learning outcomes Flashcards
what is the function and anatomy of the oesophagus
the oesophagus is a muscular tube with 3 constrictions; cervical 15cm, thoracic 28cm, and diaphragmatic 40cm.
what is the function of the stomach and anatomy
the stomach consists of the cardia, fundus (normally filled with air), the body, pyloric canal and pyloric antrum with a lesser and greater curvature and the inside is filled with gastric rugae
what is the function of the liver and anatomy
the liver has a right and left lobe, with the vena cava behind it. With the portal triad going hepatic artery, portal vein and bile duct.
what is the function and anatomy of the gall bladder?
gall bladder takes and stores bile. Bile travels from right and left hepatic ducts to the common hepatic duct where it joins the cystic duct from the gall bladder fusing to the duodenum.
what is the function and purpose of the pancreas?
the pancreas is an accessory digestive gland lying along the transpyloric plane with the portal vein forming behind its neck.
what is the anatomy and function of the spleen
the spleen is found in the left hypochondrium and coated in the peritoneum, related to the 9-11th rib and is a mobile haemo-lymphoid organ.
what is the function and anatomy of the duodeonum
the duodenum is the shortest and most fixed part of the intestine, receiving bile and the pancreatic duct
what is the anatomy of the jejunum
jejunum is thick heavy, with a deep red tinge with long vasa recta part of the small intestine.
what is the anatomy of the ileum
the ileum is a pale, thinner and lighter part of the small intestine and has short looping arcades.
what is the anatomy of the large intestine
large intestine has omental appendices, sacculations and taeniae coli (thick bands of smooth muscle)
what is the anatomy of the appendix
the appendix is a variable intestinal diverticulum with masses of lymphatic tissue
rectum is the pelvic part of the gut
Describe the common features of alimentary canal wall structure
Peritonised organs which are within the peritoneal cavity
retroperitoneal organs which are behind the peritoneum
lesser and greater omental sacs
visceral and parietal peritoneal layers
mesentery which are folding loops
describe the mesentery
The mesentery is a fold of membrane attachment. Arterial branches travel through the double folds to access peritoneal organs (within the peritoneal cavity)
what is the foregut blood supply
the foregut is supplied by the celiac trunk and it’s three branches which are the left gastric artery, the hepatic artery and splenic artery
what Is the midgut blood supply
the midgut is supplied by the superior mesenteric artery through the jejunal and ileal branches.
what is the hindgut blood supply
the hindgut is supplied by the inferior mesenteric artery with its branches the left colic, sigmoid and superior rectal artery.
what is the blood drainage of the gut
venous drainage occurs through the portal vein which is formed by the splenic and superior mesenteric veins.
describe the lymphatic drainage of the gut and the clinical significance of this
lumbar nodes have three groups pre-aortic, lateral aortic, and retro aortic. Specifically, the foregut structures are drained by the celiac group, the midgut is drained by the superior mesenteric group, and the hindgut by the inferior mesenteric group. These are all drained by the thoracic duct. It’s essential to know this for monitoring the spread of disease.
stomach formation embryology
the oesophagus forms from the cranial part of the primitive gut tube with the laryngo tracheal diverticulum forming the trachea.
In the 4rth week stomach dilation, 90 degree rotation and anterio-posterior rotation occurs in a clockwise formation.
The stomach attachments through the ventral and dorsal mesogastrium rotate, causing the dorsal mesentery to the left creating the lesser sac.
The duodenum also rotates, being dragged by the stomach.
bile duct and gallbladder embryology formation
Liver bud appears the middle of the third week, the connection from the duodenum forms the bile duct.
ventral outgrowth from the bile duct forms the gall bladder and cystic duct.
spleen embryology formation
mesenchymal condensation by the end of the 4rth week forms the spleen, initially haemopoietic by week 23 functioning lymphatically.
pancreas embryology formation
pancreas develops as two buds from the duodenum, as the duodenum rotates the two buds fuse
midgut embryology formation
there is rapid elongation of the primary intestinal loop with the cephalic part forming the distal duodenum, jejunum and proximal ileum. Then the caudal part forming the distal ileum, caecum, appendix, ascending colon and proximal 2/3rds of transverse colon. Before this happens, it must undergo rotation 90 degrees anti-clockwise, around the axis of the superior mesenteric artery and the cranial part of the midgut is carried to the right. As this occurs the gut tube herniates to allow for growth.
