Histology of Small and Large Intestines

Question 1

The small intestine is divided into?

Answer 1

1. duodenum (25-30 cm) : from Pylorus – duodenojejunal junction 2. jejunum (about first two-fifths of the rest) 3. Ileum (~ 3.5 m long) - The three segments have the same basic histological organization

Question 2

What are the functions of the small intestine?

Answer 2

1. Principal site for digestion 2. Absorption of products of digestion

Question 3

Name the structural features which increase the luminal surface area?

Answer 3

1. Pilcae circulares 2. intestinal villi 3. microvilli

Question 4

What are pilcae circulares?

Answer 4

the numerous permanent crescentic filds of mucous membrane found in the small intestine especially in the lower part of the duodenum

Question 5

Describe pilcae circulares?

Answer 5

1. permanent structures, contain core of submucosa 2. absent from the first few centimetres of the duodenum and the distal part of the ileum 3. Numerous in distal part of duodenum and proximal part of jejunum 4. well developed in the jejunum

Question 6

Describe intestinal villi?

Answer 6

1. 1 mm long 2. Unique finger-like projections of mucosa 3. Extend from mucosa to the lumen

Question 7

Intestinal villi is formed by?

Answer 7

1. core of lamina propria 2. simple columnar epithelium

Question 8

Epithelium of the villus is composed of?

Answer 8

1. enterocytes

Question 9

Describe enterocytes?

Answer 9

absorptive cells - 1. tall collumnal cells 2. basally located nuclei 3. microvilli forms striated border 4. tight junctions forms a barrier 5. secrete enzymes + water + electrolytes in secretory granules 6. have lateral plications 7. have elongated mitochondria

Question 10

Describe goblet cells?

Answer 10

unicellulare mucin secreting glands

Question 11

Describe the intestinal glands (crypts of Lieberkuhn)?

Answer 11

1. simple tubular mucosal glands 2. openings located between the villi and extend through the lamina propria down to the muscularis mucossae 3. has simple columnal epithelium 4. secrete intestinal juice (2 liters/day) e.g. enteropeptidase (or enterokinase

Question 12

Describe microvilli?

Answer 12

extensions of the apical surface membrane of enterocytes

Question 13

What are the essential features of the small intestinal mucosa?

Answer 13

1. the villi 2. intestinal glands 3. the lamina propria 4. GALT - gut associated lymphoid tissue 5. muscularis mucosa

Question 14

Describe the epithelium of the intestinal glands?

Answer 14

1. Goblet cells: -mucus-secreting 2. Enterocytes- absorptive cells 3. enteroendocrine cells – produce paracrine and endocrine hormones 4. Paneth cells are located at the bottom of the crypts -release a number of antibacterial substances 5. Intermediate cells – capable of dividing

Question 15

Describe the Paneth cells?

Answer 15

1. Found at the base of the gland 2. Regulate the normal bacteria flora in small intestine 3. Apical secretory granules contain antibacterial enzyme lysozyme 4.

Question 16

Describe enteroendocrine cells?

Answer 16

1. Concentrated in the lower portion of the gland 2. Widely distributed (diffuse neuroendocrine system)

Question 17

Describe the 2 types of enteroendocrine cells?

Answer 17

1. Open type – cellular apex presents microvilli and contacts lumen 2. Closed type – cellular apex covered by other epithelial cells

Question 18

Describe the M (microfold cells)?

Answer 18

1. specialised epithelial cells the overlie lymphoid follicles of peyer patches 2. Have numerous basal membrane inviginations (pits)- contain intraepithelial lymphocytes and macrophages 3. Can endocytose antigens and transport to macrophages 4. Basement membrane under M cells is discontinuous

Question 19

The lamina propria is composed of?

Answer 19

1. loose CT 2. blood and lymph vessels 3. nerve fibers 4. smooth muscle cells - lamina propria penetrates the core of the villi

Question 20

Describe the lamina propria?

Answer 20

1. Lamina propria penetrates the core of the villi 2. The lamina propria is, unusually cell rich 3. Lymphocytes invade the epithelium or form solitary lymphoid nodules (30-50 nodules) in the lamina propria - called Peyer’s patches

Question 21

Describe the muscularis mucosa?

Answer 21

1. has 2 layers 2. extends into the intestinal villi, where the smooth muscle cells form a longitudinal bundle in the centre of the villi

Question 22

Describe the submucosa in the duodenum?

Answer 22

1. Contains coiled tubular glands called Brunner’s glands – secret alkaline substance 2. Lamina propria and submucosa of small intestine contain Peyer patches – component of GALT 3. Peyer patches are located on the antimesenteric side

Question 23

Describe Brunners glands?

