hormones in human reproduction Flashcards
bbc bitesize
clomifene
definition
Fertility drug used to stimulate ovulation (egg release).
corpus lutuem
definition
The remains of the follicle in a mammalian ovary after it has released an ovum (egg) into the fallopian tube. The corpus lutuem secretes hormones involved in the menstrual cycle.
follicule
definition
Fluid filled ball of cells found in the ovary containing an ovum (egg).
FSH
definition
Follicle Stimulating Hormone. It stimulates oestrogen production and the growth of follicles (egg-sacs) in the ovary. It is secreted by the pituitary gland.
gland
definition
An organ or tissue that makes a substance for release, such as a hormone.
hormone
definition
Chemical messenger produced in glands and carried by the blood to specific organs in the body.
IVF
definition
The letters stand for ‘in vitro fertilisation’. This involves bringing the sperm and the egg together to create an embryo, which is placed into the woman’s womb to increase the chance of giving birth.
LH
definition
Luteinising Hormone, secreted by the pituitary gland, which stimulates ovulation.
menstrual cycle
definition
Recurring series of events in the human female reproductive system.
menstruation
definition
Also called a ‘period’. The loss of blood and tissue from the lining of the uterus through the vagina during the menstrual cycle.
negative feedback mechanism
definition
Mechanism to lower raised levels of something, and to raise reduced levels of something.
oestrogen
definition
A female sex hormone produced in the ovaries, which is responsible for puberty in girls and the regulation of the menstrual cycle.
ovulation
definition
The process of releasing an egg from an ovary.
placenta
definition
The organ in the uterus of pregnant mammals that allows the transfer of nutrients and waste products between the mother and the fetus through the umbilical cord.
progesterone
definition
Sex hormone produced by the ovaries and placenta.
uterus
definition
Also known as a womb. This is where the fertilised egg (ovum) develops.
What is a hormone?
A hormone is a chemical substance, produced by a gland and carried by the blood, which alters the activity of specific target organs (and is then destroyed by the liver).
What is menstruation?
The menstrual cycle is a recurring process that takes around 28 days. During the process, the lining of the uterus is prepared for pregnancy. If implantation of the fertilised egg into the uterus lining does not happen, the lining is then shed. This is known as menstruation.
What do the hormones involved in menstruation do?
basic
Several hormones control this cycle - for example, they are involved in controlling the release of an egg each month from an ovary, and changing the thickness of the uterus lining.
Several hormones are involved in the menstrual cycle of a woman:
- follicle stimulating hormone (FSH) causes the maturation of an egg in the ovary
- luteinising hormone (LH) stimulates the release of the egg
- oestrogen is involved in repairing and thickening the uterus lining, progesterone maintains the uterine lining
Menstrual cycle
step by step
1) Menstruation
2) Linging of the uterus builds up.
Egg is released.
3) Lining maintaining.
4) Lining breaks down (menstruation)
Menstrual cycle
What does the pituitary gland do and what does this cause?
The pituitary gland produces FSH which causes the development of a follicle in the ovary.
Menstrual cycle
hormones
What happens when the egg develops?
As the egg develops inside the follicle, the follicle produces the hormone oestrogen.
Menstrual cycle
What does oestrogen cause?
The oestrogen causes growth and repair of the lining of the uterus wall.
Menstrual cycle
What does oestrogen inhibit?
Oestrogen inhibits FSH
Menstrual cycle
When oestrogen rises to a high enough level, what does it cause?
When oestrogen rises to a high enough level it causes a surge in LH from the pituitary which causes ovulation where an egg is released from the follicle (Day 14 of the cycle).
Menstrual cycle
The follicle and negative feedback
The follicle becomes the corpus luteum and this produces oestrogen and progesterone which inhibit FSH and LH production by the pituitary. This is an example of negative feedback.
Menstrual cycle
What does progesterone do?
Progesterone maintains the uterus lining (the thickness of the uterus wall).
menstrual cycle
What happens if the egg has not been fertilised?
If the egg has not been fertilised, the corpus luteum dies and progesterone levels drop. This causes menstruation, where the uterus lining breaks down - this is known as having a period.
Interaction of oestrogen, progesterone, FSH and LH in the control of the menstrual cycle
- The pituitary gland produces FSH which causes the development of a follicle in the ovary.
- As the egg develops inside the follicle, the follicle produces the hormone oestrogen.
- The oestrogen causes growth and repair of the lining of the uterus wall. Oestrogen inhibits FSH.
- When oestrogen rises to a high enough level it causes a surge in LH from the pituitary which causes ovulation where an egg is released from the follicle (Day 14 of the cycle).
- The follicle becomes the corpus luteum and this produces oestrogen and
- progesterone which inhibit FSH and LH production by the pituitary. This is an example of negative feedback.
Progesterone maintains the uterus lining (the thickness of the uterus wall). - If the egg has not been fertilised, the corpus luteum dies and progesterone levels drop. This causes menstruation, where the uterus lining breaks down - this is known as having a period.
What happens when a woman becomes pregnant?
If a woman becomes pregnant, the placenta produces progesterone. This maintains the lining of the uterus during pregnancy and means that menstruation does not happen.
