Prenatal development Flashcards
Chordates
A figure of the tree of life, including major groups from the origins of life. Highlighted are the chordates, which include humans, as well as sea stars, fish, amphibians, mammals, birds, and reptiles.
Chordates- we all have this spinal cord
About 90% of us has a skeletal spinal collum
Species Biodiversity
True of false: the number of chordate species is relatively very small compared to other taxonomic groups, such as beetles, fungi, bacteria, plants, and many others.
True
What does the process of growth and embryological development share?
Many similarities across species as diverse as humans, chickens, frogs and fish
A cladogram depicting the emergence of jaws, lungs, claws or nails, feathers, fur, and mammary glands across different chordate taxa, from Hagfish to Chimpanzees. All these organisms will diversify into complex organisms.
Early Scientific Views on Prenatal Development
Ca. 1590s: Invention of the microscope
1695: Nicolaas Hartsoeker and the preformation theory of development
19th Century: Improvements in optics had demonstrated that embryonic development did not involve simple process of growth, but also substantial differentiation
- invention of the microscope as well as technology enabled us to see things for the first time aspects that were too small
- Nicolaas saw a little tiny human which led to pre formation- the womb was seen as a metaphor (over) in which tiny humans were expanded in size.
Pre formation definition
Development is entirely the form of growth
What is scala naturae?
Great Chain of Being. Species are fixed and arranged hierarchically.
Aristotle (384-322 B.C)
Explain the Great Chain of Being
The idea that humans were at or near the top of an evolutionary ladder. This idea is widespread outside science, but not scientifically correct or accurate
Embryos took the form of adult animals that were lower down on the ladder of creation. - known as recapitulation theory.
Lower animals and higher animals. Humans are at the top of this latter of creation. Idea that humans are the most evolved type of animal. False idea that evolutionary change is a directional process. (teleological view)
Recapitulation Theory
Drawings of embryos used to support the Recapitulation theory. Haeckel reported substantial similarity in the forms of early embryos in a wide variety of species.
Theorists saw in their microscopes the human embryo going through fish like stage of development followed by salamander ect.
We now know this isn’t correct.
Recapitulation Theory:
Differentiation of species
Early embryos are very much more differentiated across species than previously believed. Bad news for the recapitulation hypothesis.
This emphasises how our prior beliefs can impact our basic acts of perception and it also shows how reliant scientific inquiry is on technology.
What are the stages of Prenatal (Antenatal) Development?
- The Germinal Period (from conception to implantation)
- The Period of the Embryo (implantation to ~2 months)
- The Period of the Fetus (2 months to birth)
Germinal Period
Montage of photographs and drawings, with a sperm depicted near an egg, and then several depictions of early cell division within the fertilized egg.
conception - sperm cell approaching the egg in the fallopian tube. Zygote (fertilsed egg) moves down tube into the uterus. For the first 4 days after conception, the zygote continues to multiply forming a mass of cells (morula)
Mass of cells= morula. During the first few days, the daughter cells get smaller and smaller so eventually there is a ball of identical cells squeezed together in a mass. These are stem cells and they can turn into any kind of tissue. Scientists want these to use these cells to grow replacement tissues and organs
About day 5- this mass of cells is called a blastocyst- theres a mass of cells next to an empty space. This is the earliest form of physical differentiation that occurs in the developing zygote.
What is a morula?
A mass of cells
In the path of the oocyte (egg) from the ovary through the fallopian tube to the uterus, where implantation takes place, what key events take place?
- Oocyte/ ovulation
- Day 0- Fertilisation
- Fertilized egg (zygote)
Day 1:
first cleavage
Day 2:
2 cell stage
Day 3-4:
4-cell stage, 8-cell uncompacted morula
Day 4:
8-cell compacted morula
Day 5:
Early blastocyst (trophectoderm, blastocoel, inner cell mass)
Day 6-7:
Late stage blastocyst (hatching) (zona pellucida)
Day 8-9:
Implantation of the blastocyst (epiblast, hypoblast)
What key events take place in the path of the oocyte?
Fertilisation, first cell division, formation of the blastocyst, terminating in the implantation of the zygote into the uterine wall on Day 8 or 9 post-conception.
Cell Differentiation (at 2 weeks)
Blastocyst now differentiates into three distinct layers of tissue types
Further division of the early embryo into three histologically distinct layers, the ectoderm, the mesoderm, and the endoderm. As each of these areas develop they become major organ systems eg endoderm becomes the nervous system, mesoderm become muscles, toes and circulatory system.
Disposition of the three layers:
Name of the layers and their contents
Ectoderm
- nervous system
- cornea and lens of eye
- epidermis of skin
- epithelial lining of mouth and rectum
Mesoderm
- skeletal system
- circulatory system
- lymphatic sustem
- muscular system
- excretory system
- reproduction system
- dermis of skin
- lining of body cavity
Endoderm
Epithelial lining of digestive tract, respiratory tract, reproductive tract, urinary tract
- liver
- pancreas
- thyroid
- parathyroids
- thymus
Period of Embryo (at 3 weeks)
Eye is apparent, brain is beginning to bulge, heart and liver are forming, there are buds where the arms and legs will eventually be, the scaffolds for the individual vertebrae are apparent, but not yet bony, and there is a rudimentary tail.
Period of the Embryo (at 7 weeks)
Individual toes and fingers are now apparent, there is a developing bulge in the gut.
