50. Neurohormonal regulation of food intake and gastrointestinal tract Flashcards
Neuro-hormonal regulation of GI , tasks:
-chewing -swallowing -salivary secretion -defecation -stomach secretion, stomach motility -pancreatic juice secretion, gall bladder secretion -small intestine (ileum)-motility, large intestine (colon)-motility -intestinal juice production
What regulates : Motor (passing, mixing and mincing), digestive and absorptive functions?
These tasks are synchronized by the individual nervous system of the alimentary canal (enteral or intrinsic nervous system) and its hormonal activity with the effect of the central nervous system (extrinsic nervous system). The initial and terminal tract is under the control of the central nervous system, the section from the stomach until the rectum is mostly under local regulation, but influenced by the central nervous system.
The centres for hunger =
The centres for hunger = lateral nucleus of hypothalamus. The stimulation of these nuclei causes gluttony (hyperphagia), and its lesion causes the cessation of hunger and feed intake (aphagia).
The centre for satiety =
The centre for satiety = ventromedial nucleus of the hypothalamus (nucl. ventromedialis),
its lesion causes hyperphagia, while its stimulation causes aphagia.
-The activity of the satiety centre is built up from the periodic inhibitory impulses sent towards the hunger centre, so the hunger centre is inactive until the frequency of these inhibitory impulses is not decreased.
How is the formation of appetite?
Nucleus centres present in the amygdala and in the prefrontal cortex play a role.
Satietys outer effects:
Among the outer effects: -density of the population -behaviour (hierarchy), -temperature, -humidity, -the period and daily rhythm of light -characteristics of the fodder (taste, smell, even form in the case of birds, since there are no taste buds in their tongue)
The inner factors influencing hunger:
-fullness -hormones -different materials of intermediary metabolism (blood conc.)
Main regulatory factors in herbivores and carnivores?
In herbivores the catabolic products of cellulose and in carnivores the amino-acid balance can be considered as main regulatory factors.
In ruminants the fullness of the rumen has a significant effect on?
Fodder intake. If a large amount of indigestible polypropylene fibres are added into the rumen, fodder intake decreases or even ceases.
What happens if the blood sugar, amino acid and volatile fatty acid levels drops?
you will be hungry
Decrease food intake:
-serotonin -cholecystokinin -glucagon -somatostatin -VIP -neurotensin.
Increases food intake are:
the hypothalamic neuropeptide Y (NPY) -opioid peptides -GABA -dopamine.
Thermostatic theory
Food uptake depends on the body and the environmental temperature. – Increasing and decreasing blood temperature stimulates and block satiety centers, respectively. – Increasing environmental temperature decreases food uptake.
Glucose concentration
The increase in the blood glucose level leads to satiety, while its decrease evokes hunger.
Free fatty acid theory
According to the free fatty acid theory, the volatile fatty acid content of the blood plasma has a significant effect on the regulation of fodder intake. If intramurally or parenterally acetate or propionate is added to the animal, the volatile fatty acid content of the blood plasma is increased, and fodder intake is decreased or entirely terminates.
What happens when the estrogen level becomes higher?
High estrogen level decreases hunger, while low estrogen level increases hunger. Ovariectomized animals have a higher food uptake.
Dehydration status of the GI also have an effect on food uptake, explain:
Dehydration of GI decreases, hydration of GI increases food uptake. After feeding the GI produces and secretes digestive enzymes and becomes dehydrated. Dehydration inhibits further food uptake.
Explain:
The most important recently discovered regulatory factor is LEPTIN produced by the adipocytes, which under normal circumstances reduces feed uptake when enough reserves have already been formed.
(1) feed intake increases insulin secretion which increases the LPL
(2) and decreases the HSL
(3) activity of adipose cells. Triglyceride uptake and fat synthesis increases. The adipocytes grow
(4) and divide (5).
They produce more LEPTIN (6). This via blood gets into the hypothalamus and increases the local GLP-1 production (7).
This in turn depresses the effect of the feed uptake stimulating NPY (8).
The result is that the increasing amount of adipose tissue signals back, and decreases feed intake (9).
In obese strains the most probable factor inducing an overweight condition is the insensitivity of the hypothalamus towards LEPTIN.
Extrinsic neural regulation
- Plexus submucosus and plexus myentericus contain sympathetic and parasympathetic fibers.
- Although, the gastrointestinal nervous system works independently, the sympathetic and parasympathetic nervous systems are able to influence (inhibit or excite) its activity (extrinsic regulation).
- Sympathetic
- Parasymp.
- Afferent nerve fibers
Sympathetic (mainly postganglionic)
- Two ways
In general, the increase in the tone of the sympathetic nervous system inhibits the function of the intestinal tract. In two ways: These two effects together almost entirely inhibit the passing of the intestinal content.
- noradrenaline causes hyperpolarization of the smooth muscle cells. (On the other hand it increases the tone of the cells of the muscular mucosae!!);
- noradrenaline significantly decreases the resting membrane potential of the enteral plexus (intrinsic nervous system)
Parasympathetic (mainly preganglionic)
Postganglionic nerve cells of the parasympathetic nervous system can be found in the enteral plexus (plexus submucosus, plexus myentericus).
The increase in the tone of the parasympathetic nervous system causes hypopolarization of almost all enteral nerve cells, which increases nearly all gastrointestinal activities, therefore increasing motility and secretion.
Explain the afferent nerve fibers:
From the stomach and the intestinal canal several afferent nerve fibers derive. The afferent nerve fibre goes to the centre but its collateral branches stimulate both plexuses.
These fibers are stimulated by the following affects:
- excitation of the mucous membrane (irritation);
- vigorous dilatation of the intestines;
- presence of specific substances.
Intrinsic neural regulation
- The gastrointestinal canal has its own nervous system (the enteral nervous system) in the wall of the digestive canal.
- The number of these nerve cells is equal to the number of the nerve cells in the spinal cord (about 100 million). Functioning of the enteral nervous system is called intrinsic regulation. The enteral nervous system consists of two plexuses:
- Plexus submucosus under the mucosa (Meissneri)
- Plexus myentericus spreading between circular and longitudinal muscle layers (Auerbachi).
What is the most important neurotransmitters in the instrinsic neural regulations:
The most important one from among the exciting mediators is acetylcholine and from the inhibitors vasoactive intestinal peptide (VIP) and the opoid peptides.
