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55 Cards in this Set
- Front
- Back
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Describe the process of digestion.
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-Sequence of interdependent steps
-Enz are proteins -duplication of enzyme activity medium requirements: pH, ions |
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Explain digestions
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Chemical breakup to progressively smaller olec
Results from the secretory activity of a large number of exocrine glands found within and in ass't with the GIT Products released into the lumen of the digestive tract |
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Is the lumen of the idgestive tract part of the internal or external environment?
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External environment
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What kind of process is secretion?
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Active
Energy dependent Blood flow dependent ->results in the releas of a fluid containing ions and a variety of enzymes |
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What are the 3 types of enzymes involved in digestion?
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Amylases
Proteases Lipases |
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What are the types of regulation of digestion?
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Nervous: most important at the beginning of digestion: mouth, stomach, less important as you go down to the SI
Hormonal (Gut peptides): Most important further down-> large intestine, then less and less as you go to the pancreas and the liver |
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What are the major salivary glands?
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Parotid glands: serous (watery and liquid)
Submandibular gland: mixed Sublingual gland: mucous (viscous) |
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What is special about saliva?
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Only secretion that is hypotonic
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Describe saliva characteristics.
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Volume: 0.5-1.5L/day
Ions: Na+, K+, Cl-. HCO3- pH: 6.5-7 |
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Wha enzymes does the saliva contains?
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Amylase (ptyalin)
Mucin:lubricates bolus Lipase: insignificant amount in adults Lysozyme: antibacterial agent |
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What does Ptyalin do?
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Reduces starch polysac to maltose (a disac)
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Is digestion of polysac completed in the mouth?
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NO
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What regulates saliva?
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ANS (exclusively)
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How does the ANS parasym regulate saliva?
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Acts on the gland itself, release ACh which acts on muscarinic receptors to INCREASE secretion
->VASODILATION: increases blood flow so that it can secrete |
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How does the ANS sympathetically regulate saliva?
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May cause very little secretion
->VASOCONSTRICTION decrease in secretion, but some cells secrete a small amount of saliva (this is odd because the symp is doing the same as the parasymp in some salivary cells) |
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What does atropine do?
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Temporarily stops secretion by blocking muscarinic receptors from binding ACh
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What kind of reflexes are involved in the regulation of salivary reflexes?
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Simple Reflexes
Conditioned Reflexes |
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What are conditioned reflexes?
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Eyes, nose
This goes to Higher centres which then goes to Salivary centres in teh medulla |
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What are simple reflexes?
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Come from sensory receptors in the mouth
G through afferent fibers andhe impulses are sent to the salivary center in the medulla |
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What happens once impulses are sent to the salivary center in the medulla, from either the conditional or simple reflexes?
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Efferent output via the parasym, get secretion by the salivary glands
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What are the phases of secretion?
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1) Psychic: conditioned reflex, takes over when see/smell/think about food
2) Gustatory: simple reflex, tasting food ->these 2 are cephalic reflexes (3-gastric/intestinal: due to hot/irritating food, stimuli initiates in stomach) |
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Describe the characteristics of mixed gastric juice.
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Vol: 1.5-2L/day
Isotonic fluid: Na+, K+, Cl-, **H+** **pH: 1-2** very high concentraion of H+ is responsible for the low pH |
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What are the organic substances secreted found in the mixed gastric juice?
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Pepsinogen: inactive precursor of a protease
Intrinsic factor: allows absorption of vitamin B12 Mucin: very effective lubricant, protects against mech. abrasions, contains rough particles |
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What do surface epithelial cells in the stomach secrete?
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Mucous, alkaline fluid
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Which glands secrete an alkaline, mucin-rich fluid?
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Cardiac gland
Pyloric tubular glnd |
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What secretory cells are present in the gastric glands in the fundus and the corpus?
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Parietal Cells
Chief Cells Mucous neck cells |
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What do parietal cells secrete?
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HCl
Have intracelular channels |
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What do chief cells secrete?
