Human embryonic development

Question 1

Trimester

Answer 1

Three month periods from conception to birth

Question 2

Period of the egg

Answer 2

From fertilisation of egg to end of third week of development

Question 3

Period of embryo

Answer 3

From beginning of 4th week to end of 8th week of development - this is where 3 germ layers are formed

Question 4

Period of foetus

Answer 4

Beginning of third month to birth

Question 5

When is there the highest chance of genital defects?

Answer 5

First 9 weeks

Question 6

What is gametogenesis?

Answer 6

Production of gametes from primordial germ cells via meiosis

Question 7

What are primordial germ cells?

Answer 7

Specialised stem cells which give rise to germ line and formed a generation earlier when parents were embryos

Question 8

Gametogenesis in both genders

Answer 8

Oogenesis = f
Spermatogenesis = m

Question 9

Where does spermatogenesis occur?

Answer 9

Seminiferous tubules

Question 10

Where does oogenesis occur?

Answer 10

Ovary

Question 11

Stem cell

Answer 11

Undifferentiated cell that can form different cell types e.g. adult or embryonic stem celll

Question 12

What are pluripotent cells and example

Answer 12

Embryonic cells

Ability to form all mature cell types in body except placental and extra-embryonic cells - can’t form whole organism

Question 13

What are multipoint cells and example

Answer 13

Adult stem cells

Form more than one closely related mature cell types in body but not as varied as pluripotent cells

Question 14

What are totipotent cells

Answer 14

Forms all differentiated cell types - can form new organism

Question 15

Phase 1 of fertilisation

Answer 15

Penetration of corona radiate

Question 16

Phase 2 of fertilisation

Answer 16

Penetration of zona pellucida

Question 17

Phase 3 of fertilisation

Answer 17

Fusion of oocyte and sperm cell membranes

Question 18

Capacitation

Answer 18

A sperm conditioning process within the female reproductive system in preparation for fertilisation of the pvum. Involves epithelial interactions sperm and mucosal surface of uterine tube. Only capacitated sperm can pass through the corona cells and undergo the acrosome reaction

Question 19

Acrosome reaction

Answer 19

Induced by zona proteins following binding of acrosomal region of the sperm with the zona pellucida of oocyte. Acrosome reaction leads to release of enzymes needed to penetrate the zona pellucida

Question 20

Corona and zona reactions

Answer 20

Following release of acrosome enzymes (acrosin), the sperm is able to penetrate the zona pellucida. The sperm’s contact with plasma membrane of oocyte leads to release of lysosomal enzymes from cortical granules in plasma membrane which becomes impenetrable to other spermatozoa (cortical reaction) and to changes in permeability of zona pellucida. The enzymes alter the properties including structure and composition of zona pellucida (zona reaction) to prevent polyspermy

Question 21

Goals of fertilisation

Answer 21

• Restores diploid
• Zygote has unique genome from parents
• Activates egg to divide
• Used in contraceptives
• Male infertility results from quality and quantity of sperm
• Female infertility has number of causes
• Infertility in both genders assisted by ART

Question 22

What is cleavage?

Answer 22

Repeated series of rapid mitotic cell divisions of large zygote to produce an increasing number of smaller daughter cells called blastomeres
Increases nucleocytoplasmic ration

Question 23

Morula

Answer 23

Solid ball fo 12-16 cells following cleavage

Question 24

Compaction

Answer 24

Process of cells reorganising and segregating into inner cell mass and outer cell mass after cleavage

Question 25

Blastocyst

Answer 25

Morula develops into fluid filled cavity with compact cell mass to one side enclosed by trophoblast

Question 26

Parthogenesis

Answer 26

Unfertilised egg develops into new individual

Question 27

Embryonic germ disc

Answer 27

Cluster of embryonic cells (inner cell mass also called embryoblast) at the embryonic pole of the blastocyst that gives rise to tissues of embryo proper, and constitutes the germ disc formed within second week

Question 28

Two layers of differentiates embryoblast

Answer 28

Outer layer (epiblast) and inner (hypoblast)

Question 29

Primitive streak

Answer 29

Transient thickened longitudinal midline structure at the caudal end of the epiblast of the bilaminar embryonic germ disc which forms on day 15 of the developing human embryo

Question 30

Gastrulation

Answer 30

Process of epiblastic cells movement (ingression or invagination) through primitive streak that leads to transformation of bilaminar germ dsc into a trilaminar germ disc with the establishment of three primary germ layers - ectoderm, mesoderm and endoderm Starts on day 15

Question 31

Goals of gastrulation

Answer 31

Forms primitive streak and major body axes e.g. craniotomy-caudal, medic-lateral, torso-ventral, left-right

Question 32

Sirenomelia

Answer 32

Legs stuck together

Question 33

Dextrocardis

Answer 33

Heart on RHS

Question 34

Laterality and heart defects

Answer 34

Disruption of laterality pathway in specifying L and R sideness in progenitor heart cells may cause heart defects such as: Ventricular septal defects, atrial septal defect, double outlet right ventricle

Question 35

Outflow tract defects

Answer 35

Transposition of great vessels, pulmonary stenosis