Digestive system Part #1 Flashcards
(12 cards)
Digestion -
the breaking of food into smaller particles and smaller molecules so that they can enter the cells for the synthesis of new macromolecules or for the production of ATP.
Two parts to the digestive system: alimentary canal (aka gastrointestinal tract) and the accessory structures -
Alimentary canal ( aka gastrointestinal tract ) - a tube from mouth to anus that includes mouth, stomach, small and large intestines. Accessory structures - function is to aid in digestion teeth, tongue, salivary glands, liver, gallbladder and pancrease.
The digestive process -
ingestion - eating, bringing food into your mouth.
mechanical breakdown - breaking food into smaller pieces, chewing, churning, and segmentation.
propulsion - motility or movement of food through swallowing or peristalsis.
chemical digestion - cells secrete water, acid, enzymes,and buffers that function chemically.
absorption - active transport and passive diffusion are used to move molecules across membranes into blood or lymph for transportation.
defecation - aka excretion, removal of solid wastes that are not digested or absorbed.
Layers of the GI tract - from lumen out :
- Mucosa - epithelium, lamina propria, muscularis mucosae. The epithelium for the mouth, pharynx, esophagus and anal canal is NKSSE and the stomach is simple columnar. (epithelium function is to) - protection, secretion and absorption. (lamina propria is made of) - areolar connective tissue. (muscularis mucosae is) a thin layer of smooth muscle, glands - goblet cells are also present.
- Submucosa - includes blood vessels, nerves, lymphatics and glands. Its function is to bind to the muscularis. The submucosal nerve plexus innervates the muscularis mucosae.
- Muscularis externa (aka muscularis) - the mouth, pharynx, and superior esophagus have skeletal muscle for voluntary control of swallowing. At the anus there is also a ring of skeletal muscle. The rest of the tract has smooth muscle arranged in two layers: one longitudinal and one circular ( a 3rd layer, the oblique, is found only in the stomach). The myentric nerve plexus is located here and regulates the contractions of the muscularis externa.
- Serosa - a serous membrane that is made up of simple squamous epithelium and connective tissue.
For structures above and including the esophagus, this layer is know as the adventitia and below the diaphragm it is the visceral peritoneum.
Peritoneum - is the largest serous membrane. It has a periotoneal cavity that is filled with serous fluid as well as a visceral and parietal layers. The parietal layer forms the body wall of the abdominalpelvic cavity and the visceral layer is found on the outside of digestive organs.
Mesentery - two serous membranes that enclose the the abdominal organs. There are specific folds such as the greater omentum the “apron” covering the organs anteriorly. The lesser omentum stabilizes the stomach.
Retroperitoneal - organs that are located posterior to the peritoneum, they lose their mesentary during development.
Intraperitoneal - aka peritoneal, these organs keep their mesentery and are inclosed in the peritoneum.
Mouth -
aka - oral or buccal cavity which is formed by the cheeks, hard and soft palates and the tounge. Lips (labia) - form the opening of the oral cavity. The epithelium of the lips is stratified squamous but not keratinized and so the blood shows through. Labial frenulum - one located upper and one lower, each attaches the lip to the gum. Oral vestibule - pocket formed between the cheeks / lips and cheeks / gum. Oral cavity proper - the cavity formed by the teeth, gums, palate and the floor of the mouth.
Tissue types - Oral cavity : slightly keratinized stratified squamous epithelium, gums , top surface of tounge and hard palate. NKSSE, wall of the mouth and soft palate.
Fauces - opening to the oropharynx.
Uvula - muscular projection of the soft palate. The uvula and soft palate close off the nasopharynx during swallowing.
Salivary glands -
The mucous membranes of the tounge and mouth contain small salivary glands know as the minor salivary glands. There are also three pair of major salivary glands:
Parotid glands -located anterior to the ear in between the skin and masseter muscle.Each parotid duct breaks through the buccinator and opens into the vestibule next to the 2nd upper molar.
Submandibular glands - located beneath the posterior portion of the oral cavity below the jaw. The ducts open up into the lingual frenulum.
Sublingual glands - located superior and anterior to the submandibular glands. The sublingual ducts open into the floor of the oral cavity.
