Fichas
GI Physiology
Fichas del conjunto (70)
- 1State the requirements of the GI tract- Movement of food
- Secretion of digestive juices
- Absorption of water, electrolytes, vitamins & digestive products
- Circulation of blood
- Functional control via local, nervous & hormonal systems - 2Key physiological processes of the GI tract1. Motility
--> propulsion of digested food
--> mixing & decreasing particle size
2. Digestion into absorbable molecules
3. Absorption from intestinal lumen to blood stream
--> water, electrolytes, vitamins & digestive products
4. Secretion
--> salivary glands, stomach, intestine, pancreas & liver
5. Excretion
--> indigestible particles are condensed & expelled - 3What are the major defence mechanisms of the GI tract?Immunological: Mucosal immune system (GALT)
- Peyers patches & diffuse immune cells (lymphocytes & mast cells)
Non-immunological: gastric acid, mucin, peristalsis & epithelial barrier - 4Layers of the GI wall1. Mucosa - Epithelia + Lamina propria + Muscularis mucosa
2. Submucosa - connective tissue layer with larger blood vessels, lymphatics, secretory glands * submucosal plexus
3. Muscularis externa - circular & longitudinal smooth muscle + myenteric plexus
4. Serosa - connective tissue covered with epithelia - 5Submucosal plexusMeissner's Plexus
- throughout the intestine only
- local effects on glandular, epithelial & endocrine secretion
- local blood flow & absorptive effects - 6Myenteric plexusAuerbach's Plexus
- throughout the length of GI tract
- controls peristaltic movement
- when stimulated it:
increases tonic contraction
increases rate of contraction
increases intensity of contractions
increases velocity of conduction - 7Describe smooth muscle contraction1. Ca2+ from SR binds to calmodulin
2. Activates myosin light chain kinase
3. Phosphorylation of myosin head
3. Myosin actin binding - 8What is the latch state? & what does it mean?Phase of decreased detachment of myosin head causing the cross-bridge binding to be maintained & therefore reducing ATP consumption
--> allows stronger contraction with less energy expenditure - 9Define slow wave potentialConstant rhythmic increase & decrease of membrane potential
Rate of contraction is SET, but the intensity is EXTRINSICALLY controlled - 10Describe the chain of events which occur during slow wave potentials1. Voltage gated Ca2+ channels open
2. AP spike
3. Increased [Ca2+]i
4. Ca2+ dependent K+ channels open
5. Increased K+g --> slow depolarisation
6. Voltage gated Ca2+ channels close --> decreased [Ca+]i
7. Ca2+ dependent K+ channels close - 11What stimulates Depolarisation & Hyperpolarisation in Interstitial Cajal cellsDepolarisation - Stretch, ACh & Parasympathetics
Hyperpolarisation - NA & Sympathetics - 123 types of GI reflexes1. Within the enteric NS
- Secretion, peristalsis, mixing & local inhibition
2. GI -> Pre-ganglionic sympathetic ganglia -> GI
- Gastrocolic, Enterogastric & Coloileal
3. GI -> Brain / Spinal cord -> GI
- Pain reflexes
- Defecation reflex
- Control of gastric motility & secretory activity - 13State 3 ways of increases splanchnic blood flow1. Decreased O2
2. Adenosine release
3. Vasodilator release (bradykinin, VIP, CCK etc.) - 14Describe mastication- Mixes food with saliva for lubrication (mucin)
- Decreases food particle size
- Mixes food with digestive enzymes - 15Where is mastication controlled?Brain stem nuclei - Reticular areas for rhythmic control
Also in the hypothalamus, amygdala & cerebral cortex
Nerve = trigeminal - 16Describe the process of swallowing3 phases: Voluntary, Pharyngeal & Oesophageal
1. Voluntary passage of food to the pharynx
2. Trachea closes & oesophagus opens
(Upper oesophageal sphincter) then closes
3. Primary peristaltic wave is initiated by the deglutination centre --> sends signal via cranial nerves (5th, 9th, 10th & 12th) to produce a series of coordinated contractions creating an area of high pressure behind the bolus
