Chapter 12: Conception & Fetal Development

Foramen ovale

An opening into the left atrium where blood mixes with deoxygenated blood returning from fetal lungs through the pulmonary veins. [[[Revisit fetal circulation on pg. 273]]]

Why might meconium happen before delivery? (2)

Breach presentation or excessive stress

Examples of presumptive signs of pregnancy

Breast changes, amenorrhea, nausea, vomiting, fatigue, quickening

Ductus arteriosus

Bypasses the fetal lungs to allow for respiratory gas exchange; oxygen-rich blood from placenta flows rapidly through the umbilical vein into the fetal abdomen.

Human chorionic gonadotropin hormone (hCG)

Can be detected by 8-10 days after conception, shortly after implantation. Basis for pregnancy tests. Ensures continuous supply of estrogen and progesterone needed to maintain pregnancy. Reaches max. level at 50-70 days then begins to decrease.

Viability

Capability of the fetus to survive outside the uterus and is usually defined by fetal weight and pregnancy duration -- 20 weeks gestation and birth weight of 350-500 grams

By Day 14 after conception, the embryonic disk, amniotic sac, and the yolk sac are attached to the chorionic villi by the [?]

Connecting stalk

Wharten's jelly

Connective tissue that prevents compression of blood vessels and ensures continued nourishment of the embryo or fetus

Issues that may occur with multifetal pregnancies?

Cord entanglement, placental insufficiency; especially when twins are developing in the same sac

Nuchal cord

Cord is wrapped around fetal neck

Chorion becomes...

Covering of the FETAL side of the placenta. It contains the major umbilical blood vessels as they branch out over the surface of the placenta. Chorionic villi will atrophy and degenerate.

Amnion becomes...

Covering of the umbilical cord and covers the chorion of the fetal surface of the placenta

Lecithin/sphingomyelin (L/S) ratio

Determines health or maturity of fetus; fetal lung maturity

Amniotic cavity

Develops between the amnion and the outer layer of cells (trophoblast)

Amnion develops from...

Develops from the interior cells of the blastocyst.

Where does fertilization take place?

Takes place in the ampulla (outer third) of the uterine tube.

Spermatogenesis

Testes undergo process of making spermatocytes during puberty

What is meconium composed of?

Amniotic fluid byproducts

When the umbilical vein reaches the liver, it divides into two branches...

1) Circulates some oxygenated blood through the liver, 2) passes through the ductus venosus

Length of pregnancy

10 lunar months, 9 calendar months, 40 weeks, or 280 days

Beginning in Week [?], the fetus urinates into the amniotic fluid, which increases its volume

11

When does it become safe to perform an amniocentesis? Why?

14 weeks; amniotic fluid level is sufficient

[?] artery/s carry blood from the embryo to the chorionic villi, and [?] vein/s return blood to the embryo

2 arteries, 1 vein

Fetus is able to percieve sounds around [?] weeks.

24

What should the L/S ratio be in an infant?

2:1

Conception occurs approximately [?] weeks after the first day of the last menstrual period (LMP), making the post-conception age of the fetus [?] weeks less

2; 38 weeks or 266 days -- used to talk about fetal development

Pulmonary surfactants are not fully mature in a fetus until [?]-[?] weeks of gestation.

32-35

Blood type is established within the fetus at around [?] weeks gestation. Why is this important?

6; baby may be Rh+ / mother Rh- and if miscarriage occurs, mother can be infected with Rh antigen

When does renal system become functional in a fetus?

9-10 weeks

Yolk sac functions

Aids in transferring maternal nutrients and oxygen, which have diffused through the chorion, to the embryo. Blood cells and plasma cells are manufactured in the yolk sac during the SECOND and THIRD weeks while uteroplacental circulation is being established and is forming primitive blood cells until hematopoietic activity begins.

Chorion develops from...

Develops from the trophoblast and contains the chorionic villi on its surface, which burrow into the decidua basalis and increase in size and complexity as the vascular processes develop into the placenta

Vasoconstriction [?] uterine blood flow, which can occur with hypertension or cocaine use. When a woman lies on her back, blood flow to the [?] is diminished. Optimal circulation occurs when woman is on her side.

Diminishes; right atrium

Three germ layers of the embryonic disk

Ectoderm, mesoderm, and endoderm

If an infant is born post-term, why might their skin be dry and wrinkled?

Fetal circulation is working to preserve blood flow to the vital organs.

The fetus swallows amniotic fluid beginning in the [?] month.

Fifth

Chorionic villi

Finger-like projections that develop out of the trophoblast and extend into the blood-filled psaces of the endometrium. They are vascular processes that obtain oxygen and nutrients from the maternal bloodstream and dispose of carbon dioxide and waste products into the maternal blood.

Conception is part of a sequential process, which includes gamete formation [?], ovulation [?], fertilization [?], and implantation into the uterus.

