Biology Sexual reproduction in mammals

U13: Sexual Reproduction in humans

Part 1: The Male Reproductive system:

Structure and function To be used with U 13 Lesson 2

The male reproductive systemSexual reproduction is the means by which

humans produce their offspring. Humans are perhaps unique in that sexual

intercourse is not only an act of potential reproduction but also gives pleasure.

The male organs of the reproductive system are structured to produce, temporarily store and periodically release (ejaculate) male gametes called spermatozoa (sperm, for short!).

Objectives

When you complete this lesson, you should be able to :

1. use labeled diagrams to describe the arrangement of the organs of the male reproductive system.

2. annotate diagrams to show their functions.

The male reproductive system

Some organs are visible from outside the body, and some are contained inside the abdominal cavity. The organs only mature and become functional when puberty starts. The diagrams in the following slides illustrate the male reproductive system. An accessory gland is labeled on the next slide.

What is it? (The video clip below should help!) http://www.healthline.com/vpbody/reproductive-male

The male reproductive system

http://www.cartage.org.lb/en/themes/Sciences/LifeScience/GeneralBiology/Physiology/ReproductiveSystem/HumanReproduction/malerepro_1.gif

Male reproductive organs (Side view)

http://www.web-books.com/eLibrary/Medicine/Physiology/Reproductive/repdt_male.jpg

Testosterone

• You no doubt remember that you learnt about the endocrine system?

Which endocrine gland produces the hormone testosterone?

• Yes, the testes.• Let’s review the function of testosterone.

The role of testosterone• Testosterone is known as the ‘male hormone’.• It is produced by the testes. • The testes are stimulated into action by

Follicle Stimulating Hormone (FSH) produced by the pituitary gland.

• This happens even before birth. • Testosterone is produced in even larger

quantities as soon as a male hits puberty.

The role of testosterone cont’d

• Testosterone controls the development of secondary sexual characteristics.

• What are secondary sexual characteristics? • These are the physical and emotional

characteristics that distinguishes a male from a female.

• Do you now realize why testosterone is called the male hormone?

Male secondary sexual characteristics

• Let’s look at these visible secondary sexual characteristics. Most are obvious in males around you, so you should be able to state them correctly.

• Go through the following slides to see if you were correct.

Male secondary sexual characteristics cont’d

• An early sign is that deepening of the voice starts, but the voice frequently goes back to being high-pitched or ‘breaks’.

• It becomes possible to ejaculate semen, and this frequently occurs as ‘wet dreams’.

• Let’s look at some other characteristics.

Growth of facial hair starts at puberty.

The growth of facial hair is due to the action of testosterone.This hair tends to be much coarser than hair on the head.

http://i.ehow.com/images/GlobalPhoto/Articles/5471404/390269-main_Full.jpg

Chest and underarm or axillary hairs grow.

This hair growth is also due to the action of testosterone.

http://static.howstuffworks.com/gif/human-body-hair-2.jpg

Pubic hair grows.

Growth ofpenis and testes occurs.

Growth of pubic hair and enlargement of the genitals is caused by the action of testosterone

http://www.healthofchildren.com/images/gech_0001_0003_0_img0221.jpg

Broadening of the shoulders and development of muscles increase as a boy becomes a man.

.

http://www.abpischools.org.uk/res/coResourceImport/modules/hormones/en-images/male.jpg

• The testes enlarge as sperm production starts.

• The penis also enlarges to facilitate sexual intercourse during copulation in which spermatozoa in the semen are ejaculated into the female’s vagina.

Importance of secondary sexual characteristics

To Think About!

• No doubt young women would agree that all these new secondary characteristics make males more attractive! So, these characteristics attract potential partners to ensure sexual reproduction and the diversity that accompanies the production of offspring arising from that activity.

To Think About!

• Remember however, that these new characteristics will remain for a long time and are common among all males, so…. there is no need to rush into finding a partner and beginning to ‘have sex’!

• Go have a talk with a trusted relative, counsellor or your parent/guardian about the pros and cons of ‘having sex’ at your age.

• Remember… if you ‘have sex’ even once, you could yourself become a parent or contract a disease e.g. HIV/AIDS.

