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UNCW BIO 241 - The Digestive Tract Organs

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BIO 241 1st Edition Lecture 18 Test 4Outline of Current Lecture II. Introduction to digestionIII. Basic digestive processesIV. Organization V. Tissue layers of the GI tractVI. The peritoneumVII. Mouth (oral cavity)VIII. Tongue IX. Salivary glandsX. Saliva and salivationXI. Digestion in the mouthXII. Swallowing (deglutition)Current LectureII. Food is vital to life because it provides energy and provides building blocks for growth and maintenance. Because food comes to us as complex molecules, which cannot be absorbed into the bloodstream, we need a digestive system. These complex molecules are broken down via the digestive system. Carbohydrates are broken down into monosaccharides (simple sugars), proteins are broken down into amino acids, and fats are broken into fatty acids, glycerol, and glyceride. III. There are five basic digestive processes described as: ingestion (consumption), peristalsis (movement of food), digestion (can be mechanical aka chewing or chemical aka saliva), absorption, and compaction/defecation. IV. The gastrointestinal tract aka the alimentary canal is organized as follows: mouth, pharynx, esophagus, stomach, small intestine, and the large intestine. Most of these have sphincters which separate the tract into individual organs. Some accessory organs are the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. V. There are four general tissue layers of the GI tract. This is ordered deep to superficial. The firstis the mucosa which consists of the epithelium, lamina propria, and the muscularis mucosae. These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Moving superficially, the next layer is the submucosa and it contains glands. The submucosal plexus are a nerve branch that surrounds the submucosa tissue layer. Furthermore, the third layer is the muscularis externa which consists of the inner circular layer and the outer longitudinal layer. Between the circular and longitudinal layer, there is the myenteric plexus. Theoutermost layer is the serosa/adventitia which is connective tissue surrounded by the peritoneum. The plexuses help to signal peristalsis.VI. The peritoneum is a serous membrane lining the abdominal cavity and organs. Consistent with other organs, it has an outer parietal and inner visceral layer. This creates the peritoneal cavity which reduces friction and compartmentalizes the abdominal area. There is a dorsal mesentery which is a fold of the peritoneum that attaches the abdominal organs to the posterior wall of the abdomen. The ventral mesentery consists of the lesser and greater omentums, shown below. It attaches the organs to the anterior abdominal wall. The last mesentery is the mesocolon, which joins the colon to the dorsal abdominal wall.VII. The mouth (oral cavity) is the entrance to the digestive system. It is bounded superiorly by the palate, laterally by the cheeks, and inferiorly by the tongue. The hard palate (roof of your mouth) is located closest to your teeth. As you move toward your throat, you can literally feel the roof of your mouth transition to the soft palate. At the back of the mouth, there are fauces which are arches leading into the pharynx. When looking at the back of someone else’s throat, the arches you see most anteriorly are called the palatoglossal arches (palate - tongue). Further posterior, they are called palatopharyngeal arches. The epithelium consists of stratified squamous tissue which helps against abrasion. The area inside the mouth between the lips and the teeth is called the vestibule. Muscles contract involuntarily while eating to prevent food from entering the vestibule. VIII. Intrinsic muscles of the tongue provide shape, and help facilitate speech, swallowing, and eating. Extrinsic muscles of the tongue alter the tongue's position allowing for protrusion, retraction, and side-to-side movement. The frenulum is the fold of skin that goes vertically under the tongue and attaches the bottom of the tongue to the base of mouth. The mouth usesthese muscles to create a bolus (slippery, small rounded mass of food). These muscles are controlled by the hypoglossal nerve (cranial nerve XII). IX. There are over 1000 intrinsic salivary glands located in the tongue (lingual), lips (labial), and cheek (buccal). They continuously secrete low levels of saliva. There are three paired extrinsicglands: parotid (located just anterior to the ears), submandibular, and sublingual glands. They salivate more when you are eating.X. Saliva is composed of about 98.5% water with a pH range of 6.8 - 7.0. Solutes compose the final 1.5%. These solutes are salivary amylase, lingual lipase, mucus, lysozyme, immunoglobulin A, and electrolytes (Na+, K+, Cl-, HCO3-, HPO4--). Salivation is controlled by the parasympatheticinnervation via cranial nerves VII and IX. Three types of stimuli initiate salivation: psychic (seeing, smelling, thinking about food), chemical (when the food gets wet, it instantly begins to breakdown, fluctuating the typical chemical balance within the mouth), and tactile (just touching something to these nerves can initiate). XI. Digestion occurs as both chemical and mechanical processes. The mechanical process is the grinding, chewing, and crushing of food via tongue and teeth. This is known as mastication. No protein digests within the mouth, but little fat digestion does occur. Starch, which is the polymerof glucose and found in most foods, begins to be converted into maltose (glu-glu) in the mouth. The mouth accomplishes a few things. Teeth have ground food, making it easier to swallow along with increasing the food’s surface area for chemical digestion. Starch digestion has also begun. Mucus aids in bounding food particles into a bolus that is swallowed. XII. Swallowing (deglutition) has two phases. The first is the buccal/voluntary phase and is controlled by cranial nerves V and VII. The anterior tongue lifts to the hard palate and retracts ina posterior direction to force the bolus to the oropharynx. The posterior tongue is lifted, which elevates the uvula and seals the nasopharynx to prevent nasal aspiration. The second is the pharyngoesophageal/deglutition reflex phase and is controlled by cranial nerve VII and IX. The bolus enters the upper esophagus sphincter where stretch initiates peristalsis of the esophagus (enteric nervous system). The pressure at the lower esophageal


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UNCW BIO 241 - The Digestive Tract Organs

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