Small and unstable, the actual measured value is -50~-60mV

K equilibrium potential

The smooth muscle cells of the digestive tract spontaneously produce periodic mild depolarization and repolarization based on the resting potential. Because of their slow frequency, they are called slow waves.

Because the slow wave frequency plays a decisive role in the contraction rhythm of smooth muscle, it is also called the basic electrical rhythm.

Slow waves originate from the interstitial cells of Cajal between the longitudinal and circular muscles of the digestive tract, so ICC is considered the pacemaker cell of gastrointestinal motility.

When the slow wave depolarization reaches or exceeds the electrical threshold, action potentials can be triggered, and the contraction of smooth muscle cells is enhanced. The more action potentials appear on the slow wave, the stronger the contraction of smooth muscle cells.

Depolarization - Ca2

Repolarization - K

There is a good correlation between action potentials and contraction, and the number of action potentials appearing on each slow wave can be used as an indicator of the size of the contraction force.

Action potentials occur on the basis of slow wave depolarization.

Mainly from the vagus nerve and pelvic nerve

Release acetylcholine (ACh)

Promote the movement of the digestive tract and the secretion of digestive glands, but inhibit the sphincter of the digestive tract.

Postganglionic fiber is distributed to various parts of the stomach, small intestine, and large intestine

Release norepinephrine

Under normal circumstances, sympathetic nerve excitement can inhibit gastrointestinal motility and secretion

Also called gastric acid, secreted by parietal cells

After 6 hours of fasting, without any food stimulation, a small amount of gastric acid is secreted, which is called basal gastric acid secretion, with an average of 0-5mmol/h.

Gastric acid secretion is greatly increased under the stimulation of food or drugs. The maximum gastric acid secretion of a normal person can reach 20-25mmol/h.

The mechanism of hydrochloric acid secretion

The role of hydrochloric acid

If too much hydrochloric acid is secreted, it will damage the gastric and duodenal mucosa and induce or aggravate ulcers; if too little gastric acid is secreted, it can cause indigestion symptoms such as bloating and diarrhea.

Mainly synthesized and secreted by the chief cells of the gastric oxyntic gland

Stored in cells as an inactive zymogen

After pepsinogen enters the gastric cavity, under the action of HCl, a small molecule peptide is removed from the zymogen molecule and converted into active pepsin, which can hydrolyze proteins in food. Its optimal pH is 1.8-3.5. When the pH exceeds 5.0, pepsin is completely inactive.

Parietal cell secretion, glycoprotein

There are two active sites, one forming the intrinsic factor-vitamin B12 complex, and the other binding to the corresponding receptor on the ileal mucosal cell membrane.

If intrinsic factor is lacking, vitamin B12 malabsorption may affect red blood cell production, causing megaloblastic anemia.

It is jointly secreted by the epithelial cells on the gastric mucus surface and the mucus cells of the oxyntic glands, cardia glands and pyloric glands. The main component is glycoprotein.

It has high viscosity and gel-forming properties, forming a protective layer, lubrication, and reducing mechanical damage.

The HCO3 entering the stomach does not directly enter the gastric juice, but combines with the mucus on the gastric mucosa surface to form a barrier against gastric mucosal damage, called the mucus-bicarbonate barrier

There are tight junctions between the apical membrane of gastric mucosal epithelial cells and the lateral membrane of adjacent cells. This structure can prevent H in the gastric cavity from diffusing into the mucosal epithelial cells, which is called the gastric mucosal barrier.

When eating, the color, shape, smell, sound of food, as well as chewing and swallowing movements, can stimulate the receptors in the eyes, ears, nose, mouth, pharynx, etc., and reflexively trigger the secretion of gastric juice through incoming impulses, which is called cephalic gastric juice. secretion

Long duration (lasting 2-4 hours), high secretion volume (about 30%), high acidity and pepsinogen content

Injecting chyme, meat extracts, peptone liquid, etc. directly into the stomach through the fistula can directly stimulate the mechanoreceptors and chemoreceptors on the gastric wall and promote the secretion of large amounts of gastric juice.

Accounting for about 60%, the acidity and pepsin content are also high

Injecting chyme, meat extracts, peptone liquid, etc. directly into the duodenum through the fistula can also cause a slight increase in gastric juice secretion, indicating that after food leaves the stomach, it continues to stimulate gastric juice secretion.

Achieved through humoral regulatory mechanisms, neuromodulation may not be important

The amount of gastric juice is small (about 10%), the acidity is not high, and the digestive power (referring to the enzyme content) is not very strong.

Vagus nerve, histamine, gastrin

Hydrochloric acid: When HCl is secreted too much, it can cause negative feedback to inhibit gastric acid secretion.

Fat: Hormones that inhibit gastric juice secretion and gastric motility, collectively known as gastrophins

Hypertonic solution: can stimulate osmoreceptors in the small intestine and inhibit gastric juice secretion through entero-gastric reflex; it can also inhibit gastric juice secretion by stimulating the small intestinal mucosa to release several gastrointestinal hormones.

When eating, food stimulates receptors in the mouth, pharynx, esophagus, etc., which can reflexively cause the fundus and body of the stomach (mainly the head area) to relax, which is called receptive diastole.

The gastric capacity is greatly increased to accommodate a large amount of food into the stomach without a significant increase in intragastric pressure.

Mainly the tail area. There is basically no peristalsis on an empty stomach. Peristalsis starts about 5 minutes after food enters the stomach.

The physiological significance is to grind the food bolus that enters the stomach, fully mix it with gastric juice to form paste chyme, and gradually push the chyme into the duodenum

The process of emptying food from the stomach into the duodenum is called gastric emptying

Liquid food is faster than solid food, small particle food is faster than large food, isotonic liquid is faster than non-isotonic liquid

Among the three major nutrients, carbohydrates are emptied the fastest, followed by protein and fat the slowest.

Intragastric factors promote gastric emptying

Intraduodenal factors inhibit gastric emptying

α-amylase, optimal pH is 6.7-7.0

The optimal pH is 7.5-8.5, requiring colipase

The efferent nerve of the reflex is mainly the vagus nerve

The vagus nerve mainly acts on the acinar cells of the pancreas

The humoral factors that regulate pancreatic juice secretion mainly include secretin and cholecystokinin

Promote fat digestion

Promotes the absorption of fats and fat-soluble vitamins

Neutralizes gastric acid and promotes bile secretion

Tonic contractions are the basis for other movements of the small intestine and keep the small intestine in a certain shape and position

Segmented exercise is a kind of exercise in which rhythmic contraction and relaxation are mainly performed by circular muscles.

This is the most common form of exercise performed on an empty stomach and at rest

This movement is seen after eating or when parasympathetic nerves are excited