CGIER 13 - Small intestine, histology, cytology; Pancreas, pancreatic secretions

Question 1

What is the alimentary canal contained in?

Answer 1

The abdominal cavity is contained in the Peritoneal Cavity.

Question 2

What are the two layers of the Peritoneal Cavity made of?

Answer 2

Inner layer: endothelium

Outer layer: mesothelium

Question 3

What is the Parietal Peritoneum?

Answer 3

The outermost layer of the Peritoneal cavity

Question 4

What is the Visceral Peritoneum?

Answer 4

The layer of the Peritoneal cavity that covers the organs.

Question 5

Explain the formation of the gut in the embryo?

Answer 5

1. The gut extends from the dorsal body wall by a dorsal mesentery which elongates during fetal development.
2. The gut tube lengthens and coils in the abdomen
3. Some parts of the tube adhere to the dorsal body wall and lose their mesentery and becoming what is called Retroperitoneal.

Question 6

What are the circularly placed folds in the mucosa and submucosa of the small intestine called?

Answer 6

Plicae Circulares

Question 7

What is the total length of the small intestine post mortem and in life?

Answer 7

Postmortem: 7m

In life: 3m

Question 8

What are the names of the parts the small intestine is divided into?

Answer 8

1. duodenum
2. jejunum
   3 ileum

Question 9

Describe the duodenum.

Answer 9

1. 0.21m long
2. mucosa layer has villi
3. submucosa layer contains Brunner’s glands that secrete alkaline mucus to protect the duodenum from the acidic chyme of stomach
4. Pancreatic and bile ducts enter via a common duct near the pyloric

Question 10

What are the names of the common duct that the pancreatic and bile ducts share?

Answer 10

1. Papilla of Vater
2. Duodenal Ampulla
3. Major Duodenal Papilla

Question 11

Describe the jejunum.

Answer 11

1. 0.9m long
2. mucosa layer has villi
3. well developed Plicae Circulares

Question 12

Describe the Ileum

Answer 12

1. 2m long

2. mucosa layer has Peyer’s Patches

Question 13

Describe the role of villi in the small intestine.

Answer 13

Throughout the small intestine there is a large number of villi that are continually contracting and lengthening, therefore increasing the surface area of the small intestine for absorption.

Question 14

Describe the structure of villi.

Answer 14

The luminal face of villi is lined with epithelial cells, microvilli, and goblet cells. In between the villi are spaces that extend to the muscularis mucosa layer called Crypts of Liberkuhn. They contain epithelial, goblet, Paneth, zymogen, enteroendocrine cells, and stem cells.

Question 15

Describe the general structure of the small intestine from the inside to outside.

Answer 15

1. Mucosa: (inner: crypts of Liberkuhn, villi, epithelium, microvilli / outer: lacteals, lamina propria, capillaries)
2. Muscularis Muscosa: (inner: smooth muscle)
3. Submucosa: (inner: connective tissue)
4. Muscularis Externa (inner: smooth circular / outer: smooth longitudinal)
5. Serosa: (inner: loose connective tissue / outer: mesothelium)

Question 16

Describe the location and function/secretion of cells and glands found in the small intestine.

Answer 16

There are 5 cells/glands in the small intestine:

1. Columnar Epithelial Cells: function is absorption & found in all mucosa
2. Goblet Cells: secretion of mucus & found in all mucosa
3. Paneth Cells: secretion of lysozyme, antimicrobial B-defensis & found in crypts of Liberkuhn
4. Enteroendocrine Cells: secretion of secretin, cholecystokinin & found in duodenal crypts of Liberkuhn
5. Brunner’s Glands: secretion of alkaline mucus & found in the submucosa of the duodenum

Question 17

What is the function of the small intestine?

Answer 17

The digestion of food by enzymatic action and the absorption of the products through villi (columnar epithelial cells).

Question 18

What happens to chyme once it enters the small intestine?

Answer 18

1. Chyme enters the duodenum and mixes with pancreatic secretions, bile, and succus entericus.
2. Brunner’s glands secrete the alkaline mucus at a pH of 8.8-9.3, raising the pH of chyme to 5.5, which is less than optimal for the operation of pancreatic enzymes
3. Chyme continues to move through the small intestine through segmenting contractions and peristalsis
4. Lower regions of the ileum become more acidic again due to the production of organic acids by bacteria.
5. It takes 3-5hrs for chyme to go from the pylorus to the ileocaecal valve.

Question 19

What are acini?

Answer 19

A cluster of serous cells in the pancreas that secrete enzymes into a minute central duct, that drain into intercalated ducts, that then drain into interlobular ducts that eventually coalesce into the main pancreatic duct.

Question 20

How does the pancreas have endocrine and exocrine function?

Answer 20

Exocrine: the acini secrete enzymes
Endocrine: the Islets of Langerhans secrete hormones into the bloodstream

Question 21

How is secretion controlled in the pancreas and explain the process?

Answer 21

Control of enzyme secretion in the pancreas is nervous and hormonal, but mainly hormonal:

1. Entry of chyme into the duodenum stimulates the enteroendocrine cells in the duodenum crypts of Linderkuhn to secrete secretin and cholecystokinin.
2. The two hormones are carried through the bloodstream.
3. Secretin is carried to the pancreas to stimulate the centroacinar cells to release large amounts of alkaline fluid at pH 8.
4. Cholecystokinin stimulates the acini to secrete pancreatic enzymes.
5. The release of pancreatic enzymes causes the hydrolysis of carbs, proteins, and fats in the chyme into monosaccharides, amino acids, and fatty acids.
6. Most of the absorption takes place in the jejunum and ileum via the microvillar surface of the columnar epithelial cells by active transport and facilitated diffusion.

Question 22

List pancreatic enzymes & their secretions.

Answer 22

1. Trypsin
2. Chymotrypsin
3. Carboxypeptidase
4. Pancreatic Enzymes
5. Pancreatic Lipase
6. Ribonuclease
7. Deoxyribonuclease
8. Sodium Bicarbonate