Histology of Small and Large Intestines

Question 1

4 basic histological layers of small intestine wall

Answer 1

Mucosa
Submucosa
Muscularis
Serosa

Question 2

Describe epithelium of mucosa layer of small intestine

Answer 2

Simple columnar epithelium

Lamina propria

Muscularis mucosa

Question 3

What histological structures are found in the mucosal layer of the small intestine and what is their purpose?

Answer 3

Intestinal glands/crypts of Lieberkuhn = invaginations of mucosa that increase intestinal surface area

[note that glands/crypts are also often found in submucosa]

Question 4

Describe submucosa layer of small intestine

Answer 4

Dense irregular CT with neurovasculature and lymphatics, glands may be present

Question 5

Describe muscularis layer of small intestine

Answer 5

Inner circular + outer longitudinal smooth muscle

Question 6

Describe serosa of small intestine

Answer 6

Loose CT covered by visceral peritoneum

Question 7

______ = folds of mucosa projecting into the lumen of the small intestine, increasing their surface area for absorption

Answer 7

Villi

Question 8

_____ = folds of mucosa and some submucosa that differ from rugae in that they cannot lay flat if distended

Answer 8

Plicae circulares

Question 9

Where in the small intestine would you find the most plicae circularis?

Answer 9

Jejunum

They are absent in the duodenum and less prominent in the ileum

Question 10

____ = folding within the apical domain of enterocytes found in small intestine only

Answer 10

Microvilli

Question 11

In the small intestine:

The first degree of folding = ______, which is evagination of the mucosa and part of the submucosa

The second degree of folding = ______, which is evagination of the mucosa only

The third degree of folding = ______, which are invaginations of the mucosa

The fourth degree of folding = ______, which are evaginations of the apical domain of the enterocyte

Answer 11

Plicae

Villus

Glands/crypts

Microvilli

Question 12

Which histological layer of the small intestine holds the main distribution of blood and lymphatics?

Answer 12

The submucosa

[branches supply capillaries to the mucosa and muscularis layers]

Question 13

Arterioles enter the mucosa of the SI and give rise to what 2 plexuses forming the microvascular system of the villus? What do they supply?

Answer 13

Villus capillary plexus - supplies intestinal villus and upper portion of the crypts of Leiberkuhn

Pericryptal capillary plexus - supplies lower half of crypts of Lieberkuhn

[both plexuses drain into the submucosal venule]

Question 14

____ = single blind-ending central lymphatic capillary found in lamina propria of a SI villus. These structures will form a plexus that branches around a lymphoid nodule, forming the _____. They anastomose with efferent lymphatic vessels and leave the SI.

Answer 14

Lacteal; GALT

Question 15

Motility of the SI is controlled by the ANS. Intrinsic innervation consists of what 2 plexuses? Histologically, where are they located?

Answer 15

Submucosal plexus of Meissner - controls glandular secretions from submucosal and mucosal layer

Myenteric plexus of Aurbach - sits between circular and longitudinal layers of muscularis layer

Question 16

Neurons of the submucosal plexus of Meissner and the myenteric plexus of Aurbach receive intrinsic and extrinsic input from what sources?

Answer 16

Intrinsic input from the mucosa and muscle wall of SI

Extrinsic input from the parasympathetic (vagus n.) and sympathetic nerve trunks

Question 17

What type of glands are found in the duodenum? Which layer are they found in?

Answer 17

Brunner’s glands in submucosa

Question 18

Describe the Brunner’s glands found in the submucosa of the duodenum

Answer 18

Tubuloacinar mucous glands

Produce an alkaline secretion that neutralizes acidic chyme

Question 19

The duodenum collects bile and pancreatic secretions via the ________ ______. The base of the crypts of lieberkuhn may contain ____ cells

Answer 19

Hepatopancreatic ampulla; paneth

Question 20

What is unique about the histology at the gastroduodenal junction?

Answer 20

The pylorus of the stomach has simple columnar epithelium like that in the duodenum, but you will notice a massive bed of muscularis muscle at the pyloric sphincter, as will as abundant Brunner’s glands DEEP to the muscularis mucosae of the duodenum. Will also note secretory mucosa with villi, but the distinguishing featuer is usually the presence of glands at the beginning of the SI that were not present in the stomach

Question 21

Describe the jejunum including its villi, lacteals, brunner’s glands, lamina propria, and paneth cells

Answer 21

Long finger-like villi and well-developed lacteal (villus core)

Lacks brunner’s glands

Lymphoid nodules/follicles in the LP

Paneth cells in the base of the crypts

Question 22

What is the function of paneth cells found in the SI?

