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29 terms

Digestion Lecture 26

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Mouth
Mechanical and chemical breakdown, deglutition (swallowing)
Pharynx and esophagus
swallowing and avoiding airway
stomach
mechanical and chemical breakdown with some absorption
small intestine
chemical and mechanical breakdown with major absorption
large intestine
absoption of electrolytes and some vitamins
rectum and anus
defecation
Epithelium
Mucosa
-Stratified squamous in mouth, espohagus and anus
-Simple columnar in the rest of the GI tract
-Secretes enzymes and absorbs nutrients
-specialized cells (goblet) secrete mucous onto cell surfaces
-enteroendocrine cells secrete hormones controlling organ function
lamina propria
Mucsoa
-thin layer of loose connective tissue
-contains blood vessels and lymphatic tissue
Muscularis mucosae
Mucosa
-thin layer of smooth muscle causes folds to form in mucosal layer
-drives local movements to increase absorption by exposing ingested material to absorptive surfaces
Loose connective tissue
Submucosa
-containing blood vessels, glands and lymphatic tissues
Submucosal plexus
Submucosa (Meissner's plexus)
-part of the enteric nervous system
-receives input from sympathetic (thoracic and lumbar spinal cord) and parasympathetic neurons (vagus nerve and sacral spinal cord)
-Regulates blood vessel diameter, secretion from glands and neurosecretory neurons, and local motility caused by muscularis mucosae
Skeletal muscle
Muscularis Externa
--- in mouth, pharynx, upper esophagus and anus under voluntary control
-control over deglutition and defecation
Smooth muscle
Muscularis Externa
--- under involuntary control
-inner circular fibers and outer longitudinal fibers
-allows motility for mixing and propulsion
Myenteric Plexus
Muscularis Externa (auerbach's plexus)
-part of the enteric nervous system with some functions shared with submucosal plexus
-provides parasympathetic & sympathetic innervation of circular and longitudinal smooth muscle layers
Serosa
for stomach and intestines
-a serous membrane also called the visceral peritoneum
-secretes serous fluid
-consists of areolar connective tissue covered with simple squamous epithelium
Adventitia
for esophagus
-consists of areolar connective tissue without the epithelium
Peritoneum
-visceral --- covers organs
-parietal --- lines the walls of body cavity
Peritoneal cavity
-potential space containing serous fluid
Mechanical Digestion
(mastication or chewing)
-breaks food into pieces
-mixes with saliva so that it forms a moist bolus
salivary amylase
Chemical digestion
begins starch digestion in the mouth (pH 6.5-7), but when the bolus hits the acidic gastric juices (pH 2.5) digestion stops
Lingual lipase
Chemical digestion
is secreted by glands in tongue and begins breakdown of triglycerides (lipids) into fatty acids and glycerol
Salivary glands
-Major glands: parotid, submandibular and sublingual glands
-All have ducts that empty into the oral cavity
-Sight, smell, sounds, memory of food, and tongue stimulation increase salivation
-Fear and anxiety decrease salivation -> dry mouth
Saliva
-Water, HCO3-, enzymes
-Moistens food (swallow)
-Dissolves food (taste)
-HCO3- buffers acidic foods
-Protects mouth from infection with rinsing action
-Lysozyme helps destroy bacteria
Voluntary Phase
Phases of swallowing 1
-Oral cavity to oropharynx
Involuntary Phase
Phases of swallowing 2
-Pharygneal stage - pharynx to espohagus
-Esophageal stage - esophagus to stomach
Voluntary phase
Oral-pharyngeal stage
Deglutition (swallowing) starts with a ---: food bolus pushed by the tongue into the oropharynx
Involuntary phase
Oral-pharyngeal stage
--- begins when sensory nerves in the pharynx signal the deglutition center in brainstem
-breathing stops
-soft palate & uvula rise closing off nasopharynx
-vocal cords adduct
-larynx rises
-epiglottis covers the larynx
Peristalsis
Esophageal phase
-Upper esophageal sphincter relaxes
- --- pushes food down
-circular fibers contract behind bolus
-longitudinal fibers contract in front of bolus to shorten the distance of travel: solid (4-8sec) liquids (1sec)
Lower espohageal sphincter relaxes as food aporoaches
Gastro-esophageal reflux disease
GERD
-If lower sphincter fails to open: distention of esophagus feels like chest pain or heart attack
-If lower esophageal sphincter fails to close:
-stomach acids enter esophagus & cause heartburn (GERD)
-worsened by a weak sphincter
-particularly bad when laying down after a large meal
-smoking and alcohol make the sphincter relax worsening the situation