SWALLOWING & GASTRIC EMPTYING Flashcards
Inner circular layer of muscle is for ___
Outer longitudinal layer of muscle is for __
Inner - peristalsis
Outer - bowel shortening
Where do you find skeletal muscle?
Where do you find smooth muscle?
Skeletal - oropharynx to upper 1/3 of esophagus; anus
Smooth muscle - everything else
Upper tract is innervated by ___
Lower tract is innervated by ___
Upper tract - vagus n
Lower tract - pelvic n
Preganglionic fibers end on ___ within ___ and ___
Preganglionic fibers end on enteric nerves in
- Auerbach’s Plexus (motor)
- Meissner’s Plexus (sensory)
These plexuses are located between circular and longitudinal muscle layers
What hormone(s) are involved in skeletal muscle contraction?
Just acetylcholine
Contraction - Ach
Relaxation - inhibit Ach release
What hormone(s) are involved in smooth muscle contraction?
Contraction: Ach
Relaxation: Nitric oxide
Upper esophageal sphincter
Lower esophageal sphincter
Pyloric sphincter
Ileocecal valve/sphincter
Internal anal sphincter
External anal sphincter
UES: separates esophagus from oropharynx
LES: separates esophagus from stomach
Pyloric sphincter: separates stomach from duodenum
Ileocecal valve: separates small intestine from colon so bacteria in the colon doesn’t reach the small intestine
Internal & external anal sphincter
Functions of stomach, small intestine, and colon
Which compartment does food spend the longest time in?
Stomach: digest, grind up, and mix
Small intestine: mix pancreatic juice w bile; ensure optimal absorption
Colon: salt & water absorption; compact stool
Which phases of swallowing are involuntary and what are they controlled by
Oral (voluntary): chewing & swallowing by muscles of mastication
Pharyngeal & Esophageal phase are involuntary, controlled by swallowing center of the medulla
Oral phase of swallowing
Both parts are under voluntary control of cranial nerves
- Mastication
-
Decision to swallow
- Initiates the following phases by signaling to the meedulla swallowing center
Pharyngeal phase of swallowing
- Soft palate elevates to block nasopharynx
- Laryngeal muscles contract –> elevates larynx, lowers epiglottis –> epiglottis flops over the trachea
- UES relaxes so bolus enters esophagus
- Pharyngeal muscles contract to initiate peristalsis; pushes bolus through relaxes UES and into esophagus
Esophageal phase of swallowing
- 7-8 seconds
-
Peristalsis pushes the bolus down while the LES relaxes transiently to transfer the bolus into the stomach.
- Under control of the medullary swallowing center, which sends signals via vagus nerve
which is higher- pressure in teh LES or in teh stomach?
LES (+15-30mmHg)
Stomach (+5mmHg)
Major constrictor related to UES is
Cricopharyngeus muscle
Differentiate the muscle content between the upper 1/3 an dthe lower 2/3 of the esophagus
Upper 1/3 : skeletal muscle that is NOT under voluntary control
Lower 2/3: smooth muscle
Nucleus tractus solitarius
receives all sensory (afferent) signals for the medullary swallowing center
Nucleus Ambiguous
sends efferent signals to skeletal muscle segments of the esophagus (UES & upper 1/3)
–> motor end plate on skeletal muscle
–> release Ach or turn off Ach release
Dorsal motor nucleus (DMN)
Sends efferent signals to smooth muscle segments (lower 2/3 of esophagus & LES)
–> preganglionic fiber
- > myenteric plexus
- > release Ach or NO
5 different conditions that cause LES relaxation during the esophageal phase
- Primary peristalsis triggered by swallowing
-
Secondary peristalsis initiated by esophageal distension by a bolus that has failed to be propulsed into stomach by primary peristalsis
- Wave starts proximal to the bolus
- Transient LES relaxation initiated by gastric fundic distension by either food, liquid or air
- Belch reflex initiated by the same thing as #3
-
Deglutitive inhibition: initiated by rapid voluntary swallowing (e.g. chugging)
- Stops peristalsis and allows sphincter to remain open until one last peristalsis wave occurs before sphincter restores pressure again
Belch Reflex
Relaxation of LES stimulated by stretch in fundus (like after a meal)
- LES relaxes -> air enters esophagus -> cause UES to relax
- When acid reflux occurs, liquid enters esophagus and triggers LES relaxation via stretch
- Liquid stays in the esophagus until swallowed back into stomach
- Saliva (HCO3- rich) dilutes & buffers this
Receptive relaxation
NO from the myenteric plexus relaxes the fundus to store up to 1.5 L of food without increasing gastric pressure.
When more than 1.5 L is stored in the fundus, what happens?
The brain determines satiety (fullness)
The gastric pressure has increased above 1.5L –> material forced from fundus to body
Body/antrum of stomach
Gastric pacemaker: 3 contractions/min
- Strength of contractions determined by
- stretch-induced release of Ach from vagus nerve
- release of gastrin from antral G cells induced by
- antrum distension
- increased antrum pH by mixing food w gastric juice
- peptides from gastric proteases
- Reduces particle size to 2mm or less so gastric contents can be propulsed to the pyrlorus
Gastric pacemaker
Area of cells of cajal in the upper body that spontaneously depolarize and repolarize in response to Ach (vagus n) and gastrin (antral G cells)
- Max rate of 3 peristaltic contractions per minute
What is the semisolid-liquid material produced after gastric processing of the meal?
Chyme
Why does chyme get propulsed through the pylorus and into the duodenum in small amounts?
- Sample the contents
- Accelerate digestion by mixing contents with digestive enzymes from pancreas and bile salts from gallbladder
-
Begin absorption of nutrients and water from luminal contents
- enhanced by villi of duodenal epithelium
What is the purpose of duodenal sampling of chyme?
To reduce the rate of gastric emptying if the chyme is..
-
too acidic –> release secretin from duodenal epithelial cells
- release alkaline pancreatic and biliary juices
- reduce gastric contractility
-
too hyperosmolar –> vagal n reflex
- reduces the vagal release of Ach to reduce gastric contractility
-
too lipid-rich –> cholecystokinin from duodenal epithelial cells
- contract gallbladder
- reduce gastric contractility
- release pancreatic enzymes including lipases
