1.1.3 GI Histology 1

Question 1

What are the 4 layers of the gut wall?

Answer 1

innermost mucosa, submucosa, muscularis propria/ externa and serosa/ adventitial

Question 2

Mucosa- consists of 3 parts, lining epithelium, lamina propria and muscularis mucosa

Lining epithelium: mainly _____ in the gastrointestinal tract except in the oesophagus and the distal anal canal (stratified squamous)

Lamina propria: non epithelium tissue present in the mucosa over the muscularis mucosa.

• Connective tissues that help support the surface lining epithelium and the gland.
• Contains nerves, blood vesssels and inflammatory cells

Muscularis mucosa – thin layer of muscle separating the mucosa from the submucosa
- Consists of an _____ and an ______ layer – layering is important for maintaining the mobility of the mucosa and expelling glandular secretions

Answer 2

columnar; inner circular; outer longitudinal

Question 3

The mucosa shows modifications reflecting its function
o In the small intestine, the main function is absorption – mucosa forms _____
o In the stomach, the main function is secretion – epithelium thus dips down into the lamina propria to form _______
o In the colon, simple tubular glands that secrete mucous and lubricates the faecal material

Answer 3

villus projections; simple tubular glands

Question 4

Submucosa – layer of loose connective tissue with blood vessels, lymphatics and nerves which physically supports the mucosa
- In some areas e.g. oesophagus and duodenum, ______ are present in the submucosa

Answer 4

glands

Question 5

Muscularis externa/propria – thick layer of muscle beneath the submucosa, consisting of an inner circular and an outer longitudinal layer
- These smooth muscle bundles are arranged in tight and loose helices around the gut wall – contraction of the circular layer leads to constriction of the gut lumen while the longitudinal muscle shortens the gut length, pushing the food forward
o The action of these 2 perpendicular layers leads to peristaltic movement
o The muscularis externa is formed mainly of smooth muscle, with the exception of ________ (skeletal muscles present)
- Other variations include an extra oblique layer within the stomach and the longitudinal layers in the colon grouped together to form long bundles – _____
- Circular muscle also forms ________ known as sphincters (e.g. pyloric sphincter and internal anal sphincter)

Answer 5

upper oesophagus and anal canal; taenia coli; localised thickenings

Question 6

Enteric nervous system: largely autonomous system, extensive meshwork of neurones in the gut wall from the oesophagus to the anus

• This consists of over 100 million neurones and controls the gut peristalsis, epithelial secretion, absorption and blood flow (2nd brain)
• Within the gut wall, there are 2 main nerve plexuses, the myenteric plexus of Auerbach (within the __________) and the _____ (in the submucosa)
• Nerve plexuses consists of neurones and ganglion cells (large round nucleus with nucleoli and basophilic cytoplasm)
• ________ are pacemaker cells of the gut around nerve plexuses and are difficult to visualise in the regular H&E section
  o Stained brown with the immunohistochemical marker _____

Answer 6

2 layers of the muscularis propria; submucosal plexus of Meissner; Stellate myoid cells (interstitial cells of Cajal); ckit

Question 7

Serosa/adventitia – outermost layer of the gut consisting of a thin fibrovascular layer covered by _________
- Where the peritoneum is absent (e.g. oesophagus and rectum), there is a layer of connective tissue – adventitia which is in continuity with the surrounding tissue

Answer 7

mesothelium (visceral peritoneum)

Question 8

Oesophagus

• mucosa: ________ epithelium with a protective function
• submucosa: mucous glands helping to lubricate the mucosa during the passage of food
• Muscularis externa: inner circular and outer longitudinal layers of muscle. Skeletal muscle fibres are present in the upper third, smooth muscle fibres are present in the lower third and a mixed of the 2 fibres are present in the middle third
• adventitia: present except for the _______ which is intraabdominal, covered by serosa

Answer 8

non keratinising stratified squamous; lowest part of the oesophagus

Question 9

Gastro-oesophageal junction – oesophageal mucosa appears tubular and whitish but the stomach mucosa is more brownish with more folds (_____) present

Answer 9

rugae

Question 10

Stomach

• mucosa: columnar epithelium with secretory function. Surface epithelium of the gastric mucosa are mucous secreting columnar cells that dip down into the lamina propria to form ______ that have gastric glands which open into the pits
• submucosa: Submucosa layer – loose, vascular connective tissue extending into the gastric rugae (____ sections of tissue)
• Muscularis externa: additional ______ layer and the circular layer forms the _____ at the pylorus
• serosa: outer most layer

Answer 10

foveolae (gastric pits); coiled; innermost oblique; pyloric sphincter

Question 11

Fundus and body of stomach

• ____ foveolar layer with short gastric pits
• Most of the mucosa is composed of gastric glands- cells secrete ___ and ____ (required for the absorption of B12
• pits: glands = _____ which suggests shallow pits and deep glands

