Hi everyone, in today's lesson we will be elaborating more on the digestive system. Now this is not new to everyone, we have all learned this back in 26 right? But today we will be going in greater detail.
Now we all know that the digestive system is a long tube that starts from the mouth and ends at the rectum which connects to the anus. Yes? So food goes through this whole tube and it gets digested and absorbed at the end of the day.
But now that we are in secondary school, we are going to learn about two more organs, namely our liver and our pancreas. Now while these two organs are not part of the elementary canal, this means that food does not pass through this. They do help to secrete juices which will help to break down the food in itself.
So what does the liver do? The liver secretes an important thing known as bowel. B-I-L-E. So bowel is actually a yellow greenish liquid and it helps by emulsifying fats. When we talk about emulsifying, we mean that we are breaking down fats into smaller droplets.
And this is a physical digestion. We don't change the fat in itself, but we are just breaking down the fats into much smaller pieces. understand so bowel is created in the liver it is produced in the liver but before it goes straight to our elementary canal it is first stored in an organ known as the gallbladder so the gallbladder is like a storage for your bowel so from the gallbladder it is then secreted into the small intestine to break down all your fats into smaller droplets physical digestion break it down into smaller droplets.
By breaking down the fats into much smaller pieces, it increases the surface area and that is why fat digestion by another enzyme in the small intestine known as lipase will increase. Understand? The pancreas is another organ here and what it does is that it secretes pancreatic juices. This juice contains enzymes such as amylase and trypsin.
So question here, what does amylase here break down? And what does trypsin here break down? Remember that amylase here breaks down your starch to your maltose.
And your trypsin here breaks down proteins to your polypeptides. And all of the enzymes will be secreted into your small intestine where majority of digestion will take place. Let's take a look at the process of the elementary canal now. Now let's explore what happens.
happens when food enters our digestive system? How do our body digest the food? Now, most of this information can be found in page 7 and 8 in your notes.
So take a look at it as we go along. Number one, where does our food start? It starts from the mouth, right?
So the food enters your mouth. So what do you do with it? You chew and you chew and you chew. So this is called physical digestion and what it does is that it breaks down the food into smaller pieces.
as well as it increases surface area by breaking it down into smaller pieces. Why? This is for your enzymes to break it down more efficiently later down the elementary canal. Does our mouth have any enzyme?
Of course we do. What enzyme is it? It is the salivary amylase.
So what food substance does amylase breaks down? It breaks down your stomach. So as you chew, as you chew, as you chew...
you break it down into smaller pieces and the food becomes what we call a bolus. So this is a ball of food that's very moist and it will be swallowed down into your esophagus here. Okay so the esophagus actually functions as a muscular tube that helps to move the bolus from the mouth to the stomach.
So how does it do it? So as the bolus moves down the esophagus, what follows is a series of relaxation and contraction that allows the muscular wall to push the bolus down. So you can see that the diagram here right in your notes that as the foot enters the gullet, the muscles at the back of the bolus they contract and they push the bolus downwards and the muscles in front of the bolus they relax so that the bolus can come through.
And as this keeps happening, it's like squeezing a toothpaste. you keep squeezing the bolus downwards into the stomach understand so this movement is called peristalsis and once it reaches the stomach further digestion of the bolus will occur as well now in the stomach two kinds of digestion takes place physical and chemical and as food reaches your body gastric juice here is secreted so what does your gastric juice consist of it consists of mainly your hydrochloric acid and your digestive enzymes here. So as food is mixed with the gastric juice, they soften and your stomach also helps to churn the food mixture. So this is also a form of physical digestion and it breaks down the food into very very small pieces to form this liquid mixture known as chyme.
And on top of that, your stomach actually produces a protease. So these are enzymes that break down proteins. And the function of this protease known as pepsin is to break down your proteins into smaller chains of proteins known as polypeptides. Understand? Now, your stomach also produces something called hydrochloric acid.
So that is why sometimes you feel that your food is sour when you warm it out. It is because of the presence of this acid. So this acid does not...
break down food. It doesn't break down the food. Only enzymes can break down the food.
But what it does is that it prevents us from getting infected by bacteria that we might have eaten and it kills the bacteria that is present inside the food. Also, it provides an acidic environment so that the pepsin can break down the food chemically. So pepsin can only break down the food at acidic pH. at higher pH, it will not break down your proteins.
Understand? So this digestion process takes around 2 to 6 hours and then the chyme will be transported into the small intestine. So as the digested food in the stomach becomes chyme, it travels down into the small intestine here.
Now this is where most of the digestion takes place. And it's not very hard to see why there's so much digestion going on. This is because in the small intestine this time round, you have bowel coming from your liver that goes into the small intestine. You have your pancreatic juice that is also going into the small intestine that is secreted into the small intestine. And your own small intestine also secretes its own intestinal juice to work on your food in the small intestine here.
So let's take a look at the greater detail. all the digestion process that is happening in the nose. So once again, the digestive process in the small intestine is a combined effort of your liver and your gallbladder, which secretes and stores bowel, respectively, your pancreas, which produces pancreatic juice, as well as your small intestine as well.
Both physical and chemical digestion takes place here. The emulsification process is performed by your bowel. and your chemical digestion is done by your different enzymes that is present in pancreatic and intestinal juice so what does the bowel do the bowel only physically breaks down the fat molecules present in our food into fat globules so these are very small and fine fat particles and they help to increase the surface area for the lipase to work on later we call this emulsification so both the pancret the pancreatic juice and the intestinal juice contains enzymes that will help to break down your carbohydrates, your fats as well as your proteins together.
So with the combined efforts of our enzymes, our amylase and maltase here will break down our carbohydrates that we eat to become glucose. And the proteins that we take in will be broken down by your protease such as your pepsin, trypsin and erapsin, warm amino acids and our fats. here will be broken down into glycerol and fatty acids. This is shown on the previous part of the notes and all these small molecules will be absorbed to the bloodstream in the small intestine.
So what is left is the undigested matter in our food. It will go on to the large intestine. And finally in the large intestine, any excess water and mineral salts from the undigested food will be absorbed at this point and whatever that is left after that is what we call feces and this will be stored in the and this will be passed out of the body as you go to the toilet