Histology Of Small Intestine

Question 1

Histological structure of the small intestine
Mucous membrane
• Viewed with the naked eye, the lining of the small intestine shows a series of permanent circular or semilunar folds called ———
• Plicae circulares are composed of —— and ——
• They are best developed in the ——-
The entire mucosa is covered by outgrowths called ——

Answer 1

Histological structure of the small intestine
Mucous membrane
• Viewed with the naked eye, the lining of the small intestine shows a series of permanent circular or semilunar folds- plicae circulares
• Plicae circulares are composed of mucosa and submucosa
• They are best developed in the jejunum
. Villi

Question 2

What is the epithelium of the small intestine

Answer 2

Simple columnar epithelium

Question 3

Intestinal villi
• Are mucosal outgrowths (epithelium plus lamina propria) that project into the lumen
•Each villus has a core of loose connective tissue that extends from the ———-
• It contains:
- ——,—— and ——, smooth muscle fibers ,fenestrated capillaries and a lacteal(a central lymphatic)
• In the duodenum, they are —–shaped but gradually assume —–like shapes moving towards the ileum
• They are covered by a simple columnar epithelium of absorptive cells and goblet cells

Answer 3

Intestinal villi
• Are mucosal outgrowths (epithelium plus lamina propria) that project into the lumen
•Each villus has a core of loose connective tissue that extends from the lamina propria
• It contains:
- fibroblasts and lymphocytes smooth muscle fibers ,fenestrated capillaries and a lacteal(a central lymphatic)
• In the duodenum, they are leaf–shaped but gradually assume finger–like shapes moving towards the ileum
• They are covered by a simple columnar epithelium of absorptive cells and goblet cells

Question 4

• Between the villi are small openings of short tubular glands called ————

Answer 4

Intestinal crypts
• Between the villi are small openings of short tubular glands called intestinal crypts or crypts of Lieberkükn

Question 5

Epithelium of the small intestinal
• The epithelium of each villus is continuous with that of the intervening glands which contain:
❑ ————cells,
❑ —— cells,
❑ ——- cells and
❑ —— cells that give rise to all these cell types

Answer 5

Epithelium of the small intestinal
• The epithelium of each villus is continuous with that of the intervening glands which contain:
❑ Absorptive and goblet cells,
❑ Paneth cells,
❑ Enteroendocrine cells and
❑ Stem cells that give rise to all these cell types

Question 6

——- cells secrete lysozymes,defensin , as well as tumor necrotic factor

Answer 6

Paneth cells

Question 7

——- cells are the hormone secreting cells of the mucosa

Answer 7

Enteroendocrine cells

Question 8

Enterocytes/absorptive cells
• The absorptive cells are tall —— cells each with an oval nucleus in the basal half of the cell
• At the apex of each cell, is a homogeneous layer called the —- /——
• When viewed with the electron microscope, the striated border is seen as a layer of densely packed ——- covered with glycocalyx

Answer 8

Enterocytes/absorptive cells
• The absorptive cells are tall columnar cells each with an oval nucleus in the basal half of the cell
• At the apex of each cell, is a homogeneous layer called the striated /brush border
• When viewed with the electron microscope, the striated border is seen as a layer of densely packed microvilli

Question 9

Microvilli of absorptive cells
• Each absorptive cell is estimated to have an average of —— microvilli
• 1 mm2 of mucosa contains about —— million of these structures
• Microvilli greatly increase the area of contact between the intestinal surface and the nutrients:
❑ This function is shared also by the —— and the ——

Answer 9

Microvilli of absorptive cells
• Each absorptive cell is estimated to have an average of 3000 microvilli
• 1 mm2 of mucosa contains about 200 million of these structures
• Microvilli greatly increase the area of contact between the intestinal surface and the nutrients:
❑ This function is shared also by the plicae circulares and the villi

Question 10

Microvilli of absorptive cells

• It is estimated that plicae increase the intestinal surface how many fold, the villi increase it how many fold, and the microvilli increase it how many fold
• Together, these processes are responsible for a how many -fold increase in the intestinal surface, resulting in a total absorptive area of ——m2
• Enterocytes absorb the nutrient molecules produced by digestion

Answer 10

• It is estimated that plicae increase the intestinal surface three-fold, the villi increase it 10-fold, and the microvilli increase it 20-fold
• Together, these processes are responsible for a 600-fold increase in the intestinal surface, resulting in a total absorptive area of 200m2
• Enterocytes absorb the nutrient molecules produced by digestion

Question 11

Goblet cells
• Are interspersed between the —— cells
• They are less abundant in the —— and more numerous in the ——
• These cells produce glycoprotein mucins that are hydrated and cross-linked to form ——
• Mucus functions to protect and lubricate the lining of the small intestine

