GI Tract Flashcards

Question

Neurotransmitters

Answer 1

Mediators released from neurones to act locally Mainly under autonomic control Independent of CNS and voluntary control

Answer 2

Parasympathetic Transmitter = acetylcholine Receptor M1 or M2 Salivary glands - increases - watery Stomach / intestine Motility and secretion increases Sphincter tone decreases Sympathetic does the opposite Transmitter is noradrenaline - a or b2

Answer 3

Gut hormones are released by APUD cells in the gut and are truly endocrine The intrinsic nervous system of the gut may be regarded as a division of the autonomic nervous hasten

Answer 4

Muscle in GI tract is mainly arrange in 2 layers Outter longnitudinal layer Inner circular layer Muscle is predominantly smooth muscle there not under voluntary control Skeletal muscle found in pharynx upper oesophagus external anal sphincter ie voluntary control swallowing and defactation Electrical activity of smooth muscle Slow wave activity is seen in most physical smooth muscle - Do not cause contraction action potential required Spontaneous regular oscillations of membranene potential = nasal electrical rhythm of visceral smooth muscle Origin of slow waves are specialised pacemaker cells - interstitial cells of cajal Basal rate of electrical firing of cells of cajal varies from 3-20 cycles per minute Amplitude and rate of slow wave may be modulates by neurotransmitters

Answer 5

Propulsion of food from pharynx to stomach by coordinated contraction of oesphagael muscle Wave of contraction followed by a wave of relaxation Contains both smooth and skeletal muscle and is controlled by autonomic nerves coordinated by swallowing centre of medulla

Answer 6

Proximal region of stomach relaxes to accommodate passage of food with minor changes in the intragastric pressure Peristaltic contraction arising in the mid stomach move food towards the antrum band pylorus and some food back into body of stomach Wave of peristalsis move caudad and increases in intensity - the distal antrum is intensely constricted Chyme passes thought the pylorus with each contraction (3ML) Most chyme is squired back into body by retropulsion

Answer 7

Stomach emptying is determined by the tone of the pyloric muscle Stomach emptying is regulated by Myenteric reflexes in stomach due to stretch Gastrin increases Duodenal distension (decrease) Fats in duedenum via CCK release (decrease)

Answer 8

Mixing movement - segmentation Sustained contraction of rings of circular muscle Followed by contractions of adjacent segment promotes Mixing of digestive secretions with chyme Propulsive peristalisis Migrating peristaltic waves moving caudad Slow and interrupted by episodes of segmentation Migrating myoelectric complex Between meals - powerful regular cycles of peristalisis occur Spontaneous contractions originate in distal stomach possibly by motilin MMC migrates down the duodenum and ileum at rate of the slow waves MMC finished in terminal ileum and another begins Important for preventing accumulation of debris and microbial overgrowth

Answer 9

Storage Absorption of water and electrolytes Bacterial synthesis of vitimin K Regulation of chyme entry (ileoceacel sphincter) Motility generally slower than ileum with 2 major patterns - haustration - formation of sacs that store / propel contents - peristalsis movement of contents caudad and backwards

Answer 10

Mass movements are periods of intense caudad peristalsis Gut smooth muscle exhibits spontaneous slow wave activity Amplitude / rate of slow waves may be modulated by neutrotransmitters / hormones Excitation - contraction coupling in smooth muscle has similar / dissimilar features compared to skeletal muscle Peristalsis is the principal form of gut motility it occur me in response to the presence of food and the MMC

Answer 11

Primary roles - lubrication initiation of digestion salivary amylase and lingual lipase Antiinfective - lysosomes - igA binding glycoprotein Parotid gland roof of mouth - AMYLASE Submandibular - back of mouth - compound - mucous Sublingual - under tongue - mucous

Answer 12

Autonomic innervation Parasympathetic increase - general level of saliva in mouth. Drooling with food Sympathetic - nerves dehydrated Food stimulates taste receptors Parasympathetic innervation via glossopharyngael and facial nerve LITTLE TO NO REG BY HORMONES

Answer 13

Located in gastric pits - HCL pepsinogen and intrinsic factor

Answer 14

Major controller of gastric secretion. Released into the blood in response to stimuli. Produced in G cells in pylorus of gastric antrum (OPEN APUD cells) exerts action through stimulation of CCK type B receptors in parietal cells and ECL cells

Answer 15

CEPHALIC - vagal stimulation causes release of gastrin / histamine Triggered by sight smell chewing swallowing GASTRIC - chemical stimulation or distension G cells releases gastric which causes ECL cell to realise histamine which causes parietal cell to release H+ Both cause increase in acidity which increases pepsinogen release from chief cells - parasympathetic innervation INTESTINAL - presence of chyme in duodenum inhibits acid secretion and motility via release of secretin / GIP / CCK APUD cells Fats / fattys acids = CCK or GIP inhibits parietal cells from releasing H+ Gastric acid - secretin increases - increases amount of bicarbonate and inhibits gastric acid secretion Decreases gastric emptying

