Foundations Lecture - Introduction to Human Development

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Introduction

Foundsmall.jpg
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).


This Lecture is under revision for 2013.


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

Links: Printable Lecture Page | PDF version (873 KB, 6 pages)

Aims

  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: 2013 Practical | Embryology Textbooks

Human Development Timeline

Human development timeline graph 02.jpg

UNSW Embryology Online

<mediaplayer width='360' height='410' image="http://php.med.unsw.edu.au/embryology/images/6/61/Human_development_001_icon.jpg">File:Human development 001.mp4</mediaplayer> UNSW Embryo front page.jpg Front-page-image.jpg
Human development 001 icon.jpg
 ‎‎Human Development
Page | Play
Movies Original Website New Website Annotated movie

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

Textbooks

  • 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

Citation: Keith L. Moore, T.V.N. Persaud, Mark G. Torchia. (2011). The Developing Human: clinically oriented embryology (9th ed.). Philadelphia: Saunders.

The following chapter links only work with a UNSW connection.

The Developing Human, 9th edn.jpg

Larsen's human embryology

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

The following chapter links only work with a UNSW connection.

Larsen's human embryology 4th edn.jpg
Links: More Embryology Textbooks

Four Basic Tissue Types

Tissues and organs of the body consist of combinations of 4 basic tissue organisations:

  1. Epithelial
  2. Connective
  3. Muscular
  4. Nervous


  • Where do they come from?
  • How do they develop?

Human Reproductive Cycle

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

Female

  • 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

Male

  • begins at puberty
  • continuous production of sperm (spermatozoa, human male 2,000/second)
  • release millions of spermatozoa (require activation, capacitation)

Ovary

  • Paired organs
  • lying in the peritoneal cavity

Human right ovary and tube 1.jpg Ovary10x.jpg

Ovulation

Human Menstrual Cycle

Human ovulation 01.jpg

Human ovulation


Ovulation icon.jpg Follicle 001 icon.jpg

Fertilization

  • 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

Human Zygote
  • 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-oocyte to blastocyst.jpg


Human blastocyst day 1-6.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, and then invasion of the uterine wall.

Week2 001 icon.jpg Chorion 001 icon.jpg

Pregnancy

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 25, 2013

Calculate a new Birth Date

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

Trimesters

Trimesters

  • 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

Placenta

  • 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

Stage7-sem4.jpg
  • 3 Key processes commence

Gastrulation

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

Ectoderm

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

Endoderm

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

Mesoderm

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

Somitogenesis

  • segmentation of the mesoderm
  • forms the axial body plan

Neuralation

  • 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

  • Fetal Period - Second and Third Trimester
  • 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

Birth

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

Newborn

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

Human 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

Diagnosis

  • 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!

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 "germ cells" (egg, 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)
    • the effect of maternal age/health/lifestyle.

Textbooks

The Developing Human, 8th edn.jpg Moore, K.L. & Persuad, T.V.N. (2008). The Developing Human: clinically oriented embryology (8th ed.). Philadelphia: Saunders.
  • Chapter 1 - Introduction to the Developing Human
Larsen's human embryology 4th edn.jpg Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R. and Francis-West, P.H. (2009). Larsen’s Human Embryology (4th ed.). New York; Edinburgh: Churchill Livingstone.

The following chapter links only work with a UNSW connection and can also be accessed through this UNSW Library connection.

Logo.png Hill, M.A. (2011) UNSW Embryology (11th ed.). Sydney:UNSW.



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. (2019, September 21) Embryology Foundations Lecture - Introduction to Human Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Foundations_Lecture_-_Introduction_to_Human_Development

What Links Here?
© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G