Sexual Reproduction in the Human

Pregnancy, Birth & Breastfeeding

Learning Objectives

• Explain copulation• State the location of fertilisation• Explain implantation, placenta formation &

function• Outline the birth process• Explain In-vitro fertilisation & implantation• Outline milk production & breastfeeding

including biological benefits

Copulation – Sexual intercourse

• Sexual arousal– The penis becomes erect– The vagina becomes lubricated

• Copulation– The penis is inserted into and moved inside the

vagina

• Orgasm– Sperm is released from the penis (Ejaculation)– Contraction of vagina and uterus

Insemination

• Insemination is the release of sperm into the female

• Contractions of uterus and fallopian tubes move the sperm to the fallopian tubes within 5 minutes

• If an egg is present it releases chemicals to attract the sperm this is called chemotaxis

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Fertilisation

Fertilisation is the fusion of the egg and sperm nuclei to form a diploid zygote.

Fertilisation

Fertilisation usually occurs in the fallopian

tube.

Fertilisation is complete when the ovule has

been fertilised

Fertilisation

A number of sperm may reach the egg at the same time.

The acrosome releases enzymes to digest the egg membrane

The sperm loses its tail and the head enters the egg.

The sperm and egg nuclei fuse to form a zygoteA chemical reaction at the membrane prevents other sperm

cells entering.

ImplantationImplantation is the embedding of the fertilised egg

into the lining of the uterus

• This occurs 6 - 9 days after fertilisation.

• By this time the zygote has grown into an embryo.

• After implantation the placenta forms.

• During implantation a membrane called the amnion develops around the embryo. This secretes amniotic fluid which will surround the developing embryo and act as a shock absorber.

Implantation is the embedding of the fertilised egg into the lining of the uterus

Zygote

Implanted embryo

Human Pregnancy

• Zygote divides by mitosis to form a morula.• The morula moves down the fallopian tube and

implants in the uterus• Morula: Solid ball of cells• It develops into a blastocyst• Blastocyst: Fluid-filled ball of cells

Human Pregnancy

(HL)

• Blastocyst consists of – Trophoblast (will develop into placenta)– Embryo cells (will develop into embryo)

• Blastocyst imbeds itself into uterus lining (endometrium)

Placenta Formation

• After implantation the embryo forms an outer membrane called a chorion

• This chorion develops projections (chorionic villi) which, together with the blood vessels of the mother in the endometrium, form the placenta

Placenta

• Functions:– It is an organ that allows exchange of materials

between the foetus and mother – It produces hormones such progesterone– Allows passage of food and oxygen – Allows passage of antibodies – Removes waste produced by embryo

Placenta

• It is formed from tissues of the mother and the embryo (uterine tissue and embryonic

tissue)

Placenta Formation

• The blood of the mother and embryo do not mix • This is important as:– The blood groups of mother and baby might not be compatible.– The blood pressure of the mothers system may cause damage

to the embryo

Placenta Formation

• The umbilical cord connects the placenta with the embryo. It contains blood vessels which circulate blood between the embryo and the placenta

Amnion

• It is a sac or membrane • It produces fluid and protects embryo by

acting as a shock absorber

PlacentaMother’s blood

Embryo’s blood

Chorion Embryo

AmnionAmniotic fluid

Umbilical cord

Embryo

Mother

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The Placenta

Learning Check1.

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Development of Embryo (HL)

• Blastocysts organise themselves into germ layer. • Germ Layers are a layer of cells in the embryo

with the potential to give rise to specific tissues • 3 types of layers:1.ectoderm – skin and nervous system 2.mesoderm – muscles skeleton3. endoderm – inner lining of liver and lungs

Development of Embryo (HL)

• 3 weeks: Developed nervous system, alimentary canal, circulation. Heart beats.

• 8 weeks: Embryo is recognisable. Now called foetus• 12 weeks: Swallows, inhales. Arms, legs move. Sex

organs identified.• 3-9 months: Continue to grow and develop

Birth1 The hormones oestrogen and progesterone

are produced throughout pregnancy firstly by the corpus luteum (3 months) and then by the placenta. The placenta acts as an endocrine gland.

2 Immediately before birth the placenta stops making progesterone. The walls of the uterus begin to contract as a result.

3 The pituitary gland releases the hormone called oxytocin. This causes further contractions of the uterus. (HL)Labour has now begun.

There are three main stages:Stage 1 - (about 12 hours)

The contraction of the uterus pushes the foetus towards the cervix. This causes the cervix to open (dilate). During this stage the contractions cause the amnion to break releasing the amniotic fluid through the vagina. (The ‘water’s break’).

Stage 2 - (20 minutes to 1 hour)

The foetus passes through the cervix and the birth canal head first.

Stage 2 - (20 minutes to 1 hour)

The foetus passes through the cervix and the birth canal head first.

Stage 2 - (20 minutes to 1 hour)

The foetus passes through the cervix and the birth canal head first.

Stage 2 - (20 minutes to 1 hour)

The foetus passes through the cervix and the birth canal head first.

Stage 2 - (20 minutes to 1 hour)

The foetus passes through the cervix and the birth canal head first.

Stage 2 - (20 minutes to 1 hour)

The foetus passes through the cervix and the birth canal head first.

The umbilical cord is tied and cut. This leaves a scar which will eventually become the navel (belly button).

Stage 3 - (10 to 15 minutes)

The baby is now born.

The uterus now contracts again and expels the afterbirth (the umbilical cord and placenta).

Stage 3 - (10 to 15 minutes)

The baby is now born.

The uterus now contracts again and expels the afterbirth (the umbilical cord and placenta).

Stage 3 - (10 to 15 minutes)

The baby is now born.

The uterus now contracts again and expels the afterbirth (the umbilical cord and placenta).

Stage 3 - (10 to 15 minutes)

The baby is now born.

The uterus now contracts again and expels the afterbirth (the umbilical cord and placenta).

Umbilical cord is cut

Breastfeeding

Lactation: secretion of milk by the mammary

glands• The secretion of milk

from the mammary glands

• The first days after birth colostrum produced

• Milk production triggered by release of prolactin by pituitary (HL)

BreastfeedingBreastfeeding is better than bottle feeding because:

• Colostrum and breast milk provides the baby with essential antibodies protecting it against infection

• Ideal balance of nutrients for baby• Bonding between mother and baby• Reduces chances of breast cancer in the mother

Learning Check1. What is fertilisation and where does it occur2. When is fertilisation complete3. What is implantation4. 4. What is a Morula &Blastocyst5. 5. List 3 functions of the placenta6. 6. What tissues is the placenta formed from7. 7.What is amnion and its function8. List and explain the 3 stages of birth9. List 3 benefits of breastfeeding

Can you….

• Explain copulation• State the location of fertilisation• Explain implantation, placenta formation &

function• Outline the birth process• Explain In-vitro fertilisation & implantation• Outline milk production & breastfeeding

including biological benefits