A&P Chapter 25: Digestive System

digestive system

organ system that processes food, extracts nutrients and eliminates residue

five stages of digestion

ingestion, digestion, absorption, compaction and defecation

mechanical digestion

the physical breakdown of food into smaller particles, chewing food, increases surface area of food

chemical digestion

a series of hydrolysis reactions that breaks dietary macromolecules into their monomers, carried out by digestive enzymes produced by salivary glands 

digestive tract (alimentary canal

30 ft muscular tube from mouth to anus, mouth, pharynx, esophagus, stomach, small intestine and large intestine 

gastrointestinal (GI) tract 

stomach and intestines 

accessory organs

teeth, tongue, salivary glands, lier, gallbladder and pancreas

enteric nervous system

nervous network in esophagus, stomach, intestines that regulates digestive tract motility, secretion and blood flow, function independently of CNS

submucosal plexus

in submucosa, controls glandular secretions of mucosa and movements of muscularis mucosa 

myenteric plexus 

parasympathetic ganglia and nerve fibers between the two layers of the muscularis externa, controls peristalsis 

mesenteries 

connective tissue sheets that suspend stomach and intestines from abdominal wall 

parietal peritoneum

a serous membrane that lines the wall of the abdominal cavity

lesser omentum

a ventral mesentery that extends from the lesser curvature of the stomach to the liver, anchor 

greater omentum

hangs from the greater curvature of the stomach, concentrate and stores adipose tissue in abdominal pelvic cavity 

mesocolon 

extension of the mesentery that anchors the colon to the abdominal wall 

intraperitoneal

when an organ is enclosed by mesentery on both sides,

retroperitoneal

when an organ lies against the posterior body wall and is covered by peritoneum on its anterior side only

short (myenteric) reflexes 

stretch of chemical stimulation acts through myenteric plexus 

long (vagovagal) reflexes

parasympathetic stimulation of digestive motility and secretion

hormones

chemical messengers secreted into the bloodstream that stimulate distant parts of the digestive tract 

paracrine secretions

chemical messengers that diffuse through the tissue fluids to stimulate nearby target cells

oral cavity

ingestion, taste, chewing and chemical digestion, swallowing, speech and respiration

tongue

muscular, bulky, agile and sensitive organ, manipulates food between teeth, senses taste and texture of food, nonkeratinized stratified squamous epithelium 

lingual papillae

bumps and projections that are the sites of most taste buds

palate

separates oral cavity from nasal cavity

hard (bony) palate

anterior portion, supported by palatine processes of the maxillae and the palatine bones

soft palate

posterior with a more spongy tissue, composed of skeletal muscle and glandular tissue, no bone

uvula

conical medial projection visible at the rear of the mouth, helps retain food in the mouth until one is ready to swallow 

crown

portion above gum

root

the portion below the gum, embedded in alveolar bone 

neck 

the point where the crown, root and gum meet 

gingival sulcus

space between the tooth and the gum

dentin

hard yellowish tissue that makes up most of the tooth

enamel

covers crown and neck, noncellular secretion that cannot regenerate

root canal

space in a root leading to pulp cavity in the crown 

apical foramen

pore at the basal end of each root canal

occlusion

meeting of the teeth with the mouth closed

plaque

sticky residue on the teeth make up of bacteria and sugars

mastication

chewing, breaks food into smaller pieces to be swallowed and exposes more surface to digestive enzymes, first step in mechanical digestion 

saliva

moistens mouth, begins starch and fat digestion, cleanses teeth, inhibits bacterial growth

bolus

mass swallowed as a result of saliva binding food particles into a soft, slippery, easily swallowed mass 

pharynx

muscular funnel connecting oral cavity to esophagus and nasal cavity to larynx

esophagus

straight muscular tube 25-30 cm long, extends from pharynx to cardial orifice of stomach

lower esophageal sphincter

food pauses here because of constriction, prevents stomach contents from regurgitating into the esophagus 

heartburn

burning sensation produced by acid reflux into the esophagus, digestive juices making their way up the esophagus 

deglutition

swallowing 

stomach

a muscular sac in upper left abdominal cavity immediately inferior to the diaphragm, functions as a storage organ 

chyme

soupy or pasty mixture of semi-digested food in the stomach, bolus + digestive enzymes 

mucous cells

secrete mucus, predominate in cardiac and pyloric glands

chief cells

secrete gastric lipase and pepsinogen

mucous coat

thick, highly alkaline mucus resists action of acid and enzymes

cephalic phase

stomach being controlled by brain

gastric phase 

stomach controlling itself

intestinal phase

stomach being controlled by small intestine

liver

makes and secretes bile, reddish brown gland located immediately inferior to the diaphragm

gallbladder

store and concentrate bile, adheres to a depression on the inferior surface of the liver between right and quadrate lobes, pear shaped sac

hepatocytes

absorb nutrients from blood, break down stored glycogen into glucose, remove and degrade hormones, toxins, bile pigments and drugs, secrete products into the blood

bile canaliculi

narrow channels into which the liver secretes bile

common hepatic duct

formed from the convergence of right and left hepatic ducts on inferior side of liver

cystic duct

coming from gallbladder joins common hepatic duct

bile duct

formed from union of cystic and common hepatic ducts

bile 

yellow-green fluid containing minerals

pancreas

spongy retroperitoneal gland posterior to greater curvature of stomach, blood sugar regulation

hepatopancreatic sphincter

controls release of both bile and pancreatic juice into the duodenum

acetylcholine

from vagus and enteric nerves, stimulates acini to secrete enzymes during cephalic phase of gastric control even before food is swallowed 

cholecystokinin

secreted by the mucosa of duodenum in response to arrival of fats in small intestine, relaxes hepatopancreatic sphincter to discharge bile into the duodenum 

secretin 

released from duodenum in response to acidic chyme arriving from stomach, neutralizes stomach acid 

small intestine

where chemical digestion and nutrient absorption occur, coiled mass filling most of abdominal cavity 

duodenum

first region of small intestine, begins at pyloric valve, recieves stomach contents, pancreatic juice and bile, stomach acid is neutralized here, pepsin is inactivated

jejunum 

2nd section of small intestine, most digestion and nutrient absorption occurs here 

ileum

last part of small intestine,