Hormones

Topic Notes

Additional Support Materials

i.e. animations, quizzes, pictures,  worksheets

 

Reproduction and its Hormonal Control

 

 

 

Menstrual Cycle Summary
 (provided by: University of Virginia)  

How hormones work
(provided by:SLP Hormones)

Useful activity in plotting your own graph of the menstrual cycle  - this will help your understanding and give you a visual representation of the interactions of hormones.  It will hopefully help you to remember the role of each hormone and its interaction with target organs.

Reproduction Hormones Worksheet (BiologyMad)

 

 

Controlling Reproduction in Domestic Animals (Synchronising Breeding)

 

  

 


 

 

Reproduction and its Hormonal Control
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Different mammals have different patterns of reproduction

  In mammals the gametes (sex cells) are:

Gametogenesis is the formation of gametes

In the females of all mammals, there is a cycle known as:

Hormonal Control of the Female Menstrual Cycle  [back to top]

The ovaries are organs that are responsible for the development of female gametes.  At birth around 400 000 cells have reached prophase of the first meiotic division and are called primary oocytes (often called follicles).  Each month after puberty, one of these cells completes its development into an ovum.

The follicular phase is the first part of the menstrual cycle, where one or more follicles start to develop into a mature female gamete.  The follicle cells surround the oocyte (developing egg cell), and produce hormones that trigger other responses.

The Ovulatory phase is when the oocyte is released (follicle cells remain in the ovary) from the ovary and passes down the fallopian tube and towards the uterus.

The Luteal phase most of the follicle cells remain in the ovary after ovulation.  They continue to develop and form a structure called the corpus luteum, as a result more hormones are produced.

Use the diagrams below in conjunction with the flow chart.  Add some of the explanations listed below to the diagram (when you have printed it of course) or else make your own flow chart This will help to reinforce the information you need to learn!

Follicular Phase

At the start of the oestrous cycle, the pituitary gland (in the brain) secretes follicle-stimulating hormone (FSH)

FSH triggers development of one or more follicles in the ovary

As the follicle grows in size, oestrogen is secreted

Inhibits further production of FSH

Stimulates the pituitary gland to secrete lutenising hormone (LH)

Stimulate growth and repair of the uterine lining (endometrium)

Ovulatory Phase

As the follicular stage progresses, the developing follicle increases in size and becomes a mature follicle

Oestrogen levels increase rapidly

Triggers further release of LH (high concentration of LH in the blood)
Triggers a sudden release of FSH for final development of follicle

Ovulation

Oocyte leaves the ovary and passes into the fallopian tube

Female is fertile

Luteal Phase

The high concentrations of LH that brings about ovulation has an affect on the follicle cells that remain in the ovary

Follicle becomes corpus luteum

Corpus luteum secretes some oestrogen and a large amount of progesterone

                                

Progesterone stimulates mammary glands and uterus in anticipation of pregnancy

High concentrations of oestrogen and progesterone inhibit production of FSH and LH

If the Oocyte is not fertilised within 36 hours, it dies

Without FSH and LH the cells of the corpus luteum gets smaller and less progesterone and oestrogen is secreted

At day 28, a lack of progesterone brings about another menstruation

With less oestrogen and progesterone, the FSH is no longer inhibited, and the cycle can start again

**If pregnancy occurs, initially the corpus luteum secretes sufficient progesterone to maintain the uterine lining and sustain the developing embryo.  After this, the placenta takes over, where progesterone (and some oestrogen) from the placenta maintain the uterine lining and inhibit the development of further ova (egg), and prepare the breast tissue for lactation (milk production).  At the end of pregnancy, progesterone levels fall, and high oestrogen levels trigger the onset of labour.
 
** Not directly covered in the AS AQA spec. A syllabus, however is useful for understanding of the roles of the hormones

 

Menstrual Cycle Summary

 

The follicle cells (light green), follicular fluid (cyan) and developing oocyte (magenta) have been coloured to clearly demonstrate the changes in the follicle as the egg matures and is finally ovulated. The follicle undergoes changes as it becomes a hormone producing corpus luteum (gold, dark green).