By week 10 the cavity becomes more spacious as retraction occurs starting with jejunum first and caecum last with a further 180 degree anticlockwise rotation.
hindgut formation embryology
terminal portion of hindgut joins with posterior part of cloaca, the allantois enters the anterior part of the cloaca. The cloaca then acts as a boundary between the endoderm and ectoderm layers. By the end of week 7 the membrane ruptures with ectoderm proliferation sealing the caudal end.
foregut abnormalities from formation
oesophageal atresia
trachea-oesophageal fistula
annular pancreas – ventral bud migration failure leading to duodenal stenosis or accessory pancreatic tissue
midgut abnormalities from formation
abnormal rotation of primary intestinal loop or reversed rotation of primary intestinal loop.
omphalocele (herniation of abdominal viscera or retraction failure, coated in amnion)
Gastrochisis – herniation without amniotic cavity.
remnants of vitelline duct forming Meckel’s diverticulum through cyst, ligament or fistula.
hindgut abnormalities from formation
incomplete separation of the hindgut from the urogenital sinus by the urorectal septum
hindgut fistula, atresia or imperforate anus.
control of saliva secretions and glands
there are six salivary glands, with two of each one. There is the parotid salivary gland, the sublingual, and the submandibular. This is controlled by the facial parasympathetic nerve 7 and the glossopharyngeal 9 nerve.
Effects of parasympathetic and sympathetic nervous system on secretion and motility
there is the vagus nerve which stimulates secretion and motility
there is the sympathetic nerve known as the splanchnic which inhibits secretion and motility except for salivation.
arterial supply of the Gi tract
there is the celiac trunk supplying the stomach, small intestine, pancreas and liver.
there is the superior mesenteric artery supplying the small intestine, caecum, ascending colon and transverse colon.
there is the inferior mesenteric artery supplying the descending colon, sigmoid colon and rectum
venous drainage of the GI tract
the stomach feeds into the gastric vein as the pancreas feeds into the splenic. The small intestine, caecum, ascending colon, and transverse colon all feed into the superior mesenteric vein. The descending colon, sigmoid colon and rectum all feed into the inferior mesenteric vein. The SMV, IMV and the gastric, splenic veins feed into the hepatic portal vein, pass through the liver to the hepatic vein which then feeds into the inferior vena cava.
explain the concept of the portal venous system and its anastomosis
low oxygenated blood travels from the gut rich in nutrients to the hepatic portal vein which feeds into the liver, mixing with the oxygen rich blood of the hepatic artery, this then feeds back through the hepatic vein into the inferior vena cava to the heart.
basic function of mouth
chewing, salvia added as diluting and lubricant
basic function of oesophagus
passageway
basic function of stomach
digestion of protein. storage and sterilisation
basic function of pancreas
digestive enzymes and production of endocrine hormones
basic function of liver
bile salts for fat digestion/absorption
gallbladder basic function
storage for bile
small intestine basic function
digestion and absorption
large intestine basic function
water absorption and fermentation
epithelial linings of the GI
in the mouth, oesophagus and anal canal stratified squamous, in the stomach and intestines simple. Synthesis for enzymes, mucus and hormones, designed for absorption and function.
lamina propria is a
connective tissue containing vessels
the muscularis mucosae is a
thin smooth muscle layer
sub mucosa is a
thick irregular connective tissue containing vessels, glands in the oesophagus, duodenum and the neurones.
the muscularis externa is
inner circular or outer longitudinal for motility, peristalsis and segmentation.
serosa/adventitia is a
outer peritoneal – adventitia attaches oesophagus and rectum to surroundings
inner peritoneal – surrounds organs
describe the organisation of the enteric system
food/water enters the oesophagus, passing to the stomach for digestion. Then passes to the small intestine for further digestion, secretion of enzymes and fluid then nutrients are absorbed especially during the initial segments. As it then passes to the colon it begins to aggregate as the matter bacterially fermenters and water is reabsorbed and then is removed as faecal matter. Nutrients absorbed is passed through the liver through the hepatic portal vein to the heart and pumped systemically around the body.
describe the digestive processes for conversion of complex carbs to monosaccharides
starch and glycogen consist of alpha 1,4 glyosidic bonds which can be broken down by the enzyme alpha amylase. Cellulose the linear chains of glucose bound by beta1,4 glyosidic bonds cannot be broken down in vertebrates. Disaccharides can then be broken down by lactase, sucrase or maltase.
describe the mechanisms where monosaccharides are absorbed across the intestinal epithelial cells
glucose or galactose can enter through a SGLT symporter alongside sodium. Glucose is then pumped out by GLUT 2, whereas the sodium is then used in the ATPase on the basal membrane. The tight junction holding cells together is then permeable to water allowing water to pass.
fructose can then pass through the GLUT 5 and then the GLUT 2 into the blood.
