Introduction to the GI Tract Flashcards
deck complete
terms used to describe the GI tract
gut
alimentary canal
digestive tract
in simple terms, what is the GI tract
double ended tube that allows digestion and absorption of food
organs of the GI tract
- oesophagus
- stomach
- liver
- gallbladder
- pancreas
- small intestine
- ileum
- large intestine/colon
- rectum
- anus
length of the GI tract
up to 10m
body cavities of the GI tract
oesophagus in thoracic cavity, all else in abdominal
layers of the GI tract
mucosa
submucosa
muscularis
serosa
some parts of GI tract have modification to standard layers
mucosa
lining of the GI tract. itself comprises of 3 layers, including a thin layer of muscle
submucosa
connective tissue, where blood vessels and nerves lie
muscularis
layers of smooth muscle and enteric nervous system
serosa
visceral layer of the peritoneum
the mouth
aka oral/buccal cavity
key for mastication, speech, start of digestion, some absorption
what does the mouth comprise of
lips, cheeks, soft and hard palates
tongue (skeletal muscle) with taste buds on papillae
salivary glands - submandibular, parotid and sublingual - secrete salivary amylase
teeth
the pharynx
divided into 3 sections - nasopharynx, oropharynx, and laryngopharynx
what does swallowing involve
moving a food bolus from the buccal cavity to the oesophagus through the pharynx
process of peristalsis
muscles contract above food bolus, constricting passageway and pushing bolus down
muscles relax around bolus, allowing passageway to open
anatomy of the oesophagus
first segment of the true digestive tract
about 25cm
extends from pharynx to stomach, traverses the diaphragm
posterior to heart and trachea
sections of the oesophagus
cervical
thoracic
abdominal
cell types of the oesophagus
lined with stratifies squamous epithelium - thick, robust
last 1cm is columnar epithelium
muscle type of oesophagus
voluntary, striated in upper third
involuntary, smooth in lower third
mixed in middle
sphincters of the oesophagus
upper oesophageal sphincter - muscular. primarily cricopharyngeus. stops air getting into gut
lower oesophageal sphincter - comprises a thickened muscular layer in the lower oesophagus and cardia of the stomach (intrinsic) and the diaphragm (extrinsis). prevents acid/food reflux
features of the stomach
variable size - can hold up to 1.5L, usually collapsed
lies under diaphragm in central/left midline
divides into cardia, fundus, body, antram
oesophagus enters in the cardia, exit to the small intestine (duodenum) at the pylorus (pyloric sphincter)
stomach wall - 4 layers, adapted
mucosa folded into RUGAE - within these are gastric pits
muscles of the stomach
lie in oblique layers, very strong and effective
features of the gastric mucosa
glands
chief cells
parietal cells
endocrine cells
glands of the gastric mucosa
secrete mucous which protects mucosa from acid environment of the stomach
chief cells of the gastric mucosa
secret enzymes of gastric juice (pepsin)
parietal cells of the gastric mucosa
secrete hydrochloric acid and intrinsic factor (imp for B12 absorption)
endocrine cells of the gastric mucosa
secrete grelin - hormone which promotes appetite) and gastrin - digestive hormone
functions of the stomach
food reservoir - holds food until ready to be digested
digestion - started by gastric acids and juices and physically broken down by churning
secretes intrinsic factor - allows B12 absorption
some absorption - water, alcohol, some drugs
endocrine - grelin and gastrin secretion
where does the upper GI tract end
pylorus (where stomach moves to small intestine)
features of the small intestine
tube approx 2.5cm wide
6-8m long
sits concertinad and coiled in central abdomen
divided into 3
duodenum
shortest of 3 sections of small intestine
25cm long
split into 4 sections
where biliary tract enters GI tract
transitions into jejunum at the duedenojejunal flexure
jejenum
approx 2.5m long
transitions seamlessly into ileum
ileum
3.5m long
ends at ileo-caecal valve in RIF
smal intestinal mucosa
folded into villi
increased surface area for absorption
millions of villi when healthy
gives a carpet like appearance
each vilius contains blood and lymph vessels
surface cells - enterocytes - have microvilli known as the ‘brush border’
digestive enzymes found here
other cells include mucus secreting goblet cells, enteroendocrine cells, and stem cells found in deep crypts adjacent to villi
colon/large intestine
diameter approx 6cm
length 1.5m
4 sections - caecum, colon, rectum and anal canal
colon divided into ascending, transverse, descending and sigmoid sections
rectum
last 15-20cm of large intestine
repository for stool
ends at the anal canal where there is a transition to squamous mucosa
anal sphincter
internal - smooth muscle
external - striated muscle
wall of colon
multiple mucous secreting glands
no villi but crypts
muscles grouped into dense strips (taeniae coli) and rings - shorter than bowel and mean haustra (pouches) are formed
appendix
8-10cm long
variable position
vestigial
may have a role in gut microflora
peritoneum
continuous membrane covering most abdominal organs
made up of two layers - visceral and parietal
visceral peritoneum
line the organs, is their serosa
parietal peritoneum
lines walls of abdominal cavity
intraperitoneal
lies within peritoneum
extraperitoneal
outwith peritoneum
retroperitoneal
extraperitoneal and behind peritoneum
includes pancreas, kidneys, adrenals, urinary tract, parts of duodenum, colon and rectum
mesentery
a large fold of parietal peritoneum attached to small intestine and prevents knotting up
omentum
continuation of serosa of the stomach
essentially an apron hanging over the intestines
if perforation/inflammation occurs it can wrap around the segment and seal it off
gallbladder
lies below the liver
internally mucosa form rugae
functions of the gallbladder
stores bile - crucial for fab absorption
when triggered by gut hormone (CCK) it empties
pancreas
15cm long
head lies within curve of duodenum
tail touches spleen
endocrine and exocrine functions
exocrine pancreas
majority of the tissue
have an acinar arrangement like liver
complex ductal collecting system ending at pancreatic duct which empties into duodenum
secretes pancreatic juice - i.e. digestive enzymes and sodium bicarbonate
