Histology of Lower GI Tract

Question 1

what to look for on sample of duodenum

Answer 1

i. Brunner’s glands in the submucosa—produce mucous
ii. Relatively few goblet cells
iii. Leaf like villi

Question 2

what to look for on sample of jejunum

Answer 2

i. Well developed plicae circularis
ii. Irregular villi
iii. More goblet cells
iv. No Brunner’s glands or Peyer’s patches

Question 3

what to look for on sample of ileum

Answer 3

i. Many lymphoid nodules—peyer’s patches—in LP and submucosa
ii. Finger like villi
iii. Most goblet cells

Question 4

lactose intolerance

Answer 4

i. Normally, lactase breaks down lactose and it is digested
ii. Lactose intolerance means you do not have enough lactase
1. Bacteria in the gut ferment the lactose that has come into your system
2. Irritates lining of small and large intestine

Question 5

absorptive cells or enterocytes

Answer 5

1. Cells have apical domain with a prominent brush border containing about 3000 closely packed microvilli, which increase the surface luminal area 30-fold
2. Microvilli contain intramembranous enzymes, including lactase, maltase, and sucrase for terminal digestion of carbohydrates
   a. These oligosaccharides reduce carbohydrates to hexoses which can be transported into the enterocyte by carrier proteins

Question 6

Goblet cells

Answer 6

1. Columnar mucus secreting cells scattered among the enterocytes of the intestinal epithelium
2. Secretory product of goblet cells contains glycoproteins (80% carbohydrate and 20% protein) released by exocytosis
3. Mucus hydrates to form a protective gel coat to shield the epithelium from mechanical abrasion and bacterial invasion

Question 7

paneth cells

Answer 7

1. Paneth cells secrete antimicrobial proteins to limit bacteria enterocyte contact
2. Most of these proteins kill bacteria directly by enzymatic degradation of the bacterial wall or by disrupting the bacterial inner membrane
3. Antimicrobial proteins are retained in the intestinal mucus blanket

Question 8

enteroendocrine cells

Answer 8

1. In addition to its digestive function, the GI tract is the largest diffuse endocrine gland in the body
2. As in the stomach, these cells secrete peptide hormones (gastrin, secretin, CCK) controlling several functions of the GI system

Question 9

gastrin

Answer 9

a. stimulates gastric motility HCl (parietal cells), and insulin

Question 10

secretin

Answer 10

a. stimulates pancreatic bicarbonate secretion and enhances insulin secretion

Question 11

CCK

Answer 11

a. acts on pyloric sphincter to slow emptying, stimulates release of bile and pancreatic enzymes

Question 12

IBD

Answer 12

i. Defect in the protective system accounts for inflammatory bowel diseases, Crohn’s disease (involving the terminal ileum but also observed in the large intestine)
ii. Initial alteration of the intestinal mucosa consists in the infiltration of neutrophils into the crypts of lieberkuhn
iii. Process results in the destruction of the intestinal glands by the formation of crypt abscesses and the progressive atrophy and ulceration of the mucosa
iv. Inflammatory process also infiltrates the submucosa and muscularis
v. Accumulation of lymphocytes forms aggregates of cells, or granulomas
vi. Major complications of the disease are occlusion of the intestinal lumen by fibrosis and the formation of fistulas in other segments of the small intestine
vii. Segments affected by Crohn’s disease are separated by normal stretched of intestinal segments

Question 13

fecal microbiota transplant

Answer 13

i. Procedure in which fecal matter is collected from a tested donor mixed with a saline or other solution, strained, and placed in a patient, by colonoscopy, endoscopy, sigmoidoscopy, or enema
ii. The purpose of fecal transplant is to replace good bacteria that has been killed or suppressed, usually by use of antibiotics, causing bad bacteria, specifically Clostridium difficule to overpopulate the colon
1. Infection causes a condition called C. diff colitis—resulting in often debilitating, sometimes fatal diarrhea