describe the digestive processes for converting proteins into small peptides and AA
enzymes such as proteases or peptidases hydrolyse peptide bonds reducing the proteins. They are endopeptidases if they cut the chain from the centre, or exopeptidases if they cut from the end (either amino or carboxy).
describe the process for absorption for aa and small peptides
describe the process for digesting AA
sodium and an AA pass through the symporter into the cell, the AA is then separately pumped out into the blood whereas the sodium is utilised in a ATPase.
describe the process for digesting small peptides
di and tripeptides may pass through PepT1 (proton coupled transporter) alongside hydrogen ions gathered from the acid microclimate generated around the microvilli. The spare hydrogen ions are then exchanged for sodium ions (NHE3) and the sodium ions are utilised again in an ATPase whereas in a separate pump (still debate as to how) the dipeptides and tripeptides are pumped out accounting for 70% of proteins in our diet.
Describe the extracellular digestive processes for conversion of fats to triacylglycerols and monoglycerides to the cell
fats are taken as triacylglycerol droplets. Through mechanical movement generated by the muscularis externa in the stomach and the introduction of bile salts and phospholipids emulsification happens. Triacylglycerol droplets become smaller, forming micelles. As the gut is motile, micelles meet the acid microclimate allowing for the absorption of fatty acids and monoglycerol.
describe the intracellular process for fats into the lymphatic system
once inside the cell, the monoglycerol and free fatty acids are converted back into triacylglycerol in the smooth ER and bound to amphipathic proteins. It is then transported to the Golgi body to be enveloped in a membrane and undergo exocytosis to form a chylomicron which contains phospholipids, cholesterol and vitamins. This is then passed along into the lacteal components of the cell.
Explain the requirement for emulsification of ingested fats.
triacylglycerol is a lipid which is insoluble in water, the enzyme lipase is water soluble and thus only able to work at the edge of the large droplets.
emulsification breaks down the large droplets into smaller droplets increasing their surface area to enable for faster digestion.
Describe the role of bile salts in the production of emulsification droplets and micelles
bile salts and phospholipids act as amphipathic molecules, as in they have both polar and non-polar portions. This coats the droplets with the non-polar interior but repels other droplets with its polar exterior.
describe the absorption of fat soluble vitamins
fat soluble vitamins A,D,E,K follow the same route as fat, dissolving into micelles and into the chylomicrons for transport around the body.
describe the route of water soluble vitamins
water soluble vitamins such as B, folic Acid and C often have their own forms of carrier mediated transport via NA or passive diffusion. The exception to this is vitamin B12 a large and charged molecule that requires an intrinsic factor provided by the stomach that allows for it to be specifically transporter in the distal ileum to be stored in the liver.
intrinsic factor is for what vitamin
B12
Describe the absorption of the important dietary iron
Iron enters through the Divalent metal transporter 1(fe2+) through the brush border enzymes. Once inside they can bind to ferritin to from an intracellular iron store where they will remain. However, it may pass through the basolateral membrane, binding to transferrin to later bind to heme. This is the only mineral the gut will control the concentration of through the use of proteins, with increased iron comes more ferritin to permanently store
describe the general anatomy of the oesophagus and assign general physiological functions
the oesophagus is a 25cm long conduit, with its upper third containing skeletal muscle and the lower 2/3’rds containing smooth muscle. Physiologically the mouth and oesophagus makes use of saliva, which acts as a lubricant due to the mucins, the water helps by acting as a solvent and diluting the solution, alpha amylase breaks down polysaccharides, electrolytes maintain tonicity and pH whilst lysozymes kill any bacteria. Saliva is produced by the parotid glands, submandibular glands and sublingual glands.
describe the anatomy of the stomach and assign genera l physiological functions
the Stomach has a fundus, body, serosa, cardiac region, longitudinal muscle, circular and oblique layer, pyloric sphincter, rugae and antrum. This allows it to store food, initiating the digestive process whilst controlling outflow. Whilst this is occurring it sterilises food and produces the intrinsic factor for vitamin B12.
describe the features of the stomach and oesophageal canal wall structure
oesophagus contains 4 layers, the mucosa, submucosa, muscularis externa and adventitia. It is lined by a stratified squamous non keratinising epithelium with sphincters regulating movement.
he stomach too also has a luminal surface with mucus cells, gastric pits, glands containing parietal and chief cells. It has a folded submucosa and mucosa (rugae), a muscularis externae with three layers (longitudinal outer, circular middle and oblique inner) and a serosa which acts as a outer connective tissue layer.
