Section 4

Question 1

Describe the three portions of the small intestine.

Answer 1

Duodenum (25 cm):
- c-shaped
- encloses the head of the pancreas

Jejunum (2.5 m):
- most of the jejunum lies in the upper left quadrant of the abdomen

Ileum (3.5 m):
- most of the ileum lies in the right lower quadrant of the abdomen

Question 2

Describe the mucosa of the small intestine.

Answer 2

• has villi (small fingerlike projections) that extend into the lumen of the small intestine

The epithelium of the mucosa:
- found on the villi
- simple columnar
- has many absorptive cells whose apical surfaces have microvilli, also known as a brush border. the brush border is significant because it increases the surface for absorption of nutrients
- between the absorptive cells are goblet cells, which secrete mucus to help lubricate the passage of foods
- there are also enteroendocrine cells that secrete hormones involved in the regulation of satiety, blood sugar level, and growth of epithelial cells

The lamina propria of the mucosa:
- forms the core of each villus
- contains blood capillaries and lymphatic capillaries
- there are collections of lymphatic tissue located here known as Peyer’s patches, which are primarily abundant in the ileum

The intestinal glands of the mucosa:
- (crypts of Lieberkuhn)
- these glands/crypts are deep folds of mucosa between the villi and secrete intestinal juices

The plicae circulares of the mucosa:
- the mucosa and submucosa form plicae circulares, which are permanent transverse folds that help increase the surface area for absorption and causes the material to spiral through the small intestine

Question 3

Describe the submucosa of the small intestine:

Answer 3

The submucosa of the duodenum is notable as it has duodenal (Brunner’s) glands that secrete alkaline mucus.

The purpose of this mucus is to help protect the small intestine from stomach acid that may be present in partially digested food after leaving the stomach.

The glands are not found in the submucosa of the jejunum and ileum.

Question 4

Describe the outermost layer of the small intestine.

Answer 4

The outermost layer of the intestine is serosa.

Question 5

Describe the muscularis externa of the small intestine.

Answer 5

The small intestine has two smooth muscle layers which are organized into circular and longitudinal layers.

A nerve plexus is located between these two layers of muscle.

Question 6

What are the sections of the large intestine?

Answer 6

Cecum, colon and rectum

Question 7

Describe the cecum

Answer 7

• the first portion of the large intestine
• has an extension off of it called the vermiform appendix

Question 8

What are the parts of the colon?

Answer 8

The ascending colon, the transverse colon, the descending colon, the sigmoid colon, and the rectum

Question 9

What is the ascending colon?

Answer 9

• extends from the cecum up the right side of the abdomen to join the transverse colon just below the liver

Question 10

What is the transverse colon?

Answer 10

• extends from below the liver, crossing the abdomen to join the descending colon just below the spleen

Question 11

What is the descending colon?

Answer 11

• extends down the left side of the abdomen from the splenic end of the transverse colon to the sigmoid colon

Question 12

What is the sigmoid colon?

Answer 12

The S-shaped terminal portion of the colon that leads into the rectum.

Question 13

What is the rectum?

Answer 13

• extends from the sigmoid colon to the anal canal
• the last portion of the large intestine
• temporarily stores fecal matter before defecation

Question 14

Describe the mucosa of the large intestine.

Answer 14

Similar to small intestine, but does NOT contain plicae circulares or villi

Epithelium:
- simple columnar
- contains an increasing amount of goblet cells as you move towards the anus
- in the anal canal, a change from simple columnar to stratified squamous epithelium takes place

• intestinal glands are present
• accumulations or lymphatic tissue are present in the lamina propria (and submucosa)

Question 15

Describe the submucosa of the large intestine.

Answer 15

• contains blood vessels, lymphatics, glands, and nerve plexuses

Question 16

Describe the muscularis externa of the large intestine.

Answer 16

In the cecum and colon, the outer longitudinal layer forms three longitudinal bands (teniae coli) that contract and bunch up the wall of the large intestine, forming sac-like structures called haustra.

In the rectum, the three teniae coli merge to form the continuous longitudinal muscular layer.

In the anal canal, the circular muscle layer thickens into the internal anal sphincter, which is involved with waste excretion.

Question 17

Describe the adventitia/serosa of the large intestine?

Answer 17

The large intestine can be covered in either adventitia or serosa.

Question 18

It is known that Crohn’s disease can lead to malnutrition. Speculate why disruption of the mucosa could cause malnutrition.

Answer 18

The mucosa of the large intestine contains absorptive cells, which absorb nutrients from digested food. Inflammation causing disruption to the mucosa would impede and decrease the ability of these cells to function properly. With fewer nutrients being absorbed, a patient with Crohn’s disease is susceptible to malnutrition.

Question 19

What are the features of the anal canal?

Answer 19

Anal column: Longitudinal ridges in the canal

Internal and external anal sphincters: These maintain continence, and relax to enable evacuation during defecation.