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MindMap Gallery Physiology—Digestion and Absorption
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Physiology—Digestion and Absorption
This is a mind map about physiology—digestion and absorption of knowledge. It is full of useful information, interested friends can refer to it.
Edited at 2023-11-16 17:42:29
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Physiology—Digestion and Absorption
- bacteria
This is a mind map about bacteria, and its main contents include: overview, morphology, types, structure, reproduction, distribution, application, and expansion. The summary is comprehensive and meticulous, suitable as review materials.
- Plant asexual reproduction
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- Reproductive development of animals
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- Outline
digestion and absorption
the large intestine
Function
Absorb moisture and inorganic salts
Provides a temporary storage place for food residues, which are excreted as feces
secretion of large intestinal juice
Secretion by columnar epithelial cells and goblet cells on the intestinal mucosal surface
Element
mucin
Protect intestinal mucosa and lubricate feces
HCO3
Movements of the large intestine and defecation
Movement form
baggy reciprocating motion
fasting and quiet
Segmented propulsion and multi-bag propulsion movement
Post-meal/parasympathetic stimulation
squirm
Group squirming
Defecation
formation of feces
Element
Food debris, shed intestinal epithelial cells, large amounts of bacteria, bile pigment derivatives, certain metal salts
defecation reflex
Peristalsis pushes feces into the rectum, stimulating rectal receptors → primary defecation center cerebral cortex → internal anal sphincter relaxation
Bacterial activity in the large intestine
Effects of fiber in food on intestinal function
liver digestion
Function
The liver is the largest digestive gland in the human body and the center of metabolism in the body.
secrete bile
800～1000ml per day
Promote fat digestion and absorption in the small intestine
adjust
Entero-hepatic circulation (feedback)
Most of the bile acids return to the liver → less synthesis occurs
Substance metabolism
Glucose metabolism
Liver glycogen regulates blood sugar concentration
protein metabolism
Amino acids absorbed by the digestive tract → protein synthesis, deamination, and transamination in the liver → enter the blood circulation to all tissues of the body
Synthesize plasma proteins
Ammonia produced in amino acid metabolism is synthesized into urea and excreted by the kidneys
fat metabolism
vitamin metabolism
Hormone metabolism
Detoxify
chemical action
Secretion
accumulation
Phagocytosis
Liver Defense and Immune Function
Kupffer cells
Regulate circulating blood volume
liver blood supply
portal vein
Collect blood from the abdominal viscera, which contains rich nutrients absorbed from the digestive tract into the bloodstream
Harmful substances and microbial antigens in the blood are detoxified or removed
hepatic artery
Rich in O2, supplying oxygen to liver cells
Metabolic characteristics of the liver
Metabolism of three major nutrients
Liver function reserve and liver regeneration
Digestion in the small intestine
secretion of pancreatic juice
Properties, composition and effects of pancreatic juice
Daily secretion volume: 1~2L
nature
Colorless and odorless alkaline liquid (pH 7.8~8.4)
Close to plasma osmotic pressure
Element
HCO3
Neutralizes gastric acid entering the duodenum and provides an optimal pH environment for the activities of various digestive enzymes in the small intestine
Cl
HCO3 increases and CL decreases
Na,K,Ca
Protein (various digestive enzymes)
pancreatic amylase
effect
Starch → maltose
pancreatic lipase
effect
triglyceride → fatty acid glycerol
It only works in the presence of colipase
Trypsin and chymotrypsin
Existing form
trypsinogen
activator
enterokinase
activated trypsin
acid, tissue fluid
chymotrypsinogen
activator
Trypsin
effect
break down protein
Chymotrypsin also has a milk coagulation effect
Nuclease, carboxypeptidase
Cholesterol esterase, phospholipase A2
Regulation of pancreatic juice secretion
neuromodulation
Fluid Regulation (Major)
secretin
Acidic chyme → stimulates the release of secretin from the small intestinal mucosa (pH < 4.5) → pancreatic small duct epithelial cells → secretes large amounts of water and HCO3
stimulus
Hydrochloric acid (strongest), protein breakdown product, sodium lipate
cholecystokinin
effect
Promote the secretion of various enzymes in pancreatic juice
Promote gallbladder contraction and discharge bile
Nourish pancreatic tissue and promote pancreatic tissue protein and ribonucleic acid synthesis
stimulus
Protein decomposition products > Sodium fatty acid > Hydrochloric acid > Fat
gastrin, vasoactive intestinal peptide
Secretion and excretion of bile
Secreted by liver cells, stored by gallbladder
After eating, food and digestive juices stimulate the gallbladder to contract → bile is discharged into the duodenum
