đ¤āĻāĻ āĻāĻŽāĻ°āĻž āĻĒā§āĻŦā§ Notochord āĻ¨āĻŋā§ā§āĨ¤ āĻ¯āĻĻāĻŋāĻ āĻ¯āĻāĻ¨ āĻāĻŽāĻŋ embryo āĻĒā§āĻ¤āĻžāĻŽ, āĻāĻāĻž āĻā§āĻŦ āĻ āĻĒā§āĻ¯āĻžāĻā§ āĻĢā§āĻ˛āĻ¤ā§āĨ¤ đ°
âāĻĒā§āĻ°āĻĨāĻŽāĻ¤ āĻāĻŽāĻ°āĻž āĻāĻžāĻ¨āĻŋ āĻ¯ā§ , epiblast and hypoblast āĻĻā§āĻāĻāĻŋ layer āĻĨā§āĻā§āĻ āĻ¤ā§āĻ°āĻŋ āĻšā§, 3 germ layers.. đ
đŠ Epiblast is converted into amniotic cavity
đŠ Hypoblast is converted to yolk sac.
đŧāĻāĻāĻ¨ āĻāĻ epiblastic cell āĻā§āĻ˛āĻž embryo āĻāĻ° caudal region āĻĨā§āĻā§ hypoblast āĻ āĻ¯ā§āĻ¤ā§ āĻĨāĻžāĻā§āĨ¤ āĻ¯āĻžāĻ° āĻĢāĻ˛ā§ āĻ¸ā§āĻāĻžāĻ¨ā§ āĻ¤ā§āĻ°āĻŋ āĻšā§ āĻāĻāĻāĻž groove āĻŦāĻž āĻ˛āĻŽā§āĻŦāĻž āĻāĻ°ā§āĻ¤āĨ¤
đē āĻ¸ā§āĻāĻžāĻā§āĻ āĻŦāĻ˛āĻž āĻšā§ Primitive Streak
đŠIt appears at 2nd week of development which is a longitudinal ridge at the dorsal surface of germ disc..
đŠāĻāĻ°āĻĒāĻ° āĻāĻ Primitive streak āĻāĻ° cranial end āĻ āĻ¤ā§āĻ°āĻŋ āĻšā§ āĻāĻ°ā§āĻāĻāĻŋ shallow rounded groove āĻ¯āĻžāĻ° āĻ¨āĻžāĻŽ Primitive Node. đ
đŠāĻāĻāĻ¨ āĻāĻŽāĻ°āĻž āĻāĻžāĻ¨āĻŋ āĻ¯ā§, germ disc āĻāĻ° cranial end āĻ āĻāĻā§ prechordal plate. āĻāĻŦāĻ caudal end āĻ āĻ āĻŦāĻ¸ā§āĻĨāĻŋāĻ¤ primitive streak with primitive node..
đŠ āĻāĻĻāĻŋāĻā§ epiblastic cell āĻā§āĻ˛āĻž hypoblast āĻ āĻ¯āĻžāĻā§āĻžāĻ° āĻĢāĻ˛ā§ āĻ¤ā§āĻ°āĻŋ āĻšāĻ˛ā§ āĻ¤āĻŋāĻ¨āĻāĻŋ āĻ˛ā§ā§āĻžāĻ°āĨ¤
1. Ectoderm
2.Mesoderm
3.Endoderm
đŠ Mesoderm layer āĻāĻ° āĻāĻŋāĻ¤āĻ° just below the primitive node āĻ¤ā§āĻ°āĻŋ āĻšāĻ¤ā§ āĻĨāĻžāĻā§ Notochordal plate...
It is situated between the primitive node and prechordal plate.. āĻ āĻ°ā§āĻĨāĻžā§, primitive nodeāĻāĻŦāĻ prechordal plate āĻāĻ° āĻŽāĻ§ā§āĻ¯āĻŦāĻ°ā§āĻ¤ā§ āĻ¸ā§āĻĨāĻžāĻ¨ā§ mesoderm layer āĻ āĻ āĻŦāĻ¸ā§āĻĨāĻŋāĻ¤ tube like structure āĻ āĻšāĻ˛ā§ Notochord...đ
đŠđŠ āĻāĻāĻ¨ āĻĻā§āĻāĻž āĻ¯āĻžāĻ āĻāĻ° function āĻā§āĻ˛āĻžāĻ đ
1. It forms the central axis of embryo.
2. It helps in neural tube formation
3. It provides central axis around which vertebrae and intervertebral disc develop..
đŠFate of notochord: it disappeares..
only 2 ramnats remain:
1. Nucleus pulposus of Inter vertebral disc
2. Epical ligament of odontoid process of 2nd cervical vertebrae..