Waffle on White Ceramic Plate
Waffle on White Ceramic Plate

Let’s see what the tunica mucosa has to offer us, so if we were to look at this tuna mucosa at the microscopic level, we would see some really important cell types that secrete certain substances, we’re going to talk about three cell types, they are chief cells, parietal cells and mucous cells, so the chief cells secrete two very important substances, one is pepsinogen, the other one is called gastric lipase, pepsinogen gets converted to pepsin by the acid in the stomach and then it helps break down peptide bonds which essentially we’re breaking down proteins here, the gastric lipase helps break down fats so we’ve got those secretions released by the chief cells but i also mentioned another cell type called parietal cells, those also secrete two very important substances, the parietal cells secrete intrinsic factor and the hydrochloric acid intrinsic factor is necessary to absorb vitamin b12, really important vitamin that can be a whole other topic. Hydrochloric acid has other functions, hydrochloric acid helps denature proteins so it’s again helping in aiding with helping and aiding with digestion, we can also see that it’s going to kill pathogens, bacteria and certain viruses don’t like a ph of 2 and it’ll just destroy those things so we kind of have to think about this other idea though, how does the hydrochloric acid not eat away our own stomach lining, that tunica mucosa that i mentioned ,well that was the third cell type, the mucous cells. Those mucous cells secrete mucus and it coats the whole lining of the stomach, so if we go to this whole area here, the whole inside lining of the stomach gets coated in mucus so you could kind of think the lining of the stomach coated with mucus with acid on top and that helps to stop the acid from eroding the stomach or causing problems, if you take any medications that lower the mucous production which ibuprofen and advil contribute to, you can make that mucus a little bit thinner and therefore the acid can irritate the stomach a little bit more, so now we can see that the stomach coats the food in substances like hydrochloric acid and enzymes which helps aid in the breakdown of the food but the stomach doesn’t stop there, it continues to mix the food which also aids in digestion, it often gets referred to as a muscular blunder so if you take a look at the dissection here again, imagine the wall of the stomach has smooth muscle in there and that smooth muscle is going to contract and mix the food in a certain way.

Now the fancy pants phrase for the digestive system moving food downstream is called peristalsis and the stomach kind of does it with this propulsion and retropropulsion type of wave action that we’re going to talk about so if you imagine right, that here’s the beginning of the stomach where we come in here and then there’s the end going to the small bowel, the stomach tends to propel the food this direction and remember we had a really tight pyloric sphincter here and that pyloric sphincter is so tight that it typically only lets about three milliliters through, that’s not very much so really only small substances, so anything that gets pushed this direction and isn’t small enough gets pushed back and so you get this wave of back and forth with the stomach until any substance that gets pushed this direction, if it’s small enough it’ll sneak through, if it’s not, it gets pushed back for further mixing and further breakdown, one question we often get from students is how long does that wave back and forth happen in the stomach, well it depends a little bit, one it depends on how much food you ate which again we’re going to talk about in a second here and two the type of food, carbohydrates tend to be broken down the quickest so if you have a carbohydrate-rich meal, it will be digest quicker, proteins are kind of next in line and then fats the slowest so carbs, proteins and fats and the majority of the time we eat a mixture of all those but it kind of leans one towards the other depending on the type of foods you’re eating so it can be anywhere from two to four hours before you empty the stomach.

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