digestive system

gastrointestinal tract

mouth --> pharynx --> esophagus --> stomach --> small intestine --> large intestine --> anus

accessory organs

aid in digestion but no food passes

hard palate

bony anterior roof of mouth; separates oral + nasal cavity

soft palate

muscular posterior, rises during swallowing to block nasopharynx

pharynx

nasopharynx (behind nose), oropharynx (behind mouth), laryngopharynx (leads to esophagus/larynx)

voluntary phase swallowing

bolus pushed to hard palate then to oropharynx

pharyngeal phase swallowing

bolus moves into oropharynx, soft palate + uvula closes nasopharynx, larynx elevates so epiglottis closes laryngeal opening

esophageal phase swallowing

peristaltic contractions of esophageal, everything returns to pre-swallowing position

filiform

most numerous on tongue, no taste buds

fungiform, foliate, vallate

contain taste buds

taste buds

- have gustatory cells w/microvilli

- sends signal thru sensory nerves

basal cells

taste buds regenerate here

facial nerve CN VII

carries taste from anterior 2/3 tongue

glossopharyngeal nerve CN IX

carries taste from posterior 1/3

gustatory pathway signal travels

to medulla, thalamus, gustatory cortex

insula

interprets taste perception + quality

parietal peritoneum

lines abdominal wall

visceral peritoneum

covers abdominal organs

peritoneal cavity

greater sac, lesser sac, ligaments + omenta

greater sac

main space btwn parietal and visceral layers

lesser sac

small space behind stomach

ligaments + omenta

folds of peritoneum that support organs + carry vessels

mesentery

double layer of peritoneum that suspends organ from abdominal wall, allows organs to be mobile but supported

mesentry contains

blood vessels, lymphatics, and nerves

omentum

double layer of peritoneum that connects stomach to other organs

stomach longitudinal muscle

outermost, shorten stomach

stomach circular muscle

middle, constricts lumen

stomach oblique muscle

innermost, aids churning + twisting

rugae

internal folds, allowing expansion after eating

cardiac orifice

entry point from esophagus, guarded by lower esophageal sphincter

what does cardiac orifice prevent

acid reflux into esophagus

pylorus

exit of stomach, guarded by pyloric sphincter

pylorus function

regulates emptying of chyme into duodenum

small intestine

duodenum, jejunum, ileum

duodenum

receives bile + pancreatic enzymes

- primary site for chemical digestion

jejunum + ileum

suspended by mesentery

jejunum

nutrient absorption

ileum

absorbs bile salts + connects cecum to ileocecal valve

haustra

pouch-like sacs from segmental contractions

teniae coli

three longitudinal muscle bands

cecum + ileocecal junction

entry point from small intestine

vermiform appendix

immune role, possible site of appendicitis

colon

water + electrolyte absorption

rectum + anal canal

fecal storage + controlled elimination

rectum transitions into anal canal forming?

right-angle bend

puborectalis muscle

muscle that maintains anal angle, part of pelvic diaphragm

internal anal sphincter

involuntary control

external anal sphincter

voluntary control

defecation

puborectalis must relax

celiac artery

supplies blood to stomach, liver, pancreas, spleen, duodenum (1st hald)

superior mesentric artery

supplies blood to duodenum (2nd half), jejunum, ileum, cecum, ascending + transverse colon

inferior mesenteric artery

supplies blood to descending colon, sigmoid colon, rectum

venous drainage

blood drains via hepatic portal vein to liver for processing

hepatic portal vein formed by

gastric, splenic, superior + inferior mesenteric veins

portal-systemic anastomosis

provide collateral circulation during portal hypertension

backup in circulation causes?

varices (dilated veins) at esophagus, rectum, umbilicus

dilated veins are dangerous bc

can rupture + be life-threatening

4 layers of GI system from inside to outside

mucosa, submucosa, muscularis externa, serosa/adventitia

mucosa sublayers

epithelium, lamina propria (CT), muscularis mucosae

mucosa function

barrier, secretion, absorption, immune surveillance

epithelium stratified

for protection

epithelium simple columnar

for secretion/absorption

lamina propria

loose CT, houses MALT

muscularis mucosae

smooth muscle, innervated by submucosal plexus of enteric nervous system

submucosa

dense irregular CT + contains large blood + lymphatic vessels

submucosa innervated by

submucosal plexus --> regulate secretions + blood flow

what regulates submucosa

ANS (ENS)

muscularis externa function

peristalsis + segmentation (mixing)

muscularis externa inner layer

circular

muscularis externa outer layer

longitudinal

muscularis externa innervation

myenteric plexus --> coordinates peristalsis

muscularis externa specializations

form sphincters + valves

esophagus + external anal sphincter muscularis externa

striated skeletal muscle

stomach muscularis externa

has oblique muscle layer for enhanced mixing

large intestine muscularis externa

has teniae coli

enteric nervous system

regulates secretion, motility, local blood flow independently

ENS modulated by

CN X (parasympathetic input) --> stimulates GI activity, celiac plexus (sympathetic input) --> inhibits GI activity, hormonal signals

serosa

mesothelium + found in intraperitoneal organs

adventitia

CT + found in retroperitoneal/non-peritoneal organs

secretion

mucosal glands, submucosal glands, extramural glands

absorption

rugae, plicae circularis, villi + microvilli, glycocalyx

esophagus

lined w/non-keratinized stratified squamous epithelium

- has submucosal glands for lubrication

- has muscularis externa (skeletal --> smooth)

GERD

stratified squamous changes to columnar at a quick rate

barrett's esophagus

metaplasia bc of chronic acid exposure

stomach

both exocrine + endocrine function

stomach epithelial transition

stratified squamous --> simple columnar + invaginates into gastric pits

gastric ulcers

mucosal barrier breakdown causes ulcers

surface mucous cells

secrete alkaline mucin to protect lining

mucous neck cells

secrete acidic mucin

parietal cells

secrete HCl + intrinsic factor (B12)

chief cells

secrete pepsinogen + gastric lipase

G cells

secrete gastrin, stimulates parietal cells

stem cells

located in neck region

parietal cells have

a lot of mitochondria + intracellular canaliculi for increase SA for secretion

pernicious anemia

loss of intrinsic factor bc autoimmune destruction of parietal cells

crypts of lieberkuhn

simple tubular glands

celiac disease

autoimmune reaction to gluten that damages villi in small intestine

small intestine surface area adaptations

plicae circularis, villi, enterocytes

enterocytes

absorption, form brush border to maximize SA

goblet cells

mucin secretion, produce mucus to lubricate + protect epithelium