Gastrointestinal Physiology- 2 Flashcards
Small Intestine I Small Intestine II Colonic Phase
secrete histamine that regulates HCL secretion
enterochromaffic- like cells (Oxynic)
For the GI t. content to move through the sphincter, it must
relax
lower the pressure
causes relaxation of smooth muscles in wall and contraction of sphincters
as well as inc. salivary secretion
NE
CCK- Cholecystokinin- site of secretion
I cells of duodenum and jejunum
preganglionic and post ganglionic fibers of parasympathetic that regulates the GI tracts
preganglionic- long and synapses on post ganglionic soma on or near the target.
The ganglia of the postganglionic fiber is located in the walls of GI within myenteric and submucosal plexus.
From gastric parietal cells
bicarbonate is secreted into ——- in exchange with —–.
While H+ is secreted into the ———- by means of ———.
HCO3- into interstitial space, exchanged for CL-
H+ into the lumen by means of K+/H+ pump
satiety center
inhibits appetite
Ventral Posterior Nucleus (VPN) of hypothalamus
NE from adrenergic neurons
Relaxation of smooth muscle in wall
contraction of sphincters and inc. salivary secretion
two hormones that decrease the gastric H+ secretion
GIP and Secretin
vagovagal reflexes
Parasymp- CN X (Vagus n.)
afferent limb: sensory info. f. chemo/mechano receptors to CNS
Afferent triggers a reflex
Efferent limb: motor info. is also contained w/in vagus nerve
The action of NO from neurons of enteric nervous system
relaxation of smooth muscles
CCK action
inc. pancreatic enzyme secretion
inc. pancreatic HCO3- secretion
Stimulates gallbladder contraction
Stimulates the relaxation of the sphincter of oddi
inhibits gastric emptying
name 4 gastrointestinal hormones and name the specialized hormone-secreting cells of the GI t.
Gastrin, CCK, Secretin and GIP (All induce contraction of pylorus).
enteroendocrine cells
necessary step for activation of gastric protease pepsin
luminal acidification
NTs of parasympathetic postgang. cells
VIP and ACh
Lower GI tract innervated by the pelvic n.
part of the wall of transverse colon, descending colon and sigmoid colon
anterograde and retrograde flow in sphincters at rest
at rest- positive pressure
upper GI tract innervated by the Vagus n.
upper 1/3 of esophagous (striated muscles)
wall of the stomach and small intestine
wall of the ascending colon and part of the transverse n.
secreted by intestinal L cells following a meal. It acts to decrease appetite
PYY
secretin action
inc. pancreatic HCO3- secretion
inc. biliary HCO3- secretion
dec. Gastric H+ secretion
inhibits tropic effects of gastrin on gastric mucosa
secreted by gastric cells just before ingestion of a meal
Cherlin
stimuli for secretion of CCK
small peptides and amino acids
fatty acids
Leptin
Hint: secretion is proportional to the amount of fat stored
secreted from fat cells and decreasing appetite and increasing the energy expenditure.
GIP action
inc. insulin secretion from pancreatic B cells
Dec. gastric H+ secretion
Two types of gastric glands (secretory cells of stomach lining) and their location
Oxynic gland- orad
pyloric gland- caudad
feeding center
Lateral Hypothalmic Area (LHA)
GIP site of secretion
Duodenum and jejunum
Sympathetic excitation –> NE release —> A —-> B production —-> Inc Ca2+ —-> Pylorus contraction.
A- a-1 receptor activation by NE
B- IP3 production –> intracellular Ca2+
Types of parasym. postgang. fibers and the corresponding NTs:
cholinergic- ACh
Peptinergic- Y or VIP
Gastrin site of secretion
G cells of stomach
secretion of D cells and its function
(opxynic and pyloric gland) D cells secrete somatostatin that regulates HCL secretion
Striated muscles (contractile tissues) of GI t.
pharynx
upper 1/3 of esophagus
external anal sphincter
Causes contraction of smooth muscle in wall of GI tract and relaxation of sphincters
ACh from cholinergic neurons
The three neuromodulators that are secreted from the neurons of enteric nervous system and cause relaxation of smooth muscle
neuropeptide Y, NO and VIP
parasympathetic nn. of GI tract and the sites of innervations:
CN X- Vagus nerve: Upper GI tract
Pelvic n. : Lower GI tract
power for acid secretion
and the flow of ions and water
K+/H+ powers acid secretion
Cl- follows H+ due to emf. water follows due to osmotic pressure
Two hormones that increase the pancreatic HCO3- secretion
secretin and CCK
Secretin site of secretion
S cells of duodenum
stimuli for secretion of Gastrin
Small peptides and amino acids
vagal stimulation (GRP)
distension of the stomach
action of gastric lipase
fat digestion (from chief cells)
gip
glucose- dependent insulinotropic peptide
Parietal cells (oxynic gland) secretions and their function
HCL And intrinsic factor
HCL–> activation of pepsin, protein denaturation and bactericide
IF is required for B12 absoption
contraction found in the orad region of the stomach
tonic
constant tone w/o relaxation
Action of ACh from cholinergic neurons
Contraction of smooth muscles in wall relaxation of sphincters inc salivary secretion inc gastric secretion inc pancreatic secretion
mixed fibers of CNX
75% sensory- afferent
25% motor- efferent
mode of contraction of the lower esophageal, iliocecal and internal anal sphincters
tonic contraction
results in changes in sphincter pressure
coordinated with smooth muscle contraction of adjacent organs via reflexes.
The neuromodulators that are secreted from the neurons of enteric nervous system and cause contraction of smooth muscle
Enkephalines (opiates) and substance P
Substance P
cosecreted with ACh by neurons of enteric nervous system and causes:
contraction of smooth muscles and
inc. salivary secretion
gastrin action
Inc. gastric H+ secretion
stimulates the growth of gastric mucosa
stimuli for secretion secretin
H+ in the duodenum (from S cells) and
fatty acids in duodenum
Orexigenic neurons (from arcuate nucleus) secrete neuropeptide Y and —-
increases appetite
Synthesized and secreted by intestinal L cells. Among its actions, like leptin and insulin, it decreases appetite
GLP-1 decreases appetite
VIP-Vasoactive Intestinal Peptide action (from neurons of enteric nervous system)
relaxation of smooth muscle
inc. intestinal secretion
inc. pancreatic secretion
Chief cells (Oxynic) secret
pepsinogen and gastric lipase
