Gametogenesis to Fertilization

embryology

branch of animal biology that studies prenatal development of gametes, fertilization, and development of embryos and fetuses

critical period of pregnancy

third to eighth week of gestation during which the embryo is most susceptible to teratogens

time of organogenesis- when various organ systems are developed

gonads

produce gametes

germ cells

mature to become gametes

sacrococcygeal teratoma

most common tumor in newborn

arising from primordial germ cells- pluripotent

can give rise to variety of anatomic structures, including hair, teeth, pituitary gland, eye

totipotent cells

can potentially become an entire embryo

extremely rare, only first few subdivisions of the zygote

pluripotent cells

can develop into any type of cell in the adult body (cells derived from the ectoderm, endoderm, and mesoderm)

can’t develop certain embryonic cels (cells of the trophoblast)

multipotent

can produce a few types of cells

unipotent

can give rise to only one cell type

germ cells are unique from somatic cells in that they

replicated via meiosis

oogenesis

in ovary

ovum and follicular cells develop together going through the primary, secondary, and the graafian follicle stages

sertoli cells

key role in the differentiation from spermatogonia to spermatid

spermiogenesis

differentiation of spermatid to mature sperms

down’s syndrome

trisomy 21- have three of the 21st chromosome

flat broad face, oblique palpebral fissures, protruding tongue

usually have some intellectual disabilities and cardiac defects

edwards syndrome

trisomy 18- three of the 18th chromosome

low set ears, small mouth, deficient mandible, flexion of hands, absent/hypoplasia of radius and ulna

patau syndrome

trisomy 13- three of the 13th chromosome

bilateral cleft lip, sloping forehead, anophthalmia

steps in fertilization

1. capacitation- final step in sperm maturation, normally occurs within the female genital tract. consists of changes in the acrosome to prepare it to release enzymes required to penetrate the zona pellucida

2. zona pellucida sperm receptor (species specific) to which the sperm binds, binding specifically induces acrosomal enzymes to be released, which allow penetration of zona pellucida

3. fusion of cell membranes of the oocyte and sperm

4. fusion induces charges in and under the zona, altering it and rendering it impermeable to other sperms (zona reaction) thus preventing polyspermy

assisted reproductive technologies (ART)

among infertile couples: 30% female infertility, 30% male infertility, 30% both

IVF-ET: in vitro fertilization and embryo transfer

IVF-ET

1. induce superovulation

2. transvaginal ultrasound guided aspiration of ova

3. in vitro fertilization and zygote inserted into the uterus

GIFT

gamete intrafallopian tube transfer

ZIFT

zygotę intrafallopian tubę transfer

cleavage

zygotę initiates rapid series of mitotic cell divisions, 2-cell, 3-cell, 4-cell stage and so on

daughter cells are called blastomeres

each blastomere is totipotent

compaction

starting at the 8-cell stage, blastomeres flatten and become tightly packed thus maximizing cell-cell contact among adjacent blastomeres

compaction and blastocyst development

1. compaction

2. upon compaction, some blastomeres segregate to form a. centrally placed blastomeres are called the inner cell mass, which will eventually give rise to the embryo proper (embryoblast) and b. cells on the outside called the trophoblast. these cells contribute to placenta formation

3. blastocyst formation: morula absorbs fluid anf develops a cavity called the blastocoel

4. blastocyst hatches from the zona pellucida, thus allowing trophoblast to interact with endometrium