Gastrointestinal Flashcards
Factors that make the GI smooth muscle cell membrane more negative, making it less excitable.
Norepinephrine or epinephrine
Stimulation of sympathetic Nerves that secret mainly norepinephrine at their ending.
Factors that depolarize the GI smooth muscle cell membrane, making it more excitable.
Stretching of the muscle, acetylcholine (parasympathetic nerves), specific gastrointestinal hormones
Kinds os electrical waves in the GI system
Slow waves (caused by pacemakers - interstitial cells of Cajal) - do not cause the Ca++ to enter the cells, only Na - no contraction
Spikes - at peak of slow waves, Ca enter the fibers - contraction,
Tonic contractions - repetitive spike potentials, hormones or other factors
Enteric nervous system
Myenteric plexus - Auerbach (between longitudinal and circular muscle layers)
Submucosa plexus - Meissner
Parasympathetic (vagus) - cranial - mouth, pharinge, esophagus, stomach, pancreas, -sacral - sigmoid and anus
Sympathetic - inhibit intestinal tract smooth muscle, excites mucosal muscle
Stimuli to Gastrin secretion by G cells of the Antrum of stomach
Distention of stomach
Products of protein
Gastrin realizing peptide - released by nerves of mucosa during vagal stimulation.
Actions of Gastrin
Stimulation of gastric acid secretion
Stimulation of growth of gastric mucosa
Vasodilatation
Promotes stomach emptying (enhance activity of pyloric pump
Stimuli to secretion of cholecystokinin (CKK) by I cells in mucosa of duodenum and jejunum
Digestive products of fat, fatty acids and monoglycerides in the intestinal contents
Actions of Cholecystokinin
Contracts gallbladder
Relaxation of sphincter of Oddi
Secretion of pancreatic digestive enzymes by acinar cells
Inhibits stomach contraction - give time for digestion of fat
Inhibits appetite - prevent over eating during meals - stimulate sensory nerves in duodenum
Vasodilatation
Stimuli to secretin secretion by S cells in duodenum
Acid gastric juice emptying from pylorus
Action of secretin
Mild effect on GI motility
Promote pancreatic secretion of bicarbonate - neutralize acid in small intestine
Stimulates liver ducktail secretion of watery solution of Na and HCO3
Vasodilatation
Stimuli to secretion of Gastric inhibitory peptide by mucosa of upper small intestine
FA, AA and to a lesser extend, carbohydrates
Action of Gastric inhibitory peptide (GIP)
Mild effect in decreasing motor activity of stomach when usurper small intestine is already overloaded
Stimulates insulin secretion ( glucose-dependent insulinotropuc peptide.
Stimuli for secretion of motility by stomach and upper duodenum
Fasting
Actions of motilin
Increase GI motility, released cyclically and stimulates waves of GI motility called interdigestive myoelectric complexes
Where does the blood of portal vein comes from?
All the blood from gut, spleen and pancreas
What comes with the blood from portal vein to the liver?
Bacteria - removed by reticuloendothelial cells before enters vena cava
Non-fat, water-soluble nutrients absorbed from gut (CH, ptn).
Where do the fats absorbed fro GI tract go?
Absorbed into intestinal lymphatics and then conducted to systemic circulating blood by way of the thoracic duct, bypassing liver.
Factors that cause vasodilatation in GI tract after a meal
Peptide hormones: CKK, vasoactive intestinal peptide, Gastrin, secretin
Kallidin and bradykinin secreted by GI glands
Decreases oxygen concentration - increase adenosine - potent vasodilator
Factors that control small intestine peristalsis
Enhances: gastroenteric reflex (Myenteric plexus), Gastrin, CCK, insulin, motilin, serotonin
Inhibits: glucagon, secretin
Anus sphincter
Internal-circular smooth muscle
External - striated voluntary muscle - pudendal nerve
Autonomic reflexes that affect bowel activity
Excitatory: Gastrocolic, duodenocolic, gastroileal,
Inhibitory:enterogastric, peritoneointestinal, renointestinal, vesicointestinal
Secretion of oxyntic gastric glands (body and fundus)
1-mucus neck cells - mucus
2-peptic or chief cells - pepsinogen
3-parietal or oxyntic cells - hydrochloric acid and intrinsic factor
Actions of acetylcholine, Gastrin and histamine in gastric secretion
Acetylcholine - stimulates secretion of pepsinogen (chief cells), HCl (parietal cells) and mucus (neck cells)
Gastrin and histamine - stimulates secretion of HCl.
