Chapter 6: Conception and Prenatal Development Flashcards
1
Q
What is implantation?
A
Implantation of the fertilized ovum (zygote) in the uterine endometrium.
2
Q
Organogenesis
A
Organs are formed primarily during the first 8 weeks of pregnancy.
3
Q
Teratogens
A
an agent or factor that causes malformation of an embryo
4
Q
Fertilization
A
Occurs when one spermatozoon enters the ovum and two nuclei containing parents’ chromosomes merge.
5
Q
Where does fertilization usually occur?
A
In the distal third of the Fallopian tubes. (Aka ampulla)
6
Q
Entry of one spermatozoon into the ovum has three results:
A
- Zona reaction - changes in the zona pellucida surrounding the ovum prevent other sperm from getting in.
- Cell membranes of the ovum and sperm fuse and break down, allowing the contents of the sperm head to enter the cytoplasm of the ovum.
- Ovum completes meiosis (ovum now has 23 chromosomes and expulsion of 2nd polar body)
7
Q
Three periods of fetal growth?
A
- Pre-embryonic
- Embryonic
- Fetal
8
Q
What happens during the pre-embryonic period?
A
- Moment the ovum is fertilized.
- Initiation of cell division occurs.
- Entry of the zygote into the uterus
9
Q
When does the pre-embryonic period occur?
A
The first 14 days of development.
10
Q
Pre-embryonic period: Cell Division
A
- Zygote divides into 2, then 4, then 8 cells and so on, until the 16-cell stage where it becomes the morula (12-16 cells).
- Outer cells of morula secrete fluid, forming a blastocyst (a sac of cells with an inner cell mass placed off center within the sac)
- The inner cell mass develops into the fetus.
- The outer layer of cells develop as the placenta and fetal membranes.
11
Q
When does the zygote enter the uterus?
A
Around the fourth day after conception is when the blastocyst, which contains approximately 100 cells, enters the uterus.
12
Q
Pre-embryonic period: Entry of the zygote into the uterus
A
- After it enters the uterus, the blastocyst lingers in the uterus another 2-4 days before beginning implantation.
- The endometrium is now called the decidua, and is in a secretory phase of the reproductive cycle.
13
Q
Decidua
A
Endometrium of a pregnant woman; when it thickens to prepare for pregnancy.
14
Q
When does implantation occur?
A
6-10 days after conception*
15
Q
Implantation is complete by
A
The second week after fertilization.
16
Q
Why is the location and timing of implantation critical for continued development?
A
Requires a continuing supply of estrogen and progesterone to maintain decidua in the secretory phase.
17
Q
What signals a woman’s body that pregnancy has begun?
A
The zygote secretes human chorionic gonatropin (hCG) to signal the woman’s body that pregnancy has begun.
18
Q
What does hCG do?
A
Causes the corpus luteum to persist and continue secretion of estrogen and progesterone until the placenta takes over this function.
19
Q
Where does normal implantation occur?
A
Upper uterus, slightly more often on the posterior wall.
20
Q
The upper uterus is the best area for implantation and placental development because of 3 reasons:
A
- Richly supplied with blood for optimal fetal gas exchange, nutrition and waste elimination.
- Uterine lining is thick, preventing the placenta from attaching to deeply into the uterine muscle (this can facilitate easy expulsion of placenta after full-term birth)
- Limits blood loss after birth (strong interlacing muscle fibers in this area compress open endometrial vessels after the placenta detaches)
21
Q
When does the conceptus become fully embedded w/ in the mother’s uterine decidua?
A
By 10 days*
22
Q
Nourishment of the fetus
A
Nutritive Fluid passes to the embryo by diffusion in early stage d/t circulatory system not being established yet.
……
23
Q
When does the embryonic period occur?
A
In weeks 3-8.
24
Q
Embryonic Period: Teratogens
A
Structures are vulnerable to damage by teratogens because these structures are developing rapidly.
25
When does the fetal stage occur?
In week 9 when the embryo turns into a fetus.
26
When is a fetus considered viable?
By week 24. This is when the fetus will be able to survive delivery.
27
When does production of surfactant occur?
Begins at approximately 20 weeks but does not reach levels that increase the likelihood of survival outside the uterus until 28-30 weeks of gestation.
28
What interventions can be done to reduce the respiratory distress of prematurity?
1. Artificial surfactant may be given.
| 2. Maternal corticosteroid such as Bethamethsone
29
How do maternal corticosteroids such as bethamethsone help a preterm fetus with/at risk for respiratory distress?
May be given before birth to accelerate surfactant production in the preterm fetus likely to be born before completion of 34 weeks of gestation.
30
Why is a fetus born before 24 less likely to survive d/t inadequate gas exchange?
