A&P II Digestive System

digestive system

organ system that processes food, extracts nutrients, and eliminates residue

ingestion

selective intake of food

digestion

mechanical and chemical breakdown of food into a form usable by the body

absorption

uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood and lymph

compaction

absorbing water and consolidating the ingestible residue into feces

defecation

elimination of feces

mechanical digestion

the physical breakdown of food into smaller particles; cutting and grinding action of the teeth; churning action of stomach and small intestines; exposes more food surface to digestive enzymes

chemical digestion

a series of hydrolysis reactions that break dietary macromolecules into their monomers; carried out by digestive enzymes produced by salivary glands, stomach, pancreas, and small intestines

digestive tract (alimentary canal)

30 ft long muscular tube extending from mouth to anus; mouth, pharynx, esophagus, stomach, small intestine, and large intestine; gastrointestinal tract (GI) tract is the stomach and intestines

accessory organs

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

mucosa (mucous membrane)

lines the lumen

lamina propria

loose connective tissue

muscularis mucosal

thin layer of smooth muscle

submucosa

thicker layer of loose connective tissue; contians blood vessels, lymphatic vessels, a nerve plexus, and in some places mucus-secreting glands that dump lubricating mucus into the lumen

muscularis externa

consists of usually 2 layers of muscle near the outer surface; responsible for the motility that propels food and residue through the tract

inner circular layer

cells encircle tract

outer longitudinal layer

cells run longitudinally

serosa

composed of a thin layer of areolar tissue topped by simple squamous mesothelium; begins in the lower 3 to 4 cm of the esophagus, ends just before the rectum

enteric plexus

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

submucosal plexus

found in submucosa; controls glandular secretions of mucousa, and movements of muscularis mucosae

myenteric plexus

ganglia and nerve fibers between the 2 layers of the muscalaris external; controls peristalsis and other contractions of muscularis externa

mesentery

connective tissue sheet that suspends stomach and intestines from abdominal wall

lesser omentum

a ventral mesentry that extends from the lesser curvature of the stomach to the liver

greater omentum

hangs from the greater curvature of the stomach (its left inferior margin); covers small intestine like an apron

mesocolon

portion of mesentry that anchors transverse colon to posterior abdominal wall

intraperitoneal

when an organ is enclosed by mesentery (serous) on both sides; stomach, liver, and parts of small and large intestine

retroperitoneal

when an organ lies against the posterior body wall and is covered by peritoneum on its anterior side only; considered to be outside the peritoneal cavity; duodenum, pancreas, and parts of the large intestine (ascending colon, descending colon, and rectum)

short (myenteric) reflexes

stretch or chemical stimulation acts through myenteric plexus; stimulates peristaltic contractions of swallowing

long (vasovagal) reflexes

parasympathetic stimulation of digestive motility and secretion

oral fissure

anterior opening between lips

fauces

posterior opening to the throat

labial frenulum

median fold that attaches each lip to the gum between the anterior incisors

vestibule

space between cheeks or lips and the teeth

tongue

muscular, bulky, but agile and sensitive organ; manipulates food between teeth, senses taste and texture food

lungual papillae

bumps and projections that are the sites of most taste buds

vallate papillae

a V-shaped row of papillae that mark the boundary between the body and root of the tongue

terminal sulcus

groove behind the vallate papillae

lingual frenulum

median fold that attaches the body of the tongue to the floor of the mouth

lingual glands

serous and mucus glands within tongue, amid the extrinsic muscles; secrete a portion of the saliva

lingual tonsils

contained in the root

palate

separate oral cavity from nasal cavity

hard (bony) palate

anterior portion that is supported by the palatine processes of the maxillae and the palatine bones

palatine rug

transverse ridges that help the tongue hold and manipulate food

soft palate

posterior to hard palate with more spongy texture

uvula

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

teeth

collectively called the dentition

mandible

lower jaw

maxilla

upper jaw

incisors

chisel-like cutting teeth used to bite off a piece of food

canine

pointed teeth that act to puncture and shred food

premolars

broad surface teeth for crushing, shredding, and grinding

molars

even broader surface teeth for crushing, shredding, and grinding

periodontal ligaments

modified periosteum whose collagen fibers penetrate into the bone on one side and into the tooth on the other; anchors tooth firmly in alveolus; allows slight movement under pressure of chewing

gingiva (gums)

