L13 - Early Human Development

Question 1

Result of embryogenesis

Answer 1

• patterning
• definition of major acids
• definition of three germ layers (via gastrulation)
• rudiments of major organs established

Question 2

Patterning

Answer 2

Cells acquiring identity in space and time

Question 3

Major axis

Answer 3

Anterior/posterior

Dorsal/ventral

Question 4

Three germ layers

Answer 4

• ectoderm (outside)
• mesoderm (between)
• endoderm (inside)

Question 5

Ectodermal contributions

Answer 5

• all nervous tissue
• epithelium of integumentary, respiratory, digestive
  (Skeletal - pharyngeal cartilage)

Question 6

Mesodermal contributions

Answer 6

• All of:
  
  • skeletal
  • muscular
  • cardiovascular
  • lymphatic

Question 7

Endodermis contributions

Answer 7

• digestive system (gut)

- respiratory epithelium (along with ectoderm)

Question 8

Ecto/mesodermal contributions

Answer 8

• integumentary (epidermis vs. dermis/hypodermis)

Question 9

Meso/endodermal contributions

Answer 9

• urinary (kidneys vs. bladder)

- reproductive (gonads/ducts vs. stem cell)

Question 10

All germ layer contributions

Answer 10

Endocrine

Question 11

Arrest points in oogenesis

Answer 11

• Prophase I (resumed during puberty)

- Metaphase II (resumed after fertilisation)

Question 12

Polar bodies

Answer 12

Other daughter cells from meiosis that are not fertilised as all cytoplasm apportioned to one cell as it divides
- eventually gets degraded)

Question 13

Path of sperm cell

Answer 13

• corona radiata (cells from ovary itself)
• zone pellucida
• plasma membrane of secondary oocyte
• cytoplasm of secondary oocyte

Question 14

Pronuclei

Answer 14

Nucleus of gametes (haploid)

Question 15

Cleavage

Answer 15

Series of relatively rapid mitotic cell division (24hrs for each cell division in humans)

Question 16

Zone pellucida function

Answer 16

• fibrous
• prevents early implantation in Fallopian tube (which would lead to ectopic pregnancy) where a placenta cannot be formed thus no nutrient/waste exchange = death

Question 17

Ectopic preganancy

Answer 17

Implantation of zygote outside uterus

Question 18

Resulting cells from cleavage

Answer 18

Blastomeres

Question 19

Cleavage features

Answer 19

Overall volume/mass of egg doesn’t increase

- instead, cells become progressively smaller as they split without growth (rapid cell division)

Question 20

Blastocyst

Answer 20

Mammalian blastula with trophoblast & pluripotent inner cell mass instead of no inner cell mass and pluripotent blastomere/blastoderm

Question 21

Morula vs. blastocyst

Answer 21

• loosely associated vs. tightly packed cells

- absence vs. presence of inner cavity

Question 22

Blastocyst formation

Answer 22

Morula hatches our of zona pellucida which allows the blastocyst to be sticky and thus implant into uterus wall

Question 23

Embryoblast

Answer 23

Aka inner cell mass

- pile of cells inside blastocyst that give ruse to embryo (result of compaction)

Question 24

Blastocyst cavity

Answer 24

Fluid-filled (H2O enters via osmosis)

Question 25

Trophoblast

Answer 25

Give rise to placenta + other supporting tissue

Question 26

If 2 eggs released

Answer 26

Potentially 2 fertilisation events | = may give rise to fraternal twins

Question 27

Cleavage/blastulation timeline

Answer 27

``` Day 1: two cell Day 2: four cell Day 4: morula Day 5: blastocyst Day 6: implantation ```

Question 28

Types of trophoblasts

Answer 28

- syncytiotrophoblast: part of embryo that gives rise to placenta - cytotrophoblast

Question 29

Trophoblast function

Answer 29

- require/use enzymes that allow embryo to burrow deep into endometrium - promote uterine endometrium to thicken - release human chorionic gonadotropin hormone (detected by preganancy tests)

Question 30

Endometrium

Answer 30

Lining of the uterus

Question 31

Importance of placenta

Answer 31

Critical as it is the connection to the female and thus us a supply of nutrients and way of getting rid of waste products

Question 32

Bilaminar embryonic disc composition

Answer 32

- hypoblast: endoderm - epiblast: ectoderm Result of differentiation of inner cell mass (Mesoderm established from gastrulation

Question 33

Gastrulation time

Answer 33

End of 2 weeks post-fertilisation

Question 34

Amnion/amniotic cavity

Answer 34

Cavity formed by ectoderm

Question 35

Yolk sac

Answer 35

Cavity formed by endoderm

Question 36

Connecting stalk

Answer 36

Connects amniotic cavity to cytotrophoblast of blastocyst | - precursor to umbilical cord

Question 37

Primitive streak

Answer 37

Groove that determines embryo’s right/left symmetry as it develops

Question 38

Formation of mesoderm

Answer 38

- 16 days post fertilisation | - derived from ectoderm

Question 39

Invagination

Answer 39

Movement of cells to form primitive streak Cells from inner cell mass: - divide - change shape - become motile - rearrange to form flat disc with 3 distinct layers = CELL DIFFERENTIATION BEGUN

Question 40

Embryonic folding time

Answer 40

22 days - 28 days post fertilisation | 4th week

Question 41

Embryonic folding

Answer 41

- gives rise to 3D embryonic shape - allowed by cell movement (curving), proliferation, changes in cell shape = dynamic - patterning already taken place

Question 42

Organogenesis

Answer 42

Formation of organs

Question 43

Neural tube

Answer 43

Differentiated ectoderm

Question 44

Notochord

Answer 44

Differentiated mesoderm

Question 45

Differentiated cells

Answer 45

Have limited replicative potential/division

Question 46

Stem cells

Answer 46

Undifferentiated cell of a multicellular organism capable of giving rise to indefinitely more: - cells of same type (retain stem-cell properties) - other daughter cells from which certain other types of cells arise by differentiation Replace themselves

Question 47

Purpose of stem cells

Answer 47

Growth, renewal, repair

Question 48

Transient amplifying cells

Answer 48

Intermediate form | - have some replication potential

Question 49

Linage-restricted progenitor cells

Answer 49

Limited ability to renew

Question 50

Stem cell hierarchy

Answer 50

Most potent - totipotent: zygote (embryo AND placenta) - pluripotent: inner cell mass of blastocyst (only embryo) - multipotent: particular tissue or organ - nullipotent/unipotent: not capable of giving rise to other cell types

Question 51

Clinical utility of stem cells

Answer 51

For long lasting skin grafts: keratinocyte stem cells need to be gene-edited

Question 52

Keratinocytes

Answer 52

Fulfil need for source of stem cells in skin - ability to keep diving and give rise to differentiate keratinocyte - protected in stem cell niche which have signals to tell them to keep dividing - unipotent stem cells allow for constant renewal