Sexual reproduction

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Sylvia S. Mader
Immagini e
concetti
della biologia
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
C11 Reproduction
and
development
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Reproduction in animals is varied
Both asexual and sexual reproduction occur among
animals.
Asexual reproduction (some invertebrates, sponges,
cnidarians, flatworms, annelids and echinoderms): single
parent gives rise to offspring that are identical to the
parent.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Reproduction in animals is varied
Sexual reproduction (some invertebrates, earthworms,
plants and animals): sex cells, or gametes, produced by
the parents unite to form a genetically unique individual.
Copulation is the sexual union to facilitate the reception of
sperm and to protect sperm from drying out.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
The male reproductive system
The gonads are the organs that make gametes. Testes are male
gonads.
The human male reproductive system also includes epididymides,
vasa deferentia, ejaculatory duct and urethra.
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The human reproductive system
The penis is the organ of sexual intercourse.
The semen is composed of sperm and secretions from the
seminal vesicles, prostate gland and bulbourethral glands.
Orgasm (sexual climax) is the discharge of accumulated
sexual tension resulting from ejaculation of semen and
ending in rhythmic muscular contractions in the pelvic
region.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Production of sperm
Testes contain seminiferous
tubules where
spermatogenesis occurs.
Seminiferous tubules
produce:
•Sperm
•Interstitial cells
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Spermatogenesis
Spermatogenesis is the process by which spermatozoon (male
sperm cell) are produced through meiosis.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Sex hormones
The anterior pituitary secretes hormones that:
1.trigger the spermatogenesis, as the follicle-stimulating
hormone (FSH);
2.control the production of testosterone, as the luteinizing
hormone (LH).
Testosterone is a steroid hormone that influences the sex
organ function, sperm maturation and male secondary sex
characteristics.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
The female reproductive system
The female gonads are the ovaries and the reproductive system
also includes oviducts, uterus and vagina.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
The female reproductive system
The clitoris is a sexual organ located near above the
opening of the urethra. Unlike the penis, the clitoris is the
female’s most sensitive sexual organ.
The female external genital area also includes the vaginal
opening, labia minora and labia majora.
Female orgasm culminates in uterine and oviduct
contractions.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Production of oocytes
The production of an egg occurs as an ovarian follicle (aggregation
of cells) changes from primary to secondary to a vesicular follicle.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Production of oocytes
Before ovulation, the oocyte maturation requires the oogenesis, a
meiotic process whose completion is triggered by the fertilization by
a spermatozoon.
When the two gamete nuclei melt, the zygote (46 chromosomes)
forms.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Female sex hormones
Ovaries produce:
•Estrogen: promotes the development of
female secondary sexual characteristics.
•Progesterone: involved in the menstrual cycle,
pregnancy and embryogenesis.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
The ovarian cycle
The ovarian cycle starts with the production of folliclestimulating hormone (FSH) in the anterior pituitary.
•FSH causes maturation of a follicle that secretes estrogen
and some progesterone.
•During the luteal phase, LH promotes development of the
corpus luteum.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
The uterine cycle
The uterine cycle starts with menstruation, the
endometrium cleavage occurs and the blood vessels
break.
•During the proliferative phase estrogen causes uterine
lining to thicken.
•Progesterone causes the lining to become secretory.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
The ovarian cycle
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Sexually transmitted diseases
AIDS: disease of the immune system caused by the
human immunodeficiency virus (HIV).
Herpes Simplex Virus (HSV): transmitted during
reactivation phase of the virus.
Human Papilloma Virus (HPV): causes infections of the
skin or mucous membranes.
Other STD are chlamydial infection, syphilis and
gonorrhea.
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Contraceptives
Numerous birth control methods are available before and
after sexual intercourse.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Technologies to help fertility
Assisted reproductive technologies include:
•artificial insemination by a donor
•in vitro fertilization
•gamete intra-fallopian transfer
•intra-cytoplasmic sperm injection
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Embryonic development
The first step of the embryogenesis is the cellular stages.
The zygote undergoes rapid
mitotic divisions.
This cleavage results in a
multicellular mass (called
morula) and then a singlelayered blastula forms.
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Embryonic development
The second embryogenesis step is the tissue stages.
The gastrulation leads to the
formation of a three-layered
structure called gastrula
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Gastrulation
A mature gastrula has three germ layers: ectoderm,
mesoderm and endoderm.
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Gastrulation
The three germ layers will develop into specific organs.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Extraembryonic membranes
The amnion protects and moisturize the embryo in a sac
filled with amniotic fluid.
The yolk sac contains the source of food until hatching.
The chorion is below the shell and provides gas
exchanges with the outside air.
The allantois collects metabolic wastes of the embryo.
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Embryonic development
Embryonic development spans the first two months of the
gestation, from fertilization through the acquisition of
organ systems.
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Embryonic development
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Embryonic development
Eight weeks after fertilization the embryo is completed and
becomes fetus. It has recognizable external features.
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Fetal development
Fetal development occurs after the third month.
Exchanges at the placenta supply the fetus with O2 and
nutrients and collect CO2 and wastes.
During the third and fourth month, the skeleton ossifies
and the fetus sex becomes distinguishable.
During the fifth, sixth and seventh month fetal movements
begin, the fetus continues to grow and gain weight.
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Fetal development
Nine months after the fertilization, the pregnancy ends with
the birth of the newborn.
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Childbirth
1. Dilatation: uterine contractions begin.
2. Expulsion: uterine contractions occur every 1-2
minutes. The baby is born and the umbilical cord is cut.
3. Dislodging: uterine muscle contractions shrink the
uterus and dislodge the placenta, which is expelled.
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