Reproductive system day3
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Reproductive System
Day 3: Spermatogenesis, oogenesis and the menstrual cycle
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Gametes
• reproductive cells (sperm and egg)• haploid (single set of unpaired chromosomes)– In humans we have 23 pairs or 46• chromosomes are packaged DNA
• formed by gametogenesis– spermatogenesis– oogenesis
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Mitosis• cell division• undergoes several phases:
– interphase* – prophase – prometaphase* – metaphase – anaphase – telophase – cytokinesis*
• results into two identical daughter cells– IF a diploid cell undergoes mitosis, the result is a diploid cell.
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Meiosis
• Cell division• results into two daughter cells with half the
number of chromosomes– IF a diploid cell undergoes meiosis, the resulting
cells are haploid cells– Meiosis only happens in gametes.
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Spermatogenesis
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Oogenesis
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Differences in gametes
sperms• male• Meiosis results in four
sperms.• Sperms are motile.• relatively small • in the millions
ova• Female• Meiosis results in one
mature ovum and three polar bodies
• The ovum is nonmotile.• relatively large• Just one ovum is released
every month.
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The Sperm Cell
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Parts of a sperm
• head: acrosome– has enzymes to penetrate the egg cell– triggers acrosome reaction• prevents other sperms from fusing with the egg
• midpiece: ATP production (energy)– fructose from seminal fluid
• tail: flagella for movement
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The Ovum
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Parts of an ovum
• yolk– cytoplasm and nutritive
• germinal vesicle– nucleus
• zona striata or zona pellucida– protection– in between the cytoplasm and corona radiata
• corona radiata– outer protection, 2 or 3 cell layers thick
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Menstrual cycle
• monthly cycle ~28 days– In adults 21 to 35– In teens 21 to 45
• “bleeding”– shedding of the endometrium of the uterus– lasts 3 to 5 days
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What happens in the menstrual cycle?
• follicle-stimulating hormone (ripening)• increase of estrogen– prepares the uterus for pregnancy– the lining grows and thickens
• luteinizing hormone (release)– Day 14, the ovum is released from the ovary.
• Progesterone prepare and maintain the endometrium• Pregnancy can occur 3 days before or during ovulation.
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• IF fertilization does not occur:– ovum breaks– hormones drop– the uterine lining is shed
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• IF fertilization occurs– Egg is “planted” in the endometrium– Human chorionic gonadotropian (HCG)• Continues secretion of progesterone
*provide the blood vessels (endometrium)
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Complications of the menstrual cycle
• amenorrhea– Lack of menstruation• Excessive weight loss• Stress• Excessive exercising
• dysmenorrhea– painful menstruation, cramps• excess prostaglandin
– contracts and relaxes smooth muscles
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Menopause
• the menstrual cycle stops• happens at age 45 -55
What happens at menopause?
Ovulation stops.