Phys of GI Disorders Flashcards
Damage to which cranial nerves can cause paralysis of swallowing mechanism?
Fifth, ninth, tenth
Other causes: Encephalitis, MD, polio, myasthenia, botulism
Achalasia
Failure of the LES to relax during swallowing. Myenteric plexus is lower 2/3 damaged, musculature spastically contracted and no ability to transmit a receptive relaxation signal.
What two characteristics does the stomach possess that limits direct absorption of food from stomach into the blood?
1- Lining of highly resistant mucous cells
2- Tight junctions of epithelial cells
= gastric barrier
How can gastric atrophy (from chronic gastritis) lead to pernicious anemia?
Normal gastric secretions contain intrinsic factor (from parietal cells). IF is needed for absorption of Vt B12 from the ileum. IF combines with B12 in stomach, prevents from being digested as it passes to SI. When complex reaches ileum, IF binds on ileal epithelial cells, and Vit B12 is available to be absorbed. Without IF, on 1/50 of b12 is available from foods to cause new RBCs to develop mature in bone marrow.
Causes of peptic ulceration
Imbalance between rate of secretion of gastric juice and degree of protection by mucosal barrier and neutralization of gastric acid by duodenal juices.
Bicarbonate to maintain alkalinitiy and protect mucosal surfaces of the duodenum comes from which three sources?
Pancreas, secretions of large Brunner’s glands in proximal duodenum, bile coming from liver
What are two feedback mechanisms that ensure neutraliszation of gastric juices is complete?
- Excess acid entering duodenum inhibits gastric secretion and peristalsis in stomach (nervous reflex and hormonal feedback)= decreased rate of gastric emptying
- Acid in SI stimulates secretin from mucosa–> pass to pancrease via blood to promote rapid secretion of pancreatic juice (high amounts of bicarb)
Loss of pancreatic secretion due to pancreatitis, pancreatic duct blockage, or pancreatectomy (malignancy) causes loss of what important digestive enzymes? Without these, 60% of fat and 1/3-1/2 of proteins and carbs may be unabsorbed resulting in loss of nutrition and fatty, copious feces
Trypsin, chymotrypsin, carboxypolypeptidase, pancreatic amylase, pancreatic lipase.
Steatorrhea indicates a problem with digestion or with absorption?
Absorption. Fat in the stool is in the form of salts of fatty acids, not undigested fat indicating a problem with absorption and not digestion.
In severe malabsoprtive diseases of the SI, proteins, carbs, Ca, Vit K, folic acid and Vit B12 absorption is inhibited. How can these severe deficiencies manifest systemically?
1- severe nutritional deficiency without protein or carb absorption
2- osteomalacia (lack of Ca absorption)
3- Inadequate blood coags (lack of Vit K)
4- Macrocytic anemia (pernicious type) from lack of Vit B12 and folic acid
What is the neural path of the defecation reflex?
Feces accumulating in rectum causes reflex from rectum to conus medullaris of the spinal cord, then to the descending colon, sigmoid, rectum and anus.
Motor impulses that cause vomiting are transmitted from the vomiting center by what cranial nerves to the upper GI tract?
5 (trigeminal), 7 (facial), 9 (glossopharyngeal), 10(vagus), 12 (hypoglossal)
Vagal and sympathetic nerves are transmitted to the lower tract, and spinal nerves transmit motor impulses to the diaphragm and abdominal muscles
Chemoreceptor trigger zone is located on the floor of the 4th ventricle, which drugs can directly stimulate this zone?
Apomorphine, morphine, digitalis derivatives
What is the mechanism for motion sickness?
Receptors in vestibular labyrinth of inner ear stimulated, impulses transmitted by way of brain stem vestibular nuclei into the cerebellum, them to CTZ, then to vomiting center resulting in vomiting.
What acid-base status do you expect in a patient with an intestinal obstruction beyond the stomach?
Normal, possible little dhance in balance. Anti-peristaltic reflux from SI causes intestinal juices to flow backward into stomach where they are vomited along with stomach secretions. Loss of acid from stomach and base from SI balances out with little shift in acid-base status.
