GI Physiology Flashcards
Vagovagal Reflex
Information from receptors in mucosa and smooth muscle are relayed to the CNS via Vagus afferents and a response is triggered via Vagus efferents
*Dominates control of esophagus, stomach, and defacation
Extrinsic Innervation of GI Tract
Vagus- Esophagus, stomach, SI, Upper Colon
Pelvic Nerve- Descending and sigmoid colon, rectum, anal canal
Enteric Nervous System
Consists of networks formed by the myenteric and submucosal plexuses; allows for stimulus in one part of tract to produce response in another in absence of extrinsic system
*Myenteric-controls motility
Sumucosal-controls secretion & found in intestines
*Dominates control of intestines
Zollinger-Ellison Syndrome
Hypersecretion of HCl due to presence of gastrinoma; development of ulcers, diarrhea, and steatorrhea occurs
Gastrin
Secreted by: G-cells in antrum of stomach
Action: HCl secretion
Releaser: Small peptides, AAs, gastric distension, vagal stimulation
CCK
S- I cells of duodenum and jejunum
A- Gallbladder contraction
Pancreatic enzyme secretion
Bicarbonate secretion
Inhibits gastric emptying
R-Small peptides, AAs, FAs
Secretin
S- S-cells in the duodenum
A- Bicarbonate secretion
Biliary bicarbonate production
Inhibits HCl secretion
R- Acid
Glucose-dependent Insulinotropic Peptide
“GIP”
S- K-cells in duodenum and jejunum
A- Insulin release
Inhibits HCl secretion
R- FAs, AAs, oral glucose
Motilin
S- Duodenum and jejunum
A- Stimulates gastric motility
R- Nerves (during starvation)
*Helps to clear intestines for food when it arrives
Somatostatin
S- D-cells in GI mucosa
A- Inhibits GI hormone release and HCl secretion
R- Acid
Vasoactive Intestinal Peptide
“VIP”
S- GI Mucosa and smooth muscle
A- Relaxes GI smooth muscle
Stimulates pancreatic and intestinal secretion
R-?
Histamine
S- ECL cells
A- Stimulates HCl secretion
R- Gastrin
Gastrin-releasing peptide
S- Gastric mucosa
A- Gastrin release
R- Vagal stimulation
Enkephalins
S- GI mucosa and smooth muscle
A- Stimulates contraction of smooth muscle
Inhibits intestinal secretions
*Is why opiates are useful in treating diarrhea
Slow Waves
Rhythmic changes in the potential of gastric smooth muscle cells, & if the plateau phase exceeds threshold, contraction will occur; the frequency of these waves determines the maximum frequency of contractions
- Neural and hormonal input can produce bigger contractions and inhibit APs
- Only place where an AP MIGHT occur is the stomach
Greatest contribution to salivation
Submaxillary Gland
Acinus
Blind end of a duct that secretes the initial saliva
Flow of saliva
Acinus => Intercalated duct => Striated duct => Intralobular duct => Interlobular duct
Myoepithelial cells
Contraction of these cells ejects saliva into the mouth
Control of salivation
Primarily under parasympathetic control; sectioning of these nerves cause the gland to atrophy
*Some sympathetic fxn (constriction of blood vessels and contraction of myoepithelial cells)
Modification of saliva
Initially reabsorb Cl- and secrete HCO3-; later reabsorb Na+ and secrete K+ and HCO3-
Effects of increased saliva flow on ionic composition
Na- Increased
Cl- Increased
K- Initial decrease, then plateaus
HCO3- Initial increase, then plateaus
*Due to the activity of the pumps related to these ions
Xerstomia
Commonly caused by anti-depressants or Sjögren’s syndrome, this is the term for a lack of salivary secretion
*Pts. will have dental caries and chronic mouth infxns; treat w/ frequent water consumption or pilocarpine mouthwashes (cholinergic agonist)
Deglutition
Swallowing initiated by voluntary action of collecting a bolus of food; nasopharynx gets closed off by soft palate, layngeal muscles close glottis and elevate larynx, and peristalsis begins in the pharynx to push the bolus thru the relaxed UES
