Exam 3

Mechanical and chemical breakdown of foods into forms that cell membranes can absorb

Breaks large pieces into small pieces w\o altering the chem make-up of the pieces

Breaks down larger chemicals to smaller chemicals

Ingestion, propulsion, absorption & defecation

• Muscular tube about 8 meters long
• Extending from the mouth to the anus
• Passes through the thoracic and abdominopelvic cavities
• Develops from the endoderm of the embryo & the accessory organs develop as buds from the canal

• Four layers
• Mucosa
• Submucosa
• Muscular
• Serosa
• Developed to different degrees in different layers

• Protects the layers beneath it
• Provides secretions
• Absorbs nutrients & other food components (e.g., water & electrolytes)

• Surface epithelium
• Lamina propria (underlying connective tissue)
• Muscularis mucosae (smooth muscle)
• Projections into lumen increase surface area for absorption
• Glands that secrete digestive enzymes and mucous

• To nourish surrounding tissues
• To secrete chemicals
• To carry away absorbed materials

• Loose connective tissue
• Glands
• Blood vessels
• Lymphatic vessels
• Nerves

To move the contents of the canal

• Circular fibers:
• Smooth muscle
• Inner layer
• Closed spirals around tube
• Change diameter of tube
• Longitudinal fibers:
• Open spirals
• Outer layer
• Run lengthwise
• Shorten the tube upon contraction

• Protect underlying tissue
• Secrete serous fluid to lubricate and moisten the outer surface

• Visceral peritoneum:
• Underlying connective tissue
• Outer layer of epithelium

increase activities of digestive system

inhibit certain digestive actions

• Ingests food
• Mechanically breaks up solid particles
• Adds saliva
• Prepares food for chemical digestion
• Speech organ
• Sensory reception organ

• Outer layers of skin
• Pads of subcutaneous fat
• Muscles associated with expression and chewing
• Inner linings of moist, stratified layers of squamous epithelium

• highly mobile structures that surround the mouth opening
• Skeletal muscles
• Sensory receptors determine temp & texture of food.
• Outer border marks separation of facial skin & mucous membranes of alimentary canal

• Thick, muscular organ
• Occupies the floor of the mouth
• Nearly fills the oral cavity when the mouth is closed
• Covered by mucous membrane
• Mixes food particles with saliva during chewing
• Moves food particles toward the pharynx during swallowing

• Lingual frenullum
• Papillae
• Lingual tonsils

• forms the roof of the oral cavity
• Hard palate
• Soft palate

formed by palatine processes of maxillary bones & horizontal parts of the palatine bones

forms a muscular arch that extends to the cone-shaped uvula

• Palatine tonsils
• Pharyngeal tonsils

• Hardest structures in the body
• Develop in sockets w/in the alveolar processes of the mandibular & maxillary bones
• Break food into smaller pieces to begin mechanical digestion
• Loss most often due to gingivitis or endodontitis

• 20 primary (deciduous) teeth erupt through gingiva (gums) at regular intervals btw 6 months and two to four months of age
• Usually shed in the same order in which they erupted
• Roots are resorbed and, then pushed out of their sockets by the secondary teeth
• 32 secondary (permanent) teeth erupt between 6 & 25 yrs
• “Wisdom” teeth erupt last and may be “impacted”

• Incisors
• Cuspids
• Bicuspids
• Molars

• Front four teeth
• Chisel-shaped
• Sharp edges bite off pieces of food

• Aka, premolars
• Two teeth on each side of each jaw
• Flattened surfaces
• Grind food

• Aka, canine teeth
• One tooth on each side of each jaw
• Cone-shaped
• Grasp and tear food

• Three teeth on each side of each jaw
• Flattened surfaces
• Grind food

• Projects beyond gum
• Covered with glossy, white enamel
• Hardest substance in body
• Composed primarily of calcium salts
• Not replaced if eroded, abraded, or damaged
• Worn away with age

• Dentin
• Central cavity
• Root canal

• Most of tooth beneath enamel
• Living cellular tissue that is similar to, but harder than, bone

• Aka, pulp cavity
• Surrounded by dentin
• Contains blood vessels, nerves, and connective tissue (aka, pulp)

• Tubular canal through which blood vessels & nerves reach the central cavity
• Extends from base of tooth

Between crown and root

• Anchored to alveoli process of jaw
• Enclosed by cementum, a thin layer of bone-like material
• Periodontal ligament (periodontal membrane
• Composed of collagen
• Firmly attaches tooth to alveolar process
• Between the cementum and alveolar process
• Contains blood vessels and nerves near surface of the cementum-covered root

Produce a watery fluid containing salivary amylase, which breaks starch and glycogen into disaccharides

