The Digestive System

Summary

In this podcast, Mr. Andersen explores the digestive system, comparing it to a doughnut's hole to explain how food travels through without being 'inside' the body. He outlines the roles of saliva, stomach acids, and enzymes in breaking down food into absorbable monomers. The importance of the small intestine in digestion and absorption is highlighted, along with the colon's role in water reclamation and vitamin release by bacteria. The appendix's function as a bacterial reservoir is also discussed.

Takeaways

• 🪰 The flesh fly is an example of a fluid feeder, feeding on ooze from carrion.
• 🐋 Suspension feeders, like blue whales, filter food like krill from ocean water using baleen.
• 🐛 Substrate feeders, like caterpillars, eat through the substance they live in, like leaves.
• 🍽️ Humans are bulk feeders, consuming large quantities of food and then digesting it in stages.
• 🍩 The digestive system acts like a 'donut hole,' with food moving through the body but not technically inside it until fully absorbed.
• 🍕 The digestive process breaks down food into monomers that are rebuilt into the body's macromolecules like proteins, lipids, and nucleic acids.
• 🔔 Pavlovian responses, like salivating when we see food, start digestion before food even enters the mouth.
• 👅 Digestion begins in the mouth with saliva, containing amylase, which starts breaking down carbohydrates.
• 🍖 The stomach plays a key role in digesting proteins with the help of hydrochloric acid and the enzyme pepsin.
• 🧬 Enzymes from the pancreas and bile from the gallbladder further break down food in the small intestine, aiding in the digestion of fats, proteins, carbohydrates, and nucleic acids.

Q & A

What type of feeder is the flesh fly described as in the podcast?

The flesh fly is described as a fluid feeder, which sucks in ooze from carrion and then creates a bubble that evaporates to leave the material behind.

What is the role of the doughnut analogy in explaining the digestive system?

The doughnut analogy is used to illustrate how food moves through the digestive system, similar to how a finger moves through the hole of a doughnut, emphasizing that the food is not technically inside the body.

What are the four types of macromolecules that make up life?

The four types of macromolecules that make up life are carbohydrates, proteins, lipids, and nucleic acids.

How does the process of digestion begin in humans?

Digestion begins in the mouth with the secretion of saliva, which contains the enzyme amylase that starts breaking down carbohydrates.

What is the function of the epiglottis during swallowing?

The epiglottis closes to prevent food from entering the trachea and lungs, ensuring that the food moves down the esophagus instead.

What are the two types of cells in the stomach lining that play a role in digestion?

The two types of cells in the stomach lining are chief cells and parietal cells. Chief cells produce pepsin, and parietal cells produce hydrochloric acid.

How does the stomach mechanically break down food?

The stomach uses a series of muscles that move in different directions to churn up the food, a process known as mechanical digestion.

What is the role of bile salts in the digestion of lipids?

Bile salts emulsify fats, making them smaller and more accessible for lipases to break down into smaller components.

What is the primary function of the small intestine in the digestive process?

The small intestine is primarily responsible for the final stages of digestion and the absorption of nutrients into the body.

How does the large intestine contribute to the digestive process?

The large intestine, or colon, reclaims water from waste and houses bacteria that can release vitamins from food for absorption.

What is the role of the appendix in the human body?

The appendix is a vestigial structure that contains bacteria. It can become inflamed, leading to appendicitis, but it does not play a significant role in digestion in humans.

Outlines

00:00

🐛 Digestive System Introduction

Mr. Andersen introduces the podcast on the digestive system, starting with the unique feeding habits of the flesh fly, a fluid feeder. He differentiates it from other feeding types like suspension feeders (e.g., blue whales) and substrate feeders (e.g., caterpillars). The majority of humans are bulk feeders, consuming food in large quantities to be digested and absorbed. The analogy of a doughnut with a hole illustrates the path food takes through the digestive system, highlighting the absorption of nutrients from broken-down macromolecules like carbohydrates, proteins, lipids, and nucleic acids. The importance of recognizing these nutrients and their digestion process is emphasized.

05:03

🍕 The Digestive Process

The script delves into the digestive process, starting with the salivary glands and the enzyme amylase, which begins starch digestion in the mouth. The role of teeth and tongue in mechanical breakdown and the formation of a bolus that travels down the esophagus are discussed. The epiglottis's function to prevent food from entering the trachea is highlighted. In the stomach, mechanical and chemical digestion occurs with the help of muscles and enzymes like hydrochloric acid and pepsin, which break down proteins. The journey continues to the duodenum, where bile salts from the gallbladder and enzymes from the pancreas, including lipases, amylase, trypsin, chymotrypsin, and nucleases, further break down fats, carbohydrates, proteins, and nucleic acids. The small intestine's role in finalizing digestion and initiating absorption via villi and microvilli is explained, with nutrients being transported into the body through capillaries. The large intestine's function in reclaiming water and absorbing vitamins from bacteria is also covered, along with the appendix's role as a bacterial reservoir.

