50. Neurohormonal regulation of food intake and gastrointestinal tract

Question 1

Neuro-hormonal regulation of GI , tasks:

Answer 1

-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

Question 2

What regulates : Motor (passing, mixing and mincing), digestive and absorptive functions?

Answer 2

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.

Question 3

The centres for hunger =

Answer 3

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).

Question 4

The centre for satiety =

Answer 4

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.

Question 5

How is the formation of appetite?

Answer 5

Nucleus centres present in the amygdala and in the prefrontal cortex play a role.

Question 6

Satietys outer effects:

Answer 6

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)

Question 7

The inner factors influencing hunger:

Answer 7

-fullness -hormones -different materials of intermediary metabolism (blood conc.)

Question 8

Main regulatory factors in herbivores and carnivores?

Answer 8

In herbivores the catabolic products of cellulose and in carnivores the amino-acid balance can be considered as main regulatory factors.

Question 9

In ruminants the fullness of the rumen has a significant effect on?

Answer 9

Fodder intake. If a large amount of indigestible polypropylene fibres are added into the rumen, fodder intake decreases or even ceases.

Question 10

What happens if the blood sugar, amino acid and volatile fatty acid levels drops?

Answer 10

you will be hungry

Question 11

Decrease food intake:

Answer 11

-serotonin -cholecystokinin -glucagon -somatostatin -VIP -neurotensin.

Question 12

Increases food intake are:

Answer 12

the hypothalamic neuropeptide Y (NPY) -opioid peptides -GABA -dopamine.

Question 13

Thermostatic theory

Answer 13

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.

Question 14

Glucose concentration

Answer 14

The increase in the blood glucose level leads to satiety, while its decrease evokes hunger.

Question 15

Free fatty acid theory

Answer 15

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.

Question 16

What happens when the estrogen level becomes higher?

Answer 16

High estrogen level decreases hunger, while low estrogen level increases hunger. Ovariectomized animals have a higher food uptake.

Question 17

Dehydration status of the GI also have an effect on food uptake, explain:

Answer 17

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.

Question 18

Explain:

Answer 18

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.

Question 19

Extrinsic neural regulation

Answer 19

• 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

Question 20

Sympathetic (mainly postganglionic)

• Two ways

Answer 20

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.

1. noradrenaline causes hyperpolarization of the smooth muscle cells. (On the other hand it increases the tone of the cells of the muscular mucosae!!);
2. noradrenaline significantly decreases the resting membrane potential of the enteral plexus (intrinsic nervous system)

Question 21

Parasympathetic (mainly preganglionic)

Answer 21

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.

Question 22

Explain the afferent nerve fibers:

Answer 22

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:

1. excitation of the mucous membrane (irritation);
2. vigorous dilatation of the intestines;
3. presence of specific substances.

Question 23

Intrinsic neural regulation

Answer 23

• 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).

Question 24

What is the most important neurotransmitters in the instrinsic neural regulations:

Answer 24

The most important one from among the exciting mediators is acetylcholine and from the inhibitors vasoactive intestinal peptide (VIP) and the opoid peptides.

Question 25

The activity of the plexus myentericus regularly has an increasing effect on enteral motility:

Answer 25

• increases tone contraction
• raises the intensity
• frequency of rhythmic contractions
• increases the spreading speed of the stimulus, this increases the speed of peristaltic waves.

Question 26

The plexus submucosus regulates:

Answer 26

• local circulation
• secretion of gastrointestinal juices
• absorption

The submucosa muscles defining the extent of the haustrum of mucosa.

Question 27

3 reflexes regulating the gastrointestinal canal:

Answer 27

1 autonomous reflexes of the intrinsic regulation
- gastrointestinal secretion, peristalsis and the mingling movements;

2 those reflexes of which the centres can be found in the praevertebral sympathetic ganglia;

3 reflexes of the spinal cord and the brain stem where some reflexes regulating motor and secretory functions, as well as the defecation reflex belong to.

Question 28

Reflexes which arise from the gastro-intestinal canal and turn to the spinal cord or the brain stem:

Answer 28

1 gastric -colon reflex, in which the colon empties by the effect of the fullness of the stomach;

2 colon - gastric reflex, as a result the dilatation of the colon gastric motor activity and secretion terminates;

3 colon - ileum reflex, which effect is similar to the previous ones: the fullness of the colon inhibits the emptying of the ileum towards the colon.

Question 29

After signal processing the order through efferentation reaches the gastro-intestinal canal. The reflexes are:

Answer 29

1. those that arise from the stomach and duodenum and influence gastric secretion and motor activity;
2. the nociceptive reflexes, which cause the paresis of the entire gastro-intestinal canal;
3. the defecation reflex which can produce vigorous contractions of the colon, the rectum and the abdominal muscles.

Question 30

APUD

Answer 30

The gastro-intestinal canal is the largest endocrine gland. Endocrine cells can be found diffusely distributed in the tissues of the stomach, intestines and the pancreas.

• Also called amine precursor uptake and decarboxylation (APUD) cells, which synthesize those peptides and amines that are transmitted by the effect of an adequate stimulus.

Question 31

The most important gastro-intestinal peptides are:

Answer 31

• gastrin
• secretin
• cholecystokinin (CCK)
• gastric inhibitory peptide (GIP)

motilin

-enteroglucagon.

Question 32

Peptides released from nerve terminals or originated from other cells are:

Answer 32

• substance-P
• somatostatin
• vasoactive intestinal peptide (VIP)
• endorphins.

Question 33

Groups by location of hormone synthesis

Answer 33

– sympathetic nervous system

– parasympathetic nervous system

– enteral nervous system: Amine Precurs or Uptake and Decarboxylation(APUD)cells

Question 34

Groups by hormone action:

Answer 34

– paracrine

– endocrine:

• gastrin,secretin,cholecystokinin(CCK)
• pancreatic polypeptide, gastric inhibitory polipeptid (GIP),motilin, enteroglucagon

Question 35

Gastrin (and CCK)

Answer 35

STIMULATE:

– gastric juice secretion,

– motility, enzyme secretion,

– pancreatic juice secretion,

– growth of the intestinal mucosa

INHIBIT (CCK)

– gastric emptying – gastric motility

Question 36

Secretin, VIP, GIP, Enteroglucagon

Answer 36

INHIBIT

– gastric juice secretion

STIMULATE

– pancreatic juice secretion, – gall secretion,

– intestinal juice secretion