Reproduction: A Brief Review

Conception and Fertilization Conception is the fertilization of the female ovum by the male sperm Fertilization 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 Implantation occurs when the embryo buries itself in the upper segment of the uterine lining Pregnancy also referred to as gestation and lasts approximately 280 days (40 weeks)

Three Periods of Fetal Development Pre-embryonic Period: fertilization through the first two weeks. Period of the zygote Embryonic Period: 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 human Fetal Period: eighth week through the fortieth week or birth. Viability now possible at 23-24 weeks after conception.

Placental Hormones 1) Human Chorionic Gonadotropin (hCG): Stimulates corpus luteum to produce progesterone and estrogen until the placenta assumes that function 2) Estrogen: Produced by the ovaries during menstrual cycle. Placenta assumes production after the 6th or 7th week. Increases vascularity in the pregnant woman 3) Progesterone: 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

Placental Hormones 4) Human Placental Lactogen (hPL): Increases availability of glucose for the fetus. Glucose required for fetal growth and development. Levels increase steadily during pregnancy 5) Relaxin: Inhibits uterine activity, softens connective tissue, relaxes pelvic joints to facilitate birth

Fetal Development Placenta Means of metabolic exchange Filters some harmful substances from reaching fetus Covers about half uterine surface Function depends on maternal blood pressure

Placenta Fetal Side Maternal Side (attached to uterine wall)

Functions of the Placenta Endocrine Functions Produces: Human Chorionic Gonadotropin (hCG) Ensures estrogen and progesterone secretion Human Placental Lactogen (hPL) Facilitates glucose transport across placenta

Functions of the Placenta Endocrine Functions Progesterone Maintains endometrium Decreases contractility of uterus Estrogen Stimulates uterine growth Stimulates uteroplacental blood flow Stimulates myometrial contractility

Functions of the Placenta Metabolic Functions Respiration Oxygen and CO2 diffuse between the placental membrane from maternal blood to fetal blood Nutrition Water, electrolytes, carbohydrates, fat, protein, and vitamins pass across placental membrane

Functions of the Placenta Excretion Metabolic waste products cross the placental membrane from the fetal blood into maternal blood Maternal kidneys excrete the wastes Storage Carbohydrate, proteins, calcium, and iron are stored in the placenta for ready access to meet fetal needs

Placenta Viruses, drugs caffeine, alcohol, nicotine, carbon monoxide and other toxic substances can cross the placental membrane Bacteria and protozoa infect placenta first, then fetus

Membranes Chorion 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

Membranes Amnion Inner membrane Embryo draws amnion around itself forming a fluid filled sac Later adheres to the chorion to make one membrane Produces amniotic fluid *Chorioamnionitis: refers to the infection of both of these membranes

Fetal Circulation

Amniotic Fluid Full term: should have approximately 800- 1,000 mL fluid Oligohydramnios: insufficient amniotic fluid; less than 300 mL. Can be related to problem with fetal renal development Polyhydramnios/Hydramnios: Too much amniotic fluid; more than 2,000 mL. Can be related to problem with fetal GI development

Components of Amniotic Fluid Albumin Urea Uric acid Creatinine Lechithin* Sphingomyelin* Phosphatidylgycerol (PG)* *Determines fetal lung maturity *L/S ratio of 2:1 confirms fetal lung maturity Bilirubin Fat Fructose Leukocytes Proteins Enzymes Lanugo hairs

Functions of Amniotic Fluid Cushions fetus; umbilical cord Allows freedom of movement for musculo-skeletal development Keeps baby from tangling with membranes Helps maintain body temperature Source of oral fluid and waste repository

Umbilical Cord 30-90 cm in length 2 cm in diameter Two 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 **Remember “AVA”: 2 arteries; 1 vein

Umbilical Cord

Umbilical Cord Vessels

How Fetus Obtains Sufficient Oxygen from Maternal Blood 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 Remember…maternal and fetal blood should not mix. Mixing only occurs at time of delivery when placenta detaches. Only gases, nutrients, wastes… should pass through placental membrane

Respiratory System Maturity coincides with establishment of surfactants during gestational week 35 Lecithin and sphingomyelin-L/S ratio measured to determine maturity L/S ratio of 2:1 indicates fetal lung maturity

Reproductive System Male and female genitalia indistinguishable until after 9th week By week 16, ultrasound can confirm sex At birth, ovaries contain lifetime supply of ova

Embryo at 1 Month

Implantation

2nd Month Limbs begin to form and a tiny heart begins to beat

3rd Month Embryo now becomes a fetus. Tiny arms and legs can now bend.

4th Month Sex is now evident. Lanugo covers the entire body 4th Month Sex is now evident. Lanugo covers the entire body. The ball is the yolk sac which will produce blood until the fetus can make its own

4th Month Fetus can now hear 4th Month Fetus can now hear. 4-6 ounces of amniotic fluid surrounds the fetus. Size is 5 inches long; weight is 4 ounces

4th Month The legs, with their bones seen through translucent skin, are in motion, even though the mother can’t feel the movement

5th Month Meconium is forming. Brown fat begins to form also 5th Month Meconium is forming. Brown fat begins to form also. Vernix caseosa production is complete.

6th Month Bones begin to harden. Lungs begin to breathe on their own 6th Month Bones begin to harden. Lungs begin to breathe on their own. Fetus is about 10 inches long.

7th Month The eyes start to open and reacts to changes in light 7th Month The eyes start to open and reacts to changes in light. Gets into typical fetal position. Wt. is 3 lbs; 11 inches long.

8th Month Continues to grow rapidly. The testes have descended fully 8th Month Continues to grow rapidly. The testes have descended fully. Nails grow pass the fingertips

Full-term perfection!

Videos These five videos take a 3D animated look at pregnancy from week 1 to week 37 http://www.babycenter.com/2_inside- pregnancy-weeks-1-to-9_10302602.bc