Properties, composition and effects of bile
nature
Bile secretion is 0.8~1L per day
Colored, bitter, thick liquid
Liver bile is golden yellow, clear and slightly alkaline
Gallbladder bile is dark brown and slightly acidic
Element
Water, Na, K, Ca, HCO3
bile salts
effect
Promote fat digestion and absorption
aggregate into micelles
cholesterol
Products of liver fat metabolism
bile pigment
effect
The breakdown product of heme, the main component that determines the color of bile
effect
Promote fat digestion
Bile salts, lecithin, and cholesterol can all be used as emulsifiers to emulsify fat into microdroplets dispersed in aqueous intestinal fluid → increase the action area of pancreatic lipase and promote lipolysis
Promotes the absorption of fats and fat-soluble vitamins
Neutralizes gastric acid and promotes bile secretion
Regulation of bile secretion and excretion
neuromodulation
Vagus nerve releases ACh → directly acts on liver cells and gallbladder, increases bile secretion, causes gallbladder contraction/indirectly causes increased bile secretion through the release of gastrin
Fluid Regulation (Major)
gastrin
secretin
cholecystokinin
bile salts
gallbladder function
Store and concentrate bile
Regulate intra-biliary pressure and discharge bile
secretion of intestinal juice
glands
Duodenal glands (Bernardian glands)
Located in the submucosa of the duodenum
secrete mucin-containing alkaline fluid
Protect duodenal mucosal epithelium from gastric acid erosion
Small intestinal glands (Lee's glands)
Located throughout the mucosal layer of the small intestine
Secretion is the main part of small intestinal fluid
Properties, composition and effects of small intestinal fluid
nature
Weakly alkaline liquid (pH7.6), the osmotic pressure is equal to that of plasma
Secretion volume 1~3L
Ingredients and effects
Regulation of intestinal juice secretion
small intestine movements
Movement patterns of the small intestine
tonic contraction
The basis for other movements of the small intestine and keeping the small intestine in a certain shape and position
segmental motility
Begins after chyme enters the small intestine
The circular muscles of the intestine where the chyme is located contract alternately at certain intervals, dividing the chyme into many segments → the original contraction part relaxes, and the original relaxation part contracts, the original segment of chyme is divided into two halves, and the two adjacent halves are brought together , forming a new segment
There is a frequency gradient in segmented motion
High near the duodenum, low at the terminal ileum
significance
Thoroughly mix chyme and digestive juices
Increase the contact between chyme and the small intestinal mucosa, continuously squeezing the intestinal wall to promote blood and lymph return, and help absorption
The segmented movement itself has little propulsive effect on chyme, but the top-down frequency gradient has a certain propulsive effect on chyme.
squirm
effect
After pushing the chyme to the distal end of the small intestine, perform segmented movements in the new intestinal segment.
peristalsis rush
Caused by swallowing during eating or chyme entering the duodenum
Anti-peristalsis
Prevent chyme from entering the large intestine prematurely and increase the residence time of chyme in the small intestine for full digestion and absorption.
Periodic Migrant Movement Complex (MMC)
The non-digestive phase is formed by the downstream spread of gastric MMC
Regulation of small intestinal motility
ileocecal sphincter
It usually maintains a slight contraction, making the pressure in the terminal ileum greater than the pressure in the large intestine.
Prevent the contents of the small intestine from being discharged into the large intestine too quickly and facilitate complete digestion and absorption in the small intestine
Prevent the reflux of food residues in the large intestine
Overview
digestion
mechanical digestion
chemical digestion
absorption
Gastrointestinal smooth muscle properties
General physiological properties of digestive tract smooth muscle
Low excitability, slow contractions
self-discipline
tension
Stretchability
Different sensitivity to different stimuli
Sensitive to mechanical stretch, temperature, and chemical stimuli
Insensitive to electrical stimulation
Electrophysiological properties of digestive tract smooth muscle
resting potential
-50～-60mV (small, unstable)
slow wave potential
Slow wave/basal electrical rhythm (BER)
effect
Plays a decisive role in the contraction rhythm of smooth muscle
Amplitude
10～15mV
duration
Several seconds to ten seconds
cell of origin
interstitial cell of Cajal, ICC
mechanical threshold and electrical threshold
Action potential
Features
The peak potential amplitude is low and varies in size
Action potential occurs on the basis of slow wave depolarization, and contraction is mainly generated after action potential → Slow wave is the starting potential of smooth muscle contraction, which determines the directional rhythm and speed of digestive tract movement.
