GI Tract Histology

Question 1

Epithelium of the oral cavity, oropharynx and laryngopharynx?

Answer 1

Stratified squamous epithelium that is generally not keratinised , unless on dorsum of tongue and on gingivae, etc

Question 2

Describe the epithelium of the anterior 2/3rds of the tongue

Answer 2

Stratified squamous epithelium: Thin on ventral surface

Thick and with papillae on the dorsal surface

Question 3

Describe the epithelium and submucosa of the posterior 1/3rd of the tongue

Answer 3

Covered by smooth stratified squamous epithelium which, except for the circumvallate papillae, lacks papillae but does have substantial lymphoid aggregates (Waldayer’s ring) in the submucosa

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Question 4

Papillae on the tongue dorsum?

Answer 4

Fungiform
Circumvallate - have a moat around them where molecules being tasted are; these are flushed out by serous glands under the papillae
Foliate
Filiform (most common and have no tastebuds but do have gripping action)

Question 5

4 layers of the digestive tract?

Answer 5

Mucosa:
Epithelium - sits on basal lamina
Lamina propria - loose connective tissue
Muscularis mucosae - thin layer of smooth muscle

Submucosa - loose connective tissue
Muscularis externa - two thick layer of smooth muscle (inner circular layer and inner longitudinal layer)

Serosa or adventitia - outer layer of connective tissue that either suspends the digestive tract or attaches it to other organs

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Question 6

Describe the submucosa of the oesophagus

Answer 6

Has submucosal glands; the only other place in the GI tract with these is the duodenum

Question 7

What occurs at the gastro-oesophageal junction?

Answer 7

Abrupt transition from stratified squamous epithelium of oesophagus to the columnar epithelium of the stomach cardia

Inner circular layer of smooth muscle is markedly thickened to form the pyloric sphincter

Question 8

Surface view of the stomach?

Answer 8

Flat surface with holes (gastric pits, which are lined by surface mucous cells; these produce an alkaline mucous)

At the bottom of the gastric pits are 1-7 gastric glands

Question 9

Cells of the gastric gland?

Answer 9

Not evenly distributed:
Isthmus has mostly parietal cells
Neck is mostly neck mucous cells and stem cells
Base is mostly chief cells, with a few parietal cells and neuroendocrine cells (AKA enteroendocrine cells)

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Question 10

Functions of gastric gland cells?

Answer 10

Parietal cells produce HCl (pink cells with a purple nucleus); they are full of mitochondria and are highly invaginated (called canaliculi)

Chief cells secrete digestive enzymes (purple, gungy cells)

Enteroendocrine cells produce hormones

Stem cells replace the epithelial cells

Question 11

Difference in mucosa of different regions of the stomach?

Answer 11

Cardia - deep gastric pits branch into loosely packed, tortuous glands

Body - shallow gastric pits with long straight gastric glands

Pylorus - deep gastric pits with branched, coiled gastric glands at a higher density than in the cardia

Question 12

Unique feature of stomach muscularis externa?

Answer 12

Contains an additional layer, that is oblique to the usual circular and longitudinal muscle layers and is located internal to the circular layer

It aids the churning action of the stomach

Question 13

Surface view of the small intestine?

Answer 13

Villi are present, between which are pits ‘drilling’ downwards, called the crypts of Lieberkuhn.

Question 14

Comparison of small intestine regions?

Answer 14

Duodenum - contains Brunner’s glands in the submucosa

Jejunum - have the tallest villi, located on permanent circular folds of the mucosa and submucosa (called plicae circularis)

Ileum - characterized by aggregations of lymphoid follicles, called Peyer’s patches; these are found in the submucosa and often extend into the lamina propria

Question 15

Cells of the small intestinal epithelium?

Answer 15

Enterocytes (most numerous) - tall columnar cells with a brush border and are the principle absorptive cell

Goblet cells - roduce mucin to protect epithelium and lubricate passage of material

Paneth cells - found at the base of the crypts of Lieberkuhn; defensive function and have a role in regulating bacterial flora (secrete lysozyme and definsins)

Enteroendocrine cells - produce hormones that contribute to the control of secretion and motility (e.g. gastrin, cholecystokinin (CCK), vasoactive intestinal peptide (VIP))

Stem cells - found at the base of the crypts of Lieberkuhn; they divide to replenish epithelium.

Question 16

Unique feature of duodenum submucosa?

Answer 16

Other than oesophagus, only region of the GI tract to have glands within submucousa; Brunner’s glands, when stimulated by presence of chyme, produce a thin, alkaline mucous to neutralise it

Question 17

What is lymphoid tissue in the gut called?

Answer 17

Gut associated lymphoid tissue (GALT) - much of this is scattered intra-epithelial lymphocytes and there are areas of large lymphoid tissue aggregation, part. in the ileum (called Peyer’s patches)

Question 18

Cells of the large intestinal epithelium?

Answer 18

Absorptive cells - remove salts and thus water
Goblet cells - secrete mucus to lubricate the colon

Arranged in straight, tubular glands, called crypts, that extend down to the muscularis epithelium

Question 19

Unique feature of large intestinal outer, longitudinal smooth muscle?

Answer 19

Not continuous; it is found in 3 muscular strips called teniae coli

Question 20

What is the appendix?

Answer 20

Blind-ending hollow extension of the caecum; structure is similar to the rest of the colon, but the crypts are far less abundant and there is typically a circular arrangement of lymphoid tissue in the submucosa and often the lamina propria (lymphoid tissue tends to decline with age)

Question 21

What is at the rectoanal junction?

Answer 21

Distinct junction between the mucosa of the rectum and the stratified squamous epithelium of the anal canal

Anal canal is continuous with the stratified squamous epithelium of the surrounding skin

Question 22

Describe the ENS

Answer 22

ENS receives input from the autonomic nervous system, but is capable of coordinating gut motility locally

Most of the neurons live in groups called ganglia between the two muscle layers that make up the muscularis externa

Question 23

Function of the plexuses of the ENS?

Answer 23

Interconnected network of fibres is called the myenteric plexus (between two layers of muscularis externa) and it controls gut motility

Submucosal plexus, in the submucosa, controls the muscle of the muscularis mucosae and also helps regulate secretion in the epithelium