Intestine). https://www.verywellhealth.com/large-intestine-797216. Accessed on 25 Nov, 2021.

  4. Farlex. (n.d.). Omental appendices. The Free Dictionary. Retrieved December 25, 2021, from https://medical-dictionary.thefreedictionary.com/omental+appendices

  5. Mayo Foundation for Medical Education and Research. (n.d.). The Anal Canal. Mayo Clinic. Retrieved December 25, 2021, from https://www.mayoclinic.org/diseases-conditions/anal-cancer/multimedia/the-anal-canal/img-20006922#:~:text=The%20anal%20canal%20is%20a,waste%20to%20leave%20your%20body.

  6. Rgd. (n.d.). Taenia coli - ontology browser - rat genome database. Retrieved December 25, 2021, from https://rgd.mcw.edu/rgdweb/ontology/view.html?acc_id=UBERON%3A0012419

  7. Written by ReCharge Collaborator — March 02. (n.d.). 5 weird facts about the gut microbiome. Pendulum. Retrieved December 25, 2021, from https://pendulumlife.com/blogs/news/5-weird-facts-about-the-gut-microbiome

  8. Yang, F., Zheng, Y., Jiang, X., Su, Z., Wang, Y., Lin, L., Lv, H., Zhang, J., Zhao, J., Wang, B., Jiang, K., & Sun, C. (2018, January 9). Sex differences in risk factors of uncomplicated colonic diverticulosis in a metropolitan area from Northern China. Nature News. Retrieved December 25, 2021, from https://www.nature.com/articles/s41598-017-18517-1