2.4 Conception and Fetal Development Flashcards
1
Q
Conception
A
- Union of single egg and sperm
1. Gamete (Egg and Sperm Formation)
2. Ovulation
3. Fertilization
4. Implantation
2
Q
Mitosis
A
- Body cells replace and repair themselves.
- Cell division supports diploid number of 46 and facilitates growth and development or cell replacement
3
Q
Meisosis
A
- Divide and decrease chromosomal number by half from diploid (46) to haploid (23) to produce gametes
- DNA replication and cell division in meiosis allow different alleles (genes) to be distributed at random by each parent and then re-arranged on the paired chromosome.
- Random mixing of alleles are responsible for the variation in traits seen in offspring.
4
Q
Gametogenesis
A
- Oogenesis is the process of egg formation (ovum) Begins during fetal life of female
- Spermatogenesis is the process of sperm formation.
5
Q
Ovum
A
- Each month 1 ovum matures.
- During ovulation the ovum is released from the ruptured ovarian follicle.
- High estrogen increases motility of uterine tubes so cilia can capture and propel ovum through the tube towards the uterine cavity.
- Ovum is fertile for 24 hours after ovulation
6
Q
Ovum Protective Layers
A
Zona Pellucida - Inner thick layer, acellular
Corona Radiata - Outer layer, elongated cells
7
Q
Capacitation
A
- Physiological change that removes protective coating from head of sperm.
- Necessary for sperm to penetrate the protective layers of ovum
8
Q
Fertilization
A
- Takes place in ampulla (outer 3rd) of the uterine fallopian tube.
9
Q
Conception
A
- Formation of zygote (the first cell of new individual)
10
Q
Cleavage
A
- Begins within 30 hours after fertilization and ends with the formation of a blastocyte
11
Q
Morula
A
- Solid ball of cells that is produced within 3 days and is still surrounded by protective zona pellucida
12
Q
Trophoblast/Embryoblast/Blastocyte
A
Trophoblast - Creates placenta
Embryoblast - Creates embryo
Blastocyte - Whole structure of the developing embryo
13
Q
Implantation
A
- Occurs when zona pellucida degenerates.
- Trophoblasts displace endometrial cells at implantation site
- ## Blastocyte embeds into endometrium and trophoblast secretes enzymes that enable it to borrow into endothelium
14
Q
Chorionic Villi
A
- Fingerlike projections that develop from trophoblasts and extend into blood filled space of endometrium
- This is what obtain oxygen and nutrients from maternal bloodstream and dispose of carbon dioxide and waste products into maternal blood.
15
Q
Decidua
A
- Term for endometrium after implantation.
- Decidua basalis forms the maternal portion of the placenta.
- Decidua capsularis is the portion covering the blastocyte.
- Decidua vera lines the rest of the uterus.
16
Q
Length of pregnancy
A
- 9 months, 40 weeks, 280 days.
- Lasts from first day of last menstrual period until day of birth.
17
Q
Conception
A
- Occurs about 2 weeks after first day of last menstrual period.
18
Q
Embryo Layers
A
Ectoderm - Outside layer with skin, pigment, and neuron cells of the brain
Mesoderm - Skeletal, cardiac, smooth, RBC and bone cells
Endoderm - Stomach, pancreatic, lung cells.
19
Q
Post Conceptual Age
A
- Used in discussion of fetal development
- This is 2 weeks less for a total of 266 days, or 38 weeks.
20
Q
Embryonic Stage
A
- Lasts day 15 until 8 weeks after conception
- Most vulnerable to teratogens (substances or exposure that causes abnormal development)
- Developing areas have rapid cell division making it vulnerable to malformations
21
Q
Chorion
A
- Chorion develops from the trophoblast and contains chorionic villi on the surface.
- Contains major umbilical blood vessels and formation of placenta.
- Outermost membrane surrounding the embryo
22
Q
Amnion
A
- Develops from interior cells of blastocyte
- Space between inner cell mass and outer layer of cells (trophoblast) is the amniotic cavity
23
Q
Amniotic Fluid
A
- Liquid found within 12 days of conception
- Contained within amniotic sac that surrounds the growing embryo/fetus within the uterus.
24
Q
Amniotic Fluid Fun Facts
A
- 800 mL by 32 weeks of gestation
- By 39 weeks the volume is stable around 700-800 mL
- Volume steadily decreases after term. 500 mL at week 41
25
Amniotic Fluid Function
- Maintains fetal temperature
- Source of oral fluid
- Repository for waste
- Maintains electrolyte homeostasis
- Allows movement for musculoskeletal development
- Cushions fetus from trauma
- Allows face/body to form symmetrically
- Antibacterial Factors
- Prevents embryo from tangling with membrane
26
Oligohydramnios
- Less than 300 mL of amniotic Fluid
| - Associated with fetal renal abnormalities
27
Hydramnios (polyhydramnios)
- More than 2L of amniotic fluid
| - Associated with GI and other malformations
28
Lecithin/Sphingomyelin (L/S)
- L/S ratio determines health and maturity of fetus.
| - L/S ratio of 2:1 means baby has developed lungs
29
Yolk Sac
- Another blastocyte cavity that forms on the other side of a developing embryonic disc.
