Histology of the SI and LI

Question 1

what is the function of the small intestine and what are pilcae circulares?

Answer 1

Principal site for digestion of food and absorption of digestion products

Pilcae circulares:

• transverse folds with a submucosal core
• cannot lay flat if distended
• visible in jejunum less so in ileum

Question 2

what are intestinal villi?

Answer 2

Mucosal folds that project into the lumen and cover the surface of Small intestine

• covered with simple columnar epithelium of enterocytes and goblet cells
• core of loose CT with microvasculature and a lacteal (important for absorption of fats)
• has lymphatics and blood vessels

Question 3

what are the function of villi and microvilli, enterocytes, and goblet cells

Answer 3

Enterocytes produce enzymes for digestion and absorption

goblet cells provide mucus coating to shield from abrasion and bacterial invasion

villi are covered with microvilli to increase absorptive surface area

Question 4

what is the Mucosa, Submucosa, muscularis, and serosa of the small intestine

Answer 4

Mucosa: simple columnar epitheliumwith tubular intestinal glands
-lamina propria and muscularis mucosae

submucosa: dense irregular CT
- neurovasculature, lymphatics, glands may be present

Muscularis: inner circular and outer longitudinual layers

Serosa: loose CT covered by visceral peritoneum

Question 5

What is the innervation of the SI and LI

Answer 5

Motillity controlled by the ANS

Enteric (intrinsic) nervous system consists of the submucosal plexus of meissner and myenteric plexus of auerbach

• sympathetic visceral sensory fibers
• Parasympathetic ganglia
• preganglionic and postganglionic parasympathetics

Regulated by extrinsics
-preganglionic parasympathetics and postganglionic sympathetics

Question 6

what are the 4 cells of the intestinal glands and characteristics of the intestinal glands

Answer 6

SImple tubular glands lined by simple columnar eptithelium

• Enterendocrine cells
• paneth cells
• M (microfold) cells
• Intestinal stem cells

continuous with simple columnar that covers intestinal villi

open onto the luminal surface of the intestine at the base of the villi

Question 7

characteristics of the enterendocrine cell

Answer 7

Found throughout the intestinal glands

Secrete peptide hormones to control gut motility, regulate secretion of enzymes, HCl, bile and other components for digestion

Hormones it releases:

Gastrin, secretin, gastric inhibitory polypeptide (GIP). motilin, and cholecystokinin

Question 8

Characteristics and function of Paneth cells

Answer 8

Pyramidal-shaped cells at the base of intestinal glands

Large, eosinophillic secretory granules in their apical cytoplasm

Functions in innate immunity by secreting antimicrobial substances (lysozyme, a-defensins)

regulate normal bacterial flora via antibacterial action and phagocytosis

Question 9

what are intestinal stem cells

Answer 9

• Reside in a niche at crypt near the paneth cells
• repopulate epithelial linings
• Daughter cells move out of the crypts and differentiate into the goblet cells, enterocytes, and enteroendocrine cells

Question 10

what are Microfold Cells

Answer 10

Epithelial cells that specilize for transepithelial transport of particles and microorganisms

located in the ileal mucosa overlying Peyer patches

Pocket formed by deeply invaginated membrane and containing lymphocytes and macrophages

apical surface expresses receptors that bind specific macromolecules and gram negative bacteria

• internalized and transferred to immune cells
• function as highly specialized antigen-transporting cells

Question 11

Characteristics of the gstroduodenal junction

Answer 11

Pyloris:

• thick wall due to the presence of the pyloric sphincter muscle
• pyloric glands at the base of each gastric pit

Duodenum:

• Abundant brunners glands in submucosa, DEEP to the muscularis mucosae
• secretory mucosa with villi

Question 12

Characteristics of the duodenum

Answer 12

Initial segment of the SI

Brunners glands in the submucosa

• tubuloacinar mucosa glands
• produce alkaline secretion
• neutralize the acidic chyme

Collects bile and pancreatic secretions via the hepatopancreatic ampulla

Question 13

Characteristics of the jejunum

Answer 13

Long fingerlike Vili

• tubular intestinal glands
• villus core contains a well developed lacteal

No submucosal glands

Lymphoid nodules/follicles in the lamina propria

Question 14

Characteristics of the ileum

Answer 14

Finger like villi (typically shorter than the jejunum

peyers patches
-mucosal lymphoid nodules specific to ileum

Paneth cells found at base of intestinal glands

Question 15

Characteristics of the ileocecal junction

Answer 15

Food is propelled from the ileum to the cecum through the ileocecal valve

abrupt transition from villi of SI to glandular epithelium of LI

Valve has thickened extension of the muscularis mucosae
-critical function to limit reflux of colonic contents into ileum

Muscularis (externa) is also somewhat thickened

Question 16

function and hallmarks of the large intestine

Answer 16

Large intestine absorbs water, sodium, vitamins, minerals, will uptake sedatives, anesthetics and steroids

Openings of tubular intestinal glands (crypts of lieberkuhn) are hallmark of the mucosa

intestinal glands, goblet cells, but no intestinal villi

Question 17

Mucosa, submucosa, muscularis, and serosa of the large intestine

Answer 17

Mucosa:

• glandular, simple columnar epithelium: colonocytes, goblet cells, stem cells and enteroendocrine cells
• lamina propria and muscularis mucosae are present; GALT is extensive and may penetrate submucosa

Submucosa: dense irregular CT, vascularized

Muscularis:

• inner layer is typical
• outer longitudinal layer organized into taeniae coli, will form haustra of LI

intraperitoneal portions of the colon are covered by serosa

Question 18

What is hirschprungs disease?

Answer 18

aganglionosis of the distal colon due to RET gene required for migration and differentiation of NCC

Failure of neural crest cell development in both plexuses of bowel segment

can be short (85% cases) or long (10%) segmented region cases
-or total colon aganglionosis (5%)

presentation is constipation, poor feeding, and progressive abdomina distention

diagnosis: delayed BM, check with barium and rectal biopsy
treatment: surgical removal of affected colon segments

Question 19

Characteristics of the rectum

Answer 19

Rectum proper is the upper part that has typical mucosa with tubular intestinal glands, transverse rectal folds

Anal canal (lower part)

• anal columns: with mucosal folds
• anal sinuses, depressions btween columns
• anal glands extend into the submucosa and muscularis externa

circumanal glands, large apocrine glands surrounding the anal orifice

Question 20

the three zones of the Anal canal

Answer 20

Colorectal zone: simple columnar epithelium identical to the rectum (upper 1/3)

Anal transitional zone (ATZ)
-simple columnar epithelium to stratified squamous epithelium of perianal skin (middle 1/3)

Squamous zone: stratified squamous epithelium continuous with perineal skin (lower 1/3)