Higher Human Biology Unit 2 The continuation of
Higher Human Biology Unit 2: The continuation of life Chapter 17: Pre-natal Development We will look how the embryo develops inside the uterus (intra-uterine development) and the effects that the uterine environment can have on this development. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 1
What you need to know: The arrangements. Development Pre-natal development of the individual: • Intra-uterine development • Cleavage, implantation and differentiation. • Monozygotic and dizygotic twins. • Exchanges between maternal and foetal circulations, including transfer of harmful substances and pathogens. (exchange with the maternal circulation should include movement of gases by diffusion, of glucose by active transport and of antibodies by pinocytosis). • Influence of the placental hormones progesterone, oestrogen and of prolactin. • Effects of the foetus on the maternal immune system, as illustrated by Rhesus problems and their solution (The relationship between the maternal immune system and the fetus should be considered from the point of view that the system. Mrs does not normally reject the ‘foreign’ fetus). 2 2/4/2022 Smith Ch 17 Pre-natal Development
Learning Intentions Understanding how the embryo develops inside the uterus and effects that the uterine environment can have on this development 2/4/2022 Success Criteria 1. Explain what happens to the zygote as it travels towards the uterus. 2. State that implantation occurs within one week of entering the uterus. 3. Define the term differentiation. 4. Discuss the function of the placenta and the effects of harmful substances which can pass across it. 5. Compare and contrast Monozygotic and Dizygotic twins. Mrs Smith Ch 17 Pre-natal Development 3
More new words for you! Amnion Anti-D antibodies Chorion Cleavage Dizygotic Embryonic area Endometrium Fetal Foetus Gestation Immunoglobulins Villi 2/4/2022 Lactation Mammary glands Maternal Monozygotic Oestrogen Placenta Progesterone Prolactin Rhesus-D Antigen Sensitised Thalidomide 4
Video on fertilisation • http: //www. bbc. co. uk/learningzone/clips/hu man-fertilisation/12227. html 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 5
Development After fertilisation, the zygote develops into the embryo and then into a foetus, inside the uterus. • This is divided into 3 stages: – 1. Cleavage – 2. Implantation – 3. Differentiation 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 6
1. Cleavage – to split • 36 hours after fertilisation the zygote is carried along the oviduct towards the uterus. • As it does so it starts to divide by mitosis, in doing this it becomes an embryo. • The first few mitotic divisions are known as cleavage because the cells divide in two but do not increase in size between successive divisions. • As the number of cells doubles at each division a solid ball of identical cells is produced. • This then develops into a hollow ball of cells (caused by the cells from the centre migrating to the outer areas) with a fluid-filled interior. 2/4/2022 7 Mrs Smith Ch 17 Pre-natal Development
1. Cleavage – to split 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 8
Watch this http: //www. youtube. com/watch? v=Bsa. Eqwfo. CB 0&feature=related 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 9
Blastocyst – (hollow ball of cells ) The embryo is moved towards the uterus by cilia and movements in the uterine tubes. The fluid filled ball is surrounded by a thin layer of cells in the form of a membrane called the chorion. Embryonic area – will become the foetus Fluid filled interior Chorion 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 10
Question…. ? Q What happens to the number and the size of the cells at each of the mitotic division? AThe number doubles while the size decreases 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 11
Watch this http: //www. youtube. com/watch? v=Ug. T 5 r. UQ 9 Em. Q&feature=related 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 12
Summary: Cleavage and Differentiation Embryonic area Fluid-filled cavity Chorion • Zygote divides (cleavage) into 2 smaller cells forming embryo • Cleavage continues and solid ball of cells produced • Differentiation occurs when unspecialised cells alter and adapt to perform specific functions 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 13
2/4/2022 Mrs Smith Ch 17 Pre-natal Development 14
Implantation • One week after fertilisation the blastocyst arrives in the uterus. • Here it embeds itself into the endometrium ( the inner wall of the uterus). • This process is known as implantation. • The embryo secretes enzymes which digest away part of the endometrium. • This allows the embryo to burrow into the wall of the endometrium where it grows rapidly and produces finger-like projections which will form part of the placenta. • The embryo receives oxygen and nutrients from the cells of the endometrium until the placenta develops. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 15
Implantation con’t • During this time the blastocyst releases a hormone very similar to LH, which interferes with the pituitary gland to prompt the corpus luteum to continue secreting progesterone. • Therefore, menstrual cycle is interrupted and disintegration of the endometrium is prevented. • Between the second and third month, the placenta produces progesterone and oestrogen. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 16
