GI Lecture 1 - Overview

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  • Created by: LBCW0502
  • Created on: 28-09-19 12:59
Which organs are involved in the gastro-intestinal system?
Salivary glands, oesophagus, stomach, liver, gall bladder, duodenum, pancreas, jejunum, colon, ileum
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Briefly outline the stimulation of saliva secretion (1)
Stimuli detected (e.g. smell, taste, touch, mastication, nausea etc). Electrical impulse sent through neurones to hypothalamus and salivary centre. Sympathetic and parasympathetic activation
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Briefly outline the stimulation of saliva secretion (2)
Secretion of saliva from glands (parotid, sublingual and submandibular)
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After the mouth, the digestive tract is differentiated into which four organs?
Oesophagus, stomach, small intestine and large intestine (organs separated by muscular valves/sphincters with mucosal layer lining the inner surface of digestive tract)
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How is the digestion of carbohydrates initiated?
In the oral cavity through amylase
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The majority of digestion and absorption of carbohydrates and amino acids occurs where?
Across the mucosae of the stomach and small intestine
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Where do secretions from the exocrine pancreas (e.g. bicarbonate) and liver (bile salts) go to?
They pass directly into the lumen of the small intestine
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What are lymphatic vessels involved in?
Intestinal absorption of dietary fat (lymphatic vessels are distributed throughout the tract)
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Describe features of salivary glands and saliva
Salivary glands - compound organs, secrete electrolytes/proteins (e.g. amylase) as a fluid into oral cavity. Saliva lubricates food for swallowing and glycoproteins secreted from submandibular, sublingual glands, buccal glands aid in starch digestion
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What is the correlation between saliva flow rate and ion concentration in saliva?
The faster the flow rate of saliva, the less chance of ions (e.g. Na) being transported across and the ion concentration in saliva increases
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Why is the composition of saliva hypotonic?
Saliva is made by the acinar cells of the salivary gland which is impermeable to water, so water stays in the lumen and reduces the concentration of solute in the saliva
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State the components involved in the histological organisation of the digestive tract
Mucosa, submucosa, muscularis externa, adventitia/serosa
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State the components involved in the circulatory and lymphatic vessels for nutrient supply/removal
Vascular and lymphatic vessels aid nutrient absorption. Epithelial tissue requires a continual supply of nutrients for cell maintenance and repair
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State the components involved in the innervation of the GI tract
Autonomic motor and sensory fibres found in GI tract. Motor fibres are both parasympathetic and sympathetic, ramifying throughout GI tract forming a plexus in each layer
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State the components involved in the endocrine control of the GI tract
Influence of gut hormones (e.g. neurocine, paracrine, endocrine control). Endocrine cells widely distributed in epithelia of stomach, SI, LI, appendix, distal oesophageal glands and ducts of pancreas and liver
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State the phases of gastric acid secretion
Acid secretion divided into basal (fasting) and stimulated (post-prandial) phases, cephalic, gastric and intestinal phases. (Stomach, oesophagus, cardia, fundus, corpus, antrum, pylorus, duodenum, gastric pits, layers of muscle subject to distension)
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State the cell types found in the gastric pits
Oxyntic gland mucosa. Superficial epithelial cell, mucous neck cell, stem/regenerative cell, parietal (oxyntic) cell, chief cell and endocrine cell
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Compare a resting parietal cell and an activated parietal cell
Tubulovesicles found in resting parietal cell. Once activated, tubulovesicles fuse together to form intracellular canaliculus
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Describe features of parietal cell receptors and regulation of acid secretion (1)
Parietal cell acid secretion regulated by chemical messengers (ACh, His, gastrin, Soll's three receptor hypothesis). ACh release near basolateral surface of cells from postganglionic neurones (neurocrine mechanism)
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Describe features of parietal cell receptors and regulation of acid secretion (2)
Gastrin released by G cells of antral mucosa and first part of duodenum into bloodstream, which carries this hormone to parietal cells (endocrine mechanism)
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Describe features of parietal cell receptors and regulation of acid secretion (3)
