How a single fertilized egg develops into a new organism

 How long does human gestation take? (a baby to develop from fertilized egg to birth)  Which cell process occurs to allow a fertilized egg to grow?  What are the differences between a zygote, an embryo and a fetus?  What is the importance of implantation in a woman’s pregnancy?

 Human Gestation requires about 9 months from conception  Or 40 weeks from the first day of the woman’s last menstruation date  Stages of development are divided into three trimesters  The first trimester is often the most crucial:  The fundamental structures are formed during the first three months

 The formation of haploid gametes  Two Types:  Spermatogenesis  Oogenesis

 Spermocyte: the original large diploid cell into which a sperm develops  Spermatids: a haploid male gamete that results from division of secondary spermatocytes  Spermatozoa: the mature motile male sex cell of an animal, typically having a compact head and one or more long flagella for swimming.

1.Spermatogonia (male sex cells) divide by mitosis to produce 2 daughter cells. One daughter cell becomes another spermatongonia and the other becomes a primary spermatocyte. 2.The primary spermatocyte goes through meiosis I to become 2 secondary spermatocytes which will divide again by meiosis II to become 4 spermatids. After completing meiosis… Spermatids (1N) differentiate into spermatozoa (1N) by an extensive remodeling process Loss of cytoplasm, gain of acrosomal cap, and flagellum (tail) acrosomal cap develops via Golgi apparatus flagellum (tail) develops via centrioles

 Oogonia: an immature female reproductive cell that produces primary oocytes by mitosis.  Oocyte: a cell in an ovary that may undergo meiotic division to form an ovum.  Ovum: a mature female reproductive cell that can produce an embryo only after fertilization by a male spermatozoa  Polar Bodies: a small haploid cell which generally does not have the ability to be fertilized

Pre-Natal:  Ovary cells (oogonia) undergo mitosis to produce more oogonia and primary oocytes  Primary oocytes undergo interphase, but stop at prophase I until Puberty Puberty:  Meiosis I is completed just before ovulation and the secondary oocyte and a polar body is produced.  The secondary oocyte begins Meiosis II, but stops at metaphase II

Fertilization:  After ovulation, the secondary oocyte may be fertilized by a sperm cell, if this occurs, the secondary oocyte completes meiosis II to produce a second polar body and a secondary oocyte.  Fertilization is complete after the nuclei of the secondary oocyte and the sperm cell unite.

1. Fertilization 2. Implantation 3. Gastrulation 4. Neurulation

 The union of a sperm cell and egg cell forming a zygote

The zona pellucida is a thick barrier of glycoproteins that surround and protect the egg. Sperm must penetrate this barrier and bind to receptor sites on the egg’s surface before its nucleus can enter the egg. The acrosome of the sperm cell contains enzymes that will help digest through the protective layers of the egg. The membrane of the sperm will then fuse with the membrane of the egg—if the membrane receptors match up! The zona reaction prevents multiple sperm from enteriing the egg. Once a sperm cell binds with the egg, the zona pellucida hardens like concrete freezing loser sperm in their tracks!

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 Embryo: an unborn or unhatched offspring in the process of development

 Morula: a solid ball of cells resulting from division of a fertilized ovum, and from which a blastula is formed.  Blastocyst: A thin-walled hollow structure in early embryonic development that contains a cluster of cells called the inner cell mass from which the embryo arises.

 When the cells of the blastocyst roll inward to form three layers of cells (called migration)  Embryo is now a gastrula

 Endoderm  Endoderm: Innermost layer (digestive system)  Mesoderm  Mesoderm: Middle layer (internal organs and muscle)  Ectoderm  Ectoderm: Outer-most layer (skin and nervous system)

 Once gastrulation is complete, the nervous system begins to develop  Cells of the ectoderm gather and form a tube  The embryo at this stage is termed the neurula. =qisrNX3QjUg

 Stem Cells: unspecialized cells that have the potential to differentiate into any tissue.  Cell Differentiation: When stem cells are given specific functions—growth factors and hormones tell them when and how to change.

ProcessFertilizationImplantationGastrulationNeurulation Embryotic structure zygoteMorulaBlastula/ Blastocyst GastrulaNeurula

 Tissues formed outside the baby to protect and nourish the developing embryo

1. Amnion : forms the amniotic sac— fluid filled to cushion embryo  The “water” 2. Chorion : forms the placenta— combines with the uterus tissues.

AA maternal-fetal organ BBegins developing at implantation EExchanges nutrients, gases, and waste products DDrugs and alcohol have been known to cross the placenta.

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Fetus: 8 week or greater unborn offspring of a mammal

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 Labor : Hormone levels of Estrogen and Oxytocin increase—cause contractions of uterus  Positive Feedback: presence of hormones cause even more hormones to be released  Yay! Delivery of baby!  Afterbirth: Delivery of placenta  Hormones adjust, Oxytocin allows production of breastmilk

 The growth and development of the fetus is affected by the mother's age at the time of pregnancy, nutritional status, habits (diet, drug use, alcohol consumption, or cigarette smoking), medical conditions, and prenatal care.  Ex: preeclampsia - after the 20th week of pregnancy the mother can get high blood pressure and problems with the kidneys and other organs.

 IVF: (in vitro fertilization) is a process by which an egg is fertilized by sperm outside the body

 a group of conditions due to an impairment in physical, learning, language, or behavior areas  Ex: Autism Spectrum Disorder or ADHD

 Amniocentesis - is a procedure used to obtain a small sample of the amniotic to diagnose chromosomal disorders and open neural tube defects such as spina bifida.  Chorionic villus sampling (CVS) - taking a sample of some of the placental tissue. This tissue contains the same genetic material as the fetus and can be tested for chromosomal abnormalities and some other genetic problems.

 Alpha-fetoprotein screening (AFP)- This blood test measures the level of alpha- fetoprotein in the mothers' blood during pregnancy to detect problems like down syndrome.

1. What does “differentiation” mean? 2. From which germ layers do the brain, the heart and the small intestines form? 3. Which tissues (membranes) become the amniotic sac and the placenta? 4. When is an embryo considered a fetus? 5. How many weeks is considered “Full Term?”

 ns/lifecycle/index.asp ns/lifecycle/index.asp  Site for possible student research  htm htm

Also include: Zygotelocations in body Cleavage3 germ layers Differentiationplacenta development 1.FERTILIZATION Morula Blastocyst 2.IMPLANTATION3.GASTRULATION4.NEURULATION