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Role of Gastrin?
What causes its release?
Where is it found?
- Causes HCL secretion.
- Distention and proteins
- Found in the antrum of the stomach
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Role of CCK?
What causes its release?
Where is it found?
- Causes GB, pancreas and enterogastrone emptying
- Fats and Proteins
- Found in the Duodenum of the SI
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What is the Role of Secretin?
What causes its release?
Where is it found?
- Causes HCO3 (bicarbonate) and engastrone secretions
- High Acid levels
- Found in the Duodenum
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What is the role of Motilin?
Where is it found?
- it is an interdigestive hormone responsibile for continuation of motility
- Found in the upper SI
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Parasympathetics
- Use Ach as NT
- Excitatory action in the GI system
- is inhibited by NO and VIP
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Sympathetics
use NE and ACh as NT
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Intrinsic (ENS)
- Recieves its signals from the Preganglionic Parasympathetics and the Postganglionic sympathetics.
- Can act indipendant of the extrinsic system.
- Information sensed by this system can be sent to the brain via Long Vago-Vagoreflex archs .
- This system is ESSENTIAL for neural regulation of gut function.
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What are the 4 endocrine hormones
- Gastrin, CCK, Secretin, Motilin
- Remember these do not aggregate in distinct tissues but are dispersed among the epithelial cells of the mucosal lining of the gut.
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What are the 2 paracrine secretions?
Histamine and Somatostatin
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What is the role of Histamine in the GI systems?
It stimulates Parietal cells to secrete acid. Released from ECL cells in a tonic fashion.
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What is the role of somatostatin?
Inhibits acid secretion by inhibiting gastrin secretions. It is released from the antrum of the stomach and is stimulated my high concentration of acid.
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Tonic contractions verses Phasic
- Tonic- long sustained contractions. Do NOT exhibit action potentials. Change in tone is directly proportional to change in Em (Graded depolarization).
- Phasic- no contraction occurs until the Em reaches the threshold. Note: in the antrum excitatory input is required for a contraction. In the SI, they spontaneously reach theshold and exhibit a contraction.
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What are ICC cells?
Interstitial cells of cajal (ICC) are the origen of the electrical slow waves.
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What is swallowing called?
Deglutition
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what is the major muscle of the UES?
The Cricopharyngeus muscle
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Where does the CNS control of swallowing reside?
It resides within the pontine-medullary swallowing center.
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What are the 3 phases of deglutition?
- Oral phase- Contraction of mylohyoid muscle, elevation of soft palatedepends upon V,VII,XII
- Pharyngeal phase - larynx is displaced forward, relaxes the cricopharyngeus muscle.
- Esophageal phase-
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Primary paristalsis due to?
- Due to Efferent input from the nucleus ambiguous( skeletal muscle) and from the dorsal motor nucleus (smooth muscle) of the vagus.
- These nerves stimulate the inhibitory VIP/NO reflexes at the same time to create the parastalsis action.
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Secondary paristalsis is due to?
- Due to distension or irritation of the smooth muscle of the esophagus by local ENS reflexes.
- Begins that the sit of stimulation.
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Afferent and Efferent Impulses travel?
Via cranial nerves V,IX,and X.
Via cranial nerves V,VII,IX,X, and XII.
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TLESR (Transient Lower Esophageal Relaxation)
When the LES relaxation occurs in the absence of primary of secondary paristalsis. This can contribute to the developement of Gastroesophageal reflux disease (Gerd)
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What is acommodation?
When food acumulates in the stomach without an increase in pressure. This is due to high complience of the upper stomach and vagally mediated inhibitory reflexes.
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What is Trituration?
- The lower part of the stomach displays rhythmical phasic 3 per min peristalic contractions.
- Remember that liquids empy faster than solids. Food must be broken down to approx 1-2mm in size.
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When is undigestable food emptied?
It is emptied during the interdigestive phase. This is done in response to strong paristaltic contractions generated during the Migration motor complex (MMC) characteristic of this phase.
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The Orad stomach
- Thin-walled. Circular SM allways exhibits tone which is responsible for the development of intragastric pressure.
- Remember: Gastric tone is the primary determinant of liquid emptying.
- Note: With each swallow, the orad stomach briefly relaxes (called receptive relaxation).This is mediated through vagal activation of inhibitory VIP/NO secretions.
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The Caudad stomach
Thick-walled. Peristaltic contractions occur due to the electrical slow waves in the ICC cells of the corpus.
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Vagotomy (loss of Vagal imput) leads to:
No acommodation which results in a decrease in gastric complience. No receptive relaxation. This will lead to an increase in Gastric Pressure and will increase the gastric emptying rates of liquids.
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Process (steps) of Trituration.
1. Solids forward, 2. Trituration of solids, 3. retropulsion of solids back.
does this until solids are approx 1-2mm in size. Then it goes out through the pyloric sphincter.
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What is the stimulus of the caudad stomach?
Effects of a vagotomy?
Mechanical distension is the ONLY known stimulus for the initiation of the caudad stomach contraction.
Vagotomy- weaker contractions, a longer lag phase and a decrease in rate of gastric emptying.
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Control of gastric emptying is by:
- 1. Intragastric pressure
- 2. Force of antral peristalsis
- 3. Pyloric sphincter resistance
- 4. Antro-duodenal coordination
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The receptors (physical and chemical) in the SI sense?
Volume, Osmolarity, Delivery of H+, and Caloric Density of the meal.
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The receptors in the SI activate both the:
Inhibitory neural emterpgastric reflex and the inhibitory endocrine enterogastrone feedback.
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