Foundations Lecture - Introduction to Human Development
Introduction
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.
Aims
- Purpose of learning embryology
- Basic facts about early human development
- Appreciate differences between the conceptus, embryo and fetus
- 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
Human Development Timeline
<Flowplayer height="225" width="180" autoplay="true">Human development 001.flv</Flowplayer> |
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UNSW Embryology Online
Original Website | New Website |
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: The developing human : clinically oriented embryology 8th ed. Moore, Keith L; Persaud, T V N; Torchia, Mark G Philadelphia, PA : Saunders/Elsevier, c2008.
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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.
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Four Basic Tissue Types
Tissues and organs of the body consist of combinations of 4 basic tissues:
- Epithelial
- Connective
- Muscular
- 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
Male
- continuous production of spermatozoa
- begins at puberty
- release millions of spermatazoa
Ovary
- Paired organs
- lying in the peritoneal cavity
Ovulation
- ovulation is the release of the egg (oocyte) at about the middle of the menstrual cycle
Human ovulation
Fertilization
- the process of the 2 haploid gametes (egg and sperm) fusing and combining genetic material.
- conceptus - the entire product of fertilization
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)
Week 1 Development
- occurs freely floating in uterus
Week 2 Development
- Implantation - initial attachment to uterine wall, and then invasion of the uterine wall.
Pregnancy
Detect 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
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
- 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)
Week 3
- 3 Key processes commence
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)
- Ectoderm (epithelium)
- Mesoderm (connective tissue)
- 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)
Week 4
- heart formation (cardiogenesis)
- first functioning organ
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)
Birth
- birth (parturition) is a complex physiological process between the fetus and mother
- thought to be initiated by the fetus
Maternal Birth Stages
- Dilatation
- Expulsion
- Placental
- Recovery
Newborn
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:
- Genetic
- Environmental
- Unknown
- First trimester most critical
- Different effect depending on time of insult (teratogen)
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
- Gutherie card icon.jpg
Gutherie card
Finished! now here is a Link to Exam Question.....
Revision Notes
- You don't need to know everything today, this is an introduction.
- Use the glossary to 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 fertilization, 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 effect of maternal age/lifestyle.
Textbooks
Moore, K.L. & Persuad, T.V.N. (2008). The Developing Human: clinically oriented embryology (8th ed.). Philadelphia: Saunders.
The following chapter links only work with a UNSW connection and can also be accessed through this UNSW Library connection. | |
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. | |
Hill, M.A. (2011) UNSW Embryology (11th ed.). Sydney:UNSW. |
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, June 16) Embryology Foundations Lecture - Introduction to Human Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Foundations_Lecture_-_Introduction_to_Human_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G