secretions and absorption

Question 1

What are the subdivisions of the GI tract

Answer 1

mucosal
submucosal
muscle layer

Question 2

what is the sphincter that controls the passage of pancreas and gall bladder material?

Answer 2

sphincter of oddi

Question 3

what are the 3 major controls of the GI tract?

Answer 3

endocrine (hormonal) -systemically
paracrine- acts locally
neuronal

Question 4

most CNS control of the GI occurs via

Answer 4

ENS/extrinsic ( indirectly)
and
endocrine systems

Question 5

extrinsic innervation (ANS) is where cell bodies are located

Answer 5

outside of the GI tract

has parasympathetic and sympathetic innervation

Question 6

intrinsic innervation AKA ENS

Answer 6

Acts independently from the ANS

it has its own neural system in a way ( submucosal and myenteric plexuses)

Question 7

the major function of the GI tract is

Answer 7

absorption

Question 8

what factors influence GI absorption?

Answer 8

GI motility and secretions

Question 9

What is included in neural control ?

Answer 9

Extrinsic ANS and intrinsic ENS

Question 10

what is included in chemical control of the GI

Answer 10

endocrine
paracrine
neurocrine ( when one of the cells involved in the signal is neuronal )

Question 11

myogenic control?

Answer 11

muscle contraction - smooth muscle control via interstitial cells of cajal

Question 12

sympathetic innervation

Answer 12

its postganglionic fibers interact with the ENS ( assuming they synapse at the prevertebral ganglia )
postganglionic fibers will synapse in the ENS or target tissue/effector cells

inhibitory of digestion

peptide neurocrines
somatostatin

Question 13

parasympathetic

Answer 13

preganglionic 
active digestion- rest and digest
stimulatory( excitatory) of the the ENS
no intermediate ganglia! 
Neurons synapse on enteric neurons ( at the submucosal and myenteric plexus)
Use of ACh

Question 14

which branch of the ANS can bypass ENS and act on target tissue?

Answer 14

sympathetic nervous system

Question 15

whats the plexus between longitudinal and circular smooth muscle of the ENS?

Answer 15

myenteric plexus

travels along the entire GI tract- has interaction between neighboring myenteric plexuses
ex: informs the colon that there is food in the GI

Question 16

what are varicosities?

Answer 16

they are the ends of the enteric neurons

varicosities release neurocrines to effect muscle contraction/glandular secretion - not specific to one single cell

its not a direct synapse like skeletal muscle has

Question 17

enteroendocrine cells are ___

Answer 17

monohormonal

they have specific/unique distributions in the GI

Question 18

what are some stimulus that promote gastrin production?

Answer 18

High pH
vagal stimulatoin
distension
proteins

Question 19

Where is gastrin produced?
What does gastrin stimulate production of?
What suppresses gastrin production?
What produces gastrin?

Answer 19

in the distal region/pyloric
HCl
Acid suppresses gastrin production
G-cells
promotes the activity of H+/K+ ATPase

Question 20

What are the cells that produce HCl?

Answer 20

parietal cells,

located in the parietal region

Question 21

what cell secretes histamines?

Answer 21

ECL- enterochromaffin-like cells

Question 22

ECL cells

Answer 22

act locally- paracrine
Both Gastrin and ACh stimulates this cell
they stimulate parietal cells

Question 23

What is used to acidify the stomach by parietal cells

Answer 23

H+/K+ ATPase

H+ into the lumen, K+ into the cell

Question 24

Carbonic anhydrase

Answer 24

provides the H+. for the H+/K+ATPase, needed to acidify the lumen

Converts
H20 + CO2 –> H+ HCO3-
end products are bicarbonate and a proton

Question 25

what happens to the bicarbonate from the end product of carbonic anhydrase

Answer 25

HCO3- is exchanged for Cl-
HCO3- goes into the bloodstream through the basal lateral side and Cl- goes into the cell
exchange happens through an antiporter

Question 26

what is alkaline tide

Answer 26

alkalization of the blood during digestion

Base meats the acid in the duodenum to be neutralized, vomiting can cause severe levels

Question 27

what is a rate-limiting step in acidification of the stomach?

Answer 27

H+K+ ATPase activity

needs gastrin to stimulate production of this pump

Question 28

what is the cephalic phase?

Answer 28

this is prior to food entering

ACh signals are sent to target cells- signals sent via the vagus nerve

Question 29

what is the gastric phase?

Answer 29

food in the stomach

stimulates histamine release by the vagovagal reflexes

Question 30

delta cells

Answer 30

responds to stomach acidification
releases somatostatin
negative influence on G-cells ( stop gastrin production)
ACh- inhibits delta cells (stomatostatin release)

Question 31

chief cells produce what enzyme?

Answer 31

pepsinogen

chief cells are located in the pancreas

Question 32

pepsinogen is the __

Answer 32

inactive conformation of pepsin
becomes activated in the GI tract, NOT the pancreas
HCl and pepsin can activate pepsinogen

Question 33

pepsin

Answer 33

a nonspecific protease

pepsin can activate pepsinogens

Question 34

what are 3 mechanisms for Na+ absorption?

Answer 34

1. cotransport, symport (small intestine)
2. Na/Cl coupled absorption (ileum/colon)
3. passive diffusion

Question 35

what are 3 mechanisms of Cl absorption

Answer 35

1. coupled Na+ -Cl+ absorption
2. Cl travels through tight junctions
3. Cl-HCO3- exchange ( antiporter)

Question 36

Bicarbonate recovery? maybe better-phrased dilution and excretion?

Answer 36

reabsorption occurs in the ileum,cecum of excess bicarbonate in the lumen via ion exchange

new HCO3- is being made by the cells ( carbonic anhydrase) , the H+ goes into the lumen and combines with HCO3- and it turns into H20 and CO2

HCO3- from the cell goes to the blood and joins Na+

NaHCO3 -net gain