Answer 11

thinner, HCl, intrinsic factor, 1:3

Question 12

Antrum and cardia of stomach

• ____ foveolar layer with deeper gastric pits
• Underlying layer of simple mucous glands in the deeper third of the mucosa
• pits: glands = _____

Answer 12

thicker; 1:1

Question 13

What are the glandular cells of the stomach? (5)

Answer 13

Chief cells and parietal cells in the body, scattered neuroendocrine cells, regenerative cells and mucous neck cells

Question 14

Parietal cells (oxyntic acid-secreting) – large ovoid cells with a central round nucleus and a bright \_\_\_\_\_\_\_ cytoplasm
§ Scattered among the more numerous blueish-stained cells (Chief cells)
§ Parietal cells produce HCl and intrinsic factor (important for Vitamin B12 absorption in the \_\_\_\_) – main trigger for the secretion of HCl is the activation of \_\_\_\_\_ by histamine. Gastrin and acetylcholine can also stimulate the secretion by different receptors. 
§ Luminal membrane invaginations into the cytoplasm – \_\_\_\_\_\_\_
§ When receptors are activated, proton pumps actively transport H+ into the canalicular lumen, where they bind with Cl- to form HCl – acid production can be blocked at various stages

Answer 14

eosinophilic ; ileum; H2 receptor; canaliculi

Question 15

Principal secretion of surface lining cells?

Answer 15

Mucous – forms a layer on the mucosa to prevent acid from digesting the mucosa

Question 16

Principal secretions of parietal cells?

Answer 16

HCl and gastric intrinsic factor

Question 17

Principal secretions of chief cells?

Answer 17

precursors of pepsin, renin and lipasae

Question 18

Principal secretions of diffuse neuroendocrine cells?

Answer 18

hormones e.g. gastrin, somatostatin, secretin, cholecystokinin

Question 19

Small intestines – mucosa and submucosa is very distinctive
- Mucosa – presence of villi increasing the absorptive surface of the small intestines
o Villi are lined by columnar epithelial absorptive cells with striated border and interspersed with _____
o Deep to the villi are simple tubular glands – crypts of Lieberkühn, with regenerative cells, scattered cells of the _______ at the base
o Lymphoid cells aggregate and form follicles, particularly in the _______ – Peyer’s patches

• Submucosa – distinctive in the duodenum with Brunner’s glands which secrete _______
• Cells lining the villus – absorptive cells and clear cells (goblet cells)

Answer 19

goblet cells; DNES and Paneth cells; distal ileum; alkaline mucous material

Question 20

[small intestine]

• Absorptive: Columnar cells with eosinophilic cytoplasm and are basally situated. Accentuation along luminal border forming the brush border. Striated border has a layer of _____ – highlighted using a mucinstain
• Goblet cells: secretion of _____

Answer 20

glycocalyx; mucin

Question 21

[small intestine]
Crypts of Lieberkühn – situated deep to the villi,
opening into the intervillus spaces
o Absorptive epithelial cells and interspersed mucous cells
o Paneth cells – towards the base with dense eosinophilic granules in the cytoplasm are the, produce __________, and have phagocytic capabilities
o Goblet cells – mucous secreting cells with a characteristic shape (as shown below) with mucin appears unstained on H&E sections
o Scattered lymphocytes in the epithelium – appear as small blue dots

Answer 21

lysozymes, defensins and immunoglobulins

Question 22

[small intestine]

• Mucosal lymphoid tissues – scattered follicles or aggregates along the gastrointestinal tract, forming gut associated lymphoid tissue (GALT) such as Peyer’s patches in the terminal ileum
• -> M cells – scattered among the normal epithelial cells with numerous _____ instead of microvilli, helping to transport the _____ to subjacent lymphoid follicles
• In addition to the lymphoid follicles, there are numerous plasma cells present within the ______ of the small intestines
  o The villus epithelium shows intraepithelial T lymphocytes which are also present within the lamina propria

Answer 22

microfolds; luminal antigens; lamina propria

Question 23

Colon
- The colonic mucosa is distinct as it has no villi – columnar epithelial lining with surface absorptive cells (absorb water) and numerous goblet cells
o Absorptive cells are more numerous in the _____ whereas ______ increase in number towards the distal end to aid in lubrication of the faecal material
o Lining epithelial dips down into the lamina propria to form regularly spaces tubular glands (crypts of Lieberkühn)
o The bases of these glands touch the muscularis mucosa
o In the lamina propria, there are scattered inflammatory cells

Answer 23

proximal colon; goblet cells

Question 24

Appendix – mucosa and submucosa contain prominent _______

o Muscularis propria and serosa surround lymphoid follicles

Answer 24

lymphoid follicles or aggregates

Question 25

Anal canal – distinctive as the upper part is still a
columnar mucosa whereas the midpart becomes a
______ with a more protective function and the lower part of the anal canal is covered by skin
- Submucosa contains numerous vascular structures,
forming the internal haemorrhoidal plexuses
- Muscularis externa contains the circular muscle
which forms the internal anal sphincter

Answer 25

stratified squamous epithelium