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Physiology > SWALLOWING & GASTRIC EMPTYING > Flashcards

SWALLOWING & GASTRIC EMPTYING Flashcards

1
Q

Inner circular layer of muscle is for ___

Outer longitudinal layer of muscle is for __

A

Inner - peristalsis

Outer - bowel shortening

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2
Q

Where do you find skeletal muscle?

Where do you find smooth muscle?

A

Skeletal - oropharynx to upper 1/3 of esophagus; anus

Smooth muscle - everything else

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3
Q

Upper tract is innervated by ___

Lower tract is innervated by ___

A

Upper tract - vagus n

Lower tract - pelvic n

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4
Q

Preganglionic fibers end on ___ within ___ and ___

A

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

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5
Q

What hormone(s) are involved in skeletal muscle contraction?

A

Just acetylcholine

Contraction - Ach

Relaxation - inhibit Ach release

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6
Q

What hormone(s) are involved in smooth muscle contraction?

A

Contraction: Ach

Relaxation: Nitric oxide

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7
Q

Upper esophageal sphincter

Lower esophageal sphincter

Pyloric sphincter

Ileocecal valve/sphincter

Internal anal sphincter

External anal sphincter

A

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

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8
Q

Functions of stomach, small intestine, and colon

Which compartment does food spend the longest time in?

A

Stomach: digest, grind up, and mix

Small intestine: mix pancreatic juice w bile; ensure optimal absorption

Colon: salt & water absorption; compact stool

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9
Q

Which phases of swallowing are involuntary and what are they controlled by

A

Oral (voluntary): chewing & swallowing by muscles of mastication

Pharyngeal & Esophageal phase are involuntary, controlled by swallowing center of the medulla

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10
Q

Oral phase of swallowing

A

Both parts are under voluntary control of cranial nerves

  • Mastication
  • Decision to swallow
    • ​Initiates the following phases by signaling to the meedulla swallowing center
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11
Q

Pharyngeal phase of swallowing

A
  1. Soft palate elevates to block nasopharynx
  2. Laryngeal muscles contract –> elevates larynx, lowers epiglottis –> epiglottis flops over the trachea
  3. UES relaxes so bolus enters esophagus
  4. Pharyngeal muscles contract to initiate peristalsis; pushes bolus through relaxes UES and into esophagus
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12
Q

Esophageal phase of swallowing

A
  • 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
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13
Q

which is higher- pressure in teh LES or in teh stomach?

A

LES (+15-30mmHg)

Stomach (+5mmHg)

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14
Q

Major constrictor related to UES is

A

Cricopharyngeus muscle

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15
Q

Differentiate the muscle content between the upper 1/3 an dthe lower 2/3 of the esophagus

A

Upper 1/3 : skeletal muscle that is NOT under voluntary control

Lower 2/3: smooth muscle

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16
Q

Nucleus tractus solitarius

A

receives all sensory (afferent) signals for the medullary swallowing center

17
Q

Nucleus Ambiguous

A

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

18
Q

Dorsal motor nucleus (DMN)

A

Sends efferent signals to smooth muscle segments (lower 2/3 of esophagus & LES)

–> preganglionic fiber

  • > myenteric plexus
  • > release Ach or NO
19
Q

5 different conditions that cause LES relaxation during the esophageal phase

A
  1. Primary peristalsis triggered by swallowing
  2. Secondary peristalsis initiated by esophageal distension by a bolus that has failed to be propulsed into stomach by primary peristalsis
    1. Wave starts proximal to the bolus
  3. Transient LES relaxation initiated by gastric fundic distension by either food, liquid or air
  4. Belch reflex initiated by the same thing as #3
  5. Deglutitive inhibition: initiated by rapid voluntary swallowing (e.g. chugging)
    1. Stops peristalsis and allows sphincter to remain open until one last peristalsis wave occurs before sphincter restores pressure again
20
Q

Belch Reflex

A

Relaxation of LES stimulated by stretch in fundus (like after a meal)

  1. LES relaxes -> air enters esophagus -> cause UES to relax
  2. When acid reflux occurs, liquid enters esophagus and triggers LES relaxation via stretch
    1. Liquid stays in the esophagus until swallowed back into stomach
    2. Saliva (HCO3- rich) dilutes & buffers this
21
Q

Receptive relaxation

A

NO from the myenteric plexus relaxes the fundus to store up to 1.5 L of food without increasing gastric pressure.

22
Q

When more than 1.5 L is stored in the fundus, what happens?

A

The brain determines satiety (fullness)

The gastric pressure has increased above 1.5L –> material forced from fundus to body

23
Q

Body/antrum of stomach

A

​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
24
Q

Gastric pacemaker

A

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
25
Q

What is the semisolid-liquid material produced after gastric processing of the meal?

A

Chyme

26
Q

Why does chyme get propulsed through the pylorus and into the duodenum in small amounts?

A
  • 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
27
Q

What is the purpose of duodenal sampling of chyme?

A

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

Physiology (42 decks)

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