Embryology and Early Embryonic Development

Gametogenesis

The production of gametes (Meiosis)

Oogenesis

Formation of the egg (Ova or oocyte) forms 1 viable egg and 3 polar bodies

Spermatogenesis

Formation of the sperm, 4 viable gametes

Embryology

Branch of Biology that studies the formation and early development of living organisms.

Zygote

fertilized egg, 1-2 days, one cell

Embryo

1-8 weeks implantation to 8 weeks, heart formed

Fetus

8 weeks to birth

Fertilization, Implantation, Gastrulation, Cell differentiation

Order of Embryonic Development

Fertilization

egg (haploid) and sperm (haploid) come together to make a zygote (diploid). Within 24 hours the zygote divides, becomes a morula, then a blastula/blastocyst.

Cleavage

within 24 hours of fertilization, zygote begins to divide (mitosis).

Morula

around day 3, a solid ball of cells

Blastula/Blastocyst

days 5-6, hollow fluid filled ball of cells

Implantation

the blastocyst attaches to the uterine wall around 6 days after implantation (hormone HCG released one week after implantation)

Gastrulation

The process in which the cells of the blastocyst develop into 3 germ layers to form a gastrula.

Endoderm, mesoderm, ectoderm

the 3 germ layers

Endoderm

the inner-most layer, digestive, respiratory and urinary tracts form

Mesoderm

middle layer, internal organs (muscle, skeleton, blood)

Ectoderm

outer-most layer (skin and nervous system)

Cell differentiation

giving cells specific jobs

Neurulation, Organogenesis, Morphogenesis

order of cell differentiation

Neurulation

development of the nervous system, 1st system that started to form

Organogenesis

organs start to form; heart is the first organ formed (forms at 8 weeks)

Morphogenesis

limbs start to assume shape

Extraembryonic Membranes

Membranes form to protect and nourish the developing embryo (fluid filled cushions embryo

Amnion, Chorion, Placenta

order of extraembryonic membranes

Amnion

The fluid the baby is in

Chorion

the outermost membrane of the amniotic sac

Placenta

the maternal-fetal organ which begins developing at implantation of the blastocyst

nutrients, gases, and waste products

what does the placenta exchange?

Dilation of the cervix, expulsion (delivery of the infant), and delivery of the placenta

3 birth phases

dilation of the cervix

cervix relaxes causing it to dilate (10 cm) and thin out, Longest stage

Expulsion (delivery of the infant)

contractions increase in strength and cervix is fully dilated, infant delivered.

Delivery if the placenta

also called the second birth or after-birth. The placenta is expelled and other membranes.

Stem cells

unspecialized cells that have the potential to differentiate.

Identical twins

A zygote splits into two, same DNA, one egg, one cell

Fraternal twins

different DNA, two different eggs, two different sperm.

1st trimester (week 1-12)

heart, nervous system, most organs formed but not functional

2nd trimester (week 13-28)

feel movement (19 weeks), some cartilage turns to bone, gender, birth defects, fingerprints (skin starting to form), hear sounds

3rd trimester (week 28-40)

fetus gains weight (doubles in size), organs functional, eyes open.