Pathophysiology Flashcards
Stomach
Mechanical digestion- forms chyme, secretes alkaline mucous(acetylcholine and bicarb ions protect stomach lining from acidic secretions) zymogenic cells- pepsinogen (protein digesting enzyme),
parietal cells secrete- hydrochloride acid (kills bacteria, breaks down protein, converts pepsinogen into pepsin which breaks protein down further) and intrinsic factor (binds Vit B12 before absorption in the ileum).
Peptic cells secrete pepsinogen and gastric lipase
Hormones gastrin and acetylcholine stimulate histamine and this binds to histamine receptors to stimulate parietal cells to secrete juices. Prostaglandins inhibit this secretion.
Gastrin and acetylcholine also activate calcium dependant pathways through M receptor (muscarinic), and histamine binds to H (histamine) receptors and activates camp dependant pathways. Both work to activate the proton pump that exchanges hydrogen and potassium across the parietal cell membrane- responsible for maintaining the pH
Prostaglandin increases gastric cytoprotective mucous and bicarb secretion and increases mucosal blood flow
Enteroendocrine cells- gastrin, histamine, endorphins, serotonin, and somatostatin
Phases of secretory activity-
1- cephalic- prepares for digestion, triggered by sight, odour or taste of food
2- gastric phase- stomach digestion, chemical stimuli from partially digested proteins initiate this phase. Gastrin producing cells produce gastrin that stimulates gastric juices to be produced
3- intestinal phase- food enters small intestines- stimulates mucous cells of intestines to release hormone that promotes continued gastric secretion
Vomit reflex is stimulated by sensory nerve cells in chemoreceptor trigger zone and the emetic centre in the medulla
- triggered by smell, pain, emotion, raised ICP, motion sickness, endocrine disturbances, toxic reactions to drugs, GI disease, radiation/chemo. CTZ relays messages through neurotransmitters 5-HT, histamine, acetylcholine and dopamine
Antiemetics antagonise transmission of neurotransmitters. CTZ is close to resp centre so can’t completely control vomiting without affecting resps
Small intestines
Chemical digestion- duodenum ( pancreatic enzymes and bile from liver enter here), jejunum, ileum
Enzymes break down carbohydrates, protein, lipids, and nucleic acids.
Pancreatic amylase acts on starch converting them to maltose, dextrins and oligosaccarides. The intestinal enzymes ( dextrinase, glucoamylase, maltose, sucrose and lactase) continue to break down these products into monosaccharides. Pancreatic lipase digests lipids. Triglycerides enter as fat globules and are coated by bile salts and emulsified. Nucleic acids are hydrolysed by pancreatic enzymes and broken apart by intestinal enzymes
Nutrients are absorbed through mucosa into blood or lymph. Almost all food, vitamins, electrolytes and water are absorbed here. Only indigestible fibre and water do to large intestines
Large intestines
Begins at ileocaecal valve. Includes caecum, appendix, colon, rectum, and anal canal
Starts at caecum where appendix is attached, then to ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anus
Absorbs water, salt and vitamins formed by food residue and bacteria
Goblet cells produce mucous to assist lubrications and passage of faeces
Bacteria in large intestines ferments remaining carbohydrates producing CO2, hydrogen and methane gas. Bacteria also synthesises Vit K. Decompensation of bilirubin gives faeces brown colour
Liver and gallbladder
Liver has four lobes (right, left, caudate and quadrate)
Role in metabolism of waste products and drugs, synthesis of proteins, storage of glycogen, carbs etc, breakdown of haemoglobin, production bile.
Mesenteric ligament separates left and right. Encapsulated by flossing capsule
Each lobule has branch of hepatic vein (nutrients coming from intestines) hepatic artery (carrying O2) and bile duct and lymphatic vessel entering it. Central veins in the middle of each lobule join to make the hepatic vein that becomes the inferior vena cava. Sinusoids lines with kupffer cells that remove debris from blood and send bile to gallbladder.
Liver synthesises- albumin, CRP, angiotensinogen, prothrombin, fibrinogen, antithrombin
Liver stores glycogen, clotting factors, angiotensinogen
RBC broken down into haem and globin. Haem further broken into bilirubin which gives colour to urine and bowels.
Metabolises amino acids into ammonia and sent to kidneys to clear.
Bile is the livers primary digestive function. Bile contains bile salts, cholesterol, bilirubin, electrolytes, water and phospholipids
When fats enter duodenum, hormones stimulate gallbladder to secrete bile
Liver stores large amount of blood which can be released in presence of haemorrhage.
Vit K absorption is dependant of prescense of bile
Pancreas
Exocrine portion secretes alkaline pancreatic juice.
High bicarb content
Neutralises acidic chyme before it enters duodenum
Secretes liquid containing water, sodium bicarb, pancreatic amylase, trypsin and chymotrypsin through vagal nerve stimulation
Metabolism
Catabolism- break down complex structures into simpler form
Anabolism- simple molecules combine to create more complex structures
Biochemical reactions of metabolism create water, CO2 and ATP
Liver
Responsible for metabolism of protein, carbohydrates and fats, steroid hormones and drugs
Synthesis of albumin (blood protein) and clotting factors and antibodies
Stores glycogen and angiotensinogen
Detoxifies alcohol and toxic substances
Ammonia (by product of protein metabolism) is converted to urea in liver and eliminated by kidneys
Produces bile which absorbs fats and eliminates bilirubin
Minerals, fat soluble vitamins and glycogen stored in liver
Three main disruption effects-
- disrupted liver cell function
- impaired bilirubin conversion and excretion leading to jaundice
- disrupted blood flow through liver leading to portal hypertension
Mouth
Secretes amylase, breaks down polysaccharides and disaccharides
Lingual lipase breaks down triglycerides
Spleen
Filters and cleans blood.
Can store more than 300mls.
Drops in blood pressure constricts splenic sinuses and help expel stored blood back into venous system
