Lecture 7: Prenatal Development Flashcards
Conception
Results from the union of two gametes (reproductive cells), the egg and the sperm
Gametes are produced through a specialised cell division, meiosis, which results in each gamete having only half the genetic material of all other norma, cells in the body
Fertilisation (fusion of the egg and the sperm) typically takes place in the fallopian tubes
The Zygote and prenatal development
The fertilised egg, or zygote, has a full complement of human genetic material, half from each parent
Marks the beginning of the three periods of prenatal development
- Germinal (conception- 2 weeks)
- Embryonic (3rd- 8th week)
- Fetal (9th week-birth)
Germinal
Conception to two weeks/ implantation
Begins with conception and lasts until the zygote becomes implanted in the uterine wall
Rapid cell division takes place- as early as 12 hours after fertilisation
Mitosis- zygote doubles its number of cells roughly twice a day
Embryonic
Implantation to 8 weeks
Following implantation, major development occurs in all the organs and systems of the body. Development takes place through the processes of:
Cell division: results in proliferation of cells
Cell migration: movement of cells from point of origin to other locations in embryo
Cell differentiation: transformation of stem cells into roughly 350 different types of specialised cell
Cell death: selective death of certain cells (apoptosis)
The embryo
After implantation, the inner cell mass becomes the embryo and the rest of the cells develop into its support system
The neural tube is a U-shaped groove formed from the top layer of differentiated cells in the embryo
It eventually becomes the brain and spinal cord.
The embryo and its support systems
Placenta: semi-permeable, permits the exchange of materials between the bloodstream of the foetus and that of the mother
Umbilical cord- the tube that contains the blood vessels that travel from the placenta to the developing organism and back again
Prenatal development- Foetal (9 weeks- birth)
Continued development of physical structures and rapid growth of the body
Receives antibodies from mother in last month (particularly) of pregnancy
Increasing levels of behaviour, sensory experience, and learning
Protecting the foetus
The placenta membrane is a barrier against some, but not all toxins and infectious agents
The amniotic sac, a membrane filled with fluid in which the foetus floats, provides a protective buffer for the foetus
Also helps regulate temperature
Foetal behaviour - movement
Movement
Spontaneous movement from around 5 weeks
Hiccups at 7 weeks
Initially jerky movements becoming more integrated
After around 18-19 weeks- most arm movements are hand to mouth
movement 12 weeks after gestation
By 12 weeks after gestation, most of the movements that will be present at birth have appeared
Prenatal to postnatal continuity
Swallowing amniotic fluid promotes the normal development of the palate and aids in the maturation of the digestive system
Movement of the chest wall and pulling in and expelling small amounts of amniotic fluid help the respiratory system become functional
Foetal rest-activity cycles
Become stable during the second half of pregnancy
Circadian rhythms are also apparent
Near the end of the pregnancy, the foetus’s sleep and wake are similar to those of the newborn
Foetal sensation (perception)
The sensory structures are present relatively early in prenatal development and play a vital role in foetal development and learning
The foetus experiences tactile stimulation as a result of its own activity, and tastes and smells the amniotic fluid
The foetus typically responds to sounds from at least the 6th month of gestation
Foetal visual experiences
Was previously thought to be negligible, but recent evidence shows preference for “faces” in the foetus (Reid et al ., 2017) suggesting postnatal exposure is not necessary
Teratogens
Environmental agents that have the potential to cause harm during prenatal development
Timing is a crucial factor in the severity of the effects of potentially harmful agents
Many agents cause damage only if exposure occurs during a sensitive period in development
Exposure to teratogens
Amount and length of exposure to the teratogen is also important. Most teratogens show a dose-response relation
Increases in exposure to potential teratogens are associated with greater probabilities of foetal defects and with more severe problems
Individual differences also influence the effects of teratogens (often harmless but gene-dependent)
How is identifying teratogens and their effects made difficult
Their combination
(a mother with substance-abuse problems may be exposed to more than one harmful substance, also have poorer diet, polluted environment)
Sleeper effects in which the impact of a given agent may not be apparent for many years
E.g., the minamata disease of the 1950s
Hormone DES to prevent miscarriage
Environmental hazards to foetus or newborn
Drugs: alcohol, cocaine, heroin
Environmental pollutants: lead, mercury, PCBs
Maternal disease: AIDS, chicken pox, chlamydia
Teratogens - alcohol
Most common human teratogen (Ramadross, 2008)- leading cause of preventable foetal brain injury
Crosses the placenta, also found in amniotic fluid
Advice given to mothers changes regularly
Maternal alcohol abuse can lead to foetal alcohol syndrome (FAS), which is associated is associated with delays in cognitive development, facial deformity, and other problems
Teratogens- cigarette smoking
Cigarette smoking during pregnancy is linked to reduced growth and low birth weight (Reduced oxygen)
Effects can be reduced immediately by stopping smoking
Cigarette smoking has also been linked to SIDS (sudden infant death syndrome), also the ultimate causes of SIDS are still unknown
E-cigs (vaping): many pregnant women believe that e-cigarettes are healthier for their unborn baby than tobacco (e.g., Wagner et al., 2017), but nicotine itself is a risk factor for foetal cardiac, respiratory, and nervous system development
Teratogens- illegal drugs
Marijuana
- Doubles risk of still born birth
- memory , learning, attention, impulsivity
Cocaine
- Foetal growth retardation, premature birth, attentional/arousal problems
- Withdrawal
Teratogens- other hazards
Environmental hazards
E.g., pesticides, herbicides, pollutants (e.g., heavy metals, car exhausts) etc.
Memory, learning, visual skills
Occupational hazards
farmers , factory workers, chemists, nurses
Increased physical labour, noise, being around people with illnesses
Nutrition
Folic acid: spina bifida
Inadequate nutrients
Disease
E.g., Rubella, STIs (herpes, HIV)
Zika
Age
older/ younger mothers at greater risk of negative outcomes
Newborn infant interacting with the environment
state : The infant’s level of arousal and engagement in the environment
Ranges from deep sleep to intense activity
Is an important influence in the newborns exploration of the world
Six stages of arousal in newborns
most to least time:
Quiet sleep- 8hrs
Active sleep- 8hrs
Active awake- 2.5hrs
Alert awake- 2.5 hrs
Drowsing- 1hr
Newborns and sleep
Newborns sleep twice as much as young adults. The pattern of two different sleep states changes dramatically
