GI 3 Flashcards
what are GI peptides?
-hormones, neuropeptides and cytokines
-can act as hormones or paracrine signals
where are GI peptides?
-can be secreted into lumen to act on apical membrane receptors or ECF to act on neighboring cells
-some act outside the Gi tract (brain). ex: cholecystokinin-satiety, ghrelin-hunger
-more than 30 peptides have been identified from the Gi mucosa, only a handful are considered hormones
what is the graph of GI hormones?
what are the hormone families?
-gastrin family
-secretin family
-other : motilin
what is in the gastrin family?
-gastrin
-cholecystokinin
what is in the secretin family?
-secretin
-vasoactive intestinal peptide
-gastric inhibitory peptide (glucose dependent insulinotropic peptide
-glucagon-like peptide-1 (GLP-1)
what is the graph of the stages in the oral cavity, stomach, small intestine and large intestine?
integrated function within the digestive system is often described in three phases:
- cephalic/oral phase: digestive processes occurring before food enters the stomach
- gastric phase: digestive processes in the stomach
- intestinal phase: digestive process in the intestines
when do digestive processes begin?
-can actually begin before food enters the mouth and are reinforced once food enters the GI tract
what is the cephalic phase?
-long reflexes beginning in the brain known as the cephalic phase of digestion
-increased parasympathetic output from medulla to salivary glands (via facial and glossopharyngeal) and to the enteric nervous system (via vagus nerve: vagus reflex)
________________________ begins in the mouth
chemical and mechanical digestion
-tongue and lips also help to manipulate food
-joined by a flood of saliva from the three pairs of salivary glands (parotoid, submandibular and sublingual)
what is saliva?
-an exocrine secretion
-1.5L/day: 99.5%, 0.5% solutes
-Na, Cl, K, HCO3-, PO4-
-amylase, lysozyme, mucus, immunoglobin A
-primarily under parasympathetic control
where are secretory cells found in?
-clusters known as acini
how are salivary glands different?
-parotid: watery solution with amylase
-submandibular: similar to parotid plus some mucus
-sublingual: mainly mucus
what is deglutition?
-a reflex that pushes of bolus of food or liquid into the esophagus
-pressure against soft palate and back of mouth (voluntary) activate sensory neurons going to the medulla
what is the first step of deglutition?
-medulla (swallowing center): somatic motor outputs to pharynx and upper esophagus and autonomic outputs to the lower esophagus
-soft palate closes off nasopharynx, peristaltic contractions in pharynx
-contractions moves larynx up and forward, epiglottis closes trachea
-upper esophageal sphincter relaxes and opens
what are the second and third steps of deglutition?
what is gastroesophageal reflux disease (heartburn)?
-LES technically not a true anatomical sphincter
-churning action of stomach contraction can cause backflow
-negative intrapleural pressure during inspiration can cause esophagus to expand drawing gastric acid and pepsin from the stomach
what are the three general functions of the stomach?
-storage: stores food and regulates its passage into the small intestine
-digestion: chemical and mechanical digestion into chyme
-defense: destroys bacteria and other pathogens in food and pathogens trapped in airway mucus (mucociliary escalator)
what is the integrated function of the gastric phase?
-3.5 liters of food drink and saliva enter the stomach each day
-motility and secretion initiated during cephalic phase now reinforced
upon swallowing food, parasympathetic neurons to the ENS cause the fundus of the stomach to relax:
RECEPTIVE RELAXATION
-distension of stomach enhances motility
-weak peristaltic waves (15-25 secs) that increase in force proceeding down the antrum moves chyme toward pylorus (propulsion) and then larger particles are moved back to the body (retropulsion)
-mixes food with acid and digestive enzymes, small amounts of chyme squeeze through pylorus
what is the graph of the stomach?
what are the gastric secretions? (protect and digest)
G-cells release gastrin (hormone) in response to amino acids, peptides and distention (short reflex-GRP)
-parasympathetic neurons-> ENS: stimulate gastrin production during cephalic phase (long reflex)
-stimulates gastric acid secretion directly from parietal cells
-indirectly: stimulates histamine release from enterochromaffin-like cells (ECL), which then stimulates parietal cells
