Embryonic stage of gestation - is the period after implantation during which all of the major organs and structures within the growing fetus are formed
Placenta and Membranes
Serve as the fetal lungs, kidneys, and digestive tract in utero
Help to provide protection for the fetus, begins growth in early pregnancy in coordination with embryo growth
After fertilization, the corpus luteum in the ovary continues to function rather than atrophying, because of the influence of human chorionic gonadotropin (hCG), a hormone secreted by the trophoblast cells.
Endometrium - is now termed the Decidua (Latin word for “falling off”)because it will be discarded after the birth of the child.
Decidua basalis – is the part of the endometrium that lies directly under the embryo or the portion where the trophoblast establish communication with the maternal blood vessels
Trophoblast - are cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta
Blastocyst – is the stage that the human embryo reaches approximately 5-6 days after fertilization
Decidua capsularis – the portion of the endometrium that encapsulates the surface of the trophoblast
Decidua vera – is the remaining portion of the uterine lining.
Chorionic Villi - once implantation is complete, trophoblastic layer of cells of the blastocyst begins to mature rapidly.
11th or 12th day - miniature villi that resemble probing fingers, termed chorionic villi, reach out from the single layer of cells into the uterine endometrium to begin formation of the placenta
Syncytiotrophoblast (syncytial layer) – is the outer layer of cells that produces various placental hormones
Cytotrophoblast or Langhan’s layer – the middle layer, present as early as 12 days gestation.
Cytotrophoblast or Langhan’s layer
To protect the growing embryo and fetus from certain infectious organisms spirochete of Syphilis
This layer of cells disappears - between 20th and 24 wks
Passive antibody begins at 20th wks
Syphilis - is not considered to have a high potential for fetal damage early in pregnancy, only after the point at which cytotrophoblast cells are no longer present The layer appears to offer little protection against viral infection
Placenta – a flat, disc shaped organ that is highly vascular, forms in the upper segment of the endometrium of the uterus.
Placenta - is responsible in the exchange of nutrients and gases between the fetus and the mother
Placenta
15-20 cm in diameter
Weight: 400g- 600g
2-3 cm in depth
30 Cotyledons
Respiratory system – exchange of O2 and CO2 takes place in the placenta not in the fetal lungs.
Circulatory system – fetal placental circulation takes place via the umbilical vein
Renal system – waste products are excreted through the placenta.
Nutrients pass to the fetus via the placenta
12th day of pregnancy - maternal blood begins to collect in the uterine endometrium sur rounding the chorionic villi.
4 days
Zygote cells known as Totipotent
Totipotent stem cells – are undifferentiated cells that can develop a human being
After another 4 days:
Totipotent cells become Pluripotent
Pluripotent Stem cells – specific body cells (Nerve, Brain, or Skin cells
Another few days the Pluripotent cells become Multipotent
Multipotent cells - at the time of implantation, the blastocysts has two cavities in the inner structure (Amniotic cavity and Yolk sac)
2 cavities in the inner structure - Amniotic cavity & Yolk sac
Yolk sac
supply nourishment only until implantation
Provide a source of RBC until the embryo can produce its own (12th wk.
The Three Germ Layers
Ectoderm
Mesoderm
Endoderm
Ectoderm – skin, nervous system and sense organ
Mesoderm – musculoskeletal, circulatory and genitourinary
PREGNANCY
the state of having a developing embryo or fetus within the body
state from conception to the delivery of the fetus
Fetal Membranes - are membranes associated with the developing fetus.
Amnion – inner layer of the fetal membrane
Chorion – outermost membrane surrounding an embryo gives rise to the placent
Umbilical cord – is about 53 cm. (21 inches) in length at term and about 2 cm. (0.75 in.) thick
Umbilical cord – contains 2 arteries and one vein which are kept in place by the Wharton jelly
WHARTON’S JELLY - a gelatinous substance which prevents pressure on the vein and arteries.