2010 Foundations Lecture - Introduction to Human Development

From Embryology
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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.

This lecture is going to take you briefly through key 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).

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

Note this is an archive copy of 2010 lecture, many links and features may not work. Use the link below to see the current lecture version.

Current Foundations Lecture 2014


  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

Concepts: Fertilization, Early conceptus, Germ layers, Embryo, Tissue origins, Timetable/stages of development, Fetus, Placenta

Background Lectures: Cell Structure (structure and function), Cell Division (mitosis, meiosis, lifespan, cell death), 4 Basic Tissues (Epithelial, Connective, Muscular, Nervous)

Links: Embryology Textbooks | 2009 Lecture | 2009 Lecture Slides

Animated overview

<Flowplayer height="225" width="180" autoplay="true">Human development 001.flv</Flowplayer> This animation begins at the two cell (blastomere) stage following fertilization and takes you through an overview of the entire 9 months of human development in just over a minute!

Note that in this animation specific features are neither labeled or identified,at this stage in your studies the many terms and concepts will not yet make sense.

Remember the control bar features can control the movie playback.

(More? movie on separate page | annotated movie on separate page])

UNSW Embryology Online

UNSW Embryo front page.jpg Front-page-image.jpg
Original Website New Website


  • There are many different excellent embryology textbooks
  • I have included 2 that cover the clinical topics as well.
  • More Textbooks?

The Developing Human: Clinically oriented embryology

The Developing Human, 8th edn.jpg Citation: The developing human : clinically oriented embryology 8th ed. Moore, Keith L; Persaud, T V N; Torchia, Mark G Philadelphia, PA : Saunders/Elsevier, c2008.

Links: NLM ID: 101293798 | NLM Holding | UNSW Library | publisher page

Larsen's human embryology

Larsen's human embryology 4th edn.jpg Citation: Larsen's human embryology 4th ed. Schoenwolf, Gary C; Larsen, William J, (William James). Philadelphia, PA : Elsevier/Churchill Livingstone, c2009.

Links: NLM ID: 101309446 NLM Holding | UNSW Library | publisher page

Four Basic Tissue Types

  1. Epithelial
  2. Connective
  3. Muscular
  4. Nervous
  • How do they develop?
  • Where do they come from?

Human Reproductive Cycle

  • Meiosis in gonad produces haploid gametes (egg and sperm)


  • Menstrual Cycle a regular cycle of reproduction (28 days)
  • begins at puberty
  • release of 1 egg (oocyte) every cycle
  • Endocrine controlled (HPG axis)
    • Hypothalamus
    • Pituitary
    • Gonad

XXhpgaxis.jpg Menstrual cycle.png


  • continuous production of spermatozoa
  • begins at puberty
  • release millions of spermatazoa


  • Paired organs
  • lying in the peritoneal cavity

Human right ovary and tube 1.jpg Ovary10x.jpg


Human Menstrual Cycle

Ovulation icon.jpg Follicle 001 icon.jpg


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

Fertilization 001 icon.jpg Fertilization 002 icon.jpg

Early zygote.jpg

Early Development

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

Early zygote.jpg Stage2.jpg

Human-oocyte to blastocyst.jpg

Week 1 Development

  • occurs freely floating in uterus

Week1 001 icon.jpg

Week1 summary.jpg

Week 2 Development

  • Implantation
  • initial attachment to uterine wall
  • invasion of uterine wall

Week2 001 icon.jpg Chorion 001 icon.jpg


Detect Pregnancy

pregnancy test
Ovary - corpus luteum secretes hormone to support pregnancy.
  • Clinically can be detected following implantation (week 2)
  • Last Menstrual Period (LMP) - today ? ....... Birth Date - January 30, 2011

Calculate a new Birth Date (I need to update calculator for 2010)

Gestation Calculation

  • First pregnancy (primipara) 274 days, just over 39 weeks
  • Subsequent pregnancies (multipara) 269 days, 38.4 weeks

Median duration of gestation assumed from ovulation to delivery

  • Historic - Franz Carl Naegele (1777-1851), first rule for estimating pregnancy length
  • Current - Ultrasound, the most accurate staging method


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

Implantation Sites

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)

Normal Implantation

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

Early Placenta

  • 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


  • Materno/fetal organ
  • No exchange of blood
  • Many different roles
    • can be "sampled" as part of a prenatal diagnostic test

Embryonic Development

  • 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

Week 3

  • 3 Key processes commence


Trilaminar embryo
Trilaminar embryo and tissue origins
  • 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)
  2. Mesoderm (connective tissue)
  3. Endoderm (epithelium)
  • simplified explanation of the 3 layer contributions


  • forms the central and peripheral nervous system and epithelium of the skin


  • forms gastrointestinal tract organs and the epithelium of the gastrointestinal and respiratory tracts


  • forms the body connective tissues: blood, bone, muscle, connective tissue skin, gastrointestinal and respiratory tracts


  • segmentation of the mesoderm
  • forms the axial body plan


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

Week3 folding icon.jpg

Week 4

  • heart formation (cardiogenesis)
  • first functioning organ

Amnion 001 icon.jpg Chick Heart 001-icon.jpg Mouse CT E11.5 movie-icon.jpg

Week 4-8

  • early development of the other organs, tissues and limbs

Week 9 - 38

  • Second and Third Trimester (Fetal Period)
  • 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


Historic teaching model of 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


Newborn infant (perinatal period)

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

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

Critical Periods of Development

Abnormal 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.jpg


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

Finished! now here is a Link to Exam Question.....

Revision Notes

  • You don't need to know everything today, its an introduction.
  • Don't confuse "germ cell layers" (ectoderm, mesoderm, endoderm) with "germ cells" (egg, spermatazoa).
  • Remember the difference between "clinical weeks" (last menstral period) and "embryonic weeks" (from fertilization, 2 weeks later).
  • Revise meiosis and the difference between mechanism and timecourse for oogenesis and spermatogenesis in generating haploid gametes.
  • With abnormalities, think about the types of prenatal dianostic techniques that are now available, the 2 major types (genetic and environmental) and the effect of maternal age/lifestyle.

2010 Foundations Practical - Introduction to Human Development

Current Foundations Lecture 2014

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. (2021, January 18) Embryology 2010 Foundations Lecture - Introduction to Human Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2010_Foundations_Lecture_-_Introduction_to_Human_Development

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© Dr Mark Hill 2021, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G