导图社区 gastrointestinal（胃肠道生理学知识点）
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gastrointestinal（胃肠道生理学知识点）
消化系统生理学知识点总结（英文版），有问题欢迎和我讨论哦~
编辑于2020-07-30 22:51:57
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gastrointestinal
structure
innervation
autonomic nervous system
extrinsic component
sympathetic
parasympathetic
vagus nerve
组成
afferent75%
efferent25%
支配
upper gastrointestinal tract ( upper third of esophagus, stomach, small intestine, ascending colon)
pelvic nerve
lower gastrointestinal tract
intrinsic component
enteric nervous system
peptide
characteristic
hormones
criteria
secreted in response to a physiologic stimulus and carried in the bloodstream to a distant site, where it produces a physiological action
independent of neural activity
可提取
examples
gastrin
secretion的调节
products of pr digestion, 苯丙&色
distention
vagal stimulation: GRP
function
H+secretion by gastric parietal cells
growth of the gastric mucosa
related disease
Zollinger-Ellison syndrome
pancreas内分泌瘤，还见于duodenum
signs
increased H+ secretion
hypertrophy of the gastric mucosa
symptoms
duodenal ulcers
steatorrhea
acidification of intestinal lumen→inactivate pancreatic lipase→fat not digested or absorbed adequately → fat excreted in the stool
diagnosis
treatment
H2 receptor-blocking drug e.g. cimetidine
inhibitor of H+pump e.g. omeprazole
remove the tumor
remove gatrin's target tissue
CCK
性质
33-aa peptide, 结构上与gastrin相似，属于gastrin-CCK family
分泌de调节
I cells of the duodenal and jejunal mucosa
monoglycerides and FA
small peptides and aa
function
contraction of the gallbladder
secretion of pancreatic E
secretion of bicarbonate from the pancreas
促进胰液分泌
growth of exocrine pancreas and gallbladder
inhibition of gastric emptying
receptor
A receptors
selectively sensitive to CCK
B receptors
equally sensitive to CCK and gastrin
secretin
性质
27 aa, 属于secretin-glucagon family
分泌及调节
S cells of the duodenum
H+ and FA (when acidic gastric contents ph<4.5 arrive in the small intestine
function
promote
secretion of pancreatic and biliary HCO3-
中和H+
inhibit
inhibit the effect of gastrin on parietal cells
GIP
性质
42 aa, 属于secretin-glucagon family
分泌及调节
K cells of the duodenal and jejunal mucosa
唯一一种对三种营养物质都有反应的激素
function
stimulation of insulin secretion
inhibition of gastric H+ secretion
candidate hormones
motilin
secretion
upper duodenum during fasting states
function
increase gastrointestinal motility and intiate the interdigestive myoelectric complexes
pancreatic polypeptide
secretion: in response to ingestion of 三大营养物质
inhibitpancreatic secretion
enteroglucagon
in response to decreased blood glucose
direct the liver to increase glycogenolysis and glucogenesis
paracrines
somatostatin
secreted by Dcells of mucosa
histamine
stimulate H+ secretion
neurocrines
motility
structure
smooth muscle
unitary smooth muscle(gap junction)
striated muscle
pharynx
upper 1/3 esophagus
external anal sphincter
pattern
phasic contraction
tonic contraction
slow wave
frequency
stomach 3/min
duodenum 12/min
not influenced by neural or hormonal input
origin
interstitial cells of Cajal
mechanism
depolarize: cyclic open of Ca2+channel
repolarize: opening of K+ channel
relationship between slow waves, AP, and contraction
tonic contraction
sub-threshold waves
phasic contraction
chewing and swallowing
chewing； mastication咀嚼
lubricate(saliva); reduce food size; initiate carbonhydrate digestion；食物对口腔内各种感受器的刺激，发射性的引起胃肠活动加强
regulation:involuntary(口腔内感受器和咀嚼肌本体感受器→脑干→节律性的咀嚼活动); voluntary
咀嚼肌：咬肌、颞肌、翼内肌、翼外肌
swallowing/deglutition
3 phases
oral
initiated by tongue forcing a bolus of food back toward pharynx
pharyngeal
食团→咽部的触觉感受器→吞咽中枢→一系列活动（如下）
4 steps
soft palate pulled upward
epiglottis moves to cover the opening to the larynx
upper esophageal sphincter relaxes
a peristaltic wave of contraction is initiated in the pharynx and propels food through the open sphincter
esophageal phase
controlled by...
swallowing reflex
close the upper sphincter and intiate a primary peristaltic wave
enteric nervous system
如果第一个蠕动波没有肃清食物的话，initiate a secondary peristaltic wave at the site of distension
esophageal motility
upper esophageal sphincter
primary peristaltic contraction
mediated by swallowing reflex
lower esophageal sphincter
mediated by peptidergic fibers in the vagus nerve (release VIP)
secondary peristaltic contraction
mediated by enteric nervous system
intrathoracic location of the esophagus (pressure lower than abdominal pressure --- could cause gastroesphageal reflux)
gastric motility`
structure
anatomic division
fundus, body, antrum
division based on motility
orad(thin walled), caudad
3 layers of muscle
receptive relaxation容受性舒张
the orad stomach relaxes caused by the lower esophagus sphincter relaxation
vagovagal reflex(neurotransmitter of the postganglionic fibre is VIP)
mixing and digesting
retropulsion
frequency of slow waves紧张性收缩
frequency of AP and contraction蠕动
↑parasym, hormone--gastrin and motilin
↓sym, hormone---secretin and GIP
migrating myoelectric complexes 消化间期移行性复合运动
motilin
function: clear the residue
emptying
inhibition
presence of fat in duodenum
mechanism: fat--cck--inhibition
function: adequate time for digestion and absorption of nutrients
presence of H+ in duodenum
mechanism: reflexes in the enteric nervous system
function: adequate time for neuralization of gastric H+
small intestine motility
slow wave : frequency 12/min
MMC: every 90mins
regulation
主要：enteric nervous system
食糜对肠粘膜的机械、化学性刺激通过局部反射引起
autonomic nervous system
para促
vagus nerve
NT： ACh, VIP, enkephalins, motilin
sym抑
fibers that originate in the celiac and superior mesenteric ganglia
humoral regulation
促：ACh、5-HT、p物质、胃泌素、CCK
抑：促胰液素、胰高血糖素、生长抑素、肾上腺素
patterns of contraction
segmentation contractions
back and forth movement
mix the chyme
peristaltic contractions
propel the chyme
NT
orad contraction: ACh and substan P
caudad relaxation: VIP and NO
vomiting reflex
information →vestibular system,the back of the throat, the gi tract and the chemoreceptor trigger zone in the 4th ventricle→vomiting center(in the medulla)→ resulting in :1. reverse peristalsis (begin in the small intestine) ; 2, relaxation of the stomach and pylorus; 3. forced inspiration to increase abdominal pressure; 4, relaxation of lower esophageal sphinter; 5, forceful expulsion of gastric or duodenum contents
in retching, the upper esophageal sphincter remain closed
large intestine motility
segmentation contractions(haustra)袋状往返运动
mass movement
characteristic: long distances, 1-3times/d
e.g. from transverse colon to the sigmoid colon; final mass movement propels the fecal contents into the rectum and are stored until defecation
distal colon: water absorption
defecation
rectosphincteric reflex
when rectum fills with feces, the smooth muscle of rectum contracts and the internal anal sphincter relaxes
external anal sphincter (under voluntary control)
25% compacity of rectum--urge to defecation
increased by Valsalva maneuver
gastrocolic reflex
stomach(afferent)---mediated by parasym
increased motility of colon--mediated by CCK and gastrin
intestinal fluid and electrolyte transport
comes and goes

