A&P II - Digestive System

Purpose of digestive system

provide nutrients for cells

how things move and are changed by movement

motility

chemical breakdown of large molecules into its smaller components

digestion

moving building block molecules from the lumen of the GI tract to the blood or lymph to be used by the cells

absorption

what digestive organs put in the GI tract to accomplish digestion and absorption

secretion

double sheet of peritoneal membrane that provides access for blood vessels, nerves, and lymphatic, stabilizes attached organs and prevents entanglement

mesentery

innermost folded layer of digestive tract

mucosa

layer above the mucosa that is made of connective tissue and houses blood and lymph vessels

submucosa

third layer that is made up of smooth muscle

muscularis externa

layers of muscularis externa

circular and longitudinal

visceral layer of digestive tract in the abdominal cavity

serosa

visceral layer of oral cavity, pharynx, esophagus, and rectum that is made of dense collagen fibers

adventitia

purpose of villi

increase surface area for absorption

villi with double folds

microvilli

areolar tissue containing blood vessels, lymph vessels, nerves, and mucus glands that is right under villi

lamina propria

the filaments of smooth muscles allows them to

contract in many directions and twist like a corkscrew

because visceral smooth muscle cells lack direct connection with motor neurons they contract

in a wave - as a single unit

smooth muscles have plasticity which allows them to __ in the digestive tract

change shape and size

inside of a tube where digestion and absorption occur

lumen

propels the contents forward

peristalsis

mixes up the contents of the GI tract and keeps the mucosa pressed up against the contents

segmentation

local factors of digestive regulation

changes in pH

physical distortion

presence of chemicals

neural control

short reflexes - triggered by chemoreceptors or stretch receptors

long reflexes - interneurons and motor neurons of the CNS

hormonal control

18 hormones produced by enteroendocrine into the GI tract

occurs when solid food and liquid enter the oral cavity

ingestion

involves crushing and shredding food in the oral cavity and mixing in the stomach

mechanical processing

chemical and enzymatic breakdown of food into small organic molecules that can be absorbed by the digestive epithelium

digestion

the release of waters acids, enzymes, and salts

secretions

movement of organic molecules, electrolytes, vitamins, and water across the digestive epithelium into the interstitial fluid

absorption

progressive dehydration of indigestible materials and organic wastes prior to elimination

compaction

location where digestion of carbs and lipids begins

oral cavity

function of the uvula is to

prevent food from entering the pharynx

small glands on the tongue secrete

lingual lipase

oral mucosa is made up of what kind of tissue

stratified squamous epithelium

bulk of tooth is composed of this mineralized matrix that is similar to bone but has no cells

dentin

portion of crown used for crushing, slicing, or chewing

occlusal surface

covers dentin and is the hardest biologically manufactured substances

enamel

creates gomphosis articulation between root dentin and alveolar bone

periodontal ligament

narrow tunnel in the root of the tooth that acts as a passageway for blood vessels and nerves to the pulp cavity

root canal

opening into the root canal

apical foramen

shallow groove at neck - epithelial layer to block against bacteria

gingival sulcus

teeth used for clipping and cutting

incisors

teeth used for tearing and slashing

cuspids

teeth used to crush, mash, and grind

bicuspids

teeth used to grind and crush

molars

primary dentition

20 teeth

secondary dentition

32 teeth

bacteria adhere to tooth surfaces and trap food particles producing plaque which causes

tooth decay

membrane lined cavity posterior to the nose and mouth that leads to the esophagus and is a passageway for food, liquids, and air

pharynx

tube that is narrowest at the beginning and conveys food and liquids from the pharynx to the stomach

esophagus

the esophagus goes through this opening in the diaphragm to reach the stomach

esophageal hiatus

prevents air from entering the esophagus

upper esophageal sphincter

prevents backflow of stomach contents

lower esophageal sphincter

buccal phase of deglutition

compression of bolus against hard palate

tongue forces bolus into the oropharynx

pharyngeal phase of deglutition

muscle contraction moves bolus into esophagus

esophageal phase

bolus is forced through the entrance of the esophagus and is moved towards stomach by peristalsis - can have secondary peristalsis is bolus is too dry

typical bolus travel time from mouth to stomach

9 seconds

functions of stomach

store ingested food

mechanical breakdown

disruption of chemical bonds

area of stomach that receives bolus and secretes mucus to protect esophagus from acids

cardia

dome shaped top of stomach

fundus

largest portion of stomach that acts as a large mixing bowl to churn food

body

inferior portion of stomach that is the J curve

pylorus (pyloric antrum)

controls flow of ingested food between stomach and small intestine

pyloric sphincter

folds in stomach that allow for considerable expansion

rugae

unique features of stomach

very thick mucosa

extra muscle layer (oblique)

mucosa of stomach has heavily indented structures called

gastric pits

parietal cells make

HCL

G cells make

hormones (gastrin)

chief cells make

pepsinogen

gastric glands in fundus produce

1.5 L of gastric juice each day

glands in pylorus

secrete mucus and hormones that coordinate and control digestive activity

HCL and pepsinogen help

digest proteins