regulation of digestion (7b) Flashcards
what are the accessory digestive organs
teeth, salivary glands, pancreas, liver and gallbladder
characteristics of teeth
used to chew food into smaller fragments
humans have deciduous (baby) teeth and permanent teeth
characteristics of the salivary glands
components: parotid, submandibular and sublingual glands
produce/secrete saliva which cleanses mouth, dissolves food chemicals so they can be tasted, moistens food and aids in compacting it into bolus, begins chemical breakdown of starch
characteristics of saliva
contains water, salts, mucin (mucus protein), serous fluid, lysozyme (enzyme), IgA (antibodies), growth factors and amylase
pH is 6.35-6.85 to support amylase
characteristics of the pancreas
produces wide spectrum of digestive enzymes that break down all food
secretes enzymes via pancreatic ducts into the duodenum
pancreatic juice is made of the enzymes and alkaline fluid (serves to neutralize acidic chymes from stomach)
characteristics of the liver
produces bile which emulsifies/breaks down fats
bile contains salts and bile pigments (bilirubin for hemoglobin breakdown), cholesterol, phospholipids and electrolytes
liver -> common hepatic duct -> bile duct -> duodenum
characteristics of the gallbladder
liver -> cystic duct -> gallbladder
storage for bile
water is removed from bile to concentrate it
when fat enters duodenum, gallbladder releases bile by the bile duct
what happens in cholecystectomy
when bile salts cause a blockage of the cystic duct, the gallbladder becomes inflamed
the gallbladder is removed completely
what is stomach bypass surgery
either:
stitch the stomach to give it a lower volume, reducing the amount of food it can hold = less hunger = weight loss
or remove the duodenum so that less chemical digestion occurs = less absorption = less calories = weight loss
how is digestion controlled neurally
regulated by the autonomic nervous system (PS, S, E)
innervated by afferent nerve fibers, through the vagus nerves and spinal pathways
what is the enteric nervous system and what does it do
intrinsic nervous system of the GI tract
controls local activity of the smooth muscles
controls gland secretion
no brain input
how does the ENS work
it reacts to mechanical and chemical stimuli
intrinsic nerve plexuses (myenteric controls smooth muscle and submucosal controls glands) are made of small ganglia that lie in the walls of the GI tract, they perform short reflexes as a response to stimuli
also has nerve fibers that connect the ganglia and nerve fibers that supply the muscles of the gut wall, mucosal epithelium, arterioles and other effectors
can be modified by PS and S NS
how are gastric secretions controlled
long reflexes: sight/taste/thought/smell of food initiates PS simulation of increased gastric secretion via vagus nerve
short reflexes: stretching of stomach, chemical stimuli and peptide presence stimulates gastric secretion
how are the pancreas and liver regulated hormonally
by cholecystokinin (CCK) and secretin
how does CCK work
fatty chyme entering duodenum causes duodenalent eroendocrine cells to release CCK
CCK enters the blood stream and once it reaches the pancreas, it stimulates the secretion of enzyme-rich pancreatic juice
CCK stimulates the gallbladder to release stored bile and the hepatopancreatic sphincter to relax
how does secretin work
acidic chyme entering duodenum causes duodenalent eroendocrine cells to release secretin
secretin enters the blood stream and once is reaches the pancreas, it stimulates the secretion of bicarbonate-rich pancreatic juice
secretin causes the liver to secrete more bile
what does the vagus nerve stimulate in pancreas and gallbladder
stimulation of vagal nerve fibers causes pancreatic juice release and weak contractions of the gallbladder
what is the stimuli for gastrin and what does it do
stimulated by food in the stomach and ACh released by nerve fibers
stimulates release of gastric juice and emptying of stomach
what is the stimuli for intestinal gastrin and what does it do
stimulated by food in the stomach
stimulates gastric secretion and emptying (amplifies stomach digestion)
what is the stimuli for stomatostatin and what does it do
stimulated by food in the stomach and sympathetic nerve fibers
inhibits gastric and pancreatic juice secretion and stomach and gallbladder emptying
what is the stimuli for gastric inhibitory peptide (GIP) and what does it do
stimulated by food in duodenum
stimulates insulin release