the cells lining the villi---absorb; the cells lining the intestinal crypts--secrete
mechanism
cellular
paracellular
the permeability of tight junctions determines the route
small intestine: leaky: permit significant paracellular movement
colon: tight: do not permit
intestinal absorption
principle: absorption of solute---followed by water absorption(because isosmotic)
jejunum

ileum

colon

similar to the principal cells of the late distal tubule and collecting ducts of the kidney
flow-rate-dependent K+ secretion: high flow rate, increase K+secretion
intestinal secretion

disorder--diarrhea
cause
rapid loss of large volumes of extracellular-type fluid from the gastrointestinal tract
result
decreased extracellular fluid
decreased intravascular volume
decreased arterial pressure
especially
HCO3-： relatively loss(comparing to Cl-) cause hyperchloremic metabolic acidosis
K+: excessive loss cause hypokalemia
type
decreased surface area for absorption
infection, inflammation etc.
osmotic diarrhea
the presence of nonabsorbable solutes in the lumen
e.g. lactase deficiency(bacteria cound compound the problem)
secretory diarrhea
excessive secretion of fluid by crypt cells
e,g, growth of enteropathic bac such as Vibrio cholerae霍乱弧菌 or Escherichia coli大肠杆菌（具体过程看书上描述）

digestion and absorption
structure
villi
epi cells(enterocytes): the turnover rates is the highest,3-6 days to be replaced
mucus-secreting cells(globlet cell)
Kerckring's folds克尔克林襞，环形皱襞
microvilli
brush border
digestion

absorption
contents
carbonhydrates
digestion

absorption

disorders
failure to break down to absorbable form→carbonhydrates remaining in the lumen hold equivelent water→osmotic diarrhea
lactose intolerance: lack of brush-border lactase
proteins
digestion
enzymes

process

absorption

disorders
deficiency of pancreatic enzymes
e.g. chronic pancreatitis, cystic fibrosis
defect in the trasporters of the intestinal epi cells
Na+-aa cotransporters
genetic disease, defect in absorption of dibasic aa, cystine,lysine,arginine,ornithine
kidney disease
cystinuria?
intestinal disease
these aa are excreted in feces
lipids
digestion

