Lecture 4 – Embryonic Development

Which period of the prenatal period begins with fertilization?

The pre-embryonic period begins with fertilization.

The blastocyst implanting within the uterine lining marks the end of the _____________ period and the beginning of the _________________ period.

 The blastocyst implanting marks the end of the pre-embryonic period and the beginning of the embryonic period.

After fertilization the zygote forms into a 16-celled structure that still resides within the hardened zona pellucida. What is this structure called?

 This 16-celled structure is called a morula.

If the morula ‘enters’ the uterus, where does the morula form?

 The morula forms in the fallopian tube before it enters the uterus.

The blastocyst is composed of two types of cells, which type of cells surround the fluid-filled cavity and which type of cells creates an inner mass?

 The trophoblast surrounds the fluid-filled cavity, and the embryoblast forms the inner cell mass.

What is implantation and how long after fertilization does it typically occur?

Implantation is the process by which the blastocyst embeds into the functional layer of the endometrium, and it typically occurs 7-9 days after fertilization.

During implantation, the trophoblast cells divide and differentiate into what two types of cells?

 The trophoblast differentiates into the cytotrophoblast, which maintains cellular shape, and the syncytiotrophoblast, which forms a multinucleated cytoplasmic mass.

What part of the blastocyst forms into the bilaminar germinal disc? What are the two layers that make up the bilaminar germinal disc?

The embryoblast forms the bilaminar germinal disc, which is composed of the hypoblast and epiblast layers.

What are the three extraembryonic membranes?

 The three extraembryonic membranes are the yolk sac, amnion, and placenta (chorion).

    

What is the function of the yolk sac and from what layer of the bilaminar germinal disc does it form from?

 The yolk sac forms from the hypoblast and functions as an early site for blood cell and blood vessel formation.

What are the functions of the placenta?

The placenta allows exchange of nutrients, wastes, and respiratory gases, transmission of maternal antibodies (IgG), and production of estrogen and progesterone to maintain the uterine lining.

The functional layer of the endometrium forms the mother’s side of the placenta, but what makes the fetal side? Describe chorionic villi.

 The fetal side is formed by the chorion, which has chorionic villi containing branches of umbilical vessels surrounded by trophoblast cells.

 

Do the mother’s and baby’s blood need to mix to exchange nutrients and wastes? What else can cross the placental barrier besides nutrients and wastes?

 No, maternal and fetal blood do not mix. Besides nutrients and wastes, alcohol, drugs, viruses, bacteria, and toxins from smoking can cross the placental barrier.

Why do progesterone and estrogen need to be continuously secreted during pregnancy?

 Progesterone and estrogen are needed to maintain and thicken the uterine lining during pregnancy.

What secretes progesterone and estrogen until the placenta is fully formed? Usually, this structure regresses and stops producing hormones about 10 days after ovulation. What causes this structure to continue secreting hormones?

 The corpus luteum secretes progesterone and estrogen until the placenta is fully formed. It continues secreting hormones due to hCG, which is secreted by the syncytiotrophoblast.

How long after fertilization does gastrulation occur? What is gastrulation?

Gastrulation occurs about 2 weeks after fertilization. It is the process where epiblast cells form the three primary germ layers: ectoderm, mesoderm, and endoderm.

What are the three germ layers that make up the embryonic disc?

 The three germ layers are ectoderm, mesoderm, and endoderm.

What is neurulation and when does it begin?

Neurulation is the formation of all nervous tissue structures, and it begins during the third week of development.

Which germ layer forms into the neural groove? What does the neural groove form into?

The ectoderm forms the neural groove, which eventually develops into the neural tube.

What forms into the central nervous system? Which cells form into the peripheral nervous system?

 The neural tube forms the CNS, and the neural crest cells form the PNS.

The dividing of the cells within the primary germ layers is what causes the ‘folding’ of the embryo. Which layer of the embryonic disc is dividing fastest?

 The ectoderm divides the fastest.

What regions of the body forms during cephalocaudal folding? What about during transverse folding?

 Cephalocaudal folding forms the future head and buttocks regions, while transverse folding forms the trunk/torso region.

 

Four weeks after fertilization, which organ is already working?

The heart is already beating by week 4.

What is a teratogen? What types of substances could act as teratogens?

A teratogen is a substance that can cause birth defects or embryo death. Substances include alcohol, tobacco smoke, drugs, viruses, bacteria, and some medications.

What happens during the fetal period and when does it begin?

 The fetal period begins at week 9 and involves maturation of tissues and organs and rapid growth of the fetus.

1.    Match the organ with the primary germ layer it is made from.

(Write ECTO for the Ectoderm, MESO for the Mesoderm, and ENDO for the Endoderm)

 

____________ Heart

____________ Eyeballs

____________ Liver

____________ Kidney

____________ Pancreas

____________Thyroid

____________ Brain

____________ Spleen

____________ The epidermis

____________ The dermis

____________ The adrenal medulla

____________ The adrenal cortex

____________ The mucous membranes

____________ The serous membranes

____________ Pituitary gland

____________ Skeleton

 

 

 

 

____MESO________ Heart

____ECTO________ Eyeballs

_____ENDO_______ Liver

______MESO______ Kidney

______ENDO______ Pancreas

_____ENDO_______Thyroid

___ECTO_________ Brain

_____MESO_______ Spleen

___ECTO_________ The epidermis

_____MESO_______ The dermis

_____ECTO_______ The adrenal medulla

_____MESO_______ The adrenal cortex

______ENDO______ The mucous membranes

______MESO______ The serous membranes

____ECTO________ Pituitary gland

______MESO______ Skeleton