Intestinal activity and motility Flashcards
the small intstine is where
Most digestion and absorption takes place
- intense enzymatic activity
what is the small intestine divided into?
Divided into 3 sections:
* Duodenum
* Jejunum
* Ileum
large intesdtine function?
- Absorbs water and small amount of Na+ & Cl-
- Formation and temporary
storage of faeces - Microbiological activity
the large intestineis the very final satages of
digestion and sborptin
the different parts of the large intestine?
- Vermiform appendix
(AKA vermix,
vermiform process - Caecum (cecum)
- Colon
- Rectum
what is segmentation?
Primary method of motility which
mixes and slowly propels the chyme
segmentation is slight or absent between
meals
segmentations becomes very vigorous after a meal
a meal
how does segmentation tak eplace?
Local oscillating ring-like contractions of the
circular smooth muscle along the small
intestine’s length
* Between the contracted segments are relaxed
areas containing a small bolus of chyme
segmentation does not
sweep along the length of the intestine as peristaltic waves do
what are the functions of segmentation?
- To chop, churn and thoroughly mix chyme
- Move chyme through digestive tract
how does segmentation move chyme through the digestive tract?
Specialised pacemaker cells which produce a Basic Electrical
Rhythm (BER) – Rhythmic pattern of spontaneous
depolarizations
pacemaker ells spontaneously depolarise faster in the
upper small intestine then those in the lower intestine
what are the function of Interstitial cells of Cajal ?
generate slow wave
potentials that sweep down
the stomach and Intestines
interstitial cells of cajal are connceted via
gap junctions and the myenteric plexus
Therefore, more chyme is pushed forward than
backwards
Slow propulsive mechanism is advantageous as allows
adequate digestive and absorptive
processes. 3-5 hours for contents to move through small intestine
In order for a contraction to occur,
hormone or neurocrine signal must induce the smooth
muscle cell to have an action potential.
acetycholine increases
amplitude of slow wave
norepinephrine decreases
amplitude of slow wave
what modulates BER excitability?
Distension in the iintestine
Gastrin
Extrinsic nerve activity
Duodenum starts to segment primarily in response to
local distension caused by the presence of chyme.
Segmentation of the empty ileum is brought about by
gastrin secreted in response to the presence of chyme in the stomach (gastro-ileal reflex).
Extrinsic nerves can
strengthen (parasympathetic) or weaken (sympathetic) contractions.
Once nutrients have been absorbed, intestinal segmentation contractions
reduce
Segmentation contractions are replaced by
weak, repetitive peristaltic waves that move a short distance
down the intestine before dying out – migrating motility complex (MMC).
what is migrating motility complex (MMC)?
waves of electrical activity trigger peristaltic waves during the interdigestive phase
Facilitate transportation of indigestible substances into the
colon
MMC occurs every
90-230 minutes (between meals)
what experience does MMC cause?
Rumbling experienced when hungry
MMC inhibits…
… migration of colonic bacteria into the terminal ileum
Digestion is finally accomplished by
pancreatic enzymes with fat digestion being
enhanced by bile secretion
Exocrine glands of the small intestine mucosa secrete
into the lumen 1.5 litres of aqueous salt and mucus – succus entericus
exocrine glands of the small intrestine provides
mucus for lubrication and protection
and plenty of water to participate in the
enzymatic digestion → hydrolysis
The digestive enzymes that the small intestine
synthesize are restricted to
the brush border
membrane
The digestive enzymes that the small intestine
synthesize are restricted to the brush border
membrane - the enzymes are embedded in…
… those microvilli of epithelial cells which completes the
digestive process
Fat digestion is completed in the
lumen of the small intestine
Protein and carbohydrate completed in
brush border
Brush Border Cells contain
three categories of integral membrane bound proteins that
function as enzymes and complete the digestion of carbohydrates and proteins
what are the three membrane bound proteins of the brush border?
- Enterokinase
- Disaccharides
- Aminopeptidases
enterokinase function
activates pancreatic proteolytic wenzyme trypsinogen
disacchrides function
(maltase, sucrose, lactase,
Limit Dextrinase/sucrose-isomaltase)
hydrolyze remaining disaccharides into their
constituent monosaccharides (carbohydrate
digestion)
aminopeptidases function
hydrolyze peptide fragments into their amino acid components
lactase function?
hydrolase involved in hydrolysis of the disaccharide lactose
into constituent galactose and glucose monomers
lactose intolerance?
55% to 65% adults down
regulate lactase
production
what is lactase persistence?
≈ 30 to 40% adults produce Lactase after weaning
lactase persistence most common in which populations?
Mainly Europe, some of Africa, Middle East & Southern Asia
Undigested Lactose
remains in
lumen
Accumulation of undigested lactose creates
osmotic gradient
1.Undigested Lactose remains in lumen
* Accumulation of undigested lactose creates osmotic
gradient
- draws in…
… water into intestinal lumen
Bacteria digest and
feed on lactose = production of co2 and methane gas
distenstion from
increased water and gases
lactose inteorlance symptoms
diarrhoea
cramps
bloating
nausea
chronic flatulence
Primary role of the small intestine is to
absorb carbohydrate, protein, electrolytes, vitamins ,
fat and water – absorbed indiscriminately.
