Developmental conditions

Question 1

Fertilisation

Answer 1

Usually occurs in distal portion of fallopian tube, ciliated cells help transport ovum
Zygote- fertilised ovum
Acrosome- enzyme which digests outer cells of ovum

Question 2

Prenatal development- germinal period

Answer 2

First 2 weeks of developmental result in formation of primitive germinal layers

Question 3

Prenatal development- embryonic period

Answer 3

2nd to end of 8th week, organ system develop (greater potential for congenital defects to arise)

Question 4

Prenatal- foetal

Answer 4

Last 3 weeks, organ system grows and matures sufficiently to allow new born baby to survive outside the womb

Question 5

Germinal period

Answer 5

First 14 days post fertilisation
Zygote divides to form 2 cells (first cleavage)
2 cells divide to form 4, 8 etc
Cells loosely held together, single cell can break away and develop into another baby (identical twins)
Prior damage (e.g., STD), increase risk that early conceptus can become marooned in fallopian tube- ectopic pregnancy

Question 6

The morula

Answer 6

Day 3-5
Repeated cell division give rise to solid ball of 12 or more cells called morula
Cells in centre of blastocyst migrate from centre towards periphery leaving hollow cavity called blastocyst

Question 7

Germinal period- day 6- blastocyst formation

Answer 7

Consists of two magpie regions:
-trophoblast- outer lining, develops into placenta
-inner cell mass- develops into embryo

Question 8

Implantation- day 7-9

Answer 8

Blastocyst arrives in uterus
Progesterone stimulates production of uterine milk which encourages adherence to endometrium
/trophoblast invades endometrium following contact and adherence
Uterine milk provides nutrients to blastocyst
Implantation can rupture blood vessels beneath endometrium –> small amount of blood loss

Question 9

Late germinal period

Answer 9

Cells of inner cell mass repeatedly divide and inner cell mass thickens
Cells of inner mass differentiate into two distinct layers which form a convex embryonic disc Ectoderm- outer layer
Endoderm- inner layer

Question 10

Embryonic period- week 2-8

Answer 10

During 3rd week, two layered embryonic disc thickens
Cells from ectoderm, divide rapidly and form a thickening (primitive streak)
Lower ectoderm cells differentiate into third layer of tissue- mesoderm
Ectoderm, mesoderm, and endoderm referred to as germinal layer

Question 11

Organgenesis

Answer 11

Formation of organs
By 8 weeks all organ systems are recognisable