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fertilization of the female ovum by the male sperm
occurs when a sperm enters the ovum and their nuclei unite. Usually occurs in the outer third of the fallopian tube. Takes 3 days for the zygote to reach the uterine cavity
occurs when the embryo buries itself in the upper segment of the uterine lining
also referred to as gestation and lasts approximately 280 days (40 weeks)
- fertilization through the first two weeks.
- Period of the zygote
- third through eighth week. Highly
- vulnerable to teratogens, viruses, drugs, radiation, or infections. End of
- 8th week, all organ systems and external structures are formed and unmistakably
eighth week through the fortieth week orbirth. Viability now possible at 23-24 weeks after conception
Human Chorionic Gonadotropin
Stimulates corpus luteum to produce progesterone and estrogen until the placenta assumes that function
Produced by the ovaries during menstrual cycle. Placenta assumes production after the 6th or 7th week. Increases vascularity in the pregnant woman
Produced by the corpus luteum and then the placenta. Most important pregnancy hormone as it maintains the endometrium and prevents abortion. Relaxes smooth muscle in the pregnant woman
Increases availability of glucose for the fetus. Glucose required for fetal growth and development. Levels increase steadily during pregnancy
Inhibits uterine activity, softens connective tissue, relaxes pelvic joints to facilitate birth
· Means of metabolic exchange
· Filters some harmful substances from reaching fetus
· Covers about half uterine surface
· Function depends on maternal blood pressure
Endocrine Functions of the placenta produces:
- Human Chorionic Gonadotropin (hCG)
- ·Ensures estrogen and progesterone
- Human Placental Lactogen (hPL)
- ·Facilitates glucose transport across
Endocrine functions of the placenta
- Maintains endometrium
- Decreases contractility of uterus
- Stimulates uterine growth
- Stimulates uteroplacental blood flow
- Stimulates myometrial contractility
Metabolic functions of the placenta
- Oxygen and CO2 diffuse between the
- placental membrane from maternal
- blood to fetal blood
- Water, electrolytes, carbohydrates, fat,
- protein, and vitamins pass across
- placental membrane
- Metabolic waste products cross the placental membrane from the fetal
- blood into maternal blood
Maternal kidneys excrete the wastes
- Carbohydrate, proteins, calcium, and
- iron are stored in the placenta for ready
- access to meet fetal needs
What can cross the placental membrane?
Viruses, drugs caffeine, alcohol, nicotine, carbon monoxide and other toxic substances can cross the placental membrane
- Bacteria and protozoa infect placenta first, then fetus
Outermost membrane, closest to uterine lining
Contains the major umbilical blood vessels
Chorionic villi infiltrate maternal tissues and become the fetal side of the placenta
Embryo draws amnion around itself forming a fluid filled sac
Later adhears to chorion to make one membrane
Produces amniotic fluid
Infection of both of the membranes
How much amniotic fluid should a full term pregnancy have?
insufficient amniotic fluid; less than 300 mL.
Can be related to problem with fetal renal development
Too much amniotic fluid; more than 2,000 mL.
Can be related to problem with fetal GI development
Components of Amniotic fluid
- Uric Acid
- Lechithin (remember the L/S ratio!!)
- Phosphatidylgycerol (PG)
- Lanugo Hairs
What are the functions of Amniotic Fluid?
- Cushions the fetus, umbilical cord
- Allows freedom of movement for muculo-skeletal development
- Keeps the baby from tangling with membranes
- Helps maintain body temperature
- Source of oral fluid and waste repository
Describe the umbilical cord
Remember --> AVA
- 30-90 cm in length
- 2 cm in diameter
- 2 arteries: carries deoxygenated blood from fetus to placenta
- One vein: carries oxygenated blood from placenta to fetus
- Wharton's jelly: prevents compression of the blood vessels
How does the fetus obtain sufficient O2 from Maternal Blood?
Remember: maternal and fetal blood should not mix! Mixing only occurs at time of delivery when placenta detaches. Only gasses, nutrients, wastes... should pass through placental membrane
- Fetal hemoglobin carries 20-30% more O2 than
- maternal hemoglobin
- Fetal hemoglobin concentration is about 50%
- more than maternal
- Fetal heart rate is about 110-160 BPM, therefore fetal cardiac output greater than adults
When does a fetus begin to establish surfactant?
What is the L/S ratio??
What does it measure?
Lecithin and sphingomyelin-L/S ratio measured to determine maturity
L/S ratio of 2:1 indicates fetal lung maturity
Male and female genitalia indistinguishable until after the _____ week
By week ______, ultrasound can confirm sex
At ______, ovaries contain lifetime supply of ova.
Describe the 2nd month
Limbs begin to form and tiny heart begins to beat
Describe the 3rd month
Embryo now becomes a fetus. Tiny arms and legs can now bend.
Describe the 4th month
Sex is now evident. Languo covers the entire body. Yolk sac that will produce blood until the fetus can make its own (the ball in the picture)
Fetus can now hear. 4-6 oz of amniotic fluid surrounds the fetus. Fetus is 5in long, 4oz in weight.
Legs, with their bones seen through translucent skin, are in motion, even though the mother can't feel the movement.
Describe the 5th month
Meconium is forming. Brown fat begins to form also. Vernix caseosa production is complete.
Describe the 6th month
Bones begin to harden. Lungs begin to breathe on their own. Fetus is about 10 in long.
Describe the 7th month
The eyes start to open and react to changes in light. Gets to typical fetal position. Wt 3lbs, 11in long
Describe the 8th month
Continues to grow rapidly. The testes have descended fully. Nails grow past the fingertips