Digestive system lecture 2 Flashcards
How does the ANS (autonomic nervous system) modulate ENS activity (via what reflexes)
What happens when you excite and inhibitory neuron?
-via long, extrinsic reflexes, it has synaptic connection with ENS neurons
-you decrease net excitation (less NO release)
What happens when a meal comes into the stomach?
What can also affect whether the ANS gets activated/
-it strecthes the stomach
-the emotional state, for ex. if we are anxious it affects activation of ANS
What does the ANS modulation of the ENS allow for?
What is the role of parasympathetic and sympathetic?
-Allows for integrated activity over longer distances along the GIT
-long, extrinsic reflexes
In general:
PS – Excitatory may also excite inhibitory neurons
S – Inhibitory may also inhibit inhibitory neurons
How are the propulsive, secretory and absorptive activities integrated for high functional efficiency by?
-by neural (ENS And ANS)
and hormonal mechanisms
What can non GIT hormones influence vs GIT hormones?
-Non-GIT hormones may influence growth and development of GIT
GIT hormones may influence activities outside the GIT, and can also regulate activities inside the GIT
What does ghrelin stimulate, what about leptin?
What are they released by?
ghrelin=stimulate hunger and increases appetite
-releasde by glands in stomach during fasting
-leptin induces satiety (decreases appetite)
-released by fat cells with overeating
Where is the DES (diffude endocrine system)?
What is it?
-DES = Diffuse Endocrine System, scattered among other cells in mucosa
-it is the largest most diverse endocrine system in the body (more than 20 more diff hormones released)
What are the 5 most important GI hormones releasd by the DES?
-the diffuse endocrine system releases:
gastrin
CCK
secretin
GIP
VIP
What are the 3 different methods of hormonal regulation?
-autocrine= on same cell
-paracrine=on neighboring cell
-endocrine= travel through the bloodstream to affact target tissues
What is the pathway that GIT regulatory hormones take (parts of body/system)?
released from mucosa into portal blood (hepatic portal vein—>liver—>heart—> systemic circulation—> target cells
What can GIT regulatory hormone targets be?
What are the ways that they can interact with one another and with neurotrasmitters?
-excitatory and inhibitory
-synergistically (they potentiate one another)
-and antagonistically (inhibit)
What are the 3 main GIT functions?
- MOTILITY (muscular activity)—> Propulsion & Physical Breakdown
2.SECRETION (glandular activity)—>Chemical Breakdown
3.ABSORPTION Transfer to Circulation
What are the 2 ways that there is propulsion (flow) in the GIT?
-gradients of pressure (change in pressure) and variations in resistance 1/R
What produces pressure gradient in the stomach?
What is segmentation vs peristalsis?
-coordinated contractions of muscular elements in GIT wall, use the circular muscles to decrease radius of GIT
-segmentation is when tou have a single contraction then 2 at the end to have effective micing since it goes back and forth
-peristalsis=contraction moves up the GIT to create a gradient
What is the flow in the GIT normally?
What causes acid reflux?
-normally flow is slow, aboral (away from mouth) and meets little to no resistance
-heart burn/acid reflux is caused by the lower esophageal spincter when it is open when it shouldnt be
What are the phases of deglutition (swallowing)?
How many diff muscles are involved in swallowing?
oral (voluntary
-pharyngeal and esophageal (when food moves down esophagus)
-25 diff muscles
What does the pharnyx do in swallowing?
What about the esophagus?
What 2 spincters does esophagus need relaxation from?
Pharynx - conveys food from the mouth to the esophagus through a process known as deglutition (swallowing)
Esophagus - transports food into the stomach
Requires relaxation of two sphincters:
-Upper esophageal sphincter
-Lower esophageal sphincter
What is the oral phase transport from?
What is the bolus?
What parts of the body are closed/moving during oral phase?
-transport from mouth to pharynx, and it is under Voluntary Control
-bolus is food that is one mass, covered in saliva
-lips are closed ad the tongue pushes food against hard palate, then food goes to the pharynx
In the oral phase what happens to the soft palate and the epiglottis?
