Presentation on theme: "3.4 Prenatal Development Prenatal development after the eighth week is the fetal period. This is the time when structures grow and specialize. From the."— Presentation transcript:
13.4 Prenatal DevelopmentPrenatal development after the eighth week is the fetal period.This is the time when structures grow and specialize.From the start of the ninth week until birth, the prenatal human organism is a fetus.A prenatal human is considered an embryo for the first eight weeks.During this time, rudiments of all body parts form.The embryo in the fist week is considered to be in a “preimplantation” stage because it has not yet settled into the uterine lining.
2Three Trimesters of Development Human Reproduction and DevelopmentThree Trimesters of DevelopmentHuman development takes around 266 days from fertilization to birth.The time span is divided into three trimesters.
3All tissues, organs, and organ systems begin to develop. Human Reproduction and DevelopmentThe First TrimesterAll tissues, organs, and organ systems begin to develop.At the end of eight weeks, the embryo is called a fetus.
4The fetal heartbeat might be heard. Human Reproduction and DevelopmentThe Second TrimesterPeriod of growthThe fetal heartbeat might be heard.The Third TrimesterThe fetus continues to grow at a rapid rate.Fat accumulates under the skin to provide insulation for the fetus once it is born.
5FertilizationFormation of diploid zygote – single cell from fusion of haploid gametes.Gametes formed by cell division known as meiosis which is a process by which the chromosome content is reduced to 23.(Spermatogenesis or Oogenesis)Process allows for mixing of maternal and paternal genesAcknowledgement for pictures is courtesy of Alpha (Scientist in Reproductive Medicine Permission confirmed by D Cole ).
6Process of a sperm joining with an egg Human Reproduction and DevelopmentFertilizationProcess of a sperm joining with an eggSperm and eggs each are haploid, and each normally has 23 chromosomes.Fertilization restores the diploid number of 46 chromosomes.
8Human Reproduction and Development Human Development Before BirthThe tip of each sperm cell is a specialized lysosome called an acrosome that weakens the plasma membrane surrounding the egg.Eventually the plasma membrane becomes weak enough that one sperm can penetrate the egg.Immediately following this penetration, the egg forms a barrier to prevent other sperm from entering the now-fertilized egg.
9The fertilized egg is called a zygote. Human Reproduction and DevelopmentEarly DevelopmentThe fertilized egg is called a zygote.Around 30 hours after fertilization, the zygote undergoes its first mitosis and cell divisionBy the third day, the embryo, called a morula, leaves the oviduct and enters the uterus.
10Mitosis Mitotic cell division – formation of identical cells Cells have identical genetic materialTotipotent – clonesDay 4: embryo cells & is known as a MorulaAcknowledgement for pictures is courtesy of Alpha (Scientist in Reproductive Medicine Permission confirmed by D Cole ).
11By the fifth day, the morula has developed into a blastocyst. Human Reproduction and DevelopmentHuman Development Before BirthBy the fifth day, the morula has developed into a blastocyst.The blastocyst attaches to the endometrium around the sixth day and is fully implanted by Day 10.
12Blastocyst Cells division becomes asymmetrical Cells polarize Lose their totipotency and begin to differentiateOuter cell mass becomes the trophoblast which develops into the placentaImplants day 6
13By day 14From implantation of the blastocyst ,the inner cell mass is known as the embryoAmniotic & Chorionic cavities
14Embryo 3-8 weeks Co-ordinated by genes – Homeobox Cell differentiation Critical time for normal developmentParticularly sensitive to external factors, environmental hazards, pharmacological agents, drug misuseOrganogenesisTrilaminar disc folds into C shaped cylindrical embryoCo-ordinated by genes – HomeoboxCell differentiationTissue interaction & communicationFolding is due to different rate of growth
15Cells 350 different types of human cells Different functions Cells process: division, differentiation, induction, migration & death
16Extraembryonic Membranes Chapter 36Human Reproduction and Development36.2 Human Development Before BirthExtraembryonic MembranesFour extraembryonic membranes form.AmnionChorionyolk sacallantois.
17Provides food and oxygen and removes wastes Chapter 36Human Reproduction and Development36.2 Human Development Before BirthThe PlacentaProvides food and oxygen and removes wastesThe placenta has two surfacesA fetal side that forms from the chorion and faces the fetusA maternal side that forms from uterine tissue
1836.2 Human Development Before Birth Chapter 36Human Reproduction and Development36.2 Human Development Before BirthAs an embryo develops, the chorionic villi begin to grow into the uterine wall.Nutrients, oxygen, and wastes diffuse across maternal and fetal blood vessels, and are carried to and from the fetus through the umbilical cord.The placenta contains tissue from both mother and fetus.