describe the reflex control mechanism for swallowing
for saliva which is required in swallowing, cranial nerves facial (7) and glossopharyngeal (9) stimulate large volumes of watery saliva whereas sympathetic stimulate small viscous salvia due to alpha 1 adrenoreceptors on mucus content and beta 2 adrenoreceptors on amylase. There is also a reflex caused by pressure/chemoreceptors in the mouth.
voluntarily the tongue pushes food backwards, followed by a reflex of pharyngeal muscle contraction as well as the soft palate reflecting backwards to seal of the nasopharynx. The upper oesophageal sphincter relaxes and epiglottis seals. Once it has entered the oesophageal sphincter contracts.
peristaltic waves carry food to the stomach within 10 seconds, the lower sphincter relaxes, and food enters the stomach. Finally, the stomach through a vagal reflex stimulates relaxation, increasing volume from 50ml to 1500ml.
Describe the structure and various functions of the stomach.
Describe the structure and various functions of the stomach.
fundus – storage
body – storage, mucus, HCL, pepsinogen, intrinsic factor
antrum – mixing and gastrin.
pyloric sphincter - controls the flow of chyme into the duodenum
describe the basic activation of digestion in the stomach and the various forms of basic control
the initial stage of activation comes from the interaction with food, this stimulates the parasympathetic vagus nerve to secrete the neural transmitter Ach to bind to cholinergic muscarinic receptors which stimulates parietal cells to release acid. The same goes for G cells which are stimulated by the vagus to produce gastrin which travels through the systemic circulation, both Ach and gastrin stimulate a paracrine response through ECL cells producing histamine.
This process is repeated when peptides arrive in the lumen of the small intestine stimulating G cells, and the distension of the stomach as food arrives in a vagal/enteric reflex through Ach.
what does gastrin, histamine and Ach do In terms of the stomach and digestive process
what gastrin and acetylcholine do is bind to receptors that stimulate a calcium cascade activating kinases to enable the potassium hydrogen active pump which secretes hydrogen ions. Histamine works though G proteins activating Adenylyl cyclase to convert ATP into cAMP which then actives the active transporter.
what forms of inhibition are there for the stomach and the digestive process
finally stopping eating reduces vagal activity and would gradually inhibit the process. Gastrin demonstrates negative feedback and as pH would drop so does the gastrin concentration. Acid in the duodenum initiates the enterogastric reflex which reduces gastrin secretion and stimulation, the hormone secretin further aids this. The presence of fat in the duodenum also stimulates a GIP release which reduces gastrin secretion and HCL secretion.
how is pepsin in the stomach formed?
the low pH produced by the acid enables pepsinogen the zymogen to form pepsin which then becomes a self-propagating reaction.
role intrinsic factor for B12 absorption
it is produced by parietal cells to allow for the complex to be absorbed from the ileum
role of gastric mucous in the stomach?
has a cytoprotective role, protecting the surface from mechanical or chemical injury from the acid by being rich in carbonate ions forming a microclimate.
Describe basic physiology of gastric acid secretion
carbon dioxide diffuses into the cell and through the catalyst carbonic anhydrase forms the unstable carbonic acid, it quickly dissociates providing the ATPase K+/H pump a hydrogen ion in a 1:1 ratio. Carbonate is then exchanged with chloride ions which pass through the cell to leave through the apical membrane. The net movement of ions out of the apical membrane draws water through the tight junctions to form hydrochloric acid. Which is the pushed out the gastric gland from the gastric pit into the stomach.
describe the generation of peristalsis in the gut
gastric peristaltic waves are generated roughly 3 every minute by pacemakers cells in the longitudinal muscle layer. Action potentials travel through a syncytium along gap junctions, providing enough depolarization to the slow waves to induce a contraction.
Explain the mechanisms involved in the neutralisation of gastric acid in the duodenum, including control of bicarbonate secretion in the duodenum
once acid is detected in the duodenum, brunner’s glands duct cells secrete bicarbonate to neutralise the acid.
Explain the role of gastric motility in digestion and
the role of motility is to force the contents of the stomach to mix.
the peristaltic wave from the body to the antrum is increasingly more powerful the close you get to the sealed pylori sphincter, due partly to the presence of a third innermost layer, the oblique muscle.
describe the mechanisms controlling gastric emptying
this processed is maintained by the peristaltic rhythm generated by pacemaker cells in the longitudinal muscle layer..
The slow waves are known as the basic electrical rhythm, and contractions only occur when an action potential is triggered, the frequency of which determines the strength of contraction. This can be increased by gastrin, distension of the stomach wall, or however the presence of chyme in the duodenum inhibits motility.
neutralisation of gastric acid in the duodenum and the control of bicarbonate secretion in the duodenum
This is controlled through long vagal and short ENS reflexes. Hormone wise this is controlled by the release of secretin into the systemic blood flow which stimulates the pancreas and liver to produce bicarbonate, this process is halted once the acid neutralises.
