GI System 3 Roane Flashcards
How is the intestine regulated?
-Nerve signals
-Signals through the enteric nervous system (enteric = contained within the gut)
-Hormonal - through the blood
How are neurons and CNS involved in hunger?
Long loop: CNS: hunger, smell, or taste of food
Gastrointestinal wall: Nerve plexus receives signal activating smooth muscles and glands
Short loop: The gastrointestinal lumen responds with a stimulus
back to the Gastrointestinal wall: Chemo, osmo, and
mechanoreceptors activated by food?
Afferent neurons to CNS
3 phases of GI control:
Cephalic phase: about to eat, food on the plate or in the mouth
-> external stimuli: smell, see or taste food -> mediated by the vagus nerve
Gastric phase: in the stomach
-> stretches the stomach wall, acidity, and peptides in the stomach when food reaches the stomach
-> long and short flex loop involved + hormone gastrin
Intestinal phase: food and stomach acid passing the pyloric sphincter are the signal, also hormone signals: CCK, secretin, GIP
How is Saliva secretion stimulated?
By the sympathetic NS: Ach and muscarinic receptors
The sequence of swallowing:
Oropharyngeal stage: The bolus is pressed voluntarily up by the tongue to move to the Pharynx -> swallowing center in the medulla activates reflexes preventing food entry into the respiratory system - > the uvula contracts and blocks the nasal passage
Esophagal stage: the wave of peristaltic allows movement of the bolus through the esophagus -> lower esophagus sphincter relaxes and allows the bolus to enter the stomach
What are sphincters?
They are round muscles, wrapped around vessels or tubes, when the muscle constrict they close, when they relax they open
we have an upper and lower esophagus sphincter
What 3 parts does the stomach consist of?
-Fundus on top
-Body in the middle: secretes, mucus, pepsinogen, and HCl
-Antrum on the bottom: secretes mucus, pepsinogen, gastrin
What are the molecules that are secreted in the stomach?
EXAM!
Parietal cell: HCl, and (intrinsic factor to digest Vit B12)
Mucous cell: Mucus
Chief cells: Pepsinogen (precursor for pepsin)
Hormones: gastrin, ECL: histamine, somastatin
How is Cl secretion controlled?
Cl- is counter-transported in exchange for HCO3- (produced by carbon anhydrase) into the cell and transported out on the basolateral side (Cl channel)
H+ is a byproduct of H2CO3- and is pumped outside through the proton pump (ATP) (drug target, Nexium) to form HCl(-)
What are the factors affecting HCl secretion?
-Gastrin, Histamine, ACh
-Somastatin is inhibiting!
-> proton pumps move from intracellular vesicles to the lumenal membrane
What is special in histamine when affecting Cl secretion?
How is histamine blocked?
Histamine synergizes the action of gastrin and ACh
Histamine is blocked by H2 antagonists
What is the point of HCl secretion?
Making the stomach environment more acidic for food digestion
How does the cephalic and gastric phase control HCl secretion?
Cephalic phase stimuli to the brain -> increase in Enteric neural activity -> stimulates Histamin and gastrin secretion and secretion of HCl (final GOAL) with ACh
The Gastric phase stimuli are luminal distension, amino acids, and peptides -> stimulate Gastrin secretion
How are elevated HCl levels downregulated?
High levels of HCl activate D-Cells -> Somastatin decreases HCl secretion (negative feedback)
How are pepsinogen zymogens activated?
Parietal cells secrete HCl (and intrinsic factor) providing an acidic environment -> Pepsinogen converts to Pepsin and digests Proteins
