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123 Cards in this Set
- Front
- Back
- 3rd side (hint)
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From what portions of the GI tract are enzymes secreted?
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mouth through distal ileum
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Where do mucus glands in the GI tract begin and end?
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in the mouth and end in anus
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In the small intestine what are the pits called?
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The crypts of Lieberkuhn
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Aside from hormonal stimulation what are contributors of mucus secretion?
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mucus cells directly contacting food and local stimuli that excites the ENS such as tactile stim, chemical irratation, and distension
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Where in the alimentary tract does mucus secretion from parasympathetic stimulation occur most?
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upper part: salivary, esophageal, gastric, pancreas and brunners glands
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If vagal or sacral nerve damage occurred to the distal small intestine and first two thirds of the large intestine what would happen to mucus secretion?
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It would be relatively unaffected becuase this portion is primarily controlled by local enteric stimulation
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If a sympathetic signal travels to the mucus gland what results?
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It will secrete mucus; however, it will also constrict the blood vessels to the gland and as a result will decrease mucus secretion and override parasympathetic stimulation
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What effect does nerve stimulation have on chloride channels of glandular cells in the GI pathway? What follows
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It causes the active transport of chloride into the cell at the basal portion. The interior of the cell becomes electronegative which causes Na to move into the cell. Water then moves in increasing the intracellular hydrostatic pressure which forces water, ions and organic material out the apical membrane
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What would be the effect on secretion in the GI tract if someone had a mutation in a chloride channel? What disease might they have?
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They would not be able to flush digestive enzyme and mucus out of the cells and it would accumulate in the ducts. This happen in cystic fibrosis
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What is the resting membrane potential of glandular cells in GI tract?
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30-40 mV
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If parasympathetic stimulation increases the glandular epithelial cell membrane potential by +10mV will it depolarize?
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No because the nerve stimulation hyperpolarizes the cell membrane to below -40mV. This is the result of chloride ions moving into the gland. This is brief as sodium ions and water shortly follow
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What are some of the properties of mucus?
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it is adheres tightly to food, it coats wall of gut preventing contact of food with mucosal cells, decreases friction, causes food to stick together, resist enzyme digestion, has amphoteric properties so it acts as a buffer, contains bicarbonate
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What will result if a person loses glossopharyngeal n. stimulation to the buccal and submandibular glands of the mouth?
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dysphagia from lack of mucus
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How much saliva is produced daily?
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~1000mL
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What enzyme is found in serous secretions of parotid glands?
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ptyalin
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What is another name of ptyalin
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alpha amylase
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What does the parotid gland primarily secrete? Submandibular? Sublingual? buccal?
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serous fluid
serous and mucus serous and mucus mucus |
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What is the pH of saliva?
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6-7
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What is the daily volume of gastric secretion?
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1.5L
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What is the daily volume of pancreatic secretion?
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1L
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Someone is secreting 500mL of bile each day. Will they have trouble absorbing fat soluble vitamins?
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yes production is generally 1L per day
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How much daily fluid does the small intestine secrete?
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1.8L
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What is the pH of pancreatic secretions? Bile? small intestine? brunners glands?
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8-8.3
7.8 7.5-8 8-8.9 |
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What two ions are particularly high in saliva?
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potassium and bicarb
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Are the secretions of the acini similar or dissimilar to the fluid in the extracellular fluid?
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similar
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What happens to K+, Na, and Cl- as fluid leaves the acini and travels to through the duct of a salivary gland?
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More Na is removed than K is added. Thus the duct becomes electronegative (-70mV) therefore Cl- is passively reabsorbed
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By what means does bicarb enter the duct of a salivary gland?
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passive transport in exchange for Cl- and active transport
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What antimicrobial substances are in saliva?
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thiocyanate enters bacterial cell and becomes bacteriocidal, and lysozyme, and antibodies IgA
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Where do salivary parasympathetic nerves originate in the CNS?
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inferior and superior salivatory nuclei in brainstem
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What happens to K+, Na, and Cl- as fluid leaves the acini and travels to through the duct of a salivary gland?
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More Na is removed than K is added. Thus the duct becomes electronegative (-70mV) therefore Cl- is passively reabsorbed
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By what means does bicarb enter the duct of a salivary gland?
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passive transport in exchange for Cl- and active transport
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What antimicrobial substances are in saliva?
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thiocyanate enters bacterial cell and becomes bacteriocidal, and lysozyme, and antibodies IgA
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Where do salivary parasympathetic nerves originate in the CNS?
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inferior and superior salivatory nuclei located at juncture of pons and medulla
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What excites the salivatory nuclei?
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taste and tactile stimuli from mouth and pharynx
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Will a person that loses the ability to sense sour foods or sweet foods salivate less?
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sour because it causes the most salivation
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Will a rough or smooth object elicit a strong salvitory response?
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smooth
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Where is the appetite center located? What is its function?
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in the anterior hypothalamus. Receives information about smell and taste of food from cortex and amygdala
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What ganglion do nerves synapse in before they innervate the parotid gland?
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otic ganglia
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When an irritating food reaches the stomach what happens to salivation?
