Exam #5: Intestines

Question 1

Describe the mucosal surface of the small intestine.

Answer 1

The duodenum has 3x anatomical features that increase the SA:

1) Circular folds= gross structures
2) Villi= finger-like projections of the mucosa & submucosa, lined with enterocytes
3) Microvilli= ruffling of the apical membrane of the enterocytes lining the villi

*****Note that the microvilli are referred to as the “brush border”

Question 2

Describe the mucosal surface of the large intestine. How does the mucosal surface of the large intestine differ from the small intestine?

Answer 2

The mucosal surface of the large intestine is v. similar to the small intestine, except there are NO VILLI & MORE GOBLET CELLS

*****Note that because the large intestine DOES NOT HAVE VILLI, it DOES NOT ABSORB NUTRIENTS

Question 3

What are the gross differences between the small & large intestines?

Answer 3

1) Large intestine contains “haustra,” or outpouchings where circular muscle is contracted
2) Large intestine contains 3x bands of longitudinal muscle, called “tenia coli

Question 4

What are the mixing movements of the colon?

Answer 4

Segmental contractions like what is seen in the small intestine, but that are called “haustrations” in the large intestine

Question 5

What are the propulsive movements of the colon?

Answer 5

Peristaltic contractions or “mass movements” as they’re referred to in the large intestine

Question 6

What is the Gastroenteric Reflex?

Answer 6

Distention of the stomach induces peristaltic contraction of the small intestine

Question 7

What is the Colonocolic Reflex?

Answer 7

Distention of the colon causes a mass movement

• 20cm of colon will constrict proximal to distention
• Relaxation occurs distally

*****Net result is to propel fecal matter toward the anus

Question 8

What is the Gastrocolic Reflex?

Answer 8

Distention in the stomach during a meal will lead to a mass movement in the colon

Question 9

What is the Duodenocolic Reflex?

Answer 9

Distention in the duodenum after a meal will lead to a mass movement in the colon

Question 10

Describe the process of defection.

Answer 10

Once food reaches the distal colon, the defecation reflex is initiated. The defecation reflex is actually two reflexes:

1) Intrinsic reflex= distention in the distal colon signals to ENS, which causes a peristaltic wave in the descending colon, sigmoid colon, and rectum, ALSO, internal anal sphincter relaxes in response to NO & VIP
2) Parasympathetic defecation reflex= after the intrinsic reflex, distention of the rectum signals back to the spinal cord, and then again to the descending colon, sigmoid colon, and rectum via PNS nerves

• **3) Additional afferent signals= deep breath, closure or the glottis, and contraction of the abdominal wall muscles
• **4) Descried defecation= voluntary control & conscious relaxation of the external anal sphincter

Question 11

What are the three distinct anatomical features that gives the small intestines its large surface area of approximately 200 m2?

Answer 11

1) Circular folds
2) Villi or finger-like projects & crypts in the circular folds
3) Microvilli on the surface of enterocytes

Note that damage to these structures result in a decrease in absorptive capacity

Question 12

What cell types are found on the villi? What cell types are found in the crypts between villi?

Answer 12

Villi

• Goblet cells
• Absorptive enterocytes

Crypts

• Secretory enterocytes
• Endocrine cells
• Stem cells

Question 13

What are Brunner’s Glands? What are the distinguishing features of Brunner’s glands?

Answer 13

Brunner’s Glands are glands in the duodenum of the small intestine that secrete Mucous & bicarbonate to neutralize stomach acid & protect the small intestine

These are glands that are located in the duodenum

• Generally function to protect the intestine from acid in the stomach*
• Secrete MUCUS & BICARBONATE

Question 14

Describe the distinguishing features of crypts of Lieberkuhn.

Answer 14

In contrast to Brunner’s Glands, these are located THROUGHOUT the small and large intestines

• Generally function in: lubrication/ protection, absorption, & digestion
• Secrete: MUCUS, H20/ ELECTROLYTES, DIGESTIVE ENZYMES

Question 15

What are the two types of movements in the small intestine?

Answer 15

Segmental Contractions= mixing

Peristaltic Contractions= moving

Question 16

What are the primary regulators of GI smooth muscle?

Answer 16

1) ACh= stimulate
2) VIP= inhibit
3) NO= inhibit

*****Note that it is the coordination of these NTs that allow for movement

Question 17

Describe the general distribution of normal microbiota throughout the gastrointestinal tract

Answer 17

Generally, there is increased bacterial mass as you move away from the stomach (low pH)

Question 18

What are the factors that contribute to the growth of intestinal microbiota?

Answer 18

1) Secretions
2) Mucosal immunity
3) Intestinal motility
4) Pharmacologic agents

Question 19

What are the key functions of intestinal microbiota?

Answer 19

1) Conversion of primary to secondary bile acids
2) Deconjucation of compounds conjugated in the liver
3) Nutrient salvage
4) Detoxification
5) Suppression of pathogenic organisms

Question 20

Describe the symptoms and pathophysiology of IBS.

Answer 20

Irritable Bowel Syndrome= is an idiopathic chronic relapsing disorder of abdominal discomfort & alternating bowel habits

• Cause is unknown
• Those with constipation predominant are encouraged to exercise more

Question 21

Describe the symptoms and pathophysiology of IBD.

Answer 21

Inflammatory Bowel Disease= inflammation of the GI tract caused by:

1) Ulcerative Colitis= large intestine
- Originates in the Crypts of Lieberkuhn

2) Crohn’s Disease= can effect any part of the GI tract, but commonly associated with the ileum
- Originates in the intestinal submucosa
- “skip lesions”

*****associated with joint pain that may preceed GI symptoms, osteoporosis due to malabsorption of Vitamin K & D, and dehydration

Question 22

Describe the symptoms and pathophysiology of Hirschprung’s Disease.

Answer 22

This is a congenital functional motility disorder, caused by loss of ganglionic cells from the submucosal & myenteric plexuses that control the distal colon. Symptoms include:

1) Constipation
2) Megacolon
3) Narrowing of colon