Gamete -- egg and sperm formation (independently) Ovulation -- release of the egg Fertilization -- union of the gametes

Embryoblast

Gives rise to the embryo

Trophoblast

Gives rise to the placenta

Examples of probable signs of pregnancy

Goodell sign, Chadwick sign, Hegar sign, positive pregnancy test (either serum or urine), Braxton Hicks contractions, ballottement

Oligohydramnios

Having less than 300 mL of amniotic fluid; associated with fetal renal abnormalities

Hydramnios/polyhydramnios

Having more than 2 L of amniotic fluid; associated with GI and other malformations

The folding in of the embryo during the fourth week results in...

Incorporation of yolk sac into embryo's body as the primary digestive system

Placental estrogen [?] greatly toward the end of pregnancy.

Increases

Embryonic period

Lasts from Day 15 until approximately 8 weeks after conception, when embryo measures 3 cm; MOST critical time for development of organ systems and main external features

Iron is stored in the fetal [?], so if gestational anemia occurs, fetus is not drastically affected.

Liver

Amniotic fluid functions

Maintains constant body temperature; source of oral fluid and a repository for waste; assists in maintenance of F&E homeostasis; allows freedom of movement for musculoskeletal development; cushions fetus from trauma; acts as barrier to infection and allows fetal lung development; keeps embryo from tangling with membranes

Progesterone

Maintains the endometrium, decreases contractility of the uterus, and stimulates maternal metabolism and development of breast alveoli

Pinocytosis

Mechanism used for transferring large molecules, such as albumin and gamma globulins, across the placental membrane. Passive immunity.

First stool of a newborn

Meconium

Does maternal insulin cross the placenta?

No, but maternal glucose does.

Braxton-Hicks contractions

Painless contractions that occur intermittently after the first trimester; appears to enhance movement of blood through intravillous spaces and aiding in placental circulation. Prolonged contractions or too-short intervals can REDUCE blood flow to the placenta.

Ductus venosus

Passes blood into the inferior vena cava, where it mixes with deoxygenated blood from the fetal legs and abdomen on its way to the right atrium. Most of this blood passes through the right atrium and through the foramen ovale.

[?] does the majority of the work regarding removing waste products from the baby.

Placenta

Decidua basalis

Portion of endometrium directly under the blastocyst where the chorionic villi tap into the maternal blood vessels

Implantation

Process between 6 and 10 days after conception where the trophoblast secretes enzymes that enable it to burrow into the endometrium until the entire blastocyst is covered. Bleeding may occur as endometrial vessels erode.

Mitosis

Process by which body cells replicate to yield two cells with the same genetic makeup as the parent cell. Cell makes copy of DNA, then divides.

Meiosis

Process by which germ cells divide and decrease their chromosomal number by half. Ends with production of gametes (eggs and sperm).

Last system to fully develop in a fetus?

Pulmonary system

Blastocyst

Recognizable structure of developing embryo

Metabolic functions of the placenta (4)

Respiration, nutrition, excretion, and storage

Estriol estrogen

Secreted by placenta; measured to determine placental functioning. Stimulates uterine growth and uteroplacental blood flow. Causes proliferation of breast glandular tissue and stimulates myometrial activity.

Morula

Solid ball of 16 cells produced within 3 days and is surrounded by zona pellucida. Floats freely within the uterus in order to mature.

Teratogens

Substances or exposure that causes abnormal development; these can cause significant damage to areas with rapid cell division

Oogenesis

The process of egg (ovum) formation. Begins during fetal life of a female.

Conception

The union of a single egg and sperm; marks the beginning of pregnancy. Also known as formation of the zygote.

If an infant is born prematurely, what might their skin look like?

Thin and wrinkly; you can probably see their veins through the skin. Susceptible to injury.

Fluid passes through the zona pellucida into the intercellular spaces between the blastomeres, separating them into two parts: [?] and [?]

Trophoblast and embryoblast

The connecting stalk eventually becomes compressed from both sides by the amnion and forms the [?]

Umbilical cord

Zygote

United egg and sperm

Examples of positive signs of pregnancy

Visualization of fetus by real-time ultrasound exam, fetal heart tones detected by ultrasound, visualization of fetus by radiographic study, etc

Zona reaction

When a sperm successfully penetrates the membrane surrounding the ovum, both sperm and ovum are enclosed within the membrane, and the membrane becomes impenetrable to other sperm.

Fetus/fetal period

When fetus becomes recognizable as a human being; lasts from 9 weeks until delivery. Less vulnerable to teratogens, except for those affecting the CNS. Refinement of structure and function occurs to become capable of extrauterine survival.

Where does meiosis occur in a female?

Within the ovarian follicles. Leads to production of ovum, or egg.

Do fetuses make their own insulin?

Yes

When the amniotic cavity and amnion are forming, another blastocyst cavity forms on the other side of the developing embryonic disk. It becomes surrounded by a membrane and is termed [?]

Yolk sac

Hematopoesis occurs in the [?] and starts in the [?] week

Yolk sac; third week