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152 Cards in this Set
- Front
- Back
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What are the three main monosaccharides?
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Glucose, galactose and fructose |
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What are disaccharides? |
Two monosaccharides linked together by glycosidic bonds |
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What makes up lactose, sucrose and maltose?
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Sucrose = glucose + fructose Maltose = glucose x2 |
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What are the two forms of starch and how are they different?
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Amylopectin (highly branched) |
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What bond links glucose monomers in starch?
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Alpha-1-4 glycosidic bonds |
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What is cellulose composed of?
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Unbranched linear chains of glucose which are linked by beta-1-4 glycosidic bonds
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What is glycogen?
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Animal storage form of glucose, which is made up of glucose monomers linked by alpha-1-4 glycosidic bonds |
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What are the main ways, molecules can travel past a membrane such as the intestines?
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Paracellular - can travel in the small gaps in between the cells Vectorial transport - requires carrier/channel proteins to travel |
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How does glucose move through the small intestine to the blood?
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Na Is constantly being pumped out the cell by K/NA ATP pump, so there is a concentration gradient for Na to move from the lumen to the cell. Therefore the glucose is moved indirectly by an ATP pump |
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How does fructose move into the blood?
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Moves into the cell via GLUT-5 and out via GLUT-2
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How does Galactose move into the blood?
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The same mechanism as Glucose |
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What are proteins?
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Chains of amino acids linked together by peptide bonds |
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What enzymes break down proteins?
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Proteases or peptidases |
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What is the difference between endopeptidases and exopeptidases?
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Exo - cuts the terminal amino acids off |
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How do amino acids move into the blood?
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They move in with Na (so also driven by pump) via SAAT1 protein. They move out via protein that is unknown |
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What do most proteins cross into the blood as?
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Small peptides |
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How does a dipeptide move into the blood? |
Moves into the cell with H+ via PepT1 protein. The H+ then moves out via NHE3 which brings Na in at the same time (So also linked to the pump). The peptides leave by an unknown mechanism |
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What are the four distinctive layers of the alimentary canal?
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Mucosa, submucosa, muscularis externa and serosa/adventitia |
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What the three sub-layers within the mucosa?
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Lamina Propria Muscularis mucosae |
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What type of epithelium is present in the mouth, oesophagus and anal canal?
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Stratified squamous |
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What type of epithelium is present in the stomach and the intestines?
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Simple columnar |
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What is the lamina propria? |
Loose connective tissue |
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What is the submucosa?
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Thick, irregular connective tissue which supports the mucosa |
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What forms an extensive submucosal network?
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Neurones, which form the submucosal plexus which is parasympathetic
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In what parts of the gut tube are glands found in the submucosa?
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Oesophagus and duodenum |
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What is the serosa/adventitia and what's the difference between the two terms?
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Its a connective tissue outer layer. Adventitia is outside the peritoneal cavity, whereas serosa is inside. |
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What makes up the muscularis externa?
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Two concentric layers of smooth muscle. Circular muscle (to constrict the lumen) on the inside and longitudinal muscle (to shorten the tube) on the outside. |
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What is found between the two layers of muscle?
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The myenteric plexus |
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What do the submucosal and myenteric plexuses make up?
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The enteric nervous system, which allows independent control of gut function |
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Which nerve supplies the parasympathetic innervation of the gut tube? What controls salivation |
Facial and glossopharyngeal |
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What are the effects on the gut tube of PS stimulation?
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Increased secretion and motility |
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What nerve carries sympathetic fibres to the gut tube? What effects does symp have? |
Decreased secretion and motility |
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What are the three arteries that supply the gut tube?
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Celiac trunk, Sup mesenteric a and inf mesenteric a |
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What structures are supplied by the celiac trunk?
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Stomach, duodenum, pancreas and liver |
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What structures are supplied by the SMA?
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Small intestine, caecum, Ascending colon and transverse colon
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What structures are supplied by the IMA?
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Descending colon, sigmoid colon and rectum |
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What form is most ingested fat in?
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Triacylglycerol |
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Which enzyme breaks down fat in the small intestine? And what are the products?
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Monoglyceride + 2 fatty acids |
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What is the process of emulsification?
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Dividing large lipid droplets into smaller droplets, to increase the SA and accessibility to lipase action |
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How does emulsification happen?
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The smooth muscle of the SI contracts to grind and mix the luminal contents. The large lipid droplets are broken down into smaller ones. Bile salts and phosphoplipids are secreted which prevent the small droplets from reforming into large droplets. |
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What are bile salts and phospholipids?
