week 21 lower GI anatomy Flashcards
where does the small intestine run to and from
runs from pyloric sphincter of the stomach to the caecum of the large intestine
how long is the small intestine
6-7 metres long
what are the three regions of the small intestine
duodenum
jejenum
ileum
what is the smallest section of the small intestine
duodenum
the duodenum is continuous with what
stomach
the ileum is continuous with what organ
large intestine
where does the duodenum receive chyme from
stomach via pyloric sphincter
what 4 substances does the duodenum receive from the pancreas
sodium bicarbonate
amylase
lipase
precursors of proteolytic enzymes
what does the duodenum receive from the gall bladder
bile acids
in what part of the small intestine has the most absorptive properties
duodenum
what 3 (elements) does the duodenum absorb
calcium
iron
folate
in what part of the small intestine has the greatest absorptive property for bile acid
ileum
what is the only place in the small intestine that absorbs cobalamin
ileum
the jejunum specialises in the absorption of what
fat
protein
carbohydrates
what is the epithelial structure of the jejunum
simple columnar epithelium
what does the ileum specialise in absorption of
B12 and bile acid
the basic simple columnar epithelial layers are the same as other sites in the GI tract but there are additional modifications in the small intestine to maximise what
surface area
what are plicae circulares
circular folds of the mucosa and submucosa
what are plicae circulares most prominent
distal duodenum and jejunum
the number of plicae circulares decrease in size and number as…
you move along the intestine
when are there no more plicae circulares
proximal area of the ileum
what are villi
finer like projections of epithelium covered lamina propria which protrude into the lumen of the small intestine
what are the functions of the microvilli
projections of the apical surface of the epithelial cells which further increase surface area
how much do micro villi increase absorption
20-30 x
what is the “fuzzy coat” on the micro villi made out of
glycoprotein
what are crypts of Lieberkühn
invaginations of the epithelial surface to meet the underlying lamina propria
what do the cell populations in the crypts of lieberkuhn essential for
aiding digestion, absorption, and protective features
what is the epithelial structure of crypts of lieberkuhn
columnar epithelial
what are the cells in the crypts of lieberkuhn
goblet cells
intermediate cells
M cells
paneth cells
enteroendocrine cells
what is the most populous cell type in the crypts of lieberkuhns (small intestinal epithelium)
enterocytes
absorptive role in the small intestine is facilitated by what
apical and basolateral transporters, enzymes
what are the transporters that help facilitate absorptive roles in the small intestine
SGLT1 and GLUT 5 (apical membrane)
Na+/K+ATPase GLUT2 GLUT5 (basolateral membrane)
what are the roles of regenrative cells in crypts of lieberkuhns
stem cells which can proliferate and can replace any cell type of the crypt epithelium
what are the roles of intermediate cells in the crypts of intermediate cells
they are the “babies” of regenerative cells
and soon specialise to become any cell in the GI
what are the roles of paneth cells
secretory function
what do the paneth cell secrete
lysozyme
TNFalpha
paneth cells secrete lysozyme, what is its function
antimicrobial product (protectiveP pathogenic material
what do enteroendocrine cells secrete
GLP1
Cholecystokinin (CCK)
glucose dependant insulontropic polypeptide (GIP)
what does GIP respond to
secretagogues
what can GIP open
enteroendocrine cells
what can GIP increase/decrease
motility of products released from accessory glands - pancreas
in the mucosa of the small intestine, the layers extend into the villi shortening the villi rhythmically during what
digestion
the serosa is not present where
distal 2/3rds of the duodenum
what is a structural difference of the villi in the duodenum
shorter and stumpier
what glands are present in the duodenum
brunner glands (submucosa)
what is the tole of brunner glands
produce mucous, bicarbonate rich fluid and human epidermal growth factor
what is the role of bicarbonate
acts as a buffer to stomach acid
brunner glands can be site for what (bad) thing
brunner-gland adenomas
what can be said about the number of villi in the jejunum compared to the duodenum
