Download Prenatal Period - CESA 10 Moodle

Prenatal Period
• Begins with conception and continues until the birth
• Cleavage and implantation (Figure 33-6)
– Once zygote is formed, it immediately begins to divide
– Morula
• Solid mass of cells formed from zygote
• Takes approximately 3 days; continues to divide (Figure 33-7)
– Blastocyst
• Hollow ball of cells that implants into uterine lining (Figure 33-9)
• Approximately 10 days pass from fertilization until implantation in
uterine lining
• Ovum has a store of nutrients that support this embryonic
development until implantation has occurred
Prenatal Period
• Blastocyst
– Trophoblast
• Outer wall of blastocyst
• Forms the support structures
– Amniotic cavity
– Chorion
– Inner cell mass
• As blastocyst develops, yolk sac and amniotic cavity are
formed (Figure 33-9)
• In humans, yolk sac’s functions are largely
nonnutritive…production of blood cells
• Eventually forms the tissues of the body
Prenatal Period
• Cleavage and implantation (cont.)
– Placenta (Figure 33-11)
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Structural anchor
Nutritive bridge
Excretory organ
Respiratory organ
Endocrine organ
– Secretes large amounts of human chorionic gonadotropin (HCG),
which stimulates the corpus luteum to continue its secretion of
estrogen and progesterone (Figure 33-12). This prevents
mensturation and allows for successful implantation and
development.
• Placental tissue normally separates maternal and fetal blood
supplies
Prenatal Period
• Periods of development (Figures 33-13 through 3315)
– Gestation period
• Approximately 39 weeks
• Divided into three 3-month segments called trimesters
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First trimester – weeks 1 through 12
Second trimester - weeks 12 through 28
Third trimester - week 28 until birth
Zygote, morula, blastocyst, embryo, fetus
• 35 Days
– Heart beats
– 3/8 inch long
– Eyes and limb buds
visible
• 49 Days
– Heart beats
– 3/8 inch long
– Eyes and limb buds
visible
• End of first trimester
– 3 inches long
– Facial features are
apparent
– Limbs are complete
– Sex can be identified
• At four months
– All organ systems are
formed and functioning to
some extent
Prenatal Period
• Formation of the primary germ layers
– Three layers of specialized cells develop early in
first trimester of pregnancy
– Cells of embryonic disk differentiate and form each
of the three primary germ layers
– Each primary germ layer gives rise to specific
organs and systems of the body (Figure 33-16)
– There are three primary germ layers:
• Endoderm—inside layer
• Ectoderm—outside layer
• Mesoderm—middle layer
Prenatal Period
• Endoderm
– Linings of various tracts and several glands
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Respiratory and GI tract
Pancreatic and hepatic ducts
Urinary tract
Glandular epithelium of many glands
• Ectoderm
– Structures around periphery of the body
• Epidermis
• Enamel
• Cornea
– Brain and spinal cord
• Mesoderm
– Most organs between those formed by the endoderm and
ectoderm
– Dermis, muscles, bones, many glands, kidneys, gonads,
circulatory system
Prenatal Period
• Histogenesis and organogenesis
– Histogenesis
• Process by which primary germ layers develop into different
kinds of tissues
– Organogenesis
• Arrangement of tissues into organs
– Differentiation, multiplication, growth, rearrangement
take place in a definite and orderly sequence
– After 4 months, development is mainly a matter of
growth
Prenatal Period
• Changes during pregnancy
– Large size of uterus affect normal function of mother’s body
• Center of gravity is shifted forward
• Uterus presses on the rectum and may affect intestinal motility
– Constipation
– Hemorrhoids
• Pressure on the bladder reduces its storing capacity
• Upward pressure pushes the abdominal organs against the
diaphragm
– Hiatal hernia