Lengner Monogastric Stomach

what the three interlinked control systems?

paracrine, endocrine and neural

describe the innervation of the GI tract

two parts the enteric and the CNS

what is extrinsic innervation?

cell bodies outside the wall of the GI tract

does extrinsic innervation have parts?

yes, parasympathetic and sympathetic

function of parasympathetic and sympathetic

both have sensory component

what is the intrinsic innervation?

cell bodies inside the GI tract - enteric nervous system

major function of the GI tract

absorption

how is absorption regulated?

by GI motility and secretions

how is the gut physiologically controlled?

through central and local control systems

central and local control systems

neural, chemical and myogenic control

neural control

extrinsic through the ANS and intrinsic through the ENS

chemical control

secretions - endocrine, paracrine and neurocrine

muscle contraction through the interstitial cells of Cajal

myogenic control

describe the parasympathetic innervation of the ENS

pre/post ganglionic

nerve control

neurotransmitter

stimulatory or inhibitory

preganglionic

through the vagus nerve

uses acetylcholine

stimulatory

describe the sympathetic innervation of the ENS

pre/post ganglionic

neurotransmitter

stimulatory or inhibitory

postganglionic

peptide neurocrines - somatostatin, PACAP, etc

inhibitory

what is a plexus?

place where nerves branch and rejoin

what is a ganglia?

bunches of cell bodies

how are cell bodies arranged?

in 2 major ganglia - myenteric and submucosal

myenteric plexus

Ganglia between circular and longitudinal muscle (extensive)

submucosal plexus

Ganglia in submucosal layer (limited)

parasympathetic

rest and active digest

sympathetic

fight or flight; digestion slows

parasympathetic neurons

synapse with ENS neurons

sympathetic neurons

directly affect target cells and others synapse with ENS neurons

is there a synapse between enteric neurons and the target?

no, axons end in varicosities that release neurocrine affecting nearby muscle and glandular cells

neurocrines can be

stimulatory or inhibitory

regions of the stomach - monogastric

glandular portion

cardiac, fundic, body and pyloric

regions of the stomach - ruminants

nonglandular and glandular

epithelium in the non-glandular portion

stratified squamous

epithelium in the glandular portion

simple columnar

function of the stomach

storage for transition to the small intestine

grinder

two physiological portions of the stomach

proximal and distal

proximal stomach

storage

distal stomach

grinding/sieve action

function of the glandular stomach

homogenizes and process food

how is food in the glandular stomach homogenized and processed?

chemically through enzymes and acids

mechanically via muscular churning

appearance of the glandular stomach

has rugae

stomach - cells

mucous cells secrete a protective gel layer called the gastric mucosal barrier

purpose of the mucous cells

protects lining from autodigestion and abrasion of food

stomach glands

cardiac, fundic and pyloric

stomach glands: cardiac

alkaline mucous

stomach glands: fundic

secretes mucous, HCL and pepsinogen

parietal and chief cells

stomach glands: pyloric

secretes mucus/lysozyme, produce Gastrin

mucous cells, and G cells

where are glands most abundant?

fundic region

where are pits and function of them?

fundic region and mucous cells

what part of the stomach houses different cell types?

body

cell types in the body

mucous, chief, parietal, stem and enteroendocrine cells

chief cells

pepsinogen which interacts with HCL to form pepsin

parietal cells

HCL

G cells

gastrin

appearance of parietal cells

eosinophilic

appearance of chief cells

basophilic

gastric mucosal blanket

traps bicarb and keeps pH to 7.0

enteroendocrine

monohormonal

released in lamina propria and act locally or systemically to affect target cells

D cells

somatostatin

enteroendocrine cells

D and G cells

gastrin

distal stomach

stimulates acid secretion primarily and gastric motility secondarily

CCK - cholecystokinin

duodenum - ileum

CCK primary mechanism

stimulate enzyme secretion from pancreas

gastric inhibitory polypeptide

inhibit gastric motility and secretory activity

parietal cells

HCL by gastrin stimulation

enterogastric reflex - afferent

receive stimuli in duodenum and thus blocks stomach emptying induced by vagus

enterogastric reflex - CCK

CCK and secretin released into the blood which suppress gastric emptying

molecular mechanism - parietal cells

Carbonic – takes co2 and water to make carbonic acid

Carbonic acid will dissociate and become H2 (H2o and Co2)

Cl is pumped out into the lumen and exchanged for K+

K+ is pumped in and exchanged for H+ (from parietal cells)

Net result Hydrogen gets pumped out into the lumen

H and Cl in the lumen - HCL