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Menstrual cycle Shedding of the uterine lining
LH Menstrual cycle Shedding of the uterine lining Controlled by interaction of 4 hormones FSH & LH estrogen progesterone FSH ovulation = egg release egg development corpus luteum estrogen progesterone lining of uterus days 7 14 21 28
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The menstrual cycle has four phases.
Follicular phase: prepares to release ovum Ovulation phase: ovum is released Luteal phase: corpus luteum forms Menstruation phase: endometrium sheds
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The menstrual cycle stops at menopause.
cycle continues until a woman is mid-40’s or 50’s decline in hormone levels make cycles irregular eventually, cycle stops altogether
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Fertilization
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Fertilization occurs when a sperm cell joins an egg cell.
Sperm enters an egg. membrane keeps out other sperm nucleus of sperm joins with egg zygote formed
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Multiple zygotes can result from fertilization.
identical twins from the same egg fraternal twins from two separate eggs
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The fertilized egg, called a ZYGOTE, undergoes cell division to produce a two-celled embryo. These cells divide again and again to form a ball of cells. The ball of cells attaches itself to the wall of the uterus and continues to divide.
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What happens now? Development of the zygote
The zygote undergoes a series of mitotic cell divisions called cleavage. The stages of development are: Fertilized ovum (zygote) 2-cell stage 4-cell stage 8-cell stage Morula Blastula Early Gastrula Late Gastrula
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From one cell to many A fertilized egg goes through an early stage of development called an embryo. EMBRYO
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Cell Division
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Cleavage (divide via mitosis) forms the 2 cell stage
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They split again to form the 4 cell stage
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And again to form the 8 cell stage…
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And eventually form a solid ball of cells
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Next it becomes a hollow ball of cells from cleavage
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And next, the hollow ball pushes in with 3 germ layers
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Cleavage: process of cell division (Mitosis) during development
The Regents Diagram… Sperm and ovum (fertilization) Zygote (fertilized ovum) 2-cell stage 4-cell stage Morula Blastula Gastrula Cleavage: process of cell division (Mitosis) during development
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Regents Question
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Regents Question
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Regents Question
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Implantation The embryo implants in the wall of the uterus on about the 7th day of development
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Implantation can also occur anywhere outside the uterus and is called an ectopic pregnancy.
It is possible for fetus to grow in the abdominal cavity, but growth inside the uterine tube causes the tube to rupture, resulting in severe bleeding.
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Placenta Food & gases diffuse across blood vessels
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Functions of the placenta:
1 Transfer gasses 2 Transport nutrients 3 Excretion of wastes 4 Hormone production – temporary endocrine organ – estrogen and progesterone 5 Formation of a barrier – incomplete, nonselective – alcohol, steroids, narcotics, anesthetics, some antibiotics and some organisms can cross
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UMBILICAL CORD Connecting link between fetus and placenta.
Transports oxygen and nutrients to fetus from the placenta and returns waste products from the fetus to the placenta. Contains: 2 arteries and 1 vein Contains NO pain receptors.
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Human fetal development
4 weeks 7 weeks
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Human fetal development
10 weeks
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Human fetal development
12 weeks 20 weeks
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Human fetal development
The fetus just spends much of the 2nd & 3rd trimesters just growing Week 20
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Human fetal development
24 weeks (6 months; 2nd trimester)
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Human fetal development
30 weeks (7.5 months) umbilical cord
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Getting crowded in there!!
32 weeks (8 months) The fetus sleeps 90-95% of the day & sometimes experiences REM sleep, an indication of dreaming
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The value of sexual reproduction
Sexual reproduction introduces genetic variation genetic recombination during meiosis crossing over mixing of alleles across homologous chromosomes random fertilization which sperm fertilizes which egg? Driving evolution Variation for evolution
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Regents Question
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EXTERNAL VS. INTERNAL EXTERNAL FERTILIZATION: SPERM & EGG FERTILIZE OUTSIDE BODY. Examples:fish, amphibians INTERNAL FERTILIZATION: FERTILIZE INSIDE BODY. Examples: human, alligator, elephant
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