Developmental Psychology I: infancy and childhood part 3.1 Flashcards
(46 cards)
Prenatal Development
There are three key periods in prenatal development:
Germinal - First 2 weeks - Planting the seed – Fertilisation to implantation.
Embryonic - Weeks 3–8 - Laying the structure – Major organs begin to form.
Fetal - Week 9 to birth - Growth and refinement – Everything gets bigger, more complex, and functional.
🧬 Germinal Period: Days 1–14 After Conception
🚀 Launch (Fertilisation):
The sperm meets the egg in the Fallopian tube, forming a zygote—a single-celled organism that contains all the genetic information needed to build a human.
🔁 Rapid Cell Division (Mitosis):
The zygote starts dividing into identical cells (called cleavage).
Imagine a single LEGO block duplicating itself into a growing pile—this pile becomes a blastocyst, a hollow ball of cells, by day 4–5.
🌰 Two Key Cell Groups Form Inside the Blastocyst:
Trophoblast (the outer shell): Becomes structures like the placenta, which will feed and protect the baby.
Analogy: Think of this as the spaceship’s life support systems.
Embryoblast (inner cell mass): This becomes the embryo—the future baby.
Analogy: This is the astronaut inside the ship.
🌱 Implantation (Day 7–14):
The blastocyst burrows into the uterus wall to start accessing nutrients.
Analogy: Like planting a seed in fertile soil—it needs contact with the nutrients in the ground (the mother’s blood supply).
However, implantation is risky—up to 50- 75% of zygotes fail to implant successfully, ending the pregnancy very early, often without the person knowing.
Ectopic Pregnancy (Complication) in germinal period
If implantation happens in the Fallopian tube instead of the uterus, this results in an ectopic pregnancy—a dangerous condition for the mother.
Order of germinal period?
1 Fertilisation The rocket is launched (sperm + egg → zygote)
2–3 Cleavage & Compaction The rocket builds compartments (cells multiply + stick tightly together)
4–5 Blastocyst forms The spacecraft inflates into a bubble with special rooms (trophoblast & embryoblast)
6–7 Zona hatching The outer shell breaks, allowing implantation (like a chick hatching)
7–10 Implantation Seed buries into soil (blastocyst embeds in uterus wall)
9–12 Differentiation Roles assigned—some cells become skin, others organs (crew members get jobs)
12–23 Disc formation & mesoderm spreading Layers form that will become tissues/organs (building floors of a complex facility)
The Embryonic Period
The embryonic period begins after implantation (~day 14) and continues until week 8 post-fertilization.
Think of this like constructing a house:
The germinal period was when you surveyed land and laid down a concrete foundation (zygote → blastocyst).
Now, in the embryonic period, you’re framing the house, setting up the plumbing and electricity — laying down the essential structures that will support all future growth.
The Early Protective Layers: Amnion, Yolk Sac, Chorion, Allantois in embryonic period
Imagine a spacesuit designed to protect and sustain an astronaut. The embryo builds its own little “spacesuit” made up of several layers and sacs:
🫧 Amnion → Like a Bubble Wrap + Thermostat
Forms a fluid-filled sac (amniotic fluid) around the embryo.
Acts like a shock absorber, maintaining temperature and cushioning the embryo.
Like floating in a warm bath inside a sealed room.
🥚 Yolk Sac → Portable Lunchbox
Produces early blood cells for the embryo until the embryo can produce its own.
Like bringing your own food before the kitchen (liver & spleen) is installed.
🧪 Allantois → Becomes the Umbilical Cord
Connects the embryo to its life support (mom).
Like the charger cable providing energy from the wall (mom) to the phone (embryo).
🪡 Chorion → Becomes the Placenta
The outermost layer that eventually becomes the interface with the mother.
Think of it as the Wi-Fi router that connects two systems — embryo and mother — without mixing their blood directly.
Placenta in embryonic period
a semi-permeable membrane embedded in the uterus wall that separates the mother from the embryo.
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Oxygen, carbon dioxide, sugars, proteins and fats can pass through placenta.
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Maternal blood entering the placenta carries oxygen (+ nutrients) to embryo via the umbilical cord.
Nutrients, oxygen, and waste are exchanged through a semi-permeable membrane (nothing mixes directly — like a customs checkpoint).
Umbilical cord acts as the cable for delivery and return.
🔄 Two-way exchange:
IN: oxygen, glucose, amino acids
OUT: carbon dioxide, urea, waste products
Embryoblast/Embryodisc Layers
The embryoblast, also called the embryonic disc, divides into 3 germ layers — the foundational “departments” that each build part of the human body.
🧱 The 3 Germ Layers – Like Departments in a Construction Team:
Ectoderm (outer layer)
→ Like the IT department: builds all the “wiring” and interface
Nervous system (brain, spinal cord)
Skin, hair, nails
Mesoderm (middle layer)
→ The engineering & structure crew
Muscles, bones
Cardiovascular system
Endoderm (inner layer)
→ The plumbing and internal systems
Digestive tract, lungs, liver, bladder
Formation of the Neural Tube (Week 3) in embryonic period
Here, a special region in the ectoderm called the primitive streak folds into the neural tube, which becomes the brain and spinal cord.
🔧 Analogy: It’s like folding a flat blueprint into a 3D structure — imagine rolling a piece of paper into a tube to make a tunnel (the neural tube). If this process goes wrong → neural tube defects (like spina bifida) can occur.
Body Plan Develops (Weeks 4–5)
🧠 Week 4
Head, eyes, nose, mouth begin forming.
Heartbeat begins — a primitive vessel starts pulsing. A minuscule blood vessel begins to pulsate, which will become the heart.
