26. Embryonic period - stages. The “induction” theory of Spemann.

Question 1

Week 1-3:

• 7 days after fertilisation, blastula attaches to the wall of the uterus (endometrium) - implantation
• connections between mother and embryo begin to form the umbilical cord
• embryo’s growth centres around an axis - becomes the spine and spinal cord
• brain, spinal cord, tear and gastrointestinal tract begin to form
• 3rd week - embryonic development gastrulation occurs and creates a 3 lamina disk
• composed of the 3 layers: endoderm, mesoderm, ectoderm

Answer 1

Week 1-3:

• 7 days after fertilisation, blastula attaches to the wall of the uterus (endometrium) - implantation
• connections between mother and embryo begin to form the umbilical cord
• embryo’s growth centres around an axis - becomes the spine and spinal cord
• brain, spinal cord, tear and gastrointestinal tract begin to form
• 3rd week - embryonic development gastrulation occurs and creates a 3 lamina disk
• composed of the 3 layers: endoderm, mesoderm, ectoderm

Question 2

Week 4-5:

• chemicals produced by the embryo stop the women’s menstrual cycle
• neurogenesis is in progress - showing brain activity at the 6th week
• heart begins to beat around the same time limb buds appear - where arms and legs will grow
• organogenesis begins
• brain develops into fine area
• tissue formation develops into the vertebra and other bones
• heart starts to beat, blood starts to flow

Answer 2

Week 4-5:

• chemicals produced by the embryo stop the women’s menstrual cycle
• neurogenesis is in progress - showing brain activity at the 6th week
• heart begins to beat around the same time limb buds appear - where arms and legs will grow
• organogenesis begins
• brain develops into fine area
• tissue formation develops into the vertebra and other bones
• heart starts to beat, blood starts to flow

Question 3

Week 6-8:

• myogenesis and neurogenesis have progressed - embryo can now move
• eyes begin to form
• organogenesis and growth continue
• hair has started to form and essential organs
• facial features begin to develop
• at end of 8th week - embryonic stage over, foetal stage starts

Answer 3

Week 6-8:

• myogenesis and neurogenesis have progressed - embryo can now move
• eyes begin to form
• organogenesis and growth continue
• hair has started to form and essential organs
• facial features begin to develop
• at end of 8th week - embryonic stage over, foetal stage starts

Question 4

The “induction” theory of Spemman:

• his study showed - certain parts of embryo - organising centres - direct the development of groups of cells into particular organs + tussues
• then demonstrated, an absence of predestined organs and tissues in the earliest stages of embryo development
• tissue excysted from one part of the embryo and grafted onto another part
• will assume their character of the later
• this opened a new field of research on the recognition of similar organising counters in other animal groups

Answer 4

The “induction” theory of Spemman:

• his study showed - certain parts of embryo - organising centres - direct the development of groups of cells into particular organs + tussues
• then demonstrated, an absence of predestined organs and tissues in the earliest stages of embryo development
• tissue excysted from one part of the embryo and grafted onto another part
• will assume their character of the later
• this opened a new field of research on the recognition of similar organising counters in other animal groups