Animal Reproduction Ch. 46

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Animal ReproductionCh. 46
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Reproductive Variations

• More than just the mating of males and females
• Hermaphroditism
• Sessile animals such as barnacles, clams,
  tapeworms
• Change sex during a lifetime
• Bluehead wrasse (coral reef fish) and oysters
• Ability to fertilize own eggs
• Reproduce without sex
• Only a few individuals in a population capable of
  reproducing

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Asexual vs. SexualReproduction

• Asexual
• Production of offspring whose genes come from one
  parent without the fusion of gametes
• Relies entirely on mitotic cell division
• Sexual
• Production of offspring by the fusion of gametes
  to form a diploid zygote
• Gametes formed by meiosis
• Ovum
• female gamete, large, nonmotile
• Sperm
• male gamete, small, motile

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Asexual Reproduction
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Asexual Reproduction - Types

• Fission
• separation of parent into two or more individuals
  of approximately equal size
• Bacteria, amoeba, sea anemone
• Budding
• a new individual splits off the existing one
• may detach from the parent or form extensive
  colonies
• Hydra

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Asexual Reproduction - Types

• Fragmentation
• breaking of adult body into several pieces
• each piece develops into an adult
• must be accompanied by regeneration
• Sponges, flatworms, polychaete worms

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Asexual Reproduction - Types

• Parthenogenesis
• Egg develops without being fertilized
• Progeny can be 2n or n
• If n the offspring develop into adults that
  produce eggs/sperm without meiosis
• Honeybees, rotifers, Daphnia, Komodo dragon,
  hammerhead shark

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Comparing Asexual and Sexual Reproduction
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Asexual Reproduction - Advantages

• Allows animals living in isolation to produce
  offspring without finding a mate
• Production of offspring in a short period of time
• Perpetuates successful genotypes precisely

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Sexual Reproduction - Advantages

• Combination of genes inherited from both parents
• Increases genetic variability
• Advantageous in a fluctuation environment

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Reproductive Cycles

• Related to changing seasons
• Allows for conservation of resources
• Controlled by hormones which are regulated by
  environmental cues
• Timing of ovulation
• Complex form of parthenogenesis

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Fertilization

• Union of sperm and egg
• Pheromones
• Chemical signals that may be used to attract
  mates
• Two types
• External fertilization
• Internal fertilization

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External fertilization

• Eggs shed by a female and are fertilized by a
  males sperm in the environment
• Occurs almost exclusively in moist habitats
• Courtship may play a role
• Pheromones may trigger the release of gametes
• Spawning
• Clusters of individuals release gametes at the
  same time

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Fertilization
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Internal fertilization

• Occurs when sperm are deposited in or near the
  female reproductive tract and fertilization
  occurs within the tract
• More sophisticated reproductive systems needed
• Mating behaviors include specific reproductive
  signals
• Production of fewer gametes but a high survival
  rate for the zygotes

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Gamete Production and Delivery

• Sexual reproduction relies on sets of precursor
  cells to egg and sperm
• Gonads
• Gamete producing organ
• Presence of cloaca in nonmammalian vertebrates
• Monogamy rare amongst animals

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Mammalian Reproductive System
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Mammalian Reproduction - Female

• External
• Clitoris
• Homologous tissues to the erectile tissue in the
  penis
• Labia
• cover and protect clitoris and vaginal opening

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Mammalian Reproduction - Female

• Internal
• Ovaries
• contains follicles
• Which contains an oocyte
• produce estrogen
• Cervix
• neck of uterus
• opens into the vagina

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Mammalian Reproduction - Female

• Internal
• Oviduct
• Extends from uterus to ovary
• Site of fertilization
• Uterus
• Muscular organ lined with endometrium
• Holds developing fetus
• Vagina
• Repository for semen
• Forms the birth canal opens at the vulva

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Mammalian Reproduction - Female

• Internal
• Mammary glands
• small sacs of epithelial tissues that secrete
  milk
• milk drains into ducts that open at the nipple

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Mammalian Reproduction - Male

• External
• Scrotum
• hold the testes
• allow sperm development at 2oC below body temp.
• Penis
• allows semen to leave the urethra and enter the
  female

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Mammalian Reproduction - Male

• Internal
• Testes
• seminiferous tubules where the sperm form
• Leidig cells produce testosterone
• Epididymis
• storage and maturation of sperm

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Mammalian Reproduction - Male

• Vas deferens
• carries sperm from epididymis to the ejaculatory
  duct
• Urethra within the Penis
• joins the ejaculatory duct and allows semen to
  enter the female tract
• Accessory Organs
• Seminal vesicles
• secrete a fluid containing amino acids, fructose,
  and prostaglandins
• Prostate gland
• secretes a thin, milky fluid that contains many
  enzymes
• Bulbourethral gland
• secretes mucus prior to ejaculation

