4/22: Overview, Saliva, Mastication, and Swallowing Flashcards
What are the two components of the digestive system?
- Alimentary canal (GI tract)
- Accessory organs
What is the alimentary canal?
- Mouth to anus
- lumen contents considered outside body
- 30 feet in length
What are the accessory organs?
- not part of GI tract
- produce substances secreted into tract
What substances are secreted into the tract by the accessory organs?
- salivary glands
- exocrine pancreas
- liver and gall bladder
What are the 6 functions of the GI system?
- Digestion
- Secretion
- Absorption
- Motility
- Excretion
- Defense
What is digestion?
Breakdown ingested molecules into building blocks
What are the two types of digestion?
- Mechanical
- Chemical
What things are secreted in the GI tract?
Digestive enzymes
Acid/base
Bile
What are processes that assist with absorption in the GI tract?
Passive and active transport processes
What is the function of absorption?
Moves substances from lumen of gut to blood
What is the function of motility in the GI tract?
- mixing
- mechanical digestion
- move material through tract (propulsion)
What is the function of excretion in the GI system?
- removal of metabolic waste
- very little true waste in feces (bile pigments)
What is the function of defense in the GI system?
Gut associated lymphoid tissue
What are ingested nutrients?
Carbohydrates
Fats
Proteins
DNA, RNA
Water
Electrolytes
Vitamins
What are other ingested substances into the GI tract?
Pathogens
Alcohol
Drugs (Licit, illicit)
Toxins
Coins, toys, bugs
What are the 4 layers of the GI tract wall?
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
Describe the mucosa of the GI tract
- simple columnar epithelium
- lamina propria
- muscularis mucosa (movement of villi)
Describe the submucosa of the GI tract
- CT layer
- blood and lymph vessels
- submucosal plexus
(network of neurons, projections to luminal surface cells, muscularis mucosa, and to myenteric pelxus)
Describe the muscularis externa of the GI tract
- Circular muscle
- Longitudinal muscle
- myenteric plexus
Describe the serosa of the GI tract wall
- CT covering
- support GI tract in abdominal cavity
What kind of NS does the GI tract have?
Enteric NS = submucosal and myenteric pelxus
- little brain
Describe the epithelial layer of the GI tract
➢ Simple Columnar (microvilli)
➢ Goblet Cells
➢ Enteroendocrine cells (base of villi)
➢ Stem cells
What is the tremendous surface area available used for?
absorption of materials from lumen
What is used for surface area absorption?
- Circular folds
- Villi
- Microvilli (brush border)
- increases SA 600x over flat surface
What is found in the inside villus of the GI tract?
- lacteals (lymph vessels)
- capillary network
What is the function of the circular muscle?
Contraction narrows lumen
What is the function of the longitudinal muscle?
Contraction shortens tube
What is the myenteric plexus?
- network of neurons
- input from autonomic NS
- projections to submucosal plexus, circular, and longitudinal muscle
What do control systems regulate?
Conditions in lumen of tract (not ECF conditions)
What are control mechanisms governed by?
Volume and composition of luminal contents
Where are endocrine cells located?
Scattered in gut mucosa
What are specialized cells?
Endocrine cells (one cell - one hormone (mostly)
What do cells “taste”?
Luminal contents
What are paracrine cells similar to?
Endocrine
Where are paracrine cells released into?
interstitial fluid, diffuses to target (may “overflow” into the circulation)
What are two established gut paracrine factors?
Histamine (ECL cell)
Somatostatin (D cell)
What is the sympathetic nervous system inhibitory to?
Digestive function
What fibers are in the sympathetic portion of the gut?
Mainly postganglionic
What fibers are in the parasympathetic portion of the gut?
Preganglionic
Where do the myenteric plexus neurons extend?
The entire length of GI tract
What does the myenteric plexus control?
Muscle of muscularis externa
What happens when the myenteric plexus is stimulated?
- 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 control function of?
Each minute segment of tract
What is the local control of the submucosal plexus?
- intestinal secretions
- absorption
- contraction of mucosal muscle
Describe skeletal muscle of the gut
Voluntary, striated
What are organs that deal with skeletal musculature?
mouth, oropharynx, upper esophageal sphincter, upper 1/3 of esophagus,
external anal sphincter
What is skeletal musculature controlled by?
Somatic MN – CN XII (tongue), V (chewing), IX, X
(swallowing); Pudendal n. – ext. anal sphincter
Describe smooth muscle of the gut
Involuntary, unstriated
What are organs that deal with smooth musculature?
lower 2/3 of esophagus, stomach, small intestine, large intestine,
gallbladder, biliary and pancreatic ducts
What is smooth gut muscle controlled by?
Autonomic NS
Describe the sympathetic control of smooth muscle
post-ganglionic fibers (NE) to enteric nervous
system, vasculature, ducts, parenchyma; usually inhibitory
Describe the parasympathetic control of smooth muscle
(vagus, pelvic) - pre-ganglionic fibers (ACh) act
locally, postganglionic fibers are part or ENS
What are the actions of the parasympathetic smooth muscle of the gut?
actions are stimulatory or inhibitory, depending on final neurotransmitter released
What is smooth gut musculature controlled by?
