1 Intro To GI Phys Flashcards by Abby Finder

Functions of the GI tract

Digestion, absorption of nutrients, motility, secretions

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GI sphincters name (7) and function

UES, LES, pyloric, sphincter of Oddi, Ileocecal valve, internal and external anal sphincter

Fx: restrict passage of intestinal content and optimizes digestion and absorption

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Functional layers of the GI tract

Mucosal, submucosa, muscle (circular and longitudinal), Serosa

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What part of the Enteric Nervous System is in the layers of the GI tract?

What layers?

Innervated by what?

Does it need the CNS?

Submucosal plexus: submucosa

Myenteric plexus: muscle

Extrinsic autonomic nervous system

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Where does the ENS receive its information?

Parasympathetic and sympathetic NS and CNS

Sensory info from mechanoreceptors and chemoreceptors in the mucosa

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Function of the ENS

Controls contraction, secretion, and endocrine function of the GI tract

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CNS role in the regulation of the GI tract (3)

Vago-vagal reflex

Modulate ENS response

Centers that control food intake in brain

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Sensory ganglion of the Vagal N

Nodose ganglion

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Example of a vago-vagal reflex

Gastric receptive relaxation reflex

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NTS

Nucleus of the tractus solitarius

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Nerves of the parasympathetic innervation

Vagus and pelvic nerves

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Location of the parasympathetic preganglionic nerve cell bodies

Brainstem or sacral spinal cord

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Location of the parasympathetic postganglionic neurons

Wall of the organ (enteric neuron in the gut wall)

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What type of synapse is between the parasympathetic pre and post ganglionic cells?

Nicotinic (nAChRs)

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Where do the sympathetic preganglionic efferent fibers begin and end?

Begin in spinal cord (thoracic and lumbar)

End in prevertebral ganglia

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Sympathetic postganglionic fibers from the prevertebral ganglia innervate _________

Myenteric and submucosal plexuses

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Sympathetic preganglionic efferent fibers release______.

Sympathetic postganglionic efferent nerves release ______.

Ach

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Long preganglioic fibers, short postganglionic fibers

Parasympathetic NS

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Short preganglionic fibers, long postganglionic fibers

Sympathetic NS

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How do paracrine signals reach their target cells?

Where do they act?

Diffusion over short distances

Locally

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Function of paracrine regulation

Action of peptides or other messenger molecules

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Examples of paracrine signals

Somatostatin and histamine

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Secreted by D cells in the GI mucosa

Somatostatin

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Inhibits secretion of gastric H+ and other GI hormones

Somatostatin

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Somatostatin is secreted by_______.

D cells of the GI mucosa Hypothalamus Delta cells of the exocrine pancreas

Stimulated by a decrease a in luminal pH Why?

Somatostatin Low pH signals somatostatin to inhibits gastric H+ secretion

Stored and secreted by enterochromaffin-like (ECL) cells

Histamine

Histamine is secreted in the _____.

Gastric glands of the stomach

Histamine targets and action

Parietal cells in the stomach gastric glands Stimulates acid production

Action of histamine

Stimulates acid production

Endocrine regulation

Action of hormones Hormones secreted into circulation

EECs

Enteroendocrine cells Contain secretory granules filled with hormones that are released upon stimulation

Examples of endocrine regulation (4)

Gastrin, cholecystokinin, secretin, glucose-dependent insulinotropic peptide (GIP)

Gastrin site of secretion

G cells of stomach

Stimuli of gastrin (3)

Small peptides and amino acids Distention of stomach Vagal stimulation via GRP

Actions of gastrin (2)

Increase gastric H+ secretion Stimulate growth of gastric mucosa

Cholecystokinin (CCK) is secreted from _____.

I cells of duodenum and jejunum

Stimuli of CCK (3)

Small peptides and amino acids Fatty acids

Actions of CCK (7)

Increase pancreatic enzyme secretion Increase pancreatic HCO3- secretion Stimulate contraction of the gallbladder Relax sphincter of Oddi Stimulate growth of the exocrine pancreas and gallbladder Inhibit gastric emptying Act as a paracrine signal

T or F: the increase of pancreatic HCO3- by CCK is a direct effect

FALSE This is a indirect effect It potentiates the effects of secretin

T or F: when CCK stimulates the growth of the exocrine pancreas and gallbladder, it is a trophic effect.

TRUE

Secretin is secreted by ______.

S cells in the duodenum

Stimuli of secretin

H+ in the duodenum Fatty acids in the duodenum

Actions of secretin (5)

Increase pancreatic secretion of HCO3- Increase biliary secretion of HCO3- Decrease gastric H+ secretion Inhibits trophic effect of gastrin on gastric mucosa Acts as a paracrine signal

GIP

Glucose-dependent insulinotropic peptide

GIP secreted from _______.

Duodenum and jejunum

Stimuli of GIP (3)

Fatty acids Amino acids Oral glucose

Actions of GIP (2)

Increase insulin secretion from pancreatic beta cells Decrease gastric H+ secretion

What is more effective in increasing insulin secretion? And why? A. Oral glucose B. Intravenous glucose

A. Oral glucose stimulates GIP-> stimulates insulin secretion and has a direct stimulatory effect of beta cells of the pancreas

Neural regulation

Action of neurotransmitters

What is needed for a neurotransmitter release?

Action potential

Neurotransmitters diffuse across the ______ and bind to their _______ in the ________.

synapse specific receptor postsynaptic cell

Cellular communication is the key to _______.

Regulation of the GI tract

Source of ACh

Cholinergic neurons

Actions of ACh (5)

Contraction of smooth m. Relaxation of sphincters Increase salivary secretion Gastric secretion Pancreatic secretion

Source of norepinephrine

Adrenergic neurons

Actions of NE (3)

Relaxation of smooth m in wall Contraction of sphincters Increase salivary secretion

Source of vasoactive intestinal peptide

Neurons of the ENS

Actions of VIP (3)

Relaxation of smooth m Increase intestinal secretion Increase pancreatic secretion

Source of nitric oxide (NO)

Neurons of the ENS

Action of NO

Relaxation of smooth m

Source of gastrin-releasing peptide (GRP)

Vagal neurons of gastric mucosa

Action of GRP

Increase gastrin secretion

Source of enkephalins

Neurons of the ENS

Actions of enkephalins

Contraction of smooth m Decrease intestinal secretion

Source of neuropeptide Y

Neurons of the ENS

Actions of neuropeptide Y

Relaxation of smooth m Decrease intestinal secretion

Source of substance P

Co-release with ACh by neurons of the ENS

Actions of substance P

Contraction of smooth m Increase salivary secretion

Incretin Effect

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