PREGNANCYPREGNANCY

Prof. Aziza TossonProf. Aziza Tosson

OutlineOutline

FertilizationFertilizationDevelopment before BirthDevelopment before Birth

Fetal CirculationFetal CirculationEmbryonic DevelopmentEmbryonic DevelopmentFetal DevelopmentFetal DevelopmentBirthBirth

ConceptionConception

A secondary oocyte can be fertilized A secondary oocyte can be fertilized for about 24 hours after ovulationfor about 24 hours after ovulation

Sperm remain viable for up to 48 Sperm remain viable for up to 48 hours within the female reproductive hours within the female reproductive tracttract

This gives a three day “window” for This gives a three day “window” for intercourse to result in fertilization: intercourse to result in fertilization: two days before to one day after two days before to one day after ovulationovulation

FertilizationFertilization

Steps of fertilization (Steps of fertilization (ConceptionConception).).Several sperm penetrate corona radiata.Several sperm penetrate corona radiata.Several sperm attempt to penetrate Several sperm attempt to penetrate

zona pellucida.zona pellucida.One sperm enters egg and nuclei fuse, One sperm enters egg and nuclei fuse,

producing a producing a zygotezygote..Egg’s plasma membrane and zona pellucida Egg’s plasma membrane and zona pellucida

change to prevent change to prevent polyspermypolyspermy..

FertilizationFertilization

Fertilization usually takes place in Fertilization usually takes place in the outer one-third of the uterine the outer one-third of the uterine tube, but can take place in the tube, but can take place in the abdominal cavityabdominal cavity

Sperm swim up the female Sperm swim up the female reproductive tract, aided by reproductive tract, aided by muscular contractions of the uterus muscular contractions of the uterus stimulated by prostaglandins in the stimulated by prostaglandins in the semen. semen.

The oocyte may also secrete a The oocyte may also secrete a chemical that attracts spermchemical that attracts sperm

Occurrence of PregnancyOccurrence of Pregnancy

When a zygote begins dividing, it is When a zygote begins dividing, it is termed an termed an embryoembryo.. Developing embryo travels down oviduct and Developing embryo travels down oviduct and

eventually implants in endometrium. eventually implants in endometrium. ((Implantation / pregnancyImplantation / pregnancy))

Presence of Presence of human gonadotropic hormonehuman gonadotropic hormone ( (HCGHCG) in ) in the blood confirms pregnancy.the blood confirms pregnancy.

IfIf implantation does implantation does notnot occur, a woman never knows occur, a woman never knows fertilization took place.fertilization took place.

Human Development before Human Development before ImplantationImplantation

Zygote Zygote undergoes rapid mitotic cell undergoes rapid mitotic cell division, but these do not increase the division, but these do not increase the size of the zygote – called cleavage size of the zygote – called cleavage divisionsdivisions

Cleavage produces a solid sphere of Cleavage produces a solid sphere of cells, still surrounded by zona pellucida cells, still surrounded by zona pellucida – now called a – now called a morulamorula..

At 4.5 to 5 days, cells have developed At 4.5 to 5 days, cells have developed into a hollow ball of cells – into a hollow ball of cells – blastocystblastocyst..

It is at this stage that it enters the It is at this stage that it enters the uterus.uterus.

Wajed Hatamleh RN, MSN, PhD.Wajed Hatamleh RN, MSN, PhD.

Cellular differentiationCellular differentiation Embryonic membranesEmbryonic membranes

Amnion – inner layerAmnion – inner layer Chorion – outer layerChorion – outer layer

Both membranes form bag of watersBoth membranes form bag of waters Amniotic fluid Amniotic fluid

700-1000 cc normal700-1000 cc normal < 400 ml oligohydramnios< 400 ml oligohydramnios > 2000 ml polyhydramnios> 2000 ml polyhydramnios Fetus contributes to amniotic fluid volume thru Fetus contributes to amniotic fluid volume thru

fetal urinefetal urine Amniotic fluid important for fetal lung Amniotic fluid important for fetal lung

developmentdevelopment

Wajed Hatamleh RN, MSN, PhD.Wajed Hatamleh RN, MSN, PhD.