Secretory function of digestive glands
digestive juices
daily total
6～8L
Element
Digestive enzymes, mucus, antibodies, ions, water
Function
dilute food
Provide a suitable pH environment
Digestion and absorption
Protect digestive tract mucosa
Innervation and functions of the digestive tract
external nerves
Parasympathetic Nerve (Vagus Nerve/Pelvic Nerve)
transmitter
ACh
Function
Promote the movement of smooth muscles in the digestive tract and secretion of digestive glands
Inhibit gastrointestinal sphincter movement
Sympathetic nerve
transmitter
Norepinephrine
Function
Inhibit gastrointestinal motility and secretion
intrinsic plexus
Enteric nervous system (ENS)
Classification
submucosal nerve plexus
myenteric plexus
Function
Can be innervated by external nerves, or can independently exert local regulatory effects
Endocrine functions of the digestive system
APUD cells and gastrointestinal hormones
APUD cells (amine precursor uptake and decarboxylation cells)
Classification
open type
Features
More numerous, cone-shaped, with microvilli protruding into the gastrointestinal cavity
Directly sense stimulation and trigger secretory activity of cells
closed type
Features
Fewer, distributed in the acid secretion area of the fundus and body of the stomach and the pancreas, without microvilli
Secretion is regulated by changes in the nervous and peripheral humoral environment
Physiological effects of gastrointestinal hormones
Regulate digestive gland secretion and digestive tract movement
Regulates the release of other hormones
nutritional effect
brain-gut peptide
Intraoral digestion and phagocytosis
secretion of saliva (saliva)
nature
Colorless, odorless, nearly neutral, hypotonic liquid
Element
Water (99%)
Organic matter (mucin, immunoglobulin, amino acid, urea, uric acid, salivary amylase, lysozyme)
Inorganics (Na, K, Ca, Cl, SCN)
gas
(Heavy metals, rabies virus)
effect
Moistens and dissolves food for easier swallowing
Salivary amylase (inactivated when pH is lower than 4.5) hydrolyzes starch into maltose
Lysozyme and immunoglobulin kill viruses
Heavy metals and rabies virus can be excreted through saliva secretion
adjust
basal secretion
Function
Moisten mouth
neuromodulation
unconditioned reflex
Caused by food irritating the mouth during eating
installment
Oral stage
Esophageal gastrointestinal stage
Conditioned reflex
Look at plum blossoms to quench thirst
mastication
effect
cutting and grinding food
Mix food and saliva thoroughly to form a bolus for easy swallowing
Facilitate full contact between salivary amylase and food
Strengthen food's stimulation of various receptors in the oral cavity, reflexively causing increased gastropancreatic, liver and gallbladder activity
deglutition
Oral stage (mouth-pharynx)
cerebral cortex
Pharyngeal stage (pharynx-upper end of esophagus)
swallowing center
Esophageal stage (upper end of esophagus-stomach)
Esophageal peristalsis
Lower esophageal sphincter (LES)
effect
Allow food to enter the stomach and prevent stomach contents from refluxing into the esophagus
adjust
Dual innervation of inhibitory and excitatory fibers of the vagus nerve
Food stimulates the esophageal wall → Vagus nerve inhibitory fibers release VIP NO → Lower esophageal sphincter relaxes
Food enters the stomach → Excitatory fibers of the vagus nerve release ACh → Lower esophageal sphincter contracts
body fluid
Gastrin/motilin → LES contraction
Secretin, cholecystokinin, prostaglandin A2 contribute to LES relaxation
Pregnancy, excessive drinking, smoking → decreased LES tone
Digestion in the stomach
Function
Storage and initial digestion of food, forming chyme
secretion of gastric juice
exocrine glands
cardia gland
oxyntic gland
Pyloric gland
endocrine cells
G cells
distributed
gastric antrum
effect
Secretes gastrin, adrenocorticotropic hormone (ACTH)
∮Cell
distributed
gastric antrum, gastric body, gastric fundus
effect
secrete somatostatin
Enterotrophin cells (ECL cells)
distributed
oxyntic area
effect
Synthesis and release of histamine
Properties, composition and effects of gastric juice
nature
Silent acidic liquid (ph0.9～1.5)
Secretion 1.5~2.5L daily
Element
Hydrochloric acid (HCL) (gastric acid)
parietal cell secretion
basal gastric secretion
secretion rate
0～5mmol/h
circadian rhythmicity
lowest in the morning between 5 and 11 a.m.