-soft palate is closed so food doesnt go to the nose
-closed so food doesnt go into the trachea
What is voluntary and involuntary in the brain, when regarding the GIT?
-voluntary is the ability to initiate=cortex
-deglutition center is the involuntary reflexes that coordinate movements= medulla
What is the oral phase the transport of, and what does it involve?
-Oral Phase – transport of bolus (masticated, insalivated mass of food) from anterior to posterior portion of mouth
-This involves a series of reflexes coordinated in the Deglutition Center in the medulla oblongata
What is the pharynx?
Why do we not want food in resp tract, and what can it cause?
-region where respiratory and digestive tracks cross
-if you get food in resp tract it is caused by aspiration of lung and can cause infection/issues
What does bolus do in pharynx?
What happens in the pharyngeal phase when there is bolus in the pharynx?
- it stretches pharynx which pushes against epiglottis to cover airway
-reflexes cause it to move downward, as it moves downward, it presses on the epiglottis which is covered by the glottis
what 2 things do you need in pharyngeal phase?
-reflexive contraction of vocal cords (close, larynx moves upwards and forward to fit under the base of the tongue)
-and closure of glottis which protects the lower airways
What happens in last stage of pharyngeal phase when bolus is near the end of pharynx?
-UES relaxes pharangeal muscles to contract to push bolus across the relaxes UES into the esophagus
What are the 4 main phases in the pharyngeal phase?
What type of control is it under?
- Passages to nose, mouth, and trachea are blocked
- Apnea (cessation of bretahing so you dont get food in airway)
- UES relaxes
- Pharynx muscles contract (creates gradient of pressure to move food into esophagus)
under involuntary control
What does the involuntary control of pharyngeal phase consist of?
What are they initiated by, where are they organized in?
What do they close to prevent?
DEGLUTION REFLEXES: a series of protective reflexes, initiated by stimulation of afferent fibers in the pharynx,
-organized in Deglutition Centre,
-closing off nasal, oral, and laryngeal cavities, preventing misdirection of the bolus.
-Simultaneously, respiration is briefly inhibited.
What happens in pharyngeal phase when there is a transfer to the esophagus?
-Transfer to Esophagus, as pharyngeal muscles contract and Upper Esophageal Sphincter relaxes.
What happens during pharyngeal phase of swallowing, what is shut off/closed and what is moved up?
-nasal passage is sht off, glottis and epiglottis are closed
-larynx has moved up so the trachea is protected from food
What type of signal from pharyngeal receptor goes to deglutition center?
Where in the deglutition center?
WHat type of signals are sent from the deglutition center, what does this cause (4 main things)
-afferent signal to the medulla
-then efferent signals from deglutition center to relax UES, protective reactions, deglutition apnea, an contraction of phargyngeal muscles
What mediates closure of the UES?
What happens during relaxation?
-CLOSURE=impulses originate in the CNS, mediated by the vagus nerve, releasing ACh, causing muscle contraction
During deglutition =RELAXATION, cessation of impulses, results in muscle relaxation
What is the striated musle closed at rest in the UES?
What is it kept tonically active by?
-it is the cricopharyngeus which is closed at rest to keep components from moving around
-kept active by somatic vagal fibers which will constantly release ACh onto nicotinic receptor to keep muscle in contracted state
What do we use for swallowing of food after it passes the esophagus?
peristalsis
What type of muscle is in the esophagus?
What type of signal does each muscle use?
upper 1/3 is striated muscle (uses vagus (somatic) input)
and bottom 2/3 are smooth muscle (uses vagus, autonomic signal, which acts via enteric neurons
What nervous system is the vagal nerve from?
What is the signal propagation for in the esophageal phase?
the parasympathetic nervous system
-signal propagation is for peristaltic wave
Where does body of esophagus lie?
What is the pressure there
Body of esophagus lies within the thoracic cavity
Recall: Negative Pressure of -5 to-10mmhg
