Gastrointestinal tract Flashcards
What are the three most important types of tissue in the GI tract?
Modified epithelium
Well developed immune system
Stem Cells
What is the role of epithelial lining?
Secretion (mucous, HCl, hormones, enzymes)
Absorption (water, salt, nutrients)
Protection (tight junctions prevent large amounts of paracellular absorption)
What is the immune tissue called in the GI tract?
GALT (gut associated lymphoid tissue)
What are the two types of immune tissue, what are their main features?
Diffuse
Lymphocytes
Specialized dendritic cells
Macrophage subsets
Organised Tonsils Peyer’s patches Lymphoid follicles Appendix or coecal patch Mesenteric lymph nodes. Paneth cells
Other than immune tissue, what are two more protective mechanisms?
Low pH in stomach kills microorganisms
Mucous traps pathogens
After how many days do cells regenerate in the small intestine?
5 days
What cells are an exception to the 5 day regeneration and take longer (how long)?
Paneth cells (up to 30 days)
What are the common four layers of the gut tube?
Mucosa
Submucosa
Muscularis
Serosa
What does the mucosa consist of?
Epithelia lining
Lamina propria
Muscularis mucosae (smooth muscle)
What does the submucosa consist of?
Connective tissue with blood & lymph vessels
Meissner’s (submucosal) Nerve plexus
What does the muscularis consist of?
Circular internal layer
Auerbach’s (myenteric) nerve plexus
Longitudinal external layer
What does the serosa consist of?
Connective tissue with mesothelium covering
Epithelium lining producing lubricating slippery fluid to facilitate movement
How is the muscularis different in the stomach? Why?
Third innermost muscular layer (the internal oblique layer)
Allows the stomach to vigorously churn food for mechanical digestion
What organ notably does not have a muscularis mucosae?
Gall bladder
What branch of the ANS can affect the submucosal plexus vs the myenteric plexus?
Submucosal - PNS only
Myenteric - SNS and PNS
What is Hirschsprungs disease?
Congenital disorder where Auerbach’s nerve cells absent due to failure of neural crest cells to migrate.
Leads to severe constipation.
What epithelium is present in the oesophagus?
Stratified squamous nonkeratinized
What is especially prominent in the mucosa of the oesophagus?
Muscularis mucosae
What is present in the lamina propria in the oesophagus?
Mucus producing cells with secretory granules
Produces mucous to lubricate epithelium
GALT
What are Langerhans cells (oesophagus) where are the dispersed?
Interspersed through epithelium: dendritic cells involved in antigen presentation
What types of muscle are present in the oesophagus, where?
Smooth (lower two thirds) and skeletal (upper third)
What are rugae?
Longitudinal folds of mucosa and submucosa
What are the name of the epithelial invaginations into mucosa (stomach)?
Gastric pits
What lies deep to gastric pits?
Gastric glands
How many gastric glands may empty into one pit?
5-7
What 6 cells are present within the gastric glands/pits?
Surface lining cells
Mucous neck cells
Regenerative (stem) cells
Parietal cells
Chief (zymogenic) cells
Diffuse neuroendocrine (DNES) cells
What is the role of surface lining cells (stomach)?
Manufacture a thick layer of mucus known as visible mucus
Secrete HCO3- so has buffering capacity
What is the role of mucous neck cells (stomach)?
Produce soluble mucus which lubricates chyme different from surface lining cells – soluble and lubricates gastric contents
What is the difference between the mucous produced from surface lining cells and mucous neck cells?
Mucous neck cells produce more soluble lubricating mucous
What shape are mucous neck cells (stomach)?
Mucous neck cells are columnar – but are distorted by pressure from neighbouring cells
How often is gastric mucosa regenerated?
every 5-7 days
What is characteristic (cellular) about a gastric regenerative cell?
Dont have many organelles other than ribosomes in rich supply
Basally located nucleus
What is the role of parietal cells?
Manufacture and secrete HCl and gastric intrinsic factor (binds vitamin B12)
What is the role of chief cells?
Chief cells manufacture, pepsinogen, renin and gastric lipase
What are cellular features of parietal cells?
Have extensive secretory network – canaliculi lined by microvilli
Tubovesicular system and mitochondria
What are cellular features of chief cells?
Have basophilic cytoplasm with basal nucleus and rich RER and extensive Golgi
Short blunt microvilli
What are DNES cells?
