1. Introduction to developmental anatomy - embryology
Dr. Anne Pulei
University of Nairobi ISO 9001: Certified

3. He who sees things grow from the beginning will have the finest view of them.
Aristotle 384 – 322 B.C.

4. Objectives Describe: Developmental periods Embryological terminologies
Significance of embryology

5. Definition of terms Embryology
The study of the developmental process from a single cell to a baby in 9 months.
Embryogenesis-formation and development of an embryo
Organogenesis- the 3 germ layers becoming organs
Morphogenesis – Process of shape development
Ontogeny - Process of development of an organism

6. Developmental Periods
It is customary to divide human development
prenatal (before birth)
postnatal (after birth) periods

7. Stages of Prenatal Development
Spermatozoon and oocyte
Zygote: From union of an oocyte and a sperm during fertilization. 

Embryo (3-8 weeks: upto day 56)

Fetus (>9 weeks or day 57) .

9. Figure 1-2 The embryonic period terminates at the end of the eighth week; by this time, the beginnings (primordia) of all essential structures are present. The fetal period, extending from 9 weeks to birth, is characterized by growth and elaboration of structures. Sex is clearly distinguishable by 12 weeks. Fetuses are viable 22 weeks after fertilization, but their chances of survival are not good until they are several weeks older. The 11- to 38-week fetuses shown are approximately half of their actual sizes. For more information, see Chapter 6.
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10. Definitions : Gestational Age
Calculated from the presumed first day of the last normal menstrual period
Which is approximately 2 weeks longer than the fertilization age
because the oocyte is not fertilized until approximately 2 weeks after the preceding menstruation

11. Cleavage
Series of mitotic cell divisions of the zygote resulting in blastomeres
Blastomeres are early embryonic cells
The cleaving zygote size remains unchanged
because at each succeeding cleavage division, the blastomeres become smaller

12. Morula (L. morus, mulberry)
This solid mass of 12 to approximately 32 blastomeres-formed by cleavage
The blastomeres change their shape and tightly align themselves against each other to form a compact ball of cells-compaction
Occurs 3 to 4 days after fertilization, just as the early embryo enters the uterus

13. Blastocyst (Gr. blastos, germ + kystis, bladder)
Formed when a fluid-filled cavity, the blastocystic cavity, develops inside the morula
Blastocyst centrally located cells, the inner cell mass or embryoblast, is the embryonic part of the embryo

14. Implantation
Attachment of the blastocyst to the endometrium and subsequently embedding in it
(Endometrium is the mucous membrane or lining of uterus)
The pre-implantation period of embryonic development is the time between fertilization and the beginning of implantation
a period of approximately 6 days

16. Gastrula (Gr. gaster, stomach)
The blastocyst is converted into a gastrula: a three-layered or trilaminar embryonic disc forms structure during the third week
The three germ layers of the gastrula are: ectoderm, mesoderm, and endoderm
The layers differentiate into the tissues and organs of the embryo

17. Neurula (Gr. neuron, nerve)
It is the first appearance of the nervous system and the next stage after the gastrula
This occurs during the third and fourth weeks

18. Embryo (Gr. Embryon) This is the early developing human
Embryonic period extends to the end of the eighth week (56 days), by which time the beginnings of all major structures are present
The size of embryos is given as crown-rump length, which is measured from the vertex of the cranium (crown of head) to the rump (buttocks)

19. Conceptus (L. conceptio)
This the product of conception
The conceptus includes all structures that develop from the zygote,
both embryonic and extraembryonic e.g. the placenta and its associated membranes

20. Primordium (L. primus)
The beginning or first discernible indication of an organ or structure e.g. the primordium of the upper limb appears as a bud on day 26
The terms anlage and rudiment have similar meanings

21. Fetus (L. unborn offspring)
After the embryonic period (8 weeks-56 days) and until birth, the developing human is called a fetus
During the fetal period (ninth week to birth), differentiation and growth of the tissues and organs formed during the embryonic period occur
These developmental changes are not dramatic

