2TTO Ch5.4

• Biologie
• Middelbare school
• vwo
• Leerjaar 2

Paragraph 5.4 The menstrual cycle

Welcome to this lesson!

• Today, we will be discussing the menstrual cycle of women
• This is an important part of understanding how reproduction in humans work
• It can be quite difficult, so please note any questions that come up so we can discuss them later!

Planning

• Lesson goals
• Introduction to the paragraph
• Videos and explanation
• Work on exercises

Lesson goals

• You can explain when menstruation happens in a female life and what the function is of menstruation
• You can explain what happens during the different phases of menstruation
• You can explain how hormones influence the menstruation and the female body
• You can explain the role of oestrogen, progesterone, FSH and LH in the menstruation

Let's start!

Take notes during the lesson in your notebook, this will help you get an overview. Do it at your own speed!

And again: write down any questions that come up

Menstruation

Each month, the female body prepares an egg cell to be fertilised

When that egg is not fertilised, the body will get rid of it. That is done through menstruation.

Fertilisation = bevruchting

Menstrual cycle

• The menstrual cycle is the process that the female sex organs go through each month again; preparing an egg for fertilisation, and getting rid of it when it is not fertilised.

• This whole process is regulated by hormones

• This cycle generally lasts somewhere between 21 to 35 days, on average it is 28 days (that is why we normally count in months)

When do women menstruate?

• When girls are born, all their egg cells are already formed in the ovaries
• During puberty (between age of 12 and 15), most girls begin to menstruate the first time. Some start even earlier than 12, others only start at 18, which is completely normal.
• A woman stops menstruating during the menopause, mostly between the age of 45 and 55 (but again, earlier or later is possible)
• The age at which menstruation starts and ends depends on many things, including genetics, health, and diet.

Video

In the next slide you will find a short video that gives a good introduction on the menstrual cycle. 

The menstrual cycle

• Again: the whole cycle generally repeats every 28 days
• Menstruation itself is part of this cycle
• During the rest of this lesson we will discuss the phases of the cycle, the hormones of the cycle, and the effects of the cycle on the rest of the body

Phases of the menstrual cycle

The menstrual cycle contains 3 phases. During these phases changes are happening in three different places:

1. The ovaries (where the egg cells are)
2. The uterus (where the fertilised egg cell would grow)
3. The rest of the body (mainly side effects of the hormones)

Phases of the menstrual cycle

The menstrual cycle contains 3 phases:

1. The menstruation (also called period) - 4 to 6 days
2. Development of egg cell and making the uterus ready - about 8 days
3. Release of the egg cell and finishing the uterus - about 14 days

Phases

In this image, the menstrual cycle is shown. Try to find the different phases!

This image gives the phases names, we will not use them (just phase 1, 2 and 3)

Phase 1: menstruation

The menstrual cycle starts with the menstruation itself. This means that the uterus empties itself completely to prepare for the rest of the month

• Menstrual flow: blood and other substances will flow out of the uterus, towards the vagina
• This can cause cramps, bloating and other discomfort (generally not pleasant, but necessary)

Phase 2: preparing the egg and uterus

• In order for fertilisation to happen, we need an egg cell to be ready, and we need the uterus to be ready.
• The egg cell develops (grows) under influence of FSH
• The uterus starts building a lining on the inside where a fertilised egg cell could nestle         under the influence of oestrogen
• At the end of phase 2, the egg cell is ready and will come out

You could compare it to making a bed comfortable, because only a mattress is not enough. Add blankets, a pillow, ...

Ovulation

• The egg cell is ready, and will come out of the ovary to be fertilised (release is caused by LH)
• This is what we call ovulation, which happens somewhere around day 15 of the cycle
• The ovulation marks the end of phase 2 and starts phase 3

Phase 3: release of egg cell and finishing the uterus

• The egg cell has come out of the ovary, and is in the oviduct where it waits to be fertilised
• This has to happen within 24 hours, otherwise the egg cell will die
• The uterus keeps preparing for a fertilisation, so will grow the lining a bit more (caused by progesterone)

Phase 3: release of egg cell and finishing the uterus

• When the egg is fertilised: pregnancy will happen (paragraph 5.6)
• When the egg is not fertilized: the uterus lining will start to break down again, and after a few days we will arrive back to the beginning of the cyle - the menstruation
• (Phase 1 again): the uterus lining will flow out of the uterus together with blood and be disposed out of the body

That concludes the whole cycle!

• This is quite a complicated process, and is actually even more complicated than what we explained now.

• You saw that I also included a bit about the hormones already. In the next slide, I have included a video that explains very well what the different hormones do. Please take notes!
• You can ignore the part about hormones promoting and stopping each other, that's where it gets a bit difficult

Link the hormone to the function! (and take notes of it when you don't know them)

Finishing the uterus lining

Developing the egg

Development of uterus lining

Causing ovulation

Oestrogen

Progesterone

FSH

LH

Effects on the rest of the body

• The menstrual cycle can have some effects on the rest of the body as well
• Of course, during menstruation, it can cause cramps, back pain and bloating
• It also has influence on: mood, behavior, eating, attraction, ...
• It depends on the cycle and on the person how much these things are affected (changes every month)

That was it..

• This was a very short overview of the menstrual cycle. I can understand that this is quite a difficult topic, which we will repeat a few times to make sure you understand it. 
• The next slide contains a place where you can ask questions for me to answer!
• Your homework is to finish exercise 11-16, and study paragraph 5.5

Ask any questions here!

Wrapping up

• Take some time now to go over your notes and make exercise 11-16
• Write down any questions you might have
• Study paragraph 5.5
• We will see each other next week!