3.10 Menstrual Cycle

3.10 Understand the role of oestrogen and progesterone in the menstrual cycle.

- Oestrogen and Progesterone are both hormones. Hormones are produced in a structure known as an endocrine gland in the ovary. Hormones travel through the blood from this gland to its target tissue. This is where the hormone will have it's effect. Sometimes even multiple effects.

- The Ovary (as shown in diagram) is the endocrine gland for oestrogen.

1) The first effect of Oestrogen takes place in the lining of the uterus. Oestrogen is sent through the blood stream to the endometrium.  The diagram shows the difference in the thickness of the lining of the uterus. In the first half of the cycle the lining becomes increasingly thick.

2) The second effect of Oestrogen is the release of a hormone named LH. This is caused when Oestrogen flows through the blood stream to the brain. The peak of this hormone LH is about day 13 in the cycle which causes the ovary to release an egg. This is when Fertilisation is now possible to occur.

Closer look at what happens in the ovary:

- During the first 13 days of the cycle a structure called a follicle begins to grow larger and larger. The center of this follicle is the egg. It is the cells around the follicle which produce the Oestrogen. Around about day 13 the follicle reaches its greatest size at the same time as LH causes the wall of the ovary to rupture. This releases the egg into the oviducts. This process is called Ovulation.

- Once this process is complete the now empty follicle changes function and begins to turn yellow. This gives us the new name Corpus Luteum. This is known to produce Progesterone, so Corpus Luteum is the endocrine gland for Progesterone. This hormone travels through the blood stream to the lining of the uterus. This is effect 3 which makes sure that the lining of the uterus does not break down. It maintains the lining of the uterus. In this condition it is possible for the fertilised egg to implant into the wall and develop into a pregnancy (between the two lines left and right of number 3 on diagram)

- However if this does not occur the Corpus Lutiem breaks down and Progesterone levels fall. This results in effect number 4 which is the break down of the lining of the uterus. This is known as the menstrual period or bleeding. This marks the end of one menstrual cycle and the beginning of another.

3.9 Male Reproductive System

3.9 Recall the structure and function of the male and female reproductive systems.



Male Reproductive System:

- Bladder: Store urine.

- Testis: To carry out the process called meiosis which produces the gamete called sperm cells.
- Epididymis: Store sperm cells.

- Vasdeferens: To carry sperm cells to the penis during sexual stimulation. Tube pulses and pushes the sperm cells along the tube to the penis.

- Prostate: Adds about 20% to 30% of the volume of semen and is known to contain sugars and alkali. The alkaline nature of the prostate secretions neutralise the acidic secretions within the vagina.

- Seminal Vesicles: Also produce sugar based secretions which are also alkaline. Make up around about 70% of the semen in which the sperm cells can travel.

- Urethra: Common tube which joins the left and right testis. Carries semen and urine down to the penis.

- Penis: Carry sperm cells into the vagina during sexual intercourse.



Female Reproduction System:

(Note - At this point before pregnancy the uterus structure is no larger than an orange.)

- a) Ovary: Meiosis occurs to produce eggs (female gametes)

- b) Oviducts: Carries eggs to uterus. Also the location at which Fertilisation takes place.

- c) Uterus: Wall of the uterus is made of muscle. This is the part which will stretch to accommodate a pregnancy, and would contract during birth.

- g) Lining of the Uterus: Accepts and develops the fertilised egg into the embryo here. Also development of the placenta which implants into the lining of the uterus.

- d) Uterus Space: Where the baby develops.

- e) Cervix: Entrance to the uterus. Here is where the sperm cells will make their way up into the oviducts.

- f) Vagina: Where the penis is inserted and sperm cells are sent into the cervix. The vagina collects the sperm cells and allows them to make their way up into the uterus.

3.2 Fertilisation

3.2 Understand that Fertilisation involves the fussion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo.

- Process begins with the adult male and female. The cells which make up an adult are described as "diploid" meaning it has a complete set of chromosomes which for humans is 46.

- In the male the cells are divided into sperm cells by meiosis which only has 23 chromosomes. Meiosis halves the number of chromosomes in the cell turning it from a diploid cell to a haploid cell. The same happens in the female cells.

