Digestion - 3 phases of gastric control

what is the cephalic phase?

the first phase of gastric control

what does the cephalic phase do?

continues as food enters the mouth and activates neurons in the medulla oblongata and the ANS stimulates salivary secretion through the cranial nerve

when does the cephalic phase begin?

when you see, smell, taste, or think of food

what does the vagus nerve do in the cephalic phase?

stimulates stomach and accessory glands to secretion and increase motility

what cells prepare the stomach to receive food?

mucos cells, chief cells, parietal cells, and G cells

what are the functions of saliva?

soften and moisten food, digestion of starch, taste, and defense

what is the second phase of gastric control?

gastric phase

when does the gastric phase begin?

with the arrival of food in the stomach and builds up on stimulation from cephalic phase

what are the 3 functions of stomach?

storage (regulates passage into small intestine), digestion (both chemical and mechanical), and defense (destroys bacteria and other pathogens swallowed with food)

what are the 3 stimuli of the gastric phase?

distension of stomach, increase pH, and presence of undigested materials especially proteins

what is the response of the gastric phase?

neural (submucosal + myenteric plexus) and hormonal (gastrin), lasting 3-4 hours

what is the third phase of gastric control?

intestinal phase

when does the intestinal phase begins?

when chyme first enters the small intestine

what is the intestinal phase function?

to control the rate of gastric emptying; it also leads to inhibition of gastric activity

what are the signals of the intestinal phase?

duodenal stretch, presence of lipids and carbs, and decrease in pH

what is cholecystokinin (CCK)

stimulates digestion of fat and protein (stimulates gallbladder and pancreas) and acts as a hunger suppresent

what is secretin?

stimulates secretion s from liver and pancreas

what is glucose-dependent insulinotropic peptide (GIP) aka gastric inhibitory peptide?

inhibit gastric activity and stimulates insulin secretion

what is chemical digestion?

digestive enzymes that break molecular bonds into large organic molecules and divide into classes by their specific substrates

in chemical digestion, carbs…

break bonds between simple sugars

in chemical digestion, proteases…

break bonds between amino acids

in chemical digestion, lipases…

separate fatty acids from glycerides

In the pancreas, endocrine is…

pancreatic islets

in the pancreas, exocrine is…

ducts of Acini converge eventually forming pancreatic duct

what is the function of the pancreas?

carries pancreatic juice to duodenum that is rich in bicarbonate and enzyme present

what does does the pancreatic amylase break down?

starch and glycogen

what does pancreatic lipase break down?

fats

what does proteases break down?

proteins

what is the largest visceral organ?

liver

what are the 3 categories that the 200 functions of the liver?

metabolic regulation, hematological regulation, and bile production (lipid digestion)

what are the regulatory activities of liver effect?

carbohydrate metabolism, lipid metabolism, amino acid metabolism, waste removal, vitamin storage, mineral storage, and drug inactiviation

what does the pancreatic juice contain?

trypsin (proteins), lipase (lipids), amylase(carbs)

what is bile primarily for?

involved in lipid breakdown

what is the gallbladder?

stores and concentrates bile prior to secretion into the small intestine

what is chyme?

the pulpy acidic fluid which passes from the stomach to the small intestine, consisting of gastric juices and partly digested food

what happens when chyme enters the duodenum and releases CCK?

hepatopancreatic sphincter (oddi)encircling lumen of bile duct relaxes and the gallbladder contracts

what happens if CCK is not released?

hepatopancreatic sphincter of bile duct remains closed, bile exiting liver in common hepatic duct backs up and enters cystic duct and stored in gallbladder, and becomes concentrated in gallbladder

what is the hepatic portal system?

vasculature that delivers absorbed nutrients to the liver before nutrients enters the general circulation

what happens after nutrients are absorbed?

they are absorbed in the small intestine into the mesenteric veins

where do the nutrients travel from the mesenteric veins?

they travel to the liver via the hepatic portal vein

where do the nutrients travel to from the liver?

they travel to the heart (general circulation) via the hepatic vein

what does the hepatic artery provide?

it provides the liver with fresh blood to supply oxygen.