Diagram of Implantation 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 17
Nickolas Coke – The boy without a brain. Suffered anencephaly – a neural tube defect causing him to be born with his brainstem only. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 18
RIP Nicholas: 18/12/200802/12/12 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 19
Differentiation • Once the embryo has successfully implanted into the endometrium, the embryonic cells begin to differentiate to form the specialised cells (for example nerve cells, muscle cells etc) which will produce the various organs of the body. • During differentiation certain genes in different cells become ‘switched on’ or ‘switched off’. • By the time the embryo is about eight weeks old and about 2 cm long, all the adult organ systems can be identified. • At this point the embryo is known as a foetus. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 20
Differentiation 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 21
Differentiation Finger like projections of the placenta forming A. Endometrium B. chorion C. Amniotic sac D. Foetus 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 22
Intra-uterine Development 4 week old embryo 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 23
Intra-uterine Development 12 week old foetus 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 24
Intra-uterine Development 22 week old foetus 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 25
The early development of the embryo: http: //www. bbc. co. uk/learningzone/clips/the -role-of-the-placenta-in-embryo-development/1851. html 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 26
Monozygotic Twins One ovum being fertilised by one sperm. • Monozygotic twins derive from a single fertilized egg that divides in two and then goes on to form two separate embryos 2/4/2022 27
Monozygotic Twins – Identical • During cleavage/cell division, the developing embryo divides to from two separate embryonic areas within the one fluid filled ball. • (If the embryo splits at a later point, it may do so incompletely and the result is conjoined or 'Siamese' twins who share some organs. ) Since they are the product of a single zygote, monozygotic twins have identical DNA; consequently they are always the same sex. They also share a common placenta and chorion. But have separate amniotic sacs – one each. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 28
Dizygotic Twins Two ova being fertilised by two sperm - one sperm to one egg • Dizygotic twins arise from two eggs released in the same menstrual cycle that are fertilised by separate sperm and then form two separate embryos. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 29
Dizygotic Twins – Non identical • Such twins are no more genetically alike than any other siblings and can be the same sex or different sexes. • Each twin has a separate placenta and a separate amniotic sac and a separate chorion 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 30
Monozygotic (Identical) twins Embryonic areas Come from the same zygote Dizygotic (Non-identical) twins 2/4/2022 Mrs Smith Ch 17 Pre-natal Embryonic areas Development Come from separate zygotes 31
What to do now…. Draw a table contrasting Monozygotic & Dizygotic twins appearance Nos of egg & sperm Amniotic sac placenta DNA Sex Chorion 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 32
What to do now…. Draw a table contrasting Monozygotic & Dizygotic twins appearance Identical Non -identical Nos of egg & sperm One egg & one sperm 2 eggs, 2 sperm Amniotic sac Separate placenta DNA Sex Chorion 2/4/2022 Same Separate Same Different Same or different Shared Separate Mrs Smith Ch 17 Pre-natal Development 33
Task: Torrance-TYK pg 124 Qu’s 1 -2 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 34
Task: Torrance AYK pg 128 Qu’s 1 -2 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 35
Success Criteria Learning Intentions Understanding how the embryo develops inside the uterus and effects that the uterine environment can have on this development • • • 2/4/2022 Describe the changes which take place between mother and foetus Outline the problems associated with harmful substances crossing the placenta Describe the role of oestrogen and progesterone secreted by the placenta 3 months after conception State the role of prolactin secreted by the pituitary gland towards the end of gestation Explain the role of the placenta as an immune barrier preventing rejection of the foetus Mrs Smith Ch 17 Pre-natal Development 36
Useful Transfer • The developing foetus requires: • a constant supply of oxygen (diffusion) • nutrients such as glucose (active transport) • antibodies so new-born acquires passive immunity until its own immune system develops (pinocytosis) • removal of waste substances such as carbon dioxide (diffusion) 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 37
Exchange of Material between Foetus & Mother The placenta develops into a large disc bearing many finger-like villi, which project into the inner layer of the uterus wall, richly supplied with the mothers blood. This allows the mother’s (maternal) and the baby’s (foetal) blood to come very close together, separated by a very thin membrane, which allows the exchange of substances between the mothers blood and the baby’s blood. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 38
