GI Tract Histology Flashcards
Epithelium of the oral cavity, oropharynx and laryngopharynx?
Stratified squamous epithelium that is generally not keratinised , unless on dorsum of tongue and on gingivae, etc
Describe the epithelium of the anterior 2/3rds of the tongue
Stratified squamous epithelium: Thin on ventral surface
Thick and with papillae on the dorsal surface
Describe the epithelium and submucosa of the posterior 1/3rd of the tongue
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
ADD PICTURE 2
Papillae on the tongue dorsum?
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)
4 layers of the digestive tract?
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
ADD PICTURE 3
Describe the submucosa of the oesophagus
Has submucosal glands; the only other place in the GI tract with these is the duodenum
What occurs at the gastro-oesophageal junction?
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
Surface view of the stomach?
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
Cells of the gastric gland?
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)
ADD PICTURE 4
Functions of gastric gland cells?
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
Difference in mucosa of different regions of the stomach?
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
Unique feature of stomach muscularis externa?
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
Surface view of the small intestine?
Villi are present, between which are pits ‘drilling’ downwards, called the crypts of Lieberkuhn.
Comparison of small intestine regions?
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
Cells of the small intestinal epithelium?
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.
Unique feature of duodenum submucosa?
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
What is lymphoid tissue in the gut called?
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)
Cells of the large intestinal epithelium?
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
Unique feature of large intestinal outer, longitudinal smooth muscle?
Not continuous; it is found in 3 muscular strips called teniae coli
What is the appendix?
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)
What is at the rectoanal junction?
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
Describe the ENS
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
Function of the plexuses of the ENS?
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
