T6. MOTILITY, SECRETION AND ABSORPTION IN TE SMALL INTESTINE

Question 1

What are the three regions of the small intestine?

Answer 1

Duodenum, Jejunum, Ileum

Question 2

How long is the duodenum?

Answer 2

The first 25-30 cm of the small intestine

Question 3

What does the duodenum receive?

Answer 3

Stomach contents, pancreatic juice, and bile

Question 4

What happens to stomach acid in the duodenum?

Answer 4

It is neutralized

Question 5

What happens to fats in the duodenum?

Answer 5

They are emulsified by bile salts

Question 6

What happens to pepsin in the duodenum?

Answer 6

It is inactivated by increased pH

Question 7

What takes over chemical digestion in the duodenum?

Answer 7

Pancreatic enzymes

Question 8

Where does the duodenum end?

Answer 8

At the duodenojejunal flexure (a sharp bend)

Question 9

How much of the small intestine does the jejunum form?

Answer 9

First 40% beyond the duodenum

Question 10

What is the wall of the jejunum like?

Answer 10

Relatively thick and muscular

Question 11

Where does most digestion and absorption occur?

Answer 11

In the jejunum

Question 12

How much of the postduodenal small intestine is the ileum?

Answer 12

Last 60%

Question 13

What is the ileum like structurally?

Answer 13

Thinner, less muscular, and less vascular than the jejunum

Question 14

What marks the end of the small intestine?

Answer 14

The ileocecal junction

Question 15

What is the ileocecal valve?

Answer 15

A sphincter formed by thickened muscularis of the ileum

Question 16

What is the function of the ileocecal valve?

Answer 16

Regulates passage of food residue into the large intestine

Question 17

What are the tissue layers of the small intestine specialized for?

Answer 17

Nutrient digestion and absorption

Question 18

What are the two layers of the muscularis externa?

Answer 18

Thick inner circular layer and thinner outer longitudinal layer

Question 19

What increases the internal surface area of the small intestine?

Answer 19

Plicae circulares, villi, and microvilli

Question 20

What are plicae circulares?

Answer 20

Large circular folds in the mucosa and submucosa

Question 21

How much do plicae circulares increase surface area?

Answer 21

By a factor of 2-3

Question 22

How much do villi increase surface area?

Answer 22

By a factor of 10

Question 23

How much do microvilli increase surface area?

Answer 23

By a factor of 20

Question 24

Where do circular folds (plicae circulares) occur?

Answer 24

From the duodenum to the middle of the ileum

Question 25

What is the function of circular folds?

Answer 25

Cause chyme to spiral, increasing contact with mucosa

Question 26

Where are circular folds sparse or absent?

Answer 26

In the distal half of the ileum

Question 27

What are villi?

Answer 27

Fingerlike projections of the mucosa lined with absorptive and goblet cells

Question 28

What cells line the villi?

Answer 28

Absorptive cells (enterocytes) and goblet cells

Question 29

What joins the epithelial cells of the villi?

Answer 29

Tight junctions

Question 30

What is inside the core of a villus?

Answer 30

Lamina propria with arteriole, capillary network, venule, and lacteal

Question 31

What do blood capillaries in the villi absorb?

Answer 31

Most nutrients

Question 32

What does the lacteal in the villi absorb?

Answer 32

Most lipids

Question 33

What are microvilli?

Answer 33

Folds of plasma membrane on absorptive cells forming a brush border

Question 34

What is the function of brush border enzymes?

Answer 34

Carry out contact digestion on the surface of microvilli

Question 35

What is contact digestion?

Answer 35

Digestion where chyme must contact the brush border

Question 36

What ensures contact digestion occurs?

Answer 36

Intestinal churning

Question 37

What are intestinal crypts (crypts of Lieberkühn)?

Answer 37

Gland-like structures in the mucosa similar to gastric glands

Question 38

What cells are in the upper half of intestinal crypts?

Answer 38

Enterocytes and goblet cells (secrete mucin)

Question 39

What cells are in the lower half of intestinal crypts?

Answer 39

Dividing stem cells

Question 40

What do enteroendocrine cells in intestinal crypts secrete?

Answer 40

Secretin and cholecystokinin

Question 41

What do Paneth cells in crypts secrete?

Answer 41

Lysozyme, phospholipase, and defensins

Question 42

Where are duodenal glands located?

Answer 42

In the submucosa of the duodenum

Question 43

What do duodenal glands secrete?

Answer 43

Bicarbonate-rich mucus

Question 44

What is the function of the mucus secreted by duodenal glands?

Answer 44

Neutralize stomach acid and shield mucosa

Question 45

What do enterochromaffin-like cells secrete?

Answer 45

Serotonin and motilin

Question 46

Where are defensive lymphocytes found in the intestine?

Answer 46

In the lamina propria and submucosa

Question 47

What is the function of lymphocytes in the intestine?

Answer 47

Intercept pathogens before they invade bloodstream

Question 48

Where does nearly all chemical digestion and absorption occur?

Answer 48

In the small intestine

Question 49

What nutrients are absorbed in the duodenum and jejunum?

Answer 49

Sugars, lipids, amino acids, calcium, and iron

Question 50

What nutrients are absorbed in the ileum?

Answer 50

Bile salts, vitamin B12, water, and electrolytes

Question 51

What makes absorption in the small intestine very rapid?

Answer 51

Presence of villi and microvilli

Question 52

What are the three functions of small intestine contractions?

Answer 52

Mix chyme, promote contact digestion and absorption, and move residue to large intestine

Question 53

What are the two types of small intestine contractions?

Answer 53

Segmentation and peristalsis

Question 54

What is the major contractile activity of the small intestine?

Answer 54

Segmentation

Question 55

What type of contraction is peristalsis?

Answer 55

Weak, gradual movement of chyme

Question 56

What causes peristalsis?

Answer 56

Greater pressure at the pyloric end than distal end

Question 57

What produces slow waves in small intestine?

Answer 57

Pacemaker cells called interstitial cells of Cajal

Question 58

What do slow waves lead to in the muscle?

Answer 58

Action potentials and contraction

Question 59

How do contractions spread in the intestine?

Answer 59

Through gap junctions, must be regenerated in nearby pacemaker regions

Question 60

What influences the interstitial cells of Cajal?

Answer 60

The enteric nervous system via autonomic nerves

Question 61

What neurotransmitter increases slow wave amplitude and duration?

Answer 61

Acetylcholine (from the parasympathetic system)

Question 62

What do enterochromaffin-like cells respond to?

Answer 62

Pressure (filling) and food chemicals

Question 63

What do serotonin and motilin stimulate?

Answer 63

Muscle contractions in the intestine

Question 64

What is the gastroileal reflex?

Answer 64

Increased gastric activity increases ileum motility and movement through ileocecal valve

Question 65

What is the ileogastric reflex?

Answer 65

Distension of ileum inhibits gastric motility

Question 66

What is the intestino-intestinal reflex?

Answer 66

Overdistension of one part of the intestine relaxes other parts