20Gastrulation – Week 3 Primitive streak in the midline Bilaminar disc is converted into Trilaminar disc3 Germ layers (gastrula) :Ectoderm, Mesoderm & Endoderm2mm longNotochord formsPrimitive heartMother first missed menstrual period
21Trilaminar discEctoderm will form the epidermis & central nervous systemMesoderm will form the bones, muscles and heart, blood vessels, kidneys and reproductive organsEndoderm will form digestive tract, respiratory tract, glands & mucous membranes
23Formation of the Neural tube - Neurulation Starts at daysFolding starts in the middle in both the cranial and caudal direction.Cranial opening closes day 25 , caudal opening closes on day 27daysFolic acid is involved in DNA synthesisMost women at this stage do no know they are pregnant
24Development of the skeletal vertebral column Commences at week 4Week 6 cartilaginous stageWeek 8 Ossification begins
25Week 4 Heart begins to beat approximately 85 beats /minute Outline of eyesUpper limb budsLungs begin to formParts of gastrointestinal tract can be identified.
26Week 8 Heart has 4 chambers Upper limbs longer bent at the elbows Fingers distinct but webbedExternal genitalia still in sexless state but have begun to differentiateBy end of week 8 all body systems & organs are formed. FETUS
278-12 Weeks Eye lids fuse Fetal circulation functioning Moves freely Kidney’s function fetus passes urine ~10 weeksAbdominal gut needs to be withdrawn into cavity by week 10Ossification of bones begins 8 weeks
28By 20 Weeks Most organs capable of functioning Neurons formed between weeksSkin covered with vernix and lanugoBrown fat depositedLimbs are at mature proportionsMeconium present in gut
2924 Weeks Skin – thin, wrinkled, translucent & dark red Lungs terminal sac phase (surfactant started to be produced 22weeks, increases significantly after 30weeks)Sensory organs develop, fetus responds to noiseLength 32 cmWeight 700gPeriods of sleep & activity
3028 Weeks Survival possible Eyelids open Length 37cm Weight 1200g Head circumference 26cm
3132 Weeks Lanugo disappears from face Ear cartilage soft Lengths 43cm Weight 2000gAccumulation of fat
3236 Weeks Breast tissue nodule present 1-2 mm Skin pale Length 49cm Head circumference > abdominal circumferencePlantar creases visibleHead hair lengthensNails reach the tips of fingersLanugo vanishes from shoulderBreast tissue nodule present 1-2 mmSkin paleLength 49cmHead circumference 33cmWeight 2900g: Ready for birth
33Procedure in which sound waves are bounced off the fetus Chapter 36Human Reproduction and Development36.2 Human Development Before BirthDiagnosis in the FetusUltrasoundProcedure in which sound waves are bounced off the fetusDetermines if the fetus is growing properlyDetermines the position of the fetus in the uterusDetermines the gender of the fetus
34Amniocentesis is performed in the second trimester. Chapter 36Human Reproduction and Development36.2 Human Development Before BirthAmniocentesisAmniocentesis is performed in the second trimester.Fluid from the amniotic sac is removed and analyzed.
35Chorionic Villus Sampling Chapter 36Human Reproduction and Development36.2 Human Development Before BirthChorionic Villus SamplingChorionic villus sampling is performed during the first trimester.Cells from the chorion are removed and analyzed by karyotyping.
36The beginning of the birthing process is called labor. Chapter 36Human Reproduction and Development36.3 Birth, Growth, and AgingBirthBirth occurs in three stages: dilation, expulsion, and the placental stage.The beginning of the birthing process is called labor.
37Chapter 36Human Reproduction and Development36.3 Birth, Growth, and AgingDilationAnother sign the baby is going to be born is the dilation of the cervix.
38Chapter 36Human Reproduction and Development36.3 Birth, Growth, and AgingExpulsion StageThe mother consciously will contract her abdominal muscles to help push the baby, usually head first, through the vagina in the expulsion stage.
39Chapter 36Human Reproduction and Development36.3 Birth, Growth, and AgingPlacental StageThe placenta detaches from the uterus and leaves the mother’s body along with extraembryonic membranes in the placental stage.
40The first two years of life Chapter 36Human Reproduction and Development36.3 Birth, Growth, and AgingInfancyThe first two years of lifeChildhood and AdolescenceChildhood is the period of growth and development that extends from infancy to adolescence.
41Puberty marks the beginning of adolescence. Chapter 36Human Reproduction and Development36.3 Birth, Growth, and AgingPuberty marks the beginning of adolescence.Begins between ages 8 to 13 in girls and ages 10 to 15 in boys.
42Physical changes perhaps are the most noticeable signs of aging. Chapter 36Human Reproduction and Development36.3 Birth, Growth, and AgingAdulthoodAt the end of adolescence, physical growth is complete, marking the beginning of adulthood.Physical changes perhaps are the most noticeable signs of aging.Other changes include a decrease in muscle mass, a slowing of overall metabolism, and a decreased pumping ability of the heart.
4336.2 Human Development Before Birth Chapter 36Human Reproduction and Development36.2 Human Development Before Birth