stomach
lingual and gastric lipases only hydrolyze 10% of ingested triglycerides to glycerol and fa
contributions
churning action breaks the lipids into small droplets, which are emulsified by dietary proteins
empty the chyme slowly to small intestine for overall digestion
the rate of gastric emptying is slowed by CCK(triggered by lipids first appeared in small intestine)
small intestine
absorption

disorders
pancreatic enzyme secretion and function
pancreatic insufficiency
e.g. chronic pancreatitis, cystic fibrosis
inactivation of pancreatic enzyme
acidity of duodenal contents
excessive H+(胃排入十二指肠的食糜正常酸度pH2-4）
e.g. Zollinger-Ellison syndrome
pancreas fail to secrete sufficient HCO3-
e.g. pancreatitis
bile acid secretion
deficiency of bile salts
e.g. ileal resection
micille formation
肠道菌群可以使结合胆盐变成游离型胆酸（remove glycine and taurine from bile salts)，因为胆酸是非离子化状态，会在进入回肠前通过扩散被上皮细胞吸收，无法发挥它的作用
e.g. bacterial overgrowth
e.g. decreased pH in lumen
intestinal epi cells
decrease intestinal cells for absorption
e.g. tropical sprue热带口炎性腹泻
failure to synthesize apoproteins
e.g. abetalipoproteinemia
vitamin
fat soluble:vit A, D, E ,K
same with lipids
water soluble: B1,2,6,12, C, biotin生物素(Vit H), folic acid叶酸, nicotinic acid尼克酸，烟酸, pantothenic acid泛酸VitB5
most cases: Na+- dependent cotransport
special: Vit B12(cobalamin钴胺素): R protein and intrinsic factor
disorder: gastrectomy---pernicious anemia
calcium
absorption

disorders
e.g. chronic renal failure
iron
absorption

secretion
salivary secretion
1L/d
structure of the salivary glands
composition
parotid glands
serous cells
aqueous fluid composed of water, ions, E
submandibular/submaxillary glands
sublingual glands
概要
serous and mucous cells
aqeous fluid and mucin glycoproteins
cells
acinus由acinar cells 组成，产生初级唾液，通过一段短短的intercalated duct、一段striated duct
myoepithelial cells
substance they secrete
a-amylase: initial digestion of carbonhydrate
lingual lipase: initial digestion of lipid
mucin glycoproteins: lubricate
kallikrein: E (kininogen →bradykinin)
唾液腺激活的时候，该酶释放，最终使得流经腮腺的血液甚至比运动时流经骨骼肌的血液还多10倍
分泌过程

the flow-rate dependent concentration of ionic compositions

explanation
time-dependent
for HCO3-, selectively stimulated when saliva production is stimulated(para stimulation)
regulation
under neural control(no hormon control)
both sym and parasym(dominant)

sym
parasym
gastric secretion
structure and cell type
body of the stomach
oxyntic glands

antrum of the stomach
pyloric glands with deeper pits
G cells secrete gastrin into circulation
mucous neck cells secrete mucus, HCO3-, pepsinogen
components
HCL
parietal cells
mechanism

substances that alter HCL secretion

regulation
stimulation

inhibition
decreased pH
somatastatin
prostaglandin
related disease
peptic ulcer disease
mechanism
loss of the protective barrier
excessive H and pepsin secretion
另一种理解： imbalance between the protective factors and damaging factors

type
gastric ulcers
causative factors
gram-negative bac H. pylori
colonize the gastric mucus(antrum)
attach to epi cell
release cytotoxins(cagA toxin)
diagnostic test
C13 breathing
net H secretion rate is lower because its leak into the mucosa
duodenal ulcers
H+ secretion in response to a meal is increased
H , pylori colonization in gastric mucus inhibit somatostatin secretion
H, pylori infection in duodenal inhibits HCO3- secretion
Zollinger-Ellison syndrome( gastrinoma)
pepsinogen
regulation
vagal stimulation
H→ triggers local reflexes→chief cells
intrinsic factor
following gastrectomy, patients must receive injections of vitaminB12
pancreatic secretion
90% exocrine pancreas; 2% endocrine pancreas
cells
acinar; ductal; centroacinar
innervation of exocrine pancreas: para(sti); sym(inhibit)
formation of pancreatic secreation

effect of flow rate on composition

regulation

bile
biliary system

function of the gallbladder
store bile
concentration of bile-- the isosmotic fluid is removed
ejection of bile
"pulsatile spurts" because of the rhythmic contraction of the duodenum
30mins after a meal is ingested
enterohepatic circulation
回肠被切除的重大后果
腹泻
treatment：消胆胺cholestyramine--结合胆酸
原因：因为结肠内有高浓度的胆酸，胆酸刺激cAMP-dependent Cl- secretion in epi cell，Na+和水也就渗透进来，形成secretory diarrhea
脂肪泻steatorrhea
composition
bile salts50%
2*4

amphipathic( hydrophobic and hydrophilic)
meaning
emulsify dietary lipids
disperse(in blobs)→coalesce
form micelles with the products of lipid digestion, including monoglycerides, lysolecithin,FA
phospholipids and cholesterol
bilirubin