7.1- The Intestines

Question 1

Describe the the structure of chyme delivered to the duodenum

Answer 1

• hypertonic, acid and only partially digested
• and THEN becomes an isotonic and neutral solution by mixing with pancreatic juice, bile and juices from the intestinal wall

Question 2

By which 2 processes is chyme delivered to the duodenum?

Answer 2

1. Gastric empting
2. Gastric mixing

Question 3

What happens in gastric emptying?

Answer 3

• Peristaltic contraction orginates in upper fundus and sweeps down towards the pyloric sphincter
• contraction becomes more vigorous as it reaches the thick walled antrum
• strong antral peristaltic contraction propels chyme forward
• a small portion of chyme is pushed through open pyloric sphincter into duodenum, the stronger the contraction, the more chyme is emptied per wave

Question 4

What happens in gastric mixing?

Answer 4

• when peristaltic contraction reaches the pyloric sphincter, it is tightly closed and no further emptying takes place
• THEREFORE, when chyme being propelled forward hits closed sphincter, it is tossed BACK into the antrum
• THEREFORE, mixing is accomplished
• ie chyme is propelled forward, tossed back into the antrum with each peristaltic contraction

Question 5

How is intestinal absorption accomplished?

Answer 5

1. Large surface area
2. Slow movement ( pattern of motility)
3. Simple and facilitated diffusion
4. Active transport and endocytosis

Question 6

What structures of the intestinal lumen help increase surface area?

Answer 6

1. Plicae circulares
2. Villi
3. Microvilli
4. Crypts of Lieberkuhn

Question 7

What is distinct about the structure of Crypts of Lieberkuhn?

Answer 7

they are invaginations of epithelia into lamina propria forming intestinal glands

• go in the OPPOSITE direction to villi
• ie villi go towards the lumen but Crypts go towards the next layer ie submucosa/ muscularis externa

Question 8

How is the mucosa in the crypts constantly renewed?

Answer 8

• enterocytes multiply in the crypts
• and then migrate towards tips of villi, maturing as they go
• they acquire the capacity to absorb
• they are then shed from the villus tips

Question 9

Describe what each of the following cells produces:

• ​Enterocytes
• Goblet cells
• Paneth cells
• Enterochromaffin cells
• Endocrine cells

Answer 9

• Digestive enzymes
• mucus
• glycoproteins, immunoglobulin, lysozymes
• serotonin
• GI hormones e.g. secretin, CCK,

Question 10

What is the significance of the shedding cells from the renewing mucosa?

Answer 10

• enterocytes are shed from villus tips
• produce the unstirred layer of secretions that help to breakdown the main nutrients

Question 11

What happens in the brush border?

Answer 11

• cells on the villi are very active and secrete enzymes into brush border
• forms unstirred layer
• meet and react with enzymes secreted by enterocytes
• steadily releasing small molecules for molecules for absorption

therefore transport from:

1. Lumen to enterocytes
2. enterocytes into circulation

very important for digestion

Question 12

What are the secretions of the intestine?

Answer 12

1. Pancreatic juice; pancreatic exocrine secretion
2. Bile; released from GB, stimulated by CCK
3. Intestinal juice ( brush border enzymes)
   4.