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Amphipathic molecules. The non-polar parts can associate with the non-polar lipid droplets, while the polar portions can be exposed to the water surface |
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What structure enhances the absorption of lipase digestion products?
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Micelles, which contain bile salts, monoglycerides, fatty acids and phospholipids |
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How does this increase absorption?
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The micelles breakdown and release small amounts of FFA and monoglycerides, which diffuse across the membrane into cells. There is a dynamic equilibrium between fatty acids and monoglycerides in solution and in micelles |
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What happens to FA and monoglycerides in the cells?
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They enter the sER and are reformed into TAG. Then exocytosed into ECF at serosal membrane. Now called chylomicrons, which then pass into the lacteal |
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What are the fat soluble vitamins? and what absorptive pathway do they follow?
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Same as fat |
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What are the water soluble vitamins? How are they absorbed? |
Either by passive diffusion or carrier mediated transport |
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What does Vitamin B12 bind to?
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It binds to intrinsic factor in the stomach. |
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How is Vitamin b12 absorbed and what happens with Vit b12 is deficient?
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Its absorbed via a specific transport system in the distal ileum. Pernicious anaemia occurs, in which RBC fail to mature |
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Where is iron absorbed and how?
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In the duodenum, and by using carrier protein DMT1 |
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What happens to absorbed iron?
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Either incorporated into ferritin as an intracellular iron store or transported into the blood, where it binds to transferrin |
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What happens with hyperaemia and anaemia?
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An - decreased ferritin, more iron released to blood |
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Where is saliva secreted from?
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Parotid, sublingual and submandibular |
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What are the components of saliva?
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Water, mucins (lubricant), alpha-amylase (enzyme), electrolytes and lysozyme (kills bacteria) |
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Explain the effect of the parasympathetic system on salivating.
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The facial and glossopharyngeal nerves stimulate the production of a profuse watery saliva
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Explain the effect of the sympathetic system on salivating.
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Causes the production of a small volume and viscous saliva. Has high mucus and amylase content
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How do reflexes control saliva?
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Presence of food in mouth stimulates chemo/pressure receptors which stimulate saliva production |
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What epithelium lines the oesophagus?
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Stratified squamous |
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What do the submucosal glands in the oesophagus produce?
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Mucus for lubrication |
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Explain the splitting of the muscle in the oesophagus.
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The superior 1/3 is skeletal muscle (voluntary) and the inferior 2/3 is smooth muscle |
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What controls the movement of food into the oesophagus?
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The upper oesophageal sphincter and epiglottis. When the UOS relaxes to allow food in, the epiglottis covers the opening to the trachea |
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What pushes the food down the oesophagus?
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Peristalsis |
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What controls the entry of food into the stomach?
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The lower OS |
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What three parts is the stomach split into? |
Upper fundus, central body and lower antrum |
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What controls the movement of food into the duodenum? |
The pyloric sphincter |
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What is different about the muscularis externae of the stomach? |
It consists of three layers, longitudinal (outer), circular (middle) and oblique (inner) |
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What are the folds in the stomach called and which layers of the gut tube do they consist of? |
Rugae - mucosa and submucosa |
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What is the purpose of the fundus? |
Storage |
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What does the stomach secrete? |
Mucus, HCl, Pepsinogen, Intrinsic factorn (All body) and Gastrin (Antrum) |
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What cells secrete mucus, pepsinogen, HCl and intrinsic factor? |
Mucous neck cells - mucus Chief cells - pepsinogens Parietal cells - HCl and Int factor |
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What enzyme produces carbonic acid from CO2 and water? |
Carbonic Anhydrase |
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What molecules increase the production of H+ ions? |
Gastrin, Histamine, Prostaglandins, Acetylcholine |
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What three mechanisms control gastric acid secretion? |
Neurocrine - vagus/local reflexes Endocrine - gastrin Paracrine - histamine |
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What cells produce Gastrin and Histamine? |
G cells - gastrin ECL cells - Histamine |
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What is the cephalic phase? |
The sight, smell or taste of food stimulating the vagus nerve to produce ACh, which increases HCl production. It also stimulates G cells to produce gastrin, increasing HCl. Gastrin and ACh then act on ECL cells to produce histamine, again increasing acid. |