- Helps transfer maternal nutrients and oxygen through chorion to the embryo
- Blood vessels form to aid transportation
- Blood cells and plasma are manufactured in the yolk sac during second and third weeks.
30
Umbilical Cord
- Embryonic Disk, Amniotic Sac, and Yolk Sac attach to chorionic villi by the connection of a stalk.
- Blood vessels develop to supply embryo with maternal nutrients and oxygen.
- Two arteries carry blood from embryo to chorionic villi and one artery returns blood to the embryo
- Umbilical cord rapidly increases in length at term it is 40-70 cm.
31
Wharton Jelly
- Connective tissue that surrounds the vessels preventing compression of the blood vessels.
- This ensures the embryo continues receiving nourishment
32
Nuchal Cord
- Umbilical cord gets wrapped around babies neck
33
Vasa Previa and Battledore Insertion
- Variations in cord insertion that increase risk of fetal hemorrhage
34
Placenta Structure
- Begins to form at implantation
- Chorion is embryo side of placenta
- Intervillous spaces is where maternal blood supplies oxygen and nutrients to the embryonic capillaries
- Waste products and CO2 diffuse into maternal blood
35
Human Chorionic Gonadotropin (hCG)
- Detected in maternal serum 8-10 days after conception
- This hormone is the basis for pregnancy tests
- This hormone ensures continued supply of progesterone and estrogen to maintain pregnancy
- Ovarian Corpus Luteum releases progesterone and estrogen to maintain pregnancy
- Between 100-130th day the placenta becomes the primary source of estrogen and progesterone
36
Human Placental Lactogen (hPL)
- Chorionic Somatotropin
- Growth hormone that stimulates maternal metabolism to supply nutrients for fetal growth
- Increases resistance to insulin and facilitates glucose transport across placenta
- Stimulates breast development for lactation
37
Progesterone
- Maintains the endothelium
- Decreases contractility of uterus
- Stimulates maternal metabolism
- Stimulates development of breast alveoli
38
Estrogen
- By 7 weeks, placenta produces most of maternal estrogen
- Steroid Hormone
- Stimulates uterine growth and uteroplacental blood flow.
- Onset labor is caused by decline in progesterone and increase in estrogen
39
Isoimmunization
- Fetal erythrocytes leak into maternal circulation causing mother to develop antibodies to fetal red blood cells
- rH negative mother becomes sensitized to rH positive fetus
40
Circulatory Effects of Placental Function
- Placental function relies on maternal blood pressure supplying circulation
- Vasoconstriction diminishes uterine blood flow (hypertension and cocaine)
- Decreased maternal blood pressure or cardiac output also diminishes uterine blood flow
- Lying on back with pressure on uterus compressing vena cava, blood return to right atrium is diminished
41
Braxton Hicks Contractions
- Painless contractions that occur intermittently after first trimester.
- Enhances the movement of blood through intervillous spaces, aids placental circulation,
- Prolonged contractions or too short intervals between contractions reduce blood flow to placenta
42
Embryonic Stage
- Day 15 until 8 weeks
- Critical time for organ development and external features
- Rapid cell division makes this the most vulnerable time to malformations caused by environmental teratogens
43
Placenta Development
- Week 12 placenta is formed
| - Completely mature by week 34
44
Role of Placenta
- Protects fetus from detrimental substances in maternal blood (glucocorticoids and toxins)
- Protected by multidrug-resistant protein (transport protein)
- Toxins from fetus are processed in mothers liver and kidneys for elimination
45
Teratogens
- Drugs, chemicals and infections that cause abnormal fetal development.
- Pesticides, fungicides, rodenticides, harsh cleaning products.
46
Fetal Circulatory System
- Cardiovascular system first organ to function
- Week 3 blood vessels and cells form
- By the end of week 3 heart beat forms
- CVD links embryo, connecting stalk, chorion and yolk sac
47
Fetal Heart Beat
- Usually detectable by week 6.5-7
- Heart develops into 4 chamber organ by week 4-5
- 5.5-6.5 is the earliest that cardiac activity can be detected by vaginal ultrasound
48
Birth Defects due to Teratogens
- Neural tube defects
- Intellectual impairment
- Cardiac Anomalies (truncus arteriosus)
- Atrial and Ventricular septal defects
- Amelia/Meromelia in upper/lower limbs
- Cleft lip/palate
- Low set malformed ears
- Deafness
- Eye anomalies (cataracts, glaucoma)
- Staining of teeth
- Masculinization of female genitalia
49
Yolk Sack
- First extra-embryonic membrane to appear
- Produces chorionic fluid to help cushion and protect embryo
- Chorion develops and functions to nourish the developing embryo
50
Amniotic Fluid and Membranes
- Insulates baby to keep it warm
| - Contains antibodies
51
Umbilical Cord
- Serves as blood source for neonate
| - Allows fetus to obtain oxygen
52
Placenta
- Immunologic functions, respiratory, excretory, endocrine, barrier function.
