GI Day 2 Flashcards
(36 cards)
Propulsion
Movement of contents through the GI tract from the mouth to the anus, primarily involving peristalsis.
Peristalsis
Coordinated, wave-like smooth muscle contractions to move chyme through GI tract.
Contro: reflexive response to stretch of GI tract walls
Process: Contracts behind the bolus (food) while relaxing ahead, moving it forward.
Segmentation
Slow transit time: circular muscle contrantions, blocking sections of the GI tract.
Purpose: slows down transit time, allowing for more digestion and absorption.
Deglutation
(Swallowing) includes coordinated muscle contractions to move food from the mouth to the stomach.
Tonic contractions
Prolonged contractions primarily in the sphincters, controlling passage between GI segments.
Peristalsis Reflex
Sequence of events….
EC cells “real deal” stretch receptors.
- EC cells (Entrerochromaffin cells) detect stretch
- EC cells release serotonin (5-HT).
- 5-HT activation stimulates sensory interneurons leading to two pathways:
a) Ascending Interneurons - release AcH, substance P, activating motor neurons for contraction (Oral side)
b) descending interneurons - release NO or vasoactive interstinal pepride (VIP) for relaxation. (Aboral side)
**Allows for forward movement by contracting behind the chyme and relaxing infront of the chyme.
Slide 3
Interstitial cells of cajal ICCs (Role, Function)
Role: pacemaker cells in the GI tract, analagous to the SA node cells in the heart.
Functions: Provides rhythmic, spontanous depolarization
- Depolarization is driven by Ca++ influx, occuring at regular intervals (every 10 seconds)
- Spike potentials are added depolarizations from stretch reflexes result in contraction when close to action potential threshold.
- rhythm, top regions of the small intestine have faster depolarization, facilitating directional movement
Effect of AcH and Epi on Bais Electical Rhythm (BER)
AcH - decreases time between depolarization (increasing GI motility via parasympathetic)
Epinephrine - Increases time between depolarization (decreases GI motility, sympathetic)
Migrating Motor Complexes (MCC) (Purpose/Phases)
Starts in the stomach and works down sequentially to the distal ilum.
Purpose: Clears the GI tract between meals, preventing stagnation and moving material/bacteria toward the large intestine.
**Ensures chyme/bacteria etc, don’t back up into the small intestine
Cycles: Occurs every 90-100 minutes, consisting of three phases.
- phase 1 (quiescent): miniaml activity of three phases
- phase 2: small, irregular contractions
- phase 3: intense contractions lasting about 5 min, helping clear the small intestine.
Pharynx
Contains Two parts:
Nasopharynx - located behind the nose
Oropharynx - Located behind the mouth
Laryngopharynx - located below the mouth
Key structure:
- Soft palate (prevents food entry into the nasal cavity)
- Epiglottis (protects airway during swallowing)
Esophagus
Connects laryngopharynx to stomach.
Collapsible when empty, lacks cartilage rings (unlike the larynx).
Gastroesophageal sphincter- contains upper and lower sphincter (cardiac and lower esophageal sphincter).
Gastroesophageal sphincter (function, innervation)
Prevents backflow, food/acid from coming up.
Intrinsic: controlled by vagus nerve –> AcH released for contraction.
Interneurons connected to vagus nerve NO or VIP release –> relaxation.
Extrinsic sphincter:
Controlled by the phrenic nerve, coordinating with respirtaion, as we take a breath in, it closes off.
Three componets to lower esophageal sphincter:
- Intrinsic (thickening of smooth muscle)
- Extrinsic (crural portion of diaphragm)
- Flap valve (oblique fibers in stomach that block off flow).
Hiatal Hernia
When the spincter is above the diaphram, and it can not help with pintching off sphincter.
Leads to GERD
Deglutition Voluntary phase
Swallowing
Voluntary phase:
Bolus forms and tongue pushes food into the pharynx –> stimualtes 4 relflexive actions
- Peristalsis
- opening of the sphincter
- blocking nasopharynx (soft palate)
- blocking larynx (inhibits respiration/epiglottis)
Deglutition Pharyngeal phase
Relax actions:
- Upper esophageal sphincter opens
- Soft palate moves up to block the nasopharynx
- Larynx lifts and epiglottis tips down to protect the airway (close glottis)
- Pharyngeal muscle contraction moves the bolus into the esophagus
Deglutiton: Esophageal phase
- Upper esophageal sphincter opens
- Perstaltic contractions move bolus down towards stomach
- Gastroesophageal (lower esoph) sphincter opens => bolus enters stomach (via NO/VIP relaxation of muscles)
Gastic Motility (contractions)
Action 1 - relax fundaus/top part, receptive relaxation (to recieve food)
Action 2 - Peristaltic contractions of antrum: antral systole (up to 10 secs) => pyloric reion to duodenum.
Antral systole = pushes contents back and forth for mixing
Pyloric contractions = block large bood particles form reaching the pyloric sphincter, only allowing well mixed food to eneter duodenum.
What nutrients are absorved here?
Alcohol, some drugs (aspirin)
In stomach not GI!
Movement Time Course:
Liquid meal leaves in 1-2 hours
Solid meal leaves in 2-3 hours
Carbs quickest => proteins => fat
Hyper osmotic pressure => longer time in stomach (sensed by osmoreceptros in duodenum)
***Regulated by: petide YY and CCK (inhibits gastric emptying)
Gastic all together in 3 steps
- Stomach muscle contracts and propels a small amount of chume through the pyloric sphincter. The rest is propelled backward.
- The stomach peristalic waves churn the remaining chyme
- The remaining chyme is again propelled toward the pyloric sphincter. More chyme is forced through as the process repeats. (pepsin to break proteins).
Vomiting process
- Increased salivation/nausea - lubricates esophagus
- Reverse peristalsis in duodenum - moving opposite way
- Glottis closure to protect the airway
- Abdominal muscle contractions and controlled breath-hold, increase abdominal pressure without fully closing the LES.
- Stomach contraction expel contents.
Controlled by the Meulla, specifically the postrema (which detects toxins in the blood, often triggers vomiting).
Vomiting medications/triggers
Ondansetron (5HT anagonist, zofran) - a seratonin antagonist prevents vomiting by blocking serotonin recepters involved in the vomiting reflex. *** This is why antidepressents can cause nausea.
Also dopamine receptors in medulla trigger vomiting - D2 antagonists (haloperidol, haldol, antipsychotic) can block receptors.
Triggers:
Upper GI irratation
Motion sickness
Emotions
Echmoreceptors in medulla
Where do hemorroids occur?
Hemorrhoids occur in the anus and lower rectum, and can be either internal or external:
Internal hemorrhoids
Develop in the lining of the anus and lower rectum, just inside the anus. If they become large, they can prolapse and fall outside the anus.
External hemorrhoids
Develop under the skin around the anus.