22. Abortion (L. aboriri, to miscarry)
A premature stoppage of development and expulsion of a conceptus from the uterus or expulsion of an embryo or fetus before it is viable-capable of living outside the uterus
An abortus is the products of an abortion (i.e. the embryo/fetus and its membranes)

24. Trimester A period of three calendar months during a pregnancy
Obstetricians commonly divide the 9-month period of gestation into three trimesters
The most critical stages of development occur during the first trimester (13 weeks) when embryonic and early fetal development is occurring

25. Postnatal Period The period occurring after birth.
Infancy refers to the earliest period of extrauterine life, roughly the first year after birth.
An infant aged 1 month or younger is called a newborn or neonate.
The body grows particularly rapidly
total length increases by approximately one half
weight is usually triple.

26. Childhood
This is the period from approximately 13 months until puberty
Just before puberty, growth accelerates-the prepubertal growth spurt.

27. Puberty
Occurs usually between the ages of 12 and 15 years in girls and 13 and 16 years in boys,
Features
secondary sexual characteristics develop
capability of sexual reproduction is attained
Puberty ends
in females with the first menstrual period or menarche,
in males when mature sperms are produced

28. Adolescence The period from approximately 11 to 19 years of age,
Characteristics
rapid physical and sexual maturation.
extends from the earliest signs of sexual maturity-puberty-until the attainment of adult physical, mental, and emotional maturity.

29. Adulthood (L. adultus, grown up)
Attainment of full growth and maturity, is generally reached between the ages of 18 and 21 years
Ossification and growth are virtually completed during early adulthood (21 to 25 years)
Thereafter, developmental changes occur very slowly

30. Teratology (Gr. teratos, monster)
This is part of embryology and pathology that deals with abnormal development
Concerned with various genetic and/or environmental factors that disturb normal development and produce birth defects

31. DESCRIPTIVE TERMS IN EMBRYOLOGY
Descriptions based on anatomical position
Anterior or ventral (front)
posterior or dorsal (back)

32. Describing the Embryo
When describing embryos, the terms dorsal and ventral are used
Superior and inferior are used to indicate the relative levels of different structures
For embryos, the terms cranial or rostral and caudal are used to denote relationships to the head and caudal eminence (tail), respectively

33. Distance
Distances from the source or attachment of a structure are designated as proximal or distal
In the lower limb, for example, the knee is proximal to the ankle and the ankle is distal to the knee

34. Other planes 1
The median plane is an imaginary vertical plane of section that passes longitudinally through the body
Median sections divide the body into right and left halves
The terms lateral and medial refer to structures that are, respectively, farther from or nearer to the median plane of the body

35. Other planes 2
A sagittal plane is any vertical plane passing through the body that is parallel to the median plane
A transverse (axial) plane refers to any plane that is at right angles to both the median and coronal planes
A frontal (coronal) plane is any vertical plane that intersects the median plane at a right angle and divides the body into anterior or ventral and posterior or dorsal parts.

36. Figure 1-7 Drawings illustrating descriptive terms of position, direction, and planes of the body. A, Lateral view of an adult in the anatomical position. B, Lateral view of a 5-week embryo. C and D, Ventral views of 6-week embryo. E, Lateral view of a 7-week embryo. In describing development, it is necessary to use words denoting the position of one part to another or to the body as a whole. For example, the vertebral column (spine) develops in the dorsal part of the embryo, and the sternum (breast bone) in the ventral part of the embryo.
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37. SIGNIFICANCE OF EMBRYOLOGY
Bridges the gap between prenatal development and obstetrics, perinatal medicine, pediatrics, and clinical anatomy
Develops knowledge concerning the beginnings of human life and the changes occurring during prenatal development
Is of practical value in helping to understand the causes of variations in human structure
Illuminates gross anatomy and explains how normal and abnormal relations develop.

39. Textbooks of embryology
3. Textbook of Medical embryology By Fasana

40. THANK YOU