GI Physiology DSA Flashcards
What are the 7 sphincters found in the GI tract, and what sections do they separate?
Upper Esophageal Sphincter (UES) - Pharynx / Esophagus
Lower Esophageal Sphincter (LES) - Esophagus / Stomach
Pyloric Sphincter - Stomach / Duodenum
Sphincter of Oddi - Common Bile + Pancreatic Duct / Duodenum
Ileocecal Valve - Ileum / Large Intestine
Internal Anal Sphincter
External Anal Sphincter
What do you call the 4 functional layers of tissue of the intestinal wall?
Mucosal Layer
Submucosa
Muscularis Propria (Muscle Layers)
Serosa
What tissue layers make up the Mucosal Layer from most interior to most exterior?
Epithelium
Lamina Propria
Muscularis Mucosae
What tissue layers make up the Muscularis Propria from most interior to most exterior?
Circular Muscle Layer
Longitudinal Muscle Layer
What are the two Plexuses that make up the Enteric Nervous System and where are they located?
Submucosal Plexus (within the submucosa layer)
Myenteric Plexus (between the Longitudinal and Circular Muscle layers)
What innervates the ENS?
ENS is innervated by the extrinsic autonomic nervous system (sympathetic/parasympathetics)
However, ENS can exert its functions without input from the CNS
This is done by receiving sensory signals from the mechanoreceptors and chemoreceptors of the mucosa layer
How does CNS signaling interact with the ENS?
CNS communicates with ENS via Vaso-vagal reflexes (vagus nerve efferents and afferents).
One example: Center that controls Food intake is found in the brain
How does Parasympathetic signaling interact with the ENS?
Parasympathetic preganglionic nerve cell bodies are located in the brain stem or the sacral spinal cord
Axons of cell bodies in the Brain stem travel along the vagus nerve, whereas axons of cell bodies in the sacral spinal cord travel along Pelvic nerves
Postganglionic cell bodies are located within the walls of the GI organs (myenteric plexus; between the longitudinal and circular muscle layers)
The synpase of the pre- and posthanglionic nerve cells is responsive to acetylcholine (nicotinic; nAChRs)
Acetylcholine/Peptide signaling of postganglionic cell onto the muscle layers or other cells promotes motility and digestion
How does Sympathetic signaling interact with the ENS?
Sympathetic preganglionic nerve cell bodies are located in the thoracic/lumbar spinal cord.
Axons of the preganglionic cells travel to the nearby prevertebral ganglia, where the cell bodies of the postganglionic nerve cells are located.
Communication at the synapse of these two nerves occurs via Acetylcholine.
Axons of the postganglionic nerve cells travel from the prevertebral ganglia all the way to the myenteric and submucosal plexuses (where they synapse).
Communication at the synpase of the postganglionic cells and the plexuses occurs via Norepinephrine
Sympathetic signaling generally inhibits GI motility and digestion.
In general, what receptors will you find in parasympathetic communication with the ENS and at what points would you find these receptors?
Parasympathetic signaling occurs via nicotinic ACh signaling at the ganglia (nAChR) and muscarinic ACh signaling at the effector cells within the wall of the target GI organ (mAChR).
In general, what receptors will you find in sympathetic communication with the ENS and at what points would you find these receptors?
Sympathetic signaling occurs via nicotinic ACh signaling at the prevertebral ganglia (nAChR) and Adrenergic Norepinephrine signaling at the wall of the target GI organ (ADR[alpha] or ADR[beta])
What is paracrine signaling?
Signaling that occurs locally between cells.
Paracrine signals reach their target cell via diffusion over short distances
What is somatostatin, what cell secretes it, what stimulates its secretion, and what is its action?
Peptide hormone secreted by D cells found in the GI mucosa.
Somatostatin is also secreted by the Hypothalamus and the [Delta] Cells of the Exocrine Pancreas
Somatostatin is released from the D cells when GI luminal pH is too low (acidic)
Somatostatin inhibits gastric H+ secretion and inihibits secretion of other GI hormones
What is histamine, what cell secretes it, what is its target, and what is its action?
Histamine is a protein signaling molecule
It is secreted by the ECL (enterochromaffin-like) cells in gastric glands
Histamine targets parietal cells
Histamine promotes the production of acid in parietal cells
What is endocrine signaling?
Action of hormones
Chemical signaling over long distance
Enteroendocrine cells (EECs) contain secretory granules filled with hormones that are secreted into the blood upon stimulation
