2. Microanatomy of GI tract Flashcards
What are the 4 layers of the GI tract?
- Inner lining: mucosa 2. Support: submucosa 3. Muscle: muscularis external/ priopria 4. Outer wrapping: adventitia/ serosa
What does the mucosa consist of?
Epithelium - no blood vessels BM LP directly under BM. Supports epithelium structurally and nutritionally with blood and lymph Muscularis mucosa - visibly folded lining, thin layer smooth muscle. Movement and support
Which structures have stratified squamous non keratinising epithelium?
Oral cavity, pharynx, oesophagus and anal canal
protective
What epithelium does the stomach have and why?
Simple/ branched tubular glands for acid secretion Mucous columnar glandular cells
What are Enterocytes?
Columnar cells specialised for absorption with microvilli
Which structures have simple squamous?
Serosa and lining blood vessels eg vessels in LP
What does the submucosa consist of?
Connective tissue Blood vessels Lymphatic Nerves Some glands Submucosal (meissner’s plexus)
What does the SM Meissiner’s plexus do
Supplies glands and muscularis mucosa
What does the muscularis externa/ propria consist of
Smooth muscle: inner circular and outer longitudinal Responsible for movement of food along tube (peristalsis)
What is the Myenteric (Auerbach’s) plexus?
Nerve plexus between muscle layers of muscularis externa/ propria Modulated by ANS Modulates peristalsis
When does peristalsis slow down and speed up?
Slow down due to obstruction and neuro problems Speed up in irritable bowel and diarrhoea
What is the adventitia
Outer wall of gut tube Thin layer of connective tissue
What is the serosa
Outer layer of structures covered by serous membrane Squamous epithelial cells secreting small amount of fluid to allow organs glide over each other Intraperitoneum structures
What are sphincters
Thickenings of smooth muscle
5 types of sphincters
Oesophageogastric Pyloric Ileocaecal Internal anal, upper canal- retains faeces (involuntary) External anal sphincter- voluntary
What is GALT
Gut associated lymphoid tissue Located in LP Ranges from individual cells to large aggregates
What are Peyer’s patches
GALT aggregates in ileum Antigen sampling cuboidal cells
What’s different about oral cavity and pharynx compared to GI tract
Only 2 of 4 layers Mucosa and SM No muscularis mucosa SM contains small salivary glands
Histological features of lips
Folds of skeletal muscle covered by keratinised squamous without adenexal structures (no glands) Thick stratum lucidum and high dermal papillae with rich capillaries
Name the salivary glands and types of secretion
Parotid - connective tissue capsule - parotid stensen’s duct - serous Submandibular - connective tissue capsule - submandibular Wharton’s duct - mixed muco- serous Sublingual - no capsule - mixed sero- mucous secretion
Tongue
Bulk of interlaced SkM not organised Oral epithelium (strat squamous) - masticatory epithelium Attached to floor of mouth Papillae - taste buds LP, muscle core with minor salivary glands and fat Circumvallate papillae have most taste buds filliform don’t have any
Taste buds in tongue
50-100 taste receptor cells form one taste bud Long microvilli present on receptor cells Only open to surface via taste pore Sensory nerve fibres penetrate base of taste bud (4 types of cells, type 4 is stem and 3 is differentiating)
