Digestive System

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Author:
hana
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109855
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Digestive System
Updated:
2011-10-19 03:23:19
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digestion
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Ch. 23
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  1. digestive system falls into two groups
    alimentary canal; accessory digestive organs
  2. alimentary canal aka
    gastrointestinal tract/GI - is a continuous muscular digestive tube that winds through body. digests & absorbs food.
  3. organs of alimentary canal
    • mouth
    • pharynx
    • esophagus
    • stomach
    • small intestine
    • large intestine
  4. organs of accessory digestive organs
    • teeth
    • tongue
    • gall bladder
    • salivary glands
    • liver
    • pancreas
  5. main function of digestive system
    • take in food
    • break it down into the nutrient molecules
    • rid body of waste
  6. digestive process:
    ingestion
    propulsion
    mechanical digestion
    chemical digestion
    absorption
    defecation
    taking food into digestive tract (through mouth)
  7. digestive process:
    ingestion
    propulsion
    mechanical digestion
    chemical digestion
    absorption
    defecation


    ingestion
    propulsion
    mechanical digestion
    chemical digestion
    absorption
    defecation

    • move food through alimentary canal
    • (swallowing, peristalsis)
  8. digestive process:
    ingestion
    propulsion
    mechanical digestion
    chemical digestion
    absorption
    defection
    • chewing
    • mixing food with saliva
    • churning food in the stomach
    • segmentation
  9. 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
  10. digestive processes:
    ingestion
    propulsion
    mechanical digestion
    chemical digestion
    absorption
    defection
    food molecules are broken down to chemical building blocks by enzymes (into fats, carbs, proteins --> simple sugars, amino acids, fatty acids)
  11. digestive processes:
    ingestion
    propulsion
    mechanical digestion
    chemical digestion
    absorption
    defecation
    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
  12. digestive processes
    ingestion
    propulsion
    mechanical digestion
    chemical digestion
    absorption
    defecation
    eliminates indigesible substances from body
  13. prime means for regulation
    • control luminal conditions
    • - activity stimulated by mech/chem stimuli
    • - controls are intrinsic/extrinsic
  14. activity stimulated by mech/chem stimuli
    • 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.
  15. activity stimulated by mech/chem stimuli cont'd
    • 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
  16. controls of digestive activity that are int/extrinsic
    short/long reflexes
    • 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.
  17. controls of digestive activity that are int/extrinsic
    short/long reflexes cont'd
    • nerve fibers that excite smooth muscle secret Ach or substance P
    • inhibit: release vasoactive intestinal peptide or nitric oxide
  18. splanchnic circulation
    • 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
  19. histology of alimentary canal
    - mucosa
    - submucosa
    - muscularis externa
    - serosa
    • innermost layer.
    • moist epi. memb. that lines ali. canal lumen from mouth->anus
  20. histology of alimentary canal
    - mucosa functions
    - submucosa
    - muscularis externa
    - serosa
    • 1) secrete mucus, digestive enzymes, hormones
    • 2) absorb the end products of digestion into the blood
    • 3) protect against infectious disease
  21. histology of alimentary canal
    - mucosa sublayers & their functions
    - submucosa
    - muscularis externa
    - serosa
    • 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
  22. histology of alimentary canal
    - mucosa
    - submucosa
    - muscularis externa
    - serosa
    • areolar CT, contains rich supply of blood & lymphatic vessels, lymphod follicles, nerve fibers.
    • elastic fibers enable recoil in stomach
  23. histology of alimentary canal
    - mucosa
    - submucosa
    - muscularis externa
    -
    serosa
    • 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
  24. histology of alimentary canal
    - mucosa
    - submucosa
    - muscularis externa
    - serosa
    • 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
  25. nerve supply
    - enteric (aka intrinsic)
    - submucosal
    - myenteric
    • alimentary canal's "in-house" nerve supply.
    • communicates widely with one another to regulate digestive system activity
  26. nerve supply
    - enteric aka intrinsic
    - submucosal nerve plexus
    - myenteric
    • occupies the submucosa
    • includes sensory & motor neurons
    • chiefly regulates activity of glands and smooth muscle in the mucosa
  27. nerve supply
    - enteric aka intrinsic
    - submucosal
    - myenteric nerve plexus
    • 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

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