26 General Principles of GI Physiology Flashcards
what are the three gastric phases and what happens in them?
Cephalic phase
Oral phase
Gastric phase
what is the cephalic phase?
thinking of eating and so different areas like the stomach and saliva respond to that by releasing hormones into the system
what is the oral phase?
chewing the food and will mainly work on saliva secretion
what is the gastric phase?
everything from the stomach down
what are the two systems of the nervous system?
extrinsic and intrinsic nervous system
describe the extrinsic nervous system?
Parasympathetic stimulation = excitatory
Sympathetic stimulation = inhibitory
what nerve is primarily involved with parasympathetic stimulation of the extrinsic nervous system? sympathetic stimulation?
Vagus nerve: 75% afferent and 25% efferent fibers which Supplies most of GI tract to the splenic flexure and then the Pelvic splanchnic nerves supply the remainder
just note for nerve innervation that nerve fibers: 50% afferent and 50% efferent
what NT does the extrinsic nervous system use for parasympathetic nervous system?
Ach
what NT does the extrinsic nervous system use for sympathetic nervous system?
Ach and Norepi
describe the intrinsic/Enteric nervous system?
Located entirely in the wall of the GI tract
Can function independently but is influenced by extrinsic nervous system
Contains as many neurons as the spinal cord
Contains two plexuses: submucosal and myenteric
What are the types of reflexes in the GI tract?
short reflexes, long reflexes, Vagovagal reflexes
what is the short reflex?
contained entirely in the wall of the GI tract (peristalsis)
what is the long reflex?
involves extrinsic nervous system +/- CNS
what is the vagovagal reflex?
reflex with afferent and efferent limbs in the vagus nerve
what are the three principle mechanisms of hormone control?
Endocrine control
Paracrine control
Neurocrine control
what is endocrine control?
Occurs when a substance (hormone or candidate hormone) is released by enteroendocrine cells into the bloodstream and circulates to its target cell.
*independent of neural control
what are the four major hormones under endocrine control?
Gastrin, CCK, Secretin, GIP (Glucose-dependent Insulinotropic Polypeptide)
what is the benefit of endocrine control?
can affect multiple targets and be highly regulated
what is paracrine control?
Occurs when a substance is released from a cell and diffuses the interstitial space to its target organ
Some substances can have both endocrine and paracrine function (somatostatin)
Enteroendocrine cells or Enterochromaffin-like cells release paracrines in to the lamina propria
what are the key paracrines in the GI tract?
Histamine, serotonin, somatostatin
what are the benefits of paracrine control?
can act quickly and locally
what is neurocrine control?
Occurs when a substance released from a neuron (neuron) exerts its effect on a target cell.
involves reflexes
what are the benefits of neurocrine control?
can act quickly over short and long distances
What parts of the digestive system DON’T drain into the portal system?
The lower part of the rectum and the anus
What was the hormonal error we discussed?
Prader-Willi Syndrome – Associated with gene deletions on paternal chromosome 15, patients have 3x grehlin levels
what are the four GI hormones?
Gastrin
CCK
Secretin
GIP
what are the three GI Paracrines?
Somatostatin
Histamine
serotonin
what are the three GI Neurocrines?
VIP
GRP
Enkephalins (Met- and Leu-)
Actions of gastrin?
increases parietal cells to increase H+ production
seen in patients with gastrin secreting tumors
Actions of CCK?
contraction of the bladder relaxation of the sphincter of odi pancreatic enzyme secretion growth of exocrine pancreas inhibits gastric emptying
Actions of secretin?
stimulates pancreatic HCO3- secretion
increases growth of the exocrine pancreas
bile production
inhibits H+ secretion
Actions of GIP?
stimulates insulin release
oral glucose is more effective
inhibits H+ secretion
Actions of somatostatin?
inhibits the release of all GI hormones
Actions of histamine?
increases gastric H+ secretion
Actions of VIP?
produces relaxation of GI smooth muscle in lower esophageal sphincter
stimulates pancreatic HCO3- secretion
inhibits gastric H+ secretion
Actions of GRP?
stimulates gastrin release from the G cells
Actions of Enkephalins?
stimulates the contraction of GI smooth muscle
inhibits intestinal secretion
what are the most potent stimuli for gastrin?
tryptophan and phenylalanine
what is the inhibition for gastrin release?