Way to think about the relationship between the embryological period and the fetal period
The embryological period is about tissue differentiation and the fetal period is largely concerned about growth.
Period of the Foetus (at 2 months)
Limbs are now well-formed, with obvious digits, the brain has expanded substantially.
At this point, a fetus can be said to be a psychological entity as it displays ‘behaviour’.
Period of the Fetus (at 4 months)
Ears are taking their final form, eyelids are well advanced. At this age, fetuses are capable of movement, and can react to touch and sound.
Development of…
Touch
Hearing 250-500 Hz
Movement
Period of the Fetus (at 8 months)
Genitalia are now nearly fully formed and readily apparent.
Fetus’ respond to tactile stimuli, temp changes and touch. They have a writing reflex in the womb- they’ll have a preferred position- they are able to detect the gravitational field and move to re orientate themselves into a preferred position in the womb.
Variations from Typical Development
According to WHO, origins of congenital aberrations are unknown in 50% of cases.
Congenital birth defects can have genetic or environmental causes.
Genetics: cystic fibrosis, sickle-cell anemia, various chromosomal disorders
Environment:
Toxins -> thalidomide, alcohol, radiation, pesticides ect.
Nutrition -> esp., folic acid
Mitosis vs Meiosis
Mitosis n=23/ 2n=46
Meiosis n=23 gametes
Meiosis usually results in gametes that contain only 23 chromosomes is important to know. We receive, then, 23 chromosomes from each of our parents, and these combine to give us each 46 chromosomes, in the usual case. However, there are a number of variations that can occur, leading to fewer than 46 or more than 46 chromosomes in some cases.
Chromosomal Variations
Human karyotype
Female- XX (same length)
Male- XY (Y shorter)
Usually, having less than or more than 46 chromosomes is incompatible with life, but there are some exceptions
What is aneuploidy?
The condition of having fewer than usual or more than the usual number of chromosomes
What are the 3 karyotypes of three different kinds of chromosomal variations?
- Down syndrome karyotype (Trisomy 21)
- Edwards syndrome karyotype (Trisomy 18)
- Patau syndrome karyotype (Trisomy 13)
These 3 classes of aneuploidy are associated with significant developmental problems in various organ systems plus learning difficulties.
Table listing some variations in the number of sex chromosomes
What is an essential point relating to this?
Humans have a variable number of sex chromosomes; some, but not all of these variations can lead to ambiguous genitalia at birth, or, in some cases, ambiguous secondary sex characteristics at puberty.
What are teratogens?
Substances that cause birth defects
Teratogens
The bars show how sensitive or not these are vulnerable to genetic environmental impact.
Chart depicting the vulnerability of different organ systems at different times in development.
The central nervous system is vulnerable to teratogenic insult throughout prenatal development, whereas other systems are vulnerable for shorter periods in prenatal development—for example the heart and upper and lower limbs are relatively immune from insult after the embryonic period—that is, during the fetal period— whereas the external genitalia, in contrast, are more vulnerable after the embryonic period.
The thalidomide tragedy
- when was it developed?
- what was it’s purpose?
- what happened?
Developed in 1954 to treat headaches, insomnia and morning sickness by CIBA pharmaceutical company.
By 1961, approx 20,000 children in 46 different countries were born with severely misshapen limbs.
The Thalidomide Tragedy
One early theory was that these birth defects were caused by the then widespread testing of atomic bombs.
In the US, Thalidomide was never approved by Food and Drug administration, thanks to the efforts of Dr. Frances Oldham Kelsey (1914-2015)- she later earned the Presidential Award for Distinguished Federal Civilian Service.
Dr refused to approve this drug because she thought it wasn’t widely tested. Thalidomide only effected children if it was prescribed in the first trimester.
Teratogenic vulnerability chart- effect of thalidomide
The usual prescription of thalidomide during the first trimester (i.e., the embryonic period) affected the limbs during the short window of time in which they were vulnerable to this kind of chemical insult.
Affected from 3 to 8
Fetal Alcohol Syndrome (FAS)
Affects of alcohol on brain development- they suffer severe vision and brain issues.
Babies of adults who drink during pregnancy are at risk of FAS.
The brain of the children with FAS is smaller.
Features of individuals with FAS- depicting the very wide upper nose and absence of a philtrum (the vertical groove that stretches from upper lip to bottom of nose in typically developing children).
Microcephaly definition
Problems with vision and hearing
Fetal Learning study
DeCasper and Spence (1986)
N= 16 pregnant mothers with developing fetuses, Gestation ages 7.5 months
Training: Read stories 2x per day (eg. cat in the hat)
Testing: at ~2.5 days after birth, 8 babies could hear the familiar story with faster dummy sucking, whereas the other 8 babies with slower dummy sucking.
Results: Babies showed preferences for familiar over novel stories
This study demonstrates how newborn babies can discriminate between a story their mothers read during late pregnancy and a new story.
Hepper (1991)
Looked for differences in mothers who religiously watched neighbours and who never watched neighbours and looked for differences between babies and how they responded to playing this after they were born.
There were differences between learning group (mothers who watched neighbours) and the control group.
Table highlighting the significant difference in movement rates between the learning group and the control group in Hepper (1991). Learning group had mothers who religiously watched the daytime soap opera: Neighbours. No differences found in heart rate or state across the two groups.
Learning group 5.2, 2.9
Control group 4.5, 4.1
