embryology

Question 1

what happens during the first week of pregnancy?

Answer 1

• ovulation
• fertilisation
• implantation

Question 2

what is a fertilised ovum called?

Answer 2

a zygote

Question 3

what are the first cell divisions pre-embryo?

Answer 3

zygote > 2 cells > 8 cells > morula

Question 4

what is a morula?

Answer 4

a solid mass of cells 4-6 days

Question 5

what is a blastocyte?

Answer 5

a hollow ball of cells 6-10 days
- inner cell mass
- trophoblast

Question 6

what does the early embryo have to secure?

Answer 6

its nutrient supply

Question 7

what is the placenta?

Answer 7

• permeable barrier between embryo and mother, important for resources (not permeable to cells)
• the baby’s blood is replenished from the mother’s blood however the circulations DO NOT mix

Question 8

what is the bilaminar embryo?

Answer 8

implanted trophoblast containing an embryo
- 10-12 days
- 2 cell layers

Question 8

what is the bilaminar embryo?

Answer 8

implanted trophoblast containing an embryo
- 10-12 days
- 2 cell layers

Question 9

what are the two layers of the bilaminar embryo?

Answer 9

• epiblast
• hypoblast

Question 10

what does the epiblast layer of the bilaminar embryo do?

Answer 10

gives rise to embryonic ectoderm, mesoderm and endoderm

Question 11

what does the hypoblast layer of the bilaminar embryo do?

Answer 11

participates in formation of the endoderm and extraembryonic (outwith embryo) mesoderm

Question 12

what is the difference in the formations of identical twins vs fraternal twins?

Answer 12

in identical twins the trophoblast is fertilised by one sperm before dividing, whereas in fraternal twins, the trophoblast divides into two and are each fertilised by a different sperm

Question 13

what is gastrulation?

Answer 13

an early developmental process in which an embryo transforms from a one-dimensional layer of epithelial cells (blastula) and reorganizes into a multilayered and multidimensional structure called the gastrula

Question 14

describe the key points which occur during gastrultion

Answer 14

During gastrulation, the embryo develops:
- An axis (to become bilaterally symmetrical)- primitive streak
- The three embrionic cell layers
The key stage is formation of a groove, the primitive streak

Question 15

what is the primitive streak?

Answer 15

the axis that the embryo develops during gastrulation

Question 16

describe the involvement of the primitive streak?

Answer 16

Some ectodermal cells are induced to differentiate and migrate through the primitive streak, towards the hypoblast.
These new cells are the mesoderm. A “not so clear” interaction between the newly formed mesoderm and the hypoblast will form the endoderm.

Question 17

what is the trilaminar embryo?

Answer 17

the mesodermal cells push through the primitive streak and spread out to form a third layer

Question 18

what happens during weeks 3-8 of embryonic development?

Answer 18

organogenesis- the 3 basic germ cell layers form the major organs (CNS is one of the first to be developed)

Question 19

how is the neural tube formed?

Answer 19

• neural groove appears in the center of the plate, dividing the future right and left sides of the embryo
• neural folds migrate toward the midline of the embryo, eventually fusing to form the neural tube beneath the overlying ectoderm
• cells at the dorsalmost portion of the neural tube become the neural crest cells

Question 20

what are neural tube development defects?

Answer 20

spina bifida- neural groove persists

Question 21

what is the neural groove important for?

Answer 21

development of the head

Question 22

describe the steps in which the embryo takes shape

Answer 22

• trilaminar embryo front and back fold under midline
• embryo folds around the yolk sac and important organs eg heart, liver and lungs appear

Question 23

what 3 cell types do all body cells come from?

Answer 23

ectoderm, mesoderm, endoderm

Question 24

what cells does the ectoderm give rise to?

Answer 24

nervous system and epidermal skin cells

Question 25

what cells does the endoderm give rise to?

Answer 25

digestive system and other internal organs

Question 26

what cells does the mesoderm give rise to?

Answer 26

muscle cells and connective tissues

Question 27

what are stem cells?

Answer 27

Stem cells are unspecialised cells (‘undifferentiated’) that can develop into more specialised cells

Question 28

what are the characteristics of embryonic stem cells?

Answer 28

- pluripotent, meaning they can divide into more stem cells or can become any type of cell in the body- allows embryonic stem cells to be used to regenerate or repair diseased tissue and organs - totipotent stem cells are in the inner cell mass and are present during the first few cell divisions post-fertilization and can form any of the different types of cells in the body

Question 29

what are the characteristics of adult stem cells?

Answer 29

- multipotent- can form other cell types but have limited potency - generally committed cell lines eg bone marrow stem cells

Question 30

what does stem cell development involve?

Answer 30

genes and various signalling molecules

Question 31

what are the three primary embryonic layers?

Answer 31

- ectoderm- outer covering - mesoderm- middle - endoderm- inner lining

Question 32

what tissues are associated with ectoderm?

Answer 32

Skin Mucous membranes of mouth, anus Brain, spinal cord Tooth ENAMEL

Question 33

what tissues are associated with the mesoderm?

Answer 33

Most connective tissues - Dermis, tendons, cartilage, bone Muscle (most) Blood vessels Kidney and urinary system Reproductive system Serous membranes

Question 34

what tissues are associated with the endoderm?

Answer 34

Alimentary canal (pharynx – rectum) Respiratory system Parts of urogenital system

Question 35

what is the ectomesenchyme and what tissues are associated with it?

Answer 35

- ‘fourth’ layer, very relevant to dental studies. gives rise to: most of the peripheral nervous system: sensory and autonomic nerves Melanocytes in skin Adrenal medulla Most of the mesenchyme in the head (muscles, connective tissues, most dental and periodontal tissues – except enamel) Dentine, cementum, pulp, periodontal ligament, jaw bones. (next lecture)

Question 36

what is a syndrome?

Answer 36

when theres multiple phenotypes/diseases- complex

Question 37

what period of embryonic development has the greatest sensitivity?

Answer 37

week 3-12 (first trimester)

Question 38

when do most developmental defects occur in embryonic development?

Answer 38

the first trimester (weeks 3-12)

Question 39

what is the period of functional maturity of the embryo?

Answer 39

weeks 12-39

Question 40

What cells form the yolk sac?

Answer 40

Hypoblast