Week 1 Flashcards
Path of food
Mouth –> Pharynx –> Esophagus –> Stomach –> Small Intestine –> Colon –> Rectum –> Toilet
What is preventing the food from going backwards
-name the sphincters and where they reside in pathway of food
- Sphincters
- Mouth–> Pharynx–> Upper Esophageal Sphincter–> esophagus–> Lower Esophageal Sphincter–> Stomach–> Pylorus–> Small intestine–> Ileocecal Valve–> Colon–> Rectum–> Internal Anal Sphincter–> External Anal Sphincter–> Toilet
Sphincters
-anatomy
-Involuntary smooth muscles (there are a few voluntary ones in particular regions such as the external anal sphincter
characteristics when depicting the structure of the GI tract
- Continuous, open tube
- Microvilli and crypts (function to increase surface area)
- Primarily made of smooth muscle containing calmodulin, Ca++, Myosin light chain kinase (MLCK), etc.
- Lined with epithelium
main categories of function of the GI tract
- Digestion: Include Chemical and Mechanical components
- Absorption: Gets nutrients into the body
- Secretion: Secrete substances to help break the food down
- Motility: Need the food to move through the whole system
- Excretion: Get rid of waste
Digestion Overview
- broken into
- regulated by
-Cephalic- what happens prior to eating (Smell food–> salivate and stomach growls in anticipation)
Gastric- digestion in the stomach
Intestinal- digestion in the intestines
- different hormones: Paracrine- signaling neighboring cells/ cells in close proximity
Autocrine- signaling self
Endocrine- Signaling a distant organ/tissue (usually has to enter the blood stream)
GI and autonomic nervous system
-what is it innervated by?
- Parasympathetic:
- Sympathetic
Where does the Vagus nerve enter the abdomen
through the esophageal plexus at the level of T10.
Parasympathetic
-where are the pre and post ganglionis cell bodies? What neurotransmitters are included?
- Preganglionic cell bodies: are located in the dorsal nucleus of CNX (Vagus nerve), Neurotransmitters include Acetylcholine acting on nicotinic receptors
- Postganglionic cell bodies: are located in the organ wall, Neurotransmitters include Acetylcholine acting on muscarinic receptors
Sympathetic
-where are the pre and post ganglionis cell bodies? What neurotransmitters are included?
- Preganglionic cell bodies: located in the lateral horn of the spinal cord at levels T5-L3; Neurotransmitters include Acetylcholine acting on nicotinic receptors; Postganglionic cell bodies: In celiac, Aorticorenal, Superior Mesenteric, and Inferior Mesenteric ganglia;
Neurotransmitters include norepinephrine acting on adrenergic receptors
Where do fibers from preganglionic cell bodies of thoracic sympathetic innervation converge? what about lumbar?
- Fibers in the thoracic region converge to form the Greater, Lesser, and Least Splanchnic nerves.
- The fibers in the lumbar region form the Lumbar Splanchnic nerve.
Sensory information of GI
- (afferent fibers) send signals from the GI system to the brain
- Reach the brain by traveling with the sympathetic fiber pathways
Enteric Nervous System
-types of plexus
- Myenteric
- Submucosal
Myenteric
- what does it act on?
- function?
- neurotransmitters?
- acts on the smooth muscle
- Functions to regulate smooth muscle contraction and relaxation
- Neurotransmitters involved:
Excitatory/Contraction: Acetylcholine
Inhibitory/Relaxation: Nitric Oxide
Submucosal
- what does it act on?
- function?
- neurotransmitters?
- directed to the epithelium
- regulate epithelial secretory functions (enzymes for digestion as well as lubrication)
- Neurotransmitters involved:
Secretion Response: caused by Acetylcholine
mediators that regulate the afferent signal from inside the intestinal lumen
-function
- Chemoreceptors and mechanoreceptors sensing changes in macromolecules, hormones, pH, and distention/stretch of the smooth muscle
- environmental changes send sensory neurons back to engage the enteric nervous system to get an immediate response from the parasympathetic reflex
Process of mastication
- involves muscles of mastication and salivary glands
Muscles of mastication
-innervation?
- Temporalis, masseter, medial and lateral pterygoids
- Innervated by V3 (mandibular branch of trigeminal n.)
Salivary Glands
- Sublingual, submandibular, and Parotid gland
Sublingual, submandibular
- innervation
- Preganglionic nerve body
- Postganglionic nerve body
- Innervated by parasympathetics
- Preganglionic nerve body: superior salavatory nucleus; Fibers exit the brainstem through the corda tympani (branch of the facial nerve)- hitches a ride to the oral cavity along the lingual n which is going to the tongue.
- Postganglionic nerve body: in the submandibular ganglion and will continue to finally synapse at the glandular tissue.
