Digestive systems Flashcards
gastro - intestinal (GI) system
oral cavity (teeth, tongue, palate)
pharynx
oesophagus
stomach
small intestine (duodenum, jejunum, ileum secretions from liver + pancreas)
large intestine (ilio-caecal junction, caecum, ascending, transverse, descending + sigmoid colons, rectum, anus)
salivary glands
3 major pairs
serous (watery) or mucus (thick) secretions
parotid glands - serous fluid into oral cavity via very long duct
submandibular glands - seromucous into OC via long duct
sublingual glands - mucous fluid into OC via several short ducts
lots of minor SG secrete continuously
oral cavity
hard+ soft palates, gingivae (gums), uvula, palatine tonsils, tongue, opening of submandicular ducts
oral epithelium (stratified squamous) on basement membrane on lamina propria
3 basic regions of oral mucosa;
-masticatory - gingivae + hard palate, stratified squamous (keratinised, v strong)
-specialised - tongue surface, incorporates taste buds
-ordinary lining - everywhere else, strat squa (non keratinised)
OC - tongue
mash food against teeth + hard palate
1/3 posterior- lingual tonsil
2/3 anterior- covered in many taste buds
taste buds found in relation to 4 different papillae (bumps) on dorsal surface of tongue
-filiform, fungiform, circumvallate, foliate
sweet, sour, salty, bitter, umami
pharynx
sits posterior to oral cavity
-nasopharynx, oropharynx, laryngopharynx
allows food from OC -> oesophagus
3 constrictor muscles stacked, squeeze to move food inferiorly
oesophagus
muscular tube carries masticated food from pharynx -> stomach
pass through diaphragm to enter abdomen
2 important transitions:
>muscular - skeletal in superior, smooth in inferior, mixed in middle
>histology- epithelium stratified squamous non keratinised (SSNK) to simple columnar in stomach
transitions sharply at gastro-oesophaegal junction
hollow tube (GI tract aside from oral cavity + pharynx)
4 key layers
4 key layers:
mucosa- epithelium (simple columnar), lamina propria, muscularis mucosa
submucosa
muscularis externa- inner circular fibres + outer longitudal fibres (peristalsis_
adventitia/serosa
enteric nervous system
2 plexi (networks) of nervous system tissues
> meissner’s plexus- associated with muscularis mucosae. regulates fluid secretion + absorption as well as blood flow
> averbach’s plexus- muscularis externa + regulates motility in GI tract
stomach
breakdown solid food mechanically and chemically to semi-solid chyme
digest protein using pepsin
regulate rate of passage into duodenum
create intrinsic factor
proximal end guarded by lower oesophaegal (/cardiac) sphincter
distal end guarded by pylorus sphincter (duodenum regulation)
secretory sheet- large amounts of mucus needed to protect epithelium from low pH
parietal cells- produce HCl + intrinsic factor (B12 absorption)
chief cells- produce pepsin
endocrine cells- G cells -> gastrin -> D cells -> somatostatin
small intestine
duodenum (25cm)
jejunum (1m)
ileum (2m)
(proximal -> distal)
very tightly folded in abdomen
absorption of products of digestion into blood
3 components structurally quite similar
SI - duodenum
recieves chyme from stomach
pyloric sphyncter-> superior part -> descending -> horizontal -> ascending
many mucus glands (protect from acid)
bile produced in liver + stored in gall bladder- acts as surfactant + aids emulsification of fats
pancreatic juice + digestive enzymes eg amylase, lipase secreted intermittently
reach duodenum through shared duct emerging from second (descending) part
when chyme enters:
1)sphincter guarding Ampulla relaxes
2)gall bladder contracts
3)bile + pancreatic juice exits into duo + mix with chyme
SI - jejunum + ileum
principle site of nutrient absorption
peristalsis propels food along track (controlled by Au plexus)
specializations to increase SA:
-plicae circularis (circular folds) of submucosa
-villi in mucosal layer
-microvilli form brush border on apical plasma membrane
lining harsh + hostile environment
crypts of Lieberkuhn - invaginations between villi filled with stem cells to replace cells
simple cuboidal epithelium
-comprises enterocytes (intestinal absorptive cells - breakdown + transport of small molecules)
ilio - caecal junction + appendix
small -> large intestine
food arrives 3-4 hours after swallowing
entrance to caecum guarded by ilio-caecum valve
large intestine
absorption of water + ions
longitudal muscle layer forms 3 ribbons of muscles
contracted intestine forms bulges - haustra
peristalsis continues, strong waves 3/4 times a day
deep crypts of lieberkuhn - extend deep towards submucosa
anal canal
rectum remains empty until recieves faeces from sigmoid colon
when rectal walls distend - defecation triggered
1)contraction of colon
2)relaxation of involuntary anal sphincter
3)relaxation of voluntary anal sphincter
transition from simple columnar intestinal epithelium back to stratified squamous non keratinised
