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Digestion (Ch. 24)

The Digestive System

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name the organs of the alimentary canal mouth, pharynx, esophagus, stomach, small intestine, & lg. intestine
name the accessory digestive organs teeth, tongue, gallbladder & glands (salivary, liver & pancreas)
ingestion taking food into the digestive tract, usualy via the mouth
propulsion moves food through the alimentary canal; swallowing & peristalsis
peristalsis major means of propulsion; involves alternate waves of contraction & relaxation of muscles in the organ walls; main effect is to squeeze food from one organ to the next, but some mixing occurs as well
mechanical digestion physically prepares food for chemical digestion by enzymes; chewing, mixing of food w/ saliva by the tounge, churning food in the stomach & segmentation
segmentation rhythmic local constrictions of the intestine; mixes food w. digestive juices & increases the efficiency of absorption by repeatedly moving different parts of the food mass over the intestinal wall
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absorption passage of digested end products (+ vitamins, minerals & water) fm the lumen of th eGI tract into the blood or lymph; to occur substances must first enter the mucosal cells by active or passive transort processes
the major absorption site is the small intestine
defecation eliminates indigestible substances from the body via the anus in the form of feces
list the six essential activities for processing food by the digestive system ingestion, propulsion, mechanical digestion, chemical digestion, absorption & defecation
two things that apply tot eh regulatory mechanisms 1. digestive activity is provoked by a range of mechancial & chemical stimuli; controls of digestive activity are both extrinsic & intrinsic
sensors (location & response) are located in the walls of the tract organs; respond to several stimuli (streching of the organ wall by food in the lumen, osmolarity (solute concentration) & pH of the contents & presence of substrates & end products of digestion
receptors initiate reflexes that (1) activate or inhibit glands that secrete digestive juices into the lumen or hormones into the blood or (2) mix lumen contents & move them along th elength of the tract by stimulating the smooth muscle of the GI tract walls
the walls of the alimentary canal contains nerve plexuse; they extend & influence each other; aquires two kindes of reflexes (short & long)
short reflexes are mediated entirely by the local (enteric) plexuses (so-called gut brain ) in response to GI tract stimuli
long reflexes are initiated by stimuli arising within or outside the GI tract & involve CNS centers & extrinsic autonomic nerves
the stomach & sm. intestin contain hormone-producing cells that are distributed via the blood to their target cells
peritoneum most extensive of the serous membranes
visceral peritoneum covers the external surfaces of most digestive organs & is continuous with the parietal peritoneum
parietal peritoneum lines the body wall
peritoneal cavity is between the two peritoneums; is a slitlike potential space containing fluid secreted by the srous membranes
the serous fluid lubricates the mobile digestive organs & allows them to glide easily across one anothe & alon the body wall as they cary outh their digestive activites
mesentery double layer of peritoneum -- a sheet of two serous membranes fused back to back-- that extends tot he digestive organs from the body wall; provide routes for blood vessels, lymphatics & nerves to reach the digestive visceral; they also hold organs in pla
retroperitoneal organs most of the pancres & parts of the large intestine that are not suspended by a mesentery
intraperitoneal/peritoneal organs digestive organs (like the stomach) that keep their mesentery & remain in the peritoneal cavity
peritonitis inflammation of the peritoneum, can arise from a piercing wound of the abdomen or from a perforating ulcer that leaks stomach juices intot he peritoneal cavity, most commonly from a burst appendix
splanchnic circulation arteries that branch off the abdominal aorta to serve the digestive organs & the hepatic portal circulation
name the four basic tunics of the alimentary canal from the lumen outward mucosa, submucosa, muscularis externa & serosa
mucosa innermost layer; lines the lumen of the alimentary canal from mouth to anus; 3 major functions secretion, absorption & protection
explain what secretion does during the mucosa secretion of mucus, digestive enzymes & hormones
explain absorption in the mucosa absorption of the end products of digestion into the blood
explain protection in the mucosa protection against infectious disease
name the typical digestive mucosas sublayers (1) a lining epithelium (2) a lamina propria (#) a muscularis mucosae
the epithelium of the mucosa is a simple columnar epithelium that is rich in mucus-secreting goblet cells
the slippery mucus it produces protects certain digestive organs from being digested themselves by enzymes working within their cavities & eases food passage along the tract
lamina propria underlies the epithelium, is loose areolar (or reticular) connective tissue; its capillaries nourish the epithelium & absorb digested nutrients
MALT the mucosa-associated lymphatic tissue are importanct in the defense against bacteria & other pathogens, which have rather free access to our digestive tract
peristalsis mucosae is external tot he lamina propria, a scant layer of smoth muscle cells that produces local movements of the mucosa; Ex, twitching of this muscle layer dislodges food particles that have adhered tot eh mucosa
the submucosa external tot he mucosa; moderately dense connective tissue containing blood & lymphatic vessels, lymph nodules & nerve fibers; enables the stomach to regain its normal shape after temporarily storing a large meal
muscularis externa/muscularis deep to the submucosa; responsible for segmentation & peristalsis (mixes & propels foodstuffs along the digestive tract)
the musclaris externa layers are the inner circular layer & an oter longitudinal layer of smooth muscle cells
sphincters act as valves to prevent backflow & control food passage from one organ to the next; occurs from the circular lyer thickens
the serosa protective outermost layer of the intraperitoneal organs is the visceral peritoneum; formed of areolar connevtive tissue covered w. mesothelium, a single layer of squamous epithelial cells
adventitia ordinary fibrous connective tissue that binds the esophagus to surrounding sturctures; replaces the serosa (ex. esophagus which is located in the htoracic instead of abdominopelvic cavity)
enteric neurons the alimentary canals own in-house nerve supply which communicate widely w. each other to regulate digestive system activity;constitute the bulk of the two mj intrinsic nerve plexuses found within the walls of the alimentary cnal; submucosal & myenteric n
submucosal nerve plexus occupies the submucosa & chiefly regulates the activity of glands & smooth muscle in the mucosa tunic
myenteric nerve plexus lies between the circular & longitudinal layers of smooth muscle of the muscularis externa; provide the mj nerve supply tot he G
the 3 types of papillae are filiform, fungiform, & circumvallate
filiform papillae give the toung surface a roughness that aids in licking semisolid foods & provide friction for manipulating foods inthe mouth (their the smallest and most numoruse); contain keratin which stiffens them & gives tounge whitish apperance
fungiform papillae mushroom shaped; scattered widely; each has a vascular core that gives reddish hue
what is the purpose of saliva 1)cleanses the mouth 2)dissolves food chemicals so they can be tasted 3) moistens food & aids in compacting it intoa bolus 4) contains enzymes that begin the chemical breakdown of starchy foods
Created by: Brina