Parotid gland
- innervation
- Preganglionic nerve body
- Postganglionic nerve body
- Innervated by parasympathetics
- Preganglionic cell bodies: inferior salavatory nucleus; Exits the brainstem via the glossopharyngeal n
- Postganglionic cell bodies: otic ganglion; Travels via the auriculotemporal n (which is a branch of V3/mandibular n. of the trigeminal n.) to finally synapse at parotid glandular tissue.
Deglutition
- complex process that transfers food blous from mouth to pharynx and esophagus into stomach
- Stage 1: voluntary; bolus is compressed against hard palate and pushed from mouth into oropharynx
- Stage 2: Involuntary and rapid; soft palate is elevated by Levator palatini and uvula (musculus uvulae) sealing off nasopharynx; suprahyoid and logitudinal pharyngeal muscles contract to elevate larynx and close it off using the epiglottis; pharynx widens and shortens to recieve food bolus
- Stage 3: Involuntary, sequential contraction of all three pharyngeal constrictor muscles creating a peristaltic ridge that forces the food bolus inferiorly into the esophagus
How is epiglottis activated?
- by the pharyngeal lifters (stylopharyngeus, salpingopharyngeus, and palatopharyngeus) to close off the larynx/airway
- All of these are innervated by the Vagus n. except stylopharyngeus, which is innervated by the glossopharyngeal n.
How is the larynx elevated?
- Suprahyoid muscles also activate to pull superiorly on the hyoid bone to elevate the larynx; Ant Digastric, mylohyoid
- Both innervated by branch of V3 (nerve to mylohyoid)
Peristalsis
- type of contraction occuring in the esophagus during stage 3 of deglutition
Peristaltic contraction function
- Creates a pressure gradient that helps push the bolus down towards the stomach
- Superior 1/3 contraction occurs within 1-2 seconds of swallowing; Middle 1/3 within 3-5 seconds; Inferior 1/3 within 5-8 seconds and finally ends at the lower esophageal sphincter
Muscle in esophagus
-innervation
- Striated muscle: Innervated by somatic neurons (Acetylcholine acting on nicotinic receptors)
- Smooth muscle (contraction and dilation needs to happen in a coordinated, rhythmic fashion… Muscle upstream contracts while muscle downstream relaxes/dilates to accept the incoming bolus.)
Smooth muscle contraction and dilation
- Contraction: Acetylcholine acting on muscarinic receptors; Gαq–> IP3 and DAG–> Release Ca++ from Sarcoplasmic Reticulum–> Contraction
- Dilation: NO (nitric oxide); GC–>cGMP–> MLLP (myosin light chain phosphatase)–> relaxation
Primary vs. Secondary Peristalsis
- Primary: first time a bolus is swallowed
- Secondary: A second contraction that follows the first one to clear whatever is left behind
- Example: If you eat a second bolus within a 5 second window of the first bolus, the first peristalsis will stop to let the second one will catch up. Then the two will go down together.
problems swallowing and it feels like the food is getting stuck…. What could be going on
- Structural problem–> fibrosis or anatomical variation
- Functional problem–> neural control or the actual muscle that isn’t functioning correctly (our patient has uncontrolled diabetes so this(neuropathy) is a possibility)
How do we get the bolus into the stomach?
- Has to go through the lower esophageal sphincter
- As the bolus comes down, muscle stretches, and pressure increases–> causes relaxation of the lower esophageal sphincter–> can enter stomach.
lower esophageal sphincter
- resting state
- importance of relaxing and closing
- what are we trying to prevent
- resting state, it is tonically contracted/closed
- We want the lower esophageal sphincter to close back to prevent acid reflux.
- If there is a failure to relax–> cant swallow all the way and food can’t get into the stomach
- If there is a failure to contract–> acid reflux/ food can come back up
If there is an x-ray that shows food is getting stuck in esophagus and unable to get into stomach what is most likely the problem?
- Ganglion cells in the myenteric plexus
- myenteric plexus is coordinating the smooth muscle contraction and relaxation, and these events are not being regulated correctly in this patient
gastrointestinal agents used in motility disorders
- Antiemetics
- Laxatives
- Prokinetics
- Antidiarrheals
scintigraphy test
- what is it?
- what is it testing?
- normal?
- look at gastric emptying
- looking at the amnt of food that’s in the stomach after a period of time.
- After about 2.5 hours or so, you should have most of the food passing thru the stomach into the duodenum, b/c it has to get into the intestinal phase of digestion.
diabetes effects on gastric motility
-causes neurodisruption so that nerves innervating stomach do not work correctly and stomach is unable to perform functions normally
receptive relaxation
- what is it?
- when does it start?
- The ability of the stomach to relax as the volume
increases. - start in early stages of digestion