Hello and welcome to this lesson from the unit Reproduction in Humans.

The title of today's lesson is Gestation and Birth in Humans, and we're gonna be looking at that process of reproduction in which offspring are produced, how a baby develops from a fertilised egg cell, and how birth can take place so that new offspring can enter the world.

My name's Mrs. Barnard, and I'm going to be taking you through today's lesson.

So by the end of today's lesson, you should be able to describe the growth of a foetus and the process of giving birth.

Now we've got some keywords in today's lesson.

So our keywords are foetus, placenta, umbilical cord, amniotic sac, and contractions.

Now you can write these down, I'll put the definitions up for you on the next slide and I'll pause so that you can write those down.

All right, however, we will be going through them in the lesson, so if you want to write them down at that point, you can also.

So our lesson today is in three parts.

So part one is gestation.

So gestation involves the development of a embryo into a foetus, ready to be born as a baby, and then the role of the placenta, which maintains the developing foetus inside the mother's uterus.

And then finally, the process of birth itself and how that happens.

So let's get started with our first section of our lesson today, which is gestation.

So during sexual reproduction in humans, fertilisation produces a single cell, and that single cell is called a zygote.

So when the sperm and the egg come together, we make a zygote.

At that point, the DNA from both of those sex cells, those gametes, has joined together in the nucleus of the zygote.

So it's got a full set of chromosomes and DNA in there.

That zygote will then grow to make a baby through a couple of stages, and the stages are named the embryo, and then onto the foetus, and then finally a baby at birth.

Now, none of these images are drawn to scale, but we need to draw them so you'll be able to see them.

So then, after fertilisation in the fallopian tube, the zygote will divide to form a ball of cells that are called an embryo.

So we can see here in our fallopian tube at the start, you've got that sperm and that egg cell.

So that's fertilisation.

Remember that takes place in the fallopian tube.

And at that point, the two nuclei of the sperm and the egg fuse together so that you have one nuclei with a full set of chromosomes.

And then what happens is it forms the zygote, one cell, one fertilised cell.

And then as that zygote divides to form copies of itself, it forms the embryo, and then that embryo will move down the fallopian tube until it reaches the uterus.

Okay, and then when it comes to the uterus, it's going to implant in the wall of the uterus.

And you can see it there implanted in the wall, and it's made of lots of cells.

Now the cells of the embryo start to take on different jobs because when that fertilised egg cell, that zygote, first divides, it just makes an identical copy of itself.

So for a few days, all of those cells are exact copies of each other.

But over time, if we want to make a foetus, we need to make sure that it's got all those different types of tissues that's needed to make a human being.

So the groups of cells form tissues.

So those specialised cells that have the same function will form tissues.

So therefore the tissues will start to take on different functions.

So after about three to four weeks, we can see that those tissues have started to form, and we've got a foetus growing there in the uterus.

So the types of tissues you might think of are things like skin tissue, muscle tissue, neural tissue.

So our neurons in our nervous system.

All those different types of tissue have to form, and they all form from those original cells that were in the embryo.

So they developed those tissues into organs.

So remember when you have groups of tissues together that work together to have the same function, we call it an organ.

And we say that the embryo becomes a foetus at around eight weeks.

And in this picture here, we can see our foetus is there attached to the placenta.

Now the placenta we'll talk about later in the lesson, but it maintains the growth of the foetus, and it does that through the umbilical cord, 'cause the umbilical cord attaches the foetus to the placenta.

And surrounding the foetus, we've got the amniotic sac, and the amniotic sac has a fluid inside it.

Now the cells that originally came from the embryo also go to make the placenta and the amniotic sac.

And all of these structures are there to help this foetus develop.

So the different cells and tissues allow the foetus to look and function more like a human.

And you can see this picture here of a human foetus is at about 12 weeks.

And compared to the last one, the last image, this foetus has got some limbs, it's got some arms and it's got some legs.

You can see an eye starting to form.

You can see the difference between where the head and the body are going to be.

So at just 12 weeks after fertilisation, we can start to see that this is taking the shape of a human.

And as the foetus grows, it has to be protected, 'cause it's inside this very muscular organ, the uterus.

And as we know, over time, that uterus will stretch, but it needs a bit of a protection from knocks and bumps from the outside.

So it's within this bag that's filled with a fluid, amniotic fluid, and we call it the amniotic sac.

So the gestation period is how long it takes for that embryo to develop into a foetus and then into a baby ready to be born.

And in humans, this gestation period is about 40 weeks.

Now the gestation period varies a lot.

So even in mammals we can go quite low.

So a mouse, for example, would have a gestation period of about three weeks, which is really short.

But an elephant's gestation period is about 88 weeks, which is about 20 months.

Okay, so really long time for a female elephant to be pregnant.

And these are the stages that we have for a foetus.

So from week one all the way through to 40 weeks, you can see how from that fertilised egg, we get the development of tissues and organs and the structures that make this embryo develop into a foetus and then on into a baby.

So time for a quick check.

