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N113 Development
N113 - Embryo-Fetal Development
| Question | Answer |
|---|---|
| What is a zygote? | The single cell, fertilized egg. The zygote reproduces itself through mitosis and enters the uterus in about 3 days. |
| What is the blastocyst? | The inner mass of cells that will develop into the embryo and amnion. |
| What is the trophoblast? | The outer mass of cells that will develop into the chorion or placenta. |
| When does implantation occur? | 7-9 days after fertilization the blastocyst implants itself in the uterine lining. Usually in the upper posterior wall. |
| What are the germ layers? | Ectoderm, mesoderm & endoderm - differentiate into different body parts. |
| What is the yolk sac? | Forms 8-9 days after conception, forms RBCs until liver takes over at 5-6 weeks gestation. |
| What is the chorion? | It is the 1st membrane to develop. It encloses the embryo, amnion & yolk sac. |
| What are chorionic villi? | These are finger like projections that form the fetal portion of the placenta. By the 8th week, chorionic villi sampling is possible. |
| What is the amnion? | A thin protective membrane that contains amniotic fluid. |
| What are fraternal twins? | Twins that develop from two separate eggs & sperms. |
| What are identical twins? | Develop from one fertilized egg. May be one or two placentas, amnions and chorions. Always the same sex! |
| What is the function of the amniotic fluid? | To cushion against injury, control temperature, permits symmetric growth, allows freedom of movement, plays a role in lung development. |
| Does the amniotic fluid volume change? | Yes, it moves back and forth across placental membranes. The fetus swallows up to 400 ml per day. 600-800 ml flows in and out of the fetal lungs. Fetus adds to volume by excreting urine. |
| What is oligohydramnios? | Less than normal amount of fluid - less than 1000 mls |
| What is polyhydramnios or hydramnios? | More than normal fluid - greater than 2000 mls of fluid. |
| When does the placenta begin functioning? | Metabolic exchange occurs by the 4th gestational week. Most women aren't aware they're pregnant. |
| What are the metabolic functions of the placenta? | Provides glycogen, cholesterol and fatty acids to fetus. Produces enzymes needed for fetoplacental transfer. Breaks down epinephrine and histamine. |
| What are the transport functions of the placenta? | Simple diffusion - high to low concentration. Facilitated transport - carrier molecules. Active transport - from low to high concentration. Pinocytosis - transfer large molecules by being engulfed. Hydrostatic & osmotic pressure - water & solutes. |
| How does the placenta effect drug transfer? | Substances with a higher molecular weight can't cross. Heparin can't but Coumadin does. |
| What is HCG's purpose in pregnancy? | It is present 8-10 days after fertilization. Maintains corpus luteum so progesterone levels are adequate to maintain pregnancy. If progesterone level falls prior to 11th week, a spontaneous abortion will occur. |
| What is estrogens purpose in pregnancy? | Enlarges the breasts and uterus. Increases vascularity and vasodilatation. |
| What is progesterones purpose in pregnancy? | Maintains the pregnancy. Secreted by the placenta after 11th week. Decreases contractility of smooth muscle. |
| Describe the umbilical cord. | Circulatory pathway from chorionic villi to embryo. Contains one vein and two arteries. These are surrounded by Wharton's jelly to prevent compression of cord. |
| What is the ductus venosus? | Shunt that bypasses the liver, closes when cord is clamped. |
| What is the foramen ovale? | It provides a one way opening between R & L atria so blood can avoid non-functioning lungs. Closes when pressure in LA becomes higher than RA. |
| What is the ductus arteriosis? | Shunt that bypasses the lungs, opening between the pulmonary artery & aorta. Changes occur within minutes of birth with complete closure in 10-15 hours. |
| What is a funic suffle? | Purring sound heard over the uterus and having the same rate as the fetal heart beat. |
| What is the pre-embryonic stage? | 1st 14 days after fertilization - placental exchange begins at 14 days. |
| What is the embryonic phase? | 15 days to 8th week. |
| What is the fetal phase? | From end of 8th week to delivery. |
| What occurs during the embryonic phase? | Differentiation of tissues into organs, heart begins to beat at 3 to 4 weeks, sexual differences established, but not visible, most vulnerable to teratogens. At the end of 8 weeks, all body organs formed and clearly resembles human being. |
| What occurs during 9-12 weeks? | Fetal heart tones can be heard with doppler. Sexual differentiation is complete, but still not detectable by ultrasound. Palmer grasp is present. |
| What occurs during 13-16 weeks? | Lanugo begins do develop. Sex is detectable by ultrasound. |
| What occurs around 20 weeks? | Quickening first felt by mother. Heartbeat audible with fetoscope, not a stethoscope. Entire body covered with lanugo. |
| What occurs around 24 weeks? | Eyes are structurally complete, alveoli in lungs begin to form - important for preterm infant. |
| What occurs during 25-28 weeks? | Rapid brain development, most fetuses are viable at 27 weeks with immediate and prolonged intensive care. Surfactant forms at 28 weeks. |
| What occurs during 29-32 weeks? | Gaining weight - subcutaneous fat |
| What occurs during 36 weeks? | Lanugo begins to disappear, fetus has a good chance at survival - still considered preterm. |
Created by:
jrb265
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