GI- intestines Flashcards
what are the 3 divisions of the small intestine?
duodenum, jejunum, ileum
what are the 4 regions of the large intestine?
caecum, colon, rectum and anal canal
intestinal blood supply
inferior and superior mesenteric arteries w/ many anastomoses
venous drainage of the intestines
superior mesenteric and inferior mesenteric to splenic vein; all eventually draining into hepatic portal vein
what does the superior mesenteric artery drain?
the small intestine and proximal 2 thirds of the large intestine
what does the inferior mesenteric artery drain?
distal 1/3 of the large intestine
what are the alterations in the small intestine?
plicae circularis, villi, microvilli
plicae circularis
intense foldings of the mucosa to increase SA for absorption and digestion
villi
- small fingerlike projections on the mucosal surface of the small intestines that increase surface area
- has a blood supply for nutrient exchange and transport
- has a lacteal
lacteal
modified lymphatic vessel in villi allowing nutrient absorption (large molecules); GI tract lymphatic fluid dumps into the left subclavian vein
microvilli (brush border)
- projections that increase the surface area of apical surface area of absorptive cells
- contain enzymes for carbohydrate and protein digestion
duodenum features
- most dense pilcae circularies (lots of enzyme secretion)
- major sote of Ca2+ and Fe absorption
- Brenner’s gland and hepatopancreatic ampulla
Brunner’s gland
secretes bicarb. rich mucous to protect duodenum from acidic chyme
hepatopancreatic ampulla
receive liver and pancreatic duct secretions rich in bicarbonate
jejunum features
- 40% length of small intestine
- mostly absorbs glucose, a.a.’s and water
ileum features
- lumen shrinks in size as nutrients are being absorbed
- plicae circularis taper out
- abundant lymphoid nodules (MALT) - Payer’s patches in submucosa
- vitamin B12 absorbed here
gastroileal reflex
long reflex from stomach that jumps to distal portion; peristalsis to clear out residual matter into large intestine and keep bacterial count down
ileocaecal valve
sphincter muscle situated at the junction of the small intestine (ileum) and the large intestine; inefficient and requires immune complex
cephalic and gastric phase (intestinal digestion)
- vagal nerve stimulation causing release of pancreatic juice
- neural; parasympathetic nervous system stimulation
what happens when chyme enters the duodenum?
enteroendocrine cells release secretin and CCK to enter the bloodstream
upon reaching the pancreas, secretin and CCK secrete:
bicarb. rich juice and enzyme rich juice, respectively
patterns of intestinal contraction
fed and fasting patterns
fed pattern
during feeding, irregular contractions mix contents w/ digestive juices (segmentation)
fasting pattern
migrating motor complex (peristalsis) begins at duodenum and propels residual material into colon
pancreatic proteases
- secreted as inactive enzymes to protect pancreas from autodigestion (‘pro’ or ‘gen’)
- trypsin is key to activating these proteases
- trypsinogen is activated by membrane-bound enteropeptidase (brush border enzyme)
steps of fat digestion
- fat globules emulsified by bile salts
- lipases break fat down into monoglycerides and FFAs and associate w/ bile salts to form micelles
- they then recombine and package w/ protein (chylomicron)
- undergo exocytosis to lacteals which are carried away by left thoracic duct to liver for processing
in what ways may nutrients be absorbed in the small intestine?
active transport, secondary transport (using one nutrient’s chemical gradient to pull another nutrient in), facilitated diffusion, diffusion
how are fat soluble vitamins absorbed and what are they?
vitamins A, D, E, K absorbed by micelles
how are water soluble vitamins absorbed?
diffusion
how is glucose absorbed?
secondary active transport using Na+ [ ] gradient (2Na+/glucose); if glucose is high inside cell, goes to bloodstream to be processed by liver
how are amino acids absorbed?
secondary active transport w/ Na+ and simple diffusion on basolateral membrane; can also go to bloodstream
how are essential amino acids absorbed?
primary active transport (ATP)
how are short chain FAs absorbed?
simple diffusion across apical membrane
how are glycerol or long chain FAs absorbed?
first combine w/ bile salts to make micelles (active transport); repackage w/ chylomicrons to enter lacteals
water & electrolyte balance
intestines are responsible for fluid balance where lectrolytes are absorbed/reabsorbed in small and large intestine
- water via osmotic gradient
- Ca2+ and Fe2+ absorbed in duodenum, glucose and a.a. absorption are coupled w/ Na+ absorption
- lots of bicarb. ions reabsorbed in large intestines
what are alterations in the large intestines?
