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Digestion and absorption mind map
This is a mind map about digestion and absorption, including digestion and swallowing in the stomach, digestion and swallowing in the mouth, digestion and absorption in the small intestine, etc.
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Digestion and absorption mind map
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- Outline
digestion and absorption
Overview of digestive physiology
Physiological properties of digestive tract smooth muscle
Low excitability, slow contractions
Have self-discipline
tense
Highly stretchable
Different sensitivity to different stimuli
Insensitive to electrical stimulation, but particularly sensitive to mechanical stretch, temperature and chemical stimulation
Electrophysiological properties of digestive tract smooth muscle
resting potential
The potential is small, the potential is unstable and fluctuates greatly.
slow wave potential
On the basis of the resting potential, periodic mild depolarization and repolarization are spontaneously generated. Because the frequency is slow, it is called slow wave.
basic electrical rhythm
The slow wave frequencies of smooth muscles in different parts of the digestive tract are different. For example, the stomach is 3 times/min, the duodenum is 12 times/min, and the terminal ileum is 8 to 9 times/min.
The slow wave amplitude is 10~15mV, and the duration is from a few seconds to more than ten seconds.
Originates from the interstitial cells of Cajal (ICC) between the longitudinal and circular muscles of the digestive tract, so ICC is considered the pacemaker cell of gastrointestinal motility
The generation of neural electrical rhythms is neither myogenic nor neurogenic.
Action potential
Depolarization mainly relies on Ca2+ influx, and repolarization mainly relies on K+ outflux.
The amplitude of smooth muscle contraction increases with the frequency of action potentials.
Slow wave is the starting potential of smooth muscle contraction and the control wave of smooth muscle contraction rhythm, which determines the direction, rhythm and speed of digestive tract movement.
innervation of digestive tract
external nerves
parasympathetic nerve
Exciting digestive tract movement promotes secretion of digestive glands and contracts the sphincter of the digestive tract
Sympathetic nerve
Relaxes the sphincter muscles of the digestive tract; inhibits gastrointestinal motility and secretion
intrinsic plexus
submucosal nerve plexus
Located in the submucosa, mainly regulates the functions of glandular cells and epithelial cells
intercostal nerve from
Distributed between circular muscles and longitudinal muscles, mainly controlling the activity of smooth muscles
The extrinsic nerve plexus has a regulatory effect on the intrinsic nerve plexus, but after the extrinsic nerve plexus is removed, the intrinsic nerve plexus can still play a local regulatory role and can independently regulate gastrointestinal motility, secretion, blood flow, and water and electrolyte transport.
Endocrine functions of the digestive system
Gastrin (G cells)
Promote the secretion of gastric acid and pepsin, contract the gastric antrum and pyloric sphincter, inhibit gastric emptying, and promote gastrointestinal motility
Cholecystokinin (I cells)
Stimulate gastric juice, pancreatic juice, liver bile, small intestinal juice secretion, gallbladder contraction, enhance pyloric sphincter contraction, and inhibit gastric emptying
Secretin (S cells)
Stimulates HCO3- secretion in pancreatic juice and bile, inhibits gastric acid secretion and gastrointestinal motility, contracts pyloric sphincter, and inhibits gastric emptying
Gastric inhibitory peptide (K cells)
Stimulates insulin secretion, inhibits gastric acid and pepsinogen secretion, and inhibits gastric emptying
Motilin (Mo cells)
Stimulates gastric and small intestinal motility between digestions
Intragastric factors promote gastric motility, while intestinal factors inhibit gastric motility. For example, gastrin promotes gastric motility, while cholecystokinin and secretin inhibit gastric motility.
Intraoral digestion and swallowing
There are three major salivary glands in the mouth: parotid gland, submandibular gland and sublingual gland
Saliva is a colorless, odorless, neutral (pH 6.6-7.1) hypotonic liquid.
Salivary organic substances include mucin, immunoglobulin, amino acids, urea, uric acid, salivary amylase, lysozyme, etc.
salivation
moisten and dissolve food
Salivary amylase hydrolyzes starch into maltose
Remove food residue from the mouth (function to protect and clean the mouth)
Certain heavy metals (lead, mercury), cyanide and rabies viruses that enter the body can be excreted through saliva secretion
Salivary secretion is mainly regulated by nerves
Parasympathetic nerve excitement causes saliva secretion, which is mainly thin saliva secretion with a large amount and low solid content.
Sympathetic nerve excitement causes thick saliva with low saliva secretion and high solid content.
Although there is no sphincter anatomically at the lower end of the esophagus near the gastric cardia, the pressure here is higher than the intragastric pressure. This high-pressure area can prevent gastric contents from flowing back into the esophagus, acting like a sphincter, so it is called the lower esophageal sphincter.
Intragastric digestion and swallowing
The stomach is the most enlarged part of the digestive tract. The gastric capacity of adults is 1 to 2L. It has the function of storing and initially digesting food.