4. Lower oesophageal sphincter opens mediated by the vagus nerve (VIP release)
5. Receptive relaxation
6. Lower oesophageal sphincter closes - 17Receptive relaxationDistension of the lower oesophagus stimulates the relaxation of the lower oesophageal sphincter & orad region of the stomach prior to the peristaltic wave
- 18Describe the innervation of gastric motilityENS
Myenteric plexus-
- Parasympathetic via vagus:
stimulate gastric smooth muscle motility & secretions
- Sympathetic via coeliac ganglion:
inhibit motility & secretions - 19Describe the motor functions of the stomach1. Storage - food forms concentric circles --> food stretches the stomach wall --> initiates the vagovagal reflex to decrease tone & increase capacity
2. Mixing - weak peristaltic constrictor waves become more intense towards the antrum --> forces antral contents under increasing pressure --> repropulsion of food towards the body
3. Emptying - promoted by the peristaltic waves but opposed by the pylorus - 20Vagovagal reflex- Afferent vagus:
Mechanoreceptors relay information to CNS via sensory neurones
- Efferent vagus (info from the CNS):
VIP released from post-ganglionic peptidergic vagal neurones causes relaxation - 21Define retropulsionPropulsion of food material and gastric contents back into body of stomach for further mixing and churning before being passed into small intestine
- 22Explain Migrating Myoelectric complexesPeriodic gastric contraction occuring during fasting
Occur in 90min intervals
- mediated by MOTILIN
- clear stomach of residue from previous meal - 23Enterogastric inhibitory reflexes1. Distension of the duodenum
2. Irritation of the duodenal mucosa
3. Acidity / Osmolality of the chyme
4. Presence of fat or protein in chyme - 24What movement occurs in the small intestine?Segmentation contractions - chyme induced distension --> stretch --> local constrictive contractions --> segmentation)
Peristalsis - 25How is peristalsis in the small intestine controlled?Gastroenteric reflex via the enteric NS
- 26Peristaltic rushPowerful, rapid peristalsis
- Due to mucosal irritation with infectious diarrhoea - 27What causes a delay in the caecum emptying?Irritation or distension of the caecum due to the contraction of the sphincter
- 28What movements occur in the colon?Mass movement - constrictive ring forms, haustra lost, faeces moves en mass, increased contractions followed by relaxation
Haustruations - mixing movements - 29What reflexes occur in the colon?Gastrocolic & duodenocolic --> signals via ANS
Defecation reflex - intrinsic or parasympathetic - 30What controls the: 1. Intrinsic defecation reflex 2. Parasympathetic defecation reflex?1. Rectal enteric NS
2. Sacral spinal segments - 31What are the phases of GI function?1. Cephalic - initiated by the thought, smell or taste of food
2. Gastric - initiated by the presence of food in the stomach causing distension & gastrin release
3. Intestinal - initiated by the presence of food in the duodenum - 32State the sympathetic & parasympathetic changes which occur during the cephalic phase in: 1. The mouth 2. The stomach 3. Other regions1. S - Increased blood flow to salivary glands --> increased volume of saliva
P - Increased salivary secretion
2. S - increased blood flow to the stomach
P - increased gastrin, mucus, pepsin & HCL secretion
3. P - stimulation of bile ducts, hepatocytes & pancreatic acinar cells - 333 types of salivary glands1. Parotid (mostly serous)
2. Submandibular (mixed)
3. Sublingual (mostly mucoid) - 34What is the basic secretory unit of the salivary gland?Acinar cells
- 353 stages of salvation1. Acini cells
- primary isotonic saliva (alpha amylase, serine protease, lingual lipases & mucin)
2. Myoepithelial cells
- under neural control to contract & expel exocrine cell contents
3. Ductal cells
