small intestine - monday

Question 1

what does the intestine do

Answer 1

continues digestion and absorption of food and fluids

Question 2

what makes up the small intestine

Answer 2

• duodenum
• jejunum
• ileum

Question 3

what are the 4 general histological layers of the GI tract

Answer 3

• mucosa
• submucosa
• muscularis externa
• serosa/adventitia

Question 4

what type of epithelium is in the SI

Answer 4

simple columnar epithelium

Question 5

what are plicae circulares

Answer 5

fold of mucosa and submucosa encircling lumen, grossly viewable

Question 6

unlike rugae of the stomach, plicae circulares are ____ folds

Answer 6

permanent

Question 7

what are villi

Answer 7

fingerlike projections of mucosal layer only into lumen of gut

Question 8

what type of epithelium are villi lined by

Answer 8

simple columnar

Question 9

what are the 3 cell types that villi consist of

Answer 9

1. enterocytes
2. goblet cells
3. enteroendocrine

Question 10

what are enterocytes

absorptive cells

Answer 10

on the apical surface of villi and contain thousands of microvilli which form a brush border

Question 11

what do microvilli contain

Answer 11

• actin core
• enzymes - lactase, maltase, sucrase

Question 12

what are the enzymes in microvilli involved in

Answer 12

the terminal digestion of carbs and proteins

Question 13

what triggers the movement of microvilli

Answer 13

submucosal (meissner’s) plexus

Question 14

what are the two functions of the brush border

Answer 14

• increase surface area for absorption
• increase surface area for enzymes that perform final stages of extracellular digestion, preparing them for transport across the cell membrane

Question 15

what is the purpose of maximizing surface area

Answer 15

digestion and absorption require mixing of ingesta with bile and enzymes, retention of chyme, with exposure to adequate SA

Question 16

what are lacteals

Answer 16

blind-ended lymphatic vessel

Question 17

what are goblet cells

Answer 17

produce mucus to protect the lumen from abrasion and bacterial invasion

Question 18

what are enteroendocrine cells

Answer 18

cells that secrete their contents basally

Question 19

what is within the core of each villus (in the lamina propria)

4 things

Answer 19

1. capillar plexus
2. lacteal
3. thin strands of muscularis mucosae
4. lymphocytes, eosinophils, macrophages, etc

Question 20

where are crypts located

Answer 20

between villi - invaginations of the mucosa

Question 21

what are the 5 things that are in crypts

Answer 21

1. simple tubular glands
   2. stem cells
2. enteroendocrine cells
   4. paneth cells
3. sometimes goblet cells

Question 22

what are paneth cells

Answer 22

protect lining of gut from microorganims such as bacteria & parasites

in SI only

Question 23

what do paneth cells secrete

Answer 23

lysozymes and defensins

Question 24

what animals are paneth cells absent in

only some animals

Answer 24

dogs, cats, pigs, and racoons

Question 25

where are paneth cells located

Answer 25

base of crypt

Question 26

where do secretions from paneth cells enter

Answer 26

lumen directly - do NOT enter the bloodstream

Question 27

what cells are responsible for the rapid turnover of the intestinal epithelium

Answer 27

stem cells

Question 28

what is the first part of the SI

Answer 28

duodenum

Question 29

what is the unique feature of the duodenum

Answer 29

brunner's glands in submucosa

Question 30

what do brunner's glands produce

Answer 30

mucus and bicarbonate to offset acidic chyme expelled from stomach

Question 31

what does the duodenum contain

Answer 31

* brunner's glands * villi: short, broad, leaf-like with scattered enteroendocrine cells * retroperitoneal * houses bile and pancreatic ducts * paneth cells at base of crypts

Question 32

what types of nervous systems does the enterogastric reflex involve

Answer 32

CNS and ENS, endo/paracrine signals

Question 33

what is the enterogastrin reflex

Answer 33

* afferent fibers of the vagus nerve receive stimuli in duodeum * these stimuli block vagus-induced stomach empyting

Question 34

what is released from enteroendocrine cells in the duodeum | enterogastric reflex

Answer 34

CCK and secretin gets secreted into the bloodstream

Question 35

what do CCK and secretin suppress | enterogastric reflex

Answer 35

gastric empyting

Question 36

what is the second part of the SI

Answer 36

jejunum

Question 37

what are the characteristics of the jejunum

Answer 37

* **longest villi** * abundant paneth cells in crypts * no glands in submucosa

Question 38

what is the third part of the SI

Answer 38

ileum

Question 39

what are the characteristics of the ileum

Answer 39

* shorter villi * paneth cells * **peyer's patches in submucosa**

Question 40

what are peyer's patches

Answer 40

specialized lymphatic nodules

Question 41

what are M cells | microfold cells

Answer 41

specialized epithelial cells that contain small microfolds on their lateral edges

Question 42

what do M cells do

Answer 42

* trap antigens from the lumen of the gut via endocytosis * antigens released beneath M cells and taken up by APC (DC) in underlying dome * antigens presented to T cells to initate immune response