Answer 11

Goblet cells
• Are interspersed between the absorptive cells
• They are less abundant in the duodenum and more numerous in the ileum
• These cells produce glycoprotein mucins that are hydrated and cross-linked to form mucus
• Mucus functions to protect and lubricate the lining of the small intestine

Question 12

Paneth cells
• Are (exocrine/endocrine?)cells with large eosinophilic secretory granules
• They are located in the —— portion of the intestinal crypts below the —— cells (arrow heads)

Answer 12

Paneth cells
• Are exocrine cells with large eosinophilic secretory granules
• They are located in the basal portion of the intestinal crypts below the stem cells (arrow heads)

Question 13

Paneth cells
• They undergo exocytosis to release ——, ———, and ——
• All these substances bind and breakdown membranes of microorganisms and bacterial walls
• Paneth cells have an important role in innate immunity and in regulating the microenvironment of the intestinal crypts

Answer 13

Paneth cells
• They undergo exocytosis to release lysozymes, phospholipase A2, and defensins
• All these substances bind and breakdown membranes of microorganisms and bacterial walls
• Paneth cells have an important role in innate immunity and in regulating the microenvironment of the intestinal crypts

Question 14

Enteroendocrine cells
• They represent part of the widely distributed diffuse ——— system
• Upon stimulation, the enteroendocrine cells release their secretory granules (peptides) by —— and the hormones may then exert ——/local or —— effects which include:
❑ Control of peristalsis,
❑ Regulation of secretions necessary for food digestion and
❑ Sense of being satiated after eating

Answer 14

Enteroendocrine cells
• These cells are present in varying numbers throughout the length of the small intestine
• They represent part of the widely distributed diffuse neuroendocrine system
• Upon stimulation, the enteroendocrine cells release their secretory granules (peptides) by exocytosis and the hormones may then exert paracrine/local or endocrine effects which include:
❑ Control of peristalsis,
❑ Regulation of secretions necessary for food digestion
and
❑ Sense of being satiated after eating

Question 15

M (also called ——) cells
• Are specialized epithelial cells in the ileum overlying the lymphoid follicles of ———

Answer 15

M (microfold) cells
• Are specialized epithelial cells in the ileum overlying the lymphoid follicles of Peyer patches
• M cells selectively endocytose antigens and transport them to the underlying macrophages and lymphocytes
• Which then migrate to lymph nodes where immune responses to foreign antigens are initiated

Question 16

• —— cells selectively endocytose antigens and transport them to the underlying macrophages and lymphocytes
• Which then migrate to lymph nodes where immune responses to foreign antigens are initiated

Answer 16

M cells

Question 17

M cells are found where

Answer 17

Ileum

Question 18

Lamina propria of the small intestine
• It is composed of —— connective tissue with blood and lymph vessels, nerve fibers, lymphoid tissue and smooth muscle cells
• The lamina propria penetrates the core of each ———, bringing with it microvasculature, lymphatics, and nerves
• ——— inside the villi are responsible for their rhythmic movements which are important for efficient absorption
• contractions of the muscularis mucosae also produces local movements of the villi and plicae circulares that help propel lymph from the lacteals into submucosal and myenteric lymphatics

Answer 18

Lamina propria of the small intestine
• It is composed of loose connective tissue with blood and lymph vessels, nerve fibers and smooth muscle cells
• The lamina propria penetrates the core of each intestinal villus, bringing with it microvasculature, lymphatics, and nerves
• Smooth muscle fibers inside the villi are responsible for their rhythmic movements which are important for efficient absorption
• contractions of the muscularis mucosae also produces local movements of the villi and plicae circulares that help propel lymph from the lacteals into ——- and ——- lymphatics

Question 19

Submucosa of the small intestine
• Present in the proximal part of the duodenum are large clusters of branched tubular mucous glands, the —— glands with small excretory ducts opening among the intestinal crypts
• The product of the glands:
❑ Is distinctly (alkaline/acidic?)(pH—to—)

Answer 19

Submucosa of the small intestine
• Present in the proximal part of the duodenum are large clusters of branched tubular mucous glands, the duodenal /Brunner glands with small excretory ducts opening among the intestinal crypts
• The product of the glands:
❑ Is distinctly alkaline (pH 8.1-9.3)

Question 20

Bruner glands are found where

Answer 20

In the proximal part of the duodenum

Question 21

List 3 functions of the Bruner glands

Answer 21

-protects the mucous membrane
- brings the intestinal contents to the optimum pH for pancreatic enzyme action
-neutralizes chyme entering the duodenum from the pylorus

