Upper GI Tract

UPPER GI TRACT Functions ● Ingestion through the oral cavity ● Propulsion of substances from one organ to the next ● Digestion → chemical (through digestive enzymes) and mechanical ● Secretion from accessory digestive organs ● Absorption of nutrients through the walls of the tube = enters blood stream and goes throughout the body ● Defecation - elimination of undigested foods Anterior part of the oral cavity ● Mandible bony wall ● Floor formed by the muscles of the tongue ● Walls created by the mandible and maxilla ● Muscles of mastication (cheek muscles) important for pushing the food from one side of the mouth to another ● Roof = bones of the maxilla and hard palette ● Tongue ○ Muscles that rolls and moves food around in the mouth ○ Mechanical breakdown of the food ○ Propelling the food down into the pharynx ○ Strongest muscles relative to size in the body ○ Multiple muscle fibres in the tongue going in different directions ● ● ● Oropharynx ○ Bound by the tip of the soft palette (uvula) to the lid of the epiglottis Laryngopharynx Oesophagus 1. Food ingested into the oral cavity 2. Mechanical breakdown of the food using the teeth and tongue (creates the bolous) 3. Salivary glands also help with the chemical breakdown of the food to help with enzymatic breakdown of the food ● Known as the 'buccal phase' because the cheeks are responsible for pushing the food down 1. Goes through the 'pharyngeal phase' where it travels through the oropharynx and the laryngopharynx 2. 'Esophageal phase' when it goes through the oesophagus ● Steps 4 and 5 are involuntary process which occur through the peristaltic actions of the walls of the pharynx and oesophagus to push food down the stomach ● Nonkeratinized squamous epithelium Pharynx ● Common passage for air, food and fluid ● Posterior to the nasal and oral cavities ● Continuous with the oesophagus ● 3 divisions (affects the type of epithelium located here) ○ Naso = respiratory function only ○ Oro = digestive and respiratory function ○ Laryngo = digestive and respiratory functions ● Swallowing (deglutition) occurs here ○ Buccal phase ○ Pharyngeal phase ○ Esophageal phase Oesophagus ● Connection between the mouth and stomach ● Begins posterior to the larynx ● Posterior to the trachea in the mediastinum ● Passes through the diaphragm ● Muscle - Can be broken into thirds - Superior third of the oesophagus = skeletal muscle - Middle third = mix of skeletal and smooth muscle - ● ● - Inferior third = smooth muscle (smooth muscle to take over the involuntary peristaltic movements) Epithelium - Epithelium of the oesophagus is stratified squamous epithelium non keratinized - At the oesophagus-stomach junction - In the stomach there is columnar epithelium = absorption and secretions into the lumen of the stomach Sphincters (circular muscle that maintains constriction of a passage) - Superior end = sphincter that closes when inhaling air so air is directed into the larynx and trachea rather than intestinal organs - Inferior end = sphincter that controls the flow of food from the esophagus to the stomach, prevents backflow of the stomach contents back into the esophagus - Sphincter is weak so sometimes stomach juices can go into the lower parts of the esophagus = heartburn At the junction between stomach and esophagus, you can see the transition from stratified squamous epithelium (esophagus) to simple columnar epithelium (stomach) Stomach ● End of the upper GI tract ● Left upper quadrant ● Shape is dependant on what the person ate (J shaped organ) ● Hollow muscular organ ● Digestion ○ Mechanical digestion ○ Chemical digestion from the HCl produced and secreted into the stomach by the parietal cells in the stomach wall ○ Enzymatic digestion from chief cells in the stomach wall ● ● ● Can contain 3-4L of food, drink and saliva 3 layers of muscularis externa Greater and lesser curvature Muscles ● Stomach is composed of muscle ● Group of muscles = muscularis externa (mix and churn the stomach contents, facilitates the mechanical breakdown of the food) ● Layers ○ ○ ○ Outermost layer = longitudinal layer (muscle fibres go superior to inferior) Middle = circular and wraps around Innermost = oblique layer