Upper GI Tract Flashcards
Function of mouth
receive food by ingestion, break it into small particles by mastication, and mix it with saliva produced by the salivary glands that open into the oral cavity. During swallowing, the soft palate and uvula move upward to direct food away from the nasal cavity and into the oropharynx.
Function of pharynx
Food is forced into the pharynx by the tongue. When food reaches the opening, sensory receptors around the fauces respond and initiate an involuntary swallowing reflex. The uvula is elevated to prevent food from entering the nasopharynx. The epiglottis drops downward to prevent food from entering the larynx and trachea in order to direct the food into the esophagus. Peristaltic movements propel the food from the pharynx into the oesophagus
Function of oesophagus
collapsible muscular tube that serves as a passageway between the pharynx and stomach. It passes through an opening in the diaphragm, called the oesophageal hiatus, and then empties into the stomach. The mucosa has glands that secrete mucus to keep the lining moist and well lubricated to ease the passage of food. Upper and lower oesophageal sphincters control the movement of food into and out of the oesophagus
Function of stomach
food enters the stomach, which is the primary site of digestion. It is also involved in storage of food. The secretions of the exocrine gastric glands - composed of the mucous, parietal, and chief cells - make up the gastric juice. Mucus neck cells secrete a lubricatory, acid-resistant mucus; parietal cells produce HCl and chief cells produce pepsinogen and lipase. Relaxation of the pyloric sphincter allows chyme to pass from the stomach into the small intestine
Function of duodenum
After foods mix with stomach acid, they move into the duodenum, where they mix with bile from the gallbladder and digestive juices from the pancreas. The absorption of vitamins, minerals, and other nutrients begins in the duodenum. Specific functions of the duodenum include:
-Receiving the mixed, churned small pieces of food from the stomach
-Neutralising the acidity (pH level) in chyme
-Advancing the digestive process with bile from the liver, digestive enzymes from the pancreas, and intestinal juices secreted by the duodenum walls and other digestive organs
-Preparing the chyme for further digestion by mixing in bile to help break down fats
-Absorbing certain nutrients, such as folate, iron, and vitamin D
anatomy of the upper GI tract (pharynx, oesophagus, stomach and duodenum) including the course through the thoracic cavity
The upper GI tract begins with the oral cavity, which contains the tongue, teeth, gums and ducts of salivary glands. When food is swallowed, the soft palate contracts to close off the nasopharynx from the oropharynx and the epiglottis covers the trachea to prevent aspiration of food or liquid. Food then enters the oropharynx to the laryngopharynx before entering the oesophagus. The oesophagus is a muscular tube which rhythmically contracts (peristalsis) to move food down into the stomach. It then moves through the cardiac sphincter into the cardia region of the stomach. The stomach is divided into 4 cavities: cardia, fundus, body, pylorus. It then leaves the pylorus via the pylorus sphincter into the duodenum
Slow waves
generated and propagated by interstitial cells of Cajal, which initiate motility, NOT smooth muscle
Spikes
true action potentials occurring automatically when GI smooth muscle becomes move positive than -40mV
GI syncytium
Smooth muscle of the GI tract acts as a syncytium: muscle fibres connected by gap junctions allow electrical signals to initiate muscle contraction from one muscle fibre to the next rapidly along the length of the bundle.
2 types of waves contributing to membrane potential in gastro-oesophageal motility
Slow waves
Spikes
Oesophageal motility
propels food bolus from the pharynx to the stomach: the food bolus is formed in the oral cavity and when the upper oesophageal sphincter opens, it passes from the pharynx into the upper oesophagus. The upper oesophageal sphincter closes and then primary peristaltic contraction begins. A series of coordinated sequential contractions cause each segment of the oesophagus to contract which creates an area of high pressure behind the bolus, pushing it down the oesophagus. If not all food is pushed down, there is distension of the oesophageal wall and activation of mechanoreceptors in the mucosal layer. This relays afferent sensory information to the enteric nervous system and myenteric plexus, which coordinates muscle contractions above the site of distension and relaxation below it- the secondary peristaltic wave.
• the primary peristaltic wave travels approximately 3cm/sec and so solid food takes around 10s to travel from the cervical region to the stomach, and liquid takes around 1-2s.
• The movement is accelerated by gravity eg faster if sitting or standing compared to lying supine
As the food bolus approaches the lower oesophageal sphincter, it opens by peptidergic fibres of the vagus nerve and the release of vasoactive intestinal peptide (VIP), causing the smooth muscle to relax. At the same time, the cardia region of the stomach relaxes, causing the pressure to decreases and so the food bolus is propelled into the stomach. The lower oesophageal sphincter closes immediately and returns to high pressure resting tone- this prevents reflux.
Speed of primary peristaltic wave
3 cm/s
Time for solid food to travel from cervical region to stomach
10s
Time for liquid to travel from cervical region to stomach
1-2s
What increases the speed of movement of food down oesophagus
Gravity
eg faster if sitting or standing compared to lying supine
Primary peristaltic wave
Oesophageal motility propels food bolus from the pharynx to the stomach: the food bolus is formed in the oral cavity and when the upper oesophageal sphincter opens, it passes from the pharynx into the upper oesophagus. The upper oesophageal sphincter closes and then primary peristaltic contraction begins. A series of coordinated sequential contractions cause each segment of the oesophagus to contract which creates an area of high pressure behind the bolus, pushing it down the oesophagus.
Secondary peristaltic wave
If not all food is pushed down, there is distension of the oesophageal wall and activation of mechanoreceptors in the mucosal layer. This relays afferent sensory information to the enteric nervous system and myenteric plexus, which coordinates muscle contractions above the site of distension and relaxation below it- the secondary peristaltic wave.
What prevents reflux
The lower oesophageal sphincter closes immediately and returns to high pressure resting tone