sparser number of villi
what are the more of in the jejunum that the duodenum
goblet cells (synthesise and secrete mucous)
in a histological slide, how can you tell the difference between an artery and a vein
arteries are thicker and rounder
in the ileum, what can be described as “clustered lymphatic tissue in the lamina propria”
peyer’s patches
wjat do peyers patches do
help remove foreign bodies
what is there least of in the ileum compared to the jejunum and duodenum
villi
why is there fewer instances of cancer metastasis in the large intestine
there is less well developed lymphatic system vasulature
how is peristalsis achieved
activation of smooth muscle layers in the musclaris externa
in the muscularis externa, how does the inner circular layer aid in peristalsis
pinching motions
in the muscularis externa, how does the outer longitudinal layer aid in peristalsis
shortening of the length of the small intestine/regions
where is the myenteric plexus
exists between the layers of muscle
muscle layers can depolarise and stimulate the contraction without the myenteric plexus in
peristalsis
innervation of peristalsis is delivered by what
myenteric plexus
adjacent smooth muscle cells are coupled by gap junctions - _____ _____ flow from cell-cell
electrical currents
spontaneous activity across coupled cells is driven by what
pacemaker cells
spontaneous activity across coupled cells is driven by specialised pacemaker cells and is modulated by what (2)
intrinsic (enteric - myenteric plexus) and extrinsic (autonomic nerves)
numerous hormones (motilin increases) (glucagon decreases)
what are slow waves driven by
interstitial cells of Cajal
ICCs form what with eachother
gap junctions
ICCs form gap junctions with eachother and smooth muscle cells _____
electrically coupling them
slow waves in the ICC drives slow waves in the
smooth muscles cells coupled to them
why dont depolarising slow waves necessarily result in smooth muscle contraction
contraction in the small intestine occurs only if the slow wave amplitude is sufficient to reach a threshold to trigger smooth cell calcium action potentials
what are the ions involved in smooth muscle contraction by slow waves
calcium
what is needed for the contraction of smooth muscle
slow wave to reach threshold to trigger calcium release
in slow waves what is force related to
number of action potentials discharged
what are the 4 regions of the large intestine
caecum
colon
rectum
anus
what are the 4 regions in the colon
ascending
transverse
descending
sigmoid
how long is the large intestine
1 1/2 metres
what occurs in the large intestine
site of fermentation, storge, and water reabsorption
functions of the large intestine
recovery of ______
absorption of ____-____ ______ ____
fermentation
storage
defecation
water
short chain fatty acids
what is the epithelial structure in the colon
simple columnar epithelium
what is there 0 of in the colin
villi
organisation of what epithelial layer is different in the colon
muscularis externa
the lamina propria is well populated with what cells
immune cells
the mucosa (muscularis externa) contributes to what system
gut-associated lymphoid system (GALT)
in the large intestine - the muscularis externa exhibits what structure
ribbons of outerlongitudinal layer of muscularis externa = taeniae coli
in the large intestine (serosa) fat filled pouches are what
appendices epiploicae
what is the epithelial structure of the large intestine (anus and rectum)
simple comulnar
what crypts are deeper in the anus and rectum
crypts of lieberkuhns
in the anal canal - the simple columnar epithelium changes to what
simple cuboidal epithelium -> stratisfied squamous and then stratified squamous keratinised
submucosa of the anal canal contains what
venous plexi (internal and external hemorrhoidal plexi)
what is the muscle composition of the internal anal sphincter
smooth muscle - involuntary
what is the muscle composition of the external anal sphincter
skeletal muscle - voluntary
the exposure of the GI epithelium to viruses/parasites/toxins results in what
peristatic rush and release of copious volumes of fluid
diarrhoea
what is crohns disease
inflammatory bowel disease (inflammation affcets the full thickness of the GI tract
symptoms of crohns disease
abdominal pain, weight loss, malabsorption, rectal bleeding
what cancer are you at greater risk of if you have crohns disease
colorectal cancer