Secrete mucous, which binds food particles and acts as a lubricant during swallowing

Stimulate secretion of a small amount of a viscous saliva

• Reflexively stimulate secretion of large amounts of a watery saliva when thinking or sensing good food
• Reflexively inhibits secretion of watery saliva whenthinking or sensing unpleasant food

• Parotid glands
• Submandibular glands
• Sublingual glands

• Largest major salivary gland
• Located anterior and inferior to ear between the skin of the cheek and the masseter muscle
• Duct transports fluid and enters mouth opposite the upper second molar on each side of the jaw
• Secrete clear watery, serous fluid
• Rich in salivary amylase

• Located in the floor of the mouth within the lower jaw
• Duct transports fluid and enters mouth near the lingual frenulum
• Secrete fluid that is about equally serous and mucus

• Smallest major salivary gland
• Located on the floor of the mouth near the base of the tongue
• Many separate ducts
• Secrete primarily thick, stringy mucus

• The pharynx is a cavity posterior to the mouth from which the tubular esophagus leads to the stomach
• Neither structure is directly involved in digestion
• Both the pharynx and esophagus muscular walls function in swallowing

Connects the nasal and oral cavities with the larynx and esophagus

• Nasopharynx
• Oropharynx
• Laryngopharynx

• Located superior to the soft palate
• Communicates with the nasal cavity
• Provides a passageway for air during breathing
• Connects pharynx with middle ear through auditory tubes

• Located posterior to the mouth
• Opens posterior to the soft palate into the nasopharynx and projects downward to the upper border of the epiglottis
• Passageway for food moving downward frm the mouth
• Passageway for air moving into and out of the nasal cavity

• Located immediately inferior to the oropharynx
• Extends from the upper border of the epiglottis to the lower border of the cricoid cartilage of the larynx
• Passageway to the esophagus

• Constrictor muscles
• Longitudinal muscles exterior to constrictor muscles
• Skeletal muscles that can be under voluntary control to start swallowing, but they are reflexive control during swallowing

• Circular muscles that pull the walls of the pharynx inward during swallowing
• Superior constrictor muscles are attached to the bony processes of the skull and mandible and curve around the upper part of the pharynx
• Middle constrictor muscles arise from the projections of the hyoid bone and fan around the middle of the pharynx
• Inferior constrictor muscles arise from cartilage of the larynx and pass around the lower portion of the pharyngeal cavity
• Some inferior constrictor muscles are usually contracted in order to prevent air from entering the esophagus during breathing

• Three stages:
• 1.Voluntary stage
• 2.Swallowing begins when food reaches the pharynx stimulates sensory receptors which trigger the swallowing reflex
• 3.Peristalsis transports food in the esophagus to the stomach

• Food is chewed and mixed with saliva
• Food is rolled into bolus and forced into the pharynx by the tongue

• Soft palate and uvula raise to prevent food from entering the nasal cavity
• Hyoid bone and larynx elevate
• Epiglottis a flaplike structure attached to the larynx closes off top of the trachea so food is less likely to enter the trachea
• Tongue presses against the soft palate and uvula to seal off the oral cavity from the pharynx so food doesn’t back up
• After all attached cavities and tubes are blocked, muscle actions to move the food begin
• The longitudinal muscles of pharynx contract pulling the pharynx up toward the food
• The lower inferior constrictor muscles relax and the esophagus opens
• The superior constrictor muscles contract to stimulate start of a peristaltic wave in other pharyngeal muscles
• Food enters the esophagus
• Breathing is momentarily inhibited by the swallowing
• reflex.....step 3

• A straight collapsible tube that is about 25 cm long
• A passageway for food to move from the pharynx to the stomach
• Muscles in the wall push food from the pharynx to the stomach
• Located posterior to trachea
• Descends through the thorax and mediastinum
• Passes through the esophageal hiatus of the diaphragm
• Continuous with stomach
• Mucous glands in the submucosa layer moisten and lubricate the epithelial lining of the tube
• Lower esophageal (cardiac) sphincter muscles encircle the esophagus immediately above where it joins the stomach

• Receives food from the esophagus
• Mixes food with gastric secretions
• Initiates digestion of proteins
• Carries on limited absorption
• Moves food into the small intestine

• A J-shaped, pouch-like organ, about 25-30 cm long
• Maximum capacity is about 1 liter
• Located inferior to the diaphragm in the upper-left portion of the abdominal cavity
• Inner lining has rugae, thick folds of mucosal & submucosal tissue that flatten out when wall is distended

• inner circular layer
• outer longitudinal layer
• A third inner layer of oblique fibers:
• In some parts of the stomach
• Most highly developed near the lower esophageal
• sphincter and in the body of the stomach
• Strengthen stomach wall
• Help mix and churn stomach contents