Are you ready for either of those?

U 13: Sexual Reproduction in Humans

Part 2: The Female Reproductive System• Structure and function To be used with U 13 Lesson 3

Objectives

When you complete this lesson, you should be able to:

1. use annotated diagrams to describe the structure and functions of the organs of the human female reproductive system.

2. show greater appreciation for female reproductive health.

Functions of the adult Female Reproductive System

• Produce a mature egg each month, starting at puberty.

• Facilitate the deposit of spermatozoa and their transit to meet the egg.

• Prepare for and accommodate the implant of a fertilized egg, and its complex development over roughly nine months.

• Give birth to a new human being. What an absolutely amazing system!

The female reproductive system• Each part is so structured to carry out those

specific functions and all the parts work together to ensure that a female can produce offspring to continue the species.

• Because of its important function, care must be taken to practice proper hygiene, to take measures to prevent STDs and to have a diet that will keep the entire body healthy.

• The diagrams in the following slides illustrate the female reproductive system.

Location and external parts of the female reproductive system

http://www.cartage.org.lb/en/themes/Sciences/LifeScience/GeneralBiology/Physiology/ReproductiveSystem/HumanReproduction/femalerepro_1.gif

Female reproductive system - Front view

http://www.glogster.com/media/1/4/7/18/4071820.jpg

Female reproductive system - Side view

http://www.tqnyc.org/2006/NYC063547//images/femalereproductivesystem.jpg

Female Secondary Sexual Characteristics

• Having already explored the endocrine system, you know that females have an equivalent hormone to testosterone.

• This hormone is oestrogen. • It also controls development of secondary

sexual characteristics. Think about what happened in your own body

or what you observed in a female in class/at home, then list the characteristics.

Secondary sexual characteristics in females

Here’s a summary of what you should have:• Broadening and curving of hips• Enlargement of breasts• Enlargement of reproductive organs• Growth of underarm and pubic hair• Menstruation beginsAll will not appear at the same time for all females

since the age of puberty varies.

All the changes in the diagrams are due to Oestrogen.

http://www.abpischools.org.uk/res/coResourceImport/modules/hormones/en-images/female.jpg

Importance of secondary sexual characteristics

These changes ensure the continuation of the species.

• Menstruation occurs because the reproductive system is now functioning; it shows that an egg was produced each month but was not fertilized.

• The breasts enlarge to enable milk production for possibly nursing a baby.

• The hips enlarge to facilitate child bearing.

U 13: The Menstrual CycleTo be used with U 13 Les 4

Females are saying….

Mummy.. remember to buy pads for me,

OKay?

I just feel bloated and so tired

when my periods come!

I hope I don’t get

headaches and vomit

this month!

Oh Thank God! That means I’m not pregnant! Jerry and I just not ready for a second child now.

Objectives

When you finish, you should be able to:1. explain why females have monthly menses.2. state the functions of hormones in the

menstrual cycle.

The Menstrual Cycle

• Normal, healthy females such as members of this class should be ‘having a period’ each month. What is it? Why does it happen?

• A ‘period’ is the shedding of the lining or endometrium of the uterus wall.

• It happens because fertilization and subsequent pregnancy did not occur.

• Having a period is part of a cycle which is controlled by several hormones.

The menstrual cycle cont’d

• The first day of a female’s period or menses marks the first day (Day 1) of the menstrual cycle.

• This cycle normally spans between 21 to 28 days.

• Let’s look at the hormones involved and what they do. They are FSH or Follicle Stimulating Hormone, LH = Luteinizing Hormone and Progesterone.

The menstrual cycle cont’d

• Starting from day 1 of the cycle, the pituitary gland secretes FSH.

• This causes a Graafian follicle to develop. • As the follicle develops in the ovary, the ovary

secretes oestrogen.• Oestrogen causes the cells of the endometrial

wall to gradually become filled with blood and fluid.

The menstrual cycle cont’d

• At about day 14 another pituitary hormone, LH is secreted in high concentration.

• LH causes the Graafian follicle to rupture releasing the egg. This is ovulation.

