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Animal Reproduction
2 forms of reproduction

Asexual
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Creation of a new individual without the fusion of
egg and sperm
Sexual
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The fusion of haploid gametes to form a zygote
which is diploid
Asexual Reproduction

Parthenogenesis
–
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Fragmentation
–

Breaking the body into several pieces which develop into complete
adults
Budding
–
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The egg develops without being fertilized
New inviduals splitting off from existing ones
Fission
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Separation of parents into two or more individuals of approximately
equal size
Sexual reproduction

2 kinds

External fertilization

Internal fertilization
External Reproduction


Eggs are shed by the female and fertilized by
the male in the environment
Due to the special environment where an
egg can develop, it only takes place in moist
environments.
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
Mostly fish, amphibians
1 male fertilizing the eggs of one female
Internal Reproduction

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Sexual reproduction is the creation of offspring by
the fusion of haploid gametes to create a diploid
zygote.
The female gamete, the ovum, is a large and none
motile cell.
The male gamete, spermatozoon, is a small, motile
cell.
Sexual reproduction helps to increase genetic
variation by generating a unique combination of
genes inherited by both parents.
Reproductive System of a Human Male

External reproductive organs
–
Scrotum

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Penis

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Contain the testes and held outside the abdominal cavity
Reproductive structure outside the abdominal cavity responsible for
delivering sperm into the female reproductive tract
Internal reproductive organs
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Testes

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The gonads, responsible for creating sperm
Accessory glands (Ex: Prostate)

Responsible for depositing various things within the urethra and
semen to help assist the reproductive process
The Accessory Glands

Seminal vesicles
–
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Contribute about 60% of the total volume of semen
Thick, yellowish, alkaline


Prostate gland
–
Thin and milky


Contains Fructose and absorbic acid
Anticoagulant enzymes, citrate, slightly acidic
Bulbourethreal glands
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Neutralize any acidic urine located within the urethra
Sperm


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Spermatogenesis is a continuous and prolific
process
Each ejaculation of a human male contains 100 to
650 million sperm cells.
Structure of Sperm:
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Head

–
Acrosome

–
Contains the haploid nucleus
Tip of the head which helps penetrate eggs
Spiral Mitochondrian

Provides ATP for momvement of the tail
Cross Section of a Testis
Spermatogenesis
Reproductive Anatomy of a Human
Female

External reproductive structures
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–

Clitoris
Labia surrounding the clitoris and vaginal opening
Internal reproductive structures
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Ovary
Chambers to conduct the gametes and house the
embryo and fetus
The Ovary



The ovary lies within the abdominal cavity
and attached to the uterus.
Each ovary is enclosed in a tough protective
capsule and contain many follicles.
A follicle is one egg cell surrounded by many
layers of follicle cells
–
These are responsible for nourishing and
protecting the egg cell.
Internal Reproductive System


Oviduct (fallopian tube)
– Funnel-like opening and contains cilia on the inner epithelium lining
– Convey the egg cell down the duct to the uterus
Uterus
– Thick, muscular organ
 Can expand during pregnancy to accommodate a 4-kg fetus

Vagina
– The chamber that forms the birth canal through which the baby is born
– Repository for sperm during sexual reproduction
– Bartholin’s Glands, located near the opening, responsible for lubrication
during sexual intercourse

Mammary glands (Not part of the reproductive system but important)
– Small sacs of epithelial tissue secrete milk, which drains into ducts
emptying into the nipple
External Reproductive System


The vaginal opening and urethral opening are
located within a region called the vestibule, bordered
by skin folds called the labia minora.
Labia majora
–

encloses and protects the labia minora and vestibule
Clitoris
–
–
Short shaft supporting a rounded glans covered by a small
hood of skin (Prepuce)
Erectile tissue with a rich supply of nerve endings
The development of Eggs



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Oogenesis is the development of mature, unfertilized
egg cells.
The primary oocytes replicate their DNA and enter
prophase 1 of meiosis (at birth) waiting to be
activated by hormones.
At puberty FSH beings to stimulate a follicle to begin
growing again and induces the primary oocyte to
complete the first meiotic division.
The second meiotic division completes when the egg
is fertilized.
OVULATION
The differences


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1) During the meiotic divisions of oogenesis
cytokenesis is unequal because the second oocyte
monopolizes the cytoplasm.
2) While the cells from which sperm development
continue to divide by mitosis throughout the male’s
life, an ovary already contains all the cells it will ever
have that will develop into eggs.
3) Oogenesis has long down time, while
spermatogenesis produces more sperm in an
uninterrupted sequence.
Male Hormones