What gland is the hormone FSH (fllicle stimulating hormone) produced from?
Pituitary gland
What gland is the hormone oestrogen produced from?
Ovaries
What gland is the hormone LH (lutenising hormone) produced from?
Pituitary gland
What gland is the hormone progesterone produced from?
Ovaries
What is the role of the hormone FSH (follicle stimulating hormone)?
Causes an egg to mature in an ovary. Stimulates the ovaries to release oestrogen.
What is the role of the hormone oestrogen?
Stops FSH being produced (so that only one egg matures in a cycle). Repairs, thickens and maintains the uterus lining. Stimulates the pituitary gland to release LH.
What is the role of the hormone LH (luteinising hormone)?
Triggers ovulation (the release of a mature egg).
What is the role of the hormone progesterone?
Maintains the lining of the uterus during the latter part of the menstrual cycle and during pregnancy.
What is human fertility controlled by?
Human fertility is controlled by hormones, so fertility can be controlled using hormonal forms of contraception.
Hormonal methods of contraception
Oral contraceptives
What does ‘the pill’ contain and what does this do?
The oral contraceptive, which is known as the pill, contains oestrogen or progesterone or a combination of both hormones. These hormones inhibit the production of FSH, and eggs cannot mature.
Oestrogen at low levels stimulates the release of eggs. However at high doses, oestrogen will inhibit FSH production. After taking the pill for a while, egg development and release will stop completely. If there is no egg available, there can be no baby. This is why contraceptive pills are so effective.
Hormonal methods of contraception
benefits of oral contraceptives
Oral contraceptives are more than 99% effective if taken correctly and can reduce the risk of certain cancers.
Hormonal methods of contraception
Side effects of oral contraceptives
However, there are possible side effects, such as changes in weight, mood and blood pressure due to high levels of oestrogen. Modern pills contain much less oestrogen.
Hormonal methods of contraception
contraceptive methods other than oral.
Contraceptive injections, implants or skin patches contain slow release progesterone to inhibit the maturation and release of eggs.
Non-hormonal methods of contraception
Fertility can be controlled without hormones.
These methods include:
- physical barrier methods such as condoms and diaphragms, which prevent the sperm reaching an egg
- intrauterine devices (IUD) also known as a coil, prevent the implantation of an embryo or release of a hormone
- spermicidal agents which kill or disable sperm
- abstaining from intercourse when an egg may be in the oviduct
- surgical methods of male and female sterilisation - an example is a vasectomy, where the sperm ducts are cut and tied
Non-hormonal methods of contraception
Fertility can be controlled without hormones
benefits and risks of these methods
- condoms are easy and quick to use, but sometimes they can tear or rip
- diaphragms need to be put in just before sex and left in several hours afterwards
- IUDs need to be fitted by a health professional - IUD can remain in position for up to 10 years, however there is a small risk of causing an ectopic pregnancy
- spermicidal agents can be added to other physical barriers such as condoms, but some people can have allergic reactions to these
- abstaining can be used successfully, but if the timings are not accurate the chance of pregnancy is high
- surgical methods cannot be reversed, and is considered permanent
What is Assisted Reproductive Technology (ART)?
Assisted Reproductive Technology is the use of hormones and procedures, as fertility treatments, to help to achieve pregnancy. These include in vitro fertilisation (IVF) and a fertility drug, clomifene.
Fertility drugs and the hormones they contain
Some women have difficulty becoming pregnant because they don’t produce enough FSH to allow their eggs to mature. Some fertility drugs contain FSH and LH, which stimulate eggs to mature in the ovary.
Effects of fertility treatments
Fertility treatments increase a woman’s chance of becoming pregnant, although the treatment may not always work. On the other hand, because the treatment boosts the production of mature eggs, it increases the chance of twins or triplets. Multiple pregnancies carry a risk of complications, and may lead to premature or underweight babies.
What is Intracytoplasmic Sperm Injection (ICSI)
Intracytoplasmic Sperm Injection (ICSI) is a specialised method of IVF
In what cases is in vitro fertilisation (IVF) treatment used?
If a couple are having difficulty conceiving a child because there are issues with the quality of the man’s sperm, or a woman has blocked oviducts, then IVF can be used.
In vitro fertilisation (IVF) treatment
step by step
- IVF involves giving a mother FSH and LH, to stimulate the maturation of several eggs in the ovary
- the eggs are collected from the mother and fertilised by sperm from the father in a dish in the laboratory
- the fertilised eggs develop into embryos
- at the stage when they are tiny balls of cells one or two embryos are inserted into the mother’s uterus (womb)
Clomifene
Some women have difficulty becoming pregnant because they do not ovulate (release eggs).
Clomifene is a drug used as a fertility drug to stimulate ovulation, the release of eggs. It works by blocking the action of oestrogen’s negative feedback on LH. Therefore more LH is released in a surge. This mimics the LH surge which occurs just before ovulation.
Which hormone is released from the ovary and repairs the uterine lining?
Oestrogen
Which hormone is released from the ovary?
Progesterone
A drop in progesterone levels will cause what event?
menstruation
Which structure releases FSH?
Pituitary gland