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What is the gastric phase? |
Distension of the stomach causing stimulation of the vagal/enteric reflexes producing ACh. Peptides in the lumen activate G cells and the presence of Gastrin/ACh activates ECL cells |
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What is the intestinal phase? |
Acid in the duodenum caused secretin release and activates the enterogastric reflex. Gastrin secretion is reduced and therefore less acid produced. Fat in the duodenum causes GIP release which decreases gastrin secretion and acid secretion |
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What other methods inhibit gastric acid secretion? |
When you stop eating, vagal activity is reduced. Also, when ph is decreased, due to high acid, gastrin production is reduced via a negative feedback loop. |
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What are enterogastrones? |
Hormones released from gland cells in the duodenal mucosa. They are secretin, cholecystokinin and GIP. |
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What stimulates their release? |
Acid, hypertonic solutions, fatty acids or monoglycerides in the duodenum |
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What is their purpose? and how do they do this? |
To prevent further acid build up in the duodenum By inhibiting gastric acid secretion and reducing gastric emptying (inhibit motility/contract pyloric sphincter) |
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Where is pepsinogen secreted? and what is it? |
Chief cells, its in an inactive precursor to pepsin |
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How is pepsin made? |
Pepsin cleaves its precursor to make pepsin. |
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Why is it stored as a zymogen (inactive precursor)? |
To prevent cellular digestion and pepsins are inactivated at a neutral ph |
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What is the purpose of gastric mucus? |
It protects the mucosal surface from injury. Creates a neutral ph on the mucosal surface to protect against gastric acid corrosion and pepsin digestion |
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What is the role of intrinsic factor? |
Required for vit b12 absorption. Vit b12 binds to it and this complex is absorbed in the ileum. |
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How does peristalsis work in the stomach? |
It moves from the body to the antrum |
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Where is the most powerful contractions? |
In the antrum |
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Explain the production of peristaltic waves in the stomach. |
Peristaltic rhythm is generated by pacemaker cells in the longitudinal muscle layer. These cells spontaneously depolarise/repolarise to create a slow wave rhythm. Number of action potentials determines the strength of contraction. |
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What factors control motility in the stomach? |
Gastrin - increases contraction Distension of stomach wall activates long/short reflexes which increase contraction Stuff in the duodenum inhibits motility |
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How is acid in the duodenum neutralised? |
Bicarbonate (HCO3) is secreted from Brunner's Glands in the submucosa |
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What is the equation of neutralisation? |
H+ + HCO3- → H2CO3 → H20 + CO2 |
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What stimulates the production of HCO3? |
Acid in the duodenum triggers long and short reflexes which increase HCO3 production. It also triggers secretin release which stimulates HC03 release. Acid neutralisation inhibits secretin release via -ve feedback loop |
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What are long and short reflexes? |
Long is vagal and short is ENS |
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What cells release secretin? |
S cells in the duodenum |
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What is the purpose of the exocrine pancreas? |
Secretion of bicarbonate by duct cells and secretion of digestive enzymes by acinar cells |
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What are the enzymes stored as and why? |
Stored as zymogens to prevent autodigestion of the pancreas |
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How do the zymogens become activated? |
Enterokinase (bound to brush border of duodenal enterocytes) converts trypsinogen to trypsin. Trypsin converts all other zymogens to active forms |
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What enzymes categories are released by the pancreas? |
Proteases - cleave peptide bonds Nucleases - hydrolyse DNA/RNA Elastases - collagen digestion Phospholipases - phospholipIds to FA Lipases - TAG to FA + glycerol Alpha amylase - starch to maltose and glucose |
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How is pancreatic function controlled? |
Secretin - increases HC03 secretion Acid in duodenum - increases secretin CCK (released in response to fat/amino a in duodenum) increases zymogen secretion Long/short reflexes triggered by nutrients in duodenum, enhance pancreatic action |
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What are the four lobes of the liver? |
Right, left, caudate and quadrate |
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What is the alimentary role of the liver? |
The production and secretion of bile |
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What are the six components of bile? |
Bile salts Lecithin Cholesterol Bile pigments Toxic metals Bicarbonate |
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Which is the only one not secreted by hepatocytes? |
Bicarbonate - secreted by duct cells |
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Where do bile pigments come from? |
They are the breakdown products of old/damaged erythrocytes |
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What is the predominant bile pigment? |
Bilirubin |
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What are bile acids derived from? |
Cholesterol |
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What happens to bile acids before secretion? |
They are conjugated with glycine or taurine and become bile salts. This is to increase solubility |
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How are bile salts recycled? |
By absorption into the enterohepatic circulation |
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What controls the release of bile and pancreatic juice into the duodenum? |
The sphincter of oddi |
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What is the role of the gall bladder? |
To store and concentrate bile |
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What is the role of CCK in bile secretion? |
Fat in duodenum causes CCK release. This stimulates the sphincter of oddi to relax and the gall bladder to contract, squeezing out the bile. CCK also stimulates pancreatic enzyme secretion |