Endocrine and paracrine factors
What are examples of patterns of motility?
- Chewing
- Swallowing
- Esophageal transport
- Gastric storage, trituration, emptying
- Vomiting
- Gallbladder storage, emptying
- Small intestinal mixing & transport
- Colonic storage, defecation
What is the importance of the portal vein?
Collects all venous outflow from most GI organs
Where does all portal outflow go to?
Liver before entering vena cava
What is “scanned” by liver?
Nutrients, hormones, drugs, and toxins
What are the two types of saliva?
- Serous
- Mucous
Describe serous saliva
Watery secretion containing ptyalin (α amylase)
What does serous saliva do?
Moisten and dissolve food
Small amount of chemical digestion
Describe mucous saliva
Thick secretions containing mucin
What is the function of mucous saliva?
Lubrication and protection of surfaces
What are the type of salivary glands?
- Parotid - Serous Gland
- Submandibular - Mixed
- Sublingual - Mixed
- Many tiny buccal glands - Mucus
What are the components of saliva?
Water
Bicarbonate
Mucins
Amylase
Lysozyme, lactoferrin, IgA
Epidermal and nerve growth factors
What is the function of water?
Facilitates taste and dissolution of nutrients, aids in swallowing
What is the function of bicarbonate?
Neutralizes refluxed gastric acid
What is the function of mucins?
Lubrications
What is the function of amylase?
Starch digestion
What is the function of lysozyme, lactoferrin, and IgA?
Innate and acquired immunity
What is the function of epidermal and nerve growth factors?
Mucosal growth and protection
What do acinar cells form?
Unit called an acinus with a small central lumen
What do acinar cells secrete?
isosmotic serous saliva (chloride, bicarbonate and potassium ions (Na+ and water follow passively,
enzymes)
What do mucous cells secrete?
Mucous
What do myoepithelial cells do?
Contract to move saliva into and through ducts
What do intercalated duct cells move?
Saliva out of acini
What do intercalated duct cells prevent?
Backflow of saliva into acini
What do striated ducts (interlobular) contain?
Tight junctions
What do striated ducts (interlobular) cells modify?
Saliva (Na+ and Cl reabsorbed; K+ and HCO3- secreted)
What is the predominate regulator of saliva production?
Parasympathetic NS
What receptors work with the parasympathetic NS?
Ach/Muscarinic receptors
What is parasympathetic NS control of saliva critical for?
- Critical for initiation of saliva secretion
- Critical for sustaining high levels of saliva secretion
What happens as flow rate increases?
- Less time for ductal modification
- Saliva more closely resembles the plasma
- Becomes more basic
What is reflex activation of parasympathetic which stimulates saliva production?
- Taste (especially sour) and tactile stimuli (presence of smooth objects) on tongue
surface - Smell of food (especially if it is a food that is not liked)
- Ingestion of irritating foods
- Nausea
What is the role of sympathetic NS (NE/adrenergic receptors) for saliva secretion?
Minor role
Potentiates parsympathetic effects
What glands is unstimulated salivation produced by?
69% submandibular glands
26% parotid glands
5% sublingual glands
What is unstimulated salivation inhibited by?
- Fear
- Sleep
- Fatigue
- Dehydration
What glands are stimulated salivation produced by?
69% Parotid
26% submandibular
5% sublingual
What is stimulated salivation stimulated by?
- Autonomic (primarily
parasympathetic) - Thinking/seeing/smelli
ng food - Conditioned salivation
- Chewing
- Nausea
What are rates of saliva production not dependent on?
age, flow rates remain constant in spite of acinar degeneration
What is xerostomia?
Feeling of dry mouth
What are 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 is sjogren’s syndrome?
- Autoimmune destruction of mucous membranes and
moisture-secreting glands - Decreased production of tears and saliva
- Dry eyes and mouth
What can xerostomia cause?
➢ 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
What is management for 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 is mastication?
Rhythmic opening and closing of mandible that is coordinated with
tongue movements
What are functions of mastication?
- Prepare food bolus for swallowing
- Initiate digestive and metabolic activities
Describe mechanical digestion
Reduce particle size
- Break up cells
- Break up indigestible cellulose
- Increase surface area/decrease particle size for mixing with digestive
enzymes
Describe the mix of food with saliva
(serous and mucous)
- Chemical digestion (mainly carbohydrates)
- Sufficient plasticity
- Surface lubrication
- Cohesive structure
Describe the initiation of digestive and metabolic activities
- Digestion of carbohydrates in mouth
- Initiate reflexes to prepare digestive tract for incoming food
What are the three stages of deglutition?
- Voluntary stage
- Pharyngeal stage
- Esophogeal stage
Describe the voluntary stage of deglutition
- Initiate swallowing reflex
- Bolus of food moved into
pharynx by tongue - Stimulates epithelial
swallowing receptor area
Describe the pharyngeal stage of deglutition
- 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 (Respiration inhibited for < 2 sec.)
- Upper Esophageal Sphincter (UES; Pharyngoesophageal Sphincter) relaxes
Describe the esophageal stage of deglutition
- Coordinated muscle contractions to move bolus through esophagus into
stomach (aborally). - ≈ 10 sec
