Digestive System

alimentary canal; accessory digestive organs

gastrointestinal tract/GI - is a continuous muscular digestive tube that winds through body. digests & absorbs food.

• mouth
• pharynx
• esophagus
• stomach
• small intestine
• large intestine

• teeth
• tongue
• gall bladder
• salivary glands
• liver
• pancreas

• take in food
• break it down into the nutrient molecules
• rid body of waste

taking food into digestive tract (through mouth)

• move food through alimentary canal
• (swallowing, peristalsis)

• chewing
• mixing food with saliva
• churning food in the stomach
• segmentation

rhythmic local constriction of sm. intestine - mixes food with digestive juices, increases efficiency of absorption by repeatedly moving diff. parts of food mass over intestinal wall

food molecules are broken down to chemical building blocks by enzymes (into fats, carbs, proteins --> simple sugars, amino acids, fatty acids)

passage of digested end products & vitamins, minerals, water from lumen of GI tract through mucosal cells by active/passive transport into the blood or lymph. small intestine is the major absorptive site

eliminates indigesible substances from body

• control luminal conditions
• - activity stimulated by mech/chem stimuli
• - controls are intrinsic/extrinsic

• mechano/chemoreceptors are located in walls of tract organs, respond to several stimuli
• - stretching of organ by food in the lumen
• - osmolarity
• - pH of contents
• - presence of substrates & end products of digestion.

• when stimulated, receptors initiate reflexes that
• 1) activate/inhibit glands that secret digestive juices into lumen or hormones into blood
• 2) stimulate smooth muscle of GI tract walls to mix lumen contents, move them along the tract

• intrinsic-"in house" nerve plexuses or hormone producing cells.
• - short - mediated by local enteric plexuses in response to stimuli arising from GI tract
• - long - initiated by stimuli arising in/outside GI tract, involve CNS & extrinsic autonomic nerves.

• nerve fibers that excite smooth muscle secret Ach or substance P
• inhibit: release vasoactive intestinal peptide or nitric oxide

• includes those arteries that branch off abdominal aorta to serve the digestive organs and the hepatic portal circulation.
• - arterial supply normally receives 1/4 of the cardiac output -> increases after meals

• innermost layer.
• moist epi. memb. that lines ali. canal lumen from mouth->anus

• 1) secrete mucus, digestive enzymes, hormones
• 2) absorb the end products of digestion into the blood
• 3) protect against infectious disease

• 1) lining epithelium - simple columnar rich in mucus-secreting cells
• 2) lamina propria - underlies epithelium, is loose areolar CT. nourishes epitheium, absorbs digested nutrients. part of MALT, help defend against bacteria, other pathogens
• 3) muscularis mucosae - layer of smooth muscle that produces local movements of the mucosa -> twitching dislodges food particles

• areolar CT, contains rich supply of blood & lymphatic vessels, lymphod follicles, nerve fibers.
• elastic fibers enable recoil in stomach

• responsible for segmentation and peristalsis.
• has an inner circular layer & outer longitudinal layer
• circular layer thickens and forms sphincters -> act as valves to prevent backflow, control food passage from one organ to the next

• protective outermost layer; is the visceral peritoneum.
• formed of areolar CT covered in mesothelium (single layer of squamous epi. cells)
• in the esophagus (which is in thorocic cavity) - adventitia

• alimentary canal's "in-house" nerve supply.
• communicates widely with one another to regulate digestive system activity

• occupies the submucosa
• includes sensory & motor neurons
• chiefly regulates activity of glands and smooth muscle in the mucosa

• lies between circular & longitudinal muscle layers
• provide the major nerve supply to the GI tract wall, control GI tract motility
• also linked to CNS - PS inputs enhance secretory activity and motility; sym impulses inhibit digestive activities