Anatomy, Conception, Fetal Development

Pre-embryonic Stage

1 to 14 days; first two weeks. When germ layers begin to form. Heart forms during the 3rd gestational week and begins to beat and circulate blood during the 4th gestational week.

Functions of amniotic fluid

Acts as a cushion for the fetus when there are sudden maternal movements, prevents adherence of the developing human to the amniotic membranes, allows freedom of fetal movement which aids in symmetrical musculoskeletal development, and provides a consistent thermal environment.

8 weeks from conception

All organs are formed and no longer an embryo but a fetus. Vulnerable to teratogens.

Conceptus Stage

All tissue products of conception, embryo, fetal membranes, and placenta.

Polyhydramnios

Also called hydramnios, refers to excess amount of amniotic fluid (1,500-2,000 mL). These newborns have increased incidence of chromosomal disorders and gastrointestinal, cardiac, and/or neural tube disorders.

Conception

Also known as fertilization, occurs when a sperm nucleus enters the nucleus of the oocyte. Fertilization normally occurs in the outer third (ampulla) of the fallopian tube.

Monozygotic Twins

Identical twins; the result of one fertilized ovum splitting during the early stages of cell division and forming two identical embryos; a division of greater than 1,000 cells. These fetuses are genetically the same. There are 1 ova, sperm, genotype, placenta, and 1 or 2 chorions and amnions.

Embryoblast

Inner cell mass of the blastocyst which will develop into the embryo for the first 8 weeks then becomes the fetus. These cells form the amniotic membrane.

Endoderm

Inner germ layer; lungs, intestines, and bladder.

Amnion

Inner membrane; fetal portion, and develops from the embryoblast.

Mesoderm

Middle germ layer; heart, circulatory system, skeletal muscles, kidneys, bone marrow, blood, and reproductive.

Blastocyst

Mitosis continues and around day five the developing human is known as the ________ and enters the uterus, implanting in the endometrium.

17-20 weeks from LMP

Mother feels movement; some can report a lot sooner especially if its second pregnancy.

Proliferative Phase

Occurs following menstruation and ends with ovulation. The endometrium is preparing for implantation so it becomes thicker and more vascular with the help of estrogen released from the Graafian follicle.

Menstrual Phase

Occurs in response to hormonal changes and results in the sloughing off of the endometrial tissue starting cycles all over again.

Ovulatory Phase

On the 14th day, begins when estrogen levels peak and ends with the release of the oocyte (egg) from the mature Graafian follicle. The releasing of the egg is referred to as ovulation. There is a surge of LH levels 12-36 hours before ovulation and there is a decrease in estrogen levels with an increase in progesterone levels before the LH surge. Can have pain during ovulation called Mittleschmerz. Woman has thin cervical mucous and greater desire for sex.

Differentiation

Organs are formed; all major organs are formed between day 17-56 (8 weeks)

Ectoderm

Outer germ layer; epidermis, nervous system, lens and cornea, internal ear, salivary glands, and mucosa of oral and nasal cavities.

Chorion

Outermost of embryonic membrane and contains chorionic vili that attach to decidua basalis; maternal portion of placenta. Formed from the trophoblast.

Endometrial Cycle

Pertains to the changes in the endometrium of the uterus in responses to the hormone changes that occur during the ovarian cycle. Consists of three phases: proliferative, secretory, and menstrual phases.

Ovarian Cycle

Pertains to the maturation of the ova and consists of three phases: follicular, ovulatory, and luteal phases.

Ductus arteriosus

Pulmonary artery to descending aorta; the majority of the oxygenated blood is shunted to the aorta via the ductus arterioles with smaller amounts going to the lungs. After delivery the ______ constricts in response to the higher blood oxygen levels and prostaglandins.

Oligohydramnios

Refers to decreased amount of amniotic fluid (less than 500 mL at term or 50% reduction of normal amount) which is generally related to a decrease in placental function. Newborns have an increased incidence of congenital renal problems.

Multiple gestation

Refers to more than one developing embryo such as twins and triplets.

24 weeks from LMP

Respiratory movements

Foramen ovale

Right atrium to left atrium; an open channel where blood high in oxygen is shunted to the left atrium. after delivery the channel closes in response to increased blood returning to the left atrium -- it may take up to three month for full closure.

FSH (woman)

Secreted by the anterior pituitary gland, stimulates growth of ovarian follicles and stimulates the follicles to secrete estrogen.

FSH (male)

Secreted by the anterior pituitary gland, stimulates sperm production.

LH (male)

Secreted by the anterior pituitary gland, stimulates testosterone production.

Testosterone (male)

Secreted by the testes, promotes maturation of the sperm.

Estrogen (woman)

Secreted from the follicle cells, promotes the maturation of the ovum.

