Block 3. Special topics. Embryo development

Question 1

Patterning

Answer 1

cells quire identity in space and time

Ensures that tissues and organs develop in the right place in the right orientation

Question 2

What happens during embryogenesis?

Answer 2

patterning
major axis defined- anterior/posterior dorsal/ventral
3 germ layers are defined
Rudiments of major organs

Question 3

what are the 3 germ layers

Answer 3

endoderm(inner layer), ectoderm(outer layer), mesoderm( middle layer)

Question 4

After how many weeks are all cell types established in the embryo?

Answer 4

8 weeks

Question 5

What can happen if more than 1 sperm cells enter the egg?

Answer 5

Too much DNA

can lead to abnormal development of the fetus

Question 6

polar bodies

Answer 6

A polar body is a small haploid cell that is formed at the same time as an egg cell during oogenesis, but generally does not have the ability to be fertilized.

As the cell divides all the cytoplasm is portioned to one of the cell as it divides, and the other cells degrade. So one large egg is produced and 3 smaller bodies, which will eventually degrade with time.

Question 7

path of sperm cell towards the egg

Answer 7

corona radiata cells
zona pellucida
PM of secondary oocyte
cytoplasm of secondary oocyte

Question 8

trophoblasts

Answer 8

cytotrophoblast
syncytiotrophoblast
facilitates implantation of the blastocyst in the maternal endometrium by production of lytic enzymes and secretion of pro-apoptotic factors

BOTH give rise to placenta!

Question 9

bilaminar embryonic disc

Answer 9

formed when the inner cell mass forms two layers of cells, separated by an extracellular basement membrane. The external layer is called the epiblast and the internal layer is called the hypoblast. Together, they compose the bilaminar embryonic disc.

Question 10

gastrulation

Answer 10

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

formation of all 3 germ layers

Question 11

embryonic folding

Answer 11

the flat trilaminar embryonic disk becomes a more cylindric embryo due to the longitudinal and transverse folding that occurs as a result of embryonic growth, especially of the neural tube.

Question 12

when does embryonic folding occur?

Answer 12

22-28 days

Question 13

stem cells function

Answer 13

used for growth, renewal, and repair as differentiated cells have limited divisions
(e.g special tissue cells do not replicate, stem cells renew them)

Question 14

stem cell

Answer 14

a stem cell is defined as cells that divide to form one daughter that goes on to differentiate(develop into specialized cells), and one daughter that retains its stem-cell properties.

Question 15

what cell is the most potent stem cell?

Answer 15

totipotent
zygote + first 4 cells
capable of giving rise to all cell types in the body and extra-embryonic tissues.

Question 16

hierarchy of stem cells

Answer 16

1. totipotent - all tissues + placenta
2. pluripotent- epiblast( give rise to the embryo(all tissues), but not placenta
3. Multipotent- give rise to all cell types of a particular tissue or organ. eg blood(has multiple cell types- all derived from hematopoietic stem cells), gut.
4. Nullipotent(unipotent)-not capable of giving rise to other cell types(one tissue).

Question 17

name of stem cells in the skin

Answer 17

keratinocytes. Constant renewal

Question 18

clinical application of stem cells

Answer 18

when wanting to grow a sheet of skin stem cells are needed,

genetic defects in keratinocytes( eg recessive dystrophic epidermolysis bullosa)
pathogenic mutation in COL&A1( collagen 7)
blisters form, epidermis is not well supported by dermis.( lack of fibres)

Question 19

gastrulation process

Answer 19

1. a primitive streak forms along the midline of the epiblast/ amnion ( ~ 15 days after fertilization).It is the epiblast cells moving inwards that creates the streak.
   It forms the axis of the embryo- the streak forms from the caudal(tail) end towards the cranial( head).
2. the primitive streak expands on the end to create a primitive node
3. Process called invagination starts as the epiblast cells move inwards, displacing the hypoblast layer and creating a new layer-definitive endoderm.
4. The epiblast cells are now referred to as the ectoderm
5. The cells that remain between ectoderm and endoderm form a mesoderm layer. (16 days)
6. Once the formation of all layers is complete the cells of the ectoderm no longer move towards the primitive streak.

Question 20

amnion

Answer 20

a membranous sac which surrounds and protects the embryo. It is the first of the three cavities (amnion, chorion and yolk sac) in the embryo

Question 21

yolk sac

Answer 21

A yolk sac is a structure that develops inside your uterus during early pregnancy. It provides an embryo with nourishment (food). It helps circulate gasses between you and the embryo. The yolk sac also produces cells that turn into important structures, such as the umbilical cord, blood cells and reproductive organs.

Question 22

chorionic cavity

Answer 22

the space surrounding the primary yolk sac and amniotic sac, except where the connecting stalk attaches to the cytotrophoblast of the blastocyst.
The chorionic cavity contains the fluid in which the embryo floats.

Question 23

connecting stalk

Answer 23

The connecting stalk, or body stalk also known as the allantoic stalk is a yolk sac diverticulum, that by the third week of development connects the embryo to its shell of trophoblasts.

Question 24

notochord

Answer 24

flexible rodlike structure of mesodermal cells that is the principal longitudinal structural element of chordates and of the early embryo of vertebrates, in both of which it plays an organizational role in nervous system development. In later vertebrate development, it becomes part of the vertebral column.

Question 25

neural tube

Answer 25

In the developing chordate (including vertebrates), the neural tube is the embryonic precursor to the central nervous system, which is made up of the brain and spinal cord.

Question 26

Midgut and hindgut

Answer 26

The midgut develops into the distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, and proximal 2/3 of transverse colon. The hindgut becomes the distal 1/3 of the transverse colon, descending colon, sigmoid colon and the upper anal canal.

Question 27

chorionic villi

Answer 27

Chorionic villi make up a significant portion of the placenta and serve primarily to increase the surface area by which products from the maternal blood are made available to the fetus.