week 1 - prenatal development Flashcards
How many chromosomes do the nuclei of reproductive cells contain?
23, all other calls contain 46 (23 cells)
What is the role of meiosis in genetic transmission during prenatal development?
- meiosis is a form of cell division in reproductive cells
- 23 chromosome pairs are halved, creating gametes with 23 chromosomes each
- the mixing of genetic material is entirely random with 8 million possible chromosome combinations in both sperm & egg
- this process introduces genetic variability through random chromosome combinations and crossing over
- when sperm meets egg, novel combination of 46 chromosomes is created, forming the genetic code of the developing embryo
What is ‘crossing over’?
Corresponding sections of homogenous chromosomes randomly switch places
What does the process of meiosis look like?
- parent diploid cell: 46 strands of DNA (chromatids)
- these chromatids duplicate, forming chromosomes (1 chromosome = 2 chromatids)
- maternal and paternal chromosomes pair up (creates 23 pairs)
- crossing over occurs: portions of chromosomes are rearranged with one another, creating genetic diversity
- Meiosis 1: chromosomes separate, and the cell divides to create 2 cells
- Meiosis 2: chromosomes separate into chromatids, and cell devision occurs again, the 2 cells from Meiosis 1 now forming 4 daughter cells
(1 parent cell forms 4 daughter cells known as gametes, with 23 chromosomes each)
What are gametes?
reproductive cells that contain only half the genetic material of all other cells in the body
What is conception?
the union of an egg and sperm cell
What is a zygote?
a fertilized egg cell
How do identical and fraternal twins differ in their development?
- identical twins result from the splitting of a single zygote and share the exact same genes
- fraternal twins arise from two different eggs that are released in the fallopian tubes at the same time, fertilized by two different sperm cells and are only 50% genetically identical
What are the three stages of pernatal development?
- germinal stage (conception-2 weeks)
- embryonic stage (2-8 weeks)
- foetal stage (8-38 weeks)
What is the germinal stage of prenatal development?
- conception - 2 weeks
- zygote travels to the uterus from the fallopian tubes
- cells multiply rapidly in this period
- at the uterus, tendrils emerge and the zygote burrows into the uterine lining
What is the embryonic stage of prenatal development?
- 2 - 8 weeks
- rapid cell division and differentiation occurs, during which the embryo takes on ‘human’ shape
- key structures like the amniotic sac, placenta, and umbilical cord develop
What is the Foetal stage of prenatal development?
- 8 - 38 weeks
- continuous growth and major system development take place, ending in birth
- major feature: brain development (not complete at birth)
- around 4 month’s gestation: mother begins to feel foetal movement
- around 5 month’s gestation: reflexes emerge (hiccups, sucking etc)
- around 6 month’s gestation: foetus may be ‘viable’ (i.e. survival outside the womb)
During the embryonic stage, what 3 layers does the embryo develop?
- ectoderm: hair, teeth, outer skin layer
- mesoderm: inner skin layer, skeleton, muscles
- endoderm: vital organs, glands, gastrointestinal tract
What is the amniotic sac?
a transparent, fluid filled membrane that surrounds and protects the foetus
What is the placenta?
a support organ for the foetus that permits the exchange of materials carried in the bloodstream of the foetus and mother
What is the umbilical cord?
a tube containing the blood vessels connecting the foetus and placenta
What are the four developmental processes that transform a zygote to an embryo to a foetus?
- mitosis: cell division resulting in two identical daughter cells
- cell migration: newly formed cells move away from point of origin
- cell differentiation: cells start to specialize in structure and function
- apoptosis: genetically programmed cell death
How does the foetal hand plate demonstrate the role of apoptosis in foetal development?
Development of the hand: requires the death of the cells in between the ridges of the hand plate for the fingers to separate
What major milestones of prenatal development occur in week 1?
- week 1: zygote travels to the womb and embeds in uterine lining. cells arrange into a ball and begin to form embryo and support systems
When is the first trimester?
weeks 1-12
When is the 2nd trimester?
week 13-24
When is the 3rd trimester?
week 25-38
What major milestones of prenatal development occur in weeks 2-3?
- weeks 2-3: embryo forms 3 layers, which become the nervous system, skin, muscles, bones, circulatory system, organs, glands, neural tube etc
What major milestones of prenatal development occur in week 4?
- neural tube continues to develop into the brain and spinal cord. primitive heart is visible, as are leg and arm buds
What major milestones of prenatal development occur in weeks 5-9?
- facial features differentiate, rapid brain growth occurs, internal organs form, fingers and toes emerge, sexual differentiation starts
What major milestones of prenatal development occur in weeks 10-12?
- heart develops its basic adult features, spine and ribs develop more fully, brain forms major divisions
What major milestones of prenatal development occur in weeks 13-24?
- lower body growth accelerates, external genitalia are fully developed, body develops hairy outer covering, fetus can make basic facial expressions, fetal movements can be felt by mother
What major milestones of prenatal development occur in weeks 25-38?
- Fetus triples in size, brain and lungs are sufficiently developed at 28 weeks to allow survival outside of the womb. visual and auditory systems are functional, fetus is capable of learning and behaviours begin to emerge
When does foetal movement begin?
begins 5 to 6 weeks after conception
* emergence of hiccups, swallowing
* movement of limbs, fingers
* respiratory readiness for breathing independently after birth
What behavioural cycles are evident in the fetus?
Fetus exhibits rest-activity cycles, circadian rhythms, and REM sleep
- fetus shows less activity in the latter half of the prenatal period
What sensory experiences does the fetus have?
- touch: grasping umbilical cord, contact with parts of body, rubbing face, sucking thumb
- taste: can detect flavours in amniotic fluid
- smell: amniotic fluid takes on the odour of what the mother eats (polygenetic continuity)
- minimal sight
- sound: responds to various sounds from at least 6 months
How does fetal exposure to flavours influence later preference?
fetuses exposed to certain flavours in amniotic fluid or breast milk show a preference for those flavours after birth
What is the evidence of fetal flavour sensing?
foetus swallows amniotic fluid, can detect and prefer some flavours.
- longitudinal study with 46 pregnant women
- studies show infants exposed to carrot flavour in womb or via breastmilk responded more positively to carrot flavoured foods later in infancy
there is now direct evidence of early foetal avility to sense different flavours in amniotic fluid
- 4D scans of 100 pregnant women to see how their unborn babies (32 weeks) responded to flavours from foods eaten by their mothers
- foetus facial expressions differed for carrot (sweet) and kale (bitter) flavours
- Implications for acceptance/enjoyment of foods by infants & potential for establishing healthy eating habits
How does fetal motor control develop over time?
Fetuses engage in goal directed movements
- 4D scanning technology
- 15 fetuses - 4D scans at 24, 28, 32, 36 weeks gestation
- over time:
anticipatory movements, such as opening the mouth before the hand reaches it increase, while reactive movements decrease, showing improved motor control
