HRR: GI secretions and motility I Flashcards
What is considered the foregut?
Esophagus to proximal duodenum
What is considered the midgut?
Distal duodenum to proximal 2/3 of transverse colon
What is considered the hindgut?
Distal third of the transverse colon to the anal canal
What vessel supplies the foregut?
Celiac artery
What vessel supplies the midgut?
Superior mesenteric artery
What vessel supplies the hindgut?
Inferior mesenteric artery
What are the accessory organs of the GI tract?
Salivary glands, pancreas, liver, gallbladder
What is the arterial/venous supply of the GI tract?
Splanchnic circulation
What are the histological layers of the GI tract?
Mucosa, submucosa, muscularis externa, serosa/adventitia
In which layer is the myenteric plexus?
In the muscularis externa between the two muscle layers
What are the control mechanisms of GI function?
Endocrine, paracrine, Neurocrine
Briefly describe endocrine signaling.
Sensing cell in the GI tract secretes a regulatory hormone or peptide that travels in the bloodstream to target cells at a different location
What are the main sensing cells in the GI tract?
Enteroendocrine cells
Give the basic structure of an enteroendocrine cell.
Apical surface contacts the lumen and secretory granules are at the basolateral end. The apical end will sense, and cause release from secretory granules into the blood for endocrine signaling
What are G cells?
Enteroendocrine cells that sense partially digested proteins in the GI tract, and lead to the release of gastrin into the bloodstream to increase digestive function
Gastrin binds to which receptor?
CCK2
Briefly describe paracrine regulation.
Chemical messenger or peptide is released by a sensing cell and acts of a nearby cell via diffusion through the interstitial space; doesn’t necessarily involve travel via blood
What are enterochromaffin cells?
They are cells in the stomach that receive a signal and secrete histamine. They use this histamine for paracellular regulation, stimulating neighboring parietal cells that will them secrete H+ into the gastric lumen
Describe neural regulation of the gut.
The enteric and extrinsic nervous systems work together to control functioning of the GI tract. The enteric nervous system is within the gut, and the extrinsic is the autonomic nervous system
What are the two parts of the enteric nervous system?
Submucosal plexus and myenteric plexus
Which division of the enteric nervous system is involved in motility?
Myenteric plexus; has ascending and descending fibers to do this!
What are the main neurotransmitters involved in gut signaling for contraction?
Ach and substance P
What are the main neurotransmitters involved in gut signaling for relaxation?
VIP and NO
Describe impact of PSNS on the gut.
Increases motility, secretions, and digestive function
What is the main PSNS nerve for the GI tract?
Vagus nerve
PSNS preganglionic nerves are in the ___ and postganglionic neurons are found in the ___?
Brainstem, GI tract
What is the vagovagal reflex?
Vagus nerve afferent fibers bring sensory input and synapse with an interneuron, which then stimulates a motor neuron
Cell bodies for vagal afferents are in the…
Nodose ganglion
What is the effect of the SNS on the GI tract?
Decreases secretions, motility, and overall GI function
Sympathetic preganglionic neurons are in the ___, and postganglionic neurons ___?
Spinal cord; synapse in ENS or directly innervate effector cells
Where do SNS preganglionic fibers terminate?
Prevertebral ganglia
What sections of prevertebral ganglia are relevant to the GI tract?
Celiac (T5-9), superior mesenteric (T10-12), inferior mesenteric (L1-2)
What is peristalsis?
Coordinated propulsion of food forward
What is the most potent stimulator of peristalsis?
Distension/stretch
In which segments of the GI tract does peristalsis occur?
Pharynx, esophagus, gastric antrum, small/large intestine
Where does segmentation occur?
Small/large intestines
Where do tonic contractions occur?
Sphincters
What is the migratory motor complex?
Rhythmic phase peristaltic contractions that occur in the fasting state; a basal rate of motility that helps clear the GI tract
What are pathologic patterns of motility?
Spasms (maximal contractile activity) or ileus (absent contractile activity)
What are interstitial cells of cajal?
They form gap junctions with smooth muscle cells to help the cells work together as one; they’re pacemakers and highly associated with the myenteric plexus
Smooth muscle contraction in the gut results from…
Temporal summation of AP’s
GI tone is influenced by…
Neurotransmitters, hormones, paracrine substances, drugs
