Foundations Lecture - Introduction to Human Development

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Dr Mark Hill

Human development is one of the most exciting topics to study not only as a medical student, but also for our fundamental understanding of the human body. Of all health issues in Medicine, fertility and reproduction is a topic that will affect everyone. This lecture is going to take you briefly through key biological concepts in human development, these will later be explored in more detail through the BGD course. I will be using simplified terms in the lecture slides (with developmental term in brackets).

Human fertilization 01.gif

2019 PDF

Australian Population Clock - 25,278,727  
On 5 March 2019 at 10:36:24 AM (Canberra time), the resident population of Australia is projected to be:


This projection is based on the estimated resident population at 31 December 2017 and assumes growth since then of:

  • one birth every 1 minute and 40 seconds,
  • one death every 3 minutes and 16 seconds,
  • one person arriving to live in Australia every 57 second,
  • one Australian resident leaving Australia to live overseas every 1 minute and 49 seconds, leading to
  • an overall total population increase of one person every 1 minute and 15 seconds.

These assumptions are consistent with figures released in Australian Demographic Statistics, December Quarter 2017 (cat. no. 3101.0).
Australia and the World...

Australia and world population growth graph.jpg

Australian Bureau of Statistics Population Clock

Australia and the World (2010)

  Population Growth Rate | Fertility Rate | AUS, CHN, IND, IDN, USA | World Growth

The lecture will be followed by a practical class introducing online resources for independent study and working through basic embryology concepts.

Links: 2018 | 2018 PDF | 2017 | 2017 PDF | Printable Lecture Page | 2016 | 2015 | 2014 | 2013 | 2012
Other Foundations links  
The following lecture, practical and practical support pages for Foundations can be found on this current site.


  1. Purpose of learning embryology
  2. Basic facts about early human development
  3. Appreciate differences between the conceptus, embryo and fetus
  4. General understanding of the term “critical periods” of development

Lecture Concepts: Embryology Education Support, Human Reproductive Cycle, First Trimester, Second and Third Trimester, Postnatal Development, Abnormal Development

Lecture Content  
  1. Embryology Education Support - UNSW Embryology Online, Glossary Links, Textbooks
  2. Human Reproductive Cycle - Female. Male, Ovary, Ovulation, Trimesters
  3. First Trimester - Fertilization, Week 1, Week 2, Abnormal Implantation, Normal Implantation, Detect Pregnancy, Week 3, Gastrulation, Ectoderm, Endoderm, Mesoderm, Somitogenesis, Neuralation, Week 4, Week 4-8, Placenta
  4. Second and Third Trimester - Fetal, growth - weight and length
  5. Postnatal Development - Birth, Maternal Birth Stages, Neonatal, Childhood
  6. Abnormal Development - Critical Periods of Development, Diagnosis
Links: Embryology Textbooks | Practical
<html5media height="260" width="320">File:1 Min Embryo - Find Embryology.mp4</html5media>

Four Basic Tissue Types

Stomach Wall containing all 4 basic tissues.

In histology you have heard that tissues and organs of the body consist of combinations of 4 basic tissue organisations:

  1. Epithelial
  2. Connective
  3. Muscular
  4. Nervous
  • What is the origin of these tissues?
  • How do they develop?
  • What are their relationships with each other?
  • What health issues relate to their normal/abnormal development?

Human Development Timeline

Human development timeline graph 02.jpg

concepts animation

Last Menstrual Period (LMP) first day was today -> Birth Date - January 6, 2020  
Gestation Calculation (based upon a normal 28 day cycle)
  • Historic - Franz Carl Naegele (1777-1851), first rule for estimating pregnancy length
  • Current - Ultrasound, the most accurate staging method
  • First pregnancy (primipara) 274 days, just over 39 weeks
  • Subsequent pregnancies (multipara) 269 days, 38.4 weeks
  • GA - gestational age

Embryology Education Support

UNSW Embryology Online


<html5media height="384" width="352">File:Human development 001.mp4</html5media>
Human development 001 icon.jpg
 ‎‎Human Development
Page | Play


Using these resources (online navigation, organization and printing) will be covered in the introduction to the associated Practical class.

Glossary Links

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols

Practical pages general have a list of brief definitions of terms that appear on the current page, or more complete collapsed tables of terms.

Terms - highlighted text terms link to other content pages that relate to that specific term. Note that these linked pages do not generally form part of your examinable content, and are provided to aid your understanding of the concepts.


