Reproductive System

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Reproductive System
Ch 46a
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Both asexual and sexual reproduction occur in the
animal kingdom

• Asexual reproduction involves the formation of
  individuals whose genes all come from one parent.
• There is no fusion of sperm and egg.
• Sexual reproduction is the formation of offspring
  by the fusion of haploid gametes.
• Ovum female gamete - usually large and
  nonmotile.
• Spermatozooan male gamete - usually small and
  motile.
• Sexual reproduction increases genetic variation
  among offspring.

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Asexual Reproduction
Sexual Reproduction
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Sexuality

• Hermaphroditism versus Gonochorism

Hermaphroditism both sexes in the same
individuals Gonochorism sexes are separate
Acropora sp., a hermaphoditic coral
Fungia scutaria, a gonochoric coral
eggs
egg cloud
sperm packet
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Brooding vs Broadcast Spawning
Brooding eggs develop to planula stage in
gastrovascular cavity of parent polyp Broadcast
Spawning eggs and sperm are shed into the water
column where fertilization and development occurs
D. Gulko
released gametes
planula in polyp
Pocillopora damicornis, a brooder
broadcast spawner
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• Sequential hermaphroditism an individual
  reverses its sex during its lifetime.
• Protogynous female to male
• Protandrous male to female

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Parthenogenesis

• Egg development without fertilization
• Aphid
• Daphnia
• Honeybee
• Whiptail lizard

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Internal and external fertilization both depend
on mechanisms ensuring that mature sperm
encounter fertile eggs of the same species

• Internal fertilization requires cooperative
  behavior that leads to copulation.

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• External fertilization requires a moist habitat
  that will protect a developing egg from
  desiccation and heat stress.
• Specific mating behaviors assure that sperm and
  egg will be in the same place at the same time.

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• Pheromones chemical signals released by one
  organism that influence the behavior of other
  individuals of the same species.
• Many act as male attractants.

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Species with internal fertilization usually
produce fewer zygotes but provide more parental
protection than species with external
fertilization

• Internal fertilization usually results in the
  production of fewer zygotes than does internal
  fertilization.
• However, the survival rate is lower for external
  fertilization than it is for internal
  fertilization.

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• The externally fertilized eggs of fishes and
  amphibians are surrounded by a gelatinous coat.
• The internally fertilized amniote eggs of birds,
  reptiles, and monotremes are protected by calcium
  and protein shells.
• In mammals the embryo is retained within the
  females reproductive tract.

Platypus egg
New born platypuses and Mom
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• Parental care ofoffspring may occurregardless
  of whetherfertilization is externalor internal.

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Complex reproductive systems have evolved in many
animal phyla

• The least complex reproductive systems lack
  gonads.
• Polychaete worms lack gonads.
• Eggs and sperm develop from undifferentiated
  cells lining the coelom.
• Some reproductive systems, such as that seen in
  parasitic flatworms, can be very complex.

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Reproductive anatomy of a parasitic flatworm
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• Most insects have separate sexes with complex
  reproductive systems.
• In many species the female reproductive system
  includes a spermatheca, a sac in which sperm may
  be stored for a year or more.

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• The basic plan of all vertebrate reproductive
  systems are very similar.
• However, there are variations.
• In many non-mammalian vertebrates the digestive,
  excretory, and reproductive systems share a
  common opening to the outside, the cloaca.
• Mammals have separate opening for the digestive
  and reproductive systems.
• Female mammals also have separate openings for
  the excretory and reproductive systems.

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Human reproduction involves intricate anatomy and
complex behavior

• Reproductive Anatomy of the Human Male.
• The scrotum and the penis are the external
  components of the reproductive system.
• The internal reproductive organs consist of
  gonads, accessory sex glands, and ducts.

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Male Reproductive System
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Male Reproductive System
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• External structure of the penis
• The shaft of the penis is covered by relatively
  thick skin.
• The sensitive glans penis is covered by thinner
  skin.
• The glans is covered by the prepuce which may be
  removed by circumcision.
• There is no verifiable health benefit to
  circumcision.

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• The penis is composed of three layers of spongy
  erectile tissue.
• During sexual arousal the erectile tissue fills
  with blood from arteries.
• The resultant increased pressure seals off the
  veins that drain the penis.
• The engorgement of the penis with blood causes an
  erection.
• An erection is essential to the insertion of the
  penis into the vagina.
• The penis of some mammals possesses a baculum, a
  bone that helps stiffen the penis.

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• Impotence can result from the consumption of
  alcohol and other drugs, and emotional, nervous
  system, or circulatory problems.
• Treatment includes drugs and penile implant
  devices.
• Viagra acts by promoting the action of nitric
  oxide.

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Testes
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• Testes are the male gonads.
• Consists of many highly coiled seminiferous
  tubules surrounded by layers of connective
  tissue.
• Sperm form in seminiferous tubules.
• Leydig cells (interstitial cells), scattered
  between seminiferous tubules produce androgens
  (ex. testosterone).

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• Testes are located in the scrotum, outside the
  body cavity.
• This keeps testicular temperature cooler than the
  body cavity.
• The testes develop in the body cavity and descend
  into the scrotum just before birth.

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• From the seminiferous tubules sperm pass to the
  coiled tubules of the epididymis.
• It takes about 20 days for sperm to pass through
  the tubules of the epididymis.
• In the epididymis sperm become motile and gain
  the ability to fertilize.