Keywords

💡Digestive System

The digestive system is an organ system involved in the breakdown of food and the absorption of nutrients. In the video, the digestive system is likened to a doughnut with a hole, illustrating how food travels through it without being 'inside' the body. The script uses this analogy to explain the process of digestion, starting from the mouth and ending at the anus.

💡Fluid Feeder

A fluid feeder is an organism that consumes liquids or semi-liquid substances. The script mentions the flesh fly as an example of a fluid feeder, which consumes ooze from carrion and leaves the material behind after evaporation. This concept is used to contrast with other feeding methods and to highlight the diversity of digestive strategies in the animal kingdom.

💡Suspension Feeder

Suspension feeders are organisms that feed by straining solid particles from water. The script uses the example of a blue whale, which takes in water containing krill, then squirts the water out while retaining the krill with baleen. This feeding method is distinct from others as it involves filtering food particles from a fluid medium.

💡Substrate Feeder

A substrate feeder is an organism that feeds on or within a substrate, such as soil or the surface of leaves. The script mentions caterpillars as substrate feeders that live and feed within the substrate of a leaf. This term helps to illustrate different feeding behaviors and how they relate to an organism's environment and digestive processes.

💡Bulk Feeder

Bulk feeders consume food in large quantities and then digest and absorb it. Humans are described as bulk feeders in the script, taking in food in bulk form and then processing it through the digestive system. This term is central to understanding human digestion and contrasts with the other feeding types mentioned.

💡Macromolecules

Macromolecules are large molecules such as carbohydrates, proteins, lipids, and nucleic acids that are essential for life. The script discusses how the body breaks down food into these basic macromolecules, which are then absorbed and used to build the body's tissues. Understanding macromolecules is key to grasping the nutritional aspect of digestion.

💡Amylase

Amylase is an enzyme that breaks down starch into simpler sugars. In the script, it is mentioned as a component of saliva that begins the process of carbohydrate digestion in the mouth. The role of amylase is crucial for understanding how the body starts to process carbohydrates.

💡Epiglottis

The epiglottis is a flap of cartilage that prevents food from entering the windpipe during swallowing. The script describes how the epiglottis closes to direct food into the esophagus, which is a critical step in the prevention of choking and ensuring the safe passage of food.

💡Bolus

A bolus is a rounded mass of chewed food that is ready to be swallowed. The script mentions the formation of a bolus in the mouth, which is then moved down the esophagus. The concept of a bolus is important for understanding the mechanical aspects of food processing in the digestive system.

💡Sphincter

A sphincter is a circular muscle that controls the opening and closing of the digestive tract. The script refers to the sphincter muscles at the entrance to the stomach, which regulate the passage of food. Sphincters play a critical role in controlling the movement of food through the digestive system.

💡Hydrochloric Acid

Hydrochloric acid is a strong acid produced by parietal cells in the stomach. The script explains that it creates an acidic environment necessary for the activation of pepsin, an enzyme that breaks down proteins. Understanding the role of hydrochloric acid is essential for grasping protein digestion in the stomach.

💡Emulsification

Emulsification is the process of mixing fats with water by surrounding fat particles with substances like bile salts, which makes it easier to break down fats. The script describes how bile from the gallbladder emulsifies lipids in the duodenum, which is a key step in lipid digestion.

Highlights

Flesh flies are unique fluid feeders that suck in ooze from carrion and leave the material behind.

Suspension feeders, like blue whales, take in water and then use baleen to filter out krill.

Substrate feeders, such as caterpillars, live within the substrate of a leaf.

Most humans are bulk feeders, taking food in bulk and then digesting and absorbing it.

The digestive system is likened to a doughnut hole, where food moves through without being technically inside the body.

Digestion involves breaking down macromolecules like carbohydrates, nucleic acids, proteins, and lipids into monomers.

Pavlovian response is mentioned as a way to trigger salivation in anticipation of food.

Saliva contains mucus and the enzyme amylase, which begins the breakdown of starch.

The tongue and teeth work together to form a bolus that moves down the esophagus.

The epiglottis closes to prevent food from entering the trachea and lungs.

