Week #1: Fertilization……… MORULA to Implantation

Mitosis : chromosomes double 1x, the nucleus (cell) divides 1x Meiosis : chromosomes double 1x, the nucleus (cell) divides 2x – Each is haploid contains 23 chromosomes being begins with the fusion of an ovulated oocyteand a sperm called germ cells A. Fertilization (1) The development of a human fertilization – The oocyte and sperm are following meiosis this is the amount of DNA needed by somatic (body) cells

This produces a zygote single cell diploid it contains 46 A. Fertilization (2) zygote –this is a –it means “united” –it is chromosomes like all somatic cells

B. Cleavage This results in an –increase the number of cells The embryo now rapidly undergoes a series of mitotic divisions called cleavage

outer cell mass cavity “blastocyst” and the outer cell mass cavity “cavitation” D. Cavitationand the Blastocyst Next a fluid-filled inner cell mass forms between the inner cell mass This is called This gives rise to the blastocyst “blastocyst”= “germ-bag”

E. Implantation On about day 7, the blastocyst implants itself into the wall of the mother’s uterus

Week #2: BilaminarDisk Formation (1) inner cell mass now differentiates into 2 distinct cell layers bilaminar embryonic disk epiblast hypoblast The –the epiblast –the hypoblast This is called the

amniotic cavity A cavity forms next to the epiblast –It is called the amniotic cavity amniotic fluid Week #2: BilaminarDisk Formation (2a) –it becomes filled with –this will eventually surround and suspend the embryo and provide a shock-free environment a constant temperature –and allow free movement

amniotic cavity amniocentesis Week #2: BilaminarDisk Formation (2b) The cells lining the amniotic cavity are shed on occasion These cells, along with proteins, carbohydrates, fat, enzymes, hormones and embryonic excretions can be extracted and examined This procedure is called an

amniotic cavity yolk sac respiratory and digestive system structures Week #2: BilaminarDisk Formation (3) A cavity also forms next to the hypoblast and is called the yolk sac –it will contribute to

outer cell mass embryo’s A few words about the outer cell mass (1) The –is the contribution to the placenta –becomes intimately associated with the inner lining of the uterus in which the embryo is embedded

blood vessels –they exchange nutrients and wastes via diffusion A few words about the outer cell mass (2) Where the 2 surfaces join –many from the embryo and from the mom come close together –no actual blood flows between the embryonic and maternal circulation

With further cell differentiation, a 3 rd cell layer forms between the epiblastand hypoblast The embryo is now a trilaminardisk This process is called gastrulation Week #3: Gastrulation (1)…

called the ectoderm called the endoderm Week #3: Gastrulation(2)… The epiblastis now The hypoblast is now The middle layer, composed of cells that migrated from the epiblast, becomes the mesoderm These 3 cell layers give rise to all the cells of your body!

ectoderm –organs that maintain contact with the outside world epidermis (epithelial lining of the skin) nervous system Week #3: Gastrulation(3a)… The will give rise to

Theendoderm will give rise to –the epithelial lining of the digestive and respiratory tracts liver pancreas Week #3: Gastrulation(3b)… –plus outgrowths of the digestive tract that give rise to the:

Themesoderm will give rise to –connective tissues connective tissue proper That is, basically everything between the inner and outer linings of your body! bone cartilage blood –muscle Week #3: Gastrulation(3c)…

Week #3: …and Notochord formation It is called the notochord –it extends the length to tail) –it will contribute to the axial skeleton notochord cross section The formerly round, 3-layer disk elongates A rod-like structure forms in the mesoderm of the embryo (from head

Notochord at 5 weeks This is to give you a better idea of the notochord extending from head to tail It forms the basis for the axial skeleton

This is our next lecture! The Axial Skeleton gives rise to 3 Components: the skull the vertebral column the thoracic cage: –the sternum –the ribs

Week #4: Neurulation –invaginates and into–differentiates the neural tube nervous system brain spinal cord …. Ectoderm overlying the notochord now –this becomes the

Neural Tube Formation Here is a view of the neural tube as if forms superficial to the notochord

Here are the brain and spinal cord in you!

–“C”-shaped… (from side to side) (from head to toe) tube Week #4:and Formation of the Fetus(1) The shape of the embryo changes drastically – from an elongated disk it rolls up into a

–an outside lined by ectoderm –an inside lined by endoderm from mesoderm endoderm ectoderm Week #4:and Formation of the Fetus(2) The embryo now has –and everything in between –and is now called a fetus all the major organ systems have now been established

Week #4:and Formation of the Fetus(3) And the fetus now bulges into the amniotic cavity

the umbilical cord Week #4:and Formation of the Fetus(4) It remains connected to the placenta via It contains very important blood vessels!

Placental Blood Supply Oxygenated blood for the fetus is supplied by the Mom (high O 2 from mom)

Summary Week #1: – Fertilization →zygote formation – Cleavage →morulaformation – Beginning of cell differentiation and cavitation→blastocyst formation – Implantation Week #2: – Differentiation continues →bilaminardisk formation – Formation of amniotic cavity and yolk sac Week #3: – Gastrulation→trilaminardisk – Notochord formation Week #4: –Neurulation – Major shape changes in embryo – Formation of the fetus

upperand lower limb buds have the 4 th week of Four Weeks By the end of gestation the formed (The fetus is at very high risk of malformations at this age) Figure 29–7a, b

the 8 th week the fingers and toes have Figure 29–7c, d The face Eight Weeks By the end of formed now begins to look human-like (The fetus remains at very high risk of malformations through the 8 th week)

Figure 29–7c, d Twelve Weeks This is the period of functional maturation of all organ systems (By this age, the fetus is at lower risk of malformations)

Fertilization is defined as the A.increase in cell number B.joining of the sperm and oocyte C.formation of an inner and outer cell mass D.development of a cavity E.formation of a trilaminardisk

The ectoderm gives rise to A.muscle B.bones C.lining of the digestive system D.liver E.skin and nervous system

The neural tube gives rise to A.muscle B.connective tissue C.skin D.liver E.brain and spinal cord

At what developmental stage does the embryo implant into the uterus? A.fertilized oocyte B.morula C.blastocyst D.trilaminardisk E.fetus

At what developmental stage does the trilaminardisk form? A.fertilized oocyte B.morula C.blastocyst D.gastrulation E.fetus