Physiology - GI Flashcards
1
Q
Parasympathetic stimulation
A
-stimulation may be stimulatory or inhibitory depending on the type of neurotransmitter secreted by the nerve endings:
ACh : increases motility and secretions
VIP : decreases constrictions of sphincters, increases relax
GRP : increases gastrin from G cells of stomach
-An increase in PNS activity promotes digestive and absorptive processes
2
Q
Sympathetic stimulation
A
via NE results in:
- decreased motility
- decreased secretions
- increased constrictions of sphincters
-An increase in sympathetic activity slows processes
3
Q
Propulsive movements (Peristalsis)
A
- Cause food to move forward at an appropriate rate to accommodate digestion and absorption
- Stimulus is usually distension of the gut
- “Law of the gut” : The direction of the peristaltic reflex is always from the oral towards the anal direction
4
Q
Mixing movements
A
- These are local intermittent constrictive contractions
- Lasts for 5 to 30 sec
- Keeps the intestinal contents thoroughly mixed at all times
5
Q
Gastric Motility
A
Functions:
- Storage of large quantities of food until the food can be processed in the stomach, duodenum and lower intestinal tract
- Mixing with gastric secretions until it forms a semifluid mixture called chyme
- Slow emptying of the chyme from the stomach into the small intestine
Stimulated by
- Increased parasympathetic activity via acetylcholine and gastrin release
- Local distention
Inhibited by
- Low pH of stomach contents (since it inhibits release of gastrin)
- Feedback from duodenal overload (neural and hormonal)
6
Q
Salivary Secretions
A
-Almost entirely under control of the parasympathetic system
Composition:
- Low in Na+, Cl- because of reabsorption
- High in K+, HCO3- because of active secretion
- α-Amylase (ptyalin): secreted in active form and begins the digestion of CHO
- Mucus
- Glycoprotein
- Hypotonic, because of reabsorption of NaCl and impermeability of ducts to water – aids in taste