Answer 22

Regulate the microbiome by secreting anti-microbial proteins

Question 23

In which part of the SI would you find Peyer’s patches?

Answer 23

Ileum

Question 24

Describe the ileum in terms of peyer’s patches, brunner’s glands, villi, and paneth cells

Answer 24

Peyer’s patches, lymphoid follicles (also called nodules) found in the mucosa and part of submucosa

Absence of Brunner’s glands

Shorter finger-like villi compared to jejunum

Paneth cells found at base of crypts

Question 25

Intestinal mucosa and crypts of Lieberkuhn are simple tubular glands lined by what type of epithelium?

Answer 25

Simple columnar

Question 26

What cell types are associated with intestinal mucosa and crypts of lieberkuhn?

Answer 26

``` Enterocytes (absorptive cells) Goblet cells Enteroendocrine cells Paneth cells Intestinal stem cells ``` [bottom 3 are within each gland/crypt, enterocytes and goblet cells found throughout]

Question 27

How would you histologically distinguish goblet cells from enterocytes in terms of surface features?

Answer 27

Goblet cells lack microvilli at their surface

Question 28

Each enterocyte has an apical domain with a prominent _____ (striated) border that contains about 3000 closely packed microvilli to increase SA. Each ends on the _______ ____, a zone with cytoskeletal filaments

Answer 28

Brush; terminal web

Question 29

Microvilli are 0.5-1 micrometer with a core bundle of 20-40 cross-linked actin filaments. Each actin bundle: Projects into the apical portion of the cell as a ______ and is cross linked to its neighbors. The end of each rootlet attaches to _________ filaments. The cross-linking proteins form part of the terminal web, maintaining the _____ position and shape of microvillus

Answer 29

Rootlet; intermediate; upright

Question 30

Columnar mucus-secreting cells scattered among enterocytes

Answer 30

Goblet cells

Question 31

Describe the 2 domains associated with goblet cells

Answer 31

Apical = goblet-shapped, with large mucus granules released by exocytosis Basal = houses RER, golgi, and nucleus (where the granules are made)

Question 32

What is the overall purpose of the presence of goblet cells scattered among the enterocytes of the small intestine?

Answer 32

Their secretory product contains glycoprotein-based mucus that hydrates the intestine mucosa, forming a protective shield from abrasion and bacterial invasion

Question 33

What 3 important hormones are secreted by eneteroendocrine cells of the small intestine?

Answer 33

Gastrin Secretin Cholecystokinin

Question 34

What hormone, released by enteroendocrine cells of the SI, slows emptying of the stomach by acting on pyloric sphincter, stimulates bile release from gallbladder, and stimulates secretion of pancreatic enzymes?

Answer 34

Cholecystokinin

Question 35

What hormone, released by enteroendocrine cells of the SI, stimulates bicarb secretion by the pancreatic duct as well as enhances insulin secretion by B cells of the islet of langerhans?

Answer 35

Secretin

Question 36

What hormone, released by enteroendocrine cells of the SI, stimulates the secretion of HCl by parietal cells, stimulates insulin secretion by B cells of the iselt of langerhans, and stimulates gastric motility and growth of the mucosal cells?

Answer 36

Gastrin

Question 37

The basal domain of paneth cells contains the ______. the apical region shows numerous protein granules of diverse AMPS - like what?

Answer 37

RER Defensins, lysozyme, angiogenin 4 (ANG4)

Question 38

Where would you find intestinal stem cells?

Answer 38

ISCs reside in niche at crypt base, near paneth cells They repopulate the entire epithelial lining of the SI, and may differentiate as goblet cells, enterocytes, and enteroendocrine cells

Question 39

Plicae circularis and intestinal villi are not found beyond which point in the GI tract?

Answer 39

Ileocecal valve [So LI can be distinguished by lack of these things, as well as TONS of goblet cells]

Question 40

The layers of the LI are the same as those in the SI: mucosa, submucosa, muscularis, serosa. What is the main function of the mucosa in the LI?

Answer 40

Absorption of water, sodium, vitamins, and minerals

Question 41

The absorptive capacity of the colon favors the uptake of substances such as sedatives, anesthetics, and steroids. Why might this be clinically important?

Answer 41

Medications can be administered there when they cannot be taken orally - due to things like vomiting

Question 42

How are the tubular glands, or crypts of lieberkuhn, oriented differently in the LI vs. the SI?

Answer 42

In the LI, they are oriented perpendicular to the long axis of the colon, are much deeper than the SI, and have higher proportion of goblet cells

Question 43

What 4 cell types are found in the mucosa (surface epithelium and tubular glands) of the LI?

Answer 43