• The period before ovulation is the Follicular Phase and includes menstruation.

• The LH also causes the remains of the follicle to be converted to the corpus luteum or yellow body. This is now the Luteal Phase

The menstrual cycle cont’d• The corpus luteum secretes the hormone

progesterone. • Progesterone maintains the thickness of the

lining of the uterus (in case of fertilization).• Have you ever heard of ‘pregnancy hormone’? It

is progesterone. Pay keen attention as your teacher guides you

through the next slide.Answer the related questions in your SIM (pg 5)

about concentration of various hormones and endometrial thickness.

Graph showing the relationship between hormone concentration and endometrial thickness

http://images.google.com.jm/imgres?imgurl=http://8e.devbio.com/images/ch19/11.HMEM.01.thumb.jpg&imgrefurl=http://www.podnova.com/channel/174193/episode/41/&usg=__0anawtqmg5QmXU3i0IZO7CYaDrc=&h=450&w=392&sz=62&hl=en&start=2&um=1&itbs=1&tbnid=KdZPFIhFasqFTM:&tbnh=127&tbnw=111&prev=/images%3Fq%3Dgraph%2Bof%2Bmenstrual%2Bcycle%26hl%3Den%26rlz%3D1T4DMUS_enJM290JM296%26sa%3DN%26um%3D1

The menstrual cycle cont’d• Progesterone also causes the breasts to

enlarge and become tender. • It causes water retention which is

responsible for the bloating associated with periods.

• In addition, the female might experience various changes such as: cravings for specific foods, fatigue, headaches, nausea, sensitivity and she might become easily emotional.

The menstrual cycle cont’d• The uterus wall is thickened in

preparation for a possible embryo to be embedded and for pregnancy to result.

• The egg can live for just about 24 hours after ovulation.

• If no fertilization occurs, the egg dies.

The menstrual cycle cont’d

• If there is no pregnancy, the progesterone level falls and the uterus wall breaks down and passes out of the vagina as ‘a period’ or the menses, with small clumps of the endometrial lining and blood.

To Think About

Now that you have been reintroduced to the hormones that control the menstrual cycle, go back to the lessons you did already on hormones and go through them again to make sure you fully understand the many ways that hormones influence growth and development.

U 13: FertilizationTo be used with U 13 Lesson 5

• http://www.tutorvista.com/content/science/science-ii/reproduction/fertilisation.php

Objectives

On completion you should be able to:1. define and differentiate between

fertlization and implantation.2. define and differentiate between a zygote

and an embryo.3. explain how multiple births, identical and

fraternal twins are likely to occur.

Leading up to Fertilization • Perhaps you might be wondering: ‘How does

an egg become fertilized?’ • Let’s look at the natural method of

fertilization. • During sexual arousal, the penis becomes

erect. This facilitates intercourse, in which the erect penis is inserted into the vagina.

• Stimulation of the penis from rhythmic movements during intercourse causes ejaculation.

Fertilization• Ejaculation causes millions of sperms in semen

to be released into the vagina. • These swim up through the cervix and womb

and enter the fallopian tube. • Near the top they might meet/surround the

egg that was released during ovulation. • If there is an egg, one sperm enters the egg

and both haploid nuclei fuse. • A membrane is formed to prevent entry of

another sperm.

Illustration of the steps involved in fertilization.

http://images.google.com.jm/imgres?imgurl=http://www.bio.davidson.edu/Courses/Molbio/MolStudents/spring2005/Champaloux/fertilization.jpg&imgrefurl=http://www.bio.davidson.edu/Courses/Molbio/MolStudents/spring2005/Champaloux/fourth.html&usg=__qfNE_wr7Zs4viL_ERV_yKnnbtAU=&h=419&w=574&sz=19&hl=en&start=1&um=1&itbs=1&tbnid=cVGNeljSDv6rBM:&tbnh=98&tbnw=134&prev=/images%3Fq%3Dfertilization%26hl%3Den%26rlz%3D1T4DMUS_enJM290JM296%26sa%3DN%26um%3D1

Fertilization cont’d

• A zygote is formed from fertilization. What is the chromosome number of the

zygote? • Yes! The zygote is diploid. This zygote will grow into an embryo. Which

nuclear division do you think is involved?• Correct again -- mitosis.