H+ + HCO3- H2CO3 H2O + CO2
Explain the functions of the pancreas
the pancreas has both an endocrine function, producing both insulin and glucagon and somatostatin in the pancreatic islets which control glucose in the blood. The pancreas also has a exocrine function, with its acini producing zymogens which will later be activated into digestive enzymes, and in the ducts bicarbonate is produced.
Describe the actions of secretin on pancreatic and bile secretion and the stimuli which will cause their release
secretin is a hormone released by the small intestine which stimulates the secretion of bicarbonate ions by duct cells from the pancreas, duodenum, and bile duct in response to acid from the stomach encountering the duodenum. It then reduces gastric emptying and gastric acid secretion. The neutralisation of the acid then inhibits the release of secretin.
Describe the actions of cholecystokinin (CCK) on pancreatic and bile secretion and the stimuli which will cause their release
CCK is released in response to AA and FA in the duodenum by the small intestine to simulate the pancreas to release zymogens that becomes enzymes to digest fats and protein. It also reduces gastric emptying and relaxes the sphincter of Oddi allowing for the influx of bile.
Describe the control of pancreatic enzyme secretion and the role of zymogens
acinar cells produce digestive enzymes that are stored as zymogen granules to prevent autodigestion. As they are released they encounters a brush border enzyme enterokinase which converts trypsinogen into trypsin. Trypsin then activates zymogens into digestive enzymes. This process is regulated by the hormone CCK which is secreted into the blood supply by the small intestine upon the arrival of fatty acids and amino acids into the duodenum.
Describe the anatomy and histology of the pancreas
anatomically the pancreas has a body, tail and head. Combines with the common bile duct before reaching the sphincter of oddi in the duodenum.
histologically the pancreas consists of lobules connected by intercalated ducts with intralobular ducts leading into interlobular ducts ending in the main pancreatic duct.
Describe the structure of the exocrine pancreas
the exocrine pancreas consists of a lobule consisting of acini cells, leading from this is intercalated ducts containing duct cells, this leads to intralobular ducts then interlobular ducts that feed into the pancreatic duct.
Describe the structure of the liver.
structure; the liver is the largest organ in the body in the upper right quadrant of the of the abdomen. It contains 2 major lobes right which is larger than the left and 2 minors lobes the caudate and quadrate. Entry of vessels into the liver are though the porta on the inferior surface. The liver does have a bare area free from connective tissue on the diaphragmatic surface surrounded by a coronary ligament.
describe the functional structure of the liver
functional structure; the liver has ligamentous septa diving it into lobules with connecting vessels, ducts and nerves. At the corner of each hexagon is a portal triad of hepatic artery, portal vein and duct. In the centre of each lobule is hepatic veins that lead to the inferior vena cava. There are cords that radiate from the central vein, with bile canaliculus in between each cord and blood channel sinusoids.
functions of the liver
function; from the GIT oxygen depleted nutrient rich blood travels along the hepatic portal vein mixing in the hepatic sinusoids with oxygen rich, nutrient blood from the hepatic artery encounters hepatocytes. Here bile synthesis, nutrient storage, interconversion and detoxification occurs with bile being redirected to the canaliculi and hepatic ducts and blood returning to the central veins.
Describe the composition and function of bile, the mechanisms controlling its storage and release from the gallbladder and the mechanism whereby it is reabsorbed.
Bile is produced from bile acids, lecithin and cholesterol which is for solubilising fat. Pigments are from bilirubin, detoxified metals are from hepatocytes, bicarbonate is added from duct cells. Finally before release bile is conjugated with glycine or taurine to increase solubility, this is because 95% of bile is recycled through the enterohepatic circulation. The sphincter of Oddi prevents it release, allowing for it be concentrated by removing sodium, water leaves the bile. CCK hormone in response to fat In the duodenum triggers the relax of the sphincter and gallbladder contraction
pathology behind peptic ulceration
peptic ulceration originates from an imbalance between acid and the mucosal barrier and is usually associated with H. Pylori bacteria. This can lead to fibrosis, bleeding acutely or chronically or perforation.
pathology of stomach cancer
usually adenocarcinoma’s and again are associated with H. Pylori infections, chronic ulcerations or gastritis. It can spread directly or through the blood, lymph or transcoelemic.
oesophageal reflux refers to acid in the oesophagus, normally occurring due to a hiatus hernia which results in thickening of the epithelium and ulceration. Chronically this can lead to obstructions, constriction or obstruction.
