Transcript 26.2 Human Reproduction 2

Human Reproduction 2
Contents
Copulation, Fertilisation, Conception
The Human Pregnancy
Birth or Parturition
Lactation, Breastfeeding
Development of embryo up to 3rd month
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Copulation, Fertilisation &
Conception - Contents
Copulation
Flaccid and erect penis
Copulation or intercourse
– diagram
Copulation or intercourse
– diagram
What happens next?
Sperm structure
How fertilisation occurs
Egg and sperm just before
fertilisation – diagram
Viability of sperm and egg
Conception
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Copulation ???
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Copulation
(1/2)
Is sexual intercourse or making love.
Sexual arousal in the male causes the penis to
become stiff and erect (= an erection).
Caused by blood entering the blood spaces of the
penis faster than it can leave.
In the female arousal causes the erection of the
clitoris and secretion of mucus by the wall of the
vagina.
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Flaccid and erect penis
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Erections and Size Differences
The penis hangs down, but during sexual arousal it
becomes larger and points outwards and
upwards, designed to deposit sperm in the
vagina.
Penises vary in size; size has nothing to do with
masculinity, sexual performance or pleasure.
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Copulation
(2/2)
The erect penis enters the vagina. Rhythmic
movements of the penis cause semen to be
ejaculated into the vagina near the cervix.
The pleasurable experience felt during ejaculation
is called an orgasm.
Stimulation of the clitoris may also produce an
orgasm in the female.
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Copulation or intercourse
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Copulation or intercourse
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What happens next?
The sperm swim through the cervix, into the uterus
and up into the oviducts.
Numerous sperm surround the egg and try to
penetrate it.
Of the millions of sperm (approx. 400,000,000) that
are ejaculated only a few hundred will reach the
oviducts and only one will fertilise the egg.
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A reminder of sperm structure
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How fertilisation occurs
The acrosome of the sperm cell releases enzymes
that break down the outer jelly coat of the egg.
The head of the sperm cell (containing the nucleus)
enters the egg and the membrane of the egg cell
changes and prevents the entry of any other sperm.
Fertilisation occurs when the sperm nucleus (n) and
the egg nucleus (n) fuse to form a diploid zygote
(2n) i.e. the chromosomes of the sperm and egg
unite.
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Egg and sperm just before
fertilisation
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Viability of sperm and egg
Sperm: are capable of surviving and fertilising an
egg for approx. 48 hours after release into the
female body.
Egg: fertile for 24 – 48 hours.
In a 28 day menstrual cycle if intercourse occurs
between days 12 and 16 fertilisation of the egg is
possible.
fertile period = period of time in the menstrual
cycle when the egg can be fertilised.
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Conception
Fertilisation followed by pregnancy are together
refered to as conception.
After fertilisation the zygote begins to divide to form
the embryo.
It is carried down the oviduct to the uterus (takes
approx. seven days).
Embryo becomes implanted in the endometrium –
(about 14 days after fertilisation) – pregnancy is
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established.
The Human Pregnancy - Contents
Length of human
pregnancy
Gestation period – diagram
Gestation periods of some
mammals
After implantation
Foetus surrounded by
amniotic fluid
The Placenta
Placenta and foetus –
diagram
Placenta – diagram
Functions of the Placenta
Healthy Pregnancy
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Length of Human Pregnancy
Duration = 40 weeks i.e. baby will be born 40
weeks after the start of the woman’s last
menstrual period.
gestation period: length of time from conception
to birth.
This varies for different mammals.
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For clarification – gestation period
266 days after conception
280 days = 40 weeks from last period
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Birth
Menstrual cycle
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Gestation periods of some
mammals
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After Implantation
After implantation embryo cells divide and become
specialised forming all necessary tissues and organs.
After eight weeks the embryo looks human and is
known as the foetus.
Foetus is surrounded by a membrane = the amnion.
This encloses the amniotic cavity which contains
amniotic fluid.