Saliva -
Saliva is 99.5% water and 0.5% solutes. The solutes include sodium,potassium, chloride, phosphate ion, bicarbonate ion, urea, mucus,lysozyme, IgA, dissolved gases, salivary amylase and lingual lipase. The overal pH is between 6.35 and 6.85 (acidic).
Functions of saliva : Moisten food,dissolves food for chemoreceptors to work, conatins salivary amylase that break down startch, contains lingual lipase that breaks down lipids, phosphate and bicarbinate ions act as buffers for acidic or alkaline foods.
Stimulates secreation of saliva : Normal parasympathetic stimulation, touch or taste of food, thought or memory of food, sight, chewing, oral irritants.
Tounge -
The tounge is composed of multiple bundles of skeletal muscle that directs the position of food during chewing.
Lingual frenulum - attaches the toung to the floor of the oral cavity.
Types of papillae - taste buds that are embedded.
Fungiform papillae - mushroom shapped and has a red dot in the center due to a vascular core.
Vallate papillae - 10 - 12 large papillae that form an inverted “V” at the back of the tounge.
Foliate papillae - located on the posterior sides of the tounge.
Teeth -
Another accessory structure of digestion. The maxillae and mandible contain alveoli that form gomphoses with teeth.
Gingivae - aka gums, they are a type of mucous membrane with slightly keratinized stratified squamous epithelium that covers the alveolar process and extends slightly into each socket.
3 main parts of the tooth : crown - located above the gum line. neck - the narrowing of the gum line. root - the part of the tooth below the gum line.
Enamel - the outer covering of the crown made of calcium phosphate and calcium carbonate. (collagen is absent)
Dentin - highly calcified connective tissue that makes up the bulk of the tooth. The protein collagen is the main organic component.
Cement - aka cementum, the outer covering of the root of the tooth similar to dentin.
Periodontal ligament - attaches the cement to the bone socket, acts as a shock absorber and allows for the slight mobility of the joint.
Pulp cavity - filled with connective tissue (pulp), blood vessels, nerves and lymphatics.
Root canal - the narrow extension of the pulp cavity that extends into the root and allos for the passage of vessels and nerves.
Apical foramen - the opening of the root canal that allows nerves and blood vessels to exit the tooth.
2 sets of teeth - Dentitions
20 deciduous (1st dentition) 1st set of teeth, "milk teeth" , or "baby teeth" 32 permanent/adult teeth (2nd dentition) 4 types of permanent teeth : incisors ( central and lateral) - cut food, 8 total (4 top and 4 bottom). cuspids (aka canine) - tear food due to sharp point, 4 total also called eye teeth. premolars (1st and 2nd) - grinding and mashing, (8 total, aka bicuspids). molars (1st, 2nd and 3rd) grinding and mashing (12 total). (3rd molars are wisdom teeththat often do not surface or are surgically removed).
Dental caries - aka cavities, when plaque becomes food for bacteria and cause demineralization.
Gingivitis - inflamation of the gums, when plaque spreads from the teeth to the gums.
Periodontal disease - a progression of gingivitis that results in periodontal pockets from tartar ( aka calculus, calcified plaque) not being removed.
Mechanical and Chemical digestion in the Mouth -
Mastication - chewing, the mechanical digestion that occurs in the oral cavity.
Bolus - mucus covered ball of food formed by the manipulation of food in the mouth.
Chemical digestion - starch —salivary amylase—-turns into smaller chains of glucose, trisaccharides and disaccharides.
triglycerides ——lingual lipase —–fatty acid and monoglycerides.
Pharynx -
deglutition - aka swallowing, the moving of food from oral cavity to the stomach via pharynx and esophagus.
Phases of deglutition : 1. buccal stage -the bolus is voluntarily moved from the oral cavity to oropharynx.
- pharyngeal stage - involuntary movement of the bolus from oropharynx to the esophagus.
- esophageal stage -involuntary movement of the bolus from the esophagus to the stomach.
Changes that occur when bolus moves into the oropharynx : the soft palate elevates to close off the nasopharynx. The upper esophageal sphincter relaxes. The larynx is elevated and epiglottis flaps over.
