Presentation on theme: "Chapter 3: Meiosis & Development Section 3.4: Prenatal Development"— Presentation transcript:
1Chapter 3: Meiosis & Development Section 3.4: Prenatal Development
2What are the steps of prenatal development? FertilizationCleavageImplantationGastrulationOrganogenesisEmbryo development (week 1-8)Fetus development (week 9-40)
3What happens during fertilization? Capacitation- chemicals in female body activate spermOocyte secretes chemical to attract sperm
4What happens during fertilization? Sperm contact corona radiata- the covering of follicle cell that is protecting secondary oocyteAcrosome on sperm bursts and enzymes begin eating through next layer of egg called zona pellucidaConception occurs when sperm head meets cell membrane of eggThe egg cell membrane changes its charge which prevents other sperm from entering cell.Fertilization membrane forms- this will hold cells together when they start dividing.
6What happens during cleavage? Cleavage- period of frequent cell division (mitosis) that begins about 24 hours after fertilizationBlastomere- 2-4 cells massMorula- 16 cell stage. Solid ball of cellsBlastocyst- cell division continues and cells push against outer edge and form a fluid filled cyst in center of blastocystA group of cells called the inner cell mass will begin accumulating on one side of the blastocyst- cells are beginning to differentiateThis entire process takes about 6-7 days.
7What happens during implantation? Day 7, blatocyst impants into uterine liningOuter layer of cells (trophoblast) from blastocyst secrete human chorionic gonadotropin (hCG)hCG prevents menstruationThis is what a pregnancy test detects in urine or blood.
8What happens during gastrulation? Amniotic cavity forms between inner cell mass and the trophoblast layerCells in the blastocyst and inner cell mass will begin to form layersOuter layer of cells forms ectodermInner layer of cells forms endodermMiddle layer of cells forms mesodermCells in each of these layers will differentiate and have different fates.
9What are the cell fates of the 3 tissue layers? EctodermSkinNervous tissue (brain & spinal cord)EndodermDigestive organsLiverpancreasMesodermMuscleBoneReproductive organsKidneysGastrulation ends around day 14
10What supportive structures are forming during the first two weeks? Chorionic villi- finger-like extensions that extend into uterine wall and come close to mom’s blood stream.Mom and baby’s blood stream NEVER mixes but anything in mom’s blood stream can diffuse into baby’s (and vice versa)Baby sends wastes into mom’s blood streamYolk sac- makes blood cellsAllantois- makes umbilical blood vesselsUmbilical cord attaches to center of placentaPlacenta- fully formed by 10 weeks; links woman to fetus & secretes hormones to maintain pregnancy & sends nutrients & waste back & forth between mom and baby.
11What happens during organogenesis? The ectoderm, endoderm, and mesoderm begin forming organsEmbryo is sensitive to environmental influences such as chemicals and viruses
12Week 3 Heart begins to forms by day 18 Primitive streak forms along back of embryo. This is a primitive notochord which will become spineNotochord induces cells of ectoderm to fold and form hollow neural tube which eventually becomes brain & spinal cordNeural tube seals around day 20.
14What is a neural tube defect? If NT does not seal, Neural Tube Defect (NTD) will form.Ex: Spina bifidaBrain or spine is exposedBaby paralyzed from point of exposure downOccurs due to lack of vitamin B or folic acidPregnant women encouraged to take folic acid supplements/vitamins during pregnancy to prevent NTDNTD can be detected around 15 weeks with alpha fetoprotein (AFP) blood test that detects a protein from fetus’ liver that is leaked at a fast rateIf detected and caught early enough can sometimes be corrected with in utero surgery.
15Week 4 Heart begins beating around day 23 Leg and arm buds begin to formBlood cells form & fill primitive blood vesselsImmature lungs and kidneys develop
16Week 5 & 6 Enlarged head Apoptosis sculpts fingers and toes Eyes open but no eyelids or irisesGene SRY on y chromosome of a boy will begin forming male hormones that stimulate formation of male organs
17Week 7 & 8 Skeleton of cartilage is formed Embryo is about size of a paper clipAfter 8 weeks it is now called a fetus.
18Weeks 9-12 Body proportions equal out Bone begins to replace cartilage Fetus begins coordinating muscle and nerves and begins to moveFetus sucks thumb, kicksUrinates & defecates into amniotic sacBreathes in amniotic fluidWeek 12 ends 1ST TRIMESTER
192nd Trimester Weeks 13-24 Hair Lanugo- downy hair all over body EyelashesEyebrowsNipplesNailsWeek 15- gender determinedSkin appears wrinkled due to lack of fat & pink with new capillary formationCan feel distinct movementBaby is about 9 inches long
203rd Trimester Weeks 25-40Fetal brain cells grow and form numerous connections to organsFat forms under skinDigestive & respiratory systems maturePremature babies often have respiratory diseases and have difficulty digesting milk
21How can genetic disorders or birth defects be detected? Chorionic villi sampling- cells are removed from chorionic villi and tested for abnormalities in number or shape of chromosomes.Done at 10 weeksAmniocentesis- fluid from amniotic sac is removed by needle and test for abnormalitiesDone at 14 weeks
22How do multiples form? Monozygotic multiples- Dizygotic multiples- Identical twinsFertilized egg splitsTwins are genetically identicalShare placentaDizygotic multiples-Fraternal twinsTwo sperm fertilized two different eggsTwins are genetically differentDifferent placentas
23What are conjoined twins? Separation of egg cell begins to occur while organs are developing.Attachment point depends on where split was occurring & what organs were developing at the time.Ex: Brittany & Abigail Hensel
24Brittany & Abigail Hensel Dicephalic twins- have two headsShare- liver, bloodstream, all organs below navel, 3 kidneysSeparate- neck, head, heart, stomach, gallbladder, lungs, nervous systemParents chose not to separate b/c one child usually dies during surgery