pathology of chronic reflu
chronic reflux may also lead to remodelling causing a ‘Barrett’s oesophagus” when the glands undergo metaplasia aggressively, known as a precursor to oesophageal cancer.
oesophageal cancer can from Barrett’s oesophagus, obesity for adenocarcinoma or for squamous carcinoma smoking, alcohol or dietary carcinogens. Locally it causes obstruction, ulceration and perforation and can move directly, lymphatically or via the blood to the liver.
pathology of gastritis
finally we have gastritis which is inflammation of the stomach. This is due to Autoimmune diseases, bacteria or chemically. Specifically autoantibodies can attack parietal cells and intrinsic factor resulting in atrophy of acid glands and a vitamin B12 deficiency. Bacterially it can be caused by a inflammatory response and increased acid production due to H. Pylori. Chemically it can be induced by drugs (non-steroidal anti-inflammatory), alcohol or bile reflux.
state common or benign malignant disorders affecting the oesophagus
oesophagus reflux – benign
Barrett’s oesophagus – pre malignant
oesophageal cancer – malignant
H. Pylori’s role in gastric disease
H. Pylori is involved as a bacterial cause of gastritis. Severe conditions of gastritis caused by H. Pylori left unchecked may progress to ulceration. Repeated infection with H. Pylori may result in causing stomach cancer. It can only colonise within the gastric mucosa, this is due to its flagella that it can burrow with. It survives the acid within the stomach by producing an alkaline barrier through a urease enzyme. Within the mucosa the body’s innate immune system detects it and stimulates and immune response.
presentation and pathology of oesophageal reflux
difficulty swallowing, dysphagia. Can be caused by a hernia, essentially stomach acid damaging the delicate epithelium, causing remodelling and potentially if there is ulceration then fibrosis which then reduces motility and can lead to Barrett’s oesophagus.
oesophageal cancer pathology and presentation
dysphagia. Often can be caused by smoking, diet or alcohol consumption at least for squamous. Adenocarcinoma is often caused by obesity or because of Barrett’s oesophagus.
gastritis – can be the result of autoimmune disease, resulting in pernicious anaemia, bacterial (H. Pylori) or chemical such as alcohol, bile reflux or drugs.
peptic ulceration pathology
can be cause by an H. pylori infection, can result in bleeding, resulting in acute haemorrhages or chronic anaemia. However it may cause perforations, fibrosis which will then result in obstruction.
stomach cancer pathology
second most common GIT cancer, can be because of repeated H. Pylori infections. Can lead to bleeding, ulceration and spread directly, lymphatically, via the blood to the liver or trans coelomic.
structure and function of small intestine
consists of the duodenum, jejunum and ileum.
the function of the duodenum is gastric acid neutralisation, digestion and iron absorption
the function of the jejunum is nutrient absorption (95%)
the function of the ileum is salt and water absorption, resulting in chyme dehydration.
Basic eletrical rhythm explain
The basic electrical rhythm is a spontaneous depolarisation/repolarisation slow wave rhythm conducted through gap junctions along the longitudinal muscle layer.
segmentation explained
Segmentation is the change between contraction and relaxation between short intestinal segments to provide a thorough mix whilst increasing surface area contact between chyme whilst slowly migrating it towards the large intestine. It occurs during a meal.
peristalsis explained
peristalsis is a part of the migrating motility complex, following the end of segmentation, the function of this differs from segmentation it that it is designed to move undigested material into the large intestine, trying to prevent bacterial colonisation in the small intestine to prevent competition regarding nutrient absorption.
Describe the features which act to increase absorptive surface area along the alimentary canal
the intestinal shape as a cylinder increases its surface area. Having circular folds known as plicae further increase it by a third, the villi increase it by 10 percent. Finally, the microvilli increase the surface area by almost 200%. The villi themselves consist of simple columnar epithelium with scattered goblet cells, lacteal, capillary network, following a villus is a crypt of Lieberkühn where developing villi cells originate from.
Describe the neural control of intestinal motility for segmnetation
the contraction of segmentation is increased by parasympathetic vagus nerve whereas sympathetic nerves decrease contraction. It must be stressed the frequency of the segmentation is however determined by the basic electrical rhythm. The hormone motilin is the one responsible for the initiation of migrating motility complex and mediated by the neurones in myenteric plexus.
state function of the caecum
used to be useful for herbivores, but use has outgrown and now is just a sack
colon sturcture and function
ascending, transverse, descending, sigmoid.
function; actively transport sodium from the lumen to absorb water for dehydration of chyme. It’s also the site of bacterial colonisation that enables for fermentation, short fatty acid chain release, vitamin K production and gas production such as nitrogen, carbon dioxide, hydrogen, methane and hydrogen sulphide.
