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104 Cards in this Set

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what do exocrine gland cells in the stomach do?
secretions from gastric juice
what are the three types of exocrine gland cells in the stomach?
1. mucous neck cells
2. parietal cells
3. chief cells
what do mucous neck cells do?
line the pit, protection, and secretes mucous
what 4 things do parietal cells in the stomach do?
1. give us HCl (acid)
2. intrinsic factors
3. transport H+ into the stomach lumen
4. transport Cl- into stomach lumen
how is parietal cells and intrinsic factor?
help us absorb vitamin B12
what happens when pareital cells transport H+ into the stomach lumen?
-H+ generated from CO2 and H2O via carbonic annhydrase
-H+ actively transported via H+/K+ pump into lumen
what are the 4 functions of increased HCl in stomach?
1. denatures protein
2. enzyme inactivation
3. kills most microorganisms
4. activated pepsinogen to pepsin
what is an alkaline tide?
when bicarbonate ions (HCO3-) dump into blood and cause local increase in pH
what do chief cells do?
secrete pepsinogen and acid activation
what is the positive feedback of chief cells?
pepsin activation of pepsinogen
what is the function of chief cells?
protein digestion- breaking up peptide bonds and leaves fragments of smaller peptide chains
what are 2 types of enteroendocrine cells?
1. G cells
2. D cells
where are G cells and what do they secrete?
in lowest portion of stomach; secretes gastrin
what are 2 functions of the hormone gastrin?
1. stimulates secretion by parietal and cheif cells
2. stimulate gastric wall contractions by acting on muscularis externa
what do D cells secrete?
somatostatin
how is somatostatin released?
continuously released adjacent to G cells and goes through blood through the sympathetic nerve to inhibit gastrin release
when is the only time you want gastrin release?
during digestion
what overrides D cells?
hormonal and neural stimuli
what do D cells protect us from?
early gastric release
where is the cardia region?
at the top where esophagus reaches stomach
what 2 compnents make up the cardia region?
1. gastric pits (GP) lines with simple columnar epithelium
2. cardia glands (CG) make mucous secretion
what 2 compnents make up the body of fundic region?
1. cheif cells
2. parietal cells
what happens in the pyloric region?
open pyloric sphincter to release into small intestine
what 2 types of secretions are involves in pyloric region?
1. mucous secretion line for acidity
2. enteroendocrine secretions
what two hormones are involved in enteroendocrine secretions?
1. gastrin
2. somatostatin
how does the ANS and SNS affect somatostatin release?
-ANS controls release
-SNS turns down- stops release so G cells can release gastrin
what are the three phases of the stomach digestive processes?
1. cephalic phase
2. gastric phase
3. intestinal phase
what happens during the cephalic stage?
-occurs before the bolus enters stomach
-inputs activate olfactory and taste bud receptors
what happens once olfactory and taste bud receptors are activated during the cephalic stage?
they're relayed to the hypothalamus to the vagus nerve and they stimulate neurons in the medulla oblagata
what 3 things occur once neurons in the oblagata are stimulated?
1. motor impulses via vagus nerves to parasympathetic enteric ganglia
2. stimulate stomach glands
3. enhance secretory activity
briefly explain the process of the cephalic stage through flowchart
CNS-> Vagus nerve-> submucosal plexus-> stimulates: mucous (neck) cells, parietal, chief, and G cells
what 5 things happen during the gastric phase?
1. bolus enters the stomach
2. acid and enzymes process the ingested material
3. chemical stimuli and local neural and hormonal mechanisms provides release of gastric juice
4. churning and mixing of material
5. results in chyme
what is the chemical stimuli of the gastric phase?
- increase activity of chief and parietal cells
- increase pH, more alkine, activate G cells
what 2 things happen once gastric juice is release in the gastric phase?
1. protein digestion begins
2. lingual lipase (secreted from saliva) begins lipid digestion
what do local neural mechanisms activate during the gastric phase?