Three types of exocrine glands in the gastric mucosa
cardia gland
oxyntic gland
Including parietal cells, chief cells, and neck mucus cells
Pyloric gland
Three types of endocrine cells
G cells
Secretes gastrin and adrenocorticotropic hormone (ACTH)
delta cells
Secretes somatostatin, which inhibits and regulates the secretion of gastrin and gastric acid. It is distributed in the fundus, body and antrum of the stomach.
enterochromaffin-like cells
Synthesis and release of histamine, distributed in the oxyntic area of the stomach
Gastric juice components
Stomach acid (hydrochloric acid)
Secreted by parietal cells with circadian rhythm
Activate pepsinogen and provide a suitable acidic environment for pepsin
Denature the proteins in food and facilitate protein hydrolysis
Killing bacteria that enter the stomach with food is of great significance to maintaining the sterility of the stomach and small intestine
After hydrochloric acid enters the small intestine with chyme, it can promote the secretion of secretin and cholecystokinin, thereby causing the secretion of pancreatic juice, bile and small intestinal juice.
The acidic environment created by hydrochloric acid facilitates the absorption of iron and calcium in the small intestine.
pepsinogen
Secreted by chief cells and can only be activated by gastric acid to produce pepsin
intrinsic factor
Secreted by parietal cells, combines with vitamin B12 to produce a complex, protecting vitamin B12 from destruction by intestinal hydrolases
Mucus and bicarbonate
Effectively protects the gastric mucosa from damage by hydrochloric acid and pepsin in the stomach
Gastric acid secretion during digestion
gastric acid secretion
stimulated by the act of eating
Mainly regulated by nerves, gastric juice secretion lasts for a long time, the secretion volume is large (accounting for 30% of the secretion volume during the digestive period), and the acidity and pepsinogen content are both high.
gastric acid secretion
When chyme enters the stomach, it can directly stimulate the mechanoreceptors and chemoreceptors on the gastric wall and promote the secretion of large amounts of gastric juice.
Neuro-humorally regulated (vagal-vagal reflex, intramural plexus)
The amount of gastric juice secreted in the gastric stage accounts for about 60% of the secretion, and the acidity and pepsin enzyme content are also very high, but not as high as in the cephalic stage)
Intestinal gastric acid secretion
Inject chyme, etc. into the duodenum to stimulate gastric juice secretion
body fluid regulation
The amount of gastric juice secreted accounts for 10% of the total secretion
There is no self-regulation of gastric juice secretion during digestion
Factors that regulate gastric juice secretion
Main factors that promote gastric juice secretion
vagus nerve excitement
Efferent fibers directly reach the parietal cells in the acid secretion glands of the gastric mucosa and release ACh through the terminals to cause gastric acid secretion.
Fiber innervates enterochromaffin-like (ECL) cells and pyloric G cells in the mucosa of the gastric acid area, releasing histamine and gastrin respectively, indirectly causing parietal cells to secrete gastric acid. In which fibers innervating G cells release bombesin
It can also act on delta cells to release somatostatin, eliminating or weakening the inhibitory effect on G cells releasing gastrin, which essentially enhances gastrin release.
histamine
gastrin
Ca2+, hypoglycemia, caffeine and ethanol can stimulate gastric acid secretion
The main factors that inhibit gastric juice secretion
Hydrochloric acid (stomach acid)
Fat
During the digestive period, when fat and digestion products in food enter the small intestine, they stimulate the secretion of a variety of gastrointestinal hormones, such as secretin, cholecystokinin, gastric inhibitory peptide, neurotensin and glucagon, etc., which have the ability to inhibit gastric acid secretion. Hormone that acts on gastric motility
hypertonic solution
When chyme enters the duodenum during digestion, a hypertonic solution can appear in the intestinal lumen. The hypertonic solution can stimulate the osmotic pressure receptors in the small intestine, inhibit gastric juice secretion through the sing-gastric reflex, and can also stimulate the release of small intestinal mucosa. Several gastrointestinal hormones inhibit gastric secretion
cholecystokinin
It can both promote gastric acid secretion and inhibit gastric acid secretion, but overall it inhibits gastric acid secretion.
vasoactive intestinal peptide
somatostatin
epidermal growth factor
gastric inhibitory peptide
gastric motility
Movement form
tonic contraction
It already exists on an empty stomach and gradually becomes stronger after filling.
receptive relaxation
The receptors in the mouth, pharynx, esophagus, etc. are stimulated by food during eating, which can reflexively cause the relaxation of the fundus of the stomach and the body of the stomach (mainly the head area).
Specific movement patterns of the stomach
Gastric volume increased, but intragastric pressure did not significantly increase
Achieved through the vagal-vagal reflex, whose postganglionic fibers release vasoactive intestinal peptide (VIP) and NO
squirm
Mainly the tail area
Fasting rarely occurs. Peristalsis begins about 5 minutes after food enters the stomach.
