Chapter 9B Flashcards
gastric phase (the end)
The pH of the stomach chyme in/decreases and the distension of
the stomach walls lessens because chyme
has passed into the small intestine,
suppressing secretion of gastric juice
(positive/negative feedback loop)
decreases, negative
HORMONAL REGULATION: gastric secre>on during the gastric phase is regulated by the
hormone X
gastrin
Gastrin is released from the X cells
of the gastric glands in response to:
- distension of the stomach by
chyme - partially/fully digested proteins in
chyme - low/high pH of chyme
- caffeine in gastric chyme
- acetylcholine released from
parasympathetic/sympathetic neurons
- Once released, gastrin enters the
bloodstream and finally reaches its
target organs in the digestive system
G cells
partially
high
Gastrin functions:
- stimulates gastric glands to
secrete gastric juice - strengthens the contraction of the
X sphincter to
prevent reflux of acid chyme into
the esophagus - promotes gastric emptying by
increasing motiity of the stomach
and relaxing the pyloric sphincter
lower esophageal
Gastrin secretion is inhibited when the
pH of gastric juice drops below/rises above 2.0 and
is stimulated when the pH decreases/rises.
drops below
rises
Intestinal phase:
* It begins once food enters the small intestine.
* In contrast to reflexes initiated during the cephalic and gastric phases, which
stimulate stomach secretory activity and motility, those occurring during the
intestinal phase have inhibitory effects that slow X
the exit of chyme from the
stomach. This prevents the duodenum from
being overloaded with more chyme
than it can handle.
These activities of the intestinal phase
of digestion are regulated by X and X mechanisms.
NEURAL
and HORMONAL
Distension of the duodenum by
the presence of chyme causes
the X reflex.
- Stretch receptors in the
duodenal wall send nerve
impulses to the medulla
oblongata, where they inhibit
parasympathetic stimulation
and stimulate the sympathetic
nerves to the stomach. - As a result, ……..
enterogastric
gastric motility is inhibited and there is an
increase in the contraction of the pyloric sphincter, which decreases gastric emptying.
HORMONAL REGULATION: The intestinal phase of digestion is mediated by two
major hormones secreted by the small intestine:
- Cholecystokinin (CCK): is
secreted by the CCK cells of
intestinal glands in the small
intestine in response to chyme
containing X and X - Secretin: is released from the S
cells of the intestinal glands in
the small intestine in response
to X entering the
duodenum .
amino acids from
partially digested proteins and
fatty acids from partially
digested triglycerides.
acidic chyme
- Functions of CCK:
1. produces hunger/satiety (acts on
hypothalamus)
2. slows/rapids gastric emptying by promoting
contraction of the pyloric sphincter
3. stimulates secretion of pancreatic
juice (rich in digestive enzymes)
4. promotes normal growth and
maintenance of the pancreas
5. contraction of the wall of the
gallbladder (squeezes stored bile out)
6. relaxation of hepatopancreatic
ampulla sphincter (Oddi sphincter)
allowing pancrea2c juice and bile to
flow into the duodenum
7. enhances the effects of secre2n
satiety
slows
Functions of secretin:
- stimulates the flow of
X juice that is rich in
bicarbonate (HCO3 −) ions to
buffer the acidic chyme that
enters the duodenum from the
stomach - inhibits secretion of X
juice (slows production of acid
in the stomach) - promotes normal growth and
maintenance of the pancreas - enhances the effects of CCK
pancreatic
gastric
The opening from the ileum into the large intestine is guarded by a fold of mucous
membrane called the X (valve), which allows materials from the
small intestine to pass into the large intestine.
ileocecal sphincter
Structurally, the four
major regions of the
large intestine are:
Rectum
Cecum
Anal canal
Colon
put in right order
- Cecum
- Colon (ascending,
transverse and
descending) - Rectum
- Anal canal
The opening of the anal canal to the
exterior (anus), is guarded by:
* Internal anal sphincter of
smooth muscle (involuntary)
and
* External anal sphincter of
skeletal muscle (voluntary).
* These sphincters keep the anus
closed except during the elimination
of feces.
ok
Large intestine:
The epithelium contains mostly X cells (water absorption) and goblet cells
(secrete mucus that lubricates)
- Both cells are located in long, straight, tubular intestinal glands (crypts of
X) that extend the full thickness of the mucosa. - Solitary lympha>c nodules are also found.
- Large intes>ne does not have circular folds or villi; however, microvilli are present on
the absorp>ve cells.
absorptive
Lieberkühn
Muscularis consists of an external layer of longitudinal smooth muscle (teniae
coli) and an internal layer of circular smooth muscle.
* Tonic contractions of the bands gather the colon into a series of pouches
called X which give the colon a puckered appearance.
Small pouches of visceral peritoneum filled with fat and attached to teniae
coli are called omental (fatty) appendices
haustra
The passage of chyme from the ileum into the cecum is regulated by X which is normally partially closed.
* After a meal, a gastroileal X intensifies peristalsis, opens the ileocecal valve
and forces chyme from the ileum (small intes<ne) into the cecum (large
intes<ne).
* It works with the gastrocolic reflex to s<mulate the urge to defecate
* The hormone gastrin also relaxes the sphincter.
ileocecal sphincter
reflex
When substances pass the ileocecal sphincter, movements of the colon begin:
- Haustral churning: when walls contract, squeeze the contents into the next
haustrum. - Slow peristalsis also occurs.
- Mass peristalsis due to the X reflex: strong peristaltic wave that
begins at about the middle of the transverse colon and quickly drives the
contents of the colon into the rectum.
gastrocolic
The X reflex involves
an increase in motility of the
colon in response to stretch in
the stomach and the
byproducts of digestion in the
small intestine.
- This reflex is responsible for
the urge to defecate following
a meal.
gastrocolic
Mucus and enzymes are secreted by the gland of the large intestine
true/false
false: no enzymes
The final stage of diges(on occurs in the colon through the ac>vity of X that
inhabit the lumen: ferment any remaining carbohydrates and proteins
bacteria
Large intes>ne also absorbs water (osmosis), ions (sodium and chloride), and some
bacterial products such us vitamins B and K
ok
By the >me chyme has remained in the large intes>ne 3–10 hours, it has become solid
or semisolid because of water absorp>on and is now called X
feces
Func>ons of the large intes>ne:
- Haustral churning, peristalsis, and mass peristalsis drive contents of colon into
rectum. - Bacteria in large intes>ne convert proteins to amino acids, break down amino
acids, and produce some B vitamins and vitamin K. - Absorp>on of some water, ions, and vitamins
- Forma>on of feces.
- Defeca>on (emptying rectum).
ok
large intestine:
Mass peristaltic movements push fecal material into the rectum.
- Distension s>mulates stretch receptors, which ini>ates a defeca(on reflex:
- Receptors send sensory nerve impulses to the sacral spinal cord.
- Motor impulses from the cord travel along parasympathe>c nerves back to the
descending colon, sigmoid colon, rectum, and anus.
ok
- The resulting contraction of the
longitudinal rectal muscles shortens
the rectum, thereby increasing the
pressure within it. - This pressure, along with voluntary
contractions of the diaphragm and
abdominal muscles, plus
parasympathetic stimulation, opens
the internal anal sphincter. - If the anus is voluntarily constricted,
defecation can be postponed.
ok
