Intro to Physiology I Lopez Flashcards
Main functions of GI system
Digestion and absorption
Main properties of digestion and absorption
motility and secretions
Purpose of sphincters
restrict the passage of intestinal content to optimize digestion and absorption
7 sphincters of GI tube
UES, LES, Pylorus, Sphincter of Oddi, Ileocecal valve, Internal anal sphincter, external anal sphincter
4 functional laters of the GI
- mucosal
- submucosal
- muscle layer
- serosa
2 muscles in the muscle layer
circular and longitudinal muscles
What is the nervous system of the GI tract
Enteric nervous system
What are the 2 plexi in the ENS
submucosal plexus and myenteric plexus
What is the GI tract innervated by
ANS and ENS
What innervates the extrinsic nervous system
ANS
What innervates the intrinsic nervous system
END
What nervous system are the cell bodies located on the outside of the gut wall
extrinsic
Where are the cell bodies of the intrinsic nervous system located
within the wall
What innervates the parasympathetics of the GI system
vagus nerve and pelvic nerves
Where are preganglionic nerve cell bodies for vagal innervation
brainstem
Preganglionic nerve cell bodies for pelvic nerves
sacral spinal cord
Where are postganglionic neurons for parasympathetic
wall of the organ- enteric neuron in gut wall
What neurotransmitter is used for preganglionic parasymp
Ach
What is the postganglionic neurotransmitter for parasymp
Ach
What is the pathway for sympathetic neurons of the GI
spinal cord to prevertebral ganglia to ganglia to organs of the gut
Where do preganglionic efferent fibers for sympath come from
spinal cord
Where do preganglionic efferent fibers of sympathetic end
prevertebral ganglion
Where do postganglionic fibers of sympath start
prevertebral gang
What do the prevertebral ganglia innervate
myenteric and submucosal plexuses
What neurotransmitter is released by preganglionic efferent fibers of the sympathetic nervous system
Ach
What neurotransmitter is released by postganglionic efferent fibers of sympath
NE
What neurons are part of the integrating center of the ENS
afferent neurons, interneurons, efferent neurons
What are afferent neurons
sensory neurons
what are efferent neurons
motor neurons
T/F Enteric needs the CNS to function
F- the ENS can function without CNS input
What reflex is associated with the CNS regulation of GI functioning
Vago-vagal reflex
Other name for vago-vagal reflex
gastric receptive relaxation reflex
CNS effect on ENS
can modulate ENS response but ENS can function without it
Where are centers that control food intake
in the brain
What is the sensory ganglion of the vagal nerve
nodose ganglion
What is the part of brainstem that receives sensory info
nucleus of the tractus solitarius
What does the nucleus of the tractus solitarus send out
vagal efferent signals
Where do the vagal efferent signals end up
in/on the organ wall
Paracrine regulation
action of peptides or other messenger molecules on local/neighboring target cells
Two paracrine messengers/peptides
somatostatin and histamine
What cells secrete peptides/messengers for paracrine regulation
enteroendocrine cells
T/F Paracrines act locally
T
How do paracrine signals reach their targets?
diffusion over short distance
What is secreted by D cells?
somatostatin
Where are D cells located?
GI mucosa
Stimuli for somatostatin
decrease in pH (more acidic environment)
Actions of somatostatin
inhibit gastric H+ secretion (parietal cells)
Where is somatostatin released outside of the GI tract?
hypothalamus, and gamma cells of the exocrine pancreas
Where is histamine stored and secreted?
stomach
What cells secrete histamine
enterochromaffin-like cells
Where are enterochromaffin cells located?
gastric glands
What cell is the target of histamine?
parietal cells
Function of histamine
stimulate parietal cells to secrete more acid (HCl)
Endocrine regulation
action of hormones
What cells contain granules filled with hormone peptides?
enteroendocrine cells
How do hormones get to target cell?
portal circulation –> live –> systemic circulation –> specific receptors on target cell
T/F hormones can bind to target cell that doesn’t have specific receptor
F - hormone binds to target cell with specific receptor
Gastrin site of secretion
G cells of stomach
Gastrin stimuli of secretion
small peptides and amino acids, distention of stomach, vagal stimulation
CCK site of secretion
I cells of the duodenum and jejunum
CCK stimuli of secretion
small peptides and amino acids and fatty acids
Secretin site of secretion
S cells of the duodenum
Secretin stimuli of secretion
H+ (acidic) in the duodenum and fatty acids in the duodenum
Glucose dependent insulinotropic peptide site of secretion
duodenum and jejunum
GIP stimuli of secretion
fatty acids, amino acids, and oral glucose
Function of gastrin
increase gastric H+ secretion
What stimulate growth of gastric mucosa
gastrin
What is Zollinger-Ellison syndrome
gastrin-secreting tumor
S/S of Zollinger-Ellison syndrome
hypertrophy of gastric mucosa, duodenal ulcers, steatorrhea
What is steatorrhea
excretion of abnormal quantitites of fat with feces due to reduced absorption of fat by intestine
What increases during Zollinger-Ellison syndrome
increase circulatin gastrin and increase acid secretion by parietal cells
Actions of CCK
- increase pancreatic enzyme secretion
- increase pancreatic HCO3 secretion
- inhibit gastric emptying
Effect of CCK on gallbladder/sphincter of Oddi
stimulate contraction of gallbladder and relaxation of sphincter of Oddi
T/F CCK can act as a paracrine signal
T
Actions of Secretin
- increase pancreatic HCO3 and biliary HCO3 secretion
- decrease gastric H+ secretion
Secretin actions on gastrin
inhibit trophic effect of gastrin on gastric mucosa
T/F Secretin can not act as a paracrine signal
F - Secretin can act as a paracrine signal
GIP actions
- increase insulin secretion from pancreatic beta cells
- decrease gastric H+ secretion
What would be more effective increasing insulin secretion?
