Gastrointestinal System Flashcards
What are the functions and parts of the GI system?
The functions of the GI system is motility, absorption, breaking apart food into absorbable bits and secretion! Nutrients go from the lumen to the blood. Secretions go from the blood to lumen and hormones go from the cytosol of the cell to the blood.
The GI system starts with the mouth. It then goes to esophagus, stomach, small intestine, large intestine, and anus. Stuff is transported from the mouth to anus but it can also go backwards (vomiting).
Describe the wall of the GI tract.
From the lumen to the blood:
Mucosa (epithelia, lamina propia, muscularis mucosae):
The epithelia is where most absorption and secretion occur. It secretes enzymes and mucus and absorbs nutrients. It has receptors for endocrine signals that increase secretion. For absorption, the presence of food is detected and increase absorption of nutrients into the cells.
The lamina propia just contains connective tissue, a few blood vessles, etc.
Muscularis mucosa has smooth muscle and contractions change the shape of the epithelia!
Submucosa: nerves, elastin, collagen, BLOOD VESSELS found here. When you have an ulcer, this is where primary bleeding comes from.
Submucosal plexus
Circular muscle
Myenteric plexus
Longitudinal muscle
Serosa: keeps organs in place and reduces friction
– Smooth muscle is found all along the GI tract (except pharynx, upper 1/3 of the esophagus and external anal sphincter) and is the contractile force of the tract.
What is the extrinsic and intrinsic component of the ANS of the GI tract? (Remember to talk about interneurons!)
Extrinsic: PNS and SNS.
PNS: you have vagus and pelvic nerves. Has long preganglionic neurons that synapse on/ near their target organs (for GI it is usually in the myenteric or submucosal plexus). Postganglionic neurons are short and release ACh or VIP.
SNS: has short preganglionic neurons that synapse in ganglia outside the tract (celiac, superior mesenteric, inferior mesenteric, and hypogastric usually). Postganglionic neurons are long and release norepinephrine and synapse on ganglia in the plexus or go directly to the muscles.
Intrinsic: ENS
It is made from the ganglia of the submucosal and myenteric plexuses. It receives info from the SNS and PNS but also from mechano and chemoreceptors int he walls of the GI tract. Interneurons are the neurons that allow the communication between the ganglia.
What is secretion and what are the functions of salivary secretion? Why is the blood flow to the salivary glands special?
Secretion is the addition of fluids, enzymes and mucus to the lumen of the GI tract. Saliva kills bacteria, lubricates the oral cavity and food, acts as a temperature buffer, begins the process of digestion, it maintains pH and dissolves food substances.
Blood flow to the salivary glands is very very high!
What is the composition of saliva compared to the plasma? How is it made? How does flow rate affect the composition of plasma and what is special about HCO3?
Saliva has more bicarb and K+ but less Na and Cl- than plasma. It is made by a two step process.
1. You have acinar cells which secrete an initial saliva which is isotonic to the plasma. Acinar cells also secrete alpha amylase, lingual lipase, proline rich protein and mucous.
2. This saliva then passes through the striated duct which is lined with duct cells that contain 3 different transporters that modify the salvia.
— HCO3/ Cl- exchanger
— Na/H exchanger
— K/H exchanger
There is a net absorption of Na/Cl! Saliva is hypotonic even though there are exchangers because you have a net absorption and duct cells are not permeable to water so dilution effect!
Flow rate affects the composition of plasma because it becomes less hypotonic when there is a faster flow (more closely resembles plasma) because the saliva has less time for absorption secretion. When there is a low flow rate, the saliva will be even more hypotonic than normal because there is more time to reabsorb Na and Cl and to secrete K+. There is a slight difference with HCO3 however. When there is low flow, there is less HCO3 in the saliva because its secretion is selectively stimulated. When there is low flow there is less parasympathetic stimulation so less HCO3 will be stimulated. Low flow = low pH!
What are the effects of PNS and SNS on salivary glands?
PNS and SNS both increase salivary gland secretions! PNS has a greater effect! Salivary glands are only stimulated by neuronal input and is not controlled by hormonal input.
The PNS is stimulated by food, nausea, conditioning, and smell and inhibited by fear, sleep and dehydration. The PNS has long preganglionic that are carried by CN VII and IX. Postganglionic release ACh which act on muscarinic receptors to increase IP3 and Ca2+ in the cells. This increases salivary production. It causes an increase in amylase and mucous production. You also have an increase in ion transport activity. It helps with growth and metabolism and increases blood flow to the glands. If you have denervation –> atrophy of salivary glands.
The sympathetic nervous system also increases salivary production. It uses T1-T3 as short preganglionic nerves. These synapse on the superior cervical ganglion. Postganglionic fibers release NE onto B adrenergic receptors which increase cAMP in the cells and increase salivary production. Denervation has little effect.
What is xerostomia? What are the treatments?
Xerostomia is dry mouth disease and it is caused by chemotherapy or radiation. You have lower secretion rates of bicarb, lower pH, lesions in the mouth and loss of minerals from teeth. It can be treated with amifostine and you can use salivary substitutes with contain carboxymethylcellulose!
What are the functions of the stomach? Describe the components of gastric juice.
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What are the two types of glands found in the stomach and their cellular composition?
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What is the difference between basal aqueous secretion and stimulated aqueous secretion?
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What is the cellular mechanism of secreting H+ in a parietal cell? Talk about H/K ATPase.
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What are three mechanisms that increase H+ secretion? What happens to parietal cells when these mechanisms are intiated? What drugs block these mechanisms? What are four mechanisms that inhibit H+ secretion?
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What is potentiation?
It is when the sum of all the effecters is less than the sum of the actual effect.
How is protein digestion efficiency improved? What about mucus secretion?
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What is the function of the gastric mucosal barrier?
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How do H.pylori stay alive in acidic environments? What is the importance of H.pylori? What are some consequences of H. pylori?
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Why is aspirin a cause of ulcers?
It inhibits COX1 which is necessary to make prostaglandins. PGs inhibit acid secretion by acting on H2 receptors but if they are not made, acid secretion is not inhibited –> ulcers!
What are the endocrine and exocrine secretions of the pancreas? What happens to aqueous component of pancreatic secretion when the rate of secretion changes?
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Describe what happens from acinus of the pancreas to the extralobular duct of the pancreas. Talk about the cellular (and paracellular) mechanism of the extralobular duct
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What happens in cystic fibrosis?
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What is the hormone that controls aqueous component secretion? What is the stimulus for its release?
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How is the organic component of pancreatic secretion controlled?
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What is the difference in CCK regulatory effects on rats versus humans?
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