Because the capillary network around the alveoli is still very immature before 24 weeks.
31
A fetus is considered full term between what weeks?
38-40 weeks (book says 38 but she says 37)
32
What happens during the embryonic period?
- Basic structures of all major body organs are completed.
| - Body cells are differentiated and specialized.
33
What can be done to reduce the incidence of neural tube defects during organogenesis?
Taking vitamins and folic acid
34
Two most common NTD’s include
Spina bifida and anencephaly
35
Pregnancy Medication Classifications
```
Category A
Category B (i.e tylenol)
Category C (i.e antibiotics, antifungals)
Category D
Category X
```
36
Category A Drugs
Safest.
| No evidence of risk to fetus exists.
37
Dicligis
For N/V
| Category A
38
Category C Drugs
Considered OK
39
Category D Drugs
- Not so safe.
- Positive evidence of human fetal risk exists based on adverse reaction data, but potential benefits may warrant use of the drug in pregnant women despite fetal risks.
40
Category X Drugs
- Recommended to women to terminate pregnancy.
| - Positive evidence of human fetal risk.
41
Isotretinoin (Accutane)
- A vitamin A derivative for acne.
- Pregancy category: X
- Should not be taken during pregnancy because it causes fetal defects.
- Excessive intake causes spontaneous abortions or serious fetal defects.
42
Teratogens include
- Medications
- Radiation (i.e X-rays, CAT scan)
- Hot tube use (no longer than 20 minutes)
- Live vaccines (i.e rubella vaccine)
- Substance abuse
- Alcohol
43
Teratogens pose concerns for
Spontaneous abortions
Possible CNS defects
Failure of neural tube closure
44
Intrauterine Growth Restriction
- Impaired placental perfusion (i.e HTN, vasoconstriction) decreases supply of glucose and oxygen delivered to the fetus.
- As a result, the infant is likely to be small for gestational age.
45
Two types of “ages”
- Fertalization age
| - Gestational age
46
Fertilization age
```
36-40 weeks (2 weeks shorter than gestational))
From conception (conception occurs approximately 2 weeks after first day of last menstrual period)
```
47
Gestational Age
38-42 weeks
After last menstrual period.
Used more commonly because most women don’t know when conceive.
48
Placenta
Thick disk shaped organ, composed of maternal and fetal side.
49
When does placental development begin and end?
Begins at 3rd week of embryonic development.
| *Completes at the end of week 11.
50
Where does the placenta develop?
Develops at site where embryo attaches to uterine wall.
51
Maternal side of the placenta
- Is attached to uterine wall.
- Rough
- Surface is red and flesh like
52
What is the purpose of the decidua?
Provides nourishment for the embryo and protects the mother from uncontrolled invasion of fetal placental tissue into the uterine wall.
......
53
The decidua has 3 layers:
1. Decidua parietalis - lines the rest of the uterine cavity
2. Decidua basalis
3. Decidua capsularis - overlies the embryo and bulges into the uterine cavity as the embryo and fetus grows.
54
Decidua basalis
underlies the developing embryo and forms the maternal side of the placenta
55
Where does the exchange of substances between the mother and the fetus occur?
In the intervillous spaces of the placenta*
56
For placental perfusion, circulation of blood in the intervillous space must be
450 to 750 mL per minute
57
Fetal side
- Umbilical cord attached
- Smooth and silky
- Shiny, gray appearance
58
Each chorionic villus is supplied by
A tiny fetal artery carrying deoxygenated blood and waste products from the fetus.
59
The vein of the chorionic villus returns
Oxygenated blood and nutrients to the embryo and fetus.
60
What separates the capillaries in the chorionic villi from contact with the mothers blood?
Capillaries in the chorionic villi are separated from contact with the mother blood via villus membranes.
61
What are transfer functions of the placenta?
1. Gas Exchange
2. Nutrient Transfer
3. Waste Removal
4. Antibody Transfer
5. Transfer of Maternal Hormones
62
Placental Functions: Gas Exchange
-O2 and CO2 pass through the placenta by simple diffusion
63
What are 3 reasons that a fetus can thrive in this low oxygen environment (30 mm Hg)?
1. Fetal Hg can carry 20-50% more oxygen than adult Hg.
2. Fetus has a higher oxygen carrying capacity because of the higher average Hg level.
3. Hg can carry more oxygen at low PCO2 levels than it can in high levels (Bohr effect)
64
How is the Hg in a fetus able to carry more oxygen in relation to low PCO2 levels?
1. Blood entering the placenta from the fetus has high PCO2, but CO2 diffuses quickly into the mother’s blood (where the PCO2 is lower), reversing the levels of carbon dioxide in the maternal and fetal blood.