Answer 23

1. Their secretion is mucous and slightly alkaline due to bicarbonate ions (pH 7-8) 2. The secretion of Brunner’s glands protects the duodenal mucosa

Question 24

What is the large intestine made of?

Answer 24

1. cecum including the appendix 2. colon 3. rectum 4. anal canal

Question 25

The colon is subdivided into?

Answer 25

1. ascending colon 2. transverse 3. descending colon 4. sigmoid colon

Question 26

What are the gross distinctive features of the large intestine?

Answer 26

1. Longitudinal layer of muscularis externa exhibits three thickened bands called Tinea coli 2. External surface of the caecum has succulations (Haustra) 3. Serosa has small fatty projections call (omental appendices)

Question 27

What are the functions of the large intestine?

Answer 27

1. reabsorption of water and inorganic salts 2. secretion of mucus, which acts as a lubricant 3. Elimination of undigested food and wastes

Question 28

Describe the mucosa of the large intestine?

Answer 28

1. The surface of the mucosa is relatively smooth 2. no plicae circulares or intestinal villi 3. Crypts of Lieberkühn are present and usually longer and straighter than those of the small intestine 4. Luminal surface has orderly patterned gland openings

Question 29

Describe the epithelium of the mucosa of the LI?

Answer 29

1. Glands consists of simple columnal epithelium 2. Goblet cells account for more of the epithelial cells than in the small intestine 3. Contains same types of cells except paneth cells ( absent)

Question 30

Describe the lamina propria?

Answer 30

little lamina propria is squeezed between the glands.

Question 31

What are the structural features of the lamina propria?

Answer 31

1.The collagen table 2. Well developed GALT 3. Well developed pericryptal fobroblast sheath 4. Absence of lymphatic vessels

Question 32

Describe the muscularis mucosa?

Answer 32

forms 2 layers

Question 33

Describe the submucosa?

Answer 33

1. contains lymphatic vessels 2. contains considerable amount of fat

Question 34

Describe the muscularis externa?

Answer 34

1. Appears different from the small intestine 2. The inner circular muscle layer forms the usual sheath 3. The outer longitudinal muscle layer forms three flattened strands, the taenia coli 4. Only a thin layer of longitudinal muscle surrounds the inner circular muscle layer between the taenia coli

Question 35

What is the vermiform appendix?

Answer 35

small blind-ending diverticulum from the cecum

Question 36

What are the important features of the vermiform appendix?

Answer 36

1. large accumulations of lymphoid tissue in the lamina propria and submucosa 2. no intestinal villi 3. infrequent crypts 4. fatty tissue in the submucosa 5. the muscularis externa is thinner 6. no taenia coli

Question 37

What is a cause of appendicitis that has to do with lymphocytes?

Answer 37

An extreme proliferation of lymphocytes (lymphoid hyperplasia) as a consequence of bacterial or viral stimulation may lead to the obstruction of the lumen of the appendix

Question 38

Describe the rectum?

Answer 38

1. Dilated distal portion of the alimentary canal 2. Upper part has transverse rectal folds 3. Mucosa –like in colon

Question 39

Describe the anal canal?

Answer 39

1. Most distal portion of the alimentary canal (4 cm long ) 2. Extends from upper part of pelvic diaphragm to anus 3. Upper part has longitudinal folds- anal columns 4. Depressions between columns – anal sinuses

Question 40

What are the zonea of the anal canal?

Answer 40

1. colorectal zone 2. anal transition zone 3. squamous zone

Question 41

Describe the colorectal zone?

Answer 41

1. in the upper 1/3 2. Contains simple columnal epithelium

Question 42

Describe the anal transition zone?

Answer 42

1. in the middle 1/3 2. Represent transition between simple columnal (rectal) to stratified squamous epitheliun (perianal skin)

Question 43

Describe the squamous zone?

Answer 43

1. lower 1/3 2. stratified squamous

Question 44

What are the glands of the anal canal?

Answer 44

1. anal glands 2. circumanal glands

Question 45

Describe the anal glands?

Answer 45

1. extend into submucosa + muscularis mucosa 2. secrete mucus

Question 46

Describe the circumanal glands? (apocrine glands)

Answer 46

1. Found in skin surrounding anal orifice 2. Sex attractant

Question 47

Describe the submucosa of the anal canal?

Answer 47

ramified with supeior rectal arteries – enlargement of these veins constitute internal hemorroids

Question 48

Describe the muscularis externa of the anal canal?

Answer 48

circular thickens - internal sphincter muscle