GI Module 1 Flashcards
Organs of the GI (alimentary) tract
Mouth Esophagus Stomach SI / LI Rectum Anus
Accessory organs of digestive system
Liver, gallbladder, exocrine pancreas
Layers of GI tract from inner to outer
- Mucosa
- Submucosa
- Muscularis
- Adventitious (serosa)
What are the sub-layers of the mucosa from inner to outer?
- Mucosa epithelium
- Lamina propria
- Muscularis mucosae
What does the submucosa contain?
Glands and associated ducts
What are the layers of the muscularis?
Circular and longitudinal layers
What is the adventitious (serosa) composed of?
Connective tissue
Define the enteric nervous system
- Considered part of ANS
- Functions autonomously
- Influenced extrinsically via para/sympathetic nervous systems
Enteric plexuses
- Meissner plexus (submucosal)
- Auerbach plexus (myenteric)
- Subserosal plexus
Meissner plexus
- Located in submucosa
- Secretion!
Auerbach plexus
- AKA myenteric
- Located b/w circular and longitudinal layers of muscularis
- Motility!
Subserosal plexus
ANS innervation of blood vessels and connective tissue
What are the functional components of enteric plexuses?
- Sensory neurons
- Motor neurons
- Interneurons
What is the function of sensory neurons in enteric plexuses?
- Monitor distension and “chemical status” of tract
* Sympathetic nerves
What stimuli to the enteric plexuses cause GI visceral pain?
- Distension
- Chemical (inflamm response)
- Ischemia (lactate, H+, K+)
What is the function of motor neurons in enteric plexuses?
- Motility (peristalsis)
- Blood flow
- Secretions
What is the function of interneurons in enteric plexuses?
- Communication b/w sensory and motor neurons
- Mechanism for INTRINSIC control (short loop reflexes)
Define appetite
Hunger
Define satiety
Sensation of fullness/satisfied
How are appetite and satiety regulated?
2 centers (nuclei) in hypothalamus:
- Lateral center (appetite)
- Medial center (satiety)
Function of lateral center
- Stimulate appetite
- Excitatory to hunger contractions in stomach
What is ghrelin?
- Gastric hormone - “Hunger hormone”
- Fast acting
- Other roles: memory, sleep
Function of medical center
- Suppress appetite
- Inhibitory to hunger contractions in stomach
- Stimuli = GI hormones, leptin, PYY, insulin
What is leptin?
- Long term role in energy balance and suppressing food intake
- Released from fat and chief cells
What is PYY?
- Fast acting
- Counteraction to ghrelin
- Released after a meal by the small intestine
How does obesity affect hunger hormones?
- Leptin is increased (“resistance”)
- Ghrelin is decreased
Is insulin fast or slow acting?
Fast
Function of sympathetic system to GI tract
Inhibitory - decreases peristalsis and secretions
Function of parasympathetic system to GI tract
Excitatory
*Vagus, pelvic nerves of sacral plexus
What is the extrinsic regulation of the GI tract?
Sympathetic and parasympathetic
What is the intrinsic regulation of the GI tract?
*Located within GI tract wall
Auerbach (myenteric) plexus = motility
Meissner (submucosal) plexus = secretions
How does the intrinsic system of the GI tract function?
Autonomously (“brain in the gut”)
How is salivation controlled?
Autonomic - both para and sympathetic STIMULATE salivary glands
*NOT by hormones at all
What is saliva composed of?
- Water w/mucus, Na, bicarb, Cl, K
- Salivary amylase
- IgA
Where is digestion initiated?
In the mouth by salivary amylase
What is the pH of saliva?
6.4 - 7.0
What is the function of bicarbonates in saliva?
Maintain pH to neutralize bacteria (tooth decay)
What is the purpose of IgA in saliva?
Prevents infection
why animals lick their wounds
General functions of saliva
- Control pH
- Starch digestion
- Immune defense
What muscle is the upper esophageal sphincter?