Stages of Development Zygote – single cell Embryo – multicellular structure Foetus – embryo at a stage when its species can be determined Baby 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 39
Exchange of Material between Foetus & Mother • Glucose moves from mother to baby by active transport. • Maternal antibodies pass to baby’s blood by pinocytosis giving the baby passive immunity to many diseases until its own immune system develops. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 40
Harmful Transfer Effects of Foetal Alcohol Syndrome 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 41
Harmful Transfers • A developing baby is totally dependent on its mother for the nutrients it needs to grow. • Due to the shared blood supply with its mother, a foetus can also be exposed to pathogens and harmful substances that the mother takes into her body (e. g. nicotine and alcohol). 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 42
Effect of Thalidomide on a Foetus In the 1950 s Thalidomide was given to pregnant women to ease morning sickness, however many babies were found to be born with abnormal limbs. It was later discovered that this was due to taking thalidomide at a very early stage of pregnancy, which also caused mental subnormality & epilepsy 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 43
Watch this! 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 44
And again 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 45
http: //www. guardian. co. uk/society/2012/sep/01/thal idomide-scandal-timeline: 50 years on it’s still politically relevant! • 2009 Scientists at the University of Aberdeen claim they have solved a "50 -year puzzle" after discovering how thalidomide causes limb defects. They found that a component of the drug prevented the growth of new blood vessels in developing embryos, stunting limb growth. The government agrees to pay a £ 20 m grant to the Thalidomide Trust over three years, after another campaign by the Sunday Times. • 2010 The health minister Mike O'Brien makes a formal apology to thalidomide victims, expressing "sincere regret and deep sympathy" on behalf of the government. The apology gets a mixed response from victims, with some describing it as too little, too late. Eighteen Northern Irish thalidomide survivors receive a formal apology and £ 1 m compensation from the devolved assembly. • 2012 The inventor of thalidomide, the Grünenthal Group, releases a statement saying it regrets the consequences of the drug. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 46
Effect of Alcohol on a Foetus Drinking alcohol during pregnancy can be very harmful to the foetus as some alcohol crosses the placenta and causes the blood vessels in the umbilical cord to collapse temporarily. This cuts off the oxygen supply to the foetus and can cause • growth retardation Or a • facial abnormalities miscarriage! • heart defects • abnormal limbs and joints • mental retardation 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 47 Image source: www. wyco-rpc. net
Foetal alcohol syndrome (FAS) 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 48 Image source: www. wyco-rpc. net
FAS –Con’t Characteristic facial features in children of different ethnicities with fetal alcohol spectrum disorders. (A) Child of Northern European descent. (B) Native American child. (C) Black child. (D) Biracial child (white, black). 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 49
Effect of Nicotine on a Foetus Smoking during pregnancy causes growth retardation because: • Nicotine prevents glucose reaching foetal tissues including brain cells. • Carbon monoxide in the smoke produced reduces the concentration of oxygen carried by the blood Babies born to smokers (and passive smokers) are smaller and lighter and tend to have a reduced rate of intellectual development. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 50
Effect of Heroin on a Foetus If pregnant women take heroin it crosses the placenta. Women who take heroin regularly can cause the foetus to become an addict and the foetus’ vital processes to slow down. Most heroin addicts have a poor diet, by neglecting her own health, the mother further affects the baby’s physical & mental development. Baby’s born to heroin addicts are weak, undersized and have to undergo a gradual withdrawal programme. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 51
Effect of Rubella on a Foetus Rubella (German measles) is a viral infection similar to measles. The symptoms include a skin rash, a cough and a sore throat. If Rubella is contracted during the first 3 months of pregnancy it can have very serious effects on the foetus. The baby can have congenital (non-hereditary) defects affecting the eyes, ears and heart. In Britain, all girls are vaccinated against rubella aged 10 -14. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 52
Effect of HIV on a Foetus HIV is a virus that gradually destroys the immune system leaving the body vulnerable to opportunistic infections. This can happen over several years. In 25% of pregnant woman who are HIV positive, the virus crosses the placenta and infects the developing foetus. Most babies that are born with HIV develop AIDS and die at a very young age. If you discovered you were pregnant and the baby had HIV, would you keep the baby? 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 53
