26 General Principles of GI Physiology Flashcards by Nicholas de Guzman

what are the three gastric phases and what happens in them?

Cephalic phase
Oral phase
Gastric phase

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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

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what is the oral phase?

chewing the food and will mainly work on saliva secretion

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what is the gastric phase?

everything from the stomach down

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what are the two systems of the nervous system?

extrinsic and intrinsic nervous system

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describe the extrinsic nervous system?

Parasympathetic stimulation = excitatory

Sympathetic stimulation = inhibitory

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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

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what NT does the extrinsic nervous system use for parasympathetic nervous system?

Ach

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what NT does the extrinsic nervous system use for sympathetic nervous system?

Ach and Norepi

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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

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What are the types of reflexes in the GI tract?

short reflexes, long reflexes, Vagovagal reflexes

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what is the short reflex?

contained entirely in the wall of the GI tract (peristalsis)

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what is the long reflex?

involves extrinsic nervous system +/- CNS

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what is the vagovagal reflex?

reflex with afferent and efferent limbs in the vagus nerve

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what are the three principle mechanisms of hormone control?

Endocrine control
Paracrine control
Neurocrine control

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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

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what are the four major hormones under endocrine control?

Gastrin, CCK, Secretin, GIP (Glucose-dependent Insulinotropic Polypeptide)

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what is the benefit of endocrine control?

can affect multiple targets and be highly regulated

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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

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what are the key paracrines in the GI tract?

Histamine, serotonin, somatostatin

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what are the benefits of paracrine control?

can act quickly and locally

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what is neurocrine control?

Occurs when a substance released from a neuron (neuron) exerts its effect on a target cell.

involves reflexes

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what are the benefits of neurocrine control?

can act quickly over short and long distances

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What parts of the digestive system DON’T drain into the portal system?

The lower part of the rectum and the anus

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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