1. activation of myenteric plexus (chemical and stretch receptors
2. activates submucosal plexus- chemical stimulation/stretch
what is the myenteric plexus and what does it activate during the gastric phase?
chemical and stretch receptors; it activates muscularis externa and we get churning
what two type of responses are involved in the intestinal phase?
1. hormonal
2. neural
what 2 things happen dring the neural response of the intestinal phase?
1. distension of duedenum and chemical triggers
2. enterogastric reflex
what do the chemical triggers during distension of the duodenum involve?
squeezing of chyme into intestine and acid comes in, low pH around 2, and undigested lipids, peptides, and carbs
what 3 things does the enterogastric reflex do?
-inhibit vagal nuclei in medulla
-inhibit local reflexes
-activate sympathetic fibers
what happens once sympathetic fibers are activated?
puts us into flight fright stage, digestive system slows, slows pyloris phincter which controls the rate of chyme entering
what is the stomach result of the enterogastric reflex?
-gastric activity declined
what is the intestinal result of the enterogastric reflex?
-protection and time to begin digestion
what happens during the hormonal response?
enterogastrones are triggered by arrival of chyme; everytime chyme comes in there in a decrease in pH
what three hormons are involved in the hormonal response of the intestinal phase?
1. cholecystokinin (CCK)
2. gastric inhibitory peptide (GIP)
3. secretin
what is cholecystokinin (CCK)?
lipids; inhibits stomach contraction which controls sphincter (slows pyloric release)
what causes stomach contractions to be inhibited by CCK?
by gallbladder contraction and pancreatic enzyme release
what is gastric inhibitory peptide (GIP)?
lipids, CHO; inhibitys gastric secretions and contractions by stimulating insulin release
what does secretin do?
lowers pH; inhibits parietal and chief cell activity by stimulating productions of bicarbonate ions (pancrease) and secretion of bile (liver)
where does the small intestine extend?
from the pyloric sphincter to ileocecal valve
what are the 3 divisions of the small intestine?
1. duodenum
2. jejunum
3. ileum
where is the duodenum?
retroperitoneal (behind the peritoneal); curves around the pancreas
what is the duodenum's major job?
-mixing tank (chyme comes in)
-pancreatic and bile released in here
-short (10 inches)
what happens in the jejunum?
chemical digestion and absorption (nutrient); reenters peritoneal cavity
what is the ileum?
-controls flow of chyme
-longest segment; ends at ileocecal valve
what are the plicae circulares of the small intestine?
permanent fold of mucosa and submucosa
what is the villi in the small intestine?
-projections of absorptive epithelial layer
-large in duodenum and gradually narrow and shorten
-absorptive columnar epithelial cells
what does the core of the villi contain?
capillary bed and lacteal for absorption
what is a lacteal?
lymph vessels; lipid absorption, muscularis mucosa- "milks the lacteals"-->gets fluid mocing
what is the microvilli of the small intestine?
projections of absorptive epithelial cells that release brush border enzymes for digestion completion
what role does the muscularis externa contractions play in the small intestine?
segmentation: absorption efficiency
what four types of cells are in the epithelium of the small intestine?
1. goblet cells
2. intestinal glands
3. paneth
4. enteroendocrine
what do the goblet cells do?
secrete mucus
what do the intestinal glands of the small intestine epithelium do?
-Crypts of Lieberkuhn: decrease as following the length of the large intestine; secrete intestinal juice
what do paneth cells do?
-secrete lysozyme and perform phagocytosis
-clear, yellow fluid- water and mucous, slightly alkaline
what are the three cells involved in enteroendocrine cells?
1. S cells
2. CCK cells
3. K cells
what do S cells do?
secrete secretin; activates pancrease to produce more gallbladder secretions
what do CCK cells do?
increase gallbladder contraction, increase pancreatic contraction
what do K cells do?
initiate release of insulin from pancreas
what two factors make up the lamina propria?
