Lecture #24: Digestive System--Histology and Upper GI Tract Flashcards
What is the function of the mouth?
mechanical and chemical
breakdown, deglutition
(swallowing)
What is the function of the Pharynx and esophagus?
swallowing and avoiding airway
What is the function of the stomach?
mechanical and
chemical breakdown with some
absorption
What is the function of the small intestine?
chemical and mechanical breakdown with
major absorption
What is the function of the large intestine?
absorption of electrolytes and some vitamins
What is the function of the rectum and anus?
Defecation
Draw and label the parts of the GI Tract.
Mucosa
Submucosa
Muscularis
Serosa
What is the GI tract regulated by?
The Enteric Nervous and the Extrinsic set of nerves that are part of the ANS.
What is the Enteric Nervous System?
Consists of 100 million neurons that extend from the esphagus to the anus and falls into two plexus the myenteric plexus and submucosal plexus.
What is the myenteric plexus?
located between the longitundal and circular smooth muscle layers of the muscularis
Motor neurons of the myenteric plexus supply the longitundinal and circular smooth muscle layers of the muscularis, this plexus mostly controls the GI tract movment, particularly the frequency and strength of the contraction of the muscularis.
What is the submucosal plexus?
Found within the submucosa; motor neurons of the submucosal plexus supply the secretory cells of the muscosal epithelium, controlling the secretions of the organs of the GI tract.
What do the interneurons do in the ENS?
They interconnect the neurons of the myenteric and the submuscosal plexus.
What the sensory neurons do in the ENS?
Supply the mucosal epithelium and contain receptors that detect stiumuli in the lumen of the GI tract.
Contain two types of receptors: Chemoreceptors (chemical reaction of food present in the lumen) & Mechanoreceptors (strech receptors)
What is the 1st layer of the GI tract?
1st Layer of the GI Tract: Mucosa
What is in the 1st layer of the mucosa?
Epithelium
Lamina Propria
Muscularis mucosea
What is the purpose of the epithelium?
– stratified squamous in mouth, esophagus 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
What is the purpose of the lamina propria?
– thin layer of loose connective tissue
– contains blood vessels and lymphatic tissue
What is the purpose of the muscularis mucosae?
– 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
What is the 2nd layer of the GI tract?
Submucosa
What is composed of the submucosa?
Loose connective tissue Submuscosal plexus (Meissner's plexus)
What is the purupose of the loose connective tissue?
– containing blood vessels, glands and lymphatic tissues
What is the purpose of the submucosal plexus (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
What is the 3rd layer of the GI tract?
Muscularis
What parts of the body have muscularis?
Mouth, pharynx, and superior and middle parts of the esophagus contains skeletal muscle that produces voluntary swallowing.
What does the muscularis control?
• Smooth muscle under involuntary control
– inner circular fibers and outer longitudinal fibers
– allows motility for mixing and propulsion
What plexus is part of the muscularis?
• Myenteric plexus (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
What is the 4th layer of the GI Tract?
Serose or Adventitia
Where is serosa mostly found?
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
Where is the common place that adventitia is found?
• Adventitia for esophagus
– Consists of areolar connective tissue without the
epithelium
What is the peritoneum?
The largest serous membrane of the body; it consists of a layer of simple squamous eptithelium with an underlying supporting layer of areolar connective tissue.
What is it called when there is a lining within the walls of the admiominal cavity?
Parietal Peritoneum
What is it called when there is a cover over some of the organs in the cavity and is their serosa?
Visceral Peritoneum
The slim space containing lubricating serous fluid that is between the parietal and visceral portions of the peritoneum is called what?
Peritoneal cavity
What is mechanical digestion?
(mastication or chewing)
• breaks food into pieces
• mixes with saliva so that it forms a moist bolus
What is Chemical Digestion?
• salivary amylase begins starch digestion in the mouth
(pH 6.5-7.0) , but when the bolus hits the acidic gastric
juices (pH 2.5) digestion stops
• lingual lipase is secreted by glands in tongue and begins
breakdown of triglycerides (lipids) into fatty acids and
glycerol
What are the major salivary glands?
Parotid, Submandibular, and sublingual glands
Do they all have ducts that empty into the oral cavity?
Yes!
What other functions does the salivary glands do?
Sight, smell, sounds, memory of food, and tongue stimulation increase salivation
Fear and anxiety decrease salivation –> dry mouth
What is the composition and functions of the 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
What are the stages of swallowing?
Voluntary Stage
Involuntary Stage
What is the Voluntary Stage?
Oral cavity to oropharynx
What is the involuntary stage?
- Pharyngeal stage: pharynx to esophagus
2. Esophageal stage: esophagus to stomach
In the oral stage, what is happening?
• Deglutition (swallowing) starts with the voluntary stage
– food bolus pushed by the tongue into the oropharynx
In the involuntary stages, what is happening?
begin when sensory nerves in the pharynx that signal the deglutition center in brainstem
– breathing stops
– soft palate & uvula rise closing off nasopharynx
– vocal cords adduct
– larynx rises
– epiglottis covers the larynx
In the Esophageal stage, what is happening?
• Upper esophageal sphincter relaxes
• Peristalsis pushes food down
– circular fibers contract behind bolus
– longitudinal fibers contract in front of bolus to shorten the
distance of travel
• Lower esophageal sphincter relaxes as food
approaches
What is the travel time for food to travel down the esphogeal stage?
4 to 8 sec. for solids
1 sec for liquids
What is Gastro-Esophageal Reflux Disease? (GERD)
• If lower sphincter fails to open
– distension 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
