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Human Reproduction 2 Contents Copulation, Fertilisation, Conception The Human Pregnancy Birth or Parturition Lactation, Breastfeeding Development of embryo up to 3rd month 2 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 3 Copulation ??? 4 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. 5 Flaccid and erect penis 6 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. 7 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. 8 Copulation or intercourse 9 Copulation or intercourse 10 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. 11 A reminder of sperm structure 12 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. 13 Egg and sperm just before fertilisation 14 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. 15 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 16 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 17 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. 18 For clarification – gestation period 266 days after conception 280 days = 40 weeks from last period 1 14 28 Birth Menstrual cycle 19 Gestation periods of some mammals 20 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. 21 Foetus surrounded by the amnionic fluid 22 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. 23 Placenta and foetus 24 Placenta 25 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. 26 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 27 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. 28 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 29 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. 30 Labour – Stage 1 31 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. 32 Labour – Stage 2 33 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) 34 Labour – Stage 3 35 Birth 36 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 37 The role of oxytocin in the birth process 38 Lactation & Breastfeeding Contents Lactation Breastfeeding Benefits of breastfeeding 39 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 40 Breastfeeding 41 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 42 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. 43 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 44 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 45 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 46 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: 47 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. 48 Zygote to blastocyst 49 The sequence of events from ovulation to implantation 50 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. 51 Implantation 52 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. 53 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 54 1.5 days after fertilisation 55 2 days after fertilisation 56 3 days after fertilisation 57 1 week after fertilisation 58 The embryo at four weeks 4 weeks – arm and leg buds appear; primitive digestive, nervous and circulatory systems in operation; 1.5 cm long. 59 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. 60 The embryo at six weeks 61 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. 62 The embryo at nine weeks. 63 The embryo at ten weeks 64 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; 65 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 66 END 67