Alright guys, I am bored actually. But at least, a quality time with guyton was finally attempted: YEY! I am now in Gastrointestinal Block, a week more to go to finish this block off. Then comes First Aid Block then 3rd Selanjar. How tempting huh?
Okay, today I am gonna do some teaching. Do you mind? Sorry for being a nerd by posting nerdy stuff, but I just feel dang bored.
Today you gonna learn the swallowing stage. All of you knows eating. I bet most of you are munching or eating something while reading this. Nak sikit boleh? * OK gila dah* . So if you know how to eat, do you know that your swallowing process is one of the most complicated thing that happened in your body? But why? Telan mecam senang je kan? Think again then!
In the world of medicine, we called it DEGLUTITION. Of course, it sounded complicated now...but wait! There's more.
I said swallowing is complicated. But why? Well this is merely because there's 4 tracks that must be opened or closed so that food will passed safe and sound to the esophagus. It looks like a round about where you guys find everyday while driving on the roads. You have nasopharynx on the top and trachea below. Then your food must directly passed from the oral cavity to esophagus. There are various mechanisms of our anatomical feature of the oral cavity and the neck region; for the correct passage of food in term of bolus.
As you can see in the above diagram I drew, that is the pharyngeal stage. But, humans have another stage called the voluntary stage. This stage merely initiates swallowing; where we voluntarily squeezed or rolled the food posteriorly to the pharynx by pressure of the tongue against palate.
Okay, now entering the pharynx, food stimulates epithelial swallowing receptor areas around opening of the pharynx. Impulses then pass to the brain stem for the start of automatic pharyngeal muscle contractions.
1. Food must not goes into our nose. Thus, soft palate is pulled upward to close the posterior nares.
2. There's folds at the pharynx called palatopharyngeal folds on each side of the pharynx: they are pulled medially forming a small slit. This enabled only MASTICATED or small-chewed food to enter.
3. Food must not fall or enter the laryngeal inlet. Thus, the vocal cords are strongly approximated. Larynx is pulled upward and anteriorly by neck muscles. Combined with ligaments that prevent the epiglottis to move upward: cause the epiglottis to swing backward over the laryngeal inlet. These prevent food from entering into nose and the trachea. (Trachea is continuous with the laryngeal inlet).
4. As larynx is pulled upward, opening for esophagus is enlarged. Here, the upper esophageal sphincter relaxes. This helps food bolus to move easily and freely into upper esophagus. Between swallows, this sphincter remains contracted to prevent air from going into esophagus during respiration.
So the summary people:
Trachea is closed - esophagus is opened - a fast peristaltic wave initiated by nervous system of the pharynx forces the bolus into upper esophagus: the entire swallowing process takes 2 seconds only. How magnificent!