Foetus floats in this fluid and is protected and
cushioned by it.
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Foetus surrounded by the
amnionic fluid
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The Placenta
placenta: structure attached to the inner surface of
the uterus of pregnant mammals, formed from
tissues of both the embryo and the mother
(endometrium) which helps to nourish the foetus,
and discharges its waste.
In the placenta the blood supplies of mother and
embryo never mix.
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Placenta and foetus
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Placenta
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Functions of the Placenta
(1/2)
1. Exchange of materials
Diffusion of food, oxygen,minerals, antibodies and
waste products takes place in the placenta from
one bloodstream to the other.
Drugs, viruses and chemicals in cigarette smoke
can also pass into the foetus.
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Functions of the Placenta
(2/2)
2. Acts as a barrier
Against blood pressure of mother – may be too
great for foetus
Protects foetus from mother’s immune system –
may reject the foetus as foreign.
3. Endocrine gland
Secretes progesterone and oestrogen – maintain
endometrium and prepare breasts for lactation
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Healthy Pregnancy
1. Cigarette smoking increases the risk of babies
being born underweight.
2. Taking drugs and heavy drinking can damage
the foetus.
3. Eating a healthy diet before and during
pregnancy greatly improves the healthy
development of the foetus.
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Birth or Parturition - Contents
Labour – Stage 1
Labour – Stage 1 –
diagram
Labour – Stage 2
Labour – Stage 2 –
diagram
Labour – Stage 3
Labour – Stage 3 –
diagram
Birth – diagram
The role of hormones in
the birth process
The role of oxytocin in
the birth process
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Labour – Stage 1
LABOUR - divided into three stages, which get
shorter with each successive pregnancy.
Stage 1 (6 – 18 hours)
Contractions begin and increase in frequency and
intensity – cervix dilates – birth canal widens –
amnion ruptures = breaking of the waters.
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Labour
– Stage 1
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Labour – Stage 2
Stage 2 (20 – 60 minutes)
Baby is born - mother has to 'push' - baby's head
appears (most difficult part now over) then
shoulders one at a time and finally rest of body.
Baby still attached to mother by umbilical cord and
placenta.
Baby cries with first breath and umbilical is cord cut
when it stops pulsating.
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Labour
– Stage 2
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Labour – Stage 3
Stage 3 (5 – 10 minutes)
Delivery of placenta, membranes that surrounded
the foetus and the remains of the umbilical cord
(= afterbirth)
After childbirth
Endometrium is repaired and uterus returns to
normal size.
Menstruation commences again in about 6 – 8
weeks (if not breastfeeding)
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Labour
– Stage 3
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Birth
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The role of hormones in the birth
process
At birth the levels of oestrogen and progesterone
fall
– uterine wall begins to contract
– stimulates the production from pituitary of
Oxytocin – stimulates uterine contraction and
allow the baby to be born
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The role of oxytocin in
the birth process
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Lactation & Breastfeeding Contents
Lactation
Breastfeeding
Benefits of breastfeeding
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Lactation
Breastmilk is the only food a baby needs for the
first few months of life.
After placenta is expelled levels of oestrogen and
progesterone drop rapidly - stimulate pituitary to
produce
Prolactin - initiates - lactation
- inhibits - FSH production
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Breastfeeding
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Breastfeeding
(1/2)
Newborn baby will suck on the nipple of the breast.
This causes milk to be released and more milk to
be made.
Milk produced for the first 3 – 4 days is colostrum –
high in proteins and antibodies – makes baby
immune to certain diseases and allergies.
After this time the milk produced contains all the
protein, fat, sugars, vitamins and minerals the
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baby needs for the first few months of life.
Breastfeeding
(2/2)
The mother needs a healthy diet and sufficient rest
to ensure a plentiful supply of milk.
If the mother chooses not to breastfeed; then her
breasts stop making milk and return to their
normal size within a few days.
