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Questions and Answers
What is the primary purpose of propulsive movements in the gastrointestinal tract?
What is the primary purpose of propulsive movements in the gastrointestinal tract?
What initiates the peristaltic reflex in the gastrointestinal tract?
What initiates the peristaltic reflex in the gastrointestinal tract?
Which neurotransmitter is involved in activating sensory neurons during peristalsis?
Which neurotransmitter is involved in activating sensory neurons during peristalsis?
What role do cholinergic neurons play in the myenteric plexus during peristalsis?
What role do cholinergic neurons play in the myenteric plexus during peristalsis?
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In which part of the gastrointestinal tract do mixing movements primarily occur?
In which part of the gastrointestinal tract do mixing movements primarily occur?
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What type of contractions primarily cause mixing movements when intestinal contents are blocked by a sphincter?
What type of contractions primarily cause mixing movements when intestinal contents are blocked by a sphincter?
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What is the primary mechanism behind mastication?
What is the primary mechanism behind mastication?
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What nerve is primarily responsible for the nerve supply during mastication?
What nerve is primarily responsible for the nerve supply during mastication?
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What is the main function of chewing in the digestive process?
What is the main function of chewing in the digestive process?
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During which stage of swallowing does the tongue play a significant role in pushing food towards the pharynx?
During which stage of swallowing does the tongue play a significant role in pushing food towards the pharynx?
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What primarily triggers the involuntary pharyngeal stage of swallowing?
What primarily triggers the involuntary pharyngeal stage of swallowing?
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What is the role of the lower esophageal sphincter (LES) in digestion?
What is the role of the lower esophageal sphincter (LES) in digestion?
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Which factor contributes to the relaxation of the lower esophageal sphincter?
Which factor contributes to the relaxation of the lower esophageal sphincter?
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What happens during the primary peristalsis stage of swallowing?
What happens during the primary peristalsis stage of swallowing?
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What action protects air passages during swallowing?
What action protects air passages during swallowing?
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What distinguishes secondary peristaltic waves from primary peristaltic waves?
What distinguishes secondary peristaltic waves from primary peristaltic waves?
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Study Notes
Gastrointestinal Movements
- Propulsive movements move food along the gastrointestinal tract (GIT) for digestion and absorption.
- Mixing movements mix the contents of the GIT.
Peristalsis (Propulsive Movement)
- A reflex response initiated by stretching of the GIT wall.
- Stretch initiates a circular contraction behind the stimulus and relaxation in front of it, called "receptive relaxation".
- Occurs in all parts of the GIT from pharynx to the rectum, propelling contents forward in an oral to caudal direction.
- Dependent on the myenteric plexus, also known as the myenteric reflex or peristaltic reflex.
- An excellent example of the enteric nervous system.
- Local stretch releases serotonin, activating sensory neurons that activate the myenteric plexus.
- Cholinergic neurons activate neurons that release substance P and acetylcholine, causing smooth muscle contraction.
- Cholinergic neurons also activate neurons that secrete VIP, NO and ATP, producing relaxation ahead of the stimulus.
Mixing Movements
- Occur differently in various parts of the GIT.
- In certain areas, peristaltic contractions cause most of the mixing.
- If intestinal contents are blocked by a sphincter, peristaltic waves can mix the contents.
- Local constrictive contractions occur every few centimeters in the GIT wall.
Mouth & Esophagus
- In the mouth, food is mixed with saliva and propelled into the pharynx and esophagus.
- Peristaltic waves in the esophagus move food into the stomach.
Mastication (Chewing)
- Anterior teeth (incisors) provide cutting action, while posterior teeth (molars) grind.
- Nerve supply: Fifth cranial nerve.
- Center: Brain stem.
- Mechanism: Chewing reflex (stretch reflex):
- Food entry in the mouth stretches mastication muscles, initiating a stretch reflex that leads to muscle contraction.
- This raises the jaw, closing the teeth and compressing the bolus against the mouth lining.
- Compression inhibits jaw muscles, allowing the jaw to drop and repeat rhythmically.
Functions of Chewing
- Breaks down large food particles.
- Mixes food with salivary gland secretions.
- Wetting and homogenizing action aids digestion.
Swallowing (Deglutition)
- Divided into three stages:
- Oral (voluntary) stage: Initiates swallowing.
- Pharyngeal stage: Involuntary passage of food through the pharynx into the esophagus.
- Esophageal stage: Involuntary passage of food from the esophagus to the stomach.
Voluntary Oral Stage of Swallowing
- Food is voluntarily squeezed or rolled posteriorly into the pharynx by tongue pressure.
Involuntary Pharyngeal Stage of Swallowing
- A reflex act initiated by the bolus of food entering the pharynx.
- Receptors: Swallowing receptor areas around the opening of the pharynx, especially on the tonsillar pillars.
- Center: Brain stem (medulla and lower pons, called the deglutition or swallowing center).
- Response: Initiation of pharyngeal muscle contractions.
- Function: Propels food into the esophagus.
Protection of Air Passages During Swallowing
- Soft palate is pulled upward, closing the posterior nares.
- Vocal cords of the larynx are strongly approximated, preventing food passage into the trachea.
Involuntary Esophageal Stage of Swallowing
- Esophagus conducts food from the pharynx to the stomach.
- Two types of peristaltic movements:
- Primary peristalsis: Continuation of the peristaltic wave beginning in the pharynx and spreading to the esophagus during the pharyngeal stage.
- Secondary peristalsis: Occurs if the primary peristaltic wave fails to move food into the stomach, resulting from esophagus distention.
Lower Esophageal Sphincter (Gastroesophageal Sphincter) (LES)
- Composed of three components:
- Esophageal smooth muscle at the junction with the stomach (intrinsic sphincter).
- Fibers of the crural portion of the diaphragm surrounding the esophagus (extrinsic sphincter).
- Oblique fibers of the stomach wall, creating a flap valve that prevents regurgitation when intragastric pressure rises.
- Remains tonically contracted.
- Tone of LES is regulated by:
- Acetylcholine released from vagal nerve endings causes LES contractions.
- Nitric oxide (NO) and VIP cause LES relaxation.
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Description
This quiz focuses on the mechanisms of gastrointestinal movements, including propulsive and mixing movements essential for digestion and absorption. It particularly highlights peristalsis as a key reflex response in the gastrointestinal tract, detailing its initiation, neural control, and physiological significance.