The principal sex hormones are androgens
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
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Responsible for primary and secondary sex characteristics.
Primary:
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
Testosterone is the most important
Development of reproductive ducts
Development of external reproductive structures
Sperm production
Secondary:
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Deepening of the voice
Distribution of facial and pubic hair
Muscle growth
Female Hormones

GnRH – gonadotropin-releasing hormone
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
FSH
–

Secreted by the hypothalamus
Follicle stimulating hormone
LH
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Luteinizing hormone
Estrous Cycle


Similar to the menstrual cycle, but some key
differences.
Estrous
–
–
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Characterized by specific times in which the
vaginal changes permit mating
No shedding of the uterine lining occurs, rather it
is reabsorbed by the uterus.
More behavioral changes in the females.
Menstrual Cycle

Menstrual Flow Phase
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Proliferative phase
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Menstrual bleeding occurs
Lasts for a few days
Thin endometrium regenerates and thickens.
Lasts for 1-2 weeks
Secretory Phase
–
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Endometrium continues to thicken and develops glands tat
secrete fluid rich in glycogen.
If an embryo is not implanted in the uterine lining, the cycle
starts over
Ovarian Cycle


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Another cycle parallel to the menstrual cycle.
Hormonal responses and activity have a
large party to do with this cycle.
Divided into 2 phases:
Follicular phase
Luteal phase
Follicular Phase
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Follicles in the ovary begin to grow and the egg cell enlarges.
The FSH stimulates follicle growth at this point in time, while the
levels of FSH and LH are still relatively low. Follicles have no
receptors for LH at this point.
When estrogen begins to rise by the growing follicles, there is a
steep increase in the levels of both of these hormones due to a
response by the GnRH.
At this point follicles have LH receptors, and ovulation is triggered
in response to the large LH concentration.
Ovulation takes place about a day after this surge.
Ovulation is when the follicle and adjacent wall of the ovary rupture
and release the oocyte.
Luteal Phase
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The follicular tissue left behind in the ovary, form the corpeus
lateum, a glandular structure.
Under continued LH during the luteal phase, the corpus luteum
secretes estrogen and progesterone. It reaches its maximum
development about 8 to 10 days after ovulation.
As these levels rise, hormones exert negative feedback on the
hypothalamus inhibiting the secretion of LH and FSH.
The estrogen and progesterone subsequently go down.
The corpus luteum soon disintegrates.
Soon the pituitary gland secretes enough FSH to stimulate the
growth of follicles and start the cycle over again.
Conception to Birth


Placental males go through the process of
pregnancy (gestation), which is the process
of carrying developing individuals in the
uterus.
Pregnancy is preceded by conception, the
fertilization of the egg by a sperm cell, and
continues until the birth of the offspring.
Human pregnancy

It is divided into three trimesters.

The First Trimester is a period of the most
radical change for both the mother and the
baby.
First Trimester
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The egg is fertilized in the oviduct.
After 24 hours, the zygote begins dividing now called a cleavage.
By about a week, it is called a blastocyst, a sphere of cells.
This blastocyst implants itself into the endometrium, which then grows over the
blastocyst.
Until tissues grow out from the embryo and interacts with the endometrium to
form the placenta, an organ containing the embryonic and maternal blood
vessels, the endometrium provides nutrients to the embryo.
This is the main period of organogenesis.
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By the 4th week the heart starts beating
By the eigth week all major structures of the adult are present in rudimentary form.

HCG, human chorionic gondaotropin, is released which maintains secretion of
progesterone and estrogen by the corpus luteum through the first trimester.
Without this, menstruation would occur.

At this point it is known as a fetus.
Second Trimester

The fetus grows rapidly and is extremely
active.

Hormone levels stabilize as HCG declines,
the corpus luteum detoriorates, and the
placenta makes its own progesterone.
Third trimester

Once again the fetus grows rapidly.

During this trimester, Oxytocin receptors in the
uterus are formed.
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Oxytocin, produced by both the fetus and the mother’s
pituitary gland, stimulate powerful contractions by the
smooth muscles of the uterus.
It also enhances contractions
The stresses associated with contractions, stimualte
the release of more oxytocin and prostagladins, a
positive feedack system that underlies the three
stages of labor.
Birth


Birth, or parturition, occurs through a series
of strong rhytmic uterine contractions.
The second stage is the elivery of the baby.
–
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Strong contractions force the fetus down and out
of the uterus and vagina.
The final stage is the delivery of the placenta
which follows the baby.
LACTATION
THE END