Term
| What part of the brain regulates thirst and hunger behaviors? |
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Definition
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Term
| Describe how the thirst reflex works when the body is dehydrated. |
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Definition
| If the extracellular fluid volume decreases, plasma osmolality will rise. This increase is detected by hypothalamic osmoreceptors, which shrink as water leaves them to maintain homeostasis. Hypothalamus senses this shrinking of osmoreceptors. |
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Term
| Which hormones are released to retain water? |
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Definition
| Aldosterone, angiotensin II, and antidiuretic hormone. |
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Term
| How sensitive is the thirst response? |
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Definition
| It can detect a 2% increase in plasma osmolality. |
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Term
| Describe which hormones are active during the fasting state. |
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Definition
| The oxnytic cells of the stomach release ghrelin into blood. Ghrelin reaches arcuate nucleus of hypothalamus, which stimulates a release of neuropeptide y (NPY), which stimulates hunger. |
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Term
| What happens once food is ingested? How is the hunger reflex repressed? |
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Definition
| Upon eating, Peptide YY and Glucagon-Like Peptide-1 (GLP-1) are released from the jejunum, and these two supress NPY. Leptin is also secreted by adipose cells, and this also acts to supress NPY. |
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Term
| What's odd about leptin and ghrelin levels in obese people? |
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Definition
| In obese people, leptin levels are elevated, and ghrelin levels are decreased. This indicates that some hormone desensitization may be occurring. |
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Term
| Why do you sometimes get full, even after you have eaten less food? |
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Definition
| If you eat the food slowly, it'll have time to get to the jejunum, allowing a release of GLP-1 and Peptide YY, which supress hunger. |
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Term
| What do each of the three salivary glands release? |
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Definition
| Parotid glands release serous fluid with amylase. Sublingual glands release mucous. The submaxillary glands release both. |
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Term
| What determines the final tonicity of saliva? |
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Definition
| As saliva flows through the ducts, electrolytes are reabsorbed. Tonicity is thus dependent on the flow through the ducts. Saliva will ALWAYS be hypotonic to the plasma, but higher flow rates = higher tonicity (less time for electrolytes to be reabsorbed). And vice versa. |
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Term
| What are the differences in the electrolyte content of saliva vs blood plasma? |
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Definition
| Saliva is hypotonic, it has a HIGHER potassium concentration, and more bicarbonates than chlorides. |
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Term
| What are the effects of chronic vomiting? |
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Definition
| Loss of protons resulting in alkalosis, and a loss of potassium leading to hypokalemia. |
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Term
| What are the three products in saliva, and what are their functions? |
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Definition
| Alpha- salivary amylase, which digests starches. Lingual lipase, secreted by the tongue, which helps start the lipid digestion process. And R protein binders, which attach to vitamin B12, protecting it from breaking down in the stomach. |
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Term
| What controls the rate of salivary flow through the ducts? |
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Definition
| The parasympathetic nervous system. But NOT the vagus nerve. The glossopharyngeal and facial nerves provide the innervation, and they increase flow rate of saliva. |
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Term
| Sympathetic innervation doesn't do much for salivary flow rate, but there is an initial uptick in flow rate. What's causes this? |
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Definition
| Sympathetic innervation causes contraction of the myoepithelial cells surrounding the acinar cells, causing a quick, short release of fluid. |
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Term
| Which glands are the lingual lipases released from? |
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Definition
| von Ebner's glands in the tongue. |
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Term
| What are some factors that increase salivary flow? Decrease it? |
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Definition
| Increases flow: PNS (ACh), CNS (anticipating food coming in), nausea (to get ready for vomiting), esophageal distension. Decrease flow rate: Sympathetics (NE), hormones that retain water (ADH, Angiotensin 2, aldosterone), sleep, dehydration (obvi), aging. |
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Term
| What's the difference between mucous, mucus, and mucin? |
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Definition
| Mucous glands secrete mucus, which is a bicarbonate rich buffer. Mucins are glycoproteins that help form the viscosity of the mucus. |
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Term
| What are the esophageal secretions? |
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Definition
| The esophagous justhas minor serous and mucous glands, mostly in the lower segment. They lubricate the bolus. |
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Term
| Which cells release HCl in the stomach? What does HCl do? |
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Definition
| Parietal cells. It breaks down bacteria, aids in digestion by breaking stuff down. |
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Term
| In addition to HCl, what do parietal cells release? |
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Definition
| Intrinsic factor, which protects vitamin B12. |
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Term
| Where is pepsin released from and what does it do? |
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Definition
| It's released as pepsinogen from chief cells, and once it's broken down to pepsin, it breaks down protein. |
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Term
| What's the role of gastrin? |
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Definition
| Gastrin is a hormone released from G-cells in the antrum. It's released into the blood, and it causes a further increase in HCl production. It also causes mass movements in the large intestines (Gastrocolic reflex). |
