Download Biology 30 – November 10, 2014 Embryo Development Quick

Biology 30 – November 10, 2014 Embryo Development
Quick Review
Blastocyst, Cleavage, Implantation, Trophoblast, human chorionic gonadotropin (hCG), Chromosomes,
Morula, Zygote, Fertilization words you should be familiar with.
Ovulation to Implantation
An egg leaves the ovary, ovulation (day 14 of the menstrual cycle). A single sperm nucleus enters the
egg, this is fertilization, occurs in the oviduct (2 gametes 23 chromosome each combine to make 46
chromosomes). Now have a zygote moves along the oviduct undergoes cleavage (mitosis) cell division
(no growth). This produces a morula (16 cells) which will from into the blastocyst. It is the blastocyst
that implants into the lining of the uterus, endometrium.
Gastrulation and the Start of Tissue Formation
Week 2: Blastocyst continues and completes the process of implantation, the inner mass changes. A
space forms between the trophoblast and the inner cell mass.
Amniotic Cavity – the space that forms between the trophoblast and the inner cell mass. The amniotic
cavity forms within a sac called the aminon. The amion is an important embryo supporting structure.
This space fills with fluid and will be where the baby will develop.
Amnion –extra embryonic membrane that forms a transparent sac that encloses and protects the
embryo and fetus.
The inner mass of cells flattens into a disk-shape and is called the embryonic disk, it is supported by a
short stalk that connects the blastocyst with the endometrium (Umbilical Cord).
2 layers – outer ectoderm and the inner endoderm
3 layers – mesoderm forms in between
The process of forming these 3 layers is called GASTRULATION.
The three layers are called the PRIMARY GERM LAYERS. All cells, tissues, and organs of the body will
come from these layers
Zygote is now called Gastrula.
Gastrulation is the beginning of MORPHOGENESIS which is the process of forming distinct structures of
the developing organism. It depends on differentiation the ability of cells to become different types of
cells (blood cells, bone cells, stem cells, skin cells, liver cells, etc.).
Differentiation is the cellular process that enables a cell to develop a particular shape and to perform
specific functions.
Hormones during Development
Draw a graph, hand it in, use colour. The hormones are hCG, progesterone, and estrogen and they are
secreted from various sources during pregnancy. Early in the pregnancy estrogen and progesterone are
secreted by the corpus luteum. During mid-pregnancy this changes and they are secreted by the
placenta. Late in pregnancy, these hormones are secreted solely by the placenta.
Neurulation and Organ Formation
3-8 weeks: The organs begin to form, cell division in the primary germ layers cause tissues to fold into
distinct patters. The 3 layered embryo transforms into a body with separate organs and by the 8 weeks
is recognizable as a human.
Ectoderm (Outer): Outer skin and structures hair, nails, sweat glands, mammary glands. Nervous tissue
and sense organs. Pituitary Gland, thooth enamel, eye lens, adrenal medulla.
Mesoderm (Middle): Dermis of skin, cellular lining of blood vessels, lymphatic vessles, body cavities,
muscle tissue, connective tissue bone cartilage and blodd, adrenal cortex, kidneys and ureters, heart,
spleen, internal reproductive organs.
Endoderm (Inner): Cellular lining of respiratory tract, digestive tract, urinary bladder, urethra, liver,
tonsil, gallbladder, pancreas, thymus, parathyroid glands, and thyroid glands.