Highest from 6pm to 1pm
secretion mechanism
Proton pump (H,K-ATPase)
inhibitor
Omeprazole
effect
Activate pepsinogen and provide a suitable acidic environment for pepsin
Denature proteins in food and facilitate protein hydrolysis
Sterilize
After hydrochloric acid enters the small intestine with chyme, it can promote the secretion of secretin and cholecystokinin
An acidic environment facilitates the absorption of iron and calcium in the small intestine
Excessive secretion damages mucous membranes and causes ulcers; too little secretion causes abdominal distension and diarrhea.
Pepsinogen
Chief cell synthesis and secretion
Eating, vagus nerve excitement, gastrin stimulation promotes its release
Under the action of HCL/activated pepsin → pepsin (pepsin)
effect
Hydrolyzed protein
Optimum pH 1.8~3.5 (exceeding 5 it will inactivate)
intrinsic factor
Nature
glycoprotein
effect
Combines with VB12 in the stomach to form an intrinsic factor-VB12 complex, protecting it from destruction by intestinal hydrolases
VB12 malabsorption → megaloblastic anemia
adjust
Various stimuli that promote gastric acid secretion (vagus nerve excitement, gastrin, histamine) → promote increased secretion
Mucus and bicarbonate
slime
Gastric mucosal surface epithelial cells and mucus cells co-secret
Element
glycoprotein
effect
Lubricates and reduces mechanical damage to gastric mucosa caused by rough food
Tight junctions on the sides of epithelial cells form the gastric mucosal barrier
HCO3
Non-oxyntic cell secretion Interstitial fluid infiltration
effect
Formation of mucus-bicarbonate barrier
Protects the gastric mucosa from damage by gastric acid and pepsin
Water, Na, K
Cytoprotection in the stomach and duodenum
Prostaglandins (PGE2, PGI2), Epidermal Growth Factor (EGF), Somatostatin, Calcitonin, Sucralfate
Inhibit gastric acid and pepsinogen secretion
Stimulates the secretion of mucus and bicarbonate, contributing to gastric mucosal repair and integrity
Drinking a lot of alcohol or taking aspirin or indomethacin
Inhibit the secretion of mucus and bicarbonate, inhibit the synthesis of prostaglandins in the gastric mucosa → damage the gastric mucosa
peptic ulcer
Cause
Helicobacter pylori infection
Helicobacter pylori produces urease → urea is decomposed into ammonia and CO2 → ammonia neutralizes gastric acid and damages the gastric mucosa → reverse diffusion of H to the mucosa, causing peptic ulcer
gastric juice secretion during digestion
phase
first term
sham feeding
Features
Long duration (2~4h)
Large amount of secretion (30%)
High acidity and pepsinogen content
Significantly affected by appetite and mood
gastric stage
Main route of action
Vago-vegan reflex
Food directly expands the stomach and stimulates the receptors in the gastric body at the fundus → vagus nerve afferent fibers → central → vagus nerve efferent nerves → gastric juice secretion
Expansion stimulates pyloric receptors → intrinsic plexus → G cells release gastrin
The chemical components of food (peptides, amino acids) directly act on G cells to promote gastrin secretion
Features
The largest amount of secretion (60%)
High in acidity and pepsin content
intestinal stage
Path of action
body fluid regulation mechanism
Food enters the small intestine to stimulate it → secretion of gastrointestinal hormones (gastrin, oxyntotrophin) → blood circulation acts on the stomach to stimulate gastric acid secretion
Features
Low gastric juice volume (10%)
Not high in acidity and enzyme content
Neural and humoral factors regulating gastric secretion
Main factors that promote gastric juice secretion
vagus nerve
Histamine
ECL cells secrete
Mechanism
Acts on parietal cell H2 receptors through paracrine → gastric acid secretion
blockers
cimetidine
adjust
Promote
Vagus nerve releases ACh→M3 receptor
Gastrin→CCKB receptor
inhibition
Somatostatin→SST receptor
Gastrin
G cell secretion
Mechanism
Vagus nerve releases GRP → gastrin secretion → CCKB receptor
Act directly on parietal cells
Act on ECL cells
adjust
inhibition
somatostatin
Secretin, glucagon, gastric inhibitory peptide, vasoactive intestinal peptide
Stomach acid (negative feedback regulation)
Ca, hypoglycemia, caffeine, ethanol → stimulate gastric acid secretion
ACh, gastrin, (duodenal mucosa) secretin and cholecystokinin → stimulate pepsinogen secretion
The main factors that inhibit gastric juice secretion
hydrochloric acid
Negative feedback regulation (pH between 1.2 and 1.5)
mechanism
Gastric acid stimulates the intestinal mucosa to release secretin and gastrophin
HCL inhibits gastrin secretion from G cells
HCL promotes cell secretion of somatostatin
Fat
Fat stimulates the small intestinal mucosa to secrete enterogastrone
hypertonic solution