Answer 16

Block Ach - M1 antagonists - pirenzipine - ulcers Block histamine - H2 antagonists - ranitidine Block H+ - PPI omeprazole

Answer 17

Secretes as precursor zymogens - pepsinogens Primary proteolytic enzymes Secretion is stimulated mainly by Ach during cephalic and gastric phases H+ is necessary for activation Vagal innervation Chief cell releases pepsinogen, converted to pepsin by autocatalysis - H+

Answer 18

Pancreas’s has both exocrine and endocrine function Endocrine - insulin and glucagon Exocrine - pancreatic juice Non digestive endocrine hormones secretes by cells in the islets of langerhans A cells - produce glucagon B cells produce insulin & cells produce somatostatin Digestive exocrine enzymes and HCO3- secretes by ACINAR cells

Answer 19

2 major incretin peptides in intestinal secretion GIP - glucose dependant insulinotrophic peptide GLP-1 glucagon like peptide 1 GIP has a minor role to gastric secretion and a major role in insulin release by endocrine pancreas T2 diabetes - incretin effect reduced Drugs such a gliptins inhibit GIP / GLP breakdown by enzymes DPP 1V

Answer 20

Trypsinogen ——> trypsin Chymotrypsinogen —-> chymotrypsin ENZYME = ENTEROKINASE

Answer 21

Hormonal control - secretin | Neuronal control - parasympathetic stimulation during gastric and cephalic phase

Answer 22

Secreted more or less continuously by polygonal hepatocytes of the liver Caniculi —> hepatic ducts system —> bile duct In the inter digestive period hepatic bile stored in the gall bladder - concentrated by water reabsorption Primary bile acids - cholesterol derivatives synthesised in liver conjugated with a a to become water soluble Secondary bile salts Dehydroxylated forms via gut bacterial enzymes Conjugated bile salts are amphipathic which is hydrophilic n hydrophobic

Answer 23

Emulsification of fats and solubilisation Transport and absorption of fat soluble vitimins Elimination of cholesterol

Answer 24

Gall bladder contains stimulated CCK - CCK stimulated by fat in duodenum Bile duct HCO3 secretion stimulated by secretin- secretin stimulated by presence of acid in duodenum

Answer 25

Contain few unimportant enzymes Ileum - mucous HC03 water Burners glands - Colon - mucus

Answer 26

Exocrine pancreas secretion is alkaline enzyme rich stimulates by vagal tone during cephalic and gastric phases of digestion and by hormones in intestinal phase (CCK Secretin) In pancreas CCK stimulates enzyme secretion secretin stimulates HC03- In gall bladder CCK stimulates bile release, secretin promotors HC03- secretion by bile duct

Answer 27

NUTRIENT ASSIMILATION Physical reduction of food Chemical reduction of food Constituent monomoree dimers by enzymatic hydrolysis Absorption - transport of products of digestion from gut lumen across mucous membrane into the blood

Answer 28

Common dietary sugars are disaccharides Eg sucrose = glucose and fructose Lactose = glucose and galactose Cellulose - plant material indigestible fibre - helps with propulsion thought GI tract

Answer 29

Alpha 1.4 glycosidic binds - disaccharides Alpha 1.6 glycosidic binds - polysaccharide A AMYLASES - cleaves 1.4 glycosidic bonds in polysaccharides DEXTRINASE cleaves 1.6 glycosidic binds Salivary amylase - begins luminal phase digestion of starch Pancreastic amylase - continues luminal phase digestion of starches in small intestine

Answer 30

Membranous phase of digestion - on microvilli | Example = lactase sucrose Maltese a dextrinase

Answer 31

Principal monosaccharide products of carbohydrate digestion are hexoses Hexose absortption occurs by PASSIVE DIFFUSION NA GLUCOSE SYMPORT - glucose and galactose are transported from the lumen of the gut into epithelial enterocytes by na glucose co transporter SGLT-1 NA INDEPENDANT FACILIATED DIFFUSION - glucose transporter proteins expressed in all cell types - GLUT 1 GLUT 2 GLUT 5 GLUT 2 on basal membrane transports hexose from enerocyte cytosine to extracellular space

Answer 32

On the apical membrane

Answer 33

Protease cleaves peptide linkages by hydrolysis Three places for proteases are Gastric pancreatic brush border Endopeptidases - hydrolyse peptide binds IN polypeptide eg trypsin pepsin Exopeptidase - hydrolyse peptide bonds at end of the polypeptide chain Carboxypeptidase