- modify saliv a
- absorb Na+ & Cl-
- secrete K+ & HCO3- - 36Neural regulation of salivary secretionsANS
- increased by PSNS & SNS
Results in:
- increased saliva
- increased HCO3- secretion
- increased enzyme secretion
- increased myoepithelial cell contraction - 37State the gastric secretions & their cells of originHCl & Intrinsic factor via parietal cells
Pepsinogen via chief cells
Mucous via mucous neck cells - 38What factors stimulate / inhibit gastric secretions?Stimulate: ACh, Gastrin, Histamine & Parasympathetics
Inhibit: Enterogastric reflex - 39Action of pepsinogenLocal reflexes by vagus & H+ trigger secretion
Converted to active pepsin at pH <3.5 - 40Action of intrinsic factorEnables the absorption of Vit. b12 in the terminal ileum
Absence or deficiency leads to pernicious anaemia - 41Describe HCl secretionApical surface - H+ released via H+/K+ ATPase & Cl- follows by diffusion
Basolateral surface - HCO3- exchanged for Cl- via exchanger - 42Describe the inhibition of HCl secretionInhibited when it is no longer required for pepsinogen conversion to pepsin
Somatostatin:
- Directly binds to parietal cells & inhibits adenylate cyclase
- Indirectly inhibits histamine & gastrin release - 43Describe the pancreatic secretionsAqueous solution of HCO3- & enzymes
Aqueous components secreted by centro-acinar cells - isotonic (Na+, K+, Cl- & HCO3-)
Modification by ductal cells to make a HCO3- rich fluid - 44What factors increase pancreatic secretions?CCK
Secretin from S cells
Parasympathetic supply via Vagus - 45Pancreatic enzymesAmylase & lipase - secreted in active form
Proteases - secreted in inactive form & activated y enterokinase in the duodenum - 46What factors increase & decrease bile secretion?Increase - VIP & ACh
Decrease - Adrenaline & Somatostatin - 47Describe the regulation of secretion in the cephalic phase30% of gastric secretions
1. Direct stimulation of parietal cells by the vagus
2. Indirect stimulation of parietal cells by gastrin released from G-cells stimulated by vagal gastrin-releasing peptide - 48Describe the regulation of secretion in the gastric phase60% of gastric secretions
1. Direct stimulation of parietal cells by the vagus
2. Indirect stimulation of parietal cells by gastrin released from G-cells stimulated by vagal gastrin-releasing peptide
3. Local reflexes in antrum stimulated by gastrin
4. Direct effects of amnio acids & small peptides on G-cells to secrete Gastrin - 49Describe the regulation of secretion in the intestinal phase10% of gastric secretions
- at pH >3 gastrin is released
- at pH <2 buffering occurs via HCO3- & gastric inhibition occurs w/ intestinal stimulation
- CCK is released due to presence of fat & breakdown products in duodenum
- Secretin is released in response to acid - 50State the main pancreatic secretion in each of the phases of GI secretionCephalic - Mostly enzymatic
Gastric - Mostly enzymatic
Intestinal - Enzymatic & aqueous (80% of total pancreatic secretions) - 51State the exocrine secretions & their function of the Mouth, pharynx & salivary glands + of the oesophagusMouth, pharynx & salivary glands:
Salt & water - moisten food
Mucus - lubrication
Amylase - polysaccharide digestion
Oesophagus:
Mucus - lubrication - 52State the exocrine secretions & their function of the stomachHCL
- solubilisation of food particles
- kill microbes
Pepsin
- protein digestion
Mucus
- lubrication
- protection of the epithelia - 53State the exocrine secretions & their function of the small & large intestineSmall intestine:
Enzymes - food digestion
Salt & water - maintain fluidity
Mucus - lubrication
Large intestine:
Mucus - lubrication - 54State the exocrine secretions & their function of the pancreasEnzymes
- digestion of carbohydrates, fats, proteins & nucleic acids
Bicarbonate
- neutralise HCl entering small intestine from the stomach - 55State the exocrine secretions & their function of the liverBile salts
