1
Q
sexual intercourse
A
- for fertilisation occur, male spermatids needs to be brought into contact with an ovum through the method of sexual intercourse
- when the male ejaculates, the sperm are released in the vagina at the entrance to the uterus - a process called insemination
- once inside the vagina, the sperm travel through the cervix and the body of the uterus into the fallopian tubes
2
Q
sperm mortality
A
- hundreds of millions of sperm are deposited into the vagina during sexual intercourse but only a few thousand reach the fallopian tubes
- the death rate of sperm is called - sperm mortality
3
Q
fertilisation
A
- the sperm mortality is high and is one reason why a large number of sperm are required for fertilisation to occur
- is the fusion of gametes (ova and sperm) to form on diploid cell, the zygotes
- it occurs in the fallopian tubes
4
Q
two layers of the secondary oocyte
A
- the outer corona radiata
- the inner zona pellucida
5
Q
zona pellucida
A
the inner zona pellucida is a glycoprotein matrix surrounding the plasma membrane of the oocyte
6
Q
corona radiata
A
the outer corona radiata consists of follicle cells held together by cementing materials that contain acid
- at fertilisation the spermatids break through the barrier of cells to reach the zona pellucida
- once the sperm has made it through the corona radiata it encounters the zona pellucida
7
Q
acrosomal reaction
A
- the acrosome, located in the head of the sperm, contains a digestive enzyme (protease)
- contact with the zona pellucida initiates the acrosomal reaction, where digestive enzymes from the acrosome are released
- the enzymes break down the glycoprotein matrix of the zona pellucida
8
Q
what happens during fertilisation?
A
- this reaction allows the sperm’s cell membrane to fuse with the oocyte’s cell membrane
- the nucleus of the sperm enters the ovum
- the entrance of one sperm into the secondary oocyte stimulates the formation of a fertilisation membrane around the oocyte
- this prevents the entrance of any more sperm ensuring only one haploid set of chromosomes join the chromosomes of the oocyte
- once the sperm has entered the oocyte, the tail is absorbed and the nucleus begins to move through the cytoplasm in the form of a male pronucleus
- the entrance of the sperm stimulates the secondary oocyte to complete the second meiotic division
- the nucleus of the oocyte develops into a female pronucleus (haploid)
9
Q
zygote
A
- the female pronucleus and the male pronucleus fuse to form a single diploid nucleus
- fertilisation is complete and the fertilised oocyte is now called a zygote
- after fertilisation the zygote starts to travel down the fallopian tube
- within 24 hours of fertilisation, the zygote begins dividing by mitosis
10
Q
zygote to foetus
A
zygote -> blastula -> embryo -> foetus
11
Q
blastocyst
A
six days after fertilisation
- the original zygote has developed into a blastocyst by mitosis and reached the uterus
- blastocyst - hollow ball of cells surrounding a fluid filled cavity
- contains an inner cell mass
- outer layer of cells will eventually from the placenta
- the inner cell mass will form all of the tissues of the human body
12
Q
implantation
A
- occurs around day 8-10 (end of the first week after fertilisation)
- the blastocyst will then sink into the endometrium to become firmly attached to the wall of the uterus
- this process is called implantation
- the purpose for implantation is to gain nourishment for growth and development by absorbing nutrients from the glands and blood vessels of the endometrium
13
Q
cell differentiation
A
- the inner cell mass located in the blastocyst is composed of stem cells
- these stem cells will differentiate into out different body cells to form the embryo
- these embryonic stem cells are pluripotent meaning they give rise to many but not all cell types necessary for foetal development
- can specialise into foetal tissue
14
Q
embryonic stage
A
- weeks 3-9
- whilst the blastocyst is implanting into the lining of the uterus, the inner cell mass differentiates to form 3 primary germ layers
- ectoderm - the outermost layer, hair, nails, skin, nervous system
- mesoderm - middle layer, circulatory system, lungs (epithelial layer), skeletal system, muscular system
- endoderm - the inner most layer, digestive system, liver, pancreas, lungs (inner layers)
15
Q
foetus
A
after the second month the embryonic stage will end and the developing embryo is now called a foetus (8-40 weeks - fetal growth)
