Fertilisation to Trilaminar PDF

Fertilisation to Trilaminar 21/10/23, 6:02 PM Fertilisation to Trilaminar Fertilisation • Fertilisation: union of gametes - fusion of sperm and oocyte to form a zygote • Takes place in the ampulla of the uterine tube 1. Sperm binds to zona pellucida glycoprotein 2. Acrosomal enzymes released from...

Fertilisation to Trilaminar 21/10/23, 6:02 PM Fertilisation to Trilaminar Fertilisation • Fertilisation: union of gametes - fusion of sperm and oocyte to form a zygote • Takes place in the ampulla of the uterine tube 1. Sperm binds to zona pellucida glycoprotein 2. Acrosomal enzymes released from sperm head; sperm digests its way into egg 3. Egg and sperm plasma membranes fuse and sperm contents enters the egg 4. Sperm entry triggers completion of meiosis 2 and release of cortical granules by oocyte (make ZP impenetrable to other sperm) Cleavage • One cell embryo undergoes a series of cleavage divisions • Rapid mitotic division without increase in size; because cells are confined within the ZP the embryo will change shape (compaction) • • • • • Form morula (16+ cells) then blastocyst (200-300 cells) The blastocyst is comprised of two different cell types: ◦ Outer cell mass (trophoblast): contacts with the endometrium of the uterus to facilitate implantation and the formation of the placenta ◦ Inner cell mass (embryoblast): responsible for the formation of the embryo itself Cells maximize available space by coming into closer contact with each other Inner cells form cell junctions, outer cells form gap junctions Fluid enters through ZP producing a blurred cell mass - signals the formation of the blastocyst Implantation • Embryo implants into endometrial lining on posterior or anterior uterine wall • Ectopic pregnancy: implantation outside the uterus • Placenta previa: placenta lies low in uterus and partially/completely covers cervix Development of the bilaminar embryo Day 7.5 • Trophoblast divides into cytotrophoblast (individual cells) and syncytioblast (single multinucleated cell which produces hCG) • • Embryobast divides into epiblast (dorsal surface) and hypoblast (ventral surface) Amniotic cavity begins to form https://galvanized-borogovia-4fa.notion.site/Fertilisation-to-Trilaminar-656176617e0e496b813f5da9d4a64ee1 Page 1 of 3 Fertilisation to Trilaminar 21/10/23, 6:02 PM Day 9 • • Formation of 2 cavities = amniotic cavity (epiblast) and primitive yolk sac (hypoblast) Implantation complete Day 12 • • Uteroplacental circulation established Extraembryonic mesoderm develops then degenerates, forming chorionic cavity Day 13 • • • Further development of chorionic cavity Presence of existing stalk (later umbilical cord) Second wave of hypoblast cells migrate to form definitive yolk sac Gastrulation • Invagination of the epiblast cells through the primitive stream to form the 3 primary germ layers - ectoderm, mesoderm, endoderm (trilaminar embryo) Ectoderm • • Epidermis of skin, hair, nails Nervous system Mesoderm • • • Paraxial mesoderm: axial skeleton, skeletal muscle Intermediate mesoderm: urogenital systems Lateral plate mesoderm ◦ ◦ Somatic layer: dermis, lining of body wall, parts of limbs Visceral layer: cardiovascular system, mesothelial covering of organs, smooth muscle Endoderm • • • Lining of gut tube Lining of respiratory tract Lining of bladder and urethra https://galvanized-borogovia-4fa.notion.site/Fertilisation-to-Trilaminar-656176617e0e496b813f5da9d4a64ee1 Page 2 of 3 Fertilisation to Trilaminar https://galvanized-borogovia-4fa.notion.site/Fertilisation-to-Trilaminar-656176617e0e496b813f5da9d4a64ee1 21/10/23, 6:02 PM Page 3 of 3