prenatal development

Question 1

1

Answer 1

• 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.
  • All living things have evolved from a common ancestor.
  • Humans have spinal cords so that makes us part of a group of organisms called chordates, as they all share a feature of spinal cords.
• 97% of chordates have a bony sheath or a skeletal/spinal column.

Question 2

species biodiversity

Answer 2

• Shows that the number of chordate species is relatively very small compared to other taxonomic groups, such as beetles, fungi, bacteria, plants, and many others.
  
  • Comprise only between about a tenth and a hundred of a percent of all living organisms.
• The processes of growth and embryological development share many similarities across species as diverse as humans, chickens, frogs and fish.

Question 3

2

Answer 3

A cladogram depicting the emergence of jaws, lungs, claws or nails, feathers, fur, and mammary glands different chordate taxa, from Hagfish to Chimpanzees.

Question 4

early scientific views on prenatal development

Answer 4

• Ca. 1590s - invention of the microscope, allowed us to see aspects of reality that was too small to see with the naked eye
  
  • 1695 - Nicolaas Hartsoeker and the preformation theory of development - was looking at sperm and saw a tiny shape in it
• 19th century - improvements in optics had demonstrated that embryonic development did not involve simple processes of growth, but also substantial differentiation.

Question 5

Aristotle (384-322 B.C.)

Answer 5

• Scala naturae - great chain of being - species are fixed and arranged hierarchically.
  
  • 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.
  • Lower animals and higher animals

Question 6

recapitulation theory

Answer 6

• Haeckel reported substantial similarity in the forms of early embryos in a wide variety of species.
• However, in embryonic development different animals look quite different from one another.

Question 7

photographs vs drawings

Answer 7

• Comparison of photographs with drawings of various species’ embryos at the same stage of development, demonstrating that early embryos are very much more differentiated across species than previously believed.
  
  • Bad news for the recapitulation hypothesis.

Question 8

stages of prenatal development

Answer 8

1. The Germinal Period (from conception to implantation) - germinal period
   
   2. The period of the Embryo (implantation to - 2 months) - embryonic period - covers first trimester - covers tissue differentiation
      3 . The period of the Fetus (2 months to birth) - fetal stage - covers growth

Question 9

germinal period

Answer 9

• Conception begins when a sperm cell fertilises the egg, which happens in the fallopian tube.
  
  • The zygote (fertilised egg) moves down the fallopian tube and into the uterus.
  • The first 4 days after conception, the zygote continues to multiply, forming this mass of cells known as a morally

Question 10

egg and ovary

Answer 10

• A drawing of the path of oocyte (egg) from the ovary through the fallopian tube to the uterus, where implantation takes place.
  
  • Key events depicted include 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.

Question 11

cell differentiation at 2 weeks

Answer 11

• Depicting the further division of the early embryo into three histologically distinct layers, the ectoderm, the mesoderm, and the endoderm.
  
  • Implantation starts 10 days post conception, which lasts about 8 weeks.
  • The blastisis differentiates into 3 distinct layers of different tissue types: ectoderm, mesoderm, endoderm.
  • Each of these areas develop into different major organ systems:
  • Ectoderm - nervous system, teeth, fingernails, toenails, and outer surface of the skin.
  • Mesoderm - muscles, bones, circulatory system, inner surface of the skin
  • Endoderm - gastrointestinal tracks, lungs, glands, organs concerned with digestion i.e., liver and pancreas
  • Depicting the ultimate disposition of these three layers into the nervous system plus skin (ectoderm), the skeletal and circulatory systems (mesoderm), and the major organs of digestion and excretion (endoderm).

Question 12

period of the embryo at 3 weeks

Answer 12

• Post implantation, about a month after conception
  
  • 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.

Question 13

period at the embryo at 7 weeks

Answer 13

• Have a much more developed embryo
  
  • The fingers haven’t quite separated yet.
  • Individual toes and fingers are now apparent, there is a developing bulge in the gut.
  • Brain is growing rapidly

Question 14

period of the foetus at 2 months

Answer 14

• Limbs are now well-formed, with obvious digits, the brain has expanded substantially.
  
  • Foetus will respond to stimulation
  • This can be where the foetus becomes a psychological entity as it responds to stimulation.

Question 15

period of the foetus at 8 months

Answer 15

• Genitalia are now nearly fully formed and readily apparent.
  
  • Their vestibular system is functioning

Question 16

variations from typical development

Answer 16

• According to World Health Organisation, origins of congenital aberrations are unknown in 50% of cases.
  
  • Congenital birth defects can have genetic or environmental causes.

Question 17

mitosis vs meiosis

Answer 17

• Comparing cell division during mitosis and meiosis.
  
  • The details for meiosis are not important for this module, but the pint that meiosis usually results in gametes that contain only 23 chromosomes is important to know.
  • We receive 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.

Question 18

chromosomal variations

Answer 18

• Usually, having less than or more than 46 chromosomes is incompatible with life, but there are exceptions.
  
  • The condition of having fewer than usual or more than the usual number of chromosomes is known as aneuploidy.
  • These three classes of aneuploidy are associated with significant developmental problems in various organ systems plus learning difficulties.

Question 19

teratogens

Answer 19

• 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.

Question 20

the thalidomide tragedy

Answer 20

• Developed in 1954 to treat headaches, insomnia, and morning sickness by CIBA pharmaceutical company.
  
  • By 1961, approximately 20,000 children in 46 different countries were born with severely misshapen limbs.
  • One early theory was that these birth defects were caused by the then widespread testing of atomic bombs.
  • In the United States, Thalidomide was never approved by the 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.
  • Cases of Thalidomide Poisoning:
  • United States - 40
  • United Kingdom - 2000
  • Germany - 2500

Question 21

fetal alchohol syndrome (FAS)

Answer 21

· Microcephaly
· Problems with vision and hearing
· Brain of child with FAS has a smaller brain than the average person
· They have a wide upper nose and absence of a philtrum
· Philtrum - the groove that stretches from upper lip to bottom of nose in typically developing children.

Question 22

fetal learning

Answer 22

· N = 16, Gestation ages 7.5 mos.
· Training: Read stories 2X per day (e.g., 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 preference for familiar over novel stories.
· 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 heartrate or state across the two groups.