digestive - phyanalec Flashcards
- helps keep the oral cavity moist
- contains enzymes that begin the process of digestion
- secreted at rate of 1L per day
- prevents bacterial infection in the mouth by washing the oral cavity
- contains lysozyme
saliva
part of saliva that dissolves molecules, which must be in solution to stimulate taste receptors
serous
– enzyme that has a weak antibacterial action
found in saliva
lysozyme
acts as buffer to neutralize the acids produced by oral bacteria
-reduces the harmful effects of bacterial acids on tooth enamel
Bicarbonate ions in saliva
a digestive enzyme in the serous part of saliva
-breaks covalent bonds between glucose molecules in starch and other polysaccharides to produce disaccharides maltose and isomaltose
salivary amylase
have a sweet taste
-digestion of polysaccharides by salivary amylase enhances the sweet taste of food
Maltose & Isomaltose
Food spends how much time in the mouth
very little
– a proteoglycan that gives a lubricating quality to the secretions of the salivary glands
-contained in the secretions of submandibular and sublingual glands
mucin
salivary gland secretion is regulated by primarily
parasympathetic NS
-increase in response to tactile stimulation and sour tastes, thought of food, odors, sensation of hunger
SALIVARY GLAND SECRETION
-sympathetic stimulation increases
mucous content of saliva (dry mouth with thick mucus)
-breaks large food particles into many small ones, which have a larger total surface area
MASTICATION
-increases efficiency of digestion because digestive enzymes act on molecules only at the surface of food particles
MASTICATION
phase of swallowing
bolus is formed in the mouth
-bolus pushed by the tongue against hard palate
-bolus goes into the oropharynx
voluntary
phase of swallowing
– moving food from pharynx to stomach
-muscular contractions of esophagus occur in peristaltic waves
esophageal
phase of swallowing
reflex initiated when a bolus of food stimulates receptors in oropharynx
-begins with elevation of the soft palate (closes the passage between oropharynx and nasopharynx)
-pharynx elevates to receive bolus of food from mouth
-pharyngeal constrictor muscles contract in succession, forcing food through pharynx
-upper esophageal sphincter relaxes, food goes to esophagus
pharyngeal
- sufficiently forceful to allow a person to swallow even while doing a headstand or floating in the zero-gravity environment
- causes relaxation of the lower esophageal sphincter in esophagus as peristaltic waves approach stomach
peristaltic waves
• Wave of of esophageal muscles precedes the bolus of food down the esophagus
relaxation
Wave ofof circular muscles propels bolus through esophagus
strong contraction
assists movement of the material, especially liquids, through the esophagus
Gravity
- function primarily as storage and mixing chamber for ingested food
- some digestion occurs, but it’s not its principal function
stomach
– semifluid mixture of food and stomach secretions; acidic
chyme
stomach secretion
– produces a ph of 2.0 in the stomach
-kills microorganisms and activates pepsin (active) from pepsinogen (inactive)
HCl
stomach secretion
breaks covalent bonds of proteins to form smaller peptide chains
-exhibits optimum activity at a ph of about 2.0
pepsin
stomach secretion
– lubricates and protects the epithelial cells of stomach wall from damaging effect of acidic chime and pepsin
-irritation of stomach mucosa stimulates secretion of greater volume of mucus
mucus
stomach secretion
binds with Vit B12 and makes it more readily absorbed in small intestine
-important in DNA synthesis and RBC production
intrinisc factor
neural mechanisms in digestive tract
- CNS in medulla oblongata
* Enteric plexus in digestive wall
PHASES OF THE STOMACH REGULATIONS
– different sensations stimulate centers in medulla oblongata
-AP are sent along parasympathetic axons within vagus nerve
-in stomach wall, preganglionic stimulate postganglionic in enteric plexus
-postganglionic stimulate secretory activity in cells of stomach mucosa, causing release of different secretions (HCl, pepsin, etc)
-neurons stimulate release of gastrin and histamine from endocrine cells
cephalic
PHASES OF THE STOMACH REGULATIONS
– period of greatest gastric volume secretion
-activated by presence of food in stomach
-food in stomach is mixed with gastric secretions (chyme formation)
-stomach distention stimulates stretch receptors
-stretch receptors generate AP to activate CNS and local reflexes