Cellular differentiationCellular differentiation

Umbilical cordUmbilical cordWharton’s jellyWharton’s jelly2 arteries/ 1vein2 arteries/ 1vein

PlacentaPlacentaSite of metabolic and nutritional exchangeSite of metabolic and nutritional exchangeMaternal side – decidua basalisMaternal side – decidua basalisFetal side – amnionFetal side – amnion15 – 20 cotyledons: contain the complex 15 – 20 cotyledons: contain the complex

vascular system of villi vascular system of villi

Wajed Hatamleh RN, MSN, PhD.Wajed Hatamleh RN, MSN, PhD.

ImplantationImplantationThe blastocyst remains free in the uterus The blastocyst remains free in the uterus

a short time, during which the zona a short time, during which the zona pellucida disintegrates.pellucida disintegrates.

Blastocyst nourished by glycogen from Blastocyst nourished by glycogen from glands of the endometrium.glands of the endometrium.

At about 6 days after ovulation blastocyst At about 6 days after ovulation blastocyst implants – orients cell mass toward implants – orients cell mass toward endometrium, and secretes enzymes endometrium, and secretes enzymes which allow it to penetrate (digest) the which allow it to penetrate (digest) the endometrial wall. This nourishes the endometrial wall. This nourishes the blastocyst for about a week after blastocyst for about a week after implantation.implantation.

• Following implantation, the placenta originates from maternal and fetal tissues.• Placenta then produces human chorionic gonadotropin (HCG) which maintains the corpus luteum in the ovary until the placenta begins its own production of progesterone and estrogen.• Physical signs of pregnancy include : no menstruation, increased urination, morning sickness, increased size of breasts, and darkening of areolae.

As early as 8 -12 days after As early as 8 -12 days after fertilization, the blastocyst begins to fertilization, the blastocyst begins to secrete secrete human chorionic human chorionic gonadotropin or hCG.gonadotropin or hCG.

hCG keeps the corpus luteum active hCG keeps the corpus luteum active until the placenta can produce until the placenta can produce estrogens and progesterone. estrogens and progesterone.

The presence of hCG is the basis for The presence of hCG is the basis for pregnancy tests.pregnancy tests.

Inner cell mass forms two cavities:Inner cell mass forms two cavities:The yolk sacThe yolk sacAmniotic cavityAmniotic cavity

In humans the yolk sac produces In humans the yolk sac produces blood cells and future sex cellsblood cells and future sex cells

The amniotic cavity becomes the The amniotic cavity becomes the cavity in which the embryo floats. cavity in which the embryo floats. Fluid is produced from fetal urine, Fluid is produced from fetal urine, and secretions from the skin, and secretions from the skin, respiratory tract, and amniotic respiratory tract, and amniotic membranes.membranes.

Gestation periodGestation periodDivided into three trimesters.Divided into three trimesters.During first trimester individual starts During first trimester individual starts

out as a zygote, then morula, out as a zygote, then morula, blastocyst, and after implantation, is blastocyst, and after implantation, is called an embryo.called an embryo.

Embryonic phase of development lasts Embryonic phase of development lasts from fertilization until the 8from fertilization until the 8thth week of week of gestation, when it becomes a fetus.gestation, when it becomes a fetus.

By day 35 the heart is beating, and eye By day 35 the heart is beating, and eye and limb buds are present.and limb buds are present.

Five-Week-Old EmbryoFive-Week-Old Embryo

Wajed Hatamleh RN, MSN, PhD.Wajed Hatamleh RN, MSN, PhD.

Fetus at 14 and 20 weeks Fetus at 14 and 20 weeks gestationgestation

By month four, the rudiments of all By month four, the rudiments of all organ systems are formed and organ systems are formed and functioning, and from then on, fetal functioning, and from then on, fetal development is primarily a matter of development is primarily a matter of growth.growth.