H+ on the lumen side
somatostatin
this occurs when gastrin is secreted by non-beta cell tumors of the pancreas?
Zollinger-Ellison syndrome (gastrinoma)
what is the stimuli for CCK release?
I cells and duodenal and jejunal mucosa
small peptides and amino acids
fatty acids and monoglycerides
what releases secretin?
S cells of the duodenum
stimuli for secretin?
H+ and fatty acids
stimuli for the release of GIP?
fatty acids, amino acids, orally administered glucose
VIP is secreted by the pancreatic islet cell tumors and is presumed to mediate this disease?
pancreatic Cholera
the use of this neurocrine is helpful in the treatment of diarrhea?
Enkephalins
what is the satiety center?
inhibits appetite and located in the ventromedial nucleus of the hypothalamus
what is the feeding center?
stimulates appetite and located in the lateral hypothalamic area of the hypothalamus
Both anorexigenic neurons and leptin both work to increase or decrease the appetite?
decrease
Both orexigenic neurons and leptin both work to increase or decrease the appetite?
increase
what are the two main functions of the GI tract?
Absorb nutrients, electrolytes and water into the circulatory system
Eliminate waste products
what are the phases of digestion?
Cephalic Oral Esophageal Gastric Small Intestinal Colonic Liver
what are physiological mechanisms for digestion?
Motility Secretion Digestion Absorption (Excretion)
how is the endocrine related to the GI system?
regulation
how is the immune system related to the GI system?
protection
major functions of the sphincter?
Different “compartments” for different functions
Tighter control of delivery of contents
Prevention of backflow
what is the medical condition called when refluxed contents can be damaging to epithelium and disrupt GI function?
sphincter dysfunction Reflux, more commonly known as GERD
what is the solution to regulating the GI system?
reflexes and feedback loops help with the neural, hormonal, and local control of the GI function and so the major mechanisms that get regulated are secretion, motility, and blood flow
so we know that the autonomic nervous system is involved with GI regulation, what parts?
extrinsic and intrinsic
the extrinsic
- para and sympathetic NS
the intrinsic
- enteric nervous system, which contains the submucosal and myenteric plexi
what are the components of the reflux?
stimuli sensory, afferent neurons interneurons secretomotor, efferent neurons effector cells
hormones and candidate hormones participate in ______?
endocrine regulation
what are the two key hormone families?
Gastrin-CCK and Secretin-Glucagon
what is key to note about serotonin and somatostatin?
serotonin can act as a hormone, and somatostatin can function as a neurocrine
molecules that decrease appetite?
Leptin
Insulin
GLP-1
Peptide YY
molecules that increase appetite?
Ghrelin
Key regions of the hypothalamus involved in appetite?
Satiety center
Feeding center
this part of the brain signals about hunger and satiety?
Arcuate nucleus in the floor of 3rd ventricle
what is Prader-Willi Syndrome? what hormone is regulated?
voracious appetite, hyperphagia, and obesity; gene deletion on chromosome 15, elevated gherkin levels
three main arteries of the aorta supply the GI?
Celiac artery
inferior/superior mesenteric artery
veins draining the organs travel in this particular type of circulation to the liver?
portal
what drains the liver?
hepatic veins
these organs do not drain into the portal system?
Organs in the head and thorax (salivary glands, cervical and thoracic esophagus) and the lower part of the rectum and anus
When would you want decreased flow to the GI tract?
exercise
circulatory shock
mechanism
Sympathetic nervous system causes vasoconstriction of vessels to GI tract
Somatostatin can also cause vasoconstriction
what is given to patients with bleeding esophageal varices causes by cirrhosis to stop the bleeding?
Octreotide
purpose of gut flora?
Are protective
Aid in digestion
Synthesize Vitamin K
