Intestine histology

Question 1

The luminal surface of the small intestine has modifications that increase its surface area to aid absorption.
They are permanent mucosal folds present in the duodenum,
jejunum, proximal ileum that increase surface area by 2-3 fold

Answer 1

Plicae circulares

Question 2

______are finger like projections of epithelium-covered lamina propria that increase surface area by 10-fold.

Answer 2

Villi

Question 3

_____ are extensions of the epithelial cell apical plasma membrane that
increase surface area 20- fold.

Answer 3

Microvilli

Question 4

These three specialized modifications, plicae circulares, villi, microvilli will cumulatively increase the intestinal surface area by

Answer 4

400 - 600 fold

Question 5

The villi are extensions of ______that are covered in epithelial cells and contain a central lymphatic channel (lacteal) and several capillaries. Smooth muscle fibers, loose connective tissue and lymphoid cells can also be seen in the center of the villus.

Answer 5

lamina propria

Question 6

The epithelial covering of the villi are composed of what 3 things?

Answer 6

— absorptive cells (enterocytes)

goblet cells

DNES (enteroendocrine) cells

Question 7

Crypts of Lieberkuhn extend from the base of the villi into the lamina propria and contain what 3 things?

Answer 7

— DNES (enteroendocrine) cells,

stem cells

paneth cells

Question 8

The enterocytes are ____epithelial cells ~ 25µM high with an elongated nucleus

Answer 8

columnar

Question 9

The principal function of _____ are terminal digestion and absorption of water and nutrients.

Answer 9

enterocytes

Question 10

These cells re-esterify fatty acids into triglycerides, form chylomicrons, and transport the bulk of the absorbed nutrients into the lamina propria for distribution to the rest of the body.

Answer 10

Enterocytes

Question 11

The luminal surface of each enterocyte has a brush (striated)

border constructed of ~3000 microvilli/ that are covered in a____ coat made of glycosylated membrane proteins

Answer 11

glycocalyx

Question 12

The glycocalyx layer has______ roles and also is integrally involved in the
digestion of disaccharides and dipeptides into monomers for adsorption through peptide hydrolases and disaccharidases that are abundant on the____ surface.

Answer 12

protective

apical

Question 13

____ are easily recognizable in H&E stained intestinal sections because they are full of carbohydrate and so remain unstained; can be identified by PAS staining.

Answer 13

Goblet cells

Question 14

Goblet cells act as______ glands that secrete copious amounts of____ that consists of high MW glycoprotein macromolecules that have 20% protein and 80% carbohydrate.

Answer 14

unicellular

mucin

Question 15

mucin is released at reasonably constant levels by exocytosis from goblet cells. Justafter release the mucin granules become hydrated and expand to function in:

Answer 15

lubrication and protection

Question 16

• The Crypts of Lieberkuhn extend from the base of the villi into the lamina propria and addition to enteroendocrine cells, the crypts contain

Answer 16

Paneth cells, and stem cells.

Question 17

What is in the upper half of Crypts of Lieberkuhn?

What about in the basal half?

Answer 17

— Surface absorptive and goblet cells occupy the upper half of the crypt

most of the cells are regenerative cells (and their progeny), DNES cells and Paneth cells.

Question 18

The epithelial lining of the intestine is continuously being renewed by stem cells that proliferate in the______.
• New cells are born from stem cells in the crypts and migrate up the____ and are finally exfoliated from the tips of the villus.

Answer 18

crypts

villus

Question 19

The intestinal epithelium is replaced every ____ days in humans.
• Stem cells can most easily be identified in the crypts as ____since they are the only cells that are proliferating.

Answer 19

3-6

mitotic figures

Question 20

_____cells are long lived and do not participate in the upward migration of epithelial cells - instead they remain resident at the base of the crypts

Answer 20

Paneth

Question 21

Paneth cells are full of secretory granules and they continuously secrete____.

In addition they secrete____ that help neutralize bacterial and viral infections.

