Lab Exercise 44: Embryonic Development

3 basic activities that ensure the formation of a viable offspring

1. Increase in cell number and cell growth 2. Cellular specialization 3. Morphogenesis: the formation of functioning organ systems.

placenta

1. fetal portion 2. maternal portion

umbilical cord

1. umbilical artery 2. umbilical veins

Morula

At the 32-cell stage, a solid ball of cells forms called this, and the embryo resembles a raspberry in form.

stages of development: implantation

Blastocyst (consists of a sphere of trophoblast cells and inner cell mass) adheres to the uterine wall over in the inner cell mass area, and implantation begins.

gastrula stage

By the time implantation has been completed, embryonic development has progressed to this stage, and the 3 primary germ layers are present and are beginning to differentiate.

process and timing of implantation in the human

Implantation is the very early stage of pregnancy at which the conceptus adheres to the wall of the uterus.[1] At this stage of prenatal development, the conceptus is a blastocyst. It is by this adhesion that the foetus receives oxygen and nutrients from the mother to be able to grow. In humans, implantation of a fertilized ovum is most likely to occur about 9 days after ovulation, ranging between 6 and 12 days.

blastula vs gastrula

It is a hollow, spherical, one celled thick structure formed by the process called blastulation. Both holoblastic and meroblastic cleavages give rise to blastula. The cavity inside the blastula is called blastocoel, and its outer single cell layer is called blastoderm. The continuous development of blastula finally results the gastrula. The conversion process of the blastula into gastrula is called 'gastrulation'. Gastrulation is followed by the organogenesis. Gastrula is composed of three primary germ layers, which eventually give rise to organs in the late embryo.

stages of development: blastula

Morula hollows out to become the embryonic form, has inner cell mass and cavity, becomes the final product of cleavage.

allantois

Protrudes from the posterior end of the yolk sac, is also largerly redundant in humans because of the placenta. In humans, it is structural basis on which the mesoderm migrates to form the body stalk, or umbilical cord, which attaches the embryo to the placenta.

stages of development: cleavage

Series of mitotic divisions without intervening growth periods is referred as

Cleavage

Series of mitotic divisions without intervening growth periods is referred as this, and it results in a multicellular embryonic body.

decidua basalis

The area of endometrium between the implanted chorionic vesicle and the myometrium, which becomes the maternal part of the placenta.

Blastocyst

The cell mass hollows out to become the embryonic form called this, which is a ball of cells surrounding a central cavity. This is the final product of cleavage. This has the following structures: 1. inner cell mass 2. blastocyst cavity 3. trophoblast

Syncytiotrophoblast

The epithelial covering of the highly vascular embryonic placental villi, which invades the wall of the uterus to establish nutrient circulation between the embryo and the mother.

Cytotrophoblast

The inner layer of the trophoblast. It is considered to be the trophoblastic stem cell because the layer surrounding the blastocyst remains while daughter cells differentiate and proliferate to function in multiple roles.

decidua capsularis

The layer of endometrium overlying the implanted chorionic vesicle that progressively diminishes as the chorionic vesicle enlarges

fertilization

The process of an egg being penetrated by a sperm.

amniotic sac

The sac consists of two membranes (known as the amnion and the chorion) that form baby's home while in your belly. This keeps baby warm, safe and surrounded by cushiony liquids.

placenta

This includes these structures: 1. chorion 2. chorionic villi

Yolk sac

a membrane outside the embryo that is connected by a tube (the yolk stalk) though the umbilical opening to the embryo's midgut. The yolk sac serves as an early site for the formation of blood and in time, is incorporated into the primitive gut of the embryo.

Amnion

a membrane that when first formed, closely covers the embryo. It fills with the amniotic fluid which causes the amnion to expand and become the amniotic sac which serves to provide a protective environment for the developing embryo.

function of gastrulation

a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a trilaminar ("three-layered") structure known as the gastrula. These three germ layers are known as the ectoderm, mesoderm, and endoderm.

stages of development: morula

a solid ball of blastomeres (at the 32 cell stage)

blastocyst

a structure formed in the early development of mammals. It possesses an inner cell mass (ICM) which subsequently forms the embryo. The outer layer consists of cells collectively called the trophoblast. This layer surrounds the inner cell mass and a fluid-filled cavity known as the blastocoele. The trophoblast gives rise to the placenta.

Blastomere

a type of cell produced by cleavage (cell division) of the zygote after fertilization and is an essential part of blastula formation.

fetal portion

a. chorionic villi b. fetal blood vessels

maternal portion

a. decidua basalis b. maternal blood vessels

fetus

an unborn offspring of a mammal, in particular an unborn human baby more than eight weeks after conception.

embryo

an unborn or unhatched offspring in the process of development.

umbilical cord

attaches the embryo to the placenta

trophoblast

becomes an extraembryonic membrane called the chorion, which forms the fetal portion of the placenta.

Trophoblast

cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta.

stages of development: gastrulations

development of 3 primary germ layers

stages of development: organogensis

development of the nervous system

amnion

encases the young embryonic body in a fluid-filled chamber that protects the embryo against mechanical trauma and temperature extremes and prevents adhesions during rapid embryonic growth.

stages of development: zygote

fertilized egg

zygote

fertilized egg

stages of development: embryo

formation of most internal organs and external body structures.

endoderm

forms the mucosa of digestive and respiratory tracts

Inner cell mass

forms within the blastocyst, prior to its implantation within the uterus. It is a cellular mass on one side of the hollow interior of the round embryo, the outer layer of which is called the trophoblast.

ectoderm

gives rise to the epidermis of the skin and nervous system

stages of development: fetus

has developed to the point of being recognizable as belonging to its own species

yolk sac

in humans has lost its original function, which was to pass nutrients to the embryo after digesting the yolk mass. The placenta has taken over that task; also, the human egg has very little yolk. However, this is not totally useless. The embryo's first blood cell originates here, and the primordial germ cells migrate from it into the embryo's body to seed the gonadal tissue.

intervillous spaces

is the "space between the villi containing the vessels" of the mother and the embryo.

chorion

one of the membranes that exist during pregnancy between the developing fetus and mother. It is formed by extraembryonic mesoderm and the two layers of trophoblast that surrounds the embryo and other membranes. The chorionic villi emerge from the chorion, invade the endometrium, and allow transfer of nutrients from maternal blood to fetal blood.

Allantois

part of a developing amniote's conceptus (which consists of all embryonic and extra-embryonic tissues). It helps the embryo exchange gases and handle liquid waste.

decidua capsularis

portion directly overlying the implanted ovum and chorion, facing the uterine cavity.

decidua basalis

portion lying under the implanted ovum and chorion.

mesoderm

skeleton, organs, muscles

stages of development: fertilization

sperm meets and enters egg

chorionic villi

sprout from the chorion in order to give a maximum area of contact with the maternal blood.

function of cleavage

the division of cells in the early embryo.

chorionic vesicle

the saclike membrane that develops from the blastocyst wall to envelop the embryo.

Chorionic villi

tiny, finger-shaped growths found in the placenta. The genetic material in chorionic villus cells is the same as what is in fetal cells.