- solubilise water-insoluble fats
Bicarbonate
- neutralise HCl entering the small intestine from the stomach
Organ waste products & trace metals
- elimination in faeces - 56What are our main sources of nutrition?Carbohydrates
Lipids - mainly triglycerides
Proteins - exogenous or endogenous - 57Define “digestion” in the context of human nutrition and physiologyThe breakdown of nutrients into absorbable molecules
- 58Define “absorption” in the context of human nutrition and physiologyThe movement of nutrients, water, and electrolytes from the gut lumen into the internal environment
- 59How is the small intestine adapted for efficient absorption?Intestinal mucosa is arranged in circular folds of Keckring from which villi project
Villi are covered with enterocytes w/ goblet cell & in microvilli - 60Describe carbohydrate digestionDigestion begins in the mouth with salivary amylase, it continues into the stomach where the amylase is denatured by the pH. Then pancreatic amaylases secreted into the duodenum digest it further into maltriose, maltose & alpha-limit dextrin. Brush border enzymes also act on the disaccharides to produce glucose, galactose & fructose
- 61Describe carbohydrate absorptionSecondary active transport
- Glucose & Galactose
- Sodium-dependent Glucose Transporter (SGLT1)
Facilitated diffusion
- Fructose
- Glucose Transporter 5 (GLUT5) - 62Describe protein digestionBegins in the stomach w/ pepsin & is completed by pancreatic & brush border proteases
- 63ProteasesActivated by trypsin (converted by enterokinase from trypsinogen)
Endopeptidases:
- Chymotrypsin
- Elastase
- Trypsin
- Pepsin
Exopeptidases:
- A & B Carboxypeptidase
- Amino peptidase - 64Endopeptidases & ExopepidasesEndopeptidases - cleaves large polypeptides in the midd of the chain to oligopeptides
Exopeptidases - cleaves amino acids 1 at a time from either end of a protein - 65Describe protein absorptionAmino acids - Na+-dependent co-transport
Dipeptides - H+-dependent co-transport
Tripeptides - H+-dependent co-transport - 66Describe lipid digestion & absorptionBegins in the stomach w/ lingual & gastric lipase --> Bile salts emulsify the fat producing lipid droplet --> Pancreatic enzymes (lipase, cholesterol ester hydrolase & phospholipase A2) are secreted & break lipids down to monoglycerides & fatty acids stored in micelles --> Monoglycerides & fatty acids move out of micelles into the interstitial cells via diffusion --> Cholesterol moves in via membrane transporter --> Emulsified fats (re-esterified triglycerides) combine with cholesterol & proteins to form chylomicrons --> Chylomicrons are released into the lymphatic system to travel to the thoracic duct & enter the blood stream
- 67Describe the structure of a chylomicronCore of triglyceride & cholesterol ester with a phospholipid & apoprotein coat
- 68Describe the structure of a mixed micelleCore of products of lipid digestion i.e. cholesterol, monoglycerides, lysolecithin & free fatty acids) with a surface of bile salts
- 69Describe the ejection of bile saltsRelease is stimulated by CCK
Bile is synthesised & secreted by hepatocytes --> stored & concentrated in the gallbladder --> Chyme in the S.I. stimulated CCK release --> On completion of lipid absorption approx. 5% of bile salts are recirculated via the enterohepatic portal circulation - 70Describe the absorption of water in the large intestineControlled by the enteric nerve plexi & hormones (particularly aldosterone increases water reabsorption)
The process consist of ion exchange followed by osmotic absorption of water
- Na+ reabsorbed for K+
- K+ for H+
- Cl- for HCO3-
Información
- Descripción
- (Gastrointestinal System) MD3002 Fichas sobre GI Physiology, creado por Lareyna Mcmenemy el 30/04/2019.
- Creado por
- Lareyna Mcmenemy
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