Development and Inheritance

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Development and Inheritance

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Embryo

• The first two months following fertilization

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Fetus

• From week nine until birth

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Pregnancy

• Lasts about 40 weeks from the first day of the
  last menstrual period

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Fertilization

• The genetic material from a haploid sperm cell
  and a haploid secondary oocyte merges into a
  single diploid nucleus

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Fertilization

• Occurs in the fallopian tube

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Fertilization

• Occurs within 12-24 hours after ovulation

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Fertilization

• There is a total of 3 days per month during
  which coitus may result in pregnancy.

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Fertilization

• Two days before ovulation and one day after

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Fertilization

• Peristaltic contractions and cilia transport the
  oocyte through the uterine tube

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Fertilization

• Sperm swim up the uterus and uterine tube by
  movements of their tails and muscular
  contractions of the uterus

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Fertilization

• Only 200 of the 300 million spermatozoa reach the
  oocyte

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Fertilization

• Capacitation the functional changes that sperm
  undergo in the female that allow them to
  fertilize an oocyte

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Fertilization

• A sperm must penetrate the corona radiata and
  zona pellucida

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Fertilization

• Acrosomal enzymes digest a path through the zona
  pelucida

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Fertilization

• The spermatozoa that penetrates the oocyte loses
  its tail

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Fertilization

• Polyspermy is prevented by chemical changes that
  penetrate a second sperm from entering the oocyte

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Fertilization

• Once a sperm enters a secondary oocyte, the
  oocyte completes meiosis

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Fraternal Twins

• Produced from the independent release of two ova
  and the subsequent fertilization of each by
  different spermatozoa

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Monozygotic twins

• Derived from a single fertilized ovum that splits
  at an early stage in development

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Formation of the Morula

• Cleavage early rapid mitotic cell division of a
  zygote

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Formation of the Morula

• Blastomeres - The cells produced by cleavage

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Formation of the Morula

• Morula A solid mass of 16-32 cells

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Development of the Blastocyst

• The morula moves down the ciliated uterine tube
  and into the uterine cavity

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Development of the Blastocyst

• The morula develops into a blastocyst

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Development of the Blastocyst

• Blastocyst a hollow ball of cells that is
  differentiated into a
• Trophoblast
• Inner cell mass
• blastocele

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Development of the Blastocyst

• Implantation The attachment of a blastocyst to
  the endometrium seven to eight days after
  fertilization

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Development of the Blastocyst

• The trophoblast secretes human chorionic
  gonadotropin

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Development of the Blastocyst

• hCG rescues the corpus luteum from degeneration
  and sustains its function

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Development of the Blastocyst

• Trophoblast becomes the chorion

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Development of the Blastocyst

• Chorion a membrane outside the amniotic sac
  that has villi which project into the placenta

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Beginnings of Organ Systems

• Gastrulation inner cell mass of the blastocyst
  differentiates into three primary germ layers

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Development of the Blastocyst

• Three primary germ layers
• Ectoderm
• Mesoderm
• Endoderm

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Embryonic Membranes

• Lie outside the embryo and protect and nourish
  the embryo and later, the fetus

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Embryonic Membranes

1. Yolk sac
2. Amnion
3. Chorion
4. allantois

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Yolk Sac

• It gives rise to cells that migrate to the gonads
  to become spermatogonia and oogonia (ICM)

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Amnion

• Surrounds the embryo creating a cavity filled
  with amniotic fluid (ICM)

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Chorion

• Derived from the trophoblast

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Chorion

• Surrounds the embryo and later, the fetus

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Chorion

• Embryonic part of the placenta

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Allantois

• Small vascularized membrane (ICM)

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Allantois

• Umbilical cord

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Umbilical cord

• Vascular connection between mother and fetus

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Umbilical Cord

• Consists of two umbilical arteries carrying
  dexoygenated fetal blood to the placenta and one
  umbilical vein that carries oxygenated blood from
  the placenta into the fetus

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Placenta

• Developed by the third month of pregnancy

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Placenta

• Formed by the
• Chorion (embryonic portion)
• Decidua basalis (maternal portion)

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Placenta

• All exchanges to and from the embryo occur here

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Placenta

• Stores nutrients and released into fetal
  circulation as required

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Hormones of Pregnancy

• During the first 3-4 months of pregnancy, the
  corpus luteum secretes progesterone and estrogen

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Hormones of Pregnancy

• Progesterone and estrogens maintain the uterine
  lining and prepare the mammary glands to secrete
  milk

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Hormones of Pregnancy

• After the third, the placenta secretes estrogen
  and progesterone

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Hormones of Pregnancy

• Estrogen inhibits prolactin, so lactation does
  not occur

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Hormones of Pregnancy

• Estrogen increases the number of oxytocin
  receptors in the uterus

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Hormones of Pregnancy

• Relaxin softens the cervix and relaxes the
  pubic symphysis to facilitate delivery

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Hormones of Pregnancy

• Corticotropin-releasing hormone the clock that
  establishes the timing of birth

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Anatomical and Physiological Changes During
Pregnancy

• CO, HR, and SV increases

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Anatomical and Physiological Changes During
Pregnancy

• Breast enlargement

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Anatomical and Physiological Changes During
Pregnancy

• Increase in appetite

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Anatomical and Physiological Changes During
Pregnancy

• Increase in tidal volume and total body oxygen
  consumption

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Anatomical and Physiological Changes During
Pregnancy

• Increase in GFR

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Anatomical and Physiological Changes During
Pregnancy

• Increase in frequency of urination

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Anatomical and Physiological Changes During
Pregnancy

• Some women experience elevated blood pressure