Gastrointestinal Histology Flashcards
What is the basic organisation of the GI tract?
Mucosa - epithelium, lamina propria, muscularis mucosae
Submucosa - connective tissue
Muscularis externa - inner circular and outer longitudinal
Adventitia/serosa
What is the muscularis mucosae?
Very thin layer of muscle involved in fine movement
What is found in the submucosa?
Fibroblasts and collagen
Some areas have glands
What is the difference between an adventitia and a serosa?
Adventitia - merges with other connective tissue, no clear ending
Serosa - defined outer surface, thin, always surrounded by a thin layer of squamous epithelial cells
What are the three main types of epithelium found in the GI tract?
Protective
Secretory
Absorptive
Describe the epithelium of the oesophagus.
Non-keratinised, stratified, squamous epithelium
Describe the muscularis externa of the oesophagus.
Upper third - voluntary
Middle third - mixed
Lower third - smooth
What is the function of the submucosal glands in the oesophagus?
Produce mucus for lubrication
What are the three regions of the stomach?
Funduc/cardiac
Body/corpus
Pylorus
What is the main function of the fundus region?
HCl secretion
What is the main function of the body of the stomach?
Enzyme delivery and digestion
What is the main function of the pylorus?
Prepare party digested food for movement into duodenum - mucus secretion
How is the surface area increased in the stomach?
Rugae
What are the layers of the muscularis externa of the stomach?
Oblique layer
Inner circular layer
Outer longitudinal layer
What type of epithelium is in the stomach?
Secretory
What is secreted in the stomach?
Mucus
Pepsin
HCl
Intrinsic factor
Gastrin
What is another name for a gastric pit?
Foveolus
What are the regions of the gastric glands?
(Pit)
Isthmus
Neck
Base
What cells are found at the isthmus of a gastric gland?
Parietal cells
Mucous cells
What concentration of HCl is produced by the gastric glands?
0.1M
What cells are found at the neck of a gastric gland?
Stem cells
What cells are found at the base of a gastric gland?
Peptic cells
Neuroendocrine cells
What do parietal cells produce?
HCl
What do peptic cells produce?
Enzymes such as pepsinogen
What do the neuroendocrine cells of the gastric glands produce?
Gastrin
What do the neuroendocrine cells do in the GI tract?
Control local movement
Prepare duodenum and pancreas for arrival of food
What do parietal cells look like histologically?
Fried eggs
How do the gastric glands vary in the different regions of the stomach?
Fundus - lots of parietal cells (to acidify quickly)
Body - lots of peptic and parietal cells
Pylorus - mucous cells (lubricate)
Why doesn’t the stomach self-digest?
Surface epithelial cells secrete HCO3- to establish a neutral pH in mucus layer adjacent to cells
Enzymes are not active in mucus
Why don’t the gastric glands get burned by the acid?
Parietal cells secrete into the centre of the gastric gland
Below pH 4 - viscous fingering of HCl in mucus
What are the submucosal glands found in the duodenum called?
Brunner’s glands
What do Brunner’s glands do?
Produce mucus which is alkaline to neutralise stomach acid
What are two differences between the duodenum and the rest of the small intestine?
Shorter villi in duodenum
No submucosal glands in jejunum and ileum
What are the villi mounted on in the jejunum and ileum?
Plicae circulares
What are the specialisations for absorption in the jejunum and ileum?
Plicae circulares (most prominent in jejunum)
Villi with goblet cells
Microvilli
Blood supply
Lacteals
What are the epithelial cells of the small intestine?
Enterocytes
Goblet cells
Paneth cells
Stem cells
What are Paneth cells?
Neuroendocrine cells of small intestine
Where are the Paneth and stem cells found?
Crypts at base of villi in mucosa
What are Peyer’s patches?
Lymphoid tissue grouped together for surveillance
Most prominent in ileum
Describe the material leaving the ileum.
Loose and watery
Describe the colon’s wall.
No villi
Tubular glands within mucosa
Enterocytes with microvilli and goblet cells
Thick muscularis externa with discontinuous outer layer
What is the function of the enterocytes in the colon?
Sodium pumps help water absorption by osmosis
What is the function of the goblet cells in the colon?
Lubricate bolus
How does the epithelium change at the ano-rectal junction?
Sudden switch to stratified, squamous epithelium
Still lots of glands
What are the functions of saliva?
Lubricate, moisten
Begin digestion (α-amylase, lipase)
Antiseptic (IgA, lysozyme)
Where are the three main salivary glands located?
Parotid - just below ear lobe
Submandibular - below tongue and mostly below sublingual
Sublingual - below tongue
What type of secretion occurs at salivary glands?
Merocrine
What type of structure do salivary glands have?
Branched acinar
What is a serous demilune?
Artefact of fixation when an acinus has both serous and mucous cells
Describe the acini of the three main salivary glands.
Parotid - almost all serous
Submandibular - mixed
Sublingual - almost all mucous
What are myoepithelial cells?
Cells found outside acini which have processes to contract to release saliva on stimulation by the ANS
What is the tonicity of the primary salivary secretion in relation to plasma?
Hypertonic
What is the order of ducts which saliva flows through?
Intercalated –> striated –> excretory
How can you tell the difference between the salivary ducts histologically?
Intercalated = smallest with indistinguishable lumen
Striated = obvious lumen, striated simple layer of cells
Excretory = found outside acini/in connective tissue
What is the function of the striated salivary ducts?
Reabsorb Na+ and Cl- and replace them with K+ and HCO3- so saliva becomes hypotonic and alkaline
What are the functions of the tongue?
Manipulation of food
General sensory reception (touch, pressure, heat)
Special sensory reception (taste)
Speech
Why is the muscle in the tongue orientated the way it is?
Bundles of skeletal muscle arranged in all orientations to allow movement in all directions
Describe the epithelium of the tongue.
Partly keratinised, stratified, squamous epithelium
What are the three types of tongue papillae?
Fungiform
Filiform
Circumvallate
Describe filiform papillae.
Small keratinised spikes present at front of tongue
Catch and manipulate food
Most common
Describe fungiform papillae.
Thin keratinisation
Scattered
Richly vascularised core
Taste buds
Ducts from glands of Von Ebner open into base
Describe circumvallate papillae.
Chef hat-shaped
6-14 along sulcus terminalis
Taste buds
Ducts from glands of Von Ebner open into base
What are taste buds?
Pale-staining structures at base of fungiform and inner wall of circumvallate papillae
Associated with supporting cells and a nerve ending
Why are taste buds found at the base of papillae?
Prevent damage by food
What are glands of Von Ebner?
Large salivary glands
Where are the papillae of the tongue found?
Anterior two-thirds
Describe the posterior third of the tongue.
Relatively smooth oral epithelium - stratified, squamous, non-keratinised
Abundant lymphoid tissue associated with lingual tonsil
What does Waldeyer’s ring comprise of?
Lingual tonsil
Palatine tonsil
Adenoids