Gastric motility begins in the middle of the stomach
gastric emptying
The process of passing food from the stomach into the duodenum
Carbohydrates are emptied the fastest, followed by proteins and fats the slowest. It takes 4 to 6 hours for mixed food to be completely emptied
gastric emptying control
Promote gastric emptying
vagal-vagal reflex
intramural plexus reflex
Inhibit gastric emptying
gastrin
entero-gastric reflex
acid, fat
secretin
gastric inhibitory peptide
gastric emptying power
direct power
pressure difference between stomach and duodenum
driving force
contraction of gastric smooth muscle
Digestion in the small intestine
pancreatic juice
Secreted by acinar cells (secret pancreatic enzymes) and small duct wall cells (secret HCO3-, water)
Colorless alkaline liquid with a pH of 7.8 to 8.4, an osmotic pressure roughly equal to that of plasma, and a daily secretion of 1 to 2L
content
Inorganic matter
HCO3-
Neutralizes gastric acid entering the duodenum, protecting the intestinal mucosa from strong acid erosion while providing an optimal pH environment
Cl-etc.
organic matter
pancreatic amylase
pancrelipase
Break down triglycerides into fatty acids, monoacylglycerol and glycerol
Requires the presence of colipase to function
Pancreatic lipase, colipase and bile salts form a ternary complex to prevent bile salts from removing lipase from the surface of lipid droplets
Trypsin and chymotrypsin
Trypsinogen requires enterokinase to be activated into trypsin, which activates chymotrypsinogen to produce chymotrypsin
positive feedback regulation
Break down protein into peptone and peptone
Pancreatic juice is the most important digestive juice because it contains digestive enzymes that hydrolyze enzymes, fats and proteins.
When pancreatic juice secretion is impaired, even if other digestive juices are secreted normally, the fat and protein in food cannot be fully digested and absorbed, often causing steatorrhea.
adjust
Fluid Regulation (Main)
secretin
Mainly acts on the epithelial cells of the pancreatic small ducts, increasing the secretion of water and bicarbonate, thereby increasing the secretion of pancreatic juice, but the enzyme content is very low
cholecystokinin
Promote the secretion of various enzymes in pancreatic juice
Promote strong contraction of the gallbladder and discharge bile
neuromodulation
The secretion of pancreatic juice caused by vagus nerve excitement is characterized by a small content of water and bicarbonate, but a large content of enzymes.
bile
Classification
liver bile
It is weakly alkaline and neutralizes the highly acidic gastric acid in the duodenum.
gallbladder bile
Is weakly acidic
Bile is the only digestive juice that does not contain digestive enzymes
Contains organic compounds such as bile salts, lecithin, cholesterol and bile pigments, and inorganic compounds such as Na+ and K+
effect
Promote fat digestion
Bile salts can serve as a vehicle to transport water-insoluble fat breakdown products to the mucosal surface of the small intestine, thereby promoting the absorption of fat digestion products.
Promotes the absorption of fats and fat-soluble vitamins
Neutralizes gastric acid and promotes bile secretion
After bile salts are excreted, they can return to the liver and stimulate hepatic bile secretion.
Emulsified fats: bile salts, cholesterol, lecithin
Prevent gallstones
small intestinal juice
A weakly alkaline liquid with a pH of approximately 7.6 and an osmotic pressure equal to that of plasma
small intestine motility pattern
tonic contraction
segmented movement
Rhythmic contraction and relaxation mainly performed by circular muscles alternately
There is a frequency gradient, with higher frequencies in the upper part of the small intestine
Completely mix chyme and digestive juices to facilitate chemical digestion
Increase the contact between chyme and the small intestinal mucosa, and continuously squeeze the intestinal wall to promote blood and lymphatic return, which helps absorption
The segmentation movement itself has little propulsive effect on chyme, but there is a frequency gradient from top to bottom in the segmentation movement, which has a certain propulsion effect on chyme.
squirm
Can occur anywhere in the small intestine and slowly pushes intestinal contents
Peristaltic impulse: rapid advancement of intestinal contents. Occurs in intestinal lesions, obstruction, and infection of the small intestine
Anti-peristalsis
Prevent chyme from entering the large intestine prematurely through the ileocecal valve and increase the residence time of chyme in the small intestine to facilitate more complete digestion and absorption of chyme.
absorb
duodenum, jejunum
Digestion products of carbohydrates, proteins and fats
The digestion products of lipids, such as fatty acids, monoacylglycerol, and cholesterol, quickly form mixed micelles with bile salts in bile and pass through the hydrostatic layer on the surface of small intestinal mucosal epithelial cells to reach the epithelial cells. Short- and medium-chain fatty acids enter the blood circulation but do not enter the lymphatic circulation. ; Long chains re-synthesize triglycerides in intestinal epithelial cells, synthesize chylomicrons with the apolipoprotein produced in the cells, and diffuse out of the cell into the lymphatic circulation
ileum
Bile salts, vitamin B12
colon
Water and salts (80% water and 90% Na+ and Cl-)
Iron is absorbed in the upper small intestine
Fe2+ is more easily absorbed, and acidity promotes iron absorption.
Vitamin C can reduce trivalent iron to divalent iron and promote iron absorption.
calcium absorption
Vitamin D promotes calcium absorption
Oxalic acid, phytic acid, and phosphate inhibit calcium absorption