Embryonic and Fetal Structures

As early as the 11th or 12th day after fertilization, miniature villi, resembling probing fingers and termed chorionic villi, reach out from the trophoblast cells into the uterine endometrium to begin formation of the placenta. Chorionic villi have a central core consisting of connective tissue and fetal capillaries surrounded by a double layer of cells, which produce various placental hormones, such as hCG, somatomammotropin (human placental lactogen [hPL]), estrogen, and progesterone.

CHORIONIC VILLI Day Ano to? Anong nasa central core?

The middle layer, the cytotrophoblast or Langhans' layer, appears to have a second function to protect the growing embryo and fetus from certain infectious organisms such as the spirochete of syphilis early in pregnancy. Because this layer of cells disappears between the 20th and 24th week of pregnancy, this is why 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 invasion at any point, increasing the vulnerability of the fetus to viruses

CHORIONIC VILLI middle layer fxn and name when does this disintegrate?

The placenta (Latin for "pancake," which is descriptive of its size and appearance at term) grows from a few identifiable trophoblastic cells at the beginning of pregnancy to an organ 15 to 20 cm in diameter and 2 to 3 cm in depth, covering about half the surface area of the internal uterus at term it is formed by the union of the chorionic villi and the decidua basalis. It is a fleshy disk- like organ that measures 15-20 cm. in diameter and 2- 3 cm. in thickness late in pregnancy and weighs 500 g. at term. a. serves as the fetal lungs, kidney and GIT. b. serves as a separate endocrine organ throughout pregnancy. c. offers some protection to the fetus against invading microorganisms and chemical substance.

PLACENTA word? development? size? fxn?

The chorionic villi on the medial surface of the trophoblast (i.e., those that are not involved in implantation because they do not touch the endometrium) gradually thin until they become the chorionic membrane, the outermost fetal membrane. The amniotic membrane, or amnion, forms beneath the chorion. The amniotic membrane is a dual-walled sac with the chorion as the outmost part and the amnion as the innermost part. The two fuse together as the pregnancy progresses, and by term, they appear to be a single sac. They have no nerve supply, so when they spontaneously rupture at term (a pregnant woman's "water breaks") or are artificially ruptured via a procedure, neither the pregnant woman nor fetus experiences any pain It is also called the bag of water because it is filled with fluid known as the amniotic fluid. In contrast to the chorionic membrane, the second membrane (the amniotic membrane) not only offers support to amniotic fluid but also actually produces the fluid. In addition, it produces a phospholipid that initiates the formation of prostaglandins, which may be the trigger that initiates labor.

THE AMNIOTIC MEMBRANES structures? how do they form? what happens at the end of pregnancy?

After fertilization, the corpus luteum in the ovary continues to function rather than atrophying under the influence of human chorionic gonadotropin (hCG) secreted by the trophoblast cells. This hormone also causes the uterine endometrium to continue to grow in thickness and vascularity instead of sloughing off as in a usual menstrual cycle. The endometrium is now typically termed the decidua (the Latin word for "falling off") because it will be discarded after birth of the child.

THE DECIDUA OR UTERINE LINING

The placenta and membranes, which will serve as the fetal lungs, kidneys, and digestive tract in utero as well as help provide protection for the fetus, begin growth in early pregnancy in coordination with embryo growth.

The placenta and membranes, which will serve as

Amniotic fluid never becomes stagnant because it is constantly being newly formed and absorbed by direct contact with the fetal surface of the placenta. The major method of absorption, however, happens within the fetus. Because the fetus continually swallows the fluid, it is absorbed from the fetal intestine into the fetal bloodstream. From there, it goes to the umbilical arteries and to the placenta and is exchanged across the placenta to the mother's bloodstream. The most important purpose of amniotic fluid is to shield the fetus against pressure or a blow to the mother's abdomen. Because liquid changes temperature more slowly than air, it also protects the fetus from changes in temperature. Another function is that it aids in muscular development, as amniotic fluid allows the fetus freedom to move. Finally, it protects the umbilical cord from pressure, thus protecting the fetal oxygen supply. Even if the amniotic membranes rupture before birth and the bulk of amniotic fluid is lost, some will always surround the fetus in utero because new fluid is constantly being formed. Amniotic fluid is slightly alkaline, with a pH of about 7.2. Checking the pH of the fluid at the time membranes rupture and amniotic fluid is released helps to differentiate amniotic fluid from urine because urine is acidic (pH 5.0 to 5.5).

AMNIOTIC FLUID never stagnant because? fxns?