     

SUMMARY OF EFFECTS

Hormone

Site of Secretion

Target Organ

Function

Follicle Stimulating Hormone (FSH)

Pituitary gland

Ovary

  • stimulates the growth & development of the follicle

  • stimulates secretion of oestrogen

  • effect of LH in stimulating ovulation

Oestrogen

Ovary

Endometrium (lining of the uterus)

  • stimulates repair of uterine lining

  • at high conc. inhibits FSH, however during 'pituitary hormone surge' it stimulates further FSH production

  • as conc. peaks stimulates release of LH

Lutenising Hormone (LH)

Pituitary

Ovary

  • stimulates the final development of the follicle

  • stimulates ovulation

  • stimulates the development of the corpus luteum

  • stimulates production of progesterone

Progestrone

Corpus luteum

Uterus

  • maintains uterine lining endometrium)

  • inhibits release of FSH

  • inhibits release of LH

  • fall in conc. results in menstruation

  • fall in conc. removes inhibition of FSH and a new cycle begins.

 

How sex hormones work  [back to top]
(Additional information to help consolidate this topic)

The action of one hormone is used to stimulate or inhibit the production of another.  Hormones are chemical messengers, produced and secreted by organs, which travel via the blood, and exerts some influence upon a target tissue.

Hormones can be classified into two groups:

The hormones that are proteins will have its molecules that are folded in such a way that they have a tertiary structure that gives them a specific shape.  Once a protein hormone (such as LH or FSH) has reached its target organ, the hormone molecule will bind to a receptor site on the plasma membrane.  The receptor molecules are proteins and have specific receptor sites that have a complementary shape to that of the hormone.  The hormone is unable to pass through the plasma membrane and enter the cytoplasm of the cell.  Instead it binds to the receptor and activates specific events in the cell.

 

Oestrogen and progesterone are also sex hormones, however they are not proteins, they are steroids.  Steroids work in a different way to protein hormones.  Steroids are lipids and so they are able to pass through the phospholipid bilayer of the plasma membrane and enter the target cell.  Once inside, they bind to receptors in the cytoplasm.   The receptors act as carriers for the hormone and transfer it into the nucleus of the cell.  The hormone then switches on the gene responsible for the synthesis of a particular protein.

 

 

 

 

 

 

 

Controlling Reproduction in Domestic Animals

(Synchronising Breeding)
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Reproduction in non-primate mammals is characterised by the oestrous cycle (ovulation).

The behaviour of many female mammals changes around the time of ovulation (known as oestrous), Oestrous marks the time when a female will allow mating to take place often referred to as coming into season or being on heat. 

E.g., Transplanting embryos in cows  

 

 Initially farmers will treat their cows with progesterone

(Remember that progesterone inhibits FSH, and that it can be used in contraceptive pills)

Farmers will stop treatment with all cows at the same time

The reduction of progesterone will cause an increase in FSH, as it is no longer inhibited.  This allows the cows to start their oestrous cycle at the same time i.e. the cows will now be synchronised

Follicles will all develop at the same time

Farmers will inject the cow (generally one cow, - usually the one with the best features to pass onto the next generation) with a mixture of FSH and LH.  Farmers work out the hormone dose, so that the cow can be made to produce a large number of egg cells

Females follicles in her ovaries develop and ovulation occurs

When the female comes into oestrous (ovulation), she is artificially inseminated, with the best bulls sperm

Egg cells are fertilised and start to develop into embryos

6-8 days later, the embryos are removed

The embryos developing normally are transferred to other cows, which will act as surrogate mothers.  It is important that the recipient cows and the donor cow are synchronised or the uterus will not be in a suitable condition for the embryos to implant.
 

Advantages of this method:

 


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Last updated 20/06/2004