Exam 4 - Digestive System 2 Flashcards
Functions of saliva: moistens food
99.5% water and solutes
Functions of saliva: binds food together into bolus
Mucus - aids in swallowing, binds and lubricates food mass
Functions of saliva: inhibits bacteria
- Lysozyme - enzyme that kills bacteria
- immunoglobulin A - inhibits bacterial growth
Functions of saliva: begins starch digestion
Salivary amylase - works at NEUTRAL pH and is deactivated at low pH (stomach)
Functions of saliva: PREPARES FOR fat digestion
Lingual lipase - digests fat activated by stomach acid (after food is swallowed)
Mucous acinus
secretes mucus
Serous acinus
secretes thin fluid rich in AMYLASE
Mixed acinus
secretes both
Intrinsic salivary glands
indefinite number of small glands in mucosa that secrete relatively small amounts of saliva at a constant rate
CONTAIN LINGUAL LIPASE AND LYSOZYME
Extrinsic salivary glands
- parotid
- submandibular
- sublingual
Parotid
- largest, SEROUS, just anterior to the ear
- parotid duct (Stinson’s) crosses over masseter, penetrates buccinators, and ENTERS THE ORAL CAVITY ADJACENT TO THE 2ND UPPER MOLAR
Submandibular
- mixed but mostly MUCOUS
- each has 10-12 ducts that enter the floor of the oral cavity
Food stimulates receptors that signal salivatory nuclei in…?
MEDULLA AND PONS
Parasympathetic control of salivation and swallowing
salivary glands produce thin saliva, RICH IN ENZYMES
Sympathetic control of salivation and swallowing
produce less abundant, thicker saliva, w/ MORE MUCOUS
What can also stimulate salivatory nuclei to cause salivation?
higher brain centers so sight, smell, and though of food cause salivation
Skeletal muscles in pharynx
OPPOSITE FROM MOST OF GI TRACT
- deep layer has LONGITUDINALLY ORIENTED SKELETAL MUSCLE
- superficial layer has CIRCULARLY ORIENTED SKELETAL MUSCLE
(superior, middle, and inferior pharyngeal constrictors)
Upper esophageal sphincter
inferior constrictor remains contracted when not swallowing to prevent air from entering esophagus
What do the muscles of the pharynx contribute to?
swallowing by forcing food downward
Where does the esophagus begin
Cricoid cartilage, inferior to larynx, dorsal to trachea
Epithelium that lines the esophagus
NONKERATINIZED stratified squamous epithelium (abrasion resistant)
Extension of esophagus
extends from pharynx to cardiac orifice of stomach passing through ESOPHAGIAL HIATUS
Food pauses at the esophageal hiatus before entering the stomach due to
lower esophageal sphincter (LES)
purpose of lower esophageal sphincter
will keep acidic materials from refluxing back into esophagus causing GERD/heartburn
Upper 1/3 muscularis externa of esophagus
skeletal muscle (voluntary)
Middle 1/3 muscularis externa of esophagus
mixture of skeletal and smooth muscle
Lower 1/3 muscularis externa of esophagus
only smooth muscle (involuntary)
Series of muscular contractions for deglutition/swallowing are coordinated by
medulla and pons
For deglution/swallowing, motor signals from cranial nerves…?