Question 22

• In the ileum both the lamina propria and submucosa contain the lymphoid nodule aggregates known as ——, an important component of the MALT

Answer 22

Peyer’s patches

Question 23

Muscularis and serosa of the small intestine
Muscularis
• Is well developed and composed of an internal —- layer and an external — layer. Between these muscle layers is the —— nerve plexus
Serosa
• It is covered by a thin serosa with ——

Answer 23

Muscularis and serosa of the small intestine
• Is well developed and composed of an internal circular layer and an external longitudinal layer. Myenteric plexus
• It is covered by a thin serosa with mesothelium

Question 24

Lacteals
• Lymph vessels of the intestine begin as —— tubes in the cores of villi
• Lacteals run to the region of lamina propria above the muscularis mucosae, where they form a ——
• From there they are directed to the submucosa where they surround ——
• Lacteals are especially important for —

Answer 24

Lacteals
• Lymph vessels of the intestine begin as closed tubes in the cores of villi
• Lacteals run to the region of lamina propria above the muscularis mucosae, where they form a plexus
• From there they are directed to the submucosa where they surround lymphoid nodules
• Lacteals anastomose repeatedly and leave the intestine along with the blood vessels
• Lacteals are especially important for lipid absorption

Question 25

Blood vessels
• Blood vessels penetrate the muscularis and form a large plexus in the ——
• From the submucosa, branches extend through the —— and —— into the villi

Answer 25

Blood vessels
• Blood vessels penetrate the muscularis and form a large plexus in the submucosa
• From the submucosa, branches extend through the muscularis mucosae and lamina propria into the villi

Question 26

Microvasculature of the villus
• Each villus receives according to its size, one or more branches that form a —— network just below its epithelium
• At the tips of the villi, one or more venules arise from these capillaries and run in the opposite direction reaching the veins of the ——- plexus

Answer 26

Microvasculature of the villus
• Each villus receives according to its size, one or more branches that form a capillary network just below its epithelium
• At the tips of the villi, one or more venules arise from these capillaries and run in the opposite direction reaching the veins of the submucosal plexus

Question 27

Innervation of the small intestine
• Innervation is formed by intrinsic and extrinsic components comprising the ——nervous system
• The intrinsic component comprises the ——— nerve plexus located between the outer longitudinal and inner circular layers of the muscularis and the ——plexus in the submucosa

Answer 27

Innervation of the small intestine
• Innervation is formed by intrinsic and extrinsic components comprising the enteric nervous system
• The intrinsic component comprises the myenteric (Auerbach) nerve plexus located between the outer longitudinal and inner circular layers of the muscularis and the submucosal (Meissner) plexus in the submucosa
• The intrinsic innervation formed by these plexuses is responsible for intestinal contraction

Question 28

Medical application

• The hormone —— produced by enteroendocrine cells of the small intestine was the first hormone to be discovered
• Two brothers-in-law, —— and —— working at University College London (1900) observed that the factor caused the pancreas to secrete its alkaline digestive fluid

Answer 28

Medical application
• Deficiencies of disaccharides have been described in human diseases characterized by digestive disturbances. Some of the enzymatic deficiencies seem to be of genetic origin
• The absorption of nutrients is also greatly hindered in disorders marked by atrophy of the intestinal mucosa caused by infections or nutritional deficiencies producing the malabsorption syndrome
• The hormone secretin produced by enteroendocrine cells of the small intestine was the first hormone to be discovered
• Two brothers-in-law, William Bayliss and Ernest Starling working at University College London (1900) observed that the factor caused the pancreas to secrete its alkaline digestive fluid

Question 29

Medical application
—— disease- disorder of small intestine mucosa that causes malabsorption and can lead to damage or destruction of the villi (immune reaction to eating gluten, creates inflammation)
• ——— - benign tumors of smooth muscle cells
Most common type of tumors in the stomach and small: intestine
• —- disease(also called— )- chronic inflammatory bowel disease that occurs most commonly in the ileum or colon. Causes excessive lvmphocytic activity and inflammation in any or all the tract producing pain, localized bleeding, malabsorption and diarrhea

Answer 29

Celiac disease- disorder of small intestine mucosa that causes malabsorption and can lead to damage or destruction of the villi (immune reaction to eating gluten, creates inflammation)
• Leiomyomas(fibroids)- benign tumors of smooth muscle cells
Most common type of tumors in the stomach and small: intestine
• Crohn disease(ileitis)- chronic inflammatory bowel disease that occurs most commonly in the ileum or colon. Causes excessive lvmphocytic activity and inflammation in any or all the tract producing pain, localized bleeding, malabsorption and diarrhea