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DEMS: Unit 1 > Digestive System Overview > Flashcards

Flashcards in Digestive System Overview Deck (36):
1

General characteristics of GI system

  • oral cavity ==> anus
    • extracellular space/tube running through the body
  • responsible for the breakdown of consumed foods via enzymes in order to gain "building blocks" for cellular structures

2

Lining of the GI system (general)

  • tube (except esophagus and anal region) is lined by mucosae
  • mucosae = protective & creates a microenvironment
    • resistant to proteolytic digestion

3

Regulation/coordination of GI system (general)

  • intrinsic autonomic nerves = "enteric neurons"
    • control local gut motility
  • CNS input from parasympathetic/sympathetic
    • coordinates peristtalsis
    • affects blood vessels and glands
  • hormonal control via endocrine cells @ mucosal epithelium

4

Basic structures of layers in GI tract

  1. mucosa = epithelium + lamina propria
  2. submucosa = dense connective tissue
    1. large blood vessels, nerve plexes, glands, lymph nodes
  3. muscularis externa = smooth muscle + nerves
    1. inner muscular layer = circular
    2. outer muscular layer = longitudinal
    3. fxn = peristalsis & churning
  4. serosa/adventitia = outer squamous epithelial layer

5

Characteristics of mucosa layer

  • mucosa = epithelium + lamina propria
  • lamina propria = underying loose tissue + vasculature
    • contains scattered lymphs, plasma cells, macrophages
  • muscularis mucosae = thin smooth muscle layer underneath mucosa

6

Characteristics of the Esophagus

  • structure: 
    • muscular tube
      • upper 1/3 = skeletal m.
      • middle 1/3 = skeletal + smooth
      • lower 1/3 = smooth m.
    • lining = non-cornified squamous epithelium
    • some mucous glands, but lacks thick mucosal covering
    • small sphincter @ esophogeal-gastric jxn
  • function
    • conveys ingested material from pharynx to stomach
    • no digestive fxns

7

Characteristics of the Stomach structure (general)

  • structure
    • 3 zones
      • cardia = mucus glands near esophogeal entry
      • fundus = main body of stomach
      • pyloris = near intestinal end
    • ruguae ("plicae mucosae") = longitudinal folds that disappear w/distention
    • muscularis externa = 3 layers w/oblique layer deep to circular layer

8

Characteristics of stomach fxn (general)

  • chemical and mechanical digestion
  • hormone release
  • fundus
    • secretes acid, peptic digestive products, mucus
  • pyloris
    • secretes mucus
    • contains endocrine cells that secrete gastrin

9

Characteristics of the gastric epithelium

  • epithelium contains many folds w/mucous-secreting cells on the surface
  • gastric pits = between epithelial folds
    • epithelium @ deep portion of pits becomes tubular gastric glands = important in digestion @ acidic pH
  • types of epithelial cells
    • stem cells
    • surface mucous cells
    • chief cells
    • parietal cells
    • enteroendocrine cells

10

Stomach protections from autodigestion

  • stem cells 
    • surface cells replaced every 3-5 days
    • deep cells every 6-12 months
  • surface mucous cells
    • release mucins/bicarb
    • provides viscous protective layer from acid and abrasian
  • specialized digestive enzyme secretion
    • secrete inactive enzyme forms (e.g. pepsinogen) which are converted to active forms (e.g. pepsin) @ low pH

11

Characteristics of parietal cells

  • fxn = acid-producing cells
  1. pump protons into lumen of gastric glads against a steep gradiant
    • microvilli ==> large surface area
    • mitochondria ==> energy for active transport
  2. secrete intrinsic factor = required for uptake of vitamin B12
  • stimulated by gastrin (local hormone) and histamine

12

Characteristics of enteroendocrine cells

  • cells of the GI tract that produce hormones involved in regulation of digestion
  • many types present throughout digestic tract

13

A cells: location, hormone, hormonal action

  • location: stomach & small intestine
  • hormone: glucagon (entero-glucagon)
  • action: stimulates glycogenolysis by hepatocytes ==> elevated blood glucose

14

D cells: location, hormone, hormonal action

  • location: stomach, small & large intestine
  • hormone: somatostatin
  • action: inhibits release of hormones by other enteroendocrine cells nearby

15

EC cells: location, hormone, hormonal action

  • location: stomach, small & large intestine
  • hormone: 
    • stomach/small = serotonin
    • large = substance P
  • action: increases peristalsis

16

I cells: location, hormone, hormonal action

  • location: small intestine
  • hormone:cholecystokinin
  • action: stimulates release of pancreatic hormone and contration of gall bladder

17

K cells: location, hormone, hormonal action

  • location: small intestine
  • hormone: gastric inhibitory peptide
  • action: inhibts HCl secretion

18

ECL cells: location, hormone, hormonal action

  • location: stomach
  • hormone: histamine
  • action: stimulates HCl secretion

19

N cells: location, hormone, hormonal action

  • location:  small intestine
  • hormone: neurotensin
  • action:
    • increases blood flow to ileum
    • decreases peristaltic action of small/large intestines

