Lecture 7: small intestine

Question 1

what is the function of the small intestine?

Answer 1

• completion of digestion
• majority of absorption and secretion

Question 2

what are the 3 distinct regions of the small intestine?

Answer 2

• duodenum (nearest to stomach)
• jejenum (middle)
• ileum (nearest to large intestine)

Question 3

what are the** 3 main surface area adaptions** of the small intestine?

Answer 3

1. Plicae circularis (the largest folds towards the lumen of SI)
2. Villi - smaller folds on the plicae circularis
   3.** microvilli** - additional folds, ‘ brush border’, only seen on electron microscope

Question 4

What are the crypts of lieberkuhn?

Answer 4

• tubular glands found between the villi
• mostly present in the duodenum and jejenum
• contain undifferentiated cells that proliferate to replace lost enterocytes

Question 5

what are brunners glands?

Answer 5

• glands present in the duodenum that secrete an alkaline mucous

Question 6

what are the** 4 main types of cells** present in the small intestine & what is their function?

Answer 6

1. enterocytes - absorption
2. goblet cells - secretory
   3. paneth cells - defence
3. enteroendocrine cells -hormonal

Question 7

what is the sphincter of oddi?

Answer 7

• a ring of smooth muscle
• controls the entry of bile & pancreatic juice into the small intestine

Question 8

what are** histological characteristics **of the duodenum?

Answer 8

• secretory brunners glands in the submucosa
• lots of goblet cells

Question 9

what are the** key histological features** of the jejenum?

Answer 9

• lots of plicae - circular folds toward the lumen
• lots of enterocytes & goblet cells

Question 10

what are the** key histological features** of the** ileum**?

Answer 10

• fewer plicae
• presence of peyers patches - lymphoid tissue (immunity function)

Question 11

Where does secretion mostly occur?

Answer 11

in the duodenum

Question 12

what contents are present in the SI secretions?

Answer 12

• hormones (entero endocrine cells)
• mucous - goblet cells
• lysozyme (kills bacteria) - paneth cells
• isotonic fluid - secreted by the crypts
• alkaline mucous - brunners glands

Question 13

What are examples of hormones that are secreted by entero endocrine cells of the SI?

Answer 13

• Cholecystokinin (CKK)
• Motilin
• secretin
• serotonin

Question 14

what are the** 2 types of contraction **involved in SI motility?

Answer 14

* mixing contractions - called segmentation
* moving contractions- peristalisis & **migrating myoelectrical complex **

Question 15

what are segmentation contractions?

Answer 15

• mixing contraction
• segments of the SI undergo static contractions (not wave like/peristalisi contractions)
• important for **mixing the chyme in both directions with the digetsive enzymes **in the SI

Question 16

what are peristalisis contractions in the SI?

Answer 16

• sequence of adjacent contractions that result in foward movement of chyme
• occurs in response to the SI lumen stretching

Question 17

What is the migrating motor (myoelectrical) complex? what is it’s function?

‘house keeping contractions’

Answer 17

• occurs during fasting or once a meal has been processed
• slow waves of peristalisis
• occurs every 70-90 mins
• function: to sweep out the last remains of deigested foods along with bacteria into the large intestine

Question 18

what** hormone** stimulaes the migrating motor complex?

Answer 18

• motilin
• secreted by the entero endocrine M cells of the duodenum and jejenum

Question 19

What 3 things control SI motility?

remember the triangle

Answer 19

1. autonomic - parasympathetic stimulates motility
2. enteric - basal electrical rhythms always present
3. hormones - motilin (migrating motor complex) & gastrin - stimulates the ileum

Question 20

how does the vagus nerve impact motility along the GI tract?

Answer 20

• the contribution of the vagus nerve to GIT motility decreaes along the length of the GIT

Question 21

Describe 2 examples of intestinal reflexes?

Answer 21

* ileo-gastric reflex - refers to the reduction in gastric motility that occurs in response to the stretching of the ileum
* gastro- ileo reflex - describes the increase in motility of the terminal ileum that occurs whenever there is an increase in secretory/motor activity of the stomach