2 Hormones and the menstrual cycle The menstrual cycle is approximately 28 days.The menstrual cycle is regulated by hormones produced by the pituitary gland.
3 The cycle beginsFollicle – stimulating hormone (FSH) from the pituitary gland stimulates the follicle inside the ovary to developThis developing follicle secretes estrogen
4 The cycle continuesThe estrogen secreted by the developing follicle stimulates the lining of the uterus to thicken.Estrogen also stimulates the pituitary gland to produce luteinising hormone (LH).
5 The release of LH causes ovulation. Ovulation is the release of the egg into the fallopian tubes.After the release of the egg the corpus luteum will develop from the follicle.
6 The Corpus LuteumThe corpus luteum produces both progesterone and estrogen.Progesterone increases the uterine lining and causes FSH and LH to drop.This drop in FSH and LH prevents the release of another egg until progesterone decreases again.
7 If the egg is not fertilized The corpus luteum will break down causing the levels of progesterone to drop.This drop in progesterone causes the uterine lining to break down and menstruation to occur.Menstruation continues for 4 – 7 days until progesterone reaches a certain level, which causes the release of FSH by the pituitary, and the cycle starts again.
8 If the egg is fertilized – Pregnancy When sperm is deposited into the female cervix, they travel up the uterus into the oviduct.Fertilization occurs in the oviducts when one sperm enters the mature egg and their nuclei fuse to form a zygote
9 After FertilizationAfter fertilization the zygote travels down the oviduct towards the uterus.As the zygote travels, it begins the process of mitosis, with a series of divisions. By the time it reaches the uterus, 24 – 36 hours after fertilization, it is an almost hollow ball of cells called a blastocyst.
10 The BlastocystThe outer cells of the blastocyst will become the placenta while the inner cell mass will become the embryo.
11 Implantation6 – 10 days after fertilization the embryo attaches itself to the thickening lining of the uterus in a process called implantation.Once implanted the embryo sends a hormonal signal that keeps the corpus luteum producing progesterone for the next three months
12 Embryo DevelopmentIn the blastocyst stage, the cells are all similar to each other. However, in the second week of pregnancy the cells begin to specialize. This process produces a gastrula and is called gastrulation.
13 GastrulationDuring gastrulation the cells in the embryo become arranged in 3 layers called germ layers.The cells move to specific positions to produce the layers called the;Endoderm – forms the skin and nervous systemMesoderm – forms the kidneys, skeleton, muscles, blood vessels and gonadsEctoderm – forms the lungs and lining of the digestive tract
14 The outer cellsBetween the tenth and fourteenth day of pregnancy the outer portions of the embryo form four important parts;1. Yolk Sac – supplies nutrients for the first 2 months of development2. Amnion – fluid filled sac that protects the embryo3. Allantois – removes waste4. Chorion – surrounds everything
15 The PlacentaThe chorion contains many finger-like projections that contain blood vessels.These projections extend into the uterine wall to form the placenta.Once the placenta has formed it takes over the role of the yolk sac by providing nutrients to the embryo.
16 The placenta also replaces the corpus luteum in maintaining the high levels of progesterone necessary to sustain pregnancy.The placenta is the lifeline of the embryo by delivering nutrients and oxygen and ensuring that wastes are removed.The embryo is attached to the placenta by the umbilical cord.
17 Gestational Background The human gestation period is about 40 weeksIt is divided into three trimesters, each approximately 3 months long
18 First Trimester (1 – 12 weeks) At 4 weeks, limbs, eyes and spine begin to formAt 9 weeks the first bone cells form and the embryo is called a fetusAt 12 weeks, all major organs have begun to develop (liver, brain, stomach, heart)
19 First Trimester… The fetus is 100 mm long Has a noticeable head and limbsSex can be identified using ultrasound
20 Second Trimester (13 – 25 weeks) At 16 weeks the skeleton begins to form, the brain grows rapidly and the nervous system begins to formThe mother begins to feel movements as the fetus uses its new muscles (around 20 weeks)
21 Second Trimester… At 24 weeks the fetus is 300 mm long The fetus becomes more active and all organs are formed but not fully developed
22 Third Trimester (26 – 40 weeks) A rapid increase is size during this timeVital brain tissue is built and the nervous system developsBy the 8th month, the fetus can open its eyes
23 BirthDuring pregnancy, high progesterone levels have maintained the pregnancyA sharp frop in levels of progesterone and estrogen causes the muscles of the uterus to contractThe pituitary gland secretes oxytocin, which stimulates the uterus to contract and opens the birth canal
24 Three Stages of Birth Dilation Stage: Lasts about 2-20 hours Uterine contractions and oxytocin cause the cervix to dilateAmnion breaks and fluid is released (does not always occur in this stage, some babies have been born still in the amniotic sac)Early labour
25 2. Expulsion Stage: - Lasts about 0 2. Expulsion Stage: - Lasts about hours - Contractions become so forceful that the baby is pushed through the cervix into the birth canal - The head of the baby rotates making it easier to pass through the birth canal
26 3. Placental Stage: - The placenta and umbilical cord are expelled from the uterus - Usually happens between minutes after the baby is born
27 Risk Factors during Development The fetus receives all of its nutrients and oxygen from the mother’s blood.Anything that the mother east, drinks or inhales from her environment end up in her bloodThe first trimester is the critical period for the developing embryo
28 Risk Factors during Development continued Cigarette smoke constricts fetal blood vessels preventing it from getting enough oxygenAlcohol affects the functioning of the fetus’ brain and central nervous system as well as physical development (FAS)
29 Risk Factors during Development… Other factors such as radiation, pollutants such as PCB’s and mercury can lead to genetic mutationsThe mothers age is also a risk, with women under 20 having increased risk of delivering prematurely, and women over 45 having 5% chance of having a baby with chromosomal abnormalities