histology of GI tract Flashcards
Four main layers of the gut tube from lumen to outside
mucous membrane- mucosa
submucosa
muscularis externa
adventitia/serosa
three layers of the mucosa + what is present in each
surface epithelium, lying on basal lamina
lamina propria - supporting tissue with abundant neurovasculature and cells of the immune system
muscularis mucosae- thin double layer of smooth muscle
submucosa structure and components
formed of fibroelastic loose connective tissue with vessels and nerves of the submucosal plexus (Meissner’s), wandering lymphocytes and large quantities of fat
muscularis externa structure
two thick layers of smooth muscle
inner layer is circular
outer layer formed of longitudinal fibres
between the muscle layers the myenteric nerve plexus (Auerbach’s) is located
adventitia definition
thin outer layer of loose connective tissue that is continuous with the adjacent organ or tissue
structure of adventitia if gut wall is free and mobile
covered in mesothelium and connective tissue forming the serosa which is joined to the mesentery
serosa definition
smooth membrane consisting of a mesothelium and connective tissue layer containing neurovasculature
line and enclose several body cavities and secretre a lubricating fluid to reduce friction
difference between adventitia and serosa
adventitia is a connective tissue layer which binds together structures rather than reducing friction between them
mesentery definition
fold of peritoneum that attaches the small intestine, stomach, pancreas, spleen and other organs to the posterior abdominal wall
two identifiable features of the oesophagus
non-keratinised stratified squamous epithelium
folded mucosa
explain function of the adaptations
non-keratinised, as the epithelium must withstand a large amount of abrasion from food
more structural features of oesophagus + functions
small amount of mucous glands in submucosa- secrete mucus that lubricates surface epithelium for passage of food
nerve plexuses- coordinate peristalsis of food bolus
Langerhans cells- antigen presentation, helps immune response
which region is what type of muscle?
upper 1/3rd is skeletal
bottom 2/3rds is smooth
function of stomach
mix and churn food into chyme
preliminary digestion via secretion of digestive enzymes
structure present throughout the stomach + fuction
ruggae- longitudinal folds of mucosa and submucosa
allow the stomach to distend when food enters
what epithelium lines the internal stomach?
simple columnar surface epithelium
what does the surface epithelium form?
small invaginations called gastric pits (foveolae)
what do the gastric pits connect to?
various glands of the stomach
three histologically different regions of the stomach
fundus, cardia and pyloris
three different stomach glands + locations and functions
principal gastric - present in the fundus and body, produce gastric acid
cardiac- cardiac region, produce mucus
pyloric - pyloris, produce mucus
association between gastric gland and pit
gastric pit opens up into the gland
same type of cells
different cells in the gastric gland and pit
surface lining cells
mucus neck cells
parietal cells
chief cells
DNES cells
stem cells
organisation of cells
top of the pit is lined with surface lining cells
neck of pit lined with mucus neck cells
stem cells concentrated in neck
gland is formed of a mix of the other cells
surfacing lining cell function
produces mucus, to lubricate the surface epithelium and protect cells from the acidic and enzymatic properties of gastric juices
mucous neck cell function
secretes mucus, however less alkaline than that produced of surfacing lining cells
parietal cell synonym
oxyntic cell
oxyntic cell structure + function
large round or pyrimidal cells
secrete intrinsic factor and HCL
chief cell synonym
zygomatic cells
zygomatic cell function
secrete pepsinogen and gastric lipase
stem cell function + location benefit
replace damaged cells
able to move up to replace pit cells or down to replace gland cells
turnover of pit cells
5-7 days
explain relative turnover of pit vs gland
pit exposed to HCL, so more damaged, higher turnover compared to gland
what does DNES stand for?
diffuse neuroendocrine cells
DNES function
secrete endocrine, paracrine and neurocrine hormones
secrete gastrin
difference in gastric pits in different histological regions
principal glands in fundus and body- have the greatest proportion of oxyntic and zygomatic cells
cardiac glands- short, coiled and branched
pyloric region- deeper gastric pit, with mainly mucous type cells
three anatomical segments of the small intestine
duodenum, jejunum and ileum
common histological features to all regions of the small intestine
inner lining forms transverse ridges called plicae circulares
tall fingerlike projections- villi
tubular glands, crypts of Lieberkuhn extend to or beyond the muscularis mucosae
mucosal epithelium is simple columnar type covered in microvilli
what does the microvilli form?
brush border
microvilli function
increase SA, facilitating absorption and secretion
two main cell types in small intestine
enterocytes- absorptive cells
goblet cells- mucous secreting
where are the crypts of Lieberkuhn located?
in the epithelial lining between villi
crypts of Lieberkuhn structure
contain stem cells, enteroendocrine cells, Paneth cells and Peyer’s patches (only in ileum)
function of enteroendocrine cells
synthesise and secrete hormones
function of Paneth cells
secrete defensive enzymes such as defensins and lysozymes
differences in structure in small intestine
duodenum- contains submucosal Brunner glands that secrete alkaline mucoid secretion into crypts to neutralise stomach acid
jejunum- tallest villi
ileum- Peyer’s patches in crypts
what are peyer’s patches?
contain mucosal- associated lymphoid tissue (MALT) which houses white blood cells and lymphocytes
located in the submucosa
villi structure
epithelialy covered finger like protrusions of the lamina propria
contain core capillary loops
blindly ending lymphatic channel, the lacteal
lacteal structure
forms core of villi
how are the epithelial cells replaced?
division, migration and differentiation of stem cells
structure of colon
smooth surface bu appearance of infoldings due to contractions
numerous crypts
many goblet cells, outnumbered by absorptive enterocytes
colon function
supply mucus to the bowel contents, facilitating passage
extract water and electrolytes
what is the outer muscularis externa transformed into?
three longitudinal strops of smooth muscle called the teniae colae
function of teniae coloae
allow the different segments of the colon to contract independently
promotes faecal compaction and general peristalsis
are villi present in the large intestine?
no