rectum and anal canal function
defecation
Describe the importance of intestinal bacteria in the digestive process
there are lots of bacteria in the colon. It’s responsible specifically for the digestion of carbohydrate, producing short chain fatty acids a source of energy in ruminants, production of vitamin K for blood clotting, and gas.
describe the rectum
Rectum – straight muscular tube with simple columnar epithelium and thick muscularis externa
describe the anal canal
muscularis is thicker than the rectum, and the epithelium here changes from simple columnar to stratified squamous
describe the structures of the rectal sphincters
internal anal sphincter - thick muscularis, smooth muscle automatic control
external anal sphincter – skeletal muscle, voluntary control
describe the mechanisms controlling defecation
mass movement contraction forces the faecal matter from the colon to the rectum, the distension of the rectal wall is detected by mechanoreceptors that then stimulate a defaecation reflex. The reflex itself is under splanchnic parasympathetic control and determines the contraction, relaxation of internal sphincter and contraction of external anal sphincter and increases peristaltic activity.
Describe the mechanisms which cause secretory diarrhoea
diarrhoea can be caused by pathogenic bacteria, protozoans, toxins, viruses, food and anxiety. They manipulate the process within crypt cells for chloride secretion, specifically Vibrio cholerae or E. coli through enterotoxins elevating cAMP, cGMP, calcium. Since these unbalances the osmolarity the movement of ions, water follows through and swamps the villus cells preventing efficient absorption.
innate versus adaptive immune cells
granulocytes, mast cells, monocytes, dendritic cells, macrophages and natural killer cells are all innate originating from myeloid progenitor cells
CD4+, CD8+, B cells, plasma cells and memory cells are adaptive originating from lymphoid progenitor cells.
secretory diarrhoea and explain how this can be treated with simple salt/sugar solutions.
the villus cells aren’t damaged however, so by using salt/sugar solution you can generate a ion uptake, to draw water back into the gut causing rehydration.
innate versus adaptive immune cells
innate overall is a universal system revolving around infection by microbes recognized by their molecular pattern and as a result can induce general inflammatory responses.
adaptive immunity is induced by specialised pathogen and require recognition through professional antigen presenting cells. It’s mainly conducted through T and B cells.
structure and function of cytokines
cytokines are key determinants in T cell differentiation. They are soluble mediator of immune responses and capable of being anti or pro inflammatory and can trigger amplification or cascades of effects. Cytokines consist of two sub units that will dramatically alter their function.
antigen presentation at the GI mucosa
inside the GI tract there are spots called Peyer’s patches containing large numbers of immune cells. Bacteria may enter through an M cell, or be grabbed by a dendritic cell, and then brought to a lymph node for antigen presenting to a naïve T cell, depending on the subset of dendrite it can give rise to a variety of response. As well as macrophages that can also present antigens.
IBD and coeliac disease, treatments used to target immune response discussed
Anti TNF therapies for IBD (targeting a single cytokine through neutralisation, modulation, apoptosis)
vedolizumab – targets integrins for lymphocyte movement to intestinal mucosal.
ustekinumab – mutlicytokine blockade.
Fecal matter transfer
for Coeliac Gluten free diets.
dyspepsia presentation
pain or discomfort in upper abdomen, anorexia, nausea, vomiting, bloating, early satiety and heartburn.
dyspepsia pathology
organic versus functional causes. Many likely scenarios ranging from anatomical to metabolic. Including ulcers, gastritis, gallstones, coeliac disease, cancer, drugs or cardiac problems.
dyspepsia managment
endoscopy, history, exam, bloods (FBC, ferritin, LFT, U&E’s, calcium, glucose, serology IgA, drug history and lifestyle management
gastritis pathology
inflammation caused either by Autoimmune, bacterial or chemical and can be diagnosed through endoscopy, or histological.
peptic ulcer presentation
smoker or use of NSAIDS, epigastric pain, nocturnal hunger pains, back pain, nausea, anorexia, weight loss or haematemesis or melaena, or anaemia.
peptic ulcer pathology
H. Pylori
peptic ulcer management
treated using antacid medication (proton pump inhibitors, H2 receptor antagonists) surgery only in complications. Alongside eradication therapy
gastric outlet obstruction presentation
; vomiting lacking bile, fermented food. Early satiety, abdominal distension, weight loss and gastric splash with dehydration.
gastric obstruction pathology
underlying cause of ulcer, stricture, fibrosis or cancer.
managment of gastric obstruction
diagnosis UGIE, blood of low Cl, low Na, low K or renal impairment. Loss of H+ and Cl- in vomit. Treat the underlying cause or endoscopic balloon dilatation surgery.