Medical advances have improved the odds! • • • What are the risk factors for transmitting HIV during pregnancy? If a woman is infected with HIV, her risk of transmitting the virus to her baby is reduced if she stays as healthy as possible. New treatments can reduce the risk of a treated mother passing HIV to her baby to a <2%. Factors which increase the risk of transmission include: – Smoking – Substance abuse – Vitamin A deficiency – Malnutrition – Infections such as STD’s – Clinical stage of HIV, including viral load (quantity of HIV virus in the blood) – Factors related to labour and childbirth – Breastfeeding 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 54
Success Criteria Learning Intentions Understanding how the embryo develops inside the uterus and effects that the uterine environment can have on this development 2/4/2022 • Describe the role of oestrogen and progesterone secreted by the placenta 3 months after conception • State the role of prolactin secreted by the pituitary gland towards the end of gestation • Explain the role of the placenta as an immune barrier preventing rejection of the foetus Mrs Smith Ch 17 Pre-natal Development 55
Placental Hormones • Months 1 -3 oestrogen and progesterone secreted by the ovary and corpus luteum • >3 months corpus luteum degenerates and placenta produces these hormones • Oestrogen and progesterone inhibit menstrual cycle, maintain endometrium, stimulate growth of breasts in preparation for milk production and inhibit secretion of prolactin 56 2/4/2022 Mrs Smith Ch 17 Pre-natal Development
Placental Hormones During the first 2 -3 months of pregnancy the chorionic cells on the outside of the embryo secrete a hormone that stimulates the corpus luteum to secrete oestrogen & progesterone. These hormones inhibit ovulation and menstruation thus maintain the endometrial layer of the uterus wall throughout pregnancy. After 2 months the corpus luteum degenerates and the placenta secretes oestrogen & progesterone instead. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development Image source: embryology. med. unsw. edu. au 57
2/4/2022 Mrs Smith Ch 17 Pre-natal Development 58
Prolactin is a hormone secreted by the anterior pituitary gland which stimulates milk production. Prolactin becomes active following the birth of the baby, when the placenta is expelled from the body and the oestrogen level drops. As no prolactin is produced during pregnancy, no milk is produced. 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 59
Mammary Glands • After birth, oestrogen and progesterone levels suddenly drop, removing their inhibitory effect • Prolactin released by anterior pituitary • Lactation stimulated • Milk secreted by lobes 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 60
Mammary Glands All mammals produce milk to suckle their young. oestrogen and progesterone produced milk-secreting tissues of the mammary glands are stimulated breasts get bigger and prepare for milk production (lactation) Lactation is inhibited during pregnancy as it requires the action of Prolactin 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 61
Task: Torrance-TYK pg 128 Qu’s 1 -2 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 62
Learning Success Criteria Intentions Understanding how the embryo develops inside the uterus and effects that the uterine environment can have on this development. 2/4/2022 Describe problems which can occur when a Rhesus –ve mother has two Rhesus positive babies in succession Mrs Smith Ch 17 Pre-natal Development 63
Rhesus Factor Sometimes a Rh- mother has a Rh+ foetus developing inside her. The baby has antigen D on its red blood cells which are foreign to the mother’s immune system. The mothers immune system normally remains unaware of the ‘foreign’ foetus because the placenta prevents the mother and baby’s blood from mixing. Image source: www. pennhealth. com 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 64
However, during birth a small quantity of foetal blood becomes mixed with the maternal blood and the mothers immune system produces anti-D antibodies (she is said to have become sensitised). If during future pregnancy’s the baby is also Rh+, the baby is at risk of haemolytic disease of the new-born (HDNB). Cause - Mother’s immune system produces antibodies against antigen D which cross the placenta, attacking and destroying foetal red blood cells. Prevention – injecting the mother with anti-D immunoglobulins soon after the birth of each Rh+ baby, to destroy any D antigens from the foetus before the mother’s immune system can respond 2/4/2022 Mrs Smith Ch 17 Pre-natal Treatment - massive blood transfusions Development 65
Rhesus Factor – 1 st Pregnancy If mother is Rh- and father Rh+: • foetal blood gets into mother’s blood stream during birth • anti-D antibodies produced by mother’s immune system • mother is “sensitised” • first baby usually safe as foetal and maternal blood usually do not mix until delivery 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 66
Rhesus Factor – Subsequent Pregnancies If foetus is Rh+: • anti-D antibodies pass back through the placenta • developing baby's red blood cells harmed • causes very mild to very serious anaemia in the foetus • Treatment – giving baby blood transfusions • Prevention - injecting mother with anti-D immunoglobulins after 2/4/2022 Mrs Smith Ch 17 Pre-natal birth Development 67
Task: Torrance-TYK pg 128 Qu’s 3 -4 2/4/2022 Mrs Smith Ch 17 Pre-natal Development 68
- Slides: 68