Oogenesis

The formation of a mature ovum (egg). Regulated by FSH and estrogen. For each primary oocyte that undergoes meiosis, only one functional ovum (egg) is formed. Unfertilized oocytes die 12-24 hours after ovulation.

Spermatogenesis

The formation of mature spermatozoa (sperm). Regulated by FSH, LH, and testosterone. For each primary spermatocyte that undergoes meiosis, four functional sperm cells are formed. Sperm cells survive from 48-80 hours in the uterus.

Fetal Circulation

The heart begins to beat during the 4th gestational week; high levels of oxygenated blood enter the fetal circulatory system from the placenta via the umbilical vein.

Trophoblast

The outer cell mass which will assist in implantation and become part of the placenta. These cells grow into the chorion and chorionic villi.

Decidua Basalis

The portion directly beneath the blastocyst, forms the maternal portion of the placenta.

Cleavage

The single-cell zygote undergoes mitotic cell division.

Fundus

The upper portion of the uterus.

Morula

Three-days after fertilization, the zygote forms 16-cell, solid sphere.

Embryonic Stage

Time of fertilized ovum 2nd week to fetus 8th week.

Functions of placenta

Transport Immunologic Metabolic Endocrine

Ductus venosus

Umbilical vein to inferior vena cava; this allows the majority of the high levels of oxygenated blood to enter the right atrium.

Teratogens

Any drugs, viruses, infections, or other exposures that can cause embryonic/fetal developmental abnormality. The developing human is most vulnerable to the effects of teratogens during the period of organogenesis, the first 8 weeks of gestation.

Chorionic Vili

Are projections from the chorion that embed into the decider basalts and later form the fetal blood vessels of the placenta.

Proximosdistal

Arms are developed before fingers

A.V.A

Artery, vein, artery named in relation to fetus; oxygenated fetal blood via umbilical vein and oxygen depleted fetal blood via 2 arteries.

28 weeks from LMP

Baby can breathe but lacks surfactant; if born this early, will instill surfactant to promote functional lungs.

11 weeks from LMP

Baby's sex may be able to be seen but does have a lot of room to move.

Secretory Phase

Begins after ovulation and ends with the onset of menstruation. Endometrium continues to thicken with primary hormone being progesterone secreted by corpus luteum. If pregnancy occurs, the endometrium will continue to develop and begins to secrete glycogen. If pregnancy does not occur, the corpus luteum degenerates and endometrial tissue degenerates.

Luteal Phase

Begins after ovulation and lasts approximately 14 days. The cells of the empty follicle forms into the corpus luteum. The corpus luteum produces high levels of progesterone along with low levels of estrogen. If pregnancy occurs, then the corpus luteum continues to release progesterone and estrogen until the placenta matures and takes over. If pregnancy doesn't occur, the corpus luteum degenerates and results in a decrease in progesterone and the beginning of menstruation.

Follicular Phase

Begins first day of menstruation and lasts 12-14 days. The Graafian follicle is maturing under the influence of LH and FSH. The maturing Graafian follicle is producing estrogen. Woman begins to bleed.

Cephalocaudal

Brain is developed before lungs

Amniotic fluid

Contained within the amniotic sac; it is clear and composed mainly of water with proteins, carbs, lipids, electrolytes, fetal cells, lanugo, and vernix caseosa. It is produced by the amniotic membrane in first trimester and by the fetal kidneys in second/third trimesters.

Implantation

Embedding of the blastocyst into the endometrium of the uterus around day 5-8th days post fertilization.

Zygote

Fertilized oocyte and contains the diploid number go chromosomes (46).

4 weeks from conception

Fetal heart begins to beat; can be picked up on ultrasound.

Organogenesis

Formation and the development of body organs occurring during the 8th week of gestation. Primary germ layers begin to develop around day 14.

Placenta

Formed from both maternal and fetal tissue; the placental membrane separates the maternal and fetal blood and prevents fetal blood from mixing with maternal blood, but allows for the exchange of gases, nutrients, and electrolytes. Becomes fully functional in the 8th-10th weeks of gestation.

Amniotic Sac

Formed from two membranes, the amnion and chorion. Also referred to as the bag of waters. The embryo and amniotic fluid is contained within. These membranes stretch to accommodate the growth of the developing fetus and the increase of amniotic fluid.

Dizygotic Twins

Fraternal twins; the result of two separate ova being fertilized by two separate sperm. These fetuses are not genetically the same. There are 2 ova, sperm, placentas, chorions, amnions, and can be same or different sex.

Fetus Stage

From 8th week until birth 40 weeks later. The developing human has formed from the primary germ layers to a clearly defined human that is 3 cm in length will all organ systems formed.

9-12 weeks from LMP

Heart beat is heard on the doppler if mom is not fluffy.