(03) ST: Human Development

Question 1

what is embryogenesis?

Answer 1

the first eight weeks of development after fertilisation
transforming from single cell to organism with multi-level body plan

Question 2

what four things are achieved in embryogenesis?

Answer 2

PATTERNING - cells acquire identity
MAJOR AXIS - anterior / posterior, dorsal (back) / ventral (tummy) defined
THREE GERM LAYERS
RUDIMENTS OF MAJOR ORGANS

Question 3

name and define the three germ layers

Answer 3

ECTOderm = outside, skin + nervous system tissue
MESOderm = between (skeleton / muscle)
ENDOderm = inside (typically the gut)

Question 4

Name the steps in the process of embryogenesis

Answer 4

Fertilisation
Cleavage + formation of blastocyte
Implantation
Development of Trophoblast
Gastrulation
Embryonic folding
Foetal Development

Question 5

What is fertilisation?

Answer 5

Sperm + oocyte fuse, producing a DIPLOID zygote

Question 6

path of sperm cell

Answer 6

corona radiata - the somatic cells outside of the egg
zona pellucida - fibrous mat, activates sperm
fuses with plasma membrane of secondary oocyte
through cytoplasm of secondary oocyte to get to the nuclei

Question 7

what is cleavage?

Answer 7

relatively rapid type of cell division that occurs after fertilisation
the cell size DOES NOT INCREASE! literally cleaves

Question 8

what is the morula?

Answer 8

a loosely packed ball of cells by day four of cleavage
(comes from the greek word for raspberry)

Question 9

process from morula to blastocyst

Answer 9

cells pack closer together, greater adhesion, first epithelial layer forms as water flows inside ball of cells
some cellular differentiation - embryoblasts (inner cell mass) –> embryo, tropoblast cells (outside) eventually give rise to extra-embryonic tissues

Question 10

processes from morula to blastocyte

Answer 10

cells packed, greater adhesion
first epithelial layer forms as water flows inside ball of cells
cellular differentiation - embryoblasts (inner) give rise to the embryo, tropoblast cells (outer) give rise to extra-embryonic tissue

Question 11

describe blastocyst

Answer 11

ball of cells with a blastocyst cavity
embryoblasts = inner cell mass, trophoblasts on the outside

Question 12

function of blastocyst cavity

Answer 12

gives some room for stuff to move around in relation to each other

Question 13

where does fertilisation and cleavage occur?

Answer 13

fertilisation occurs in the uterine tube
early cleavage events also occur in the tube
developed into a blastocyst by the time it reaches the uterine cavity
implantation must occur in the uterine wall, about 6 days after fertilisation

Question 14

development of trophoblast cells after implantation

Answer 14

forms the chorionic villi of the foetal placenta (required for nutrient / gas exchange with mother)
role = secrete enzymes to allow embryo to burrow into wall
keeps wall intact (secretes enzyme human chorionic gonadotropin (HCG) prevents menstruation)

Question 15

what is gastrulation?

Answer 15

the developmental process where a blastula (1D layer of epithelial cells) transforms to a gastrula (multilayered and multidimensional)

basically, the formation of the three germ layrs

Question 16

what is gastrulation?

Answer 16

the developmental process where a blastula (1D layer of epithelial cells) transforms to a gastrula (multilayered and multidimensional)

basically, the formation of the three germ layers

Question 17

what is the bilaminar embryonic disc

Answer 17

two different tissue types in the inner cell mass - hypoblast (internal = primitive endoderm) and epiblast (external = primitive ectoderm)

gives rise to the embryo itself

Question 18

describe the development of the amnion and yolk sac

Answer 18

the amnion develops from the epiblast, and the yolk sac from the hypoblast

(the bilaminar disc remains sandwiched in the middle of the two lobes - they are extraembryonic)

Question 19

what is the connecting stalk

Answer 19

connects the bilaminar disc to the tropho / ectoderm cells

Question 20

visible signs of the beginning of gastrulation

Answer 20

the formation of the primitive streak on the dorsal side of the embryo
in posterior to anterior direction

Question 21

where is the future posterior of the embryo

Answer 21

where the bilaminar disc connects to the extra embryonic tissue by the connecting stalk is the future posterior

Question 22

what happens in the process of the formation of the primitive streak

Answer 22

ectoderm cells rising up, moving in, and displacing the endodermal tissue underneath, forming the mesodermal layer
(three germ layers established)

Question 23

what is the notochord

Answer 23

thick of rod of cells develops in mesoderm layer, defines where future backbone develops

Question 24

describe the processes of embryonic folding

Answer 24

anterior and posterior folding (like a comma)

ectodermal lateral fold forming tube - gut on the inside, ectoderm on the outside, mesoderm in the middle, pinching off the yolk sac
the amnion now completely surrounds the embryo

Question 25

by what time have all key organs been formed?

Answer 25

by around 8 weeks

Question 26

define cell differentiation

Answer 26

the process were immature unspecialised cells take on individual characteristics, reaching their mature form and function

differentiated cells have limited divisions

Question 27

what do stem cells do

Answer 27

replace themselves AND generates differentiated daughter cells

Question 28

what are stem cells needed for?

Answer 28

growth
renewal
repair

Question 29

name the four layers of the Stem Cell Hierarchy

Answer 29

totipotent
pluripotent
multipotent
nullipotent

Question 30

example of a totipotent cell

Answer 30

zygote - capable of giving rise to ALL types of cells of the body and extra-embryonic tissue

Question 31

examples of pluripotent cells

Answer 31

inner cell mass cells of blastocyst (or embryonic stem cell) - some divisions have taken place and cells have become committed to certain differentiation pathways
capable of giving rise to ALL cells in the body (but not extraembryonic tissue), or for trophoblasts, vice versa

Question 32

examples of multipotent cells

Answer 32

within organs - can only give rise to a particular type of tissue or organ
eg. haematopoietic stem cell gives rise to all different types of cells in blood

Question 33

define and give examples of nullipotent / unipotent stem cells

Answer 33

can only give rise to one cell type
eg. keratinocyte stem cells present in skin