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Spermatogenesis

• Continuous production in adult males
• Process takes 7 wks
• 100-650 million sperm/ejaculation
• After meiosis, 4 sperm cells result
• gt 100 acrosomal enzymes to fertilize an egg

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Figure 46.11x Spermatogenesis Seminiferous
tubules (left), sperm in semen (right)
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Oogenesis

• Development of ova
• mature, unfertilized egg cells
• At puberty meiosis I occurs once during each
  menstrual cycle
• Upon fertilization,meiosis II occurs
• results in ova and polar bodies

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Ovulation

• Egg expelled from the follicle
• Remaining follicular tissue results in the corpus
  luteum
• Egg enters oviduct
• No fertilization ? corpus luteum degenerates
• Travels to uterus and implants

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Female Reproductive Cycle

• Menstruation
• Cyclic shedding of the blood rich endometrium
• Menstrual/Uterine Cycle
• Proliferative phase
• Secretory phase
• Menstrual flow phase
• Ovarian Cycle
• Follicular phase
• Luteal phase
• Menopause

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Male Reproductive Cycle

• Sertoli cells
• Nourish sperm
• Lydig cells
• Secrete testosterone
• Negative Feedback

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Key Hormones

• Gonadotropin Releasing Hormone GnRH
• hypothalamus
• stimulates release of LH and FSH
• Follicle Stimulating Hormone (FSH)
• anterior pituitary
• male spermatogenesis
• female initial development of ovarian follicle

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Key Hormones

• Luteinizing Hormone (LH)
• anterior pituitary
• male release of testosterone
• female promote release of estrogen and
  progesterone further development of follicle
  peak of LH is trigger for ovulation event

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Key Hormones

• Testosterone
• interstitial cells
• prenatal development of male organs
• puberty development enlargement of sexual
  organs
• adulthood raises metabolic rates, increases sex
  drive, stimulates sperm production maturation,
  increases bone and muscle mass

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Key Hormones

• Estrogen
• follicle cells, corpus luteum
• development of primary secondary sex
  characteristics
• high levels inhibit GnRH
• Progesterone
• follicle cells, corpus luteum
• development of mammary tubules
• high levels inhibit GnRH

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Key Hormones

• Oxytocin
• maternal and fetal sources
• levels are cyclic highest at night
• increases force and frequency of contractions (
  feedback)
• induces milk letdown (suckling causes feedback)

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Key Hormones

• Prolactin
• anterior pituitary
• stimulates milk production
• as long as milk is removed, more prolactin is
  produced

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Fusion of egg and sperm

• Acrosome
• Specialized vesicle at the tip of the sperm
• Acrosomal reaction
• Discharge of hydrolytic enzymes make a hole in
  the jelly coat of the egg
• Fertilization

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Chromosomes fusing
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First Cleavage
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Conception to Birth

• Conception
• fertilization of egg by sperm cell
• Cleavage
• Division of the zygote after 24 hrs.
• 5 daysblastula(blastocyst)
• Gestation/Pregnancy
• Condition of carrying one or more embryos in the
  uterus
• hCG hormone
• 266 days from conception

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Conception to Birth
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Conception to Birth
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Conception to Birth
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Conception to Birth

• First trimester
• Cleavage begins 24 hours after fertilization
• Ball of 16 cells pass to the uterus
• 3-4 days embryo reaches the uterus and becomes a
  blastocyst
• Implants in the endometrium of the uterus within
  5 days

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Conception to Birth

• First trimester
• Determination
• Process by which a cell or group of cells becomes
  committed to a particular fate
• Differentiation
• Specialization in structure and function
• 3 germ layers differentiate
• endoderm (contributes to gut lungs)
• mesoderm (contributes to muscles, bone, and
  cardiovascular)
• ectoderm (skin and neural tube)

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Conception to Birth

• First trimester
• HcG produced to inhibit menstruation
• Morphogenesis
• Cellular and tissue based processes by which an
  animal body takes shape
• Organogenesis
• Development of body organs
• Placenta begins to form by the third week
• After 8 weeks embryo ? fetus

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Figure 46.18 Human fetal development
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Conception to Birth

• Second trimester
• Fetus grows rapidly to 30 cm
• May feel movement
• Hormone levels stabilize
• Uterus grows significantly

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Conception to Birth

• Third trimester
• Fetus grows to 50 cm in length and 3-3.5 kg
• High estrogen levels trigger oxytocin
• stimulates uterus to contract
• Childbirth begins with labor
• A series of strong, rhythmic uterine contractions
  that push the fetus and placenta out of the body
• Oxytocin stimulates prostaglandins
• causes vaginal wall to contract

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Fetal Development and Birth
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Birth