Question 14

colorectal tumors

Answer 14

1. Develops from a polyp, a tumoral mass that protrudes into the lumen of the intestine.
   a. Some are non-neoplastic and are relatively common in persons 60 yo and older
2. Polyps can be present in large numbers in familial polyposis syndromes such as familial adenomatous polyposis
3. Familial polyposis and colorectal tumorigenesis is determined by a defect in the protein adenomatous polyposis coli (APC) gene
4. Excess of this protein, activates genes leading to colorectal tumorigenesis

Question 15

chyme and peristalsis

Answer 15

• chemicals plus the contraction of the stomach make a substance called chyme
  
  • partially digested food that goes into small intestine
• peristalsis mixes food with gastric secretions including HCl, pepsinogen, gastric lipase, intrinsic factor to create chyme

Question 16

plicae circularis

Answer 16

• big permanent folds in the wall of the intestine
• permanent folds of mucosa and submucosa
• begin in duodenum, distinct in jejunum, disappear mid ileum

Question 17

intestinal villi

Answer 17

• smaller folds in the plicae
• finger like projections of mucosa covering the entire surface of the small intestine–inc SA
• villi extend deep into the mucosa to form crypts of lieberkuhn ending at the muscularis mucosae
• length of the villi depends on the degree of distention of the intestinal wall and contraction of SM fibers

Question 18

crypts of lieberkuhn

Answer 18

• intestinal glands and mucus/enzymes
• simple tubular glands that increase SA
  
  • formed by invaginations in mucosa b/w adjacent villi
• have goblet absorptive, panted, and enteroendocrine cells

Question 19

enterocytes

Answer 19

epithelial cells lining the lumen

• surface simple columnar epithelium formed by absorptive enterocytes and goblet cells
• enterocytes have short apical microvilli and the cells participate in the transport of ions and water
• all regions of the colon absorb Na and Cl ions facilitated by plasma membrane channels that are regulated by mineralocorticoids
• aldosterone increases the number of Na channels and increases the absorption of Na

Question 20

mesothelioma

Answer 20

an aggressive form of cancer affecting the membrane lining the pericardial, pleural, or peritoneal cavities
-mesothelium–membrane composed of simple squamous cells that forms the lining of several body cavities

Question 21

peristalsis

Answer 21

• regulated contraction from a more proximal part to a more distal part
• moves food
• coordinated activity

Question 22

segmentation

Answer 22

• not for movement of food but for mixing of food
• pattern of annular contraction of the SM layers in the walls of the small intestine which temporarily seems to cut the region affected by individual compartments
• serves to mix the chyme in the small intestine

Question 23

what is the main distribution site of blood and lymphatic flow in the small intestine?

Answer 23

submucosa

Question 24

arterioles derived from the submucosal plexus enter the mucosa of small intestine and give rise to 2 capillary networks:

Answer 24

• villus capillary plexus–supplies intestinal villus and upper part of crypts of lieberkuhn
• pericryptal capillare plexus–supplies lower half of the crypts of lieberkuhn

Question 25

lacteals

Answer 25

• centrally located lymphatic vessels in the villi
• they pull toxins into them and won’t let them back out
• convey chyle (lymph containing lipids absorbed from the meal and packaged in fat droplets)

Question 26

glands of lieberkuhn

Answer 26

• contain goblet, enteroendocrine cells, and stem cells

- paneth cells are not observed

Question 27

taeniae coli

Answer 27

• characteristic feature of the large intestine, formed by fused bundles of the outer SM layer
• contraction of the taeniae coli and the inner circular SM layer produces periodic saccular structures–haustra

Question 28

appendix

Answer 28

• small blind ending diverticulum from the cecum
• has a thickening of its wall that is mainly due to large accumulations of lymphoid tissue in the lamina propria and submucosa
• no villi or crypts
• often is fatty tissue
• thinner muscularis externa
• acts as a safe house for good bacteria which the body uses as a system to reboot the digestive system

Question 29

anorectal junction

Answer 29

• simple columnar epithelium is replaced by stratified squamous epithelium
• inner circular layer of SM thickens to form the internal anal sphincter
• external anal sphincter–formed by skeletal muscle