The large intestine, consisting of the cecum, colon, rectum, and anus, is the final part of the intestine where the meal passes through. Its main role is to recover water used in digestion and absorption and to store the leftover meal until it is socially convenient to defecate.

Colonic motility primarily aims to mix and delay the movement of the contents in the intestinal lumen, except during occasional strong contractions that move fecal material to the rectum.

The colon plays an active role in transporting water, electrolytes, and substances salvaged by colonic bacteria from undigested components of the meal.

Throughout life, the colon maintains a mutually beneficial relationship with a vast microbial ecosystem that metabolizes endogenous substances, nutrients, and drugs while protecting the host from pathogenic infections.

Defecation involves both involuntary and voluntary relaxation of the muscles surrounding the anus, controlled by reflex pathways.

The liver contributes essential metabolic, detoxification, and excretory functions vital for life.

The liver is composed of different cell types with a unique arrangement, and it receives blood supply through the portal system.

Bile serves as an excretory fluid, and its formation is governed by specific mechanisms. The enterohepatic circulation plays a role in bile recycling.

The gallbladder stores and concentrates bile, and mechanisms coordinate its emptying when a meal is ingested.

Ammonia and bilirubin are eliminated from the body through specific processes.

This chapter provides an overview of the liver and its functions, addressing the questions mentioned above.
The final segment of the intestine through which the meal traverses is the large intestine, which is composed of the cecum, colon, rectum, and anus. The primary role of the large intestine is to reclaim water used during the process of digestion and absorption and to store the residues of the meal until defecation is socially convenient.
2.
Colonic motility primarily serves to mix and delay passage of the luminal contents, other than during periodic large-amplitude contractions that convey fecal material to the rectum.
Bharucha AE, Brookes SJR. Neurophysiologic mechanisms of human large intestinal motility. In: Johnson LR, ed. Physiology of the GI Tract. 5th ed. Waltham, MA: Academic Press; 2012.
Bharucha AE, Hasler WL. Motility of the small intestine and colon. In: Podolsky DK, et al., eds. Yamada’s Textbook of Gastroenterology. 6th ed. Hoboken, NJ: Wiley Blackwell; 2015.
3.
The colon is highly active in transporting water and electrolytes as well as products salvaged from undigested components of the meal by colonic bacteria.
4.
The colon maintains a lifelong mutually beneficial relationship with a vast microbial ecosystem that metabolizes endogenous substances, nutrients, and drugs and protects the host from infection with pathogens.
5.
Defecation involves both involuntary and voluntary relaxation of muscle structures surrounding the anus and reflex pathways that control these structures.
Kau AL, et al. Human nutrition, the gut microbiome and the immune system. Nature. 2011;474:327-336.
Kendig DM, Grider JR. Serotonin and colonic motility. Neurogastroenterol Motil. 2015;27:899-905.
Koren A, Ley RE. The human intestinal microbiota and microbiome. In: Podolsky DK, et al., eds. Yamada’s Textbook of Gastroenterology. 6th ed. Hoboken, NJ: Wiley Blackwell; 2015.
Upon completion of this chapter the student should be able to answer the following questions: 1.
How does the liver contribute metabolic, detoxification, and excretory functions that are vital to life?
2.
What cell types make up the liver, what is their unusual arrangement, and what is the liver’s unique portal blood supply?
3.
What is the function of bile as an excretory fluid, what are the mechanisms that underlie its formation, and what is the role of the enterohepatic circulation?
4.
How is bile is stored and concentrated in the gallbladder, and what are the mechanisms that coordinate gallbladder emptying with ingestion of a meal?
5.
How are ammonia and bilirubin eliminated from the body?
Overview of the Liver and Its Functions