Functions and secretion of the alimentary tract: part 1 Flashcards
food ingestion is stimulated by
Hunger = intrinsic for food
appetite= preferential of food
Mastication ( chewwing)
Teeth= designed for cutting (incisors) and grinding (molars) of food.
Muscles for chewing= controlled by nuclei in brain stem.
Stimulation of specific reticular areas (brain stem taste centers)
causes rhythmic chewing action.
what other stimulation causes chewing ?
hypothalamus
brain cerebral cortex
amygdala
mastication reflex
takes place in response to presence of reflex inhibition of mastication muscles (at first)→ lower
jaw drops→ initiates stretch reflex of jaw muscles→ rebound contraction→ automatically raises jaw→
closes teeth + compresses bolus against mouth linings→ inhibits jaw muscles again→ jaw drops→
rebound contraction again= process repeated again and again
mechanical digestion of all food
chewing
chemical digestive
digestive enzymes
initiation of the swallowing process.
voluntary stage
food bolus pushed and compressed by the tongue against the palate to the pharynx.
initiation of the swallowing process.
voluntary stage
food bolus pushed and compressed by the tongue against the palate to the pharynx.
pharyngeal stage( in the pharynx )
involuntary stage/ process
Bolus stimulates epithelial swallowing receptor areas in
the pharynx, and tonsillar pillars→ to send action potentials to the brain stem.
initiates a series of automatic pharyngeal muscular contractions.
soft palate will elavate and closes the posterior nares
to prevent food reflex intp the nasal cavity
palatopharyngeal folds
are pulled medially to form sagittal slit: selectively allow properly masticated food to pass.
function of epiglosttis
closes the larynx
elevation of the larynx ………………. and …………..
enlarges the oesophageal opening and upper oesophageal sphincter relaxes.
contration of the pharyngeal muscular wall= peristalsis propulsion of food into oesophagus.
Pharyngeal Stage of Swallowing Momentarily Interrupts Respiration:
last for 6 seconds
Swallowing center inhibits respiratory center of the medulla during this
time (within the 6 secs period)
Esophageal Stage of Swallowing involves 2 Types of Peristalsis:
primary and secondary perilstalisis.
primary peristalsis.
begins in the pharynx and terminates in the stomach.
last about 8-10 seconds in an upright person.
last about 6-8 secs due to gravitational force.
secondary peristalsis.
when primary peristalsis fails, secondary peristalsis wave results from distention of oesophagus by retained food.
Secondary peristalsis initiated by:
a) Intrinsic neural circuits in myenteric nervous system
b) Pharyngeal reflexes transmitted upward through vagal afferent fibers to medulla and back to esophagus
through glossopharyngeal & vagal efferent nerve fibers.
Pharyngeal wall & upper 3rd esophagus.
has striated/ skeletal muscles= controlled by skeletal nerve impulses of
glossopharyngeal & vagal efferent nerve fibers.
while the lower 2/3 of the esophagus
strongly controlled by vagal nerves associated with myenteric
nervous system.
When vagus nerve is cut→ myenteric plexus of esophagus takes over & stimulate secondary peristalsis
when the vagus nerve is cutted what is happens?
→ myenteric plexus of esophagus takes over & stimulate secondary peristalsis.
Esophageal peristaltic waves approaching stomach→
relaxation of the stomach through the inhibitory neurons accouring
Function of the Lower Esophageal Sphincter (LES) (Gastroesophageal Sphincter):
Peristaltic wave moving down esophagus→ receptive relaxation of lower esophageal sphincter occurs→ food
enters stomach.
Tonic constriction of the LES prevents reflux of stomach contents into esophagus
Prevention of Esophageal Reflux by Valve-like Closure of the Distal End of Esophagus:
a valve-like mechanism of a short portion of the oesophagus extending slightly to the stomach is called cardia prevents high intra-abdominal pressure from forcing stomach contents into oesophagus.
storage function of the stomach
Food enter stomach→ stomach stretches→ vagovagal reflex
(from stomach—brain stem—back to stomach) reduce muscular
tone→ stomach stretches more (with limit of 0.8L to 1.5L).
mixing of the food in the stomach is controlled by
gut wall basic electrical rhythmical waves called constrictor waves.
when food enters the stomach
Gastric glands secret gastric juices→ juices mix with food
material→ mixing waves (constrictor waves) initiated by gut wall
basic electrical rhythm (“slow waves”) (move from body to
antrum)→ constrictor waves become more powerful→ food
moves towards pylorus→ pyloric muscles contracts→ impedes
emptying through pylorus→ food contents mixed (retropulsion
mixing mechanism)→ chyme formed.
stomach emptying
Caused by strong peristaltic contractions in stomach
Pylorus controls the degree of chyme being emptied.
Role of Pylorus in Controlling Stomach Emptying:
Pyloric circular muscles= pyloric sphincter
pyloric sphincter remains tonically contracted normally.
degree of pyloric contraction increases or decreases depending on the influence of nervous or hormonal signals.
Gastric Factors Promoting Emptying:
Gastric Food Volume: increased food volume → promotes stomach emptying
Stretching of stomach wall→ stimulate local myenteric reflexes→ increase pyloric pump activity.
hormones stimulating emptying if the stomach?
Stretching of the stomach wall and presence of certain foods.
G cells are stimulated to secrete gastrin then stimulate parietal cells to H ions –> Hcl to promote activity of pyloric pump
Mixing Contractions (Segmentation Contractions):
Chyme in duodenum→ cause distention→ stretching
intestinal wall→ elicit local concentric contractions=
segmentation contractions→ cause mixing of chyme with
small intestine secretions.
propulsive movement of chyme in the intestine
Peristalsis in Small Intestines: chyme moves through
small intestines by peristaltic contractions
Control of Peristalsis by Nervous & Hormonal
Signals:
peristaltic activity increase by the gastroenteric
reflex initiated by stomach distention & conducted through
to small intestines by myenteric plexus.
Hormonal factors include gastrin, CCK, insulin, motilin,
serotonin; all enhance small intestinal motility
Hormones that inhibits motility
Glucagon and secretin
The Ileocecal Valve Prevents Backflow From The
Colon to The Small Intestine:
Ileocecal valve protrudes into cecum→ increased cecum
pressure→ forcefully closes it= preventing backflow into
ileum.
Ileocecal sphincter→ remain mildly constricted→ allows
slow emptying of ileal content into cecum
main function of the colon.
absorption of water and electrolytes and storage of faecal matter until expelled.
process of the large circular and longitudinal muscles contractions occurs in the large intestines. is called
Haustrations
which will the result-slowly dug into & roll over faecal material→ faecal
material exposed to mucosal surfaces→ absorption
occurs
After meals, mass movement facilitated by gastrocolic
and duodenocolic reflexe due to
stretching of stomach and duodenum.
peritoneointestinal reflex
Stimulated by irritation of the peritoneum→ Inhibits
excitatory enteric nerves→ cause intestinal paralysis
(patients with peritonitis
Renoitestinal and vesicointestinal reflexes
stimulated by irritation the kiddney and gallbladde
