small inestine Flashcards
what is it made up of
duodenum
jejunum
ileum
how is the surface area increased
mucosal folds called villi
how is the surface area on villi increased
microvilli
what does villus core contain
- blood vessels
- lacteals
- cells
what are the spaces between the villi called
crypts of Lieberkuhn
where are enterocytes formed
at the bottom of the crypts
where do enterocytes migrate to
tops of the villi
what is the blood supply to the small intestine via
branches of the superior mesenteric artery
what are the terminal branches
end arteries
are there anastomoses in small intestine
no
what does the enteric nervous system coordinate
- absorption
- secretion
- blood flow
- motility
what are the 2 plexus of the enteric nervous system
myenteric
submucosal
how does the enteric nervous system communicate with the central nervous system
via the autonomic afferent and efferent pathways
where do interstitial cells of cajal lie within
smooth muscle
when does migrating motor complex occur
during fasting
how many phases is the MMC
3
how long does MMC cycle last
90 minutes
what is MMC like after a meal
irregular lasts for 2-5 hours
what cells secrete CCK
I cells
what does CCK cause
gall bladder contraction and sphincter of oddi relaxation
what cells secrete gastrin
G cells
what does gastrin stimulate
acid secretion
what cells secrete secretin
S cells
what does secretion stimulate
pancreatic bicarbonate secretion
what releases glucagon
alpha cells
what does glucagon do
opposes insulin in blood glucose control
what cells secrete VIP
enteric nerves
what cells secrete GIP
K cells
what does GIP cause
greater insulin release by islets
what cells release glucagon-like peptide-1
L cells
what does GLP1 cause
insulin synthesis
inhibits glucagon secretion and gastric emptying
what cells release pancreatic polypeptide
PP cells
what does pancreatic polypeptide cause
inhibits pancreatic and biliary secretions
what cells secrete peptide YY
L cells
what does peptide YY do
inhibit pancreatic exocrine secretion
reduces food intake and appetite
what does motilin do
increase gastric emptying and small bowel contraction
what does ghrelin do
stimulate appetite, increase gastric emptying
what does obestatin do
opposes ghrelin
what does oxyntomodulin do
inhibit appetite
what cells secrete somatostatin
D cells
what does somatostatin do
inhibit secretion and action of most hormones
what cells secrete insulin
pancreatic beta cells
what does insulin do
increases glucose utilisation
what do epithelial cells of small bowel form
physical barrier that is selectively permeable to ions
what cells produce protease and disaccharides
intestinal cells
what organ produces lipase
pancreas
does simple diffusion require energy
no
when does simple diffusion take place
when there is a concentration gradient
where is vitamin B12 absorbed
jejunum
what kind of concentration gradient does facilitated diffusion need
that down a concentration gradient
example of facilitated diffusion
fructose transport
what is sodium/glucose transporter called
SGLT1
what is SGLT1 powered by
energy from the flow of Na+ ions
how does glucose leave the cell
through GLUT 2
where is GLUT2
basolateral membrane
what do dietary carbohydrates consist mainly of
starch
what is starch
polysaccharide
what must starch be converted to for absorption
monosaccharide
what is polysaccharide breakdown catalysed by
salivary amylase
what are the breakdown products of starch
maltose and maltotriose
sucrose
lactose
what is dietary protein digested by
pancreatic proteolytic enzymes
what is dietary protein broken down into
amino acids and peptides
what does dietary fat consists of
triglycerides mainly
some cholesterol and fat soluble vitamins
how is fat emulsified
by mechanical action in the stomach
what does bile do
solubilise fat and promote hydrolysis of triglycerides
what is it called when there is a cluster of bile acids, phospholipids and products of fat digestion
mixed micelles
what is trapped in the centre of a micelle
hydrophobic monoglycerides, fatty acids and cholesterol
what do unabsorbed lipids do to gastric emptying
delay it via peptide YY to allow more time for absorption
what are medium chain triglycerides transported via
portal vein
what is the absorption of water and electrolytes coupled with
monosaccharides, amino acids and bicarbonate
what does commensal bacteria maintain
the integrity of the small bowel
what makes up the physical defence
- mucus layer
- continous shedding of surface epithelial cells
- physical movements of luminal contents
- colonisation resistance
what cells secrete lysosomes and phospholipase A2
paneth cells at the base of crypts
what cells secrete trefoil peptides
goblet cells
what is the principal mucosal antibody
IgA
how does IgA mediate mucosal immunity
agglutinating and neutralising pathogens in the lumen
what is IgA secreted from
immunocytes in the lamina propria
as dimers
how are antigens from the bowel transported by
M cells and dendritic cells
what do activated B cells produce
IgA
what does lamina propria contain mostly
CD4
what are most common symptoms of small bowel disease
- diarrhoea
- steatorrhoea
- abdominal pain
- weight loss
- nutritional defences
when does steatorrhoea occur
when stool is fat
what do stools look like in steatorrhoea
pale, bulky and offensive and float leaving a fatty film on the water
they are difficult to flush away
what is weight loss due to
anorexia
occurs because of malabsorption
what are nutritional defences of
- iron
- vitamin B12
- folate
what does nutritional deficiencies lead to
anaemia
what does vitamin K deficiency cause
bruising
what does calcium deficiency cause
tetany
what does vitamin D deficiency cause
osteomalacia
what symptoms can multiple deficiencies cause
- stomatitis
- sore tongue
- aphthous ulceration
what deficiency can occur in Crohn’s
vitamin B12
what disease of small intestine cause malabsorption
- coeliac disease
- dermatitis herpetiformis
- tropical sprue
- Whipple’s disease
- radiation enteropathy
- parasite infestation
examples of anaerobic bacteria
anaerobes
e.g. bacteroides
what’s more abundant anaerobic or aerobic
anaerobic
what is function of the gut microflora
fermentation of non-digestible dietary residues into short chain fatty acids
what does bacteria initiate
vitamin K production
is the upper part of the intestine sterile
TRUE or FALSE
true
what bacteria does the terminal ileum contain mainly
e.coli
what does a bacterial overgrowth occur with
stricture or diverticulum
what are clinical features of overgrowth
- diarrhoea
- steatorrhoea
why does steatorrhoea occur with bacterial overgrowth
conjugated bile salt deficiency
why can B12 deficiency occur with bacterial overgrowth
bacteria cna metabolise vitamin B12 and interfere with its binding to intrinsic factor
how to treat bacterial overgrowth
antibiotics such as metronidazole, tetracycline or ciprofloxacin