- In sexual reproduction, these two cells are joined/fused together so that they form one cell. This process is known as Fertilisation which involves the combining of two haploid cells (23 chromosomes each) to form a new diploid cell with 46 chromosomes known as a "zygote". This new cell has the same number of chromosomes as any other regular adult, which is a combination of the male and female chromosomes.

- The newly formed Zygote now goes through a process called Mitosis. This is when the new cell divides to form two cells. Both cells will still have 46 chromosomes. These two cells would then divide again in the same way until their are sufficient cells for the structure to be called an embryo.

3.1 Sexual and Asexual reproduction

3.1 Describe the differences between sexual and asexual reproduction.

Sexual Reproduction:
- Sexes exist (can identify male/female)
- Cells called gametes are produced (sperm cell and egg cell)
- Meiosis (type of cell division; halves the number of chromosomes in the gamete cell)
- Fertilisation (sperm cell and egg cell fuse together)
- Large Variation in the population. Sexual reproducing populations have a wide variety or variation (differences).

Asexual Reproduction:
- No sexes
- No gametes
- Mitosis (type of cell division; number of chromosomes is maintained constantly. So a cell with 20 chromosomes will divide to produce two cells each with 20 chromosomes. The two cells are identical)
- No Fertilisation
- Small Variation in the population. Asexual reproducing populations are identical ("clone") with the only variations as a result of mutation.

3.12 Understanding how the developing embryo is protected by amniotic fluid.

- Surrounding the embryo inside the uterus is a fluid which is called the Amniotic fluid.

- One of the main functions of this fluid is protection. It comes from the fact that the fluid cannot be compressed, which means when we try and squeeze the fluid it absorbs the pressure. This means that any blows or force that is applied to the uterus wall will be absorbed by the amniotic wall relieving the pressure and protecting the child.

- A way to experience this would be in a Swimming Pool. If you try to kick your leg in a swimming pool it is difficult to do this at speed and your leg won't move quickly. It is really difficult to generate any force. This is an example of how the amniotic fluid protects the unborn child.

- Another way in which the amniotic fluid protects the child is by keeping it floating in the uterus. The unborn child has no calcified bones to support its weight so it is important that the fluid prevents the child from bearing weight on it's bones.

3.11 Describe the role of the placenta in the nutrition of the developing embryo.

- When the child is in the uterus; which is a water filled environment containing amniotic fluids, the child cannot digest, breath or excrete. To obtain nutrition the embryo has an umbilical cord which grows out of the embryo and leads to the Placenta.

- Note: The placenta grows out of the embryo and not the mother. The blood vessels inside the placenta are the child's blood vessels (arteries and veins)

- Placenta grows into the wall of the uterus.

- The Mother continues to eat during pregnancy which means in her bloodstream there will be the normal Glucose, Amino acids and Fats. This will travel through her blood stream and into the wall of the uterus. From there they will cross into the child's bloodstream and into the child. This crosses at the Placenta. (reason why the Placenta has a large surface area and thin wall).

- Nutrients that the child receives as an embryo comes from the mother. The child also produces molecules which are exchanged back into the mothers blood which includes things like Carbon Dioxide.

Recall the names given to different trophic levels to include producers, primary, secondary and tertiary consumers and decomposers. 

- Word "Trophic" means to feed, so we are looking at the names given to the different feeding levels.

- A carrot plant here is doing photosynthesis. The carrot fly is eating parts of the carrot plant because it is a herbivore. And the Flycatcher is eating the carrot fly because it is a carnivore. And a carnivore eating another carnivore makes it the Top Carnivore because it is at the top of the food chain.

- Other names exist used in ecology are given to each level.

The Carrot Plant = Producer (turning light energy into chemical energy)

The Carrot Fly = Primary Consumer (taking in the chemical energy of the plant, and turning it into chemical energy of the fly.

The Fly Catchers = Secondary Consumer (eats the primary consumers - changing chemical energy from one form to another)

Top Carnivore = Tertiary Consumer (eats the secondary consumer - changing chemical energy from one form to another)

- All of these organisms at some point will DIE, at which point they are broken down by organisms called Decomposers

Examples of Decomposers: Fungi and Bacteria

They are important in the recycling of molecules - often breaking down the complex molecules into nitrates and phosphates.