GI Flashcards
Properties of the enteric nervous system and it’s relationship to the autonomic nervous system
Post ganglionic plexuses which can work independently to control motility and secretions. Activity is controlled by autonomic innervation with the brain
Describe the fluid balance of the gut
1l of food
1.5l of saliva
2.5l gastric secretions
9l alkali and water
12.5 small intestine
1.35 large
Deficate 150g
Why might a patient have dysphasia?
Anaesthetic, neurological defect, oesophageal blockage/ defect in musculature or a tumour tumour
Functions of saliva
Protection- contains I-, alkaline and Ca to protect teeth, contains lysozyme.
Moistens food to assist swallowing
Digestion- amylase
Prevents xerostomia
Components of saliva secreted by each salivary gland
Sub maxillary - serous and mucus 70% Parotid - serous 25% Sublingual - mucus 5% Hypotonic. Mucous contains mucins Contains Ca, I, low Cl, K, low Na, hCO3, enzymes, bacteriostats
Mechanism of secretion of serous saliva. Different with STIM?
Secreted isotonically by acini
Ducts impermeable to h2o and have Na ATPase on Basolateral surface creating conc gradient.
More Na reabsorbed so hypotonic
HCO3 secreted via h+ reabsorption on Basolateral NHX co2 back into cell, HCO3 into lumen via anion exchanger.
Acini secrete I and enzymes. Secretes Cl so ions and h2o follow.
Resting saliva is neutral or slightly acid
Stimulated then
More hco3
Less hypotonic so more Na and less k
More enzymes
Control of salivary secretion and effect of atropine
Largely nervous control
Sympathetic decreases volume - from the superior cervical ganglion, decreases blood flow
Parasympathetic stimulates acinar secretion, ductal secretion of HCO3 and co-transmitters increase blood flow.
From the medulla - afferent information from nose, mouth and tongue but also conditioned reflexes
Describe the process of swallowing
Voluntary phase- formation of a bolus, move into pharynx
Pharangeal phase- pressure receptors in palate and anterior pharynx afferent to brain stem swallowing centre. Causes larynx to lift, glottis to close, upper oesophageal sphincter to open and inhibits respiration.
Oesophageal phase- first 1/3 is voluntary. Rapid peristalsis conducted by extrinsic nerve via the swallowing centre. Lower oesophageal sphincter opens.
Outline how disordered swallowing may occur
Anaesthesia/ surgery may affect the brain stem so that swallowing I not coordinated- risk of aspiration.
Motility problem e.g. Achalasia- smooth muscle does not relax, diffuse oesophageal spasm (DES), scleroderma
Obstruction/ compression e.g. Tumours, squamous cell carcinoma, adenocarcinoma or lymphoma
Categorise different types of dysphasia based on pathology
Dysphgia - difficulty swallowing solids
Oesophageal dysphagia- difficultly swallowing liquids as they cannot form a bolus so harder to coordinate. Due to problems in lower sphincter or cardia.
Mechanical obstruction often solids then liquids.
Motility then both.
Odynphagia - pain on swallowing
Investigate with barium swallow (especially solids), endoscopy
Mechanisms that prevent GORD
Lower oesophageal sphincter physiological.
Right Cruz of the diaphragm has a pinch cock effect
horizontal connection of oesophagus to cardia at an acute angle.
Positive intra abdominal pressure closes
Folds in mucosa occlude lumen at the gastro oesophageal junction
Results in Barrett’s oesophagus, cough, hoarseness of voice and asthma.
Describe the development of the muscular and fascial layers of the abdominal wall including the inguinal canal
Rectus muscles grow within the transversalis fascia
Two sides of developing abdominal wall meet at the linear alba. Develop from somatic mesoderm.
Inguinal canal- oblique through the layers of abdominal wall, testes pushes wall through during development which become the fascial covering of the spermatic cord
Explain the developmental basis of umbilical and inguinal herniea
Weakness in umbilicus due to malformation after the gut grows outside of the abdominal canal.
Weakness at inguinal rings due to the passage.
Describe how the coelomic cavity and peritoneal cavity develop
Cephalocaudal folding causes the gut tube to pinch leaving a cranial and caudal section with only he vitaline duct.
Lateral folding creates an endoderm tube. Around this the intra coelomic space gets pinched off to create one cavity or coelom. This later surrounds the viscera and in the abdomen is called the peritoneum.
Describe the fate of the embryonic dorsal and ventral mesenteries
Ventral in foregut becomes liver, gall bladder and biliary tree and the head of the pancreas and lesser omentum.
Dorsal foregut becomes the tail, neck, body and superior head of the pancreas. Connects stomach to transverse colon.
Explain how the omenta and the mesentary of the small intestine form and relate this to their arrangements in the adult
Rotation of the stomach so that ventral mesentary lies to the right. Growth of cells on the left is quicker resulting in anteroposterior rotation of the stomach and greater curvature. The greater omentum on the greater curvature fuses with the transverse colon. Mesenteries of small intestine fuse forming a fan shape.
Why do some abdominal organs possess mesenteries and some are retro peritoneal
Retroperitoneal organs never had a mesentary or had a peritoneum e.g. Kidneys- intermediate mesoderm
Secondary retro peritoneal organs dorsal mesenteries regressed and peritoneum fused so they are attached to the abdominal wall and only have an anterior covering of peritoneum. E.g. Duodenum - posterior peritoneum forms fusion fascia
Describe the respiratory primordium development.
Respiratory diverticulum forms off the pharyngeal gut. Becomes respiratory primordium. Divided by the trachealoesophageal septum
Describe the functions of the stomach
Digestion - pepsin and mechanical break down
Kills pathogens- low pH
Storage
Describe the components of gastric secretion and their cellular origins
HCO3/ mucus - neck cells/ foveolar cells
Pepsin - chief cells
Gastric - G cells/ endocrine cells
HCl- Parietal/oxyntic cells (canaliculi)
Explain the mechanism of stomach acid secretion
Proton pump into lumen from canaliculi, HCO3 into blood stream. Both produced via mitochondrion
Control of gastric acid secretion including phases of control
H+ and prostaglandins (neck cells) Controlled by
Gastrin - distension and peptides increase, H+ decreases
ACh/ parasympathetic - stomach distension and CNS
Histamine- gastric and ACh stim, produced by mast cells and act on H2 receptors to stimulate CAM. Sensitive, antagonists are effective.
Phases:
Cephalic phase- CNS stims acid
Gastric phase- neutralisation and peptides and distension stim gastrin
Intestinal phase - hormones inhibit gastrin secretion, pH and peptides fall. Less distension.
Outline the ways in which gastric acid secretion may be reduced by drugs
Proton pump inhibitors and H2 antagonists
Describe the function of the stomach defenses, what can damage these?
Unstirred layer of mucus and HCO3 prevents degredation of gastric cells by h+ and pepsin.
NSAIDs inhibit prostaglandins which decreases mucus production.
Alcohol dissolves mucus.
H pylori damages via inflam.