Lecture 3 - Embryology - unit 1

What are the three prenatal periods?

pre-embryonic, embryonic, fetal period

When does the prenatal period occur?

first two weeks

When does the embryonic period occur?

weeks 3-8

When does the fetal period occur?

week 9 to birth

what happens during the pre-embryonic period

zygote becomes blastocyst

what happens during the embryonic period

embryo develops into major organ systems

what happens during the fetal period

embryo increases in size and complexity

What are the three phases of embryosis

cleavage

gastrulation

organogenesis

cleavage

zygote divides into 16 celled morula and becomes blastocyst

what does a blastocyst consist of

trophoblast, blastocyst cavity, and embryoblast

Gastrulation

3 primary germ layers form

what are the three primary germ layer?

ectoderm, mesoderm, endoderm

organogenesis

organs develop

Meiosis Phases

prophase, metaphase, anaphase, telophase, cytokenesis

What is the primordial form of a sperm?

spermatogonium

After spermatogonium undergoes mitosis it becomes what

a primary spermatocyte

After a primary spermatocyte undergoes meiosis 1 it becomes what

2 2n secondary spermatocytes

After two secondary spermatocytes undergo meiosis 2 they becomes what

four haploid spermatids

What must the 4 spermatids undergo before becoming mature sperm?

spermiogenesis

What is the primordial form of an ovum?

an oogonium

After an oogonium undergoes mitosis it becomes a what

a diploid primary oocyte

Which phase of meiosis is the utero phase of oogenesis stopped by meiotic arrest?

prophase 1

When does the primary oocyte start undergoing meiosis again?

after puberty

After a primary oocyte completes meiosis 1 it becomes what

a haploid secondary oocyte and a polar body

After a secondary oocytes undergoes meiosis 2 it becomes what

an ovum and another polar body

Which phase of meiosis is the puberty phase of oogenesis stopped by meiotic arrest?

metaphase 2

When does the secondary oocyte resume meiosis two?

after fertilization

What happens to the two remaining polar bodies after fertilization

they fully degrade by the 44-cell stage of the cleavage

What are the three stages of fertilization

Corona radiata penetration

zona pellucida penetration

fusion of sperm and ovum plasma membranes

What occurs in the corona radiata penetration phase of fertilization?

sperm mechanically pushes through cell wall using the flagellum

What occurs in the zona pellucida penetration phase of fertilization?

sperm releases a digestive enzyme to break down the ECM

What occurs in the fusion of sperm and ovum plasma membranes during the third phase of fertilization?

sperm releases its pronucleus to combine with the ovum’s pronucleus

where does the blastocyst implant in the lumin?

in the functional layer of the endometrium

What derivatives of the trophoblast become the placenta

the cytotrophoblast and the syncytiotrophoblast

Where is the cytotrophoblast?

the inner part of the placenta

where is the syncytiotrophoblast?

the outer part of the placenta

What does the embryoblast form adjacent to the blastocyst cavity?

the hypoblast

What does the embryoblast form that is not adjacent to the blastocyst cavity?

the epiblast

what does the hypoblast form

the yol sac

What does the epiblast form?

amnion (surrounds the embryo eventually)

the amniotic cavity

embryo

What do the hypoblast and epiblast make up

the bilaminar disk

What is the purpose of the yolk sac

hydrate the fetus

what is the function of the amnion

protect and cushion embryo

what is the function of the chorion (placenta)

exchange nutrients between the fetus and mother

What is the chorion

a membrane that is part of the placenta that surrounds the embryo

What is the chorionic villi

place where maternal blood and fetus’s blood come close for diffusion but never mix

What is the endometrium

part of the uterine lining that the fetus occupies

What is the order of events for gastrulation?

primitive streak forms

primitive node signals development

Epiblast cells fall into the primitive pit

cells under the epiblast form endoderm and mesoderm membranes

hypoblast membrane degenerates

once complete, epiblast is referred to as ectoderm

What are the three primary germ layers that make up the embryonic disk?

the ectoderm (upper), mesoderm (middle), and endoderm (bottom layer)

What does the ectoderm become structurally?

epidermis of skin, nervous system (brain and spinal cord), sweat glands, mammary glands, hair, nails, and enamel of teeth

What does the mesoderm become structurally?

Dermis, muscle, skeleton, heart, blood vessels, lymph, serous, spleen and reproductive organs

What does the endoderm become structurally?

liver, gallbladder, pancreas, and the epithelial tissue of the respiratory tract

What is cephalocaudal folding

head-to-tail folding along the longitudinal axis

What is transverse folding

side to side folding across the transverse axis

What is neurulation

formation of the neural tube

what germ layer forms the neural tube

the ectoderm

what are the steps to forming a neural tube

The neural plate folds into the neural groove, which folds into the neural tube

What germ layer are the notochord and somites in?

mesoderm

What is the notochord

A flexible backbone that provides support

What is a somite

early stage vertebrae