🧭 Direction of development:
Cephalocaudal (head to tail) – The brain develops before legs.
💪 Week 5
Limbs emerge: upper arms → forearms → fingers
Legs follow: thighs → knees → feet → toes
🧭 Direction:
Proximodistal (center to outer) – Inner organs first, then limbs. Internal to external
🧠 Week 6–8 in embryonic period
🧠 Week 6–8: Final Preparations
Fingers and toes separate.
Skeleton starts to form.
Brain rapidly develops — movements start (but not controlled yet). (however, deliberate movements are still not possible)
Liver and spleen take over red blood cell production.
Embryo reaches about 1 gram and 2.5 cm.
Neuropore closure failure
Failure of closure of the anterior neuropore during embryogenesis will lead to anencephaly, the failure of the brain and skull to develop
Fetal Period: Week 9 to Birth
At week 9, the developing individual is officially called a fetus.
By this point, most major organs and support structures are already laid down. The focus now shifts to growth, refinement, and activation.
🧬 7–8 Weeks: The “Indifferent Gonad” fetal period
If the embryo is male, the 23rd pair of chromosomes will consist of an X and a Y chromosome:
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A Y-chromosome gene (SRY gene) triggers the indifferent gonad to produce testes.
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If the embryo is female, no message is sent (because there is no Y-chromosome; females’ 23rd pair is XX) and ovaries are produced.
🧠 4–6 Months: Brain Boom fetal period
The brain increases 6x in size due to Neurogenesis = making tons of new neurons. Imagine installing miles of wiring in a building.
Synaptogenesis = creating connections between those wires — the switchboards and communication lines.
Development is proximo-distal — from the inner to outer brain:
hindbrain (pons, medulla & cerebellum) develops first, then the midbrain and then the forebrain (cortex + subcortical structures e.g. thalamus etc)
The cerebral hemispheres grow to cover other subcortical structures — like a dome growing over an older, central town.
🚨 5,5~6 Months: The Age of Viability in fetal period
This is the threshold (~22–24 weeks) where, with medical help, a fetus could potentially survive outside the womb.
Why? The central nervous system (CNS) starts regulating vital life functions like breathing and sucking.
However, this is only possible due to technology and healthcare conditions:
🍼 7–9 Months: The Final Countdown in fetal period
- The brain overproduces neurons and synapses — up to 25–75% will be pruned via apoptosis.
🔧 Think of this like sculpting a statue: you start with more clay than needed, then chip away the extra to reveal the form.
Unnecessary connections die off.
Useful ones are strengthened and reorganized for efficient neural circuitry.
- CNS-Mediated Coordination
Organs begin to act in concert — like an orchestra syncing under a conductor.
E.g., heart rate rises during activity and slows during rest. - Lung and Heart Maturation
Lungs practice breathing by “inhaling and exhaling amniotic fluid”.
Cardiovascular system finishes development — valves, veins, arteries all optimized. - Sensory & Emotional Connections
The fetus hears the mother’s voice and responds to rhythmic stimuli like singing or heartbeat.
Food flavors pass into amniotic fluid — a literal taste of the outside world. the fetus is considerably heavier (average of 3.4 kg at birth) and is able to move
Auditory communication in fetal period (7 months)
Auditory communication between mother and fetus is possible around 28 weeks (7 months) as hearing ability improves: the fetus may kick in response to loud noises or be comforted by the mother’s voice or rhythmic sounds (e.g., singing/music).
What is Apoptosis in fetal period
Apoptosis is the process of programmed cell death. It is used during early development to eliminate unwanted cells. The initial over-production of neurones ensures the fetus will have all the neurones it needs to function properly (rather than not having enough)
🧪 What Are Teratogens?
Teratogens are non-genetic agents that increase the risk of prenatal abnormalities or birth complications.
🔶 Non-genetic means they’re external—they’re not part of the baby’s DNA, but rather come from the environment.
🧪 Examples:
Drugs (prescription or recreational)
Viruses (like rubella or herpes)
Pollutants (like lead or mercury)
Radiation (think Chernobyl levels)
🔍 Important Note: Teratogens don’t affect all pregnancies equally—95% of pregnancies still result in normal births, and when problems do occur, they are often mild or reversible.
⏳ Sensitive-Period Principle
teratogen’s effect is most severe if it hits while an organ is forming.
📌 Most organs form during the embryonic period (3 to 8 weeks post-fertilization).
🧠 Examples of vulnerability:
Central Nervous System (CNS): 3–5 weeks
Heart: 3–6 weeks
Other organs: 5–9 weeks
🔬 So exposure to a teratogen before week 3 may not be harmful (implantation stage), but exposure between weeks 3–9 is high risk.
📊 Teratogen Timing Chart
🧠 CNS: vulnerable throughout entire pregnancy
❤️ Heart: mainly early (3–6 weeks)
🧬 Genitals, eyes, and ears: remain vulnerable even into the fetal period
🧠 Once Formed, Less Fragile – But Still Sensitive
Generally, formed organs are less susceptible.
But some parts (e.g., eyes, genitals, and nervous system) remain somewhat vulnerable all the way to birth.
👶 Individual Difference Principle. Why does the same drug harm some fetuses but not others?
🧬 Genetics plays a big role. Every embryo has different vulnerability thresholds, depending on both embryo/fetal and maternal genes.
Example:
Thalidomide: A drug that caused severe limb deformities—but only in certain pregnancies.
⚖️ Dosage Principle
Like poison, the dose makes the difference.
A small amount of alcohol might pass unnoticed.
Large doses? Fetal Alcohol Spectrum Disorders.
So:
Longer exposure = Higher risk
Greater quantity = More damage
