Histology of the Lower GI Tract

Question 1

What is chyme?

Answer 1

semifluid mass of partly digested food expelled by the stomach into the duodenum

Question 2

What are villi in the small intestines?

Answer 2

folds of the mucosa projecting into the lumen. cover entire surface of S.I. increase the absorptive surface of the mucosa
Extend deep into mucosa to form crypts of lieberkuhn and end at muscularis mucosae

Question 3

What are plicae circularis?

Answer 3

permanent folds that are distinct in jejunum what include mucosa and submucosa
begin in duodenum and disappear in mid-ileum

Question 4

What are crypts of lieberkuhn?

Answer 4

intestinal simple tubular glands that increase surface areaby adding another separate fold btwn the villi

Question 5

What epithelium lines the crypts and what 4 types of cells are included in crypts of lieberkuhn?

Answer 5

Lined by simple columnar epithelium Absorptive, goblet, paneth, and enteroendocrine cells

Question 6

What are enterocytes?

Answer 6

Absoprtive cells: epithelial cells lining the lumen that have microvilli on apical surface
Have tight junction barrier linking adjacent enterocytes

Question 7

What do the length of the villi depend on ?

Answer 7

degree of distention of intestinal wall and contraction of Sm m in villus core

Question 8

What are microvilli?

Answer 8

evagination of apical part of enterocytes to increase SA
Produce brush border on apical border of enterocytes
Contain intramembranous enzymes, including lactase, maltase, sucrase, for terminal digestion of carbs

Question 9

What layer is the main site of blood and lymph vessels?

Answer 9

submucosa

Question 10

What covers the serosa (thin layer of loose CT)?

Answer 10

visceral peritoneum (mesothelium)
- a membrane composed of simple squamous cells taht forms the lining of several body cavities

Question 11

What is mesothelioma?

Answer 11

an aggressive form of cancer affecting the membrane lining the pericardial, pleural or peritoneal cavities

Question 12

What is segmentation ?

Answer 12

pattern of annular contraction of sm m layers in walls of SI which temporarily seems to cut the region affected into individual compartments; mixes chyme and controlled by ANS
NOT coordinated

Question 13

What is peristalsis?

Answer 13

Contents advance along intestine when proximal contraction is corrdinated with relaxtion below

Question 14

The arterioles derived from the submucosal plexus enter the mucosa of the SI and give rise to two capillary networks called….

Answer 14

villus capillary plexus: intestinal villus and upper portions of crypts of L
Pericryptal capillary plexus: lower half of crypts

Question 15

Where are lacteals located? what is the function?

Answer 15

In the core of villus
Single blind-ending central lymphatic vessel
pull material (chyle) in and send to lymphoid follicles and follow the portal vein

Question 16

What is chyle?

Answer 16

lymph containing lipids absorbed from the meal and packaged in chylomicrons

Question 17

There are brunner’s glands in the submucosa
Relatively few goblet cells
and leaf-like villi
What part of the intestines is this in?

Answer 17

Duodenum

Question 18

Well developed plicae circulares 
Irregular villi
more goblet cells
NO brunners glands or peyer's patches
What part of the intestines is this in?

Answer 18

Jejunum

Question 19

Many lymphoid nodules (peyer’s patches) in LP and submucosa
Finger-like villi and the most goblet cells
What part of the intestines is this in?

Answer 19

ileum

Question 20

Oligosaccharides reduce carbs to hexoses in enterocyte microvilli and can now be transported into the enterocyte by what?

Answer 20

carrier proteins

Question 21

Why does lactose sometimes cause gas, irritation, and increased motility?

Answer 21

Lactose intolerance due to lack of lactase

Bacteria instead ferment lactose producing organic acids and gas

Question 22

What are goblet cells?

Answer 22

columnar mucus-secreting cells scattered among enterocytes
Secretory product: glycoproteins
Exocytosis
Protective gel coat from abrasion and bacterial invasion

Question 23

Enteroendocrine cells secrete secretin. What does secretin do?

Answer 23

stimulate prancreatic bicarb secretion and enhances insulin secretion

Question 24

What does CCK do?

Answer 24

released by enteroendocrine cells: acts on pyloric sphincter to slow emptying, stimulates release of bile and pancreatic enzymes

Question 25

What doe paneth cells do?

Answer 25

Secrete antimicrobial proteins to limit bacteria-enterocyte contact
Most proteins kill bacteria directly by eating through bacterial wall
Proteins retained in mucus blanket

Question 26

What is the function of peyers patches

Answer 26

survey antigens to create immune reaction

Question 27

What Ig can be found in SI?

Answer 27

IgA

Question 28

How is the propulsive intestinal motility protective?

Answer 28

prevents bacterial colonization

Question 29

What accounts for IBD and Crohn’s disease?

Answer 29

Defect in protective system
Infiltration of neutorphils into crypts
Destruction of intestinal glands by formation of crypt abscesses and progressive atrophy and ulceration of mucosa
Inflammatory process goes into submucosa and muscularis
Formation of granulomas
Cuase fibrosis and fistulas

Question 30

What part of the GI does Crohn’s disease involve?

Answer 30

terminal ileum but also large intestine

Question 31

What is the purpose of fecal transplant?

Answer 31

to replace good bacteria that has been killed or suppressed bc of antibiotics

Helps C.diff colitis

Question 32

What is the major function of enterocytes in the large intestine?

Answer 32

transport of ions and water

Question 33

What is the mucosa of the large intestine lined by?

Answer 33

simple columnar epithelium formed by enterocytes iwht short apical microvilli and abundant goblet cells

Question 34

Describe the mucosa of the large intestine

Answer 34

No plicae circulares and intestinal villi
Straight tubular glands or cyrpts of lieberkuhn
Goblet cells
enteroendocrine cells
stem cells

Question 35

ALL regions of the colon absorb Na and Cl ions facilitated by plasma membrane channels that are regulated by what?

Answer 35

mineralocorticoids

Question 36

What increases the # of Na channels and increases the absorption of NA?

Answer 36

Aldosterone

Question 37

What is the current theory on the appendix function? What is the most important feature

Answer 37

Acts as a safe house for good bacteria. Body uses this to reboot the digestive system when one suffers from dysentery or cholera
Thickening of wall due to large accumulations of lymphoid tissue in lamina propria and submucosa

Intestinal villi absent
Longitudinal Sm m does not become taenia coli

Question 38

What is the upper and lower regions of the rectum called?

Answer 38

Upper: rectum proper with simple columnar
Lower: anal canal with keratinized stratified squamous epithelium

Question 39

What sm m layer thickens to form internal anal sphincter?

Answer 39

inner circular layer

Question 40

What two muscle layers form haustrae?

Answer 40

longitundinal: teniae coli

Circular layer

Question 41

What gene is defected in colorectal tumors?

Answer 41

APC gene: excess activates genes leading to colorectal tumorigenesis
develop from polyp
Can be tracked by lymph nodes
If in right colic flexure ->superior mesenteric LN
if in sigmoid colon->inferior mesenteric LN (follows pattern of blood supply)