3. DSA Intro to GI Physiology Flashcards
(32 cards)
The main functions of the gastrointestinal tract is digestion and absorption of nutrients. What are the main properties?
Motility and secretions
GI tract sphincters restrict the passage of intestinal content to optimize digestion and absorption. What are all 7 sphincters throughout the GI tract?
Upper esophageal sphincter (UES) Lower Esophageal sphincter (LES) Pylorus (end of stomach) Sphincter of Oddi Ileocecal Valve Internal anal sphincter External anal sphincter
What are the functional layers of the small intestine wall structure? (5)
Mucosal layer
Submucosa
Muscle Layers: Circular/Longitudinal
Serosa
What are the two plexuses that make up the enteric nervous system (ENS) or nervous system of the GI tract?
Submucosal plexus
Myenteric plexus
What consists of the mucosal layer of the intestinal wall? (3)
Epithelium, lamina propria, muscularis mucosae
What consists of the muscularis propria of the intestinal wall? (3)
Myenteric plexus, circular muscle and longitudinal muscle
The ENS is known as the second brain or little brain in the gut because it is innervated by the extrinsic autonomic nervous system and can exert functions without CNS input. What are the steps to get a response from the ENS? (4)
Stimuli in wall of gut
Sensory neuron
interneuron
motor neuron = Output Response!
the ENS receives information from para/sympathetics, CNS, and sensory information from mechano/chemoreceptors in the mucosa. What does the ENS control? (3)
contraction
secretion
endocrine function
The CNS has important roles in regulating GI function. What does it have?
the vago-vagal reflex (gastric receptice relaxation reflex)
The vago-vagal reflex modulate ENS responses, as well, the centers that control food intake are in the brain. How does the reflex work?
Vagal afferents sent via nodose ganglion to the NTS (nucleus of th tractus solitarius) and back to the stomach via vagal efferents
Parasympathetic innervations modulate the Gi functions via vagus and pelvic nerves. Where are pre/post ganglionic neurons and how do they synapse?
Preganglionic nerve cell bodies in brainstem/sacral spinal cord
Postganglionic neurons lie in wall of organ
Synapse via nicotinic (nAChRs)
Sympathetic innervations via nerves running between SC and prevertebral ganglia, and between ganglia and GI. Where are the pre/post ganglionic and how do they synapse?
Preganglionic efferent arise in SC and end in prevertebral ganlia
Postganglionic from prevertebral to myenteric/submucosal plexuses
Synapse: pre: ACh post: NE
Overview of parasympathetic innervation…?
CNS ganglion to PNS ganglion on the wall of the organ within plexus releasing ACh to nAchR. Goes to smooth muscle via ACh/mAChR
Overview of sympathetic innervation?
CNS ganglion synapse before PNS via ACh/nAChR outside of GI tract. releases norepinephrine as effector to smooth muscle via ADRa or ADRb
Cellular communication via paracrine regulation is key in GI regulation via for example somatostatin or histamine. What are the characteristics of paracrine regulation?
paracrine acts locally and signals reach their target cells by diffusion over short distances
Somatostatin is secreted by D cells of the GI mucosa when there is a decrease in luminal pH. What are its actions? (2)
Where else is it secreted? (2)
inhibits gastric H+ secretion
Inhibits secretion of other GI hormones
(also secreted by hypothalamus and sigma cells of exocrine in pancreas)
Histamine in the stomach is stored and secreted by enterochromaffin-like (ECL) cells in gastric glands. What is histamines target and action?
target is parietal cells to stimulate acid production
GI is also regulated via endocrine regulation- the action of hormones. How are the hormones stored and secreted?
Enteroendocrine cells (EECs) contain secretary granules filled with hormones that are released upon stimulation and secreted into circulation to travel via blood (long distances) to target cells
Gastrin is secreted from G cells of the stomach due to small peptides, distention of the stomach and vagal stimulation. What are its actions? (2)
Increase gastric H+ secretion
Stimulates growth of gastric mucosa
Cholecystokinin (CCK) is secreted from I cells of the duodenum and jejunum due to small peptides/AA and fatty acids. What are its actions? (5)
- Increase pancreatic enzyme secretion
- Increase pancreatic HCO3- secretion
- Stimulates contraction of the gallbladder and relaxation of the sphincter of oddi
- Stimulates growth of exocrine pancreas and gallbladder
- Inhibits gastric emptying (paracrine signaling)
Secretin is secreted by S cells of the duodenum due to H+ or fatty acids in the duodenum. What are its actions? (4)
Increase pancreatic HCO3 secretion
Increase biliary HCO3 secretion
Decrease gastric H+ secretion
Inhibits trophic effect of gastrin on gastric mucosa (paracrine signaling)
Glucose dependent insulinotropic peptide (GIP) is secreted by the duodenum and jejunum in response to fatty acids, AA, and oral glucose. What are its actions? (2)
increase insulin secretion from pancreatic B cells
decrease gastric H+ secretion
What would be more effectin in increasing insulin secretion? Oral glucose or IV glucose? Why?
Oral because it stimulates GIP which stimulates insulin secretion and has direct stimulatory effects on B cells… Incretin effect
Neural regulation is also a key cellular communication for regulation of GI. Action via NTs, need APs to release the NTs. How do NTs work?
They diffuse across the synapse and bind to their specific receptors in the postsynaptic cell