By the end of the third month the By the end of the third month the placenta is functioning.placenta is functioning.

Three-to-Four Month-Old Three-to-Four Month-Old FetusFetus

Fifth through Seventh MonthsFifth through Seventh Months

Mother begins to feel fetal Mother begins to feel fetal movement.movement.

Wrinkled skin covered by fine hair, Wrinkled skin covered by fine hair, lanugolanugo, is covered by a greasy , is covered by a greasy substance substance vernix caseosavernix caseosa..

Lungs lack surfactant so if baby is Lungs lack surfactant so if baby is born prematurely it will have to be born prematurely it will have to be on a respirator (respiratory distress on a respirator (respiratory distress syndrome).syndrome).

Six-Month-Old-FetusSix-Month-Old-Fetus

The placentaThe placentaThe chorion develops into the fetal part The chorion develops into the fetal part

of the placenta.of the placenta.The chorionic villi connect the fetal The chorionic villi connect the fetal

circulation to the placentacirculation to the placentaComposed of both fetal and maternal Composed of both fetal and maternal

tissuestissues

Functions of the placenta:Functions of the placenta:1 Transfer gasses1 Transfer gasses

2 Transport nutrients2 Transport nutrients

3 Excretion of wastes3 Excretion of wastes

4 Hormone production – temporary 4 Hormone production – temporary endocrine organ – estrogen and endocrine organ – estrogen and progesteroneprogesterone

5 Formation of a barrier – incomplete, 5 Formation of a barrier – incomplete, nonselective – alcohol, steroids, narcotics, nonselective – alcohol, steroids, narcotics, anesthetics, some antibiotics and some anesthetics, some antibiotics and some organisms can crossorganisms can cross

Wajed Hatamleh RN, MSN, PhD.Wajed Hatamleh RN, MSN, PhD.

Placental functionsPlacental functionsSimple diffusion - water, oxygen, carbon Simple diffusion - water, oxygen, carbon

dioxide, sodium and chloridedioxide, sodium and chlorideFacilitated transport – glucose and Facilitated transport – glucose and

galactosegalactoseActive transport – amino acids, calcium, Active transport – amino acids, calcium,

iron, iodine, vitamins, and glucoseiron, iodine, vitamins, and glucosePinocytosis – albumin and gamma globulinPinocytosis – albumin and gamma globulinHydrostatic and osmotic pressureHydrostatic and osmotic pressureEndocrine – hCG, hPL, estrogen and Endocrine – hCG, hPL, estrogen and

progesteroneprogesterone

HORMONESHORMONES

OESTROGENOESTROGEN

Produced in corpus luteumProduced in corpus luteum

Produced by placenta after 12 weeksProduced by placenta after 12 weeks

Responsible for growth particularly Responsible for growth particularly of uterus and breastsof uterus and breasts

progesteroneprogesterone

Produced in corpus luteum and then the Produced in corpus luteum and then the placentaplacenta

Relaxes smooth muscleRelaxes smooth muscle

Inhibits uterine contractions until uterus is Inhibits uterine contractions until uterus is prepared for labourprepared for labour

Regulates storage of body fatRegulates storage of body fat

Human chorionic gonadotrophicHuman chorionic gonadotrophic

Secreted from trophoblast of the Secreted from trophoblast of the developing embryodeveloping embryo

Maintains corpus luteum until Maintains corpus luteum until placenta takes overplacenta takes over

Used in tests to confirm pregnancyUsed in tests to confirm pregnancy

Human placental lactogenHuman placental lactogen

Alters maternal metabolismAlters maternal metabolism

Diverts glucose to fetusDiverts glucose to fetus

Mobilises free fatty acids from Mobilises free fatty acids from maternal storesmaternal stores

RELAXINRELAXIN

Released by corpus luteum then the Released by corpus luteum then the PlacentaPlacenta

Softens pelvic ligamentsSoftens pelvic ligaments

Reduces myometrial tone Reduces myometrial tone