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Benefits of Breastfeeding
(1/2)
1. gives a baby all the nutrients it needs in exactly
the right proportions for optimum development.
2. is a source of antibodies which are passed on
to the baby and protect it against allergies and
illness
3. is always at the correct temperature.
4. encourages bonding between mother and
baby, and develops in the mother a high
degree of sensitivity to her baby and produces
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feelings of calm and helps a mother relax.
Benefits of Breastfeeding
(2/2)
5. helps get back into shape after the pregnancy
i.e. helps get her figure back and the womb
returns to its original shape and position
quicker.
6. breastfeeding can cause a cessation of
menstruation.
Note: See Breastfeeding Slide Presentation for
more information
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Development of embryo up to the
rd
3 month - Contents
Zygote  Morula 
Blastocyst
Trophoblast  Embryo
Zygote to blastocyst –
diagram
Events from ovulation to
implantation – diagram
Implantation
Implantation – diagram
Development of embryo –
germ layers
Calendar of events after
fertilisation
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Zygote  Morula  Blastocyst
After fertilisation the zygote begins to divide by
mitosis.
This forms a solid ball of 32 cells = the morula –
moves into uterus – continues to divide – forms a
hollow ball of several hundred cells = the
blastocyst, which is made of two types of cell:
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Trophoblast  Embryo
• an outer layer of cells - the trophoblast - will
become the placenta and other membranes
(chorion and amnion) which surround and
protect the developing embryo. The placenta is
formed partly from the tissues of the embryo and
partly from the uterus wall.
• a clump of cells inside will develop into the
embryo.
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Zygote to blastocyst
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The sequence of events from
ovulation to implantation
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Implantation
When the blastocyst reaches the uterus (about
seven days after fertilisation) it sinks into the
endometrium - this is implantation.
The trophoblastic layer forms villi, which embed in
the endometrium and absorb nutrients for the
embryo cells – placenta takes on this nutritive
role later.
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Implantation
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Development of embryo – germ
layers
The cells in the blastocyst organise themselves
into the three primary germ layers (ectoderm,
mesoderm, and endoderm).
Each germ layer forms different parts of the body.
Ectoderm – skin, nails, hair, brain & spinal cord.
Mesoderm – muscles, skeleton, reproductive
organs, kidneys, blood & blood vessels.
Endoderm – lining of alimentary canal, lungs, liver.
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Calendar of events after
fertilisation
(1/5)
24 hours – zygote divides to form two cells
3 days – morula reaches uterus
7 days – implantation of blastocyst
1.5 weeks – notocord is formed; blood cells
forming
3.5 weeks – CNS develops; heart forms and
beats; blood vessels form
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1.5 days after fertilisation
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2 days after fertilisation
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3 days after fertilisation
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1 week after fertilisation
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The embryo at four weeks
4 weeks – arm and leg
buds appear; primitive
digestive, nervous
and circulatory
systems in operation;
1.5 cm long.
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Calendar of events after
fertillisation
(2/5)
5 weeks – internal organs form – liver, kidney, lungs,
sex organs.
6 weeks- eyes visible; nose and ears form; limbs
grow rapidly.
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The embryo at six weeks
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Calendar of events after
fertillisation
(3/5)
8 weeks - all organs present in miniature – muscle
and bones develop; now called a foetus; 2.5 cm
long.
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The embryo at nine weeks.
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The embryo at ten weeks
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Calendar of events after
fertillisation
(4/5)
12 weeks – can swallow, inhale & exhale;
urinates and defecates;
eyes are low and widely spaced;
bone tissue appears – cartilage is replaced by harder
tissue;
nerves and muscles coordinated – arms and legs move;
sex of child can be determined;
sucks its thumb;
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teeth begin to grow; 7.0 cm long.
Calendar of events after
fertillisation
(5/5)
Continues to grow and develop over the next six
months until it is ready to be born.
Newborn baby:
Average weight = 3.4 kg
Average length = 51 cm
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END
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