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Signals are transmitted to increase salivation to wash food away
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What effect does the sympathetic system have on salivation?
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it increases it slightly
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What type of local feed back does salivating have on the production of more saliva? What is the mechanism?
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It is a positive effect. Blood flow is increased to glands by kallikrein secreted by salivary cells which in turn splits alpha-2-globulin to form bradykinin a vasodialotor
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What type of gland lines the main body of the esophagus? What about near the cardia?
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simple mucus glands
compound mucous glands |
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What substances do the oxyntic glands secrete?
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pepsinogen, HCl, intrinsic factor and mucus
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What substances does the pyloric gland release?
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mainly mucus and some gastrin
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Where are the oxyntic glands located in the stomach?
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In the body and fundus
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What glands are in the antrum of the stomach?
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The pyloric glands
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What glands occupy most of the stomach?
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oxyntic glands
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What are the 3 cell types of the oxyntic gland and what are their functions?
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mucous neck cells- secrete mainly mucus
peptic or chief cells - secrete pepsinogen parietal or oxyntic cells - secrete HCl and IF |
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parietal cells when stimulated secrete large amounts HCl that is isotonic to blood. What is the pH when 160 millimoles of HCl are secreted?
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pH=0.8
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Do oxyntic cells use a lot of energy to produce HCl or is it mostly passive?
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It uses about 1500 calories/liter of gastric juice
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What special membrane feature do oxyntic cells have?
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canaliculi with microvilli to increase surface area
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Desribe the process of chloride secretion from parietal cell! Where does the H+ come from and how does it get into canaliculi? What happens to the OH- formed
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Chloride is actively pumped into canaliculus and Na is actively pumped into cytoplasm generating negative potential in canaliculus. K+ then passively diffuses out.
H+ comes from the cleavage of water and is exchanged for K+ at apical surface via a H+,K+-ATPase The OH- combines with CO2 and is excreted to blood as bicarb |
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How active is pepsinogen at a pH of 6?
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Not very functions best at 1.8-3.5
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Where is vitamin B12 absorbed?
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ileum
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What condition tends to develop with chronic gastritis and achlorhydria?
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pernicious anemia
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What cell predominates in the pyloric gland? What hormone is secreted from this gland?
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mucus neck cells
gastrin |
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What cell type secretes histamine and in what gland are they found and in what part of the gland?
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Entorochromafin cells are located deep in the oxyntic glands
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What induces the release of histamine from ECL cells?
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gastrin, acetylcholine from vagus nerve
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What stimulates the release of gastrin?
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proteins in food
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Where are G cells located?
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gastrin cells are located in the pyloric glands in the distal stomach
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Which gastrin hormone is produced more?
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G-17 is more abundant than G-34
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What are the signals for pepsinogen release?
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peptic cells are stimulated by acetylcholine from nerves and acid
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What are the 3 phases of gastric secretion?
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cephalic, gastric, intestinal
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When does the cephalic phase of gastric secretion occur?
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when food is seen, smelled, thought of, tasted, and great appetite
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Where do the neurogenic signals of the cephalic phase originate?
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cerebral cortex, appetite centers of amygdala and hypothalamus.
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What occurs during the gastric phase?
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vasovagal reflex, enteric reflex, gastrin mechanism
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What occurs during the intestinal phase?
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Food in the upper portion of the small intestine will continue to cause stomach secretion of small amounts of gastric juice
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How is gastric secretion inhibited?
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1) food in the small intestine initiates a reverse enterogastric reflex through all nerve pathways to inhibit secretion of HCl
2) acid, fat, protein, hyper/hypo isomotic fluids or irritation causes release of secritin, GIP, VIP, somatostatin |
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In the reverse enterogastric reflex what type of mechanims initiates it?
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stretch receptors, protein and irritation
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Is any gastric juice secreted during the interdigestive period?
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a few mililiters
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During the interdigestive period what is the composition of the gastric juice?
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primarily mucus with some pepsinogen and no acid
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How are CCK and gastrin similar?
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They have the same 5 terminal amino acids
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Where is the functional activity of gastrin? CCK? Secritin?
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1) last 4 amino acids
2) last 8 3) All |
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What is a the synthetic form of gastrin called?
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pentagastrin
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What are the 3 main digestive enzymes of the pancreas?
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trypsin, chymotrypsin, carboxypolypeptidase
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How do trypsin and chymotrypsin and carboxypolypeptidase cleave proteins?
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into peptides but not free amino acids. Carboxypolypeptidase can split into individual amino acids
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What enzymes are availble in the pancreas to cleave lipophilic molecules like fats?
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cholesterol esterase, phospholipase, pancreatic lipase
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How is trypsinogen activated?
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The intestinal mucosa releases entorkinase to cleave trypsinogen to trypsin
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Is enterokinase needed once trypsin is formed for amplification of more enzyme?
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No trypsin can activate trypsinogen, Carboxypolypeptidase, chymotrypsin
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What prevents trypsin from becoming active in pancreas?
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trypsin inhibitor
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What cells are primarily responsible for secreting fluid to wash the pancreatic enzymes through the pancreas?