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Pepsinogen
->chief cells have zymogen granules tha secrete pepsinogen |
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What do mucus cells secrete?
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Mucin secretion
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What is the structure of the parietal cell?
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Cery active cell .: has a lot of mitochondria
Has lots of microvilli Located in the fundus and corpus Has canaliculus: channels that communicate with lumen and project into cell interior |
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What is the maximum secretion proportional to?
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The number of parietal cells
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What are proton pump inhibitors for?
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For ppl who secrete more acid than normal
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What does nexin do?
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H+/K+ ATPase
Prevents excessive acid secretion |
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What is the H+/K+ ATPase used for?
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Involved in last step, in HCl release
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What happens for every H+ that is secreted in the lumen?
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An HCO3 is secreted in plasma
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What is the concentration of H+ in the plasma?
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4 x 10^-5mEq
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What is HCl in the lumen?
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Isotonic
(150 mEq H+, 150 mEq Cl-) |
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What happens to the urine when the stomach produces a lot of H+?
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NEed to make a lot of HCO3, which increases the alkalinity in urine
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What kind of port is the H+/K+ ATPase?
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Antiporter
pumps H+ outand K+ in (leaves OH- in cell) |
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Describe thescheme for HCl secretion
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1) Cl- entering the cell is actively transported across the canalicular mb
2) H+ abailable from the diss't of intracellular water is also actively pumped into the canaliculi in exchange for K+ 3) Secretion of H+ leaves an excess of OH- in the cell, .: get increase of intracellular pH. This causes more CO2 to diffuse in from the plasma (with metabolic CO2) and combines with water in the presence of Carbonic Anhydrase to makeH2CO3 H2CO3 reacts with excess OH- to get H2O and HCO3-. HCO3- diffuses into the circulation, restoring the intracell status quo, and giving rise to anincreased alkalinity in the venjous blood 4) Water moces into the canaliculi passively |
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hat is the parietal cell secretion?
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Pure HCl fluid
Constant composition, pH= 0.8 Independent of tpe/magnitude of stimulus |
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What modifies mixed gastric juice?
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Non-parietal alkaline gastric secretion
.: mixed gastric juice pH: 1-2 |
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What does the pH of mixed gastric juice depend on?
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# of parietal cells that are active
(if a lot are active, pH is closer to 1) |
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What are the fcts of HCl?
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1) Ppts soluble ptns: important, if ptns ppt, they will remain in the stomach longer and be released in duodenum more slowly
2) Denatures ptns: exposes more bonds to proteases **3) Activates pepsin and Provides optimal pH for it activity |
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How is pepsin activated?
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Pepsinogen --> pepsin
Need HCl so that pH < 6 Pepsin: + fdbk, autocatalytic activity, to cleave more pepsinogen to pepsin |
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What does pepsin do?
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at pH 2-3:
proteins-> polypeptides |
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Is pepsin required for ptn digestion?
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No, because the pancres producves more powerful proteases
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What is the intrinsic factor?
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Not an Enzyme
Only secretion of the STOMACH that is essential to life -a glycoptn -secreted by parietal ell **required for the absorption in distal small intestine (ileum) of physiological adequate amounts of dietary vit B12 (imp in dev'l of nervous system) |
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What happens if there is a deficiency in intrinsic factor?
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Pernicious anemia
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What produces mucin?
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Surface epithelial cells
Cardiac and pyloric sphincter Mucous neck cells |
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I"s mucin permeable to acid?
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YES
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What does the gastric mucosal barrier (GMB) do?
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Prevents penetration of acid (has apical surfaces and tight junctions)
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What does the muci-bicarb layer do?
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Neutralize the H+ that does penetrate
1st line of defense vs the acid |
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What is the pH of the mucous gel? Surface epithelial cells?
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Mucous gel: pH 2
Surface epithelial: pH 7 |
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What do surface epithelial cells contain to prevent acid?
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Tiht junctions that are relatively impermeable to ions
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