Chapter 26: Digestive System Flashcards
six main functions of the digestive system
1- ingestion
2- motility
3- secretion
4- digestion
5- absorption
6- elimination
ingestion
solid and liquid nutrients into oral cavity
motility
- voluntary and involuntary muscular contractions
- mixing and moving materials through the GI tract
secretion
producing and releasing fluid products to aid in digestion
digestion
breakdown of ingested food into smaller structures
2 kinds of digestion
1- mechanical digestion
2- chemical digestion
mechanical digestion
material physically broken down by chewing and mixing
chemical digestion
large complex molecules to smaller molecules - enzymes break chemical bonds
absorption
digested molecules, electrolytes, vitamins, water from GI tract INTO BLOOD AND LYMPH
elimination
expulsion of indigestible components that are not absorbed
enzymes are
catalysts
catalysts are
- proteins that speed up a chemical reaction
- not changed or used up in the reaction
4 layers/tunics of the GI tract
1- mucosa
2- submucosa
3- muscularis
4- serosa
serosa
is the outermost layer of the GI tract; superficial serous membrane
mucosa
the innermost layer; deep mucous membrane
muscularis
consists of smooth muscle
submucosa
consists of blood vessels, lymph, and nerves
functions of the muscularis to mix and propel contents within GI tract
- peristalsis
- mixing
- mass movements
peristalsis
propels ingested materials through tract
mixing
blends ingested materials with secretions
mass movements
forces fecal matter from the transverse colon through the rest of the large intestine
submucosal nerve plexus
innervates smooth muscle and glands
MALT
mucosa-associated lymphatic tissue
Peyer patches
larger aggregates of lymphatic nodules in distal small intestine
muscularis (externa) inner circular layer
smooth muscle; contraction constricts tube lumen
muscularis outer longitudinal layer
contraction shortens tube
muscularis myenteric nerve plexus
between layers, control contractions
sphincter
closes off the lumen, controls movements
propulsion
forward movement down the tract
2 nervous systems that communicate with the digestion system
1- enteric nervous system (ENS)
2- autonomic nervous system (ANS)
enteric nervous system (ENS)
- includes submucosal plexus and myenteric plexus
- innervates smooth muscle and glands of GI tract
- coordinates mixing and propulsion reflexes
autonomic nervous system (ANS)
- parasympathetic innervation promotes GI tract activity
- sympathetic innervation opposes GI tract activity
nerve receptors in the digestive system
- baroreceptors
- chemoreceptors
short reflex
LOCAL reflex only involves ENS; coordinates small segments of the GI tract
long reflex
involves sensory input to CNS and ANS motor output; coordinate GI tract motility, secretions, and accessory digestive organs
hormonal control
three primary hormones in the regulation of digestion:
1- gastrin, from stomach
2- secretin, from SI
3- cholecystokinin (CCK), from SI
upper GI tract organs and accessory structues
- oral cavity and salivary glands
- pharynx
- esophagus
- stomach
- duodenum
oral cavity and salivary glands
- mechanical digestion
- saliva secreted in response to food
- mixed with ingested materials form bolus
saliva enzymes secreted in response to food
- salivary amylase
- lingual lipase
pharynx
bolus moved to the pharynx during swallowing
bolus
a ball of food that you are ready to swallow
esophagus
- bolus transported from pharynx into stomach
- lubricated by mucus secretions
stomach
- bolus mixed with gastric secretions by smooth muscle contractions
- secretions produced by epithelial cells of stomach
- chyme formed from mixing
chyme
the contents in the stomach;
food and stomach secretions
tongue within the oral cavity
on interior surface of cavity
- manipulates and mixes materials during chewing
- important functions in swallowing and speech
2 kinds of salivary glands
- intrinsic
- extrinsic
intrinsic salivary glands
- located within the oral cavity
- unicellular
- continuously release secretions independent of food
extrinsic salivary glands
- located outside the oral cavity
- larger
- stimulated to release by food
3 pairs of salivary glands
1- parotid salivary glands
2- submandibular salivary glands
3- sublingual salivary gland
parotid salivary glands
- largest salivary glands
- 25-30% of saliva
submandibular salivary glands
60-70% of saliva
sublingual salivary gland
3-5% of saliva
saliva
1.0 - 1.5 L secreted daily, most produced during mealtime
functions of saliva
- moistens ingested food to help become bolus
- dissolves chemicals that stimulate taste buds
- cleanses oral cavity
- antibacterial substances inhibit bacterial growth
antibacterial substances that inhibit bacterial growth
- lysozyme
- IgA antibodies
regulation of salivary secretions are regulated by
salivary nuclei within brainstem
another name for swallowing
deglutition
3 phases of swallowing
1- voluntary phase
2- pharyngeal phase
3- esophageal phase
voluntary phase
bolus of food is pushed by tongue against hard palate and then moves toward oropharynx
pharyngeal phase
- soft palate and uvula close off the nasopharynx
- larynx elevates so the epiglottis closes over laryngeal opening
esophageal phase
- bolus passes through esophagus
- propels bolus toward stomach
- esophageal sphincters closed at rest
salivary amylase
enzyme for carbohydrate digestion