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Term
| Where is gastric lipase secreted from and what's it role? |
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Definition
| It's also secreted from chief cells (as is pepsinogen), and it continues the lipid breakdown. |
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Term
| What other two local hormones affect HCl production in the parietal cells? |
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Definition
| Somatostatin inhibits HCl production and histamine increases it. |
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Term
| How does mucus protect the stomach epithelium? |
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Definition
| It creates a bicarbonate layer right next to the epithelial cells, and it acts as a buffer. |
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Term
| What factors regulate HCl secretion, directly and indirectly? |
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Definition
| Gastrin (more HCl) and GIP (gastrin inhibitory protein) act directly on parietal cells to recruit more H/K pumps. Secretin and peptide YY act indirectly to reduce HCl levels by supressing gastrin. |
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Term
| Why is the blood leaving the parietal cells alkayltic? |
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Definition
| Once CO2 is comes into the parietal cells, it's converted to bicarbonate and a proton. The proton stays in (and gets pumped into the lumen of stomach), but the bicarbonate gets transported back to blood, as a chloride ion comes into the parietal cell. |
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Term
| Describe the morphological change that occurs to parietal cells during stimulation and de-stimulation. |
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Definition
| If a parietal cell is stimulated, it forms canaliculi to increase surface area. This allows more proton pumps to become activated. |
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Term
| Of the inhibitors of HCl secretion, which ones act directly on parietal cells? |
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Definition
| Somatostatin and prostaglandins. |
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Term
| Wat are the three phases of neural control of acid secretion? |
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Definition
1. Cephalic -> anticipation of food increases HCl production via vagal stimulation.
2. Gastric: Once chyme reaches stomach, vagal effects, and gastrin increase HCl production.
3. Intestinal: Once chyme gets to duodenum, there's a decrease in HCl production via secretin. |
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Term
| How can chronic use of NSAIDs/aspirin lead to ulcers? |
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Definition
| NSAIDs and aspirin block prostaglandins, which promote mucus secretion and HCl inhibition. With prostaglandins blocked, you get a decrease in mucus and increased HCl levels which obviously isn't good. |
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Term
| Which bacteria is the most common cause of gastric ulcers? And how do they survive and do work? |
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Definition
| Helicobacter pyolori. It survives by secreting urease, which produces NH3 that can neutralize the acid around it. Ammonia is also toxic to epithelial cells of the stomach. |
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Term
| What are the differences between the brush border cells and the crypts of lieberkuhn? |
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Definition
| The crypts secrete chloride ions, and thus water and sodium as well. Via the CFTR protein. The brush border cells have villi/microvilli, so they're used for absorption of nutrients. They have a lot of brush border hydrolases. They absorb water instead of secreting it. |
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Term
| What cells make up the pancreatic duct? What do they secrete? |
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Definition
| Acinar cells release digestive enzymes, centroacinar and extralobular cells secrete electrolytes, bicarbonate, and water. |
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Term
| What are acinar cells and centroacinar/extralobular cells stimlated by? |
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Definition
| CCK stimulates acinar cells, and secretin stimulates centroacinar/extralobular cells. |
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Term
| What are pancreatic enzymes secreted as? |
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Definition
| Zymogens, so they don't eat up the pancreatic cells, leading to pancreatitis. |
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Term
| How is trypsinogen activated in the duodenum? What does it go on to do? |
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Definition
| It's activated by enterokinase to trypsin. Trypsin activates all the other zymogens. |
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Term
| What is the primary hormone released if the chyme in the duodenum consists mostly of peptides and amino acids? |
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Definition
| Gastrin from G-cells. Gastrin's effects: increase in HCl at parietal cells, increases antral and intestinal motility. |
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Term
| What is the primary hormone released if the chyme is a long fatty acid chain? |
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Definition
| Secretin, from S-cells. Secretin increases pancreatic, biliary, and intestinal electrolyte secretions. Reduces HCl levels and Gastric emptying. |
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Term
| What's the primary hormone released if the chyme in the duodenum is mostly peptides and fats? |
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Definition
| CCK. Increases pancreatic enzyme secretion, gall bladder contraction, relaxes sphincter of oddi, reduces gastric emptying, and causes increased motility in small and large intestines (mass movements). |
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Term
| If the chyme in the duodenum consists of fatty acids, protein, and sugars, what hormone is released? |
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Definition
| Gastrin inhibitory peptide. This increases insulin secretion, lowers gastric emptying and motility. |
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Term
| What does the Ileum secrete? In exhange for what? |
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Definition
| Ileum secretes protons in exchange for sodium ions, and bicarbonate in exchange for chloride ions. |
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Term
| What's secreted/absorbed in the colon? What happens during diarrhea? |
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Definition
| Potassium ions and bicarbonate are secreted, while sodium (and thus water) is absorbed. With diarrhea, we can get hypokalemia (as with vomiting), and acidosis (unlike with vomiting). |
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