Twins and Multiples• Sometimes more that one egg matures and

ovulates, and they may be fertilized separately. This can result in fraternal twins or fraternal multiples who can be either same sex or different-sex children.

• If the fertilized egg separates as it is undergoing its early divisions, identical twins and identical multiples could result.

Identical twins/multiples are always the same sex. Tell your teacher why this is so.

“Twincredibles”

• Go to this website to see and read about two incredible sets of twins!

http://www.thesun.co.uk/sol/homepage/news/article2082429.ece

Is each set an identical pair or not? Explain how you think each set of twins

came about!

Fertilization and Implantation

• As the zygote divides by mitosis an embryo is formed.

• As it divides, the ball of cells moves down the Fallopian tube into the uterus.

Now think back to the menstrual cycle. Describe how you would expect the endometrium to be. Give a reason for your answer.

Fertilization and implantation cont’d

• Yes…You are correct again! The endometrial wall is thickened with blood due to the action of oestrogen secreted as the follicle developed. Progesterone from the corpus luteum is also responsible.

• The embryo sinks and becomes embedded in this nice soft bed in the endometrial wall.

This is implantation. Look carefully at the next slide that show it.

Fertilization and implantation cont’d

http://images.google.com.jm/imgres?imgurl=http://www.mayoclinic.com/images/image_popup/r7_fertilization.jpg&imgrefurl=http://www.mayoclinic.com/health/medical/IM02017&usg=__qhGj4Tcts6xssrDQn_2pFfCtqCk=&h=306&w=400&sz=22&hl=en&start=3&um=1&itbs=1&tbnid=xwf4d6yuCZebSM:&tbnh=95&tbnw=124&prev=/images%3Fq%3Dfertilization%26hl%3Den%26rlz%3D1T4DMUS_enJM290JM296%26sa%3DN%26um%3D1

Summary

• Sexual reproduction is the production of offspring from two parents. It involves:

1. Meiosis - the special cell division that makes haploid gametes (eggs and sperms).

2. Ovulation – release of an egg from the ovary.3. Sexual intercourse with Ejaculation of sperms.4. Fertilisation - fusion of two haploid gametes (an

egg and a sperm) to form a diploid zygote which develops into an embryo.

5. Implantation of the embryo in the uterus.6. Pregnancy/Gestation followed by Birth.

U 13: Lesson 6 Pregnancyand Birth

.

http://www.tutorvista.com/content/science/science-ii/reproduction/fertilisation.phpPhotopraph at lower right © K.Muir 2008, with kind permission

Objectives

When you finish, you should be able to:1. describe the development of the

embryo (gestation) in humans.2. list the steps that result in birth or

parturition.

Pregnancy

• Pregnancy starts after fertilization occurs when the new embryo implants itself in the lining of the uterus wall and begins to develop.

Pregnancy cont’d• I am sure you have been associated with

pregnant persons. So, what are the changes that occur during

pregnancy? • No doubt you are thinking of: swelling of

feet… nose/face looking fat… abdomen getting larger…

But, what else happens?

Some changes during pregnancy

• Nausea and vomiting usually occur, due to the increase in progesterone levels. They are among the first changes that occur in pregnancy.

• The menses cease. • There may be lethargy/tiredness.• Breasts and abdomen begin to enlarge.• There may be mood swings and food cravings

or food rejections.

Pregnancy cont’d• Many changes also take place in the embryo! Many structures can be recognized by 6 weeks.• The foetus is attached to the placenta by the umbilical cord.

http://www.mydr.com.au/babies-pregnancy/baby-development-in-the-womb

Pregnancy changes cont’d• But what causes these changes?• Yes, hormones and in particular, the

‘pregnancy hormone’ which is progesterone. • Where does the progesterone come from? • You would remember that the corpus luteum

secretes progesterone. • However, the majority of the progesterone

secreted during pregnancy is not done by the corpus luteum.