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bicarb and water are secreted mainly by the ductule epithelium
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How is bicarb delivered to the lumen?
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CO2 and H2O form bicarb and H+. The H+ exchanges with Na to enter the capillary via secondary active transport and the bicarb and Na+ are actively shuttled to the lumen. H2O follows ion gradient passively
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Where is CCK released and what is the stimulus for release?
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food entering stomach causes release of cck by mucosa of duodenum and proximal jejunum
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Where is secritin released and what is the stimulus?
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acid entering duodenum and proximal jejunum causes release from mucosal cells
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Would CCK, acetylcholine, or secritin act ductle epithelium?
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secretin, CCK and acetylcholine act on acinus
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What is the effect of the gastric and cephalic phases on pancreatic secretion? Is CCK involved?
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Vagal stimuli travel to the pancreas and stimulate the release of some enzymes during theses phases. This is independent of CCK becuase food has not entered duodenum
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Will pancreatic enzymes reach the small intestine during the gastric and cephalic phase even though they are being secreted?
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Very little if any because secretin has not stimulated bicarb secretion to wash enzymes through
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What is the main stimulation for secretin release from S cells? Where are S cells located?
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S cells are in duodenal and jejunal mucosa and are stimulated by acid chyme particulary less than a pH of 5
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Is secretin or cck a propeptide?
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secretin is present as prosecretin
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How is HCl neutralized in small intestine?
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bicarb binds H+ forming H2CO3 which forms CO2 which is absorbed and expelled in lungs
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What cells release cck?
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I cells in the deudenum and jejunum
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what stimulates cck release?
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peptones, proteoses and long-chain fatty acids
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Does vagal or cck have a greater effect on enzyme release from pancreas?
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cck
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How do bile acids help absorption of lipid molecules?
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they emulsify lipids and increase the surface area of the particle so that lipase can work more efficiently. They also aid in absorption
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Describe the passage of bile to the gall bladder from the liver?
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it enters canaliculi goes to the terminal bile ducts then to larger ducts then to the hepatic duct to the cystic duct
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What is the max volume the gall bladder can hold? How can more be held?
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30-60 mL max, but it can be concentrated by removing electrolytes and water from the bile so that up to 450mL can be stored (12 hours worth)
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What are the main components of bile?
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cholesterol, bilirubin, lecithin and electrolytes and bile salts
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30 minutes after a meal the gallbladder releases bile. How?
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cck and acetylcholine cause contraction
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when bile concentration occurs most electrolytes are reabsorbed. What 2 electrolytes increase in concentration in bile that has been concentrated for 6 hours?
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calcium and potassium
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What is the main stimulus needed for bile release?
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fat in the food
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How long does it take for the bile to completely empty itself?
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1 hour with fatty meal
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How much bile does the liver synthesize daily?
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6 grams of bile salts
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what is the process of bile formation?
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cholesterol is converted to equal amounts of cholic and chenodeoxycholic acid. These combine with glycine or taurine
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About how much bile is reabsorbed and where does absorption occur?
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About 94% reabsorbed. Most is taken up in early portions of small intestine and the remainder in illeum
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On average how many times will the same bile salt recirculate before being excreted in feces?
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17
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What determines the rate of enterohepatic circulation of bile salts?
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the quantity of bile salts
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Does secretin work any where else than the pancreas?
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Increases bile secretion by producing bicarb and water solution
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How many grams of cholesterol are removed each day to make bile on average?
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1-2 grams
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What is a high fat diet promotes gall stones
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a product of fat metabolism is cholesterol which increases cholesterol concentration in the bile
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Where are Brunners glands located?
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in the first few centimeters of duodenum between pylorus and ampulla of vater
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What do brunners glands secrete? What stimulates them?
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alkaline mucus via stimulation from irratation, tactile stim, vagal stim, and secretin
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Highly stressed people may be prone to ulcers in the proximal duodenum. Why?
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sympathetic stimulation decreases brunners gland secretion
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What cell types are in the crypts of Leiberkuhn?
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goblet cells, and enterocytes which secrete large quantities of water and electrolytes over surface of adjacent villi to help absorb products of digestion
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What is the mechanism for the secretion from enterocytes?
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active secretion of both bicarb and chloride creating electrical drag that causes Na to follow and H2O
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What enzymes do enterocytes have?
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peptidases, sucarse, maltase, isomaltase and lactase, lipase. these act while food substances are being absorbed
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What is the average life span of an intestinal epithelial cell?
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5 days
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What is the most important means for regulating small intestine secretion?
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enteric nervous reflexes especially those by tactile or irritating factors
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Where are crypts of Lieberkuhn located?
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all throughout the small and large intestine
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1
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George Washington
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1789-1797
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What markedly increases mucus production in the distal 2/3 of the large intestine?
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parasympathetic stim from pelvic nerves
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What is the protective mechanism of the large intestine during enteritis?
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secrete lots of water and electrolytes to wash away irratating substance producing diarrhea
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Does Soap, peptone or HCl cause the release of equal amounts of water, bicarb, and enzymes?
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soap
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Where does passive bile absorption occur?
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Every where in small intestine except distal ileum. In distal ileum it is actively transported
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