1. MALT
2. Brunner's glands (duodenal glands)
what are 3 components of MALT in the lamina propria of the small intestine?
1. solitary lymphatic nodules
2. aggregated lymphatic follicles also in ileum: Peyer's patches; increase as we near large intestine
3. submucosa only in duodenum
what are brunner's glands?
duodenal glands that have alkine mucus only to neutralize chyme
where is the last part of digestion always done?
at the lining
what 3 things contribute to digestion in small intestine?
1. brush border enzymes
2. digestion takes place at cell surface
3. sloughing of cells releases enzymes
where are the brush border enzymes of the small intestine?
inserted in plasma membrane of microvilli
what are 3 types of brush border enzymes?
1. 4 CHO digesting enzymes
2. Protein digesting enzymes
3. Nucleotide enzymes
what are the 4 CHO digesting enzymes?
dextrinase, maltase, sucrase, lactase
what are protein digesting enzymes?
peptidases (aminopeptidase and dipeptidase)
what are nucleotide enzymes?
nucleosidases and phosphatases
what are the 2 types of mechanical digestion?
1. segmentation
2. peristalsis
what is segmentation?
-circular muscles only; stimulus is distention to segment
-localized mixing contractions
where are the localized mixing contractions most rapid? progressively slower?
rapid- in duodenum where chyme comes in starting digestion
slow- ileum
what is peristalsis?
-begins after absorption success-less distension
-migrating motility complex= slow
-chyme remains in small intestine ~3-5 hours
what are the six chemicals involved in chemical digestion within the small intestine?
1. CHO's
2. Monosaccharides
3. proteins
4. amino acids
5. lipids
6. nucleic acids
what is involved in CHO's?
-pancreatic amylase
-a-dextrinase
-sucrase, lactase, and maltase
what is pancreatic amylase?
-glycogen and starches, mostly disaccharides
-acts on starches not already broken down into maltose, maltotriose, and a-dextrins
what is a-dextrinase?
-brush border enzyme
-clips off glucoses one at a time from a-dextrins; left over from pancreatic digestion
what is sucrase, lactase, and maltase?
brush border enzymes that digest disaccharides into monosaccharides
what happens to monosaccharides during chemical digestion?
they are absorbed by facilitated diffusion and cotransport mechanism
what are proteins?
-enzymes in pancreatic juice
-continue to breakdown proteins into peptides
-Peptidases (brush border enzymes): aminopeptidase and dipeptidase
what are the 4 enzymes in pancreatic juice?
1. trypsin
2. chymotrypsin
3. carboxypeptidase
4. elastase
what is the most abundant lipid?
triglyceride
what are 3 compnents of lipids?
1. bile
2. lipases
3. micelles
what is bile?
-salts of bile acids (Na+, K+)
-emulsification of large lipid globules
what does emulsification of large lipid globules do?
-amphiphatic
-breaks into smaller droplets (surround the fat)
-increases surface area for enzymatic action
what are pancreatic lipases?
-split triglycerides and phospholipids
-interact with bile salts in chyme
-form micelles
what happens to micelles?
they're absorbed and surrounded by bile; free, fatty acids and trigly. and monogly.
what are the four different types of nucleic acids?
1. ribonuclease (pancreas)
2. deoxyribonuclease (pancrease)
3. nucleosideases and phosphatases
4. pentoses, phosphates, nitrogenous bases absorbed by active transport
what does ribonuclease digest?
RNA in the pancreas
what does deoxyribonuclease digest?
DNA in the pancrease
what are nucleosidases and phosphatases?
brush border enzymes that digest nucleotides into pentoses, phospates and nitrogrnous bases
what do ribonuclease and deoxyribonuclease breakdown to?
phosphatases
what is the smallest of DNA and RNA breakdown?
nitrogenous bases
how are pentoses, phosphates, nitrogenous bases absorbed?
active transport