lecture 2

• What is the recurrent theme discussed in the study material?

  Propulsion
• What is peristalsis and its function?

  • Involves alternate waves of contraction and relaxation of muscles in organ walls
  • Allows mixing of digestive juices

  
• What is the process of chewing called?

  Mastication
• Which nerve controls chewing?

  Trigeminal nerve
• How does mastication affect food?

  It increases the surface area of food, improving access to digestive enzymes
• What is masticated food called?

  Bolus
• To what extent is mastication a reflex?

  It is a reflex to a large extent
• What happens to the lower jaw muscles when food is present?

  Food causes a reflex inhibition of the lower jaw muscles
• What occurs when the jaw drops during mastication?

  It causes a stretch reflex
• What is the result of the stretch reflex during mastication?

  It causes muscle contraction and closure of the mouth
• What role does the hard palate play during mastication?

  It keeps the bolus away from the nasal cavity
• How does the tongue assist in mastication?

  The tongue moves and pushes food against the hard palate
• What happens to the soft palate when swallowing commences?

  It moves up

  
• What is another term for swallowing?

  Deglutition
• What role do saliva and mucus play during swallowing?

  They reduce friction
• Where does swallowing occur in relation to the laryngopharynx?

  At the inferior border of the laryngopharynx connected to the esophagus
• What is the most important action when the bolus reaches the pharynx?

  Closing alternative routes
• What are the phases of deglutition?

  1. The voluntary phase: Tongue moves up and back, pushes bolus into oropharynx
  2. The Pharyngeal Phase: Signals sent to the deglutition center, closes off nasopharynx, prevents aspiration
  3. The Esophageal Phase: Entry of food initiates peristalsis, bolus propelled toward stomach

  
• What occurs during the voluntary phase of deglutition?

  The tongue moves up and back, pushing the bolus into the oropharynx
• What happens during the pharyngeal phase of deglutition?

  Signals are sent between the oropharynx and the deglutition center
• How is the nasopharynx closed during swallowing?

  By movement of the uvula and soft palate

  
• What prevents aspiration of food into the trachea during swallowing?

  Laryngeal muscles contract
• What is deglutition apnea?

  It is when the epiglottis closes covering the entrance to the trachea
• What allows food to enter the esophagus during swallowing?

  Relaxation of the upper esophageal sphincter
• What initiates peristalsis in the esophageal phase?

  Entry of food
• Which part of the brain controls peristalsis during the esophageal phase?

  Medulla oblongata
• What happens as the bolus approaches the stomach?

  The lower esophageal sphincter relaxes and allows the bolus into the stomach
• What are the characteristics of mechanical digestion in the stomach?

  • Mixing waves mix and soften food with gastric juices to create chyme
  • Occurs at intervals of approximately 20 seconds after ingestion
  • Initial mixing waves are gentle, followed by more intense waves
  • Starts at the body of the stomach and increases in force as they reach the pylorus
• How much volume does the pylorus hold?

  Approximately 30 mL
• How much chyme is forced through the pyloric sphincter at a time?

  About 3 mL
• Why is the release of chyme into the duodenum controlled?

  To avoid overwhelming the capacity of the small intestine
• What are the causes of vomiting (emesis)?

  • Irritation
  • Toxins
  • Infections
  • Motion
• What are the three stages of vomiting?

  1. Nausea
  2. Retching
  3. Emesis
• Which part of the brain is involved in vomiting?

  Brainstem, specifically the medulla
• What are the two centers in the brainstem related to vomiting?

  Bilateral vomition centers and chemoreceptor trigger zone
• What are the movements involved in mechanical digestion in the small intestine?

  • Segmentation
  • Migrating motility complexes (MMC)
  • Peristalsis
• How often does segmentation occur in the duodenum?

  12 times per minute
• How often does segmentation occur in the ileum?

  8 times per minute
• What hormone increases segmentation in the small intestine?

  Gastrin
• What is the function of the migrating motility complex (MMC)?

  • Contractile activity that occurs after chyme absorption
  • Duodenal mucosa secretes the hormone motilin
  • Known as "housekeeping" activity
  • Removes leftovers and bacteria