GI 1: Overview; Mastication and Swallowing Flashcards
What is digestion?
Breakdown ingested molecules into building blocks
What is absorption?
➢ Passive and Active transport processes
➢ Moves substances from lumen of gut to blood
What are the four layers of the GI tract wall?
- mucosa
- submucosa
- muscularis externa
- serosa
What is in the mucosa layer of the GI?
➢ Simple Columnar Epithelium
➢ Lamina Propria
➢ Muscularis Mucosa (moves villi)
What is in the submucosa layer of the GI?
➢ Simple Columnar Epithelium
➢ Lamina Propria
➢ Muscularis Mucosa
What is in the muscularis externa?
➢ Circular Muscle
➢ Longitudinal muscle
➢ Myenteric Plexus
What is in the serosa?
➢ CT covering
➢ Support GI tract in abdominal cavity
What allows for the increased surface area in the GI tract?
- Circular Folds
- Villi
- Microvilli
Control Systems regulate conditions in the…
lumen of the tract or in the ECF?
lumen of tract
Control mechanisms are governed by volume and composition of _________ contents
luminal
What cells are localized to specific regions in the gut and “taste” the luminal contents?
endocrine cells
What is the brain of the gut?
enteric nervous system (ENS)
What hormone is associated with sympathetics in the gut?
Norepinephrine (NE)
What hormone is associated with parasympathetics in the gut?
acetylocholine (ACh)
What controls the muscularis externa?
myenteric plexus
When the myenteric plexus is stimulated what happens?
- Increase tone of gut wall
- Increase intensity of rhythmic contractions
- Slight increase in rate of rhythmic contractions
- Increase conduction velocity of electrical waves along gut wall
- Inhibition of sphincter contraction
What does the submucosal plexus do?
➢ Controls function of each minute segment of tract
➢ Local control of
- Intestinal secretions
- Absorption
- Contraction of mucosal muscle
Is the vago-vagal reflex assocaited with long or short reflexes?
long reflexes
What type of muscle and nervous control do the mouth, oropharynx, upper esophageal sphincter, upper 1/3 of esophagus, and external anal sphincter have?
- skeletal muscle (voluntary)
- somatic motor neuron
What type of muscle and nervous control do the lower 2/3 of esophagus, stomach, small intestine, large intestine, gallbladder, biliary and pancreatic ducts have?
- smooth muscle (involuntary)
- Autonomic nervous system
— sympathetic post fibers (inhibitory)
— parasympathetic pre fibers (stimulatory/inhibitory)
What is the importance of the portal vein?
➢ Collects all venous outflow from most GI organs.
➢ All portal outflow goes to liver before entering vena cava.
What are the characteristics of serous saliva?
- watery
- contains ptyalin (alpha-amylase)
- moisten and dissolve food
- small amount of chemical digestion
What are the characteristics of mucous saliva?
- thick secretions with mucin
- lubrication and protection of surfaces
What salivary gland has all serous saliva?
parotid
What salivary gland has all mucus saliva?
buccal glands
What salivary glands have mixed saliva?
submandibular
sublingual
How much saliva is produced in a day?
1.5 L/day
Secretion of saliva is strictly under _______ control
neural reflex control
What are the parts of saliva?
water
bicarbonate
mucins
amylase
lysozyme, lactoferrin, IgA
epidermal/nerve growth factors
What does the bicarb in saliva do?
neutralizes refluxed gastric acid
What are the characteristics of acinar cells?
- pyramidal
- form a acinus with a central lumen
- secrete isosmotic serous saliva
What are the characteristics of mucous cells?
- columnar
- organized into tubules
- secrete mucus
What are the characteristics of myoepithelial cells?
- around the serous acini
- contract to move saliva into and through ducts
What are the characteristics of intercalated duct cells?
- move saliva out of acini
- prevent backflow of saliva into acini
What are the characteristics of striated ducts (interlobular)?
- columnar epithelial cells
- tight junctions
- modify saliva (Na+ and Cl- reabsorbed, K+ and HCO3- secreted)
As saliva flow rate increases…
➢ Less time for ductal modification
➢ Saliva more closely resembles the plasma
➢ Becomes more basic
Sympathetic NS plays what role in saliva secretion?