Pregnancy changes cont’d

• After implantation, some of the dividing cells form fingerlike projections that dig into the endometrium of the uterine wall.

• These fingerlike projections along with the mother’s tissue that surrounds them form the placenta.

• The placenta performs several roles including an endocrine one; it secretes progesterone.

Pregnancy changes cont’d

• The placenta facilitates the exchange of material between the mother and foetus.

• Nutrients and oxygen diffuse from the mother to the foetus via the umbilical cord; waste from the foetus diffuses in the opposite direction.

• The placenta is also a barrier to some pathogens and harmful materials.

Pregnancy changes cont’d

• So…. back to the pregnancy changes. Can you suggest the importance of the changes

in the mother’s body that occur during pregnancy? Click CheckCheck for the answer:

• (The breasts enlarge as the mammary glands expand to facilitate milk production.

• The uterine wall actually grows new cells so that it can enlarge to hold the foetus.

continued…

Pregnancy cont’d

Note enlarged breast, abdomen and uterus, also the placenta and umbilical cord attached to foetus

http://health.howstuffworks.com/pregnancy-pictures6.htm

Pregnancy changes cont’d

• The high levels of progesterone inhibit the production of FSH and LH.

• This ensures that no more eggs are released from the ovaries, so the menses stop temporarily during pregnancy.

• The placenta continues to support the foetus throughout gestation.

• The abdomen expands to facilitate the growth of the foetus.)

Pregnancy cont’dhttp://www.mydr.com.au/babies-pregnancy/baby-s-development-in-the-womb

What is the function of amniotic fluid?

Pregnancy cont’d

• Pregnancy normally ends with labour and birth.• The foetus changes its position so that during birth the head will emerge first (in normal births!).

http://www.mydr.com.au/babies-pregnancy/baby-development-in-the-womb

What ‘triggers’ Birth?

• Have you ever wondered what causes a woman to go into labour? Hormones again??

• Yes, the onset of birth is controlled by a hormone.

• When the foetus is large and it becomes uncomfortable to remain in such a small space (usually at 40 weeks), the foetus pushes against the uterus.

What ‘triggers’ Birth?

• Stretch receptors in the uterine wall start to send signals to the brain (pituitary gland).

• The pituitary stimulates the secretion of the hormone oxytocin.

• The hormone stimulates the muscles of the uterus to contract even further.

Birth cont’d

• So, the stimulus is enhanced and the receptors in the distorted uterus continue to send signals to the brain, and it continues to stimulate the secretion of even more oxytocin.

• This positive feedback loop is what sustains contractions during labour.

Birth cont’d

• The cervix and vaginadilate and as the uterinemuscles continue to contract, the baby ispushed out, normally,head first.

Note the umbilical cord still attached to the new-born baby

http://www.medicinenet.com/stages_of_pregnancy_pictures_slideshow/article.htm

Summary of Birth• The signal that birth is imminent is that uterine contractions start, the amniotic sac or

‘the water-bag’ bursts and the amniotic fluid runs out as the ‘show of water’.

• Then the following stages of birth occur:1. Dilation of the cervix and birth canal.2. Delivery of the baby with its umbilical cord.3. Cutting the umbilical cord.4. Extrusion of the placenta as the ‘after-birth’.

After Birth • After the baby is delivered, the placenta is

useless, so, it also is expelled by uterine contractions. If not, it can cause complica-tions that can lead to death of the mother.

• Oxytocin causes milk to be secreted from the breasts especially under stimulation from sucking by the baby.

• The vagina and uterus gradually contract.• The menstrual cycle will start again later.

Parental Care Oxytocin is believed to help create a bond

between mother and baby. Parental care activities that follow the birth of a child are very important. They involve both parents:

• feeding the baby with (breast) milk;• carrying, cleaning and taking care of the baby

until s/he is able to do those things;• imparting knowledge and teaching skills to

enable the baby to grow and develop into the human being that can function normally on its own.

Awesome tasks!!

Basic life cycle of humans

http://www.nclark.net/Biology

Websites to visit

• http://www.healthline.com/vpvideo/stages-of-labor

• http://www.healthline.com/vpvideo/normal-birth