Transcript Biology 105
Biology 105 Chapter 51: Development Pages 1106-1126 Student Outcomes Describe the processes involved in fertilization Trace the generalized pattern of early development of the embryo from zygote through early cleavage Identify the significance of gastrulation in the developmental process Student Outcomes • Define Organogenesis and the three germ layers Fertilization • Process of joining of egg and sperm to form a zygote. Known as conception. • Spermatogenesis and oogenesis • Involves 4 events: Fertilization events 1. sperm contacts the egg and recognition occurs 2. sperm or sperm nucleus enters the egg 3. egg becomes activated, beginning developmental changes 4. sperm and egg nuclei fuse. Polyspermy the fertilization of the egg by more than one sperm. Results in extra chromosomes and is usually lethal. Zygote Is totipotent Cleavage occurs shortly after fertilization Cell goes through 2 cell, 4 cell, 8 cell stages, etc. At the 32 cell stage – known as morula, and eventually a blastula Morula-Blastula • 32 cell stage – Usually at this stage when entering the uterus. These cells are known as blastomeres. Continued mitotic divisions (Cleavage) results in a Blastula (hollow ball of cells with a blastocoel) Gastrulation Blastula becomes a gastrula which forms the 3 germ layers: – Ectoderm – Mesoderm – Endoderm – The three germ layers will give rise to organogenesis - the formation of organs. Notochord, brain and spinal cord are the first organs to develop Ectoderm – Outer layer – Will give rise to: • Nervous system and sense organs • Outer layer of skin, nail and hair • Pituitary Mesoderm Middle layer – Will give rise to skeleton muscles circulation excretory reproduction dermis Endoderm • Will give rise to: – Lining of the digestive tube – respiratory Implantation Occurs on about the 7th day of embryo development. It imbeds in the endometrium of the uterus. Human Development Timeline • Fertilization • 24 hours – 2 cell stage • 3 days – Morula travels through fallopian tubes • • and reaches uterus 7 days – implantation 17 days – tissue that will give rise to heart is differentiating, neural plate is formed Human development continued • 25 days – primitive eye and ear visible, heart begins to beat • 4 weeks – limb buds appear, brain division forming • 8 weeks – muscles differentiation, embryo capable of movement, sex organs can be seen, bone is ossifying Human development continued 3 months- sex can be determined 4 months – face takes on a ‘human’ form with eyes, ears and nose Third trimester – known as a fetus, tremendous growth of the body, cerebrum growth is rapid 266 days – Birth All Development Stages • Gametogenesis-Fertilization • Embryo: Cleavage-Morula-BlastulaImplantation-Gastrula-Organogenesis • Fetus: 2 month-Birth (organogenesis) • Birth-Neonate-Infant-Child-AdolescentYoung adult-Middle aged adult-Elderly adult • Death Multiple Births • Twins – Identical - one egg, one sperm, seperation after the 2 cell stage or the inner cell mass divides into 2 separate masses (monozygotic) – Non identical - two eggs, two sperm (dizygotic) – Conjoined - Same as identical, seperation does not occur completely. Births cont. • Triplets – Identical - one egg, one sperm – Non identical - more than one egg and sperm