Actions of pepsinogen
Activated to form pepsin when in contact with HCl
Pepsin - proteolytic enzyme when in highly acid medium ( digestion of colagen)
Intrinsic factor
Produced by parietal cells
Essential for absorption of vit B12 (maturation of red cells) in the ileum
Absence of intrinsic factor = pernicious anemia
Inhibit gastric secretion:
Reverse enterogastric reflex
Secretin (mainly), gastric inhibitory peptide (glucose-dependent insulinotropic peptide), vasoactive intestinal polypeptide, somatostatin.
Side effect of chronic use of proton pump inhibitor
Increase Gastrin secretion
What occurs in the stomach between meals?
Increase of secretion of somatostatin by D cells
The cephalic phase of HCl gastric secretion is mediated by:
Parasympathetic nervous activity
Stimuli that causes pancreatic secretion
1) acetylcholine and cholecystokinin - secretion of pancreatic digestive enzymes
2) secretin - secretion of water solution of sodium bicarbonate
Functions of bile salts and lecithin
Emulsification of fat particules - make the fat globules readily fragmentable by agitation with water
Helps absorption of FA, monoglycerides, cholesterol and other lipids - transport medium to carry these particules to brush borders of intestinal epithelial cells
Composition of bile
1) Bile salts - produced from cholesterol
2) Cholesterol
3) Bilirubin- end product of hemoglobin destruction
4) Lecithin - phospholipid
5) Electrolytes
What are Brunner’s glands?
Mucous glands at duodenum, between pylorus and papilla of Vater, that secrets mucus is response to: tactile or irritating stimuli, vagal stimulation and GI hormones (secretin)
A 20 year old male develops severe diarrhea for 2 days. Will this condition alter his ventilation? If so, how?
Yes, increase minute ventilation
A 20 year old male develops severe diarrhea for 2 days. Will this condition affect his acid-base status? If so, how?
Yes, metabolic acidosis.
Jim had severe diarrhea for 2 days. What would be the best way to rehydrate his body?
drink isotonic salt solution containing sugar
What is the dominant mechanism for entry of amino acids into the body?
Secondary active transport
Na is actively transported through the intestinal membrane. What are the other substances that are dragged (co-transport) with it (secondary active absorption)?
1) glucose
2) amino acids
3) sodium-hydrogen exchanger
How are chloride ions absorbed in the intestine?
1)By diffusion following electrical gradient created by Na absorption
2) in the ileum and large intestine by chloride-bicarbonate exchanger
Obs: chloride excites cell on basolateral membrane through chloride channels
How bicarbonate is absorbed in duodenum and jejunum?
1) hydrogen ions are secreted in exchange for Na
2) hydrogen ions combine with bicarbonate ions =>H2O+CO2
3) CO2 is absorbed into the blood and expired through lungs
What is the importance of the bacterial activity in the colon?
To form vitamins K, B12, thiamine, riboflavin.
Digestion of small amounts of cellulose.
Form gases
Which hormone stimulates strong smooth muscle contractions in the stomach?
Motilin - initiates migrating motor complex - sweeping of GI
What are the consequences of loss os stomach secretions in gastric atrophy?
Achlohydria=>pepsin is nit activated
Pernicious anemia
Most frequent sites os peptic ulcer
Within a few centimeters of the pylorus
Lesser curvature o the antral end of the stomach
More rarely in the lower end of the esophagus
Marginal ulcer - wherever a surgical opening has been made between the stomach and the jejunum
