Digestive System

GI tract wall

• mucosa

• submucosa

• muscularis externa

mucosa function

• secrete mucus, enzymes, hormones

• absorb digestion end products

submucosa

• contain submucosal nerve plexus / ENS component

muscularis externa

• GI tract motility

• contain myenteric nerve plexus

GI muscle tone

firmness of muscle when it is relaxed

where is muscle tone found in

sphincter muscles

sphincter muscle function

• regulate food movement

• prevent backflow

digestion system functions

• ingestion

• digestion

• propulsion / motility

• absorption

• defecation

mouth activities

• ingestion

• digestion

• absorption

• motility

mouth ingestion

taking in any substance e.g. food

mouth digestion

• mechanical = chewing

• chemical = salivary amylase and lingual lipase

mouth absorption

mostly none!

mouth motility

swallowing

swallowing phases

• buccal phase

• pharyngeal-esophageal

• peristalsis / gastro-esopahgeal

buccal phase of swallowing: where does food go, structures involved

UES relaxes

food: mouth → pharynx

pharyngeal-esophageal phase: where does food go, structures involved

food: pharynx → esophagus

UES closes

peristalsis / gastroesophageal phase: where does food go, structures involved

food: esophagus → stomach

gastroesophageal sphincter closes

saliva functions

cleanse mouth, dissolve food, breakdown starch

stomach general functions

• storage

• secrete gastric juice

• churn food & secretions = chyme

stomach activities

• chemical digestion

• motility

• absorption

stomach chemical digestions

• gastric gland secretions

• cells at gastric glands

gastric gland cells

• surface mucous cell

• chief cell

• parietal cell

• enteroendocrine cell

surface mucous cell

secrete mucous to prevent stomach lining digestion

chief cell

produce pepsinogen and gastric lipase

parietal cell

secrete HCI and intrinsic factor

enteroendocrine cells

secrete hormones e.g. gastrin

gastrin

stimulates parietal cells to secrete HCI

stomach absorption

minimal e.g. alcohol and medication

small intestine activities

• absorption

• motility

• digestion — chemical and mechanical

small intestine absorption

• organic molecule / nutrients absorbed

• nutrients → liver for metabolism

small intestine motility

• segmentation

• migrating motility complex (peristalsis)

small intestine mechanical digestion

segmentations

small intestine chemical digestion

brush border enzymes and substances

small intestine substances

• pancreatic juice from pancreas

• bile from gallbladder and liver

pancreatic juice components and function

bicarbonate → neutralize acid / maintain basic pH

pancreatic enzymes → amylase, lipase, coenzymes / inactive protease

bile components

bilirubin — break down hb

bile salt — mechanically break down lipids

brush border

microvilli of membrane, breaks down carbs and lipids

large intestine activities

• chemical digestion

• absorption

• motility

• defecation

large intestine chemical digestion

bacteria at cecum ferment carbs

large intestine motility

• haustral contractions (slow segmentation)

• mass movement (slow peristalsis)

which fibers are responsible for defecation

PSNS fibers