Function of the small and large intestine Flashcards
why are muscle contractions of the small intestine important?
to mix the content
ensure luminal content contracts with the epithelial cells
transport chyme along the tract
what are the two types of contractions of the small intestine in the digestive phase?
segmentation (mixing contractions)
peristalsis (propulsive contractions)
what are type of contractions are mixing movements?
non-propulsive
during propulsive movements, what muscles are contracting and what muscles are relaxing?
the longitudinal muscle relax and the circular muscle contract WHICH makes the small intestine squeeze together
the longitudinal muscle contracts and circular muscle relaxes which allows chyme to move through the small intestine as the small intestine increases in diameter
what type of contraction are the segmentation contractions?
mixing movements
non-propulsive
contracted ?
now distended
which muscle, longitudinal/circular is closest to the lumen?
circular muscle and the longitudinal is on the outside
MMC?
migrating motility complex?
MMC - Intergidestive
Propulsive movements consists of?
This process sweeps the intestines clean between meals
Between periods of peristaltic contractions
Also gets rid of bacteria and sloughed off epithelial cells
Meal consumption interrupts the MMC
what are the pacemaker cells?
intersticial cells of Cajal = ICC
what type of muscle cells are the pacemaker cells?
modified smooth muscle cells
in the pacemaker cells, describe the membrane potential?
there are spontaneous oscillations in membrane potential
where are pacemaker cells present?
throughout the smooth muscle portions of the GI tract
what are pacemaker cells responsible for?
the slow waves of smooth muscle, whether it is contracting or not
how do pacemaker cells control muscle contractions?
they can only occur at the same or a lesser frequency than the slow waves
what stimulates the smooth muscle cells after a meal?
after a meal, the smooth muscle cells are stimulated by acetylcholin released by nerve impulses and by gastrin
number of pacemaker cells (ICC) throughout small intestine?
numerous throughout
what does each area of ICC do?
controls a small area of the intestine
where is the frequency of slow waves the highest?
in the proximal small intestine
slow waves are not enough to cause? what does there need to be?
not enough to cause contractions on their own
there needs to be sufficient membrane depolarisation to cause action potentials
11
13 and 12
digestion of chyme in non-ruminants?
digestion of chyme has not proceeded far when it leaves the stomach
where does most digestion and absorption occur?
in the small intestine
carbs and protein digestive in small intestine
if not broken down in SI then they are moved to LI for microbial digestion
what are the three structures of the SI that increase surface area?
folds in the inner surface of the small intestine (mucosa)
the mucosa is covered in villi
villi have microvilli
what does the enterocyte structure consist of?
apical membrane: contact w/ intestinal lumen
tight junctions (loose) : connect adjacent enterocytes
Basolateral membrane: extracellular space
(EC fluid)
describe the transfer of nutrients from thelumen of the digestive tract to blood or lymph capillaries?
from lumen across the apical membrane into the enterocyte :organis
aciorss or between enterocytes (tight nunctions): water and ions
from extracellular fluid (lateral space) into blood of lymph: water and ions
endocytosis mechanism and when released on the other side?
`exocytosis mechanism
luminal phase of digestion occurs where?
inside lumen of SI
what produces amylase?
pancreas
anti-peristaltic movements?
moving the contents backwards in the intestine (large)`
how many types of contractions in caecum?
2
how many types of contractions in the colon?
4 types of contractions
ICC?
intersticial cells of Cajal
slow waves of the pacemaker cells are not enough to what?
cause contractions on their own
what does there need to be in order to cause action potentials?
there needs to be sufficient membrane depolarisation to cause action potentials
what releases peptides and neurotransmitters in the vicinity of the smooth muscle cells - thus affecting the membrane potential?
the ENS (enteric nervous system) the enteric endocrine and paracrine cells
what happens to the smooth muscles when the membrane potential is depolarised?
the action potentials will fire and the smooth muscle contracts
what increases contraction strength of the smooth muscle of the GI tract?
