GI Tract (W3) Flashcards
Explain the process of digestion through the GI tract
- mouth
- osesophagus
- stomach
- small intetsine
- large intestine
- anus
What 2 mechanism propel food down the GI tract
- voluntary muscle acrion in oral cavity, pharynx and upper third of oesphagus
- Peristalsis - involuntary wave of smooth mucle contraction
How is the ANS involved in the mechanisms
modulates the 2 mechanims and also secretes a variety of neuorendocine hormones
Name the 4 layers that make up the GI tract
Mucosa
- made up of 3 layers (epithelium , lamina propria & muscularis muscosae
Submucosa
- collagenous collective tissue
- contains larger BVs, lymphatic and nerves
Muscularis propria
- smooth muscle usally arranged as an inner circular layer and longitudinal layer
Adentitia
- outer layer loose supporitn tissue
- conducts major vesssl nerves
- contains adipose tissue
What types of epithelial cell make up the GI tract
- stratified squamos epithelium
What are the basic muscosal forms in the GI tract
- protective
- absorptive
- secretory
- absorptove/protective
Describe the structure of the oesophagus
- lined with non-keratinsed squamos epithelium epithelium
- in submucosa there are groups of small mucos -secreting glands (oesphageal glands) for lubrication and protection
- conatins a basal layer (stem cells)
What is the difference in tissue type between the oesophagus and the oesophagus gland
the gland is columnar not squamous
What is the function of the oesophagus
- transport of food and water to the stomach
What is the gastro oesophageal sphincter in humans and what is its function
where the oesophagus and stomach meet
- the muscles constrict the opening at the stomach and orevent the escape of acid/pepsin and food back into the oesophagus
What happens to the cells at the gastro oesophageal junction
junction where the oesophagus and stomach meet and the mucosa abruptly change to glangular secretory phenotype
What is the most proximal area of the stomach
the cardia
stomach
Describe the sturcture of the gastric cardia
- narrow circular band
- mucosa conatins simple or branched cardiac glands coiled with large lumens
- most of the glands produce muscis and lysozymes
- few parietal cells
Describe the sturcture of the fundus and body of the stomach
- fundus is above the body
- mucuosa coinatins numerous gastric glands (secrete acid and pepsin)
- distrubution of epithelium cells aren’t uniform
Describe the gastric glands and where are they located
- straight tubular glands that synthesis and screte gastric jucie
- hydrolyse proteins into polypeptide fragments
- mucosa layer
What stops the stomach from self digestion by gastric glands
thick surface covering of mucos
Where are the gastric glands stem cells located
isthmus/ neck region immediately below the pit
Nmae the cells which are in the gastric glands and at what level
- fovela - surface mucos cells
- parietal cells - isthmus
- neck, stem and parietal cells - neck
4.peptic, parietal, neuroendocrine cells - base of gland
What are the foveolar cells
- sometimes called pit cells
- secrete protective mucins
- MUC5AC (resistant to degrdation)
What is the role of stem cells in the gastric glands
- high proliferation rate
- move upwards to replace muscous cells (4-7day turnover)
- some migrate downwards to differentiate into parietal,cheif and endocrine cells
What are parietal (oxyntic) cells
- secret hydrocholric acid
Describe the shape of parietal cells and how do we know they are active
- large round cells (‘fried egg shape’) with eosinophilic cytoplasm
- prescence of numerous mitochondria and intracellular canaliculi
What ions are involved in the secretion of HCl by parietal cells
H+, K+, Cl-
What are chief (zymogenic) cells
secret pepsinogen (inactive enzyme)
- it rapidly converts into the active from pepsin in the prescene of acid
- also secretes lipase
What are neuroendocrine cells
hormne secretng cells of the glands
What are the gastric hormones and their functions
- Gastric (from G cells)
- activates parietal cells to secret acid
- parasympathetic stimulation , AAs and stomach disentions directly stimulate G cells to secret gastrin - Somatostatin (from D cells)
- inhibits the relase of gastrin
- stimulated by HCl and counterbalances acid secretion
What is pylorus and its function
final part after the antrum beofre the small intestine
- secretes mucos and lysozymes
What cells line the small intestine
simple columnar epithelium
What cells are in the small intestine
- enterocytes
- goblet cells
- paneth cells
- neuroendocrine cells
- stem cells
How does the small intestine structire aid in the function
Mutiple villi and microvilli to increase SA for absorption
What are enterocytes and their function
- most sbundnat cell in the villus
- absorptove cell of the intestine
- APC
What are glycocalyx
filament network convoluted into villi projections that serve to increase the absorptive muscosal surface area
What does the glycocalyx consist of
acidic mucopolysaccharodes and glycoproteins
What is the small intestine crypt
pocket at the base of villus where stem cells produce transmit amplyfying cells which are commited to produce mature cell lineages
Describe goblet cells
- secrete mucos
- contian dense secretory granules which provide a protective gel barrier
What are paneth cells
- function to keep the crypt sterile
- produce lysozome
What are Brunner glands
- specific to duodenum
- produce alkaline mucus to neutrlaize the acid content entering the duodenum from the stomach
Describe the structure of Brunners glands
- compound tubular mucous glands located in the submucosa duodenum
What are pilcae circulares
lining of small intestine that consists of permenant spiral or ciruclar folds to amplify the organs SA
What arer Peyers patches
- unique to small intestine
- provide immune surveillance of small intestine
What is the ileocaecal valve
where food from the small intestine passes to the large intestine
Describe the transition of the ileum to the colon
- from villous mucosal surface of ilum to flat mucosa of large intestine
- change of villi to crypt
What is the appendix
- blind-ended tubular sac attached to caecum
- masses of lymphoid tissue in submucosa
- glands spaced more widely then elsewhere in large intestine
What is the function of the colon
- recovery of water,peistalsis of faecal material
Describe the structure of the colon
- thick muscular wall
- absorptive cells and mucus-secreting cells
- commensal bacterisa
What happens to the cells at the recto-anal junction
abrupt transition to stratfired squamo epithelium
What is Meissners plexus
network of unmyelinated nerve fibres (generally inconspicuous)
- also called submucoal plexus
- considered part of the ANS
What is Auerbachs plexus
a group of ganglia that run throughout the entire GI tract and innervate its multiple layers of smooth muscle.
- circulr and longitudinal muscles