The stomach uses mechanical and chemical digestion to break down food.

Chief cells and parietal cells in the stomach produce mucus and hydrochloric acid, respectively.

Protein digestion begins in the stomach with pepsin and continues in the duodenum with trypsin and chymotrypsin.

The duodenum receives bile from the gallbladder to emulsify fats and enzymes from the pancreas to further digest food.

The jejunum and ileum in the small intestine are responsible for completing digestion and beginning absorption.

Villi and microvilli in the small intestine facilitate the absorption of nutrients into the body.

The large intestine, or colon, reabsorbs water from waste and houses bacteria that release vitamins from food.

The appendix is a vestigial structure that houses bacteria but has no significant function in humans.

Digested nutrients are absorbed through the small intestine and eventually woven back into the body's cells.

Transcripts

Hi. It's Mr. Andersen and welcome to my podcast on the digestive system. One

of my favorite animals is the flesh fly. The flesh fly sucks in ooze from carrion. It then

creates a little bubble that evaporates so it can leave the material behind. Because

there's so much fluid inside here. And so the flesh fly is an example of a fluid feeder.

And it's kind of a unique way of feeding. We also have suspension feeders. An example

would be like a blue whale taking in a bunch of ocean water, squirting the water out and

then using baleen to to hold the krill behind it. Or a substrate feeder like a caterpillar

that lives within the substrate of a leaf. But most of us are bulk feeders. That means

that we take our food in in bulk and then we have to digest it and then eventually absorb

it into our body. And so I want to start with a picture of a doughnut. The reason why is

it starts you salivating because you might want to eat a doughnut. But it also has a

hole in it. And if you were to stick your finger through the hole in a doughnut, that's

a lot like food moving through the hole that is your digestive system. In other words it's

going to move all the way from your mouth out your anus, but it's not really inside

you. When you stick your finger through the hole of a doughnut it's not technically inside

the doughnut. Just like the food that goes through your digestive system, is not technically

inside your body. It's just moving through the hole in your body. We can eventually absorb

that material inside our body, but not until it gets very small. And so you are what you

eat. What does that mean? Well there are basically four types of macromolecules that make up

life, from carbohydrates to nucleic acids. And so you're going to take food, like this

pizza. You're going to break those polymers down into tiny little monomers and then you're

going to weave that back into you. So when you look at me right now, what you're really

seeing is protein that was in food I ate weeks or months ago. And so a good way to see if

you understand the digestive system is if when we're done with this podcast, I'm going

to show this pizza again, could you review each of these four major macromolecules from

carbohydrates to proteins, lipids, nucleic acids? Where it's digested? And if you have

an understanding where and how it's digested, then you really understand what's going on.

But the whole thing begins with our Pavlovian response. And this was a Russian scientist

who used dogs. He'd measure the amount of saliva they had. There was a bell that he

would ring. But basically he conditioned them so that when he rang the bell they'd start

to salivate. And the same thing works with us. There's a great episode of "The Office"

where Jim gets Dwight to Pavlovian respond to a little ringing of a bell and a mint.

So you may want to watch that. So basically when we see it, we start to salivate. We have

glands, three big glands, that are going to produce saliva. And those are going to empty

into our mouth. Now the saliva has water in it. But it mostly has mucus. And then an enzyme

called amylase. And amylase breaks down starch, amylose starch. And so it's going to breakdown

or start the breakdown of that carbohydrate. And so basically our teeth are there to chew

up that bulk food. Our tongue is there to move it back to the teeth. But eventually

we're going to form a bolus and that bolus is going to move down our esophagus. Now,

right here we have an epiglottis that will close because we don't want our food to go

into our trachea and into our lungs. And so if you swallow, right now you can actually

feel that epiglottis moving as we slide that food down into our esophagus. We have control

up here, but it eventually moves into smooth muscle. Eventually ends up in the stomach.

So what's going on in the stomach? Well we'll have a sphincter right here which closes it

off. And a sphincter right here. And so the food will sit inside our stomach. We're going

to break it down chemically and mechanically. There are a series of muscles that go this

way. Muscles that go this way. And muscles that go this way. And basically they're going

to churn up your food. And if there's nothing inside there you can hear that, your stomach

growling as it tries to grind up nothing. So basically that's mechanical digestion and

it will sit there for minutes if not hours grinding up the food. But we also have chemical

digestion here. And there are two cells that you should remember. Those are the chief cells

and the parietal cells. Basically they're going to be cells in the lining of the stomach.

