Animal Reproduction

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Animal Reproduction

• Chapter 46

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Reproduction in the Animal Kingdom

• Sexual
• Asexual
• Fission
• Budding
• Fragmentation Regeneration
• Parthenogenesis? egg develops without being
  fertilized

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Parthenogenesis

• Development