PREGNANCY

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PREGNANCY HUMAN DEVELOPMENT

• Mutiara Budi Azhar
• Faculty of Medicine Sriwijaya University

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Embryology

• Embryology is a science that studies the normal
  development as well as birth defects of a human
  being in the maternal uterus.

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Historical gleanings
Hippocrates, Father of Medicine, first recorded
embryological studies bird embryo can be likened
to that of man.
Aristotle studied chick and other embryos, which
resulted from union of semen with menstrual
blood.
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From Egg to Fetus

• Pregnancy events that occur from fertilization
  (conception, conceptio) until the infant is born.
• Conceptus the developing offspring.
• Gestation period from the last menstrual period
  until birth.
• Preembryo conceptus from fertilization until it
  is two weeks old.
• Embryo conceptus during the third through the
  eighth week.
• Fetus conceptus from the ninth week through
  birth

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Relative Size of Human Conceptus
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Gametes and Gametogenesis
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Gamete

• A gamete (from Ancient Greek ?aµet?? translated
  gamete wife, gametes husband) is a cell that
  fuses with another gamete during fertilization
  (conception) in organism that reproduce sexually.
• In species which produce two morphologically
  distinct types of gametes, and in which each
  individual produces only one type, a female is
  any individual which produces the larger type of
  gametecalled an ovum (or egg)and a male
  produces the smaller tadpole-like typecalled a
  sperm.

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Gamete. Cont

• Anisogamy or heterogamy the condition wherein
  females and males produce gametes of different
  sizes in humans, the human ovum is approximately
  20 times larger than the human sperm cell.
• Isogamy is the state of gametes from both sexes
  being the same size.

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Gamete. Cont

• The name gamete was introduced by the Austrian
  biologist biologist Gregor Mendel
• Gametes carry half the genetic information of an
  individual, one chromosome of each type.
• In human an ovum can only carry X chromosom (of
  the X and Y chromosom)
• As a sperm can carry either an X or a Y, males
  have the control of the gender of any resulting
  zygote as the genotype of the sex-determining
  chromosomes of a male must be XY and a female XX.
  

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The Human Life Cycle

• Haploid pertaining to a single set of unpaired
  chromosomes or an organism or cell that comprises
  of a single set of chromosomes
• Diploid Contain two homologous sets of
  chromosomes

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Gametogenesis
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Spermatogenesis
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Ooogenesis
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Spermatogenesis
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Oogenesis
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Sperm Meiosis
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Spermatozoa
Spermatozoa
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Oocyte
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hypothalamus
GnRH
anterioir pituitary
FSH
LH
Mid-cycle peak of LH (triggers ovulation)
hypothalamus
Blood levels of FSH (purple) and LH (lavender)
anterior lobe of pituitary gland
FSH
LH
LH
growth of follicle
ovulation
corpus luteum
estrogens
progesterone, estrogen
Blood levels of estrogens (light blue) and
progesterone (dark blue)
estrogens
progesterone, estrogen
endometrium of uterus
menstruation
Days of one menstrual cycle (using 28 days as the
average duration)
FOLLICULAR PHASE OF MENSTRUAL CYCLE
LUTEAL PHASE OF MENSTRUAL CYCLE
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Fertilization
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Accomplishing Fertilization

• The oocyte is viable for 12 to 24 hours
• Sperm is viable 24 to 72 hours
• For fertilization to occur, coitus must occur no
  more than
• Three days before ovulation
• 24 hours after ovulation
• Fertilization when a sperm fuses with an egg to
  form a zygote

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Sperm Transport and Capacitation

• Fates of ejaculated sperm
• Leak out of the vagina immediately after
  deposition
• Destroyed by the acidic vaginal environment
• Fail to make it through the cervix
• Dispersed in the uterine cavity or destroyed by
  phagocytic leukocytes
• Reach the uterine tubes
• Sperm must undergo capacitation before they can
  penetrate the oocyte

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Acrosomal Reaction and Sperm Penetration

• An ovulated oocyte is encapsulated by
• The corona radiata and zona pellucida
• Extracellular matrix
• Sperm binds to the zona pellucida and undergoes
  the acrosomal reaction
• Enzymes are released near the oocyte
• Hundreds of acrosomes release their enzymes to
  digest the zona pellucida

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Acrosomal Reaction and Sperm Penetration. Cont.

• Once a sperm makes contact with the oocytes
  membrane
• Beta protein finds and binds to receptors on the
  oocyte membrane
• Alpha protein causes it to insert into the
  membrane

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Acrosomal Reaction and Sperm Penetration. Cont.
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Blocks to Polyspermy

• Only one sperm is allowed to penetrate the oocyte
• Two mechanisms ensure monospermy
• Fast block to polyspermy membrane
  depolarization prevents sperm from fusing with
  the oocyte membrane
• Slow block to polyspermy zonal inhibiting
  proteins (ZIPs)
• Destroy sperm receptors
• Cause sperm already bound to receptors to detach

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Completion of Meiosis II and Fertilization

• Upon entry of sperm, the secondary oocyte
• Completes meiosis II
• Casts out the second polar body
• The ovum nucleus swells, and the two nuclei
  approach each other
• When fully swollen, the two nuclei are called
  pronuclei
• Fertilization when the pronuclei come together

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Events Immediately Following Sperm Penetration
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Preembryonic Development
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Preembryonic Development

• The first cleavage produces two daughter cells
  called blastomeres
• Morula the 16 or more cell stage (72 hours old)
• By the fourth or fifth day the preembryo consists
  of 100 or so cells (blastocyst)

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Preembryonic Development. Cont.

