Unit 12 Flashcards
What are the 2 types of electrical activity in gastrointestinal smooth muscle?
Slow waves
Spikes
Which intestinal cells act as electrical pacemakers?
Interstitial cells of Cajal
How do ion channels in GI smooth muscle differ from nerve cells?
Channels responsible for action potentials predominantly allow calcium ions to enter with a smaller amount of sodium - calcium-sodium channels
Slower to open and close
What factors can alter the resting potential of GI smooth muscle?
Depolarised by:
Stretch
ACh stimulation
Stimulation by GI hormones
Hyperpolarised by:
NEp and Ep
Stimulation of sympathetic nerves
Describe the structure of the enteric nervous system
Myeneteric plexus - between longitudinal and smooth muscle layers - GI movement
Submucosal plexus - in submucosa - secretions and blood supply
Which nerves supply the parasympathetic input to the GIT?
Cranial - vagus
Caudal - pelvic
Where is gastrin secreted?
G cells of stomach
What stimulates gastrin secretion?
Stomach distension
Products of protein digestion
Gastrin-releasing peptide - released during vagal stimulation
What are the actions of gastrin?
Gastric acid secretion
Gastric mucosal growth
Where is CCK secreted?
I cels of duodenum and jejunum
What stimulates CCK secretion?
Digestive products of fat
What action does CCK have?
GB contraction
Inhibits stomach contraction
Inhibits appetite
Where is secretin released?
S cells - duodenum
What stimulates secretin release?
Acidic gastric juice entering duodenum
What are the effects of secretin?
Promotes bicarbonate secretion
Mild effect on motility
Where is glucose-dependent insulinotropic peptide (GIP) released?
K cells of mucosa of upper small intestine
What stimulates GIP release?
Fatty acids and amino acids
What are the effects of GIP?
Slows gastric emptying into duodenum. Reduces secretion of gastric acid
Stimulates insulin secretion
Where is motion secreted?
M cells. Stomach and upper duodenum
What stimulates motion secretion?
Fasting
What is the action of motilin?
Stimulates interdigestive myoelectric complexes
Which GI hormones have a vasodilator effect?
CCK, VIP, gastrin, secretin
What 3 factors increase local GI blood flow?
Hormones
Kinins - kalliidn and bradykinin
Reduced oxygen concentration
What is the main promotor of gastric emptying?
Gastrin
What neurological factors inhibit stomach emptying?
Enterogastric reflex
- directly to stomach through enteric nervous system
- through extrinsic nerves via pre vertebral sympathetic ganglia
- through vagus nerve to brainstem
What factors activate the enterogastric inhibitory reflex?
Distension of duodenum
Irritation of duodenal mucosa
Acidity of duodenal chyme
Osmolality of the chyme
Presence of protein in chyme
What hormone inhibits gastric emptying?
CCK
Secretin and GIP to lesser extent
What hormones increase intestinal peristalsis?
Gastrin, CCK, insulin, motilin, serotonin
What hormones inhibit small intestinal motility?
Secretin and glucagon
What nerves are responsible for a) conscious and c) unconscious control of defecation?
a) Pudendal
b) Pelvic
Are anaerobic/aerobic bacteria more common in the lower intestine?
Anaerobic
What are the predominant cells in the a) body, b) fundus and c) antrum of the stomach?
a) Mucus neck cells, parietal cells, chief cells
b) Enterochromaffin-like cells, somatostatin-producing cells
c) Gastrin and somatostatin-producing cells
What stimulates gastrin release?
Luminal peptides, digested protein, acetylcholine, gastrin-releasing peptide
What stimulates gastric acid secretion?
Gastrin, histamine, acetylcholine
What stimulates somatostatin release? How does it affect the stomach?
pH <3
Reduces gastrin, histamine and acid secretion
What acid-base abnormalities are seen in combination with vomiting?
Metabolic acidosis - most common
Metabolic alkalosis - when gastric outflow/proximal duodenum obstructed
In what situations is metabolic alkalosis recognised in patients with GI signs?
Outflow obstruction, CPV, pancreatitis, gastrinoma
DDX elevated gastrin and low gastric pH?
Gastrinoma
Hepatic/renal disease
How is gastrinoma diagnosed?
Elevated gastrin + low gastric pH
Gastrin measurement following secretin or Ca infusion
How is achlorhydria diagnosed?
Elevated gastrin and gastric pH >3
Pentagastrin or bombesin stimulation
What does a metabolic alkalosis, hypochloraemia, hypokalaemia and acidic urine suggest?
Upper GI obstruction or hypersecretory state
Where are NSAID-related ulcers most often found?
Antrum
How is gastrinoma medically managed?
Omeprazole + somatostatin analogue (eg octreotide)
What is a potential treatment for large gastric ulcers?
Octreotide
Metoclopramie MOA
Antagonises D2-dopaminergic and 5ht3-serotonergic receptors
Cholinergic effect on smooth muscle
Ondansetron MOA
Peripheral 5HT3 antagonism
Maropitant MOA
NK-1 antagonist
What is the risk of maropitant in dogs <8 weeks old
Bone marrow hypoplasia described
What parasites are associated with gastritis? What species do they infect?
Ollulanus Tricuspis - cats
Physaloptera - cats and dogs
How is ollulanus tricuspis spread? How is it diagnosed/treated?
Cat to cat - ingestion of vomitus/autoinfection
Evaluation of gastric juice, vomit or histo
Fenbendazole
What stain is used to confirm pythosis?
Gomori’s methenamine silver
How does gastric pythosis present?
Thickening of gastric outflow tract
How is gastric pythosis treated?
Aggressive resection
Itraconazole and terbinafine for 2-3 months
In which breed has atrophic gastritis been described?
Lundehund
What enzyme is responsible for the majority of carbohydrate digestion?
Pancreatic amylase
Where does the majority of protein digestion occur?
Upper small intestine - pancreatic enzymes
Which cranial nerves are involved in swallowing?
V, IX, X