  • There are many different excellent embryology textbooks.
  • I have included below embryology textbooks accessible online through the UNSW Library that cover the clinical topics as well.
  • As an introduction try the chapter in The Developing Human - Introduction to the Developing Human

The Developing Human: Clinically Oriented Embryology (10th edn) 
The Developing Human, 10th edn.jpg

UNSW Students have online access to the current 10th edn. through the UNSW Library subscription (with student Zpass log-in).

APA Citation: Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.

Links: PermaLink | UNSW Embryology Textbooks | Embryology Textbooks | UNSW Library
  1. Introduction to the Developing Human
  2. First Week of Human Development
  3. Second Week of Human Development
  4. Third Week of Human Development
  5. Fourth to Eighth Weeks of Human Development
  6. Fetal Period
  7. Placenta and Fetal Membranes
  8. Body Cavities and Diaphragm
  9. Pharyngeal Apparatus, Face, and Neck
  10. Respiratory System
  11. Alimentary System
  12. Urogenital System
  13. Cardiovascular System
  14. Skeletal System
  15. Muscular System
  16. Development of Limbs
  17. Nervous System
  18. Development of Eyes and Ears
  19. Integumentary System
  20. Human Birth Defects
  21. Common Signaling Pathways Used During Development
  22. Appendix : Discussion of Clinically Oriented Problems
Larsen's Human Embryology (5th edn) 
Larsen's human embryology 5th ed.jpg
UNSW students have full access to this textbook edition through UNSW Library subscription (with student Zpass log-in).

APA Citation: Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R., Francis-West, P.H. & Philippa H. (2015). Larsen's human embryology (5th ed.). New York; Edinburgh: Churchill Livingstone.

Links: PermaLink | UNSW Embryology Textbooks | Embryology Textbooks | UNSW Library
  1. Gametogenesis, Fertilization, and First Week
  2. Second Week: Becoming Bilaminar and Fully Implanting
  3. Third Week: Becoming Trilaminar and Establishing Body Axes
  4. Fourth Week: Forming the Embryo
  5. Principles and Mechanisms of Morphogenesis and Dysmorphogenesis
  6. Fetal Development and the Fetus as Patient
  7. Development of the Skin and Its Derivatives
  8. Development of the Musculoskeletal System
  9. Development of the Central Nervous System
  10. Development of the Peripheral Nervous System
  11. Development of the Respiratory System and Body Cavities
  12. Development of the Heart
  13. Development of the Vasculature
  14. Development of the Gastrointestinal Tract
  15. Development of the Urinary System
  16. Development of the Reproductive System
  17. Development of the Pharyngeal Apparatus and Face
  18. Development of the Ears
  19. Development of the Eyes
  20. Development of the Limbs
Ebook - Kyoto Collection (1st edn) 
Kyoto Embryo Collection - cover.jpg UNSW students can download this free iBook that describes embryos from the first 8 weeks of development showing whole embryos, histological features, movies and high resolution 3D scans. The iBook also contains a linked glossary with descriptions of embryology terminology, and related terms.

Note - Only available for the Apple iPhone, iPad and laptop and desktop computers. No PC version currently available.

APA Citation: Hill MA. Shiota K. Yamada S. and Ho C. Kyoto Embryology Collection. (2016) Apple iTunes. Retrieved from:

Links: iTunes link | Kyoto Collection | Embryology iBooks | UNSW Embryology Textbooks | Embryology Textbooks | UNSW Library
Links: Embryology Textbooks - UNSW | More Embryology Textbooks

Human Reproductive Cycle

  • Meiosis in gonad produces haploid gametes
  • there are key differences in when and how gametes are formed in the male and female gonad.


  • menstrual cycle a regular cycle of reproduction (28 days)
  • begins at puberty
  • all oocytes produced before birth
  • release of 1 egg (oocyte) every cycle
  • Endocrine controlled axis: Hypothalamus - Pituitary - Gonad (HPG axis)

XXhpgaxis.jpg Menstrual cycle.png


  • begins at puberty
  • continuous production of sperm (spermatozoa, human male 2,000/second)
  • release millions of spermatozoa (require activation, capacitation)
Testis Pre-Puberty Testis Post-Puberty
Testis histology 006.jpg Testis histology 007.jpg


