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1

structures of GI tract

oesophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (cecum, ascending, transverse, descending, sigmoid), rectum, anal canal

2

primary functions of GI system

motility, secretion, digestion and absorption

3

accessory organs

salivary glands, pancreas, liver, gallbladder, appendix

4

what is peritoneum

Serous membrane made of simple squamous epithelium with underlying thin layer of connective tissue

5

types of peritoneum

  1. Parietal peritoneum - lines abdominal and pelvic cavities

  2. Visceral peritoneum - covers external surfaces of most abdominal organs, including intestinal tract

  3. Mesentery - double layer of peritoneal membrane from the body wall to the organ - gives passage to blood vessels, nerves and lymphatics 

  4. Omentum - double layer of peritoneal membrane from organ to organ 

6

function of peritoneum

  • Form covering (partial or complete) for abdominal organs
  • Smooth lining - frictional surface
  • Hold organs in position
  • Omentum and mesentery serve as fat store
  • Fats of peritoneum prevents infections of abdominal organs

7

3 main subdivisions of abdominal GI blood supply

  • Celiac trunk supplies foregut with blood
  • Superior mesenteric supplies midgut with blood
  • Interior mesenteric supplies hindgut with blood

8

divisions of celiac trunk

common hepatic, left gastric and splenic arteries

9

divisions of superior mesenteric artery 

intestinal arteries, ileocolic artery, colic artery

10

divisions of inferior mesenteric artery

left colic artery, sigmoid arteries, superior rectal artery

11

why is there large blood supply to small intestine

maintain concentration gradient for absorption of nutrients from GI tract

12

4 layers of gut tube

  1. mucosa
    • has gland ducts
  2. submucosa
    • connective tissue
    • glands
    • nerves called meissners plexus
  3. muscularis
    • smooth muscle
    • myenteric plexus
    • inside = circular
    • outside = longitudinal
  4. adventitia
    • FCT

13

3 layers of mucosa

  1. epithelium - mucus secreting
  2. lamina propria (loose FCT)
    • lymph nodes
    • nerve fibres
    • blood vessels
  3. muscularis mucosa (thin layer of smooth muscle)

14

control of digestion

  • enteric NS (primary control - independent, short, local reflexes)
  • CNS (modulates activity of ENS - long neural reflexes)
  • hormones
  • receptors

15

types of epithelium in GI tract

  • Simple squamous in peritoneum

  • Simple cuboidal lining ducts

  • Simple columnar lining stomach to rectum - this is modified to carry out specific functions

  • Stratified squamous lining oesophagus and anal canal (hardwearing protects against abrasion)

  • Glandular epithelium secrete mucus in small intestine

16

how are epithelial cells in GI tract joined

joined by tight junctions, zonula adherens and spot desmosomes to form a continuous and relatively impermeable membrane

17

function of mouth in GI tract

mechanical digestion via mastication (chewing) 

18

3 pairs of salivary glands, where they are and what they secrete

  1. sublingual - under tongue, mainly mucous, 3-5% of total saliva
  2. parotid - anterior and inferior to ear, serous fluid, 25-30% of total saliva
  3. submandibular - floor of mouth, both mucous and serous fluid, 60-70% of totoal saliva 

19

how are salivary glands controlled

parasympathetic NS

20

function of saliva

  • moisten ingested material 
  • moistens, cleanses and lubricates structures of oral cavity
  • begins chemical digestion of carbohydrates with amylase
  • antibacterial action with lysozyme
  • dissolves food to stimulate taste receptors

21

structure of oesophagus

  • appears collapsed when there is no food going down
  • mucosal epithelium - protective stratified squamous
  • muscularis externa - move food bolus, transitions between skeletal and smooth

22

structure of oropharynx

  • posterior to oral cavity
  • contains palatine and lingual tonsils
  • stratified, squamous epithelium for protection

23

regions of stomach

  • fundus is round bit at top
  • cardia is where oesophagus joins
  • body is main region
  • pylorus is where it leads into duodenum
  • greater omentum attached to greater curvature
  • lesser omentum attached to lesser curvature

24

greater omentum structure and function

  • large apron-like fold of visceral peritoneum that hangs down from the stomach over the small intestines and doubles back up to the transverse colon
  • functions are fat deposition, immune contribution, infection isolation

25

structural features of stomach

  • pyloric sphincter separates stomach and duodenum - controlled release
  • lower oesophageal sphincter separates stomach from oesophagus - prevents gastric juices flowing up
  • 3 layers of smooth muscle: oblique (inside), circular and longitudinal - mechanical digestion
  • rugae are folds in inside of stomach - allow expansion

26

mucosal layer of stomach

  • infolding of epithelium forms pits and glands
  • glands contain mucous neck cells, chief cells, parietal cells and endocrine cells

27

functions of stomach

  1. storage of food - rugae
  2. mechanical digestion - 3 layers of muscularis externa
  3. chemical digestion - breakdown of proteins
  4. some absorption (fat soluble substances e.g. alcohol)

28

function of liver

accessory organ that produces bile salts, which emulsify lipids, aiding their digestion and absorption

29

chief cell function and structure

  • secretes enzymes – pepsinogen converted to pepsin
  • Has many rough ER
  • Tight junctions between them to prevent acid moving between them
  • granules near apical surface

30

parietal cell function and structure

  • Pumps H+
  • Lots of mitochondria
  • Large SA
  • Folded with microvilli