His released from mast-like cells of lamina propria of oxyntic (acid secreting) mucosa into EC fluid and diffuses to parietal cells (paracrine mechanism)
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Outline the mechanism for acid secretion and the regulation (1)
Food present. G-cell releases gastrin into bloodstream. Binds to ECL-cell which causes release of histamine. Binds to another cell to secrete acid. E.g. of positive feedback
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Outline the mechanism for acid secretion and the regulation (2)
Presence of acid causes D cell to send a signal to stop the G cell producing gastrin (e.g. of negative feedback)
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Which drug can be used to prevent acid secretion?
Omeprazole (PPI)
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Which drug can be used to prevent the release of histamine?
Famotidine (H2 receptor antagonist)
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Outline the steps in the gastric phase for gastric-acid secretion (1)
2 mechanisms - mechanical stretch and presence of digested protein fragments. Distention of stomach by food - local ENS reflexes/vagovagal reflex - ACh (causes G cell to release gastrin/ECL to release his, to parietal cell)
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Outline the steps in the gastric phase for gastric-acid secretion (2)
GRP (gastrin releasing peptide). Digestion of protein - peptides and amino acids (also stimulates G cell to release gastrin)
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Describe the secretion of pancreatic juice (1)
Highest rate of protein synthesis of any secretory tissue with exception of lactating mammary gland. Aqueous component rich in HCO3 which neutralises duodenal content and enzyme component
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Describe the secretion of pancreatic juice (2)
Proteolytic enzymes - trypsinogen, chymotrypsinogen, procarboxypolypeptidase, ribonuclease, deoxyribonuclease. Amylase (starch/glycogen). Lipase (hydrolyses neutral fat into glycerol and fatty acids)
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Describe the secretion of pancreatic juice (3)
Involvement of CCK-PZ and secretin (stimulates bile production and enzyme activity)
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Outline the electrolyte concentrations in pancreatic juice
Constant high Na, high HCO3, low Cl and low K
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Outline the digestion and absorption of carbohydrates
Amylase used to break down carbohydrates. Conversions to maltose, glucose, lactose, sucrose. Transport across intestinal lumen, glucose, galactose and fructose in the blood for absorption
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Outline the digestion and absorption of amino acids and oligopeptides
Proteins broken down by pepsins and protease enzyme. Amino acids formed, transported across epithelial cell to portal vein
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Describe the regulation of bile secretion and role of endocrine hormones (1)
Parasympathetic impulses along vagus nerves stimulate bile production by liver. Acidic chyme entering duodenum stimulates secretion of secretin into blood. Fatty acids and amino acids in chyme stimulate secretion of CCK into blood
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Describe the regulation of bile secretion and role of endocrine hormones (2)
CCK causes contraction of gall bladder. Secretin enhances flow of bile rich in bicarbonate from liver
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Outline the role of bile fats in absorption of dietary fats
Fats digested by lipase and pancreatic lipase. Break down to form micelles for absorption in the small intestine
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Describe the stimulatory mechanisms regulating digestion and absorption of dietary nutrients
Hypoglycaemia, psychic stimuli, taste, smell, CNS, parasympathetic, release of gastrin into vascular system, contact and distension in the stomach
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Describe the inhibitory mechanisms regulating digestion and absorption of dietary nutrients
Pain, psychic stimuli, CNS, sympathetic stimulation, SIH, secretin, GIP enters vascular system. Receptors for H+ ions, osmolarity, neutral amino acids
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Outline components of the reflex control of gut activity
CNS (parasympathetic/sympathetic efferents, splanchnic/vagal afferents). Chemoreceptors, mechanoreceptors in gut wall, local afferents, myenteric plexus, submucosal plexus. Gut wall muscle, endocrine cells, secretory cells, blood vessel
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Other cards in this set

Card 2

Front

Briefly outline the stimulation of saliva secretion (1)

Back

Stimuli detected (e.g. smell, taste, touch, mastication, nausea etc). Electrical impulse sent through neurones to hypothalamus and salivary centre. Sympathetic and parasympathetic activation

Card 3

Front

Briefly outline the stimulation of saliva secretion (2)

Back

Preview of the front of card 3

Card 4

Front

After the mouth, the digestive tract is differentiated into which four organs?

Back

Preview of the front of card 4

Card 5

Front

How is the digestion of carbohydrates initiated?

Back

Preview of the front of card 5
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