16
Q
embyronic membranes
A
- during the embryonic period, four embryonic membranes form
1. amnion
2. chorion
3. yolk sac
4. allantois
17
Q
amnion
A
- these lie outside the embryo and serve to protect and nourish it as it develops
- first membrane to develop
- surrounds the embryo and encloses the cavity unto which it secretes amniotic fluid
- the amniotic fluid protects the embryo by acting as a shock absorber
- also helps to maintain a constant temperature and allows the foetus to move freely - developing joint and muscle movement
- ruptures just before childbirth expelling the amniotic fluid - “breaking of waters”
18
Q
chorion
A
- formed from the outer cells of the blastocyst
- surrounds the embryo and the other three embryonic membranes
- the chorion will eventually become the main part of the foetal portion of the placenta
19
Q
yolk sac and allantois
A
form the outer structures of the umbilical cord
20
Q
development of placenta
A
- the placenta is an organ that forms from both foetal and maternal tissues
- the endometrial tissue and chorionic villi become interlocked and form the placenta
- develops during the first three months of gestation
- the foetal portion develops from part of the chorion
- completely formed by the end of the third month
21
Q
role of placenta
A
- supply nutrients to and remove wastes from the foetus
- serves as an endocrine organ producing hormones to maintain pregnancy
22
Q
mother’s flood - foetus’ blood
A
- when the blastocyst has implanted into the endometrium, chorionic villi, (developed from the chorion membrane) grow into the endometrium they become surrounded by pools of the mother’s blood
- the villi are bathed in the mothers blood
- the chorionic villi contain numerous blood vessels
- the exchange of materials (oxygen and nutrients) from the mother’s blood to the foetus’ blood occurs through diffusion and active transport
- waste and Co2 go from foetus blood to mothers blood
23
Q
umbilical cord
A
- the placenta is attached to the foetus by the umbilical cord
- inside the umbilical cord are two umbilical arteries that carry blood to the capillaries if the chorionic villi
- a single umbilical vein carries blood from the chorionic villi back to the foetus
- on the maternal side, blood from the mother enters the placenta through the uterine arteries, flows through the blood pools where the exchange of substances occur
- blood leaves through the uterine veins
24
Q
gestation
A
the time that the embryo or foetus is carried in the uterus is called gestation
25
how long is the gestation period?
the gestation period in humans is around 280 days or 40 weeks
26
premature baby
a premature baby is delivered before 37 weeks
27
embryo to foetus
weeks 4 to 8
28
week 4 of embryonic stage
- after 1 month of growth embryo is 4mm long
- most obvious feature - development of muscle segments either side of tube that will become brain and spinal cord
- brain heart and liver begins to form, tail is evident
- embryo’s tiny heart begins to beat by day 21
29
weeks 5-6 of embryonic stage
- arm and leg buds are visible and the formation of the eyes, lips and nose has begin
- neural tube closes
- if the neural tube doesn’t successfully close then the baby will be born with spina bifida
30
week 7 of embryonic stage
- major organs have all begun to form
- the embryo developed its own blood
- hair follicles and knees and elbows are visible
- facial features are also observable
- major muscle system is developed and the embryo is able to move
31
week 8 of embryonic stage
- recognisable human form
- all organs are present but not all functional
- 3cm in length and weighs 1g
- hands, fingers and toes are formed
- external sexual organs are evident
- at the end of wk8 the embryonic period is over and the foetal stage begins
32
foetal development period
weeks 9 to birth
33
fourth month (16th week)
- uterus expands, the woman’s abdomen begins to bulge
- the foetus grows rapidly during month to about 18 cm long
- posture is more erect, fingerprints appear
- foetus starts to move stretching its arms and legs
34
Fifth month (20th week)
- the foetus is about 25cm longs and weighs about 300g
- foetal moving such as kicking and turning can be feeling clearly by the mother
35
Month 6 and 7 (week 24-28)
- mother is showing obvious signs of pregnancy
- by the end of week 28m the foetus is about 38cm in length
- the brain has enlarged considerably
