Preclinical Paediatrics · MU Sofia

1. Prenatal human development - periods, stages, and processes of development after fertilization.

Outlines the three phases of human prenatal development, from the proliferative period after fertilisation through the embryonic period to the foetal period. It then follows the main events in order: cleavage, blastocyst formation and implantation, bilaminar and trilaminar disc formation, gastrulation, notochord and neural tube development, and head and pharyngeal arch formation. Several picture-based steps are included, with a short closing summary of developmental stages.

Inside: 1 section · 11 labelled pictures · 14 flashcards · 9 min

Topic 1 of 40 in the MU Sofia syllabus for Preclinical Paediatrics (Dental Medicine, Year 3). The free AceMed note covers it in 1 section, about 1,353 words (9 min of reading), with 14 flashcards.

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  1. PRENATAL HUMAN DEVELOPMENT - PERIODS, STAGES, AND PROCESSES OF DEVELOPMENT AFTER FERTILIZATION.

PRENATAL HUMAN DEVELOPMENT - PERIODS, STAGES, AND PROCESSES OF DEVELOPMENT AFTER FERTILIZATION.

Human prenatal development lasts for around 10 months and split into 3 phases:

  • Proliferative Period
  • After fertilization and spans the first 2 weeks
  • Fertilization and implantation
  • Large cellular proliferation and migration
  • Embryonic disk takes place and formation of blastocyst
  • Embryonic Period
  • 2nd to 8th week of development
  • Induction, proliferation, differentiation, morphogenesis and maturation
  • Largely the differentiation of all major internal and external organs= morphogenesis
  • Foetal Period
  • 9th week to end of pregnancy
  • Active growth and maturation

Proliferative Period

  1. 1. Origin of tissue begins with fertilization of the egg or ovum which occurs when sperm contacts egg in distal part of uterine tube
  2. 2. Fertilization happens in upper 1/3 of oviduct/fallopian tube
  3. 3. After fertilization, one large cells known as zygote
  4. 4. First period of prenatal development is the preimplantation period
  • Happens in first week of development
  1. 5. In the centre of zygote can be seen the female and male genetic material in the forms of two nucleolus
  2. 6. Stages of Cell Division
  • Two cell stage
  • Four cell stage
  • Morula (10-32 cells)
  • Morula grows and begins migration medially to uterus at the end of 1st week
  1. 7. Following the morula’s entry into the uterus from fallopian tube, morula becomes the blastocysts through cellular differentiation and cavitation
  • Differentiates into two types:
  • Inner Mass: on the interior surface of blastocoel
  • Trophoblast cells: grow on the exterior
  1. 8. Implantation: blastocyst attaches to the uterine wall by digesting the uterine endometrium, allowing for deeper penetration

Formation of Blastula marks the beginning of morphogenesis, shaping of embryo

Migration of diving cells to specific locations

Inner mass of cells at one end- Totipotent embryonic stem cells or embryoblasts

Outer cells: forms extraembryonic tissues i.e. yolk sac, placenta

Embryonic Period (2nd to 8th Week)

Week 2

Embryonic Disk

  • Two small cavities form on either side of inner cell mass
  • Reach the other in the centre, where small disk is formed
  • Embryo disk becomes the embryo, composed of common walls of two adjacent sacs
  • One sac lined with ectodermal cells which forms the outer body covering- epithelium
  • Other sac lined with endodermal cells
  • Embryonic disk is called the embryoblast
  1. 1. Blastocyst increases in size by differentiation
  2. 2. Blastocyst cavity forms between the inner cell mass and trophoblasts
  3. 3. Differentiation of inner mass begins, which results in formation of bilaminar disc composed of two layers
  4. 4. Two layers- Epiblast and Hypoblast
  • Upper Layer- Epiblast- will become ectoderm, mesoderm, endoderm

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