Stomach Flashcards
What are the primary functions of the stomach?
- STORE FOOD
- needs to be released at an appropriate rate for optimal digestion & absorption - SECRETE HCl & ENZYMES
- begins protein digestion - CREATE CHYME
-mixing food with secretions via movements through contractions of muscle layers.
Produce a liquid mixture (chyme)
What is gastric filling?
Eating triggers relaxation of stomach (folds)
[RECEPTIVE RELAXATION]
Process is mediated via vagus nerve
If >1L consumed, stomach becomes distended,
THUS, increasing intra-gastric P (= discomfort)
What is gastric mixing?
INTERSTITIAL CELLS OF CAJAL
-(in fundus) act as pacemaker cells!
Slow waves, entire length of stomach (~3/minute)
PERISTALSIS activated when slow wave potential reaches threshold, triggering an AP
Having food in stomach means the starting point of which SLOW WAVES OSCILLATES IS SET CLOSER TO THE THRESHOLD, & thus more likely to result in APs.
MUSCULATURE THIN IN FUNDUS (pocket of gas) + BODY (storage)
-THUS, less mixing
When peristaltic wave reaches the antrum,
- stronger contractions
- THUS, thicker musculature
- THUS increased mixing
What role does the pyloric sphincter play in terms of gastric mixing?
Peristaltic wave pushes chyme towards pyloric sphincter
Tonic contraction of the sphincter keeps it almost closed, but open enough for fluid to pass through
(amount of chyme that gets through is proportional to the strength of the antral contraction!)
Peristaltic waves reaches sphincher --> Sphincter contracts more forcefully --> Closes tightly --> Chyme hits sealed-off sphincter --> Chyme tumbles back into antrum --> More mixing!
What is gastric emptying (& motility)?
Digestion triggers increased gastric motility through a direct effect of stretch on the smooth m., as well as involvement of the intrinsic plexuses, vagus nerve and gastrin.
Chyme can only be released once it reaches appropriate degree of fluidity.
What factors increase gastric (antral) motility?
- Intensity of antral peristaltic contractions (motility) controls mixing and emptying.
- Factors change excitability of stomach by depolarising/hyperpolarising smooth m. cells
-Increase excitability –> basic electrical rhythm generates more frequent APs
What factors inhibit gastric (antral) motility?
NEURAL
(Intrinsic & Extrinsic nerves)
-Emotion and Pain
ENTEROGASTRONES
(Secretin, CCK)
DUODENUM::
-FAT: slowly digested, needs time to process fat
- ACID: chyme must be neutralised or inactivates enzymes & irritates duodenal mucosa
- HYPERTONICITY: a.a’s & glucose; draws H20 from plasma to reach istonicity
- DISTENSION: too much chyme, excess vol.
What is Emesis?
VOMITING
-coordinated by the vomiting centre in the medulla oblongata (in brainstem)!
Deep inspiration, glottis closed, uvula raised –>
Stomach, oesophagus & gastroesphageal sphincter RELAXED –>
Respiratory muscles (diaphragm & abdominal) are CONTRACTED. Stomach is squeezed between descending diaphragm & increasing intra-abdominal P
[Sensation of nausea, salivation, sweating, rapid heart rate - ANS]
Name the different types of gastric secretions?
SURFACE MUCOUS CELLS - secrete mucus
MUCOUS NECK CELLS - “ “
PARIETAL CELLS - secrete HCl & intrinsic factor
CHIEF CELLS - secrete pepsinogen & gastric lipase
G CELLS - secrete gastrin
What is gastric juice?
Collective exocrine secretions!
What type of mucosa is located in the fundus + body?
OXYNTIC MUCOSA
-predominately secretes acid
What type of mucosa is located in the antrum?
PYLORIC GLAND AREA
-predominately secretes mucus
Where are secretory cells located in the stomach?
IN MUCOSAL INFOLDINGS!
[may be exo-, para- or endocrine)
What is volume of chyme proportional to?
DISTENSION
stretch, intrinsic plexuses, vagus nerve, gastrin
Why is fluidity important in the stomach?
(CHYME) - MORE EASILY EMPTIED