Answer 21

lysozyme

defensins

Question 22

Paneth cells stain intensely with____ and also with phloxine-tartrazine which stains the secretory granules scarlet.

Answer 22

eosin

Question 23

forms the core of the villi and extends down to the muscularis layer and is highly vascularized to accept the products of absorption.

Answer 23

Lamina propria

Question 24

Lamnia propria contains an abundance of___ cells that protect the intestinal lining from microbial invasion

Answer 24

lymphoid

Question 25

The muscularis mucosae is present as an

Answer 25

inner circular and outer longitudinal layer of smooth muscle fibres.

Question 26

How does a lacteal empty?

Answer 26

Some fibers enter the villus and extend to the tip. During digestion the fibers contract causing shortening of the villus.

Question 27

The lamina propria maintains an extensive immune defense system in the form of lymphoid tissue called:

Answer 27

- Gut-Associated Lymphoid Tissue (GALT)

Question 28

GALT exists as individual lymphocytes within the mucosa and epithelium as well as dense aggregates called ______ - in some regions multiple of these coaelsce to form \_\_\_\_\_\_

Answer 28

lymphoid nodules Peyer’s Patches.

Question 29

30 - 40 permanent Peyer’s Patches are found throughout the ileum with some more in the\_\_\_\_\_, nodules are least numerous in\_\_\_\_.

Answer 29

jejunum duodenum

Question 30

\* The duodenal submucosa differs from the rest of the G.I. due to the presence of large numbers of glands called ____ these are an identifying histological feature of the duodenum

Answer 30

Brunner’s glands -

Question 31

Brunners glands appear similar to\_\_\_\_\_\_ They ascend through the muscularis mucosae layer and enter the crypts to deposit their secretions into the lumen.

Answer 31

mucous acini.

Question 32

What do Brunners glands secreate

Answer 32

The secretions contain an alkaline mucus that neutralizes the pH of the gastric chyme and protects the duodenum and epidermal growth factor for stem cell proliferation in the crypts

Question 33

The small intestine secretes about 2 litres of fluid/day. Secretion is mainly under neural control from the submucosal _________ and hormones produced by enteroendocrine cells.

Answer 33

(Meissner’s) plexus

Question 34

causes the release of digestive enzymes from the pancreas and bile from the gallbladder.

Answer 34

Cholecystokinin

Question 35

regulates the pH of the duodenal contents via control of gastric acid secretion and buffering with bicarbonate.

Answer 35

Secretin

Question 36

The muscularis externa is composed of an inner layer of circular smooth muscle and an outer layer of longitudinal smooth muscle. • Between the smooth muscle layers lies the

Answer 36

myenteric plexis (Auerbach’s).

Question 37

Two purposes of the Myenteric plexis

Answer 37

provides motor inervation to the muscularis externa and secretomotor innervation to the mucosa. — The enteric nervous system is a part of the nervous system which directly controls the GI system

Question 38

Control of peristaltic movement is mediated by the myenteric plexis in response to

Answer 38

gastric distension.

Question 39

The main functions of the small intestine are to complete digestion and absorb the products into the bloodstream and lymphatic system-

Answer 39

7l of fluid, 30g of sodium, 0.5kg of carbohydrate and protein, and 1kg of fat are absorbed by the intestine daily

Question 40

•Luminal digestion of most foodstuffs results in individual molecules that can be absorbed by the enterocytes. Enterocytes also generate enzymes that are incorporated into the brush border that digest carbohydrate and polypeptides to

Answer 40

monomeric units

Question 41

the shortest segment of the small intestine, only 25 cm in length. It receives bile from the liver and digestive juices from the pancreas via the common bile duct and pancreatic duct, respectively

Answer 41

Duodenum

Question 42

How is the duodenum different then the jejunum and ileum?