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What are the three parts of the small intestine? |
Duodenum, jejunum and ileum |
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What are the main functions of the duodenum? |
Acid neutralisation, digestion and iron absorption |
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What is the main function of the jejunum? |
Nutrient absorption |
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What is the main function of the ileum? |
NaCl/H20 absorption which dehydrates chyme |
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What features enhance the surface area of the small intestine? |
Its a cylinder, plicae, villi and microvilli |
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What is the function of the villus cells? |
To absorb nutrients |
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What is the function of the crypt of lieberkuhn? |
Its cells produce Cl and water, which are used to aid the absorption of nutrients into the villus cells. The crypt cells are also rapidly dividing as they replace the cells on the villus |
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What is the function of goblet cells? |
To produce mucus? |
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What are the functions of intestinal fluid (secreted from crypt cells)? |
It mixes lumenal contents in liquid state, promotes mixing of nutrients with enzymes, aids nutrient presentation to absorbing surface and dilutes and washes away potentially harmful substances |
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What carrier protein pumps Cl into the lumen so water follows. |
CTFR |
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What types of movement are performed in the intestine? |
Segmentation and Peristalsis |
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What is segmentation? |
Is the contraction and relaxation of short intestinal segments. |
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When is segmentation most common? |
During a meal |
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What is the purpose of segmentation? |
It provides thorough mixing of contents with enzymes and brings chyme into contact with absorbing surface |
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What generates the segmentations contractions? |
Initiated by pacemaker cells in the longitudinal muscle layer. The intestinal basic electrical rhythm produces oscillations in membrane potential with produce the segmental contractions. The Action potential frequency determines strength of contraction and the BER determines segmentation frequency. |
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What are the effects of the autonomic nervous system on segmentation? |
PS - increased contraction Symp - decreased contraction |
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What effect does the ANS have on the intestinal BER? |
It has no effect |
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What happens to the BER as you move down the intestines? |
It decreases, therefore segmentation produces slow migration of chyme towards the large intestine |
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When does peristalsis begin? |
Following absorption of nutrients, segmentation stops and peristalsis starts |
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What is the Migrating Motility Complex? |
Pattern of peristaltic activity which travels down small intestine. As one ends in the terminal ileum another begins. Arrival of food in the stomach stops the MMC |
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What are the functions of the MMC? |
Its moves undigested material into the large intestine and limits bacterial colonisation of the small intestine |
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What hormone is involved in the initiation of the MMC? |
Motilin |
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Explain the law of the intestine. |
If intestinal smooth muscle is distended, then muscle on the oral side of the bolus contracts and muscle on the anal side relaxes. The bolus is moved into the area of relaxation towards colon. |
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What mediates this? |
Neurones in the myenteric plexus |
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What effect does gastric emptying have on segmentation? |
It increases it |
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How does food move from the ileum to the large intestine? |
The ileocaecal valve opens and chyme moves into the large intestine. The colon distends and there is reflex contraction of the ileocaecal valve to prevent backflux into the small intestine. |
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What are the four parts of the colon? |
Ascending, transverse, descending and sigmoid |
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Which layer of muscle is incomplete in the colon? |
Longitudinal |
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What runs along the colon longitudinally? |
Teniae coli |
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What do contractions of the teniae coli cause? |
Pouches or haustra |
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What type of epithelium is found in the colon? |
Simple columnar epithelium |
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What cell is abundant in the colon and why? |
Goblet cells which produce mucus for lubrication for the movement of faeces |
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What epithelium is found in the rectum? |
Simple columnar epithelium |
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What layer is thicker than normal in the rectum? |
Muscularis Externa |
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What change is found in the anal canal? |
The epithelium changes from simple columnar to stratified squamous |
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What is the difference between the internal and external anal sphincters? |
Internal is smooth muscle and involuntary, whereas external is skeletal muscle and voluntary |
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What is the function of the colon and how does it do this? |
To dehydrate chyme. It actively transports sodium out of the lumen so water leaves by osmosis |
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What is present in great number in the colon |
Bacteria |
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What effect does distension of the rectal wall have? |
It stimulates mechanoreceptors, initiates the defecation reflex and gives you the urge to defecate |
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What is the defecation reflex? |
Its under parasympathetic influence. The rectum contracts, IAS relaxes and the EAS contracts. There is also increased peristalsis in the colon. There is increased pressure on the EAS, which the individual relaxes and expulsion of faeces occurs. |
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What allows delay of defecation? |
Descending pathways |