36
Month 8-10 (week 32 to 40)
- the foetus continues to grown in length and weight
- the circulatory system is fully developed and ready for birth
- by week 40 the pregnancy is at full term
- the foetus occupies all the space in the uterus
- 50cm in length
37
before birth
- shortly before birth, the foetus changes its position in the uterus and lies with its head resting inside the curved shape of the pelvis
- antibodies from the mother will diffuse across the placenta into the baby’s blood
- this will give the newborn child temporary immunity against diseases to which the mother is immune
38
Maintaining a healthy pregnancy
- mothers must take care of their own body so that her developing child will have the best chance for a healthy life
- ensures a developing child will be born healthy
- women wishing to become pregnant can make lifestyle choices that will reduce the risk of damage to the baby
39
Supplying the foetus’ requirements
- during foetal development, large amounts of oxygen and nutrients are needed
- adjustments must be made to the women’s body to adapt to this
- functions slow down - nutrients stay in the blood for longer periods of time
- this leads to constipation (alimentary canal is less active, her stomach empties slower)
- increase in blood volume and faster rate of circulation - to meet the large quantity of blood that needs to flow through the placenta
40
Diet
- increase in energy intake
- increase protein intake
- folic acid - essential for normal cell division and preventing neural tube defects
- adequate calcium - bone growth, teeth, heart, nerve and muscle development
- steady intake of vitamin A - normal growth of cells
- avoid foods like pre-packed salads, soft cheeses, raw or smoked seafoods, cured meats to prevent listeria infection
41
exercise
pregnant women that have a good exercise program:
- are more likely to carry their babies to full term
- better able to maintain their stamina during labour
- regain their pre-pregnancy health and fitness after birth
42
Exposure to Teratogens
- teratogenic agent: causes physical defects in the developing embryo
- effects of teratogens vary significantly and depend on the substance dose and stage of development
43
examples of teratogens
- alcohol
- smoking
- chemicals
- other drugs
- rubella
44
alcohol effect on embryo
- foetal alcohol spectrum disorders (FASD) is a term used to describe the group of conditions and effects of foetal exposure to alcohol
- lower than normal birth weight
- slow growth before and after birth
- small head
- irregularities of the face - narrow eyes, sunken nasal bridges
- heart defect
- malformed arms and legs
- intellectual disabilities
- behavioural problems: hyperactivity, extreme nervousness, poor attention spam
45
smoking effect on embryo
- lower birth weight
- increased risk of miscarriage
- higher incidence of respiratory problems like bronchitis and pneumonia during the first year of life
- strong association between smoking during pregnancy and sudden infant death syndrome (SIDS)
46
chemicals effect on embyro
- thalidomide - originally used in sleeping peels and was effective in preventing morning sickness
- two years after it went on sale in 1958 there was a sharp rise in the incidence of rare limb malformations - led to the discovery of thalidomide as a teratogenic agent
47
other drugs effect on embyro
illegal drugs such as heroin and LSD can cause damage to the foetus when that during pregnancy
48
rubella effects on embryo
- viral infection, a fairly mild disease that is highly infectious
- if contracted by a pregnant woman, it can have disastrous consequences
- child may be born deaf, blind or with heart malfunctions
- vaccines recommended in the National Immunisation Program Schedule for children is MMR - measles, mumps and rubella
49
stages of labour
- First Stage of a labour - Dilation of the Cervix
- Second stage of labour - birth of the baby
- Third Stage of Labour - delivery of placenta/afterbirth
50
parturition
- parturition: process by which foetus is expelled from the mothers body at the end of gestation
- parturition is followed by a sequence of events known as labour
51
Birth Process Prior to Labour
- hormonal changes - cause the ligaments of the pelvis to soften and strength the contraction of uterine muscles
- before labour begins the foetus has settled with its head in the mother’s pelvis
- cervix has softened, shortened in length and has begun to open a little