Most absorption takes place in the
duodenum and jejunum – very little occurs in the ileum
Specialised transport mechanisms exist in
the terminal
Ileum
Specialised transport mechanisms exist in the terminal
Ileum for:
- vitamin b12 - intrinsic factor from stomach - secreted by parietal cells.
- bile salts (enterohepatic circulation)
in the small intrstine, usually only the absorption of calcium and iron are …
…adjusted to the body’s needs
Thus, the more food consumed, the more
is digested and absorbed.
Small intestine has enormous
absorptive capacity
Up to ≈30% of small intestine can be
removed with little interference to overall absorption
Mucous lining of the small intestine is remarkably
well adapted for its special absorptive finction
Mucous lining of the small intestine is remarkably
well adapted for its special absorptive function for two
reasons:
- Large surface area - Permanent
circular folds, Villi, Microvilli - Epithelial cells in lining have variety
of specialized transport mechanisms
slide 25
Epithelial cells in the mucosa have a variety of…
specialiszed transport mechanisms
epithelial cells cover
the survace of the villus
epithelial cells are joined at
lateral borders by tight junctions (limit the passage of luminal contents between cells
what do microvilli contain
contain transport carrier proteins for
absorption of specific nutrients and electrolytes
what do membrane bound digestive enzymes do?
complete
carbohydrate protein digestion
what is the connective tissue core?
lamina propria
what is the capillary network?
Artery enters, differentiates into a capillary network
and then rejoins as a venule that drains away
what is the terminal lymphatic vesseL?
central lacteal – single blinded lymphatic vessel – absorbs fats
central lacteal function
absorbs fats
In between the villi are
shallow invaginations – crypts of Lieberkühn
what do crypts of Lieberkühn secrete?
water
electrolytes
no digestive enzymes
water, electrolytes, no digestive enzymes, + mucus from specialised epithelial cells =
succus entericus
crypts of Lieberkühn function as…
… “nurseries”
crypts of Lieberkühn function as nurseries.
thet contain…
… high mitotic rate stem cells,
which create new cell which continually migrate up the villus
and push the older cells off at the tips
how many cells shed per minutes?
100 million cells shed per minute
100 million cells shed per minute; takes
3 days to migrate
Highly sensitive to
Lost cells are digested and the cell constituents
absorbed
paneth cells function ?
defensive function, safeguarding stem cells.
Produce lysozyme to lyse bacteria and defensins
the small intestine jioins the colon at the
caecum
what is the caecum?
The caecum is a blind-ended pouch below the junction of the small and large intestines at the ileocecal valve
When contents from small intestine push forward…
…they open the valve , but the folds are forcibly closed by any backward movement
At the bottom of the caecum is
the appendix
what is the appendix?
gut associated lymphoid tissu. B cell mediated immune response and extra thymus t cell
appendix is involved in the
maintence of gut flora
how much chyme does the hcolon receive each day?
500 ml of chyme from the small intesinte each day
The colon receives ≈ 500 ml of chyme from the small intestine
each day, most of which is …
… indigestible and unabsorbed food residues, biliary components and water.
the colon extracts
more water, and electrolytes with the remainder eliminated as
faeces
The outer smooth muscle layer does not
completely
surround the large intestine
The outer smooth muscle layer does not
completely surround the large intestine
Consists of
three separate longitudinal bands
of muscle
The outer smooth muscle layer does not
completely surround the large intestine
Consists of three separate longitudinal bands
of muscle:
taeniae coli which run the length of the large intesrtine
Taeniae coli are shorter than the
underlying circular smooth muscle: the
underlying layers are gathered into pouches
called haustra
what are haustria?
small pouches caused by sacculation, which gives
the colon its segmented appearance.
Alkaline (NaHCO3) mucus is secreted from
numerous goblet cells
function of goblet cells?
to protect the mucosa from mechanical and chemical injury. No digestive enzymes are secreted
large intestine secretion of mucus is in response to ..
… mechanical and chemical stimulation of the colonic mucosa,
mediated by parasympathetic innervation.
NaHCO3 neutralises
acids produced by the local bacteria fermentation.
Majority of the time, movements of large intestine are
slow and non-propulsive (appropriate for absorptive and storage functions)
Contractions controlled by
autonomic smooth muscle cells at approx 30 minute intervals
- Majority of the time, movements of large intestine are slow and non-propulsive
(appropriate for absorptive and storage functions) - Contractions controlled by autonomic smooth muscle cells at approx. 30 min intervals
These movements shuffle…
… the contents back and forth which exposes the
colonic contents to the absorptive mucosal surface
Three to four times a day (generally after meals) marked
increases in motility
Ascending / transverse colon contract
simultaneously
Ascending / transverse colon contract simultaneously; drives
faeces one third to three quarters of the length of the colon in a few seconds – Mass movement
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