- Supplies oxygen, output of CO2 (via diffusion)
- Supplies nutrients via umbilical cord
- Clears out waste such as urea, creatinine, uric acid
- Metabolizes and releases food substances required into maternal/fetal blood
- Protects fetus from xenobiotics (food/drug/environmental pollutants)
- Produces steroids and peptide hormones that help in growth and development of baby.
53
Fetal Maturation
- Fetal stage lasts 9 weeks until end of pregnancy
54
Viability
- Capability of fetus to survive outside uterus
- Defined by fetal weight and pregnancy duration
- Standard is at least 20 weeks of gestation
- Birth weight of 350,400, or 500g depending on state
- Limitations on survival at an early stage depend on CNS function and oxygenation capability
55
Ductus Arteriosus
- Fetal artery connecting aorta and pulmonary artery. (allows blood to detour away from lungs). Closes within first few days of life
56
Fetal Respiratory Characteristics
- Fetal hemoglobin has high affinity for oxygen
- Can carry 20-30% more oxygen than maternal hemoglobin
- 50% higher hemoglobin concentration in fetus than mother
- Fetal heart rate is 110-160 bpm
57
Hematopoietic System
- Formation of blood (occurs in yolk sack)
- Blood type is determined in the 6th week
- rH negative women are at risk for isoimmunization in pregnancy lasting longer than 6 weeks after fertilization
58
Respiratory System
- 32 weeks is when sufficient surfactant is present in developed alveoli.
- Surface-active phospholipids in amniotic fluid determine lung maturity
- Once L/S ratio reaches 2:1 infant lungs are mature.
59
Gastro-intestinal System
- Fetus swallows amniotic fluid at 5th month
- Gastric emptying and peristalsis occur
- Fetal waste products accumulate in intestines called meconium, black tar.
60
Hepatic System
- Glycogen and iron are stored in fetal liver
- Coagulation factors cannot be synthesized in the liver due to GI sterility and lack of Vitamin K synthesis.
- This is why vitamin K is given prophylactically to a newborn.
61
Renal System
- Kidneys are fully developed at term
- GFR is low and kidneys lack ability to concentrate urine
- Newborns are more susceptible to overhydration and dehydration
- Most newborns void within the first 24 hours
62
Neurologic System
- Originates from ectoderm during 3rd week after fertilization.
- Open neural tube occurs during 4th week
- Neurologic insults can cause cerebral palsy, neuromuscular impairment, intellectual disability, learning disabilities.
- Fetus can feel pressure and pain
- Fetus responds to sound at 24 weeks.
63
Endocrine System
- Insulin produced at week 20
- Mothers with uncontrolled diabetes can pass hyperglycemia to fetus
- This causes a rise in insulin and islet cell hyperplasia.
- This produces a macrosomic (large) fetus.
- Increased insulin also blocks lung maturation
- This puts neonates at risk for respiratory distress and hypoglycemia when maternal glucose is lost at birth.
64
Reproductive System
- Sex differentiation begins at 7th week
- Distinguishing characteristics appear around 9th week and fully differentiated by the 12th week.
- Pseudomenstruation - Vaginal discharge at birth
- High level of maternal estrogen stimulate secretion of "witch's milk"
65
Musculoskeletal System
- Can be perceived by mother at 16-20 weeks
| - Fetus sucking thumbs, somersaults, arm and leg movement
66
Integumentary System
12th week - Fine hairs (lanugo) appear on eyebrows and upper lip
20 week - covers whole body
67
Immune System
- 3rd trimester albumin and globulin are present
- IgG is the only immunoglobin that passes placenta providing passive immunity to specific bacterial toxins
- Fetus produces IgM by end of first trimester
- Normal term neonate can fight infections but pre-term is at much greater risk.
68
Dizygotic Twins (Fraternal)
- Multiple eggs fertilized by separate sperm.
- Results in 2 zygotes
- 2 Amnions, 2 chorions, 2 placentas that may fuse.
- Most often happens with African Americans least with Asians
- Not genetically similar
- Separate placenta
69
Monozygotic Twins (Identical)
- Develops from 1 fertilized egg.
- Placentation varies depending when zygotic division occurs
- Shared placenta
70
Siamese Twins
- Cleavage is incomplete and occurs after 13 days of conception
71
Triplets and Higher-Order Birth
- Triplets occur when 1 zygote divides into 2 and then divides again (identical)
- Triplets can also occur from 2 zygotes (fraternal) and 1 zygote dividing into a monozygotic (identical).
- Triplets can also be 3 fraternal zygotes
72
Teratogens
- Substances that cause physical harm to embryo or fetus
- Can cause pre-term labor or spontaneous pregnancy loss
- Medications
- Recreational drugs
- Chemicals
- Hormones
- Viruses in maternal system that transfer to fetus
- Maternal Stress
73
Folic Acid
- Women who are planning pregnancy should avoid taking folic acid daily before contraception to avoid neural tube defects.
High Risk
- Had child with neural tube defect before
- If mom was a neural tube defect baby
- If partner was a neural tube defect baby
- Coeliac disease (immune system attacks your own tissue when eating gluten) or epilepsy
