Embryology Formation Of Germ Short Essay Question And Answers

Question 1. Somites
Answer:

• Cells of paraxial mesoderm gets segmented into somitomeres and somites
• Somites are cubical and more distinctly segmented
• Most cranial somites are located in occipital region New somites are formed caudal to them
• There are about 44 pairs of somites
  • 4-occipital
  • 8-cervical
  • 12-thoracic
  • 5-lumbar
  • 5-sacral
  • 8-10-coccygeal

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Somites Fate of Somites:

• Ventromedial part called sclerotome gives rise to the vertebral column and ribs
• Lateral part called dermatome give rise to the dermis of the skin and to subcutaneous tissue
• Intermediate part called myotome gives rise to striated muscle
  Cranial to it:
  • Occipital somites give rise to muscles of the tongue and supplied by hypoglossal nerve
  • Pre-occipital somites are supplied by third, fourth and sixth cranial nerves

Question 2. Yolk sac
Answer:

• As the fluid from the uterine cavity enters morula, it gets converted to blastocyst The outer layer of it is formed by trophoblast and inner layer by inner cell mass
• Some of the inner cell mass layer cells become flattened – these are called hypoblast
• Remaining cells become columnar to form epiblast
• The space between epiblast and hypoblast is called amniotic cavity
• Flattened cells from hypoblast spread and line blastocytic cavity and form primary yolk sac
• After formation of extra-embryonic coelom, the yolk sac becomes smaller and lined by cubical cells and form secondary yolk sac

Question 2. Effects of fertilization:
Answer:

Effects of fertilization Fertilization:

• It is the process by which male and female gametes fuse is known as fertilization.
• Site: In the ampullary region of the uterine tube.
• Effects:
  • Binding of sperm to zona pellucid of the ovum.
  • Penetration of the sperm through the zona pellucida
  • Fusion of the cell membranes of the sperm and the ovum.
  • Release of acrosomal enzymes.
  • Prevention of entry of other spermatozoon into the oocyte.
  • Metabolic changes within the ovum.
  • The diploid chromosome number is restored.
  • Sex determination takes place.

Question 3. Intraembryonic mesoderm.
Answer:

• The embryonic disc is made up of three germ layers – ectoderm, mesoderm and endoderm.
• The mesoderm layer present within the embryonic disc is known as intra – embryonic mesoderm.
• It spreads throughout the disc except in the region of the prochordal plate,
• It shows three subdivision.
  1. Paraxial mesoderm.
     • It is the mesoderm next to the middle line.
     • It undergoes segmentation to form somites.
  2. Later plate mesoderm.
     • Lateral plate mesoderm.
     • It contains intra-embryonic coelem.
  3. Intermediate mesoderm.
     • It is a strip of mesoderm present between the lateral plate mesoderm and the paraxial mesoderm.

• Time of formation: 19 days of IU life.

Question 4. Fertilization
Answer:

• It is the process by which male and female gametes fuse
• It occurs in the ampullary region of the uterine tube

Question 5. Morula
Answer:

• A process called cleavage occurs which divides the ovum into smaller cells
• When ovum comes to have 16 cells it looks like mulberry so called morula

Morula Layers:

1. Inner cell mass
   • Gives rise to embryo proper
2. Outer layer of trophoblast
   • Completely surrounds the inner cell mass
   • Helps to provide nutrition to embryo
3. Fluid from uterine cavity separates the inner cell mass and cells of trophoblast