2. Therefore, fetal blood becomes more alkaline and the maternal blood becomes more acidic, which allows the mother’s blood to release oxygen and fetal blood to combine with oxygen readily.
65
Placental Function: Nutrient Transfer
- Glucose, fatty acids, vitamins and electrolytes pass readily across the placenta from the mother to fetus.
- Glucose is a major energy source for fetal growth and metabolic activities.
66
Placental Function: Waste Removal
- CO2, urea (protein -> ammonia -> urea), uric acid, and bilirubin are readily transferred from fetus to mother for disposal.
- Metabolic defects of PKU are not evident until after birth.
67
Placental Function: Antibody Transfer
Many of the IgG class of antibodies are passed from mother to fetus via placenta; confers passive (temporary) immunity to the fetus against which diseases the mother is immune (e.g. measles)
68
How is antibody transfer beneficial for newborns?
Passage of antibodies against disease is beneficial because the newborn does not produce antibodies for several months after birth.
69
Why do preterm or small-for-gestational age infants receive little protection from the transfer of maternal antibodies?
Because they are transferred during late pregnancy or poorly transferred if placental function is inadequate.
70
Why is the passage of antibodies not always beneficial?
- Not always beneficial especially if the mom has acquired antibodies against fetal erythrocytes. (Rh - mom, Rh + baby)
- May cause fetal anemia or even death.
71
Placental Function: Transfer of Maternal Hormones
-Most maternal protein hormones do not reach the fetus in significant amounts
-The female fetus exposed to androgenic hormones may has masculinization of her genitalia and her true gender may be difficult to visually determine at birth
(Not sure if need to know)
72
What are the endocrine functions of the placenta?*
1. Placenta takes over estrogen and progesterone production for the corpus luteum as the corpus luteum regresses.
2. Secretes human placental lactose (aka human chorionic somatomammotropin)
3. Secretes steroid hormones (estrogen and progesterone)
73
Human Placental Lactogen promotes:
- normal nutrition and growth of the fetus
- maternal breast development for lactation
- decreases maternal insulin sensitivity and glucose use,making glucose available for fetal nutrition
74
What is the purpose of estrogen?
Causes enlargement of the uterus, breasts and growth of the ductal system of breasts and enlargement of external genitalia.
75
Progesterone is essential for
Continuation of pregnancy.
76
Functions of Progesterone include:
1. Causes secretory changes in the endometrium, providing nourishment as the conceptus enters the uterus
2. Converts endometrium -> decidua
3. Reduces muscle contraction of uterus to prevent spontaneous abortion
4. May induce some immune tolerance in the mother’s body for the conceptus
5. Acts w/estrogen and other hormones to cause growth of the breasts, budding of alveoli that will secrete milk, and development of secretory characteristics in the alveolar cells
77
Mechanisms of Placental Transfer includes
- Simple diffusion
- Facilitated diffusion
- Active transport
- Pinocytosis
78
Two fetal membranes form the
Amniotic sac which holds amniotic fluid.
79
Amnion
- Inner membrane of the amniotic sac.
| - Continuous with the surface of the umbilical cord, joining the epithelium of the abdominal skin of the fetus.
80
Chorion
Outer membrane of the amniotic sac.
81
If the membranes of the amniotic sac rupture during labor,
They usually rupture together releasing amniotic fluid.
82
Primary functions of amniotic fluid include*
1. Protection against mechanical injury to fetus
2. Controls the embryo’s temperature
3. Prevents adherence of the amnion to the embryo-fetus
4. Reduces compression of umbilical cord
5. Provides fluid analysis (through amniocentesis)
6. Allows room for fetal movement
83
Amniotic fluid is derived from
- fetal urine
| - fluid transported from maternal blood across amnion
84
The fetus doesn’t urinate until what week?
Week 11
85
Vernix
Cheese-like white substance coating the skin of the newborn
86
Lanugo
- Fine, downy layer of hair that covers the baby’s body while he or she is in the womb.
- Helps hold the vernix in place to ensure your baby’s delicate skin doesn’t become chapped.
87
Oligohydramnios
<400 mL at term (too little fluid)
88
Oligohydramnios is associated with
1. less oxygen -> inhibits fetal growth -> decreased kidney perfusion -> inhibits fetus from urinating and the cycle will stop
2. Premature rupture of membranes (PROM)
3. Decreased renal development
4. Postdates
89
How does postdates lead to oligohydramnios ?
1. Placenta holds on for so long and will eventually calcify
2. This leads to less perfusion to the fetus
3. This causes less perfusion to the kidneys and inhibits urination
90
What are the metabolic functions of the placenta?
Produces nutrients need by the embryo and for placental functions including glycogen, cholesterol and fatty acids.