Manufacture and secrete hormones
What are the three regions of the small intestine?
Duodenum
Jejunum
Ileum
What are plicae circulares, what do they do?
Transverse folds increase surface area by factor 2-3 and decrease velocity of movement of chyme
What are villi, what do they do?
Epithelial covered finger like protrusions
Increase surface area by factor of 10
What are microvilli, what to they do?
Modifications of apical plasmalemma of epithelial cells covering villi, increase surface area by factor of 20.
What do villi contain?
Capillary loops and blindly ending lymphatic channel (lacteal).
Are there any organelles present in the microvilli protrusions?
No
What are crypts of Leiberkuhn?
Invaginations of epithelium into lamina propria forming intestinal glands.
What are the main cell type that lines villi?
Enterocytes
What are enterocytes (type of epithelium and features)?
Columnar epithelium
Absorptive cells with a brush border
What is the core of microvilli?
Cross-linked actin filaments, serves as structural core
attached to the plasma membrane by myosin and calmodulin
What is the role of goblet cells (SI)?
Manufacture mucinogen whose hydrated from is mucin, provides protection
What do DNES do in SI?
Produce paracrine and endocrine hormones
Where in the crypts do regenerative cells lie (SI)?
Deep
Describe the process of renewal of the small intestinal mucosa?
Proliferative cells (stem cells) reside at the crypt
The new cells migrate upwards and out of the crypt, maturing along the way.
Eventually, they undergo apoptosis and are shed off into the intestinal lumen.
What is the role of paneth cells?
Host defence cells, manufacture lysozome, defensin, and TNF alpha
What is distinct about the duodenum?
Brunner’s glands present
What do Brunner’s glands produce?
Produce mucous, bicarbonate rich fluid, neutralises acid
What about the duodenum microvilli helps in the terminal phase of digestion?
Glycocalyx - enzymes adhere to
What is distinctive about the jejunum?
Tallest villi
Brunners glands are not present
Single lymphoid follicles are infrequent.
What is distinctive about the ileum?
Aggregated lymphoid follicles (or nodules), the Peyer’s patches
Where are Peyer’s patches within the ileum tube?
Submucosa and often breaching the muscularis mucosae extending into the lamina propria.
What are Peyer’s patches?
Collections of lymphocytes and antigen presenting cells (APCs/dendritic cells)
Where are M cells mainly present?
Ileum
What is the role of M cells?
Specialised epithelial cells, perform survelliance of antigens.
Epithelial-cell recognition of bacteria
Where do M cells lie above?
Peyer’s patches
How is the smooth muscle layer of the gut tube different in the large bowel?
Transformation of the smooth muscle coat of the outer muscularis externa into three distinct longitudinal strips called tendinae coli
What do the tendinae coli allow?
Segments of the bowel can contract independently
Do large bowel cells have folds/villi?
No
The colon is rich in crypts true or false?
True
What happens to the number of goblet cells from cecum to sigmoid?
Increases
After how many days does to colon mucosa regenerate?
6-7 days
Are there less DNES cells in colon than SI or more?
Less
How is the rectum mucosa histologically different to the colon (3)?
Deeper mucosa
Shorter glands
More goblet cells
At the junction of rectum and anus what replaces the crypts of leiberkuhn?
Stratified squamous surface epithelium characteristic of the anal canal.
What happens to the muscularis externa as it reaches the anus?
Thickens (internal anal sphincter)
How is the histology of the appendix different to the colon?
The crypts of Lieberkuhn are far less abundant
Circular arrangement of lymphoid follicles sometimes extending into the submucosa.
What part of the GI tract has very distinct TJs?
Small intestine
What are the two words for both nerve plexi?
Aubach’s/Myenteric
Meissners/Submucosa
Describe the epithelia of the colon
Simple columnar epithelium with goblet cells
A foregut derived part in which portal-systemic anastomotic veins are located in the submucosa
Lower part of the oesophagus
A part characterised by an obvious sphincter of thickened smooth muscle…
Pyloric canal
A part of the large bowel with complete circumferential layers of longitudinal and circular smooth muscle
Rectum
A part in which the lining mucosa is derived from ectoderm…
Anal canal
The type of epithelium found lining the jejunum
Simple columnar epithelium with numerous microvilli
Where is B12 absorbed?
Terminal ileum