- minor role
- potentiates parasympathetic effects
What does parasympathetics do to the control of saliva secretion
- predominate regulator of saliva
- criticial for initiation of saliva secretion
- critical for sustaining high levels of saliva secretion
- vasodilation of blood vessels supplying salivary glands
What are the parasympathetic stimulati for salivary reflux activation?
- taste (sour) and tactile stimulation on tongue surface
- smell of food
- ingestion of irritating foods
- nausea
What percents of salivary gland secretion are during unstimulated salivation?
69% submandibular glands
26% parotid glands
5% sublingual glands
What percents of salivary gland secretion are during stimulated salivation?
69% Parotid
26% submandibular
5% sublingual
What is salivation inhibited by?
- fear
- sleep
- fatigue
- dehydration
What is salivation stimulated by?
- autonomics (mostly parasympathetic)
- thinking/seeing/smelling food
- conditioned salivation
- chewing
- nausea
What are the common causes of xerostomia?
- Polypharmacy (>4 drugs/day)
- Anxiety and depression (and medications used for treatment)
- Insufficient hydration
- Radiation to the head and neck
- Sjogren syndrome
What are the consequences of xerostomia?
➢ Increased caries due to reduced oral clearance of sugars, dietary acids, oral bacteria
➢ Halitosis
➢ Disrupted sleep due to dry mouth; wake up to sip water and moisten mouth
➢ Difficulty lubricating and swallowing food
➢ Dry mouth (feel thirsty, dry, cracked lips)
– Burning mouth sensation
– Dry/sore oral mucosa
➢ Impaired sense of tastes
➢ Heartburn
– Low saliva; decreased buffering
– Loss of protective growth factors in saliva
– Lengthened healing time for ulcers
How do you manage xerostomia?
- Avoid acidic, spicy, crunchy and coarse foods.
- Alcohol-free toothpastes and rinses.
- Oral moisturizers, sips of water, sugarless chewing gum.
- Sialogogues such as pilocarpine and cevimeline before meals (cholinergic agonists)
What are the functions of mastication?
- prepare food bolus for swallowing
— mechanical digestion
— mix food with saliva - initiate digestive and metabolic activities
What are the three stages of swallowing (deglutition)?
- Voluntary stage
- Pharyngeal stage
- esophageal stage
What happens during the voluntary stage of swallowing?
➢Initiate swallowing reflex
➢Bolus of food moved into pharynx by tongue
➢Stimulates epithelial swallowing receptor area
What happens during the pharyngeal stage of swallowing?
➢Involuntary Reflex – mediated by contraction of skeletal muscles
➢Mediated by swallowing center in brainstem
➢Soft palate pulled upward and closes off nasopharynx
➢Epiglottis closes off trachea
➢Upper Esophageal Sphincter relaxes
What happens during the esophageal stage of swallowing?
➢Coordinated muscle contractions to move bolus through esophagus into stomach (aborally).
➢≈ 10 sec
What are the functions of the esophagus?
- Transport of solids and liquids from Pharynx to stomach
- Prevents air intake - UES
- Prevents reflux (stomach to esophagus) -LES
What are the two types of peristalsis in the esophagus?
➢ Primary Peristalsis-continuation of peristaltic wave initiated during pharyngeal phase of swallowing (8-10 sec)
➢ Secondary Peristalsis-activated by esophageal distension from retained food in esophagus
What nerves control the upper 1/3 of the esophagus?
somatic motor
What nerve control the lower 2/3 of the esophagus?
autonomic nerves
What is the name for the swallowing center in the brainstem?
dorsal vagal complex (DVC)
Wave of __________ in front of bolus
relaxation
Wave of _________ behind bolus
contraction
What hormone acts in front of the bolus and causes relaxation?
NO
What hormone acts behind the bolus and causes contraction?
ACh
What is the function of secondary peristalsis?
➢ Clearing a bolus that was not wholly expelled by primary wave
➢ Removing any gastric contents that reflux back into the lower esophagus
Upper and lower esophageal sphincters remain ________ between swallows
closed
Upper esophageal sphincter ________ during swallow.
relaxes
Lower esophageal sphincter ________ as peristaltic wave approaches
relaxes
What is gastro-esophageal reflux disease (GERD)?
➢ Reflux of gastric contents into esophagus
➢ Common and potentially disabling
➢ Treated by inhibiting gastric acid secretion