• Blastocyst a fluid-filled hollow sphere
  composed of
• A single layer of trophoblasts
• An inner cell mass
• Trophoblasts take part in placenta formation
• The inner cell mass becomes the embryonic disc

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The Period of the Zygote

• Zygote ? blastocyst
• Cell differentiation
• of blastocysts that fail to implant?

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The Period of the Zygote. Cont.

• Outer layer of blastocyst develops into
• Amnion
• Chorion
• Placenta
• Umbilical cord
• note that these structures actually develop
  during the period of the embryo

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Implantation
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Implantation

• Begins six to seven days after ovulation when the
  trophoblasts adhere to a properly prepared
  endometrium
• The trophoblasts then proliferate and form two
  distinct layers
• Cytotrophoblast cells of the inner layer that
  retain their cell boundaries
• Syncytiotrophoblast cells in the outer layer
  that lose their plasma membranes and invade the
  endometrium

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Implantation. Cont.

• The implanted blastocyst is covered over by
  endometrial cells
• Implantation is completed by the fourteenth day
  after ovulation

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Implantation of the Blastocyst
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Implantation of the Blastocyst. Cont.
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Implantation of the Blastocyst
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Implantation of the Blastocyst. Cont.
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Implantation of the Blastocyst. Cont.
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Implantation of the Blastocyst. Cont.

• Viability of the corpus luteum is maintained by
  human chorionic gonadotropin (hCG) secreted by
  the trophoblasts
• hCG prompts the corpus luteum to continue to
  secrete progesterone and estrogen
• Chorion developed from trophoblasts after
  implantation, continues this hormonal stimulus
• Between the second and third month, the placenta
  
• Assumes the role of progesterone and estrogen
  production
• Is providing nutrients and removing wastes

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Hormonal Changes During Pregnancy
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Placentation
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Placental Development
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Placentation

• Formation of the placenta from
• Embryonic trophoblastic tissues
• Maternal endometrial tissues

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Placentation. Cont.

• The chorion develops fingerlike villi, which
• Become vascularized
• Extend to the embryo as umbilical arteries and
  veins
• Lie immersed in maternal blood
• Decidua basalis part of the endometrium that
  lies between the chorionic villi and the stratum
  basalis

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Placentation. Cont.

• Decidua capsularis part of the endometrium
  surrounding the uterine cavity face of the
  implanted embryo.
• The placenta is fully formed and functional by
  the end of the third month.
• Embryonic placental barriers include
• The chorionic villi
• The endothelium of embryonic capillaries

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Placenta

• Permits the exchange of materials between the
  bloodstream of the fetus and that of the mother
• Produces progesteron gradually take over the
  role of corpus luteum.
• The placenta also secretes other hormones human
  placental lactogen, human chorionic thyrotropin,
  and relaxin.

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Placentation. Cont.
Figure 28.7a-c
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Placentation. Cont.
Figure 28.7d
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Placentation. Cont.
Figure 28.7f
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Germ Layers
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Gastrulation

• During the 3rd week, the two-layered embryonic
  disc becomes a three-layered embryo
• The primary germ layers are ectoderm, mesoderm,
  and endoderm
• Primitive streak raised dorsal groove that
  establishes the longitudinal axis of the embryo

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Germ Layers

• The blastocyst develops into a gastrula with
  three primary germ layers ectoderm, endoderm,
  and mesoderm.
• Before becoming three-layered, the inner cell
  mass subdivides into the upper epiblast and lower
  hypoblast these layers form two of the four
  embryonic membranes

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Gastrulation. Cont.

• As cells begin to migrate
• The first cells that enter the groove form the
  endoderm
• The cells that follow push laterally between the
  cells forming the mesoderm
• The cells that remain on the embryos dorsal
  surface form the ectoderm
• Notochord rod of mesodermal cells that serves
  as axial support

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Three Germ Layers

• Endoderm formed from migrating cells that
  replace the hypoblast
• Mesoderm formed between epiblast and endoderm
• Ectoderm formed from epiblast cells that stay
  on dorsal surface
• All layers derive from epiblast cells!

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Primary Germ Layers

• Serve as primitive tissues from which all body
  organs will derive.
• Ectoderm nervous system, skin, hair, sensory
  receptors.
• Endoderm digestive system, lungs, urinary
  tract, other internal organs.
• Mesoderm muscles, bones, circulatory system,
  reproductive system, excretory system.
• Endoderm and ectoderm are securely joined and are
  considered epithelia.

