Lecture 2 pregnancy

Conceptus

The developing offspring

Gestation period

Time from last menstrual period until birth (~280 days)

Embryo

Conceptus from fertilization through week 8

Fetus

Conceptus from week 9 through birth

How long is oocyte viable for

12 to 24 hours

How long after ejaculation is sperm viable

24 to 48 hours

For fertilization to occur, intercourse must occur no more than

Two days before ovulation, 24 hours after ovulation

Fertilized egg

Zygote

How many sperm are allowed to penetrate the oocyte

Only one!

What is cleavage

Mitotic divisions of zygote

Cleavage at 72 hours

Morula (16 or more cells)

Cleavage at day 3 or 4

Blastocyst (~100 cells) has reached uterus

Implantation begins blank days after ovulation

6-7

Early pregnancy hormone

Human chorionic gonadotropin (hCG)

What does hCG tell corpus luteum to do

Continue secretion of progesterone and estrogen

What causes hCG to decline

Placenta begins secreting progesterone and estrogen at end of second month

Formation of placenta from embryonic tissues

Mesoderm cells develop from the inner cell mass and line the trophoblast, together these form the chorion and chorionic villi

Formation of the placenta from maternal tissues

Decidua basilis (stratum functionalis between chorionic villi and stratum basilis of endometrium) develops blood filled lacunae

Which cells form endoderm

The first cells

Which cells form the mesoderm

Cells that push laterally

Which cells form ectoderm

Cells that remain on the embryos dorsal surface

Notochord

Rod of mesodermal cells that serves as axial support

What is gastrulation

An early embryonic development process where three layered structures called gastrula are formed. This process establishes primary germ layers - ectoderm, mesoderm, and endoderm - precursors of all tissues and organs

Ectoderm

Nervous system and skin epidermis

Endoderm

Epithelial linings of the digestive, respiratory, and urogenital systems

Mesoderm

Forms all other tissues

At what point are all organ systems recognizable

At eighth week

Organogenesis

Formation of all body organs and systems