Intro to GI tract Flashcards
what terms are used to describe the GI tract?
gut
alimentary canal
digestive tract
gastrointestinal tract
what does the GI tract do?
double open-ended tube that allows digestion and absorption of food
what does the GI tract include?
oesophagus
stomach
liver
gall
pancreas
small intestine
ileum
colon
rectum
anus
how long is the GI tract?
very long - up to 10 metres
what cavities is the GI tract found in?
oesophagus - thoracic cavity
all other organs are in the abdominal cavity
what is the wall of the GI tract formed of?
mucosa - the lining of the GI tract, comprises of 3 layers including a thin muscular layer
submucosa - connective tissue, where blood vessels and nerve lie
muscularis - layers of smooth muscle and enteric nerve system
serosa - the visceral layer of the peritoneum
some areas of the GI tract have modifications to these standard layers
what is found in the mouth?
lips, cheeks, soft and hard palates
tongue (skeletal muscle) with taste buds on papillae
salivary glands: submandibular, parotid and sublingual (secrete salivary amylase)
teeth
what is the mouth key for?
mastication
speech
start digestion
some absorption
what makes up the pharynx?
nasopharynx
oropharynx
laryngopharynx
what is the pharynx involved in?
swallowing - food bolus moves from the buccal cavity to the oesophagus through the pharynx
what is peristalsis?
contracting of muscles behind food bolus and relaxing of muscles in front of food bolus, allowing it to pass through the oesophagus
what is the oesophagus?
first segment of true digestive tract
where is the oesophagus located?
extends from pharynx to stomach, traverses the diaphragm
posterior to heart and trachea
has cervical, thoracic and abdominal sections
what cells line the oesopahgus?
stratified squamous epithelium (thick and robust) until last cm when it become columnar epithelium
what type of muscle control does it use?
voluntary in the upper third, mixed in the middle and involuntary in the lower third
what are the two sphincters found in the oesophagus?
upper and lower oesophageal sphincter
features of the upper oesophageal sphincter?
muscular
primarily cricopharyngeus
stops air getting into the gut
features of the lower oesophageal sphincter
thickened muscular layer in lower oesophagus, cardia of stomach (intrinsic) and the diaphragm (extrinsic)
prevents food/acid reflux
location of stomach
lies under diaphragm in central/left midline
features of stomach
can hold up to 1.5l
usually collapsed
divided into cardia, fundus, body, antrum
oesophagus enters in the cardia, exits to duodenum at the pylorus
mucosa is folded into rugae, within these are gastric pits
muscles lie in oblique layers - very strong and effective
what is the function of the stomach?
food reservoir - stores food until its ready to be digested
digestion - started by gastric acids and juices, physically broken down by churning
some absorption - water, alcohol, some drugs
what are the features of gastric mucosa
glands
chief cells
parietal cells
endocrine cells
what do glands in gastric mucosa do?
secrete mucous which protects the mucosa from the acid environment of the stomach
what do chief cells in gastric mucosa do?
secrete enzymes of gastric juice (pepsin)
what do parietal cells in gastric mucosa do?
secrete hydrochloric acid and intrinsic factor (important for b12 absorption)
what do endocrine cells in gastric mucosa do?
secrete grelin (hormone that promotes appetite)
gastrin (digestive hormone)
what is the small intestine?
tube approx 2.5cms wide
6-8ms long
divided into three
features of duodenum
shortest section of small intestine
4 sections - superior duodenal flexure, descending, horizontal, ascending
transitions into the jejunem at the duodenojejunal flexure
where the biliary tract enters the GI tract
features of jejunum and ileum
jejunum is 2.5ms long
transitions seamlessly into the ileum
iluem ends at the ileo-ceacal valve in the right illiac fossa
features of small intestinal mucosa
folded into villi
surface cells (enterocytes) have microvilli known as the brush border
digestive enzymes
goblet cells (mucus-secreting)
enteroendocrine cells
stem cells (found in deep crypts adjacent to villi)
features of villi
increased surface area for absorption
million of villi when healthy
has a carpet-like appearance
each villi contains blood vessels and lymph vessel
what makes up the large intestine
caecum
colon - ascending, transverse, descending, sigmoid
rectum
anal canal
features of rectum
last 15-20cm of large bowel
repository for stool
ends at the anal canl where there is a transition to squamous mucosa
internal (smooth muscle) and external (striated) anal sphincter
features of the colon wall
multiple mucus secreting glands
no villi - crypts instead
muscles are grouped into dense strips (taeniae coli) and rings, these are shorter than the bowel and mean pouches (haustra) form
appendix (idky its literally so irrelevant)
8-10cms long
variable position
vestigial (basically means it does fuck all, probably used to do something though)
may have a role in gut microflora
features of peritoneum
continuous membrane which covers most abdominal organs
visceral layer - lines the organs, is their serosa
parietal layer - lines the walls of the abdo cavity
peritoneum terms
intraperitoneal - lies within peritoneum
extraperitoneal - outwith the peritoneum
retroperitoneal - intraperitoneal and behind the peritoneum
mesentery - large fold of parietal peritoneum that is attached to the small intestine and prevents it knotting up
omentum - continuation of the serosa of the stomach, apron hangs over intestines, if there is perforation/inflammation it can wrap around the segment and seal it off
location of gallbladder
lies below the liver
features of gallbladder
mucosa from rugae
function of gallbladder
stores bile (crucial for fat absorption)
when triggered by CCK (gut hormone) it empties
location of pancreas
head lies within the curve of duodenum
tail touches the spleen
features of the exocrine pancreas
majority of the tissue
has an acinar arrangemtn
complex ductal collecting system, ends at the pancreatic duct and empties into duodenum
secrete pancreatic juice (digestive enzymes and sodium bicarbonate)