Answer 34

Endopeptidase Secreted by Chris cells as pepsinogen activated by pepsin autocatalysis) Have acidic Ph optimum and initiate luminal phase of protein hydrolysis

Answer 35

Secreted from acinar cells in response to neural and hormonal stimuli Secreted as zymogens trypsinogen activated by enterokinase in small intestine

Answer 36

Apical surface of epithelial enterocytes in duodenum jejenum ileum ENTEROKINASE oligopeptidase aminopeptidase

Answer 37

Products of protein digestion are amino acids dipeptides Further hydrolysis of tripeptides occur by cytosolic peptidases within enterocytes Absorption from lumen across brush border occurs by PASSIVE DIFFUSION NA AMINO ACID SYMPORT NA INDEPENDANT FACILIATED DIFFUSION

Answer 38

Monosaccharide absorption utilised two types of transporters - a na+ cotransporter - SGLT-1 and GLUT 1,2,5 by FACILIATED diffusion

Answer 39

Digestive lipase hydrolyse triglycerides to fatty acids and mono/ di glycerides and glycerol Acidic lipase - gastric and lingual Pancreatic lipase

Answer 40

Gastric lipase produced by peptic cells of fundus Lingual lipase by serous glands of tongue Potent and rapidly acting lipases - Ph = 4-5.5 Initiate lipid hydrolysis in stomach INDEPENDANT of bile forming fatty acids and diglycerides

Answer 41

Acts on tri/ di glycerides in duodenum - neutral ph optimum Major hydrolysis products are fatty acids and mono glycerides Complete hydrolysis initiates by acidic lipases Optimal activity requires BILE ACIDS These smiley fat into small droplets maximising the exposure of the glycerol head structure to the enzyme Colipase - peptide cofactor prod by pancreas Essential for optimum pancreatic lipase activity Prevents bile acids from inhibiting lipase activity

Answer 42

Formation of mixed Micelle Diffusion across apical membrane of mono glycerides free fatty acids and glycerol Binding to fatty acid binding protein in the cytosol for transport to smooth ER Resynthesis of triglyceride Packaging of triglyceride with cholesterol app proteins and phospholipids to fork CHYLOMICRONS transport of chylomicrons across basal membrane into lacteals Ie lipids are re processed within enterocytes cells unlike carbs and amino acids

Answer 43

Major regulation of fluid balance is via kindeys GI tract breathing and skin Electrolytes have chemical bonds that allow dissociation into ions which carry an electrical charge They are of critical important in fluid balance Fluid balance can be maintained only if intake equals output Bidirectional fluid flux in the GI tract Water movement into lumen (secretion) Water moment from lumen (absorption) Bet absorption of water by passive movement respond to osmotic and hydrostatic pressure Luminal fluid generally remains isotonic with plasma Most solutes and water are reabsorbed in the ileum some in colon Major mechanism is Na+ glucose transporter SGLT1 Malabsorption of solutes and water by ileum may overwhelm the colons absorptive capacity Leads to diarrhoea and electrolyte loss

Answer 44

Passive - trans cellular and para cellular ``` In the ileum Coupled with water in distal ileum Cotransporter mechanisms Coupling to na/h exchange Cl- absorption is coupled to na+ absorption ```

Answer 45

Divalent cation eg ca2+ are poorly absorbed Osmotic laxative effect - milk of magnesia Ca2+ absorption by enterocytes is tightly regulated to maintain total body ca2+ stores 1,2,5 dihydroxy vitimin D3 stimulates synthesis in enterocytes of ca2+ bonding which transports ca2+ accords the apical membrane Inorganic fe2+ is complexed with transferrrin in the lumen and absorbed into enterocytes by a receptor mechanism

Answer 46

Water soluble are absorbed by simple passive diffusion eg C Some absorbed by specialist mechanisms eg vit B12 by ileal enterocyte receptors for vit B12 intrinsic factor complex Fat soluble - ADE depend on solubilisation by bile salts for intestinal absorption Inactive transport in the ileum - bact synthesised passively colon

Answer 47

Approx 9L of fluid enters the small intestine each day 2.3L ingested in food drink rest is GI secretions 90% of water is reabsorbed in small intestine water absorption driven by conc gradients of water as the conc of water is higher in chyme than in epithelial cells so it moves down its conc gra doesn’t from chyme into epithelial cells Remaining absorbed in colon

Answer 48

Triglycerides are digested to fatty acids and mono glycerides by lipase Bile from liver emulsified fat to form fat droplets At the apical membrane of microvilli the fatty acids and mono glycerides diffuse into cell The triglycerides reform within the enterocyte cell and are coupled with proteins to from chylomicrons which diffuse from the Golgi to lacteals