Prenatal Development and the newborn period
Epigenesis The emergence of new structure and functions during development (Aristotle)
Conception
Gametes a mature haploid male or female germ cell which is able to unite with another of the opposite sex
in sexual reproduction to form a zygote
Meiosis cell division in which eggs and sperm receive only one member from each of the 23 chromosome
pairs contained in all other cells of the body
Start: 46 diploid chromosomes End. 4 x 23 haploid chromosomes
Process of reproduction launching of an egg from the ovary into the adjjóinting fallopian tube → egg moves through the
tube towards the uterus → emits a chemical substance that attracts sperm toward it →
conception (union of sperm and egg) is possible → sperm penetrates the membrane of the egg,
chemical reaction seals membrane, preventing other sperm from entering → tail of sperm falls
off, head rushes into the egg, the nuclei of the two cell merge → prenatal development: 9 months
(38 weeks/ 266 days)
Sperm in ever ejaculation about 500 sperm cells, for contraception must travel 6 hrs, 6-7 inches into
egg-bearing fallopian tube
Zygote the fertilized egg has a full complement of human genetic material, 23 chromosomes from the
mother, 23 chromosomes from the father
Developmental processes 1. Cell division: mitosis
2. Cell migration: during the embryonic period: movement of newly formed cells away from
point of origin
3. Cell differentiation: embryonic stem cells (~350 different cells) are initially equivalent,
after cell divisions cells have a specific structure and function → ‘switched on’/expressed
→ location
4. Apoptosis
Apoptosis Selective cell death
Androgens class of hormones that includes testosterone, causes the development of male or female genitalia
(8th week after contraception production of androgens starts)
Early development Zygote doubles its number of cells about twice day (fallopian tube to the womb)
Inner cell mass mass of cells inside the primordial embryo that will eventually give rise to the definitive structures
of the fetus
Initially: single layer
2nd week: three layers → top layer: Nervous system, nails, teeth, inner ear, the lens of the eyes,
the outer surface of skin → middle layer: muscles, bones, circulatory system, the inner layer of
skin, internal organs → bottom layer: digestive system, lungs, urinary tract, glands
,Identical twins result from the splitting in half of the zygote, resulting in each of the two resulting zygotes having
exactly the same set of genes
Fraternal twins result when two eggs happen to be released into the fallopian tube at the same time and are
fertilized by two different sperm, half of their genes in common
Implantation 1 week following fertilization: zygote embeds itself in the uterine lining and becomes dependent
on the mother for sustenance
→ Before the end of 2nd week: completely embedded within the uterine wall
Neural tube a groove formed in the top layer of differentiated cells in the embryo that eventually becomes the
brain and spinal cord
Amniotic sac: a transparent, fluid-filled membrane that surrounds and protects the fetus (even temperature,
cushioning against jolting, exercise muscles due to floating in fluid)
Placenta support organ for the fetus: keeps the circulatory system of fetus and mother separate, but
permits an exchange of materials (semipermeable membrane)
- Oxygen and nutrients: mother → fetus
- carbon dioxide and waste: fetus → mother
→ production of estrogens Hormones which increase the flow of maternal blood to the uterus
→ production of progesterone Hormones which suppresses uterine contractions that could lead to premature birth
Umbilical cord Containing blood vessels running from placenta to the embryo and back again
Cephalocaudal development The pattern of growth in which areas near the head develop earlier than areas farther from head
Prenatal development 4 weeks old: facial features, primitive heart is visible, arm and leg bud present
5 ½ weeks: nose, mouth, palate formed into different structures
8 weeks: nose and mouth fully formed → cleft palate (birth defect: malformations)
9 weeks: brain grow (bulging forehead), all internal organs, sexual differentiation started, ribs,
fingers toes, nails, umbilical cord, small movements
11 weeks: the heart has basic adult structure, development of sine, ribs, divisions of the brain
Last 5 months: the growth of lower body parts accelerates, increased movement, reflexes e.g.
grasping, swallowing, sucking
16 weeks: intense kicks, substantial development of external genitalia
18 weeks: hair, greasy coating protecting skin, facial expressions, weight increase, cramped
amniotic sac→ decreased movements
28 weeks: brain and lungs developed, eyes can open and move (REM sleep), auditory system,
neural activity
Last 3 months: weight x 3
Fetal behaviour
movement 5-6 weeks after contraception, prenatal hiccups (week 7), swallowing of amniotic fluid, breathing
→ more active fetuses: greater level of emotion regulation
, Behavioural cycles Rest-activity cycles (10 weeks), later half of the development: moves only 10%-30% of the time
→ long term patterns Including daily circadian rhythms: less activity in the morning and more activity in the evening
Fetal experience
Sight and touch Minimal visual experience, but tactile stimulation, the vestibular system is functioning
Vestibular system Sensory apparatus in the inner ear that provides information about movement and balance
Taste Sweet tooth → flavour preference
Smell Olfactory experience due to the smell of mothers’ amniotic fluid
Hearing External noises elicit changes in movement and heart rate
Fetal learning Persistent effect e.g. sound, taste
Habituation Learning that involves a decrease in response to repeated and continued stimulation
dishabituation Introduction of a new stimulus rekindles interest following habituation to a repeated stimulus
Teratogens An external agent that can cause
damage or death during prenatal
development
Sensitive period More sensitive to the effects of teratogens
→ thalidomide (1960s) Morning-sickness drug → limb deformities when born if taken between 4th and 6th week of
pregnancy
Dose-response relation Effect of exposure to an element (teratogen) increases with the extent of exposure (damage)
Fetal programming Belated emergence of effects of prenatal experience
Low calorie intake during pregnancy → higher risk of obesity later in life
Sleeper effect Impact of agent may not be apparent for many years (e.g. hormone diethylstilbestrol (DES))
Postpartum depression 20% are affected, suboptimal maternal-infant interactions → social and cognitive challenges
→ SSRIs Inconclusive evidence, but might increase risk of cardiac malformations, preterm birth, low birth
weight, short-lived withdrawal symptoms, autism spectrum disorder (ASD)
→ therapy CBT, mindfulness-based cognitive therapy