  • Paired organs
  • lying in the peritoneal cavity

Human right ovary and tube 1.jpg Ovary10x.jpg


Human Menstrual Cycle

Human ovulation 01.jpg

Human ovulation

Ovulation icon.jpg Follicle 001 icon.jpg


  • Divide the pregnancy into 3 "blocks" of about 3 months (trimesters)
  • First Trimester - embryonic period (organogenesis)
  • Second and Trimester - fetal period (growth)

First Trimester

  • Embryonic Period - Week 1 to 8 (first trimester)
  • Establish the basic structure of organs and tissues (Organogenesis)
  • development and growth of the placenta (Placentation)

Human Carnegie stage 1-23.jpg

Embryo stages 002 icon.jpg


  • the process of the 2 haploid gametes (egg and sperm) fusing and combining their genetic material.
  • conceptus - the entire product of fertilisation.

Human fertilization movie 2 frame 01.jpg Fertilization 002 icon.jpg

Early zygote.jpg

Week 1

Human fertilization movie 1 frame 05.jpg Week1 001 icon.jpg

  • (GA week 3)
  • occurs freely floating in uterus
  • occurs during week 1 following fertilization
  • last menstrual period (LMP) week 3
  • mitosis to form solid ball of cells (morula), then hollow ball (blastocyst)

Human blastocyst day 1-6.jpg

Week1 summary.jpg

Week 2

(GA week 4)

  • implantation - initial attachment to uterine wall, and then invasion of the uterine wall. Note - this is where the placenta will form.

Week2 001 icon.jpg Chorion 001 icon.jpg

Normal Implantation

  • Uterine body
    • posterior, anterior, superior, lateral (most common posterior)
    • inferior implantation - placenta overlies internal os of uterus Placenta Previa

Abnormal Implantation

Tubal pregnancy.gif
  • Ectopic Sites
    • external surface of uterus, ovary, bowel, gastrointestinal tract, mesentery, peritoneal wall
    • If not spontaneous then, embryo has to be removed surgically
  • Uterine - tubal pregnancy (most common ectopic)

Detect Pregnancy

  • Clinically can be detected following implantation (week 2)
  • Last Menstrual Period (LMP) - today ? ....... Birth Date - January 6, 2020
Pregnancy test.gif Ovary corpus luteum.jpg
Pregnancy test (maternal urine) Ovary - corpus luteum secretes hormone (hCG) to support pregnancy

Week 3

  • (GA week 5)
  • 4 Key processes commence

1. Gastrulation

  • the formation of the 3 layer embryo (trilaminar embryo)
    • All tissues of the body are formed from these 3 embryonic tissue layers (germ layers)
  1. ectoderm (epithelium) - forms the central and peripheral nervous system and epithelium of the skin
  2. mesoderm (connective tissue) - forms the body connective tissues: blood, bone, muscle, connective tissue skin, gastrointestinal and respiratory tracts
  3. endoderm (epithelium) - forms epithelium of the gastrointestinal and respiratory tracts, gastrointestinal tract and endocrine organs
Trilaminar embryo.jpg Inner cell mass cartoon.jpg

2. Somitogenesis

  • segmentation of the mesoderm into somites
  • forms the axial body plan

3. Neuralation

  • segmentation of the ectoderm
  • separates the neural tissue from the skin (epidermis)

Week3 folding icon.jpg

4. Folding

  • folding of the whole embryonic disc
  • all edges of the disc fold ventrally
    • left and right of the disc come together to form a "tube" of the 3 layers
    • top and bottom of the disc bend to form a "C" shaped embryo.

Week 4

Stage 13 - Left Ventrolateral View

Stage13 bf4.jpg

 ‎‎Mobile | Desktop | Original

Stage 13 | Embryo Slides
  • heart formation (cardiogenesis) first functioning organ
  • extra-embryonic cavities develop

Amnion 001 icon.jpg Chick Heart 001-icon.jpg

Stage13 MRI 3D03 icon.jpg
 ‎‎Embryo Stage 13
Page | Play
Stage13 MRI 3D02 icon.jpg
 ‎‎Embryo CNS
Page | Play
Stage 13 MRI S01.jpg
 ‎‎Heart Sag MRI
Page | Play

Week 5 to 8

  • early development of the other organs, tissues and limbs
Week 5 Week 8
Stage 14 - Lateral View