- Oral glucose administration
- Intravenous glucose administration
Oral- because stimulates GIP which stimulates insulin secretion and directly effects stimulation of beta cells
Neural regulation
action of neurotransmitters to make action potential and diffuse across synapse to bind postsynaptic cells
Where are the neurotransmitters released from during neural regulation
nerve terminals stimulated by action potential
Source of Ach
cholinergic neuron
Action of Ach
contraction of smooth muscle and relaxation of sphincters
What does Ach increase
salivary secretion, gastric secretion, pancreatic secretion
Source of norepinephrine
adrenergic neurons
Function of NE
Relaxation of smooth muscle and contraction of sphincters
What does NE increase
salivary secretion
What does the neuronal centers of the hypothalamus control
feeding and satiety
What are the 5 neuronal centers of the hypothalamus
lateral nucleus, ventromedial nucleus, paraventricular nucleus, dorsomedial nucleus, arcuate nucleus
What occurs in the lateral nucleus
feeding center
What occurs in the ventromedial nucleus?
satiety
What maintains energy balance?
neural and hormonal regulations
5 ways hypothalamus can receive a signal
- neural signals from GI
- chemical signals from nutrients in blood
- GI hormones
- signal from adipose tissue
- signal from cerebral cortex (sight, smell, and taste)
Where does most of the integration of signaling/regulating food intake and energy expenditure occur?
arcuate nucleus
What are the two pathways of the arcuate nucleus
Alpha melanocortin pathway, and neuropeptide Y pathway
What releases a-MSH
pro-opiomelanocortin (POMC) neurons
Receptor for a-MSH
MCR-4
Where is the MCr-4 receptor located
second-order neurons
Main function of the a-MSH pathway
inhibit food intake and increase metabolism (anorexigenic)
What stimulates the NPY pathway
hunger
Receptor for NPY pathway
Y1R
What can neurons that release NPY also release
agouti-related peptide (AGRP)
Main function of NPY pathway
Increase feeding behavior and storage of calories (orexigenic)
How do the a-MSh pathway and NPY pathway work together
antagonize one another
- peptides that stimulate a-MSH, inhibit NPY
- AGRP released from NPY antagonize MCR-4
Pathway of vagus nerve
vagal –>NTS–>hypothalamus circuit
Where is ghrelin secreted?
by endocrine cells in the stomach
What receptor does ghrelin bind to?
growth hormone secretagogue
Ghrelin function in hypothalamus
stimulates neurons that release NPY
What does ghrelin increase
appetite, gastric motility, gastric acid secretion, adipogenesis, insulin secretion
What can initiate feeding response?
ghrelin
What centers does insulin initiate in the hypothalamus?
satiety and hunger centers
What are the receptors insulin binds to?
POMC and NPY
Insulin effect on NPY pathway
inhibit
Insulin effect on POMC pathway
stimulate
Actions of insulin
decrease appetite and increase metabolism
Insulin in diabetes mellitus type I patients
increase in food intake associated with decrease in insulin
CCK function
elicits satiety
CCK on ghrelin
decrease ghrelin
CCK on gastric secretion
decrease gastric emptying and increase gastric distention
PYY is released by…
L cells of enteroendocrine cells of the ileum and colon following a meal
What receptors do PYY bind to?
Y2 receptors
Where are the Y2 receptors located
hypothalamus
PYY on NPY neurons
inhibit
PYY on POMC neurons
inhibit
PYY on appetite
suppressor
Where is leptin secreted?
adipose tissue and endocrine cells in stomach
Where are the receptors that leptin binds to?
satiety and hunger centers in hypothalamus
Leptin on NPY pathway
inhibit
Leptin on POMC pathway
stimulates
Appetive-supressing hormone function
- decrease appetite
- increase metabolism
- ghrelin release
Appetive-supressing hormone on food intake
negative feedback system for regulation of food intake
