Lecture 13: Digestive system part 2 Flashcards
What are the 5 primary functions of the digestive system
- ingestion
- Propulsion
- Digestion
- Absorption
- Defecation
define ingestion
ingestion of food to the alimentary canal
define propulsion
movement of food along the canal
What are the 2 subcategories of propulsion
- voluntary : deglutition or swallowing (oropharynx)
2. Involuntary : Peristalsis (esophagus, stomach, small intestine, large intestine)
define digestion
reduction of food into particles to be assimilated
What are the 2 categories
- Mechanical degestion: physical alteration of food by chewing (mastication), churning (stomach), and segementation (small intestine)
- Chemical digestion: by catabolic enzymes
define absorption
passage of digested end-products of the alimentary canal to (active or passive transport)
- cardiovascular system
- Lymphatic system
define defecation
expulsion of non-digestible or non-absorbed material
What parts are involved in transforming food to a bolus that is swallowed (mastication)
lips cheeks palate tongue salivary glands gums teeth
what controls mastication
voluntary + many stretching reflexes (mechanoreceptors)
What causes the propulsion of the bolus
deglutition (swallowing)
food goes from mouth -> oropharynx -> laryngopharynx ->oesophagus
what coordinates the propulsion / deglutition of the bolus
tongue, soft palate, pharynx, esophagus
- 2 phases
1. buccal
2. pharyngeal-esophageal
What happens in the 1st phase of propulsion the Buccal (oral) phase
- it is a voluntary action
- bolus pushed by tongue against palate & towards the back of oral cavity up to oropharynx; upper esophageal sphincter contracted
What happens in th 2nd phase of propulsion the pharyngeal - esophageal phase
- involuntary action
- bolus in oropharynx stimulate mechanoreceptors
- oropharynx sends an impulse to center of deglutition (medulla oblongata, inferior part of pons)
- medulla sends impulse that provokes elevation of soft palate & uvula to close the nasopharynx & elevation of larynx that cause epiglottis to tip over the larynx (interrupt respiration)
- bolus reaches esophagus (respiration restarts)
What is peristalsis
smooth muscle
- wave-like ripple
- stretch in tract causes reflex contraction of circular muscle -> forward movement
- causes additional contractions
what is segmentation
smooth muscle
- mixing movement
- forward and backwards movement in single region
- helps mix food and digestive fluids
when bolus mixes with gastric juices it turns to
chyme
what happens a few minutes after bolus enters stomach
mixing wave ( churning) which is specific peristaltic movement of stomach (involuntary-propulsion) every 15 - 20 seconds
How does stomach empty chyme into small intestine
a bit of chye is pushed into duodenum via pyloric sphincter while rest returns into stomch (retropulsion)
-this cycle keeps repeating until stomach is empty
Gastric motility: how long does it take to empty stomach and what controls it
- takes ~ 2-6 hours
- controlled by hormonal and nervous mechanisms
What are the hormonal mechanisms that control gastric motility
- fats in duodenum stimulate the release of gastric inhibitory peptide (GIP)
- which decreases peristalsis of gastric muscle and slows passage of chyme into duodenum
what are the nervous mechanisms that control gastric motility
- enterogastric reflex
- receptors in duodenal mucosa are sensitive to presence of acid and distention
- impulses over sensory and motor fibers in the vagus nerve cause a reflex inhibition of gastric peristalsis
- increases in acid and distention in duodenum -> inhibitor of peristalsis -> decreased chyme entering duodenum
Intestinal motility includes what 2 types of movement
peristalsis and segmentation
What does segmentation in duodenum and upper jejunum do
mixes chyme w/ digestive juices frfom the pancreas, liver, and intestinal mucosa