We also produce mucus because we don't want to digest the stomach itself. So there's going

to be mucus here. But the two things that are produced are hydrochloric acid. Those

are going to be produced by the parietal cells. So hydrochloric acid is going to move out

here. The function of that isn't to digest the food, it is to create an acidic environment

where the other chemical, which is called pepsin can start to breakdown proteins. And

so protein digestion starts to occur right here in the stomach as we start to unravel

those big proteins into single strands of amino acids that we can eventually breakdown

in the duodenum. Okay. So that's the stomach. Next we move into the duodenum. The duodenum

is going to be this first portion of the small intestine. There are a few important things

that connect here. The first one is going to be the gall bladder. And then we're going

to have this bile duct that will empty down into the duodenum. What does that contain?

It contains bile salts. Bile salts are important because if you've ever tried to mix fat with

water or oil with water, since it's hydrophobic you can't break it down. And so the nice thing

about these bile salts is that they will actually surround the lipids. Make them much smaller

so they emulsify the fat. And so we can start breaking that down. Okay. So that's going

to be important. Next we have a bunch of enzymes that come, oops, let me go back, a bunch of

enzymes that come out of the pancreas. So the pancreas is important because remember

it can regulate blood sugar. But it's also producing, it's a gland, it's producing all

of these enzymes. And so lipases are going to come into the duodenum and those are going

to breakdown lipids. Pancreatic amylase is going to be important because it's going to

breakdown carbohydrates. We also have trypsin and chymotripsin. Those are going to breakdown

different types of amino acids. Or breaks between different amino acids so we can breakdown

those proteins into the building blocks. We also have nucleases that are going to be produced

in the pancreas as well. And so we have tons of enzymes that are produced by the pancreas

and they're going to breakdown the different bulk food as it comes into our body. Next

we move and continue down the small intestine to the jejunum and the ileum. And so if we

kind of follow, this would be the duodenum. And now if we follow food it's going to kind

of move almost like a maze all the way through our small intestine. This first section is

called the jejunum. Basically what happens in here is we're going to finish digesting

the food and then we're going to start absorbing the food. How does that work? Well if these

are the lining of the small intestine, we have these villi and microvilli. There are

going to be capillaries that move in here and basically move out and they're going to

take the nutrients into our body. How do we get those nutrients into our body? Well some

of it's diffusion but a lot of it is active transport actively moving that material in.

And so by the time we get down to the end of that ileum we've pretty much digested and

absorbed most of the food that we need to take in. In fact we're not going to do much

more digestion of those monomers as we move into the large intestine. So what's it do?

Well it's called the colon. It's got three different types to it. It's got the ascending,

transverse and descending colon. But basically as our waste moves through the colon or the

large intestine, we're reclaiming water from our waste. And also there are a bunch of bacteria

that live in here and they can release vitamins from our food so we can get that as well.

And it's important that we have that there. This is one thing that I didn't mention. This

is the appendix. The appendix is actually a vestigial structure. It has a bunch of bacteria

in it. Sometimes it becomes inflamed and that's a big deal because if we release those bacteria

into our body we're in trouble. It doesn't really do anything. But if we look at certain

animals like a koala bear, for example, their appendix or their secum is really large kind

of a thing that looks like this. And so basically what happens is leaves will get pushed down

in here. And bacteria are going to help them break that down. But since we don't eat a

lot of that it's not required. And so let's see how well you did. Could you do each of

these. Where were carbohydrates broken down? Do you remember? What about proteins? What

about lipids? What about nucleic acids? Well let's start with carbohydrates. Carbohydrate

digestion begins in the mouth because we've got amylase in the mouth. But it also is in

the duodenum. Because we have pancreatic amylase. What about proteins? Proteins start in the

stomach, not in the mouth. But in here we're going to have pepsin remember? Hydrochloric

acid to lower the pH. And as we move out here it's going to be trypsin and chimotrypsin

that are going to help break that down. What about lipases or excuse me lipids? Lipids,

there are two things that you should remember. We've got the gall bladder. The gall bladder

is going to give off bile salts to emulsify the lipids. And then we're going to have lipases

that come out of the pancreas. And then finally we have nucleases that are going to breakdown

those nucleic acid. So basically we then reabsorb all these nutrients in through the small intestine.

All of those vessels lead to the liver where we figure out what we want to do with all

those building blocks of life. But eventually we weave it back into our cells. In other

words, where did you get your DNA? Where did you get your sugars? Where did you get your

proteins? It's in your food. And now you've taken all that broken down in the small monomers

and then we can weave it back into the polymers that make us the way we are. So that's your

digestive system and I hope that's helpful.