Cricopharyngeus
Where is the UES located?
- Junction of lower pharynx and esophagus
- Approx at level of cricoid cartilage
What is the function of the UES?
Prevent air from entering esophagus during ventilation
Is the UES considered a ____ (true/false) anatomical sphincter?
TRUE
Location of lower esophageal sphincter
Just proximal to junction of esophagus and stomach
Functions of the LES
Barrier to reflux from the stomach
How is the LES maintained?
Increased smooth muscle tone
What is belching a result of?
Air pressure in stomach exceeds LES pressure
What is the normal “tone” of the esophagus?
20 mmHg
Phases of swallowing and their lengths
- Voluntary (1-2 secs)
2. Esophageal (5+ secs) - UES contracted (closed)
What comprises the voluntary phase of swallowing?
- Oropharyngeal phase - UES closed
2. Pharyngeal phase - UES relaxed
What is the range of esophageal muscular pressures?
35 - 80 mm Hg
- Upper and lower esophagus tend to be higher (60-80)
- Mid esophagus tends to be lower (30-45)
Peristaltic contractions of
30 mm Hg
How is peristalsis controlled?
Parallel vagal inhibitory (NO) and excitatory (ACh) pathways
What hormones excite and inhibit peristalsis?
Excite = ACh Inhibit = NO
Define primary peristalsis
"Normal" wave as bolus descends Swallow reflex (voluntary) + esophageal wave (involuntary)
Define secondary peristalsis
Food residue from ineffective primary peristalsis or a bolus that is “stuck”
*Consists of esophageal wave (involuntary) ONLY
Difference between primary and secondary peristalsis
- Primary consists of both swallowing AND esophageal phases
- Secondary is ONLY esophageal (involuntary) phase
Process of swallowing food
- Single swallow initiates esophageal peristalsis lasting 5-10 secs
- Short refractory period inhibits more swallowing
Process of swallowing liquids
- Swallow every 1-2 seconds
- Quick subsequent swallows creates an inhibitory reflex (deglutitive inhibition) that prevents esophagus from ongoing contraction (allows more liquid to descend)
Deglutitive inhibition
- Occurs with swallowing LIQUIDS
- Quick subsequent swallows creates a reflex where esophagus cannot contract
- Allows more liquid to descend
- Last swallow will end the reflex and start full peristaltic contraction
LES tone is a result of 3 factors:
- Myogenic tone (independent of any neural input)
- Excitatory vagal tone (cholinergic)
- Inhibitory vagal tone (nitric oxide)
Factors that increase LES pressure:
- Vagus nerve excitatory pathway (ACh)
- Gastrin
- Meds to treat GERD
* Increased LES pressure = closed LES
Factors that decrease LES pressure:
- Vagus nerve inhibitory pathway (NO, VIP)
- Hormones (progesterone, secretin, glucagon)
- Foods/substances (fried food, tomatoes, citrus, tobacco, alcohol, caffeine)
GERD
Decreased LES pressure and ineffective clearance mechanism of secondary peristaltic waves
Achalasia
- LES fails to relax - pain w/eating and drinking
- “Cardiospasm”
- Etiology is unknown but thought to be defect of intrinsic esophagus plexus
Treatment for achalasia
Pneumatic dilation (stretch LES to relax) Meds to relax LES (Botox an option)
Esophageal varices
- Severely dilated sub-mucosal veins in esophagus
- MC caused by portal HTN
- Increases risk of bleeding
Barrett’s esophagus
- Normal esophageal squamous epithelium is replaced by abnormal metaplastic cells due to exposure to stomach acids
- GERD can cause this but not always
- Increased risk of cancer
What is the MC esophageal cancer in the US?
Adenocarcinoma (polyploid mass)
Where is adenocarcinoma of the esophagus most commonly found?
Lower esophagus
What is the MC esophageal cancer in the world? What part of the esophagus is it mostly found?
Esophageal squamous cell carcinoma
Upper esophagus