[Music] today we’ll explore how food is digested and absorbed into the body from the first bite food travels through the mouth stomach small intestine and large intestine to finally end up in the rectum where the remainder is evacuated from the body as fecal matter this is nian and nian likes a hearty breakfast today’s meal consists of two eggs on a slice of bread a cup of coffee and a glass of milk it contains a lot of energy very nutrients such as protein carbohydrates and fats but it also contains a lot of micronutrients in the form of vitamins and minerals the response to food actually starts before you take your first bites this is called to the cephalic phase or the anticipation to a meal seeing hearing or smelling food triggers a response in higher brain senses which for example stimulates the secretion of saliva and gastric acid it also relaxes the muscles in your stomach to accommodate the incoming volume naeun’s body is already preparing itself for the food that is about to be consumed actual digestion starts in the oral cavity through chewing and the production of saliva chewing mechanically breaks down foods to make it more accessible and saliva mainly contains a lot of amylase an enzyme that starts the process of breaking down complex starchy carbohydrates from the slice of bread the tongue also produces small amounts of lipase an enzyme that breaks down fats present in the eggs and milk it then moves to a 25 centimeter long tube called the esophagus which delivers food to the stomach via rhythmic muscle contractions known as peristalsis and here a food will often stay for at least a couple of hours the stomach purposefully has a very low pH value due to the presence of gastric acid in addition to killing ingested bacteria this serves to alter the shape of proteins from the milk and eggs by a process called denaturation this allows for another enzyme pepsin to access the proteins and break them down the stomach intermittently mixes and grinds your foods to make sure that it consists only of small particles and that it mixes well with the gastric acid and enzymes at this point the food bolus is called chyme how fast the kind exits the stomach largely depends on what you eats but eventually all food will move on to the small intestine two things happen when the chyme answers the first part of the small intestine lead to adenine first the liver will send bile a yellowish liquid to the gallbladder which in turn sends it to the duodenum the main function of bile is to aid in the digestion and absorption of dietary fats and fat soluble vitamins second the pancreas delivers a wealth of enzymes that aim to further digest nutrients proteins are broken down into amino acids fats into fatty acids and glycerol and carbohydrates into glucose now that all nutrients are free so to speak they can be absorbed into the bloodstream this predominantly happens in the second part of the small intestine the jejunum and to a lesser degree in the final part the alien the jejunum is covered in what we call villi small projections in the lining of the intestinal wall that maximize surface area and allow for efficient absorption of nutrients but not everything is absorbed in the small intestine compounds such as fiber water dead cells and surplus nutrients travel all the way to the large intestine or the colon and here the vast majority of water is removed through the intestinal wall the colon is also home to an entire ecosystem of microorganisms that perform bacterial digestion on some of the leftover nutrients this process can generate methane gas which has a rather distinct odor and can exit through the anus in the form of flatulence the remaining stool ultimately ends up in the rectum where it is stored until your body sends a signal to the sphincter that it’s time to relax luckily it gives you time to find an appropriate location to relieve yourself of the fecal matter and that completes the 24 to 72 hour long journey of food through the entire digestive system next episode we’ll discuss how the macronutrients that have made it into your body are metabolized to provide energy to your cells thank you for watching and I’ll see you next time [Music]