smoother mucosa, teniae coli, thinner circular muscle and haustra
teniae coli
three bands of longitudinal smooth muscle in muscularis
haustra
pouches that form in the large intestine when the longitudinal muscles are shorter than the colon; contractions are every 30 min
histology of the large intestine
mucosa, submucosa, muscularis and serosa; intestinal glands are covered by mucous cells that lubricate to ease passage of feces
colonic movement
slow (3-12/min) and contractions aid water reabsorption
gastrocolic reflex
increased peristalsis of the colon after food has entered the stomach
role of bacteria in the colon
aid digestion of complex starches and sugars present in dietary fiber, as well as synthesizinf vitamin K and some B vitamines
rectum and anal canal
20 and 2 cm respectively, anal columns have highly vascular longitudinal folds (dilation of vascular sinusoids = hemorrhoids), have voluntary and involuntary sphincters
defecation reflex
- gastrocolic reflex stretches rectal wall to send afferent signal to spinal cord
- parasympathetic reflex initiated at sacral level contract rectal wall, relax internal anal sphincter
- defecation occurs by relaxing external anal sphincter (stretch info. from sigmoid colon shared in cortex - voluntary control)
Mechanical Digestion
- chewing within oral cavity
Chemical Digestion
- by enzymes or low pH
Where does chemical digestion begin?
begins in mouth with salivary amylase and continues in the stomach with HCL, pepsin and gastric lipase
Function of pepsin
breaks down proteins
function of gastric lipase
breaks down fats
Absorption
- absorbing nutrients of food stuff
Where does absorption occur?
entire length of small intestine and some of large intestine
Where can absorption go?
into blood stream (water soluble) or lymphatics (immune vessels)
Propulsion
occurs during entire length of the tube
- swallowing or deglutition
Where does peristalsis begin?
in esophagus and goes throughout the tube
How do blood vessels, lymphatics and nerves travel to and from the majority of the small intestine?
by the mesentery
What do immune cells use to travel down lymph nodes?
lacteal
Absorptive cell
most abundant within the villi
Goblet cell
secrete mucus the entire length of the tube
- help protect stomach lining from burning from acid
- helps lubricate or ease passage of food
Enteroendocrine cells
release hormones and are at the base of the villi
Paneth cell
specialized epithelial cells that talk to immune cells
- constantly sample stuff to see if immune response needs to be activated
Where is the major site of Ca and Fe absorption?
duodenum; only place this is done
What does duodenum mean?
means ‘12’- shortest
Where does brunners gland exist?
only within the first 10cm of 25cm of duodenum
Why do we not require brunners gland after 10cm?
accessory organs provide mucus
What does jujunum mean?
means empty; no residual matter here when people die
T: F- Pilicae circulares is not as dense as duodenum
true
What does ileum mean?
twisted
How much does the ileum occupy?
60% of small intestine (2m)
Function of Ileum
- absorbs fats
- most nutrients and vit b12 are absorbed here
- separates small and large intestine
- gastroileal reflex (pushing of food to large intestine)
- contains lymph nodules
CCK will
talk to talk to pancreas and liver tell them to release their enzymes to continue chemical digestion
- liver= bile to emulsify fats
- pancreas= plethora of enzymes
What detects the presence of food in the duodenum?
enteroendocrine cells because food is slightly acidic which will release CCK and secretin
Carbohydrates
- sugar breakdown begins with enzymes released from parotid gland
- amylase, lactase, maltase, sucrase
Proteins
- broken down by peptidases
- stomach releases pepsin
- pancrease release trypsin, chymotrypsin, and carboxypeptidase
Fats
- difficult to digest so they require bile salts
What are bile salts?
amphipathic molecules that help pull on the edges of fat globule and turn it into little droplets
Where do lipases come from?
Lingual (tongue), gastric (stomach), pancreatic (pancreas)
Nucleic acids
- nuclease, deoxy/ribonucleases to recycle nucleic acids
Where and how are enzymes release?
by pancreas found at brush border
What makes trypsin active?
enteropeptidase makes trypsinogen into trypsin
Fat soluble vitamins
A, D, E K- absorbed via micelles
Water soluble vitamins
C, by diffusion
Where are electrolytes absorbed and reabsorbed?
small intestine mostly with some large intestine
Where are Ca and Fe absorbed?
duodenum
Diarreha
not enough time in large intestine to absorb water and bicarb; less buffer
Constipation
fecal matter has too much time in large intestine; absorb too much bicarb and water and too much base in blood
Bristol- Separate hard lumps
very constipated
Bristol- lumpy and sausage like
slightly constipated
Bristol- sausage shape with cracks in surface and smooth, sausage like
normal
Bristol- soft blobs with clear cut edges
lacking fibre
Bristol- mushy consistency with ragged edges
inflammation
Bristol- liquid consistency with no solid pieces
inflammation
Where does large intestine begin?
ileocecal valve
Appendix
- important for ruminant animals that eat a lot of grass and cellulose
Hepatic flexure or right colic flexure
• Ascending colon goes up the right side and make a 90 degree turn under the liver
What is suspended by mesocolon?
transverse segment
splenic flexure or the left colic flexure
Descending colon makes 90 degree turn underneath the spleen
sigmoid colon
At distal end of large intestine, it takes an S turn
Rectum
is the last straight part of the tube and it will aid in defecation
Anus
has skeletal muscle around it for us to decide when it is appropriate to defecate
Measurement of rectum and anus
20cm for rectum; 2cm for anus