- it is common for the mother to experience ‘false labour’ or Braxton Hicks contractions, in the last weeks of pregnancy as the uterus ‘practices’ contracting and relaxing in preparation for actual labour
52
First Stage of a labour - Dilation of the Cervix
- waves of contraction travel from the upper part of the uterus downward towards the cervix
- as contractions become more frequent and stronger, the head of the foetus is pushed more forcefully against the slowly dilating
- when the cervix completing dilated (10cm) the uterus, cervix and vagina form the birth canal
- the first stage of labour lasts until the complete dilation of the cervix
53
Second stage of labour - birth of the baby
- the delivery of the foetus - the stage of expulsion
- begins with the bursting of amniotic sac and a gust of amniotic fluid from the vagina
- as the foetus moves through the dilated cervix, its head stretches the vagina
- the distension of the vagina stimulates the women to contract her abdominal muscles
- abdominal contractions and uterine contractions push the foetus through the vagina
- the baby’s head turns to face the mothers back
- with each contraction the head advances a small amount
- once the head has emerged it turns sideways again to face the mother’s hip, the rotation allows the shoulders and the rest of the body to move more easily through the birth canal
54
Third Stage of Labour - delivery of placenta/afterbirth
- once the baby is born it begins to breathe with its own lungs
- the amnion, chorion and placenta are still inside the uterus at this stage
- the umbilical cord is clamped and cut
- the uterus continues to contract and about 5 minutes after delivery the other membranes are expelled - afterbirth
55
what structures allow for the dependency of
- during pregnancy, the foetus is totally dependant in the mother for all its needs, and there are certain structures (ductus arteriosus, foramen ovale, ductus venosus)in the baby’s circulatory system that cater for this
- at birth the infant must be self supporting, so for the baby to meet it’s own needs, these structures subside
56
Before Birth: Ductus venosus
- foetal blood is carried to and from the placenta by blood vessels in the umbilical cord
- when blood flow returns to the foetus, some of the flood flows through the liver into the interior vena cava
- the remainder bypasses the liver by flowing through a vessel called the ductus venosus
- the fact that much of the blood does not pass through the liver causes no problems at this stage as the mother’s liver is serving the foetus’ needs
57
before Birth: ductus arteriosus and foramen ovale
- blood returning to the foetal heart enters the right atrium, from there it can follow several pathways
1. blood flows into the right ventricles and then the lungs like normal - although little blood (due to resistance, deflated) reaches the lungs as the lungs are collapsed and not functioning
2. blood flows into the right ventricle and through the ductus arteriosus to the aorta. the ductus arteriosus is a vessel that bypasses the lung, allowing the blood from the pulmonary artery to flow directly into the aorta.
- foramen ovale
1. blood in the right atrium may flow directly in the left atrium through an oval opening between the two chambers called the foramen ovale. most of the blood entering the right atrium travel through it
58
changes at birth
- at birth, the lungs and liver must become fully functional and for this to occur blood must flow through them
- this means the ductus venosus, ductus arteriosus and foramen ovale close
- as the baby takes its first breath, the lungs expand and they no longer resist blood flow - blood flow through the ductus arteriosus decreases
- this causes the ductus arteriosus to shrink and close on its own
- as larger amounts of blood return to the heart from the lungs, the pressure in the left atrium increases
- this increases pressure forces the flap of the foramen ovale to be forced closed
- eventually tissue will seal the opening and it will become permanently closed
- with the cutting of the umbilical core, blood no longer flows through the umbilical vessels or the ductus venosus
- as no blood is being carried through it the ductus venosus gradually constricts until it is permanently closed off, the liver bypass is lost, and all blood must now pass the liver
Human Biology Y11
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