Stage14 bf18.jpg

 ‎‎Mobile | Desktop | Original

Stage 14 | Embryo Slides
Stage 21 - Left Lateral

Stage21 bf11.jpg

 ‎‎Mobile | Desktop | Original

Stage 21 | Embryo Slides
Stage23 MRI 3D01 icon.jpg
 ‎‎Embryo Surface
Page | Play
Stage23 MRI 3D02 icon.jpg
 ‎‎Embryo CNS
Page | Play
Stage23 MRI S02 icon.jpg
 ‎‎Sagittal Embryo
Page | Play


  • Materno/fetal organ
  • No exchange of blood
  • Many different roles
    • can be "sampled" as part of a prenatal diagnostic test
  • interaction between implanting conceptus and uterine wall (endometrium)
  • The uterine lining following implantation (Decidua)
    • forms 3 distinct regions, at approx 3 weeks
    • Decidua Basalis - implantation site
    • Decidua Capsularis - enclosing the conceptus
    • Decidua Parietalis - remainder of uterus
  • uterine cavity is lost by 12 weeks

Placenta term anatomy 01.jpg

Second and Third Trimester

  • Week 9 to 37 - Fetal Development
  • Continuing growth and differentiation of organs formed in embryonic period
    • some organs have a later development - neural, genital, respiratory, bones
    • some continue to develop after birth - neural, genital, respiratory, bones
  • growth in size, length (Second Trimester)
  • growth in weight (Third Trimester)

Fetal growth icon.jpg Ultrasound12wk 3D image2.jpg 19weeklabel1.jpg

Postnatal Development


Historic teaching model of birth
MRI Birth
  • birth (parturition) is a complex physiological process between the fetus and mother
  • thought to be initiated by the fetus

Maternal Birth Stages

  1. Dilatation
  2. Expulsion
  3. Placental
  4. Recovery

Australian Birth Rate 1998-2007


Newborn infant (perinatal period)

Newborn (perinatal) needs to activate many systems and establish independent regulation (homeostasis)

  • Lung function - Fluid drainage, Gas exchange, muscular activity, continued development
  • Circulatory changes - Closure of 3 vascular shunts
  • Thermoregulation - metabolic rate, fat metabolism
  • Nutrition - gastrointestinal tract function, peristalsis, continued development
  • Waste - kidney function, continued development
  • Endocrine function - loss of placenta, maternal hormones, continued development

Abnormal Development

Critical Periods of Development

Three main causes:

  1. Genetic
  2. Environmental
  3. Unknown
  • First trimester most critical
  • Different effect depending on time of insult (teratogen)

Human-critical periods of development.jpg


  • Maternal diagnosis - often pregnancy will expose maternal health problems
  • Prenatal diagnosis - number of different techniques (non-invasive, invasive) for determining normal development
  • Neonatal diagnosis - (Apgar test, Guthrie test), hearing test

Finished! Now lets get ready for the Foundations Practical!

Additional Information

Additional Information - Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page.

Revision Notes

Human development timeline
  • You don't need to know everything today, this is an introduction.
  • Use the glossary to help understand new terms.
  • Don't confuse "germ cell layers" (ectoderm, mesoderm, endoderm) with the "germ cells" (oocyte, spermatazoa).
  • Remember the difference between "clinical weeks" (last menstral period) and "embryonic weeks" (from ovulation/fertilisation, 2 weeks later).
  • With abnormalities
    • think about the types of prenatal dianostic techniques that are now available
    • the 2 major types (genetic and environmental) and the unknown??
    • the effect of maternal age/health/lifestyle.


Logo.png Hill, M.A. (2020). UNSW Embryology (20th ed.) Retrieved April 21, 2024, from
The Developing Human, 10th edn.jpg Citation: Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.

UNSW Students have online access to the current 10th edn. through the UNSW Library subscription.

Links: UNSW Library | NLM ID: 101649439

Chapter 1 - Introduction to the Developing Human

Larsen's human embryology 5th ed.jpg Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R., Francis-West, P.H. & Philippa H. (2015). Larsen's human embryology (5th ed.). New York; Edinburgh: Churchill Livingstone.

UNSW students have full access to this textbook edition through UNSW Library subscription (with student Zpass log-in).

Read the introduction before Chapter 1.

Foundsmall.jpg Foundations Practical - Introduction to Human Development

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

Cite this page: Hill, M.A. (2024, April 21) Embryology Foundations Lecture - Introduction to Human Development. Retrieved from

What Links Here?
© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G