covers the alveolar bone

crown

portion of the tooth above the gum

root

portion of the tooth below the gum, embedded in alveolar bone

neck

point of the tooth where 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

noncellular secretion that cannot regenerate; covers crown and neck of tooth

cement

covers root

root canal

space in root leading to pulp cavity in the crown; contain nerves and blood vessels

apical foramen

pore at the basal end of each root canal

plaque

sticky residue on teeth made of bacteria, sugars

gingivitis

gum inflammation

peridontal disease

when gingivitis progresses to affect bone

mastication (chewing)

breaks food into smaller pieces to be swallowed and exposes more surface to digestive enzymes

mucus

binds and lubricates a mass of food and aids in swallowing

lysozyme

enzyme that kills bacteria

immunoglobulin A (IgA)

antimicrobial antibody

salivary amylase

enzyme that begins starch digestion on the mouth

lingual lipase

enzyme that begins fat digestion in the mouth (but mainly after the food is swallowed)

intrinsic (minor) salivary glands

small glands dispersed amid other oral tissues; secrete saliva at constant rate (whether we are eating or not)

extrinsic (major) slaivary glands

three pairs of larger, more discrete organs connected to oral cavity by ducts

parotid glands

located beneath the skin anterior to the earlobe; parotid duct passes over master, peirces buccinator, and opens into mouth

submandibular gland

lacated halfway along the body of the mandible; duct empties at the side of the lingual frenulum, near the lower central incisors

sublingual gland

located in the floor of the mouth; has multiple ducts that empty posterior to the papilla of the submandibular duct

pharynx

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

esophagus

straight muscular tube 25 to 30 cm long between pharynx and stomach

heartburn

burning sensation produced by acid reflux into the esophagus

swallowing or deglutition

a complex action involving over 22 muscles in the mouth, pharynx, and esophagus

oral phase of swallowing

under voluntary control; tongue collects food, presses it against palate forming bolus, and pushes it posteriorly; food accumulates in oropharynx in front of epiglottis; epiglottis tips posteriorly and food bolus slides around it and into laryngopharynx

pharyngeal pahse of swallowing

involuntary; prevents food and drink from reentering mouth or entering the nasal cavity; breathing is suspended; infrahyoid muscles pull larynx up to meet epiglottis and cover laryngeal opening; vocal cords adduct to close airway; upper esophagus widens; food bolus is driven downward of constriction of the upper, then middle, and finally the lower pharyngela constrictors

esophageal pahse of swallowing

waves of involuntary contractions called peristalsis; peristalsis coordinated by both swallowing center and myenteric pplexus in esophageal wall; circular muscle constricts above bolus, relaxes below bolus; when standing or sitting upright, food and liquid drops through esophagus by gravity faster than peristalsis can keep up with itl peristalsis ensures you can swallow regardless of body position; liquid reaches the stomach in 1 to 2 seconds; food bolus in 4 to 8 seconds; when it reaches lower end of the esophagus, the lower esophageal sphincter relaxes to let food pass into the stomach

stomach

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

cyme

acidic, soupy mixture of semidigested food that passes on to the small intestine

cardiac part

small area within about 3 cm of the cardiac orifice

fundic region (fundus)

dome superior to the esophageal attachment

body

makes up the greatest part distal to cardiac orifice

pyloric part

narrower pouch at the inferior end

pylorus

narrow passage to duodenum

pyloric sphincter

ring of smooth muscle around pylorus; regulates the passage of chyme into the duodenum

gastric pits

depressions in gastric mucosa, lined with the same columnar epithelium as the surface

mucous cells

predominate in cardiac and pyloric glands; secrete mucus

regenerative (stem) cells

found in the base of pit and in neck of gland; divide rapidly and produce continual supply of new cells to replace cells that die

parietal cells

found mostly in the upper half of the gland; secrete hypochloric acid (HCl), intrinsic factor, and a hunger hormone called ghrelin

chief cells

most numerous cell type; secrete gastric lipase and pepsinogen; dominate lower half of gastric glands; absent from pyloric and cardiac glands

eteroendotocrine cells

concentrated in lower end of a gland: secrete hormones and paracrine messengers that regulate digestion; at least eight kinds of these cells, each which produces a different chemical messenger

gastric juice

2 to 3 L per day produced by the gastric glands; mainly a mixture of water, hydrochloric acid, and pepsin

zymogens

digestive enzymes secreted as inactive proteins; converted to active enzymes by removing some of their amino acids