20

S cells: location, hormone, hormonal action

  • location: small intestine
  • hormone: secretin
  • action: stimulates bicarb-rich fluid from pancreas

21

Segments of the small intestine

  • duodenum
    • pyloric sphincter = between stomach and duodenum
  • jejunum
  • ileum

22

Characteristics of structure of small intestine

  • fxn = major center of digestine and absorption
  • large surface area neccessary created by topographic features:
    • plicae circulares = transverse folds covered w/villi
    • enterocytes = absorptive/digestive eptithelial cells covered w/microvilli
  • goblet cells = mucous cells between enterocytes
  • other structures include:
    • intestinal glands
    • enteroendocrine cells
    • lymphoid tissue

23

Characteristics of intestinal glands

  • intenstinal glands = tubular glands = "crypts of Lieberkuhn"
  • "penetrate from the base of the villi deeper into the mucosa" (https://www.youtube.com/watch?v=Q8p1PPjht-I)
  • Paneth cells contain large eosinophilic granules w/defensin (antibacterial peptides)
  • Brunner's glands = only @ duodenum
    • secrete bicarb/mucins to neutralize stomach acid

24

Characteristics of intestinal villi

  • villi = loose lamina propria core + small blood vessels + some lymphatic structures
    • lymphatics =
      • lympocutes
      • small lymphatic spaces join @ lacteal (large lymph vessel)
    • lacteal = passes fluid + transports chylomicrons (lipoprotein dops)
  • capillaries ==> hepatic portal system
  • lacteal ==> lymphatic system ==> bloodestream

25

Characteristics of lymphoid tissue @ GI tract

  • lymph tissue @ GI = scattered + nodules
  • Peyer's patches = groups of lymphatic nodules
    • Plasma cells @ nodules release IgA ==> lumen to act as antibacterial agents

  • M-cells = antigen-uptake and presentation

26

Regional differences of small intestine: Brunner's glands

  • Duodenum = present
  • Jejunum = absent
  • Ileum = absent

27

Regional differences of small intestine: Goblet cells

  • Duodenum = +
  • Jejunum = ++
  • Ileum = +++

28

Regional differences of small intestine: lymphatic tissue

  • Duodenum = +
  • Jejunum = ++
  • Ileum = ++++

29

Regional differences of small intestine: plicae circulares

  • Duodenum = +
  • Jejunum = best developed
  • Ileum = +

30

Regional differences of small intestine: numer of villi

  • Duodenum = most numerous
  • Jejunum = decrease distally
  • Ileum = less abundant

31

Structure of exocrine pancreas

  • acini = clusters of pancreatic acinar cells arranged at the end of a common duct
    • @ basal portion = rough ER for protein synthesis
    • @ apical = zymogen granules = secretory granules
    • centroacinar cells = begining of duct system: secrete pancreatic juice (water + bicarb)
  • secreted enzymes ("zymogens") pass through progressively larger ducts ==> main pancreatic duct ==> common bile duct near entry to duodenum

32

Enzymes released by pancreas

  • zymogens = inactive enzymes released by pancrease; require partial degredation before becoming active
    • e.g. trypsin, chymotrypsin, elastase, carboxypeptidase, tracylglycreol lipase
  • trypsinogen (pro-trypsin) is released and activated by entorokinase @ duodenal apical membrane
  • trypsin activates other zymogens
  • certain enzumes released in active form
    • amylase ==[starch & glucose]
    • ribonuclease ==[RNA]

33

Locations/mechanisms of digestion (general)

  • Oral cavity
    • mechanical
    • enzymatic (e.g. amylase)
  • Stomach
    • mechanical
    • chemical (pH)
    • enzymatic (pepsin)
  • Small intestine
    • enzymatic (pancreatic enzymes)
    • @ glycocalyx (=glycoprotein layer at the surface of enterocytes)
      • e.g. starch, lactose

34

Characteristics of paristalsis (general)

  •  muscularis externa = inner circular and outer longitudinal layers
  • provides for movement of luminal contents by peristalsis
  • segmented movement = alternate contraction and relaxation of segments cause ==> agitates the lumenal contents
  • Efferent fibers of the myenteric nerve plexus (of Auerbach) innervate the externa. 

35

Characteristics of large intestine

  • major regions  = cecum and appendix, transverse and descending colons, and the rectum 
  • structure
    • smooth, lacks plicae and villi
    • contains tubular glands/cyrpts
    • cells = mucous producing & absorptive
    • contains many lymphocytes
    • very muscular wall
  • fxn
    • recovery of water and salt
    • concentration of fecal material

36

Characteristics of oral cavity

  • major fxn = initiate digestion via chewing + saliva
  • salivary glands
    • submandibular = mixed secretor
    • sublingual = mucous secretor
      • mucous = lubricative adn protective
    • parotid glands = serous secretor
      • serous secretions = watery w/enzymes and IgA