A & P - Gastrointestinal System, Small Intestine

Front 1

What is the average length of the small bowel in a living person?

In a cadaver?

Why the discrepancy?

Back 1

3 m in a living person

6.5 m in a cadaver due to the loss of smooth muscle tone after death.

Front 2

From proximal to distal, what are the three regions of the small intestine?

Back 2

Duodenum

Jejunum

Ileum

Front 3

What is the name of the sphincter present where the ileum joins the large intestine?

Back 3

Ileocecal sphincter

Front 4

Which is the principle enzyme responsible for digesting carbohydrates in the small bowel lumen?

Back 4

Pancreatic amylase

Front 5

Which is the principle enzyme responsible for digesting lipids in the small bowel lumen?

Back 5

Pancreatic lipase

Front 6

Which is the principle enzyme responsible for digesting protein in the small bowel lumen?

Back 6

Trypsin

Front 7

Name the two brush-border enzymes responsible for completing digestion of proteins in the small bowel.

Back 7

Aminopeptidase
-cleaves off the amino acid at the amino end of a peptide

Dipeptidase
-splits dipeptides

Front 8

Name the three brush-border enzymes responsible for digesting disaccharides and thus completing carbohydrate digestion in the small bowel.

Back 8

Sucrase
-breaks sucrose into glucose and fructose

Lactase
-breaks lactose into glucose and galactose

Maltase
-breaks maltose into glucose molecules

Front 9

Where are Paneth cells located and what do they secrete?

Back 9

Paneth cells are located in the mucosal epithelium of the small intestine.

Paneth cells secrete lysozyme, a bactericidal enzyme.

Paneth cells are also capable of phagoyctosis.

Front 10

Name the three types of neuroendocrine cells present in the glands of the small intestine.

What substances do each of these cell types secrete?

Back 10

S cells
-secrete secretin

CCK cells
-secrete cholecystokinin, or CCK

K cells
-secrete glucose-dependent insulinotropic peptide, or GIP

Front 11

What are Peyer's patches? Where are they located?

Back 11

Peyer's patches groups of lymphatic nodules (nodules consisting of lymphatic tissue, or MALT).

Peyer's patches are found in the ileum.

Front 12

What are Brunner's glands?

Where in the small intestinal wall are they located?

What do they secrete?

Back 12

Brunner's glands, also known as duodenal glands, are located in the submucosa of the duodenum.

Brunner's glands secrete alkaline mucous that helps neutralize incoming gastric acid.

Front 13

What glands are found in the submucosa of the duodenum?

What do they secrete?

Back 13

Brunner's glands, also known as duodenal glands, are located in the submucosa of the duodenum.

Brunner's glands secrete an alkaline mucous that neutralizes incoming stomach acid.

Front 14

What are the crypts of Lieberkuhn?

Back 14

The crypts of Lieberkuhn are the crypts formed by the intestinal glands.

The intestinal glands are essentially deep crevices lined with secretory epithelium.

Front 15

Describe the landscape of the intestinal mucosa.

Back 15

The intestinal mucosa has both peaks and valleys, as it were.

The peaks are the villi, fingerlike projections of the mucosa that vastly increase the surface area of the epithelium available for absorption and digestion. The villi are lined by epithelium that contains absorptive cells and goblet cells.

Individual absorptive cells also possess microvilli, further increasing the surface area.

The valleys are the crypts of Lieberkuhn, or intestinal glands. The intestinal glands are lined by epithelium containing the enteroendocrine cells of the small bowel as well as bacteria-killing Paneth cells.

Front 16

Which cell types are present in the epithelium that lines the small bowel villi?

Back 16

1) Absorptive cells

2) Goblet cells

Front 17

Which cell types are present in the crypts of Lieberkuhn/intestinal glands?

Which substances do each of these cells secrete?

Back 17

Neuroendocrine cells (x3)

1) S cells
-secretin

2) CCK cells
-cholecystokinin (CCK)

3) K cells
-glucose-depedent insulinotropic protein (GIP)

Immunologic cells:

Paneth cells:
-lysozyme

Front 18

What is the cause of lactose intolerance?

Back 18

Lactose intolerance is caused by a deficiency of the brush border enzyme lactase, which digests the disaccharide lactose into a molecule of glucose and galactose.

Front 19

What are segmentations?

Back 19

Segmentations are localized, mixing contractions that occur in portions of the small intestine distended by a large volume of chyme.

Segmentations mix chyme with digestive juices and bring the particles of food into contact with the mucosa for absorption; they do not push the intestinal contents along the tract.

Front 20

What is the name of the peristaltic movement that pushes intestinal contents along the tract after most of a meal has been absorbed?

Back 20

Migrating motility complex (MMC)

Front 21

What is the migrating motility complex?

Back 21

The migrating motility complex is a peristaltic movement that pushes intestinal contents along the tract after most of a meal has been absorbed.

The MMC begins in the lower portion of the stomach and pushed chyme forward along a short stretch of small intestine before dying out.

The MMC slowly migrates down the small intestine, reaching the end of the ileum in 90-120 minutes.

Front 22

How long does chyme from a single meal remain in the small intestine for?

Back 22

3-5 hours

Front 23

What are the two types of movements performed by the small intestine wall?

Back 23

1) Segmentations
-mix chyme with digestive juices and bring the particles of food into contact with the mucosa for absorption
-do not push the intestinal contents along the tract

2) Migrating Motility Complexes (MMCs)
-push chyme along intestinal tract after most of the meal has been absorbed

Front 24

What is the brush border composed of?

Back 24

The brush border is composed of projections of the apical membrane of the absorptive cells called microvilli.

The microvilli add surface area along which nutrients can be digested and absorbed.

The microvilli also have brush-border enzymes along their plasma membranes that complete the final steps of digestion of carbohydrates and proteins.

Front 25

What is the role of brush-border enzymes?

Back 25

Brush-border enzymes, synthesized and presented on the plasma membrane of absorptive cells, are responsible for the final steps in the digestion of carbohydrates and proteins.

Carbohydrates are broken down in the lumen by amylase. The remaining disaccharides are further broken into monosaccharides by the brush border enzymes sucrase, lactase, and maltase.

Proteins are broken down in the intestinal lumen by the enzyme trypsin (among others). The job is finished off by the brush border enzymes aminopeptidase and dipeptidase.

Front 26

Which cells are responsible for synthesizing and presenting brush-border enzymes on their surface?

Back 26

Aborptive cells (present in the villous epithelium)

Front 27

What three structural features of the small bowel mucosa facilitate the processes of digestion and absorption?

Back 27

1) Circular folds
-folds of mucosa and submucosa that begin near the proximal portion of the duodenum and end at about the midportion of the ileum

2) Villi
-fingerlike projections of the mucosa

3) Microvilli
-projections of the apical membrane of the absorptive cells

These structural features facilitate digestion and absorption by drastically increasing the area of the surfaces across which these processes take place.

Front 28

Which of the intestinal mucosal cells secretes mucus?

Back 28

Goblet cells

Front 29

What is the name of the valve present where the small intestin empties into the large intestine?

Back 29

Ileocecal valve