-result is increased secretion
-peptides ~ gastrin ~ additional HCl
gastric
PHASES OF THE STOMACH REGULATIONS
– inhibits gastric secretion
-controlled by the entrance of acidic chime into duodenum, which initiates both neural and hormonal mechanism
-when chime ph in duodenum is 2.0 or below, the inhibitory influence of IP is greatest
-secretin is released in response to low ph
-cholecystokinin is released in response to fatty acids and peptides, inhibits gastric secretions
-acidic chime inhibits CNS stimulation, initiates local reflexes that inhibit gastric secretion
intestinal
TYPES OF STOMACH MOVEMENT
– cause relatively weak contractions
-thoroughly mix ingested food with stomach secretions to form chime
-more fluid part of chyme is pushed toward pyloric sphincter
-more solid part of chime is pushed toward body of stomach
mixng waves
TYPES OF STOMACH MOVEMENT
cause stronger contractions
-force chyme toward and through pyloric sphincter
-pyloric sphincter usually remains closed because of mild tonic contraction
-each peristaltic contraction is sufficiently strong to cause partial relaxation of pyloric sphincter
-↑motility, ↑emptying
peristaltic waves
– major inhibitor of motility and emptying
-stomach emptying is slower after a fatty meal due to the release of
cholecystokinin
major stimulus of gastric motility and emptying
Distension of stomach wall –
uncomfortable sensation resulting from low blood glucose levels
-begin 12 – 24 hours after the previous meal
HUNGER PANG –
ENZYMES OF SMALL INTESTINE:
break peptide bonds In proteins to form amino acids
Peptidases –
ENZYMES OF SMALL INTESTINE:
– break down disaccharides (like maltose) into monosaccharides (glucose)
disaccharidases
ENZYMES OF SMALL INTESTINE:
produced by duodenal glands and goblet cells
-dispersed throughout the epithelial lining of small intestine
mucus
type of contraction
– proceed along the length of the intestine for variable distances and cause chyme to move along small intestine
peristaltic
propagated for only short distances and mix intestinal contents
SEGMENTAL CONTRACTIONS –
most absorption occurs in
duodenum and jejunum, some in ileum
contains no digestive enzymes
-dilutes and neutralizes stomach acid
- dramatically increases efficiency of fat digestion and absorption
- contains excretory products (cholesterol, fats, bile pigments like bilirubin)
bile
– major function of small intestine
ABSORPTION IN SMALL INTESTINE
– bile pigment that results from hemoglobin breakdown
bilirubin
- emulsify fats, breaking the fat globules into smaller droplets (digestive enzymes cannot act efficiently on large fat globules)
- most are reabsorbed in the ileum
BILE SALTS
BILE SECRETION
-stimulated by (3)
parasympathetic stimulation through vagus nerve
by secretin
cholecystokinin
stimulates gallbladder to contract and release bile into duodenum)
cholecystokinin
EXOCRINE SECRETIONS of pancreas
neutralize acidic chyme that enters small intestine from stomach
-increased ph resulting from HCO3 secretion stops pepsin digestion but provides proper environment for the function of pancreatic enzymes
bicarbonate ions
EXOCRINE SECRETIONS of pancreas
major proteolytic enzymes
-continue protein digestion that started in the stomach
- TRYPSIN, CHYMOTRYPSIN, CARBOXYPEPTIDAS
EXOCRINE SECRETIONS of pancreas
continues polysaccharide digestion that began in oral cavity
- PANCREATIC AMYLASE –
EXOCRINE SECRETIONS of pancreas
lipid-digesting enzyme
. LIPASE
EXOCRINE SECRETIONS of pancreas
enzymes that degrade DNA and RNA to their component nucleotides
- NUCLEASES
initiates release of watery pancreatic solution that contains large amount of HCO3
-stimulus of secretin release: presence of acidic chyme in duodenum
SECRETIN –
– stimulates pancreas to release an enzyme-rich solution
-primary stimulus: presence of fatty acids and amino acids
CHOLECYSTOKININ –
KIND OF STIMULATIONSTIMULATION – stimulates secretion of pancreatic juices
PARASYM
inhibits secretion of pancreatic juices
SYM
time required for material to pass through large intestine
18 – 24 hrs –
time required for chyme to pass through small intestine
3 – 5 hrs –
chyme in the colon (converted to feces in colon)
FECES
– elimination of feces
Defecation
stores feces until defecation
-inhabited by many bacteria
COLON
– strong contractions undergone by large parts of colon every 8-12 hours
- propel the colon contents toward anus
- very common following some meals, especially breakfast
MASS MOVEMENTS