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Derivatives of Germ Layers
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Embryonic Membranes

• Amnion epiblast cells form a transparent
  membrane filled with amniotic fluid
• Provides a buoyant environment that protects the
  embryo
• Helps maintain a constant homeostatic temperature
• Amniotic fluid comes from maternal blood, and
  later, fetal urine

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Embryonic Membranes. Cont.

• Yolk sac hypoblast cells that form a sac on the
  ventral surface of the embryo
• Forms part of the digestive tube
• Produces earliest blood cells and vessels
• Is the source of primordial germ cells

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Embryonic Membranes. Cont.

• Allantois a small outpocketing at the caudal
  end of the yolk sac
• Structural base for the umbilical cord
• Becomes part of the urinary bladder
• Chorion helps form the placenta
• Encloses the embryonic body and all other
  membranes

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Embryonic Period
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Embryonic Period
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Embryo at 4 Weeks
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Face Development from 5½ to 8 Weeks
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The Period of the Embryo. Cont.

• By 4th week, heart has formed and begun to beat
• Becomes more human in appearance during 2nd month
• Sexual differentiation during 7th 8th weeks

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The Period of the Fetus
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The Period of the Fetus

• Final 7 months of pregnancy
• Fetus
• Digestive and excretory systems functional
• Sex detected by ultrasound by end of 3rd month
• Kicks and movements strong enough to be felt
• Organ systems mature rapidly during final 3 months

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The Period of the Fetus. Cont.
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Fetus at 9 Weeks
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Fetus at 11 Weeks
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Fetus at 16 Weeks
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Fetus at 18 Weeks
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Fetus at 20 Weeks
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Fetus at 28 Weeks
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Fetal development
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Twins
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The Period of the Fetus. Cont.

• Viable between 22-28 weeks
• Receives antibodies
• Assume upside-down position in final weeks
• Weight of head
• Shape of uterus

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A Brief View of Prenatal Development
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A Brief View of Prenatal Development. Cont.
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Developmental Events of the Fetal Period
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Developmental Events of the Fetal Period
Table 3.1 (2 of 3)
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Developmental Events of the Fetal Period
Table 3.1 (3 of 3)
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Trends in Development

• Cephalocaudal Trend
• Proximodistal Trend

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Teratogens
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Susceptible period
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Teratogens

• Root word means formation of monsters
• Harm isnt always simple or straightforward
• Amount and length of exposure
• Genetic makeup of mother/baby
• Presence of several negative factors

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Teratogens. Cont.

• Same defect ? different teratogens
• One teratogen ? different defects
• Some effects seen later
• Age of baby
• Sensitive period

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Teratogens. Cont.

• Paternal influences often overlooked
• Direct and indirect effects
• Second hand smoke
• Chemicals
• Cocaine can hitchhike
• Smoking, alcohol, drug use ? sperm
• Diets low in vitamin C

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Other Factors Teratogens. Cont.

• Exercise
• Nutrition
• Emotional stress
• Rh blood incompatibility
• Maternal/Paternal age
• Older ? less fertile, more risk of disorders
• Younger ? increased risk of prematurity, infant
  death

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Other Factors Teratogens. Cont.

• Infectious diseases
• Prenatal care
• Previous births

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Congenital malformations (Birth defects)
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Chemical nitrite, benzol lead, arsenic,
cadmium, mercury, etc. Drugs thalidomide
(amelia and meromelia),
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Drugs aminopterin (anencephaly, hydrocephalus,
cleft lip) streptomycin
(deafness). Hormones estrogens, progestins
Social drugs cigarettes (small babies) alcohol
(fetal alcohol syndrome).
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Perinatal Environment

• Environment surrounding birth
• Stages of childbirth
• Contractions
• Delivery
• Afterbirth
• Newborn appearance

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Birth

• Labor
• Oxytocin
• Uterine contractions

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Perinatal Environment

• Assessing the Newborn
• Apgar scale
• 1 minute and 5 minutes after birth

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The Apgar Test
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Perinatal Environment

• Assessing the Newborn
• Neonatal Behavioral Assessment Scale (NBAS)
• Several days after birth
• 20 inborn reflexes
• Reactions to comforting and social stimuli
• Unresponsiveness may indicate neurological
  problems
• Can be a parent teaching tool

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Perinatal Environment

• Complications
• Anoxia
• Severe ? cerebral palsy, mental retardation
• Mild ? irritability, motor/cognitive delays
• Chances have been reduced with fetal monitoring
• Respiratory distress syndrome
• Complicated delivery
• Forceps
• Cesarean
• Medications

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Preterm and Small-for-Date

• Preterm born more than 3 weeks early, but
  appropriate weight for time in womb
• Small-for-Date underweight due to slow fetal
  growth
• Greater risk than preterm
• Causes include smoking, drug use, stress, lack of
  prenatal care, multiple births, social support
• Postterm born after 42 weeks

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Thank you very much for your kind attention