Answer 42

its villi are broader, taller, and more numerous per unit area. It has **fewer goblet cells** per unit area than the other segments, and there are **Brunner's glands** in its submucosa

Question 43

villi of the\_\_\_\_\_\_\_ are narrower, shorter, and sparser than those of the duodenum. The number of goblet cells per unit area is greater in the \_\_\_\_\_\_than in the duodenum.

Answer 43

jejunum jejunum

Question 44

Describe the vili in the ileum

Answer 44

The villi of the ileum are the sparsest, shortest, and narrowest of the three regions of the small intestine.

Question 45

The lamina propria of the\_\_\_\_\_\_\_ houses the Peyer's patches in the wall. In the region of Peyer's patches the villi are reduced in height and may even be absent.

Answer 45

ileum

Question 46

Large intestine is ~ 1.5M long composed of the

Answer 46

cecum, appendix, colon (ascending, transverse, descending, and sigmoid), rectum and anus.

Question 47

absorbs most of the water from chyme and compacts the remaining material into feces for excretion.

Answer 47

large intestine

Question 48

Cecum and colon are histologically indistinguishable. The ileum enters on the medial side of cecal-colonic boundary and is closed by the \_\_\_\_\_ that prevents reflux of cecal/colonic content back into the ileum

Answer 48

ileocecal valve

Question 49

The\_\_\_\_ is not folded into plicae cirularis and villi are absent from the mucosa giving it a relatively smooth surface.

Answer 49

colon

Question 50

The colonic epithelium consists of cells similar to the small intestine, with the exception of the \_\_\_\_\_ that are absent from the colonic Crypts

Answer 50

Paneth cells

Question 51

• villi are absent but the colonic mucosa is full of _______ that are made up of cell types similar to those of the small intestine.

Answer 51

Crypts of Lieberkhun

Question 52

How are the crypts in the colon different than in the small intestine?

Answer 52

• The crypts in the colon are longer than in the small intestine and are highly glandular with an abundance of goblet cells. The Crypts open into the lumen at the surface of the colon and can be seen as a regular array of holes across the mucosa.

Question 53

As with the small intestine the mucosal cells are born from stem cells at the base of the crypts and migrate up the walls of the crypts until the are sloughed off from the apex - the colonic mucosa is replaced every

Answer 53

6 -7 days.

Question 54

The muscularis externa outer longitudinal muscles are arranged in three distinct bands called \_\_\_\_\_\_that remain partially contracted and cause the large intestine to be puckered into sacculations called haustra coli.

Answer 54

taenia coli

Question 55

The\_\_\_\_ is blind-ended tube extending from the cecum distal to the ileocecal junction. • In some animals it is involved in digestion of cellulose but in human it has an unknown function.

Answer 55

appendix

Question 56

How is the tunic layer in the appendix different then in the intestine?

Answer 56

It follows the similar tunic pattern to the intestine in general but a characteristic feature is the presence of masses of lymphoid tissue in the mucosa and submucosa and mucosal glands are more disperse.

Question 57

\_\_\_\_\_\_\_\_is an inflammation of the appendix - left untreated it can rupture resulting in infection of the peritoneal cavity with gut contents that can lead to fatality. Very common with about 1/500 people suffering per year.

Answer 57

Appendicitis

Question 58

The terminal 12cm portion of the G.I. tract is the rectum. The rectal mucosa is similar to the colon except that the Crypts are somewhat deeper and the goblet cells more abundant.

Answer 58

Recto-anal Junction

Question 59

The end of the rectum joins the anal canal at the recto-anal junction where the epithelium transitions from simple columnar to \_\_\_\_\_\_\_

Answer 59

stratified squamous.

Question 60

In Recto-anal junction, the Crypts disappear just prior to this junction and are replaced by \_\_\_\_\_\_\_\_

Answer 60

large circumanal glands.

Question 61

Two venous plexi are found in the submucosa of anal canal - _______ plexus and \_\_\_\_\_ plexus. In older people and during pregnancy an increase in the size of the vessels in these plexuses can result in hemorrhoids.

Answer 61

internal hemorrhoidal external hemorrhoidal