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33 Cards in this Set
- Front
- Back
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Voluntary and reflex control of chewing |
Voluntary - somatic nerves - skeletal muscles of mouth/jaw Reflex - mechanoreceptors sense increased pressure - inhibits jaw muscles - reduced pressure - contraction of jaw muscles |
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Components of saliva |
Water Mucins - protein component, mucins + water = mucus Amylase Electrolytes - controls tonicity and pH levels Lysozyme - breaks down bacterial cell wall |
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Components of a salivary gland |
Serous acinus - secretes proteins in isotonic watery fluid Mucous acinus - secretes mucin |
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Control of salivary secretion |
Parasympathetic = cranial nerves VII and IX - stimulate watery secretions Sympathetic = small volume, high protein content Chemoreceptors/Mechanoreceptors |
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Phases of Swalloing |
1. Oral phase 2. Pharyngeal phase 3. Bolus approaches oesophagus 4. Bolus entered oesophagus 5. Oesophageal phase 6. Bolus nears stomach 7. Receptive relaxation of stomach |
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Functions of Stomach |
- Temporary storage of food - Dissolve food particles/initiate digestion - Sterilise ingested material - Control delivery of contents to small intestine - Produce intrinsic factor |
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Layers of the stomach wall |
- Serosa - Muscularis externae - 3 layers not 2 - Submucosa/mucosa - folded when empty (rugae) - Lumenal surface - mucus cells, gastric pits, gastric glands, mucus neck, parietal and chief cells |
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Villus vs crypt cells |
Villus cells absorb nutrients Crypt cells secrete Cl- (H2O) |
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Mechanism for most absorption |
Na+ coupled secondary active transport |
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Mechanism for intestinal fluid secretion |
- Epithelial cells in crypts of Lieberkuhn actively secrete Cl- into intestinal lumen -Cl- move through CFTR protein - H2O secreted passively as consequence |
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Role of H2O in normal digestive process |
- Maintains luminal contents in liquid state - Mixes nutrients with digestive enzymes - Aids nutrient presentation to absorbing surface - Dilutes and washes |
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Two modes of intestinal motility and when they occur |
Segmentation (during meal times) and peristalsis (after absorption of nutrients) |
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Generation of segmentation contractions |
- Intestinal basic electrical rhythm (BER) - oscillations in membrane potential - Depolarisation generated by pacemaker cells in longitudinal layer - AP frequency determines strength - BER determines frequency |
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Epithelium of the colon |
Simple columnar epithelium - lumen is flat With large straight crypts lined with goblet cells |
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Explain the symbiotic relationship with bacteria in the gut |
Bacterial fermentation of undigested carbohydrates |
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Defaecation reflex |
1. Contraction of the rectum 2. Relaxation of internal and contraction of external sphincters 3. Increased peristaltic activity in the colon External anal sphincter relaxes under voluntary control |
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Symptoms associated with constipation |
- Headaches - Nausea - Loss of appetite - Abdominal distension |
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Causes of diarrhoea |
- Pathogenic bacteria - Protozoans - Viruses - Toxins - Food - Stress |
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Function of the body of the stomach |
- Storage - Mucus - HCl secretion - Pepsinogen secretion - Intrinsic factor |
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Different cells and their function in gastric glands |
- Mucus neck cell: secrete mucus - Chief cells: secrete pepsinogens - Parietal cells: HCl and intrinsic factor Cell proliferate up the pit to replace the surface mucus cells every 5 days |
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Mechanism for acid secretion from parietal cells |
- CO2 diffuses into cell from blood - CO2 combines with H2O forms carbonic acid - Carbonic acid dissociates to H+ and HCO3- - HCO3- exchanged for Cl- from blood - H+ exchanged for K+ from the gut lumen by ATPase protein - Cl- moves into the intestinal lumen - Water moves down osmotic gradient into the gut |
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Three mechanisms that control acid secretion |
- Neurocrine (vagus/local reflex) - Endocrine (gastrin) - Paracrine (histamine) |
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Two phases increased acid secretion |
- Cephalic phase: sight, smell, taste of food - Increased vagal tone - Gastric phase: - distension of stomach (vagal/enteric reflex) - peptides in lumen (G cells) - gastrin/ACh (ECL cells) |
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Three phases for inhibiting acid secretion |
- Cephalic phase: stopping eating (decreased vagal activity) - Gastric phase: decreased pH (decrease gastrin) - Intestinal phase: Acid in duodenum (secretin release/enterogastric reflex) Fat in duodenum (GIP release) |
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What are Enterogastrones |
Secretin Cholecystokinin (CCK) GIP |
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Enterogastrones are released in response to |
Gastric emptying Any of these in the duodenum: Acid Hypertonic solutions Fatty acids Monoglycerides Act to prevent further build up of acid |
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Formation of pepsin from pepsinogen occurs in... |
Acidic conditions (pH < 3) Pepsin is inactivated by neutral pH |
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Site of gastric mucus production and secretion |
Surface epithelial cells and mucus neck cells HCO3- secreted from Brunner's glands in the duodenum |
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What is CCK released in response to? |
Fatty acids and amino acids in the duodenum |
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What are the actions of CCK? |
- Stimulate secretion of digestive enzymes from the pancreas - Contraction of the gall bladder - Relaxation of the sphincter of Oddi - Increase activity of the intestinal smooth muscle - Contraction of pyloric sphincter |
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What is secretin released in response to? |
Acid in the duodenum |
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What are the actions of secretin? |
- Inhibits secretion of HCl - Stimulates HCO3- secretion from pancreas and Brunner's glands |
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What are the actions of gastric inhibitory polypeptide (GIP)? |
- Decreases secretion of gastin and HCl |