Other factors affecting gastric juice secretion
Cholecystokinin (CCK)
CCK receptor
CCKA
High affinity for CCK
CCKB
Equal affinity for CCK and gastrin
Mechanism
Promote
CCK stimulates gastric acid secretion in fasted animals (basal gastric acid secretion)
Inhibit (primary)
CCK competitively inhibits gastrin → inhibits gastric juice secretion
CCK binds to CCKA receptors on ∮ cells → stimulates the release of somatostatin → inhibits gastric acid secretion
Vasoactive intestinal peptide (VIP)
inhibition
Inhibit food, histamine, gastrin, etc. to stimulate gastric acid secretion
Promote cells to secrete somatostatin
Promote
Stimulates the increase of cAMP in parietal cells to promote gastric acid secretion
Bombesin (gastrin-releasing peptide)
Nature
Neurotransmitters
Mechanism
Acts directly on G cells to increase gastrin
Valosin
Stimulates basal gastric acid secretion
somatostatin
Mechanism
Acts on parietal cells, ECL cells, and G cells → inhibits gastric juice secretion and gastric motility
Inhibit the stimulatory response of histamine, ACh, and bombesin to gastric acid secretion
Gastric acid acts on gastric mucosal cells → somatostatin secretion (negative feedback inhibition)
Epidermal growth factor (EGF)
Inhibit gastric acid secretion (occurs when gastric epithelium is damaged, which is beneficial to gastric mucosal repair)
Gastric inhibitory peptide (GIP)
Inhibits gastric acid secretion caused by histamine and insulin-induced hypoglycemia
Somatostatin-mediated
High-dose gastric inhibitory peptides can also inhibit the release of pepsinogen
stomach movements
structural partition
Head area (fundus of stomach and upper 1/3 of body of stomach)
Features
weak movement
Function
store food
Tail area (lower 2/3 of the gastric body and antrum)
Features
Stronger in movement
Function
Grind the food, mix it thoroughly with gastric juices, form chyme and gradually pass it into the duodenum
Stomach movements
tonic contraction
Features
It exists when the stomach is empty and becomes stronger after filling.
effect
Keep the stomach in a certain shape and position to prevent gastroptosis
Maintain a certain pressure in the stomach to facilitate the penetration of gastric juice into the food bolus
receptive expansion
effect
greatly increase the capacity of the stomach to accommodate large amounts of food
mechanism
vagal-vagal reflex
intrinsic plexus reflex
squirm
Features
Mainly in the tail area, rarely appears on an empty stomach
significance
Grind the food bolus that enters the stomach, mix it thoroughly with gastric juice to form paste chyme, and push the chyme into the duodenum
gastric emptying
It starts about five minutes after food enters the stomach
Features
Liquids are faster than solids, small particles are faster than large particles, isotonic liquids are faster than non-isotonic liquids, carbohydrates are greater than proteins > fats
control
Intragastric factors
Promote
Vagal-vagal reflex and intrinsic plexus reflex
inhibition
G cells in the gastric pylorus release gastrin → promote gastric motility and enhance contraction of the pyloric sphincter (the total effect is to delay gastric emptying)
Intraduodenal factors inhibit gastric emptying
Chyme stimulates receptors on the duodenal wall → entero-gastric reflex → inhibits gastric movement and slows down gastric emptying
power
direct power
pressure difference between stomach and duodenum
driving force
contraction of gastric smooth muscle
process (intermittent)
Gastric motility is enhanced → intragastric pressure is greater than intraduodenal pressure, gastric emptying occurs → chyme enters the duodenum, and gastric emptying is inhibited by factors in the duodenum → gastric acid is neutralized and food is digested The product is gradually absorbed → the inhibitory effect on gastric emptying is eliminated and gastric emptying occurs again
significance
Allow the emptying of gastric contents to better adapt to the speed of digestion and absorption in the duodenum
Movements of the stomach between digestions
Interdigestive migrating motor complex (MMC)
Starts in the upper part of the stomach and spreads toward the intestines
cycle
90～120min
phase
Phase I (resting phase) (may be related to NO release)
45～60min
slow wave potential
No gastrointestinal contractions
Phase II
30～45min
irregular peak potential
Beginning of irregular gastrointestinal motility
Phase III (related to motilin secretion)
5～10min
Clustered peak potentials appear on the slow wave potential
Regular gastrointestinal motility
Phase IV
A short transition period of 5 minutes
effect
Keep the gastrointestinal tract in continuous motion and clean the gastrointestinal contents (food residues, bacteria, saliva, etc. after the last meal)
vomiting