gastric cancer symptoms
common malignancy, dyspepsia, early satiety, nausea, vomiting, weight loss, GI, bleeding, iron deficiency, gastric obstruction
gastric cancer pathology
; majority of adenocarcinoma or MALT/GIST. Can be caused by chronic H. pylori infections and can be intestinal or diffuse types. Often sporadic with little genetic history or background, and other factors that are environmental.
gastric cancer management
endoscopy and histological for diagnosis. CT of abdomen and then multi-disciplinary team discussion. Then treatment of surgery or sometimes chemo.
describe investigation of H. Pylori
its management requires culture, serology but they are less common. We now more commonly use carbon tagged urea breathing tests to detect the urease enzyme or stool antigen ELISA. If necessary, a endoscopy with biopsy and rapid slide urease test. If it’s in the antrum it can cause ulcer, if in the body/fundus can cause cancer.
describe the role of H pylori in gastric diseas
Helicobacter pylori has infected 50% of the world. It can only colonise within the gastric mucosa, this is due to its flagella that it can burrow with. It survives the acid within the stomach by producing an alkaline barrier through a urease enzyme. Within the mucosa the body’s innate immune system detects it and stimulates and immune response.
describe treatment of H. Pylori
to eradicate the infection it require 7 days of triple therapy; clarithromyocin 500mg, amoxycillin 1g (or tetracycline) or omeprazole 200mg. there are second line therapies available.
Describe the role of screening as applied to colon cancer
those over the age of 50 receive a card for sampling to see whether they require any further investigation due to the demographic age of colon cancer. 14-30 people report rectal bleeding to their GP, out of that one will have bowel cancer.
Describe the management of colorectal cancer.
investigations involve colonoscopy, biopsy, rarely contrast imaging, cross sectional imaging, MRI. The treatment itself depends on the individuals wishes whether it is medical or surgical, endoscopic or invasive.
review structure and function of colon and rectum
Cecum, ascending colon, transverse colon, descending colon, sigmoid colon and rectum.
production of faeces through dehydration, and fermentation.
describe arterial supply and innervation to the colorectal area
superior mesenteric artery branching to the middle, right, ileocolic arteries.
inferior mesenteric artery branching to the left colic, sigmoid and superior rectal artery.
pain receptors are within the smooth muscle, afferent sympathetic fibres accompany segmental vessels.
describe presentation of colorectal
Rectal bleeding is a common occurrence, with 1 in 2000 presenting with rectal bleeding. The high risk features is persistent change in bowel habit, persistent rectal bleeding. A right sided abdominal mass, palpable rectal mass, or unexplained iron deficiency.
state differential for actue abdomen
peitonitis, obstruction and body wall pain
Describe the principles of investigation and clinical assessment of a patient with acute abdomen
assess + resuscitate if necessary, investigate, observe and treat. Not necessarily in this order, in terms of sepsis then it will be necessary to start broad spectrum antibiotics, and fluids until whilst investigating.
essentially what is the problem, effects and what should I do.
Discuss the investigations and management of patients with acute abdominal pain (including conditions such as peritonitis, obstruction and pancreatitis)
urine tests, Full blood count, U+E, liver function test, endoscopy, laparoscopy, laparotomy, CT, ultrasound or MRI. If resuscitating then restoring fluid volume, enhance oxygenation and perfusion, treating sepsis, decompressing the gut and analgesia. Similar line of reasoning goes for any treatment.
• Describe the aetiology, presentation and management of intestinal obstruction
intestinal obstruction is due to when the passage along the GI track becomes obstructed, compressed or the wall itself is compromised. It can present with pain, vomiting, distension, constipation, or borborygmic (gut noises). The severity will depend greatly on the location.
the basic histological organisation gut tube
in the gut tube there is
- mucosa
a. epithelium
b. lamina propria
c. muscularis mucosae - Submucosa
- Muscularis externa
a. inner circular
b. outer longitudinal - Adventitia/serosa
Describe the basic blood supply and function of the liver
dual blood supply, hepatic artery, portal vein
function; protein synthesis, metabolism of fat and carbs, detoxification of drugs and toxins including alcohol. formation of bile.
what are the different causes of jaundice
hepatic causes include cholestasis or intra-hepatic bile duct obstruction.
extra-hepatic causes include duct obstruction, diseases of the gall bladder or cholelithiasis.
what is roughly the normal metabolism of bilirubin
jaundice is caused by increased circulating bilirubin. During the hepatic metabolism of bilirubin, it is taken up by hepatocytes, conjugated to make it more soluble and then excreted. It then joins the biliary system and is broken down with a small fragment reabsorbed