the increased activity in parasympathetic vagal fibres
what leads to a decrease in contraction strength of the smooth muscle within the GI tract?
increased sympathetic activity
what contractions does the enteric nervous system primarily regulate?
the strength of peristaltic and segmentation contractions is primarily regulated by the enteric nervous system
when chyme enters the intestine, what happens?
the pacemaker cells (ICC) are activated (depolarisation)
where does most digestion and absorption occur?
in the small intestine
where are carbs and proteins digested?
in the small intestine
if the carbs and proteins are not broken down in the small intestine, what happens to them?
then they are moved to the large intestine for microbial digestion
what does the enterocyte structure consist of?
apical membrane
tight junctions (loose)
basolateral membrane
Describe the location of the apical membrane?
it is in contact with the intestinal lumen
what do tight junctions do?
they connect adjacent enterocytes
where is the basolateral membrane found?
in the extracellular space
describe the ORGANIC transfer of nutrients from the lumen of the digestive tract to the blood or lymph capillaries?
from lumen across apical membrane into the enterocyte
describe the transfer of nutrients (water and ions) from the lumen of the digestive tract to the blood or lymph capillaries?
across or between enterocytes (tight junctions)
describe the transfer of nutrients (water and ions) from the lumen of the digestive tract to the blood or lymph capillaries in the extracellular fluid?
from extracellular fluid (lateral space) into blood or lymph
what is transcellular absorption?
organic nutrients are transported from intestinal lumen to the interstitial fluid by going across the enterocytes
what is paracellular absorption?
where inorganic ions and water can diffuse through tight junctions connecting enterocytes
what are the two mechanisms of absorption?
transcellular absorption and paracellular absorption
what types of transport are involved within the transcellular absorption?
simple diffusion - passive transport (ions)
carrier proteins (facilitated diffusion) - passive transport
endocytosis/exocytosis - active transport
describe why we need to use diffusion as a way of transport for transcellular absorption?
cell membranes act as a barrier
only water-soluble and lipid-soluble non-polar substances can permeate
water diffuses rapidly due to aquaporins
why do we need carrier proteins as a way of transport for transcellular absorption?
water-soluble nutrients that are too large to diffuse through channels go through protein pumps
why do we need to use endo/exocytosis for transcellular absorption?
large molecules need this way of transport and vesicles form around nutrients to transport it across the cell
what nutrients does the small intestine absorb?
monosaccharides
amino acids
lipids
vitamins
Ca2+
Fe2+
what does the ileum absorb?
bile salts and vitamin B12
what does the large intestine absorb?
volatile fatty acids (VFAs)
what do both the large and small intestine absorb?
water and salt (NaCl)
phases of the chemical digestion?
luminal and membranous phase
chemical digestion is…
catalysed by enzymes
where are the enzymes that are catalysing the chemical digestion found?
in the lumen of the salivary gland, gastric gland and pancreas (luminal phase) and in the membrane surface of the epithelium (membranous phase)
where are the digestive enzymes coming from?
from salivary, gastric and pancreatic glands
where are the digestive enzymes in the membranous phase synthesised?
synthesised in the enterocytes and attached to apical membrane
what does the production of amylase result in?
results in disaccharides, trisaccharides and oligosaccharides
what produces amylase and in all species and what produces amylase in some species?
ALL = pancrease
SOME = salivary gland
what enzyme catalyses luminal phase digestion?
amylase
what enzyme catalyses membranous-phase digestion?
substrate specific enzymes
what are the enzymes that catalyse the membranous-phase digestion synthesised by?
synthesised by enterocytes which are exposed at apical membrane
what do the substrate specific enzymes used in membranous-phase digestion result in?
formation of monosaccharides
maltose > glucose
sucrose > glu + fruc
lactose > glu + galac
what is glucose absorption linked to?
sodium absorption
what pump is involved in carbohydrates absorption?
the Na-K-ATPase pump
what happens to monosaccharides following absorption?
they are transported via the portal vein to the liver where they are stored as glycogen
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