• Cardiac region
• Fundus
• Body of stomach
• Pyloric region
• Pyloric region

• Adjacent to lower esophageal sphincter
• Where swallowed food enters stomach

• Top of stomach
• Superior to cardiac region
• Storage area
• Sometimes fills with swallowed air

Central and largest region

Funnel-shaped area that narrows to become the pyloric canal

• Circular muscular layer around the pyloric canal immediately above where it joins the small intestine
• A valve that controls gastric emptying

• Tubular glands embedded in thick mucosa of stomach
• Gastric pits:
• Small openings at the surface of the mucosa
• Located at the ends of gastric glands
• Structure & composition of secretions vary in different areas of the stomach

• Mucous cell
• Chief cells (aka, peptic cells)
• Parietal cells (aka, oxyntic cells)

• In the necks of the glands
• Near the opening of the gastric pits

Secrete digestive enzymes

Secrete a solution containing hydrochloric acid

• Pepsinogen
• Pepsin
• Gastric lipase

• From the chief cells
• Inactive, nonerosive, precursor form of pepsin

• Formed from pepsinogen in the presence of hydrochloric acid
• Most active under acidic conditions
• Is a protein splitting enzyme
• Begins digestion of almost all dietary proteins
• Breaks down pepsinogen to form more pepsin

• Small quantities in gastric juice
• A fat-splitting enzyme that works mostly on butterfat
• Weak activity due to acidity of gastric juice

• Hydrochloric acid
• Mucus
• Intrinsic factor

• From the parietal cells
• Needed to convert pepsinogen to pepsin

• From the mucous cells of the gastric glands:
• Thin mucus
• Produced in large amounts
• From cells of the mucous membrane, associated with the inner lining of the stomach and between the gastric glands:
• More viscous mucus
• Alkaline secretion
• Coats the inside wall of the stomach
• Prevents pepsin from digesting proteins of stomach tissues
• Protective to stomach wall

• From the parietal cells
• Is required for vitamin B12absorption from the small intestine

• Somatostatin
• Acetylcholine
• Gastrin
• Histamine

• Produced by specialized cells closely associated with parietal cells
• Inhibits acid secretion

• Released from nerve endings upon stimulation by parasympathetic nerve impulses from the vagus nerve
• Suppresses secretion of somatostatin
• Stimulates release of large amounts of gastric juice from the gastric glands

• Peptide hormone
• Produced by certain cells, mostly in the pyloric region
• Secretion stimulated by same impulses as acetylcholine secretion
• Induced increased secretory activity of gastric glands

• Release stimulated by parasympathetic impulses and gastrin
• Released from gastric mucosal cells
• Stimulates additional gastric secretions

• Cephalic phase
• Gastric phase
• Intestinal phase

• Induced by taste, smell, sight, or thought of food and before food enters the stomach
• Parasympathetic reflex signal from vagus nerve
• Stimulates secretion of gastric juices
• Level of hunger reflected in amount of secretion
• Responsible for 30 – 50 % of the secretory response to a meal

• Starts when food enters the stomach
• Presence of food and resulting distension of the stomach wall trigger release of the hormone gastrin
• Gastrin stimulates release of more gastric juice
• Higher pH in stomach due to mixing of food with stomach secretions induces release of additional gastric juice
• Decreasing pH inhibits, then stops, secretion of gastrin
• Responsible for 40 – 50 % of the secretory response to a meal
• Acid release into stomach is accompanied by removal of hydrogen ions from the blood and release of equivalent number of bicarbonate ions into the blood Excess bicarbonate ions excreted in urine during the alkaline tide

• Begins when food leaves the stomach and enters the small intestine
• Intestinal gastrin secretion induced by food contacting the intestinal wall
• Intestinal gastrin stimulates secretions from the gastric glands
• Acid in the upper part of the small intestine triggers a sympathetic nerve impulse that inhibits secretion of gastric juice from the stomach wall
• Cholecystokinin:
• A peptide hormone
• Release stimulated by presence of fats in the upper region of the small intestine
• Released from cells in the intestinal wall
• Decreases gastric motility
• Intestinal somatostatin:
• A hormone
• Release stimulated by presence of proteins and fats in the upper region of the small intestine
• Released from cells in the intestinal wall
• Inhibits release of gastric juice
• Gastric secretions and motility decrease as small intestine fills with food

• Gastric enzymes begin breaking down proteins, but the stomach is not well-adapted to absorb digestive products
• The stomach does absorb:
• Some water
• Certain salts
• Certain lipid-soluble drugs
• Alcohol
• Most nutrients are absorbed in the small intestine