91
Development occurs simultaneously in all embryonic organ systems: Direction of growth includes
- Cephalocaudal: Head to toe
- Central to peripheral direction: From center outward
- Simple to complex: early cells become any cell of the body before they are specialized into specific structures/specific functions
- General to specific: upper extremities begin as limb buds before detailed development of bones, joints, muscle, ligaments and fingers.
92
Mechanism of Implantation
1. Enzymes produced by the conceptus erodes the decidua, exposing maternal sources of nutrition.
2. Primary chorionic villi (tiny projections on the surface of the conceptus) extend into the endometrium.
3. Endometrium is now called decidua basalis
4. As the conceptus implants, usually near the time of the next expected menstrual period, a small amount of bleeding “spotting: may occur at the site. (May be confusion with a normal menstrual period. Especially if their periods are usually light)
92
Chorionic Villi
- Microscopic projections from the outer membrane (chorion) that develop and burrow into endometrial tissue as the placenta is formed.
- The villi are fetal tissues and reflect the chromosomal, metabolic and genetic makeup of the fetus.
92
What are complications of oligohyrdramnios?
- Skeletal anomalies
- Poor lung development
- Cord compression (fetus is laying on cord, ultimately leads to fetal death)
- Membrane adhesion to the fetus
92
What is considered a post date fetus?
42 weeks
92
Hydramnios
>2,000 mL (too much fluid)
92
Hydramnios is associated with
- Uncontrolled DM
- CNS anomalies (can irritate CNS -> increased urination)
- GI tract anomalies (baby must swallow fluids in order to keep the cycle going -> if there is a fistula, will interfere with swallowing and leave fluid to sit in the sac)
- Multifetal (multiple fetuses producing urine)
- Chromosomal abnormalities
92
Umbilical Cord
- Lifeline between fetus and placenta. (Provides pathway from chorionic villi to embryo)
- Develops from amnion.
92
Umbilical Cord: Arteries
Carry deoxygenated blood and waste products away from fetus to the placenta
93
Umbilical Cord: Veins
Carry freshly oxygenated blood and nutrient-laden blood from placenta back to fetus.
94
Wharton’s Jelly
- Provides insulation and protection within the umbilical cord.
- Also prevents obstruction resulting from pressure.
95
What is the purpose for the fetal circulatory system?
- Maintains BF to placenta
- Provides fetus with O2 and nutrients
- Removes CO2 and waste products
96
What areas of the fetus that receives the highest O2 levels?
Head
Neck
Brain
Heart
97
Blood flows through 3 shunts in the fetal circulation including
1. Ductus Venosus
2. Foramen Ovale
3. Ductus arteriosus
98
What is the purpose of the 3 shunts found in fetal circulation?
Allows blood with highest oxygen content to be sent to the fetal heart and brain.
99
What are the changes in fetal blood circulation after birth?
-Fetal shunts are not needed after birth because infant oxygenates blood in the lungs and is not circulating blood to the placenta. Therefore, they close.
100
What causes the foramen ovale to close after birth?
- As the infant takes its first breaths, blood flow to the lungs increases.
- Pressure in the right side of the heart falls as the pressure in the left side of the heart rises causing the foramen ovale to close.
101
What causes the ductus arteriosus to close after birth?
As arterial oxygen levels rise, the ductus arteriosus constricts.
102
What can cause the ductus arteriosus to remain open?
Persistent hypoxia may cause the ductus to remain open for a prolonged period of time
103
What happens to the ductus venous after birth?
The ductus venosus constricts when flow of blood from the umbilical cord stops and eventually becomes a ligament.
104
What is the difference between the affect of teratogens on the fetus during the embryonic period vs. the fetal period?
During the fetal period, teratogens may damage already formed structures but are less likely to cause major structural alterations.
105
How is the conceptus nourished before the placenta is established?
The endometrial glands secrete at their maximum, providing rich fluids to nourish the conceptus before placental circulation is established
106
Why are the intestines mostly contained within the umbilical cord until the tenth week?
- The intestines have been growing faster than the abdominal cavity during the embryonic period.
- The relatively large liver and kidneys also occupy much of the abdominal cavity.
- Therefore, most of the intestines are contained within the umbilical cord while the abdominal cavity grows to accommodate them.
- The abdomen is large enough to contain all its normal contents by 10 weeks.
107
Brown fat
- Is a special heat-producing fat deposited during this period that helps the newborn maintain temperature stability after birth.
- It is located on the back of the neck, behind the sternum, and around the kidneys
108
Implantation occurs in what phase?
Secretory
109
When can quickening begin to be felt?
17-20 weeks
110
When does ovulation begin?
14 days prior to the start of next menstrual period