All cells that form the foetus are produced from the zygote.

Now, do you think this is true or false? And once you've decided, could you choose which of the statements below best justifies your answer? So I'm gonna pause.

Just pause the video and come back when you've made your decision and we'll check if you are right.

Okay, so let's see how you got on.

So all cells that form the foetus are produced from the zygote.

So this is true.

And the statement that best justifies this answer is the zygote divides to form lots of cells, which then change to form the different tissues that make up the foetus.

So they do all originally come from those cells from the zygote and the cells that were in the embryo, but they change to form different cells to form tissues and organs.

Okay, time for our first practise task.

So for each of these key words, could you please match it up with the correct definition? Again, pause while you do this, and then we'll check you that you've got this right.

Okay, let's see how we got on then.

So embryo, we should have matched that up with a ball of cells forming from the zygote dividing.

And foetus, the growth stage after the embryo and before birth.

And zygote is the fertilised egg cell formed in the fallopian tube.

And the amniotic sac contains the amniotic fluid to protect the foetus.

So if you got those right, then well done.

Otherwise correct your answers, 'cause you're going to need them later on.

So we're onto the second part of our practise task, and we've got the key structures involved in embryo growth.

And we've got female reproductive system here, and this shows pregnancy.

So if you could label the key structures in this image that ensure that a foetus can develop.

Let's see how we've got on then.

So we should have our foetus labelled and the placenta and the umbilical cord.

And then we should have the amniotic sac around the outside there, and then the amniotic fluid within the amniotic sac.

Okay, it's time to move on to the second part of our lesson, which is the placenta.

So the foetus relies upon its mother as it develops.

There are some things that it needs from its mother, and those are protection.

So it needs protection against knocks and bumps and temperature changes.

'Cause obviously the temperature changes a lot in the outside world and the mother's got to protect the foetus against those temperature changes.

Oxygen for respiration.

Remember respiration is one of the common processes of all living things.

So that foetus is going to need its own supply of oxygen.

And then nutrients is gonna need some food in order to have energy and to grow, and water for all of its chemical processes.

And the developing foetus also will need its waste removing.

So waste products from chemical reactions like carbon dioxide.

So you produce carbon dioxide in respiration and you breathe it out.

And the foetus also needs to get rid of the carbon dioxide that it makes during respiration too.

So let's look at some of these in a little bit more detail.

So the placenta.

So the placenta is an organ.

It's like a pancake organ.

It's like a fat, fat pancake.

And it attaches to the wall of the side of the uterus, and that provides the nutrients and oxygen that the foetus needs from the mother.

It also removes the waste substances.

We're gonna look at that in more detail in a moment.

Now that placenta can form anywhere inside the uterus.

It's more helpful if it's slightly higher up so it doesn't cover the cervix when the baby needs to be born.

But it basically forms wherever the embryo embeds in the uterus.

And then we've got the umbilical cord.

And the umbilical cord attaches the placenta to the foetus, and that's how your belly button is formed.

So your belly button is where the umbilical cord attached to you to the inside of your mum.

So to the placenta.

And then we've got the amniotic fluid.

Now the amniotic fluid's really important, because that's one of the things that provides you with, provides the foetus with, sorry, protection against the bumps.

So it sort of buffers those bumps.

And also it buffers the temperature changes.

So if the temperature's going up and down inside the mother or in the external world, then that amniotic fluid, the temperature won't raise or decrease too much.

So it keeps the baby or the foetus at a more stable temperature.

So the oxygen and the nutrients pass from the mother's blood into the placenta.

And then they pass down through the umbilical cord to the foetus.

And waste substances such as carbon dioxide will pass from the fetus's blood that's in their blood vessels into the mother's blood in their blood vessels, and then the mother's blood can carry it away.

So for example, the baby will carry out respiration.

So it'll use the oxygen for respiration and it'll produce carbon dioxide as a waste product.

Now 'cause it can't breathe out the carbon dioxide like we can, that carbon dioxide will pass into the mother's blood vessels and into the blood.

The mother's blood will carry up to her lungs, and she will breathe out the fetus's carbon dioxide along with her own carbon dioxide.

And the fetus's blood travels along the umbilical cord, and that's how the foetus can get its oxygen and the nutrients that it needs.

So time for a quick check.

There are two correct descriptions of the role of the placenta in the four options below.

So it protects it, the foetus, from bumps.

It provides the foetus with blood.

It removes carbon dioxide and it provides oxygen and nutrients.

So choose the ones that you think are the correct descriptions and pause the video.

Okay, how did we get on with that, then? So the two correct answers are it removes carbon dioxide, and it provides oxygen and nutrients.

And it protects the foetus from bumps with the amniotic fluid and the amniotic sac, and it doesn't provide blood, okay? Just the blood vessels come close to each other to provide the nutrients and oxygen.

So time for a practise now.

So Laura and Lucas are discussing the role of the placenta, and Laura says the placenta is where the blood vessels of the mother and foetus are close so that the mother can provide carbon dioxide and nutrients to the foetus.

