CH 35 - gastrointestinal structure & function

length of GI tract

7 m running from mouth to butt

GI tract consists of

oral cavity; pharynx; esophagus; stomach; small intestine; large intestine

function of oral cavity

breaks up food

function of pharynx (throat)

swallowing

function of esophagus

transports food

function of stomach

stores & churns food

function of small intestine

absorption

function of large intestine

reabsorbs water & stores poop

parts located OUTSIDE GI tract

salivary glands; pancreas; liver; gallbladder; bile ducts

function of salivary glands

• saliva

• starts carbohydrate digestion

function of pancreas

secrete pancreatic enzymes

function of liver

MAKES bile

function of gallbladder

STORES & SECRETES bile

function of bile ducts

transport bile

the site of initial breakdown of nutrients into a usable form

the mouth (oral cavity & salivary glands)

food is broken down & moistened by

saliva

3 pairs of salivary glands (= 6 total)

• parotid

• submandibular

• sublingual

mumps disease

• swelling of the PAROTID salivary glands

• puffy cheeks & jaw pain

halitosis (bad breath)

caused by reduced saliva (dry mouth) cs it allows odor-causing bacteria to thrive

pharynx

• serves as entryway for respiratory & GI systems

• transports food to esophagus

• protects airway from aspiration/inhalation of food particles

esophagus

• transports food (food tube)

• food facilitated by stratified squamous epithelium

• includes the lower esophageal sphincter (LES)

lower esophageal sphincter (LES) aka cardiac sphincter

• above juncture of the lower esophagus & stomach

• remains constricted

• prevents highly acidic gastric contents from moving up

if the lower esophag. sphincter (LES) is not working properly, it can lead to

reflux (GERD) or heartburn/dyspepsia

barrett’s esophagus

condition where tissue lining of esophagus changes due to stomach acid exposure from GERD

the site of initial digestion of proteins (pepsin)

the stomach

stomach

• reservoir for food, mixing, & digestion

• secretion of HCl, intrinsic factor, & gastrin

• normal capacity: 1000-1500mL

stomach consists of

cardia; fundus; body; antrum; pylorus

part of stomach that differs from every other part because of the absence of ugae

antrum

pylorus/pyloric sphincter

• sphincter btwn stomach/duodenum

• controls gastric emptying

• limits bile reflux

specialized cells in the stomach

chief; parietal; mucous; & gastrin cells

chief cells

• digestive enzymes

• secrete pepsinogen (inactive form of pepsin)

parietal cells

PRODUCE HCl & intrinsic factor (enhances vit. B12 absorption)

mucous cells

• neutralize acid

• protect stomach wall

• produce an alkaline mucus

gastrin cells

• located in the ANTRAL EPITHELIUM

• have surface microvilli that monitor intragastric pH

longest portion of the GI tract

stomach intestine (5-6 cm long)

small intestine

• digestion & absorption of nearly ALL nutrients

• absorbs bile salts in terminal ileum

• secretin & cholecystokinin (enzymes) secreted by intestinal mucosa

parts of small intestine

• duodenum (first 22 cm)

• jejunum

• ileum

• ileocecal sphincter

ileocecal sphincter

• area where food passes into large intestine

• normally closed to prevent reflux

• peristalsis causes valve//sphincter to open

peristalsis

wave-like muscle contraction & relaxation that moves food/fluid/wastes through the digestive tract

plicae circulares (in small intestine)

circular folds of mucous membrane

intestinal villi (in small intestine)

• fingerlike projections contained in the lining

• increase surface are for digestion & absorption of nutrients by 600 times

microvilli (in small intestine)

• microscopic projections covered w/ a fuzzy coat called BRUSH BORDER

• contains many digestive enzymes

crypts of lieberkuhn (in small intestine)

intestinal glands that secrete abt 2L of fluid/day

goblet cells & brunner glands

secrete large amounts of mucus to protect small intestines from acidic gastric juices

brunner glands are located in the

1st few centimeters of the duodenum

large intestine

• forms frame around small intestine

• contains no villi or digestive enzymes

• primarily (re)absorbs (water & electrolytes)

• storage of poop

• goblet cells produce mucus

parts of the large intestine

• (vermiform) appendix (worm shaped tube)

• colon (cecum to rectum)