5, 7, 9, 12
Two phases of swallowing
- Buccal phase
- Pharyngeal-esophageal phase
Buccal phase of swallowing
tongue collects food and pushes it back into oropharynx
Pharyngeal-esophageal phase
- soft palate rises and blocks nasopharynx
- infrahyoid muscles lift larynx; epiglottis folded back (prevents food going to lungs)
- pharyngeal constrictors push bolus down esophagus
Primary function of stomach
food storage organ
- mechanically breaks up and liquefies food AND begins chemical digestion of protein and fat (lingual lipase needs acidic environment( resulting in a soupy mixture called CHYME
Volumes of stomach
- 50 mL when empty
- 1.0-1.5 L after a typical meal
- May hold up to 4.0 L and extend to pelvis
Absorption in stomach
the stomach DOES NOT ABSORB A SIGNIFICANT AMOUNT OF NUTRIENTS, but can absorb aspirin and some lipid-soluble drugs
Innervation of the stomach
- PARASYMPATHETIC fibers from VAGUS
- SYMPATHETIC fibers from CELIAC GANGLIA
Blood in the stomach
enters HEPATIC PORTAL CIRCULATION and is “filtered” through liver before returning to heart
Secrete mucous
Mucous cells
Divide rapidly to produce new cells
Regenerative cells
Secret HCL acid and intrinsic factor
Parietal cells
Secrete pepsinogen and chymosin and lipase in infancy
Chief cells
Secrete hormones and paracrine messengers
Enteroendocrine cells
Secrete gastrin
G cells
Mucous
- VISCOUS and ALKALINE
- PROTECTS STOMACH from the acidic chime and enzyme pepsin
Intrinsic factor
- BINDS W/ VITAMIN B12 AND HELPS IT TO BE ABSORBED
- B12 is necessary for DNA synthesis
HCl
- kills bacteria
- STOPS CARBOHYDRATE DIGESTION BY INACTIVATING SALIVARY AMYLASE
- HELPS CONVERT PEPSINOGEN TO PEPSIN (ACTIVATES IT AND LINGUAL LIPASE
- converts ingested FERRIC iron to FERROUS iron
Pepsinogen
- packaged granules released by exocytosis
- pepsin catalyzes breaking of covalent bonds in PROTEINS
How does the stomach produce HCl?
Parietal cells contain CARBONIC ANHYDRASE (CAH)
- CO2 goes from bloodstream into parietal cells
- CO2 and water make H2CO3
- H2CO3 breaks down so we put acid in the stomach lining and we put HCO3- back into the bloodstream
Action of pepsin
autolytic effect - as some pepsin is formed it converts more pepsinogen into more pepsin (both are proteins)
Gastric motility
swallowing center (medulla) signals stomach to relax and food stretching stomach also activates a receptive response which allows stomach to accommodate more food (when you swallow the stomach will automatically expand because it is anticipating that food is en route; once the food gets there it expands even more)
What controls rhythm of peristalsis
pacemaker cells in longitudinal muscle layer
Gentle ripple of contraction every 20 seconds
churns and mixes food w/ gastric juice
Stronger contraction at pyloric regions
ejects content in 3mL boli
- enables duodenum to neutralize acid
- allows for digestion of nutrients a little at a time (duodenum is not a storage area)
- requires 4 HOURS for a typical meal to be emptied from stomach
Cephalic phase of gastric function
in response to sight, smell, taste, or though of food, vagus never stimulates gastric secretion and motility
Gastric phase of gastric function
Secretion stimulated by ACh (parasympathetic fibers), gastrin (from pyloric G cells) and histamine (from gastric enteroendocrine cells).
Stimulate all parietal cell secretions
ACh
Gastrin
Histamine
Stimulate CHIEF CELL secretion (which secrete pepsinogen)
ACh and Gastrin
Stimulates mucous secretion
ACh
What does protein digestion produce during the gastric phase?
Produces peptides and amino acids (that stimulate G cells to secrete more gastrin) that buffer stomach acid (which stimulates parietal cells)
stimulate gastrin to stimulate pepsinogen to do something about the peptides; the pH of the stomach is supposed to be low, protein buffers it so you need something to digest the proteins to get the stomach to its normal acidic environment
Negative feed back during gastric phase
as stomach empties and peptides and amino acids leave, BUFFERING CAPACITY GOES DOWN AND pH FALLS BELOW 2 which INHIBITS PARIETAL CELLS and G CELLS
as the protein leaves, you don’t need the pepsinogen anymore, protein leaving leads to less buffering and the pH of the stomach falls which will tell the parietal cells that they don’t need to make anymore acid
Intestinal phase
(Enterogastric reflex)
- acid (and semi-digested fats) in duodenum, sends inhibitory signals to stomach via enteric nervous system and then to medulla which REDUCES VAGAL STIMULATION of stomach
What do duodenal endocrine cells release during intestinal phase?
- secretin
- cholecystokinin (CCK)
- gastric inhibitory peptide
ALL 3 SUPPRESS GASTRIC SECRETION AND MOTILITY