Simple columnar absorptive cells - with apical microvilli Goblet cells Stem cells at base of glands Enteroendocrine cells

Question 44

Describe mucosal layer of LI

Answer 44

Simple columnar epithelium formed by enterocytes and goblet cells Glandular epithelium with enterocytes, goblet cells, stem cells, and enteroendocrine cells (+paneth cells in cecum) Lamina propria and muscularis mucosae present, isolated lymphoid follicle penetrate submucosa

Question 45

Describe submucosa of LI

Answer 45

Dense irregular CT that lacks glands, vascularized

Question 46

Describe muscularis layer of LI

Answer 46

Inner circular layer is typical (same as SI) Bundles of the outer longitudinal layer fuse to form taenia coli 3 longitudinally oriented ribbon-like bands that draw the colon into sacculations (haustra)

Question 47

What is unique about the serosa of the LI as compared to SI?

Answer 47

Epiploic appendices present (aggregates of adipocytes surrounded by serosa)

Question 48

Describe histological layers of appendix

Answer 48

Similar to that of LI Mucosa of simple columnar with goblet cells (no villi); lymphoid follicles and lymphocytes within LP that extend into submucosa Submucosa contains adipocytes and dense irregular CT Muscularis: inner circular layer is well developed, but outer longitudinal layer is NOT Covered with serosa

Question 49

Abnormal form of constipation caused by aganglionosis in the distal colon

Answer 49

Hirschprung’s Disease (congenital megacolon) [Failure of NCC development (NCCs are what form the ganglion cells in plexuses of Meissner and Auerbach)]

Question 50

What causes Hirschprung’s Disease?

Answer 50

Mutations of the RET gene encoding a RTK RTK signaling required for formation of Peyer’s patches, migration of NCC into distal portions of large intestine, and differentiation of NCC into neurons of the enteric nervous system

Question 51

In a patient with Hirschprung’s disease: What would an intestinal biopsy show? How is it treated?

Answer 51

Biopsy shows thick, irregular nerve bundles, a lack of ganglion cells, and abundant AChE staining Treatment = surgical removal of affected colon segment

Question 52

The rectum is divided into 2 parts. Describe them histologically

Answer 52

Upper part (rectum proper): similar to colon - simple columnar epithelium with tubular glands Lower part (anal canal): 8-10 rectal/anal columns with mucosal folds forming anal valves

Question 53

The lower part of the rectum (anal canal) contains columns that form anal valves. What 2 structures are contained within the valves?

Answer 53

Anal sinuses | Anal mucous glands

Question 54

At the base of the columns of the lower part of the rectum (anal canal) is the _________, which represents the epithelial transformation zone. What epithelial transformation occurs here? Why is this transformation functionally important?

Answer 54

Pectinate line Epithelium goes from simple columnar to non-keratinized stratified squamous (so that continuous shedding of cells d/t defecation may occur without issue)

Question 55

Describe histology of the rectum as it transitions to anus below the pectinate line

Answer 55

Below the pectinate line, at the level of the anus, the inner circular layer of muscularis thickens to form the internal anal sphincter. At this location, the mucosa consists of stratified squamous epithelium with circumanal glands in the submucosa. The external anal sphincter (skeletal m.) and levator ani m. also present. Epithelium of the anus is highly keratinized stratified squamous

Question 56

IBD includes what 2 diseases? How do those 2 differ?

Answer 56

Ulcerative colitis and Crohn’s disease Both are characterized by diarrhea, pain, and periodic relapses. UC affects mucosa of LI Crohn’s affects any segment of intestinal tract, usually terminal ileum and LI

Question 57

Describe pathology of Crohn’s disease

Answer 57

Inflammatory cells produce cytokines that cause damage to the intestinal mucosa Infiltration of neutrophils into crypts of Lieberkuhn —> destruction of intestinal glands d/t crypt abscesses —> progressive atrophy, ulceration of the mucosa

Question 58

Major identifying feature of esophagus histo

Answer 58

Mucous glands in submucosa (only found here and in duodenum)

Question 59

Major identifying feature of stomach histo

Answer 59

Inner oblique layer of muscularis externa (near border to submucosa)

Question 60

Major identifying feature of duodenum histo

Answer 60

Glands in submucosa (Brunner’s)

Question 61

Major identifying feature of jejunum histo

Answer 61

Long villi

Question 62

Major identifying feature of ileum histo

Answer 62

Peyer’s patches

Question 63

Major identifying feature of appendix histo

Answer 63

Abundant lymphoid tissue

Question 64

Major identifying feature of colon histo

Answer 64

Tons of goblet cells

Question 65

Major identifying feature of rectum histo

Answer 65

Anal columns in submucosa