Features of implantation and fertilisation

• What is fertilisation ?

  the fusion of a haploid male and haploid female gamete (sperm and egg).
• What is a zygote?

  
  

  A diploid cell resulting from the fusion of gametes.
• What is a morula?

  an early stage of cell division with no differentiation.
• What is a blastocyst ?

  A cell division where differentiation has occurred.
• What is the inner cell mass ?

  will form the embryo and the outer layer will form the placenta.
• What is a trophoblast?

  
  

  cells that form the outer layer of a blastocyst, providing nutrients to the embryo, and developing into a large part of the placenta.
• what s implantation ?

  the attachment of the blastocyst to the uterus wall.
• What is an embryo ?

  A developing human from fertilization to the 8th week of pregnancy.
• What is a fetus?

  
  

  An embryo from the 8th week onwards, which begins to look more human like.
• 3 TYPES OF MAMMALS 

  • Monotremes (egg laying) 
  • Marsupials (pouched) 
  • Eutherians (placental)
• Testes produce haploid spermatozoon through meiosis : 

  • Head contains densely packed DNA and is capped by the acrosome 
  • Neck containing centrioles to support early zygote divisions.
  • Mitochondria (for energy).
  • Flagellated tail to aid in swimming.
• Males release semen containing spermatozoon from the penis through a process called ejaculation :  

  • In monotremes and marsupials, it enters the cloaca/urogenital sinus
  • In placental mammals it enters the vagina.
• THE 2 LAYERS OF THE OOCYTE (EGG CELL)

  • Corona Radiata
  • Zona Pellucida
• Ovary contains follicles in which meiosis occurs to produce the oocyte. Process of meiosis is only fully complete after the entry of the spermatozoon, when the oocyte becomes the ovum
• FIRST STEP OF FERTILISATION

  Sperm makes contact with outer layer of oocyte (zona pellucida of the egg) and releases enzymes to help it penetrate
• SECOND STEP OF FERTILISATION

  One sperm cell  attaches to the receptors of the zona pellucida (Once this occurs, a chemical is released that causes a change in the egg’s membrane to stop other sperm cells from attaching)
• THIRD STEP OF FERTILISATION

  The acrosome of the sperm releases digestive enzymes which allow the sperm to burrow through the zona pellucida
• FOURTH STEP OF FERTILISATION

  Once sperm enters the cytoplasm, the oocyte (egg) completes its meiotic cell division 
• FIFTH STEP OF FERTILISATION

  The plasma membrane of the sperm and egg then fuse together 
• SIXTH STEP OF FERTILISATION

  Sperm nucleus enters the egg, giving rise to eh first diploid cell (zygote)
• DAY 1 OF IMPLANTATION

  Fertilization occurs (union of egg and sperm)
• DAY 2 OF IMPLANTATION

  Zygote has formed and is moving through the fallopian tube
• DAY 3 - 4 OF IMPLANTATION

  Mitotic cell division occurs to form small solid ball of cells called the morula. In the uterus, the morula divides into the blastocyst (with distinct features)
• DAY 7 OF IMPLANTATION

  Implantation occurs; trophoblast burrows into the endometrium and is when the development of the placenta occurs. Endometrium undergoes decidualization to support the implanted blastocyst (endometrial thickening and increase in blood supply)
• DAY 7 - 9 OF IMPLANTATION

  Blastocyst releases digestive enzyme that break down cellular matrix and trophoblast intrudes the epithelium. After implantation, the stem cells start differentiating and the body plan of the new embryo starts to develop
• DAY 9-25 OF IMPLANTATION

  Significant embryonic development, continued differentiation and specialization occurring, increased maternal blood flow, umbilical cord has started developing
• IMPLANTATION IN PLACENTAL/EUTHERIAN MAMMALS

  Trophoblast turns into placenta and the ICM urns into teh  embryo
• IMPLANTATION IN MONOTREMES

  No implantation; embryo develops in egg which is nourished in the secretions from the uterine wall before the shell is added
• IMPLANTATION IN MARSUPIALS

  gestation (period of development during the carrying of an embryo and later foetus)  is one month. Early nutrition from the yolk of ovum and uterus secretions
• An immature egg cell is called a oocyte which through the ovulation process matures and turns into ovum
• The oocyte is formed after the first cycle of meiosis and the ovum is formed after the second cycle meiosis