And Lucas says the placenta is the organ where the foetus and the mother's blood mix and substances are exchanged.

Now, in both of those examples, both pupils have made an incorrect statement somewhere in their response.

So what I would like you to do is to identify their mistakes and for each one, can you correct it? So pause the video while you do that, and then we'll come back and we will see how you've got on.

Okay, let's see how we got on with this one then.

So Laura and Lucas were discussing the placenta and they made a mistake in their responses.

So Laura said the placenta is where the blood vessels of the mother and the foetus are close so that the mother can provide carbon dioxide and nutrients to the foetus.

Now she was incorrect because she said that the mother provides carbon dioxide.

So in your correction, you should say the mother provides oxygen and nutrients, not carbon dioxide.

And carbon dioxide passes from the fetus's blood into the placenta and is taken away by the mother's blood.

And Lucas said that the placenta is the organ where the foetus and the mother's blood mix and substances are exchanged.

And he was incorrect in saying that the foetus and the mother's blood mixes.

So the correct statement should be that the blood vessels of the mother and foetus are close to each other, but the blood does not mix.

So if you identified those and you corrected them, then well done.

So let's move on to the next part of our lesson, which is birth.

So here we are.

We've got a foetus that's ready to be born, so about 40 weeks.

So the foetus and the mother will release hormones to start the process of birth.

Now this is a long process which takes place where waves of muscle contractions will start to push that baby out through the vagina into the outside world.

So first of all, the cervix relaxes.

So the cervix is the entrance to the uterus, and it's a muscular ring, and it's closed very tightly shut to keep that foetus in place during development.

So these waves of contraction help to open up that cervix.

And also the walls of the uterus will start to contract, which means to squeeze, and start to push that baby down towards the cervix, putting a lot of pressure on that cervix in order for the baby to come out.

These waves of muscle contraction continue all the way through labour.

Now labour is the name for the process that a woman goes through as the baby has been ready to be born and it is controlled by hormones.

And these contractions happen over quite a long number of hours for some women, sometimes days.

And for some other women, it can happen really, really quickly.

But these contractions have to build up from quite weak contractions to very strong contractions to make sure that that cervix opens and that that baby can be born.

So these are the stages.

So first of all, muscle contractions in the walls of the uterus will start, and the woman will be able to feel these as mild aches and pains.

And then the cervix starts to open.

And again, that is caused by muscles.

And that cervix has got to go from not being open at all, up to 10 centimetres wide in order that the baby's head can fit through the gap and get down into the vagina.

And the vagina is a muscular tube as well.

So as the head of the baby comes through the cervix, the vagina is going to widen and stretch in order to let that baby's head through.

Once the baby's head comes through, they call this crowning, and then what usually happens is that the baby's body will follow.

Now, not all pregnancies and births happen like this, so sometimes the baby is the other way around and it hasn't turned round to be headfirst.

So some babies might be born with their bottom first or their feet first.

And sometimes doctors and parents might decide that giving birth might be a bit too risky.

So a woman might have a surgery.

So a caesarean section where a baby is taken out in an operation, incisions are made and then the baby is taken out of the uterus that way instead of through the vagina.

Let's have a quick check.

So put these stages of birth into the correct order.

So I'll let you read those yourself, pause the video, and once you've got them in the correct order, we'll check back.

Okay, so let's see how we got on then.

So the first stage is that the hormones are released.

So both the foetus and the mother will release hormones.

And then we've got the muscles in the wall of the uterus start to contract.

And then the cervix opens, and then the baby is pushed out through the vagina.

So now time for a practise task.

So we've got a diagram here of some of the organs that were involved in childbirth, and I would like you to label this diagram with everything that's involved and add a description of how they are involved in the birth.

Okay, so it'll take you a little bit of time to do this.

So if you just pause the video and then we'll come back and make sure that you've got some good descriptions on your diagram.

Okay, let's check those descriptions then.

So first of all, we should have the uterus labelled, and on your uterus you should have put that the muscles in the walls contract to push the baby down into the vagina or through the cervix.

And then we should have the vagina, which the baby passes out of this muscular tube.

You could say it stretches.

It's a muscle and it stretches to allow the baby to pass out.

And then the cervix, so that the cervix is, remember the entrance to the uterus, and hormones and muscle contractions cause this to open so the baby can pass from the uterus through and out into the vagina.

Okay, so now it comes to the summary for today's lesson, which is gestation and birth in humans.

So a zygote divides to become an embryo in the fallopian tube, which then develops into a foetus made of different cells and tissues.

The foetus grows in an amniotic sac, which is filled with amniotic fluid for protection until it is ready for birth.

The human gestation period is about 40 weeks.

The mother provides all the nutrients and oxygen that the growing foetus needs and gets rid of waste products through the placenta and the umbilical cord.

During birth, hormones are released, causing muscle contractions in the uterus and the cervix to open.

This pushes the baby out through the vagina.

So, well done for your work on today's lesson.