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• Semen
• Seminal fluid is thick, yellowish, and alkaline.
• It contains mucus, fructose, a coagulating
  enzyme, ascorbic acid, and prostaglandins.
• Accessory glands
• seminal vesicle
• prostate gland
• bulbourethral gland

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• Seminal vesicle
• A pair of glands that secrete a liquid component
  of semen into the vas deferens.
• Secretion is alkaline, which neutralizes the
  acidic condition of the female genital tract.
• Seminal fluid contains fructose.

Seminal Vesicle
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• Prostate gland
• Location- surrounds and opens into the urethra
  where it leaves the bladder.
• Secretion- slightly alkaline fluid that activates
  the sperm and prevents them from sticking
  together
• Prostate problems are common in males over 40.
• Prostate cancer is one of the most common cancers
  in men.

Prostate
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• Bulbourethral gland (Cowpers gland)
• Location- paired glands that lie beneath the
  prostate
• Secretion- a thick, clear alkaline mucous that
  drains into the membranous urethra.
• Function- It acts to wash residual urine out of
  the urethra when ejaculating semen-- raises pH
  neutralizes acidity of urine.

Bulbourethral gland
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Ejaculation

• Ejaculation propels sperm from the epididymis to
  the vas deferens.
• The vas deferens run from the scrotum and behind
  the urinary bladder.
• Here each vas deferens joins with a duct from the
  seminal vesicle to form an ejaculatory duct.
• The ejaculatory ducts open into the urethra.
• The urethra drains both the excretory and
  reproductive systems.

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Ejaculate

• A male usually ejaculates about 2 5 mL of
  semen each milliliter containing about 50 130
  million sperm.
• Bulbourethral fluid also carries some sperm
  released before ejaculation.
• This is one of the reasons why the withdrawal
  method of birth control has a high failure rate.

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Spermatogenesis
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Mature Spermatozoa
acrosome
head
nucleus
tail
mitochondria
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Seminiferous Tubules
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Seminiferous Tubules
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Sperm Maturation Development
(maturation 62-72 days)
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Hormones Involved in Spermatogenesis

• Gonadotropin Releasing Hormone (GnRH)
• Follicle Stimulating Hormone (FSH)
• Interstitial Cell Stimulating Hormone (ICSH),
  also called LH
• Testosterone
• Inhibin

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Hormonal Control of Spermatogenesis
Hypothalamus
GnRH
Anterior Pituitary
FSH
ICSH/LH
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Hormonal Control of Spermatogenesis
ICSH/LH
Interstitial Cells
Testosterone
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Hormonal Control of Spermatogenesis
Testosterone
FSH
Sertoli Cells
Spermatogenesis
Inhibin
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Feedback Inhibition
Hormonal Control of Spermatogenesis
Inhibin Acts on anterior pituitary Inhibits FSH
production Testosterone Acts on
hypothalamus Inhibits GnRH production
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Some Other Effects of Testosterone

• muscle and bone growth
• facial and pubic hair growth
• thickening of vocal cords
• growth of pharyngeal cartilage
• hair follicle effects
• stimulates sebaceous glands

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• Reproductive Anatomy of the Human Female
• External reproductive structures
• labia
• clitoris
• vaginal opening
• Internal reproductive structures
• ovaries
• fallopian tube (uterine tube)
• cervix
• uterus
• vagina
• fimbrae

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Biology 100 Human Biology
Female Reproductive System
uterine tube
fimbriae
ovary
uterus
bladder
cervix
urethra
clitoris
vagina
l. minora
l. majora
vaginal orifice
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egg
Biology 100 Human Biology
uterine tube
ovary
ovary
uterus
perimetrium
endometrium
myometrium
cervix
vagina
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Oogenesis in the Ovary
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• Oogenesis
• Ovary- contains 400,000 oocytes release about
  500 in a lifetime
• Ovary- under influence of FSH. The follicles
  mature every 28 days
• Primary follicle produces estrogens
• And primary oocyte completes its 1st division
  produces 2ndary oocyte and polar body

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• Oogenesis
• Aprox 1/2 way through the 28 day cycle the
  follicle reaches the mature Vesticular or
  Graffian follicle stage.
• Estrogen levels rise and release LH and FSH and
  triggers ovulation.
• The 2ndary oocyte travels down the uterine tube
  to the uterus.
• If fertilized by sperm, it will produce a zygote

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Oogenesis
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Ovum
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Hormones Involved in the Female Reproductive Cycle

• Gonadotropin Releasing Hormone (GnRH)
• Follicle Stimulating Hormone (FSH)
• Luteinizing Hormone (LH)
• Estrogen
• Progesterone

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Female Hormonal Cycle
Hypothalamus
GnRH
Anterior Pituitary
FSH
LH
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Female Hormonal Cycle
LH
FSH
Follicle Cells
Estrogen
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The Uterine Cycle
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Ovarian Cycle
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Hormone Fluctuation
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Some Other Effects of Estrogen

• breast development
• external genitalia growth
• stimulates bone growth
• increases HDL and lowers LDL

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• Menopause cessation of ovarian and menstrual
  cycles.
• Usually occurs between ages 46 and 54.
• Due to ovaries decreased responsiveness to
  gonadotropins.
• Menopause affects
• changes in sexual desire
• triggers mood swings
• causes debilitating hot flashes
• may lead to bone and heart problems
• short-term memory loss
• insomnia

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• Mammary glands.
• Are present in both males and females.
• Are not a component of the reproductive system.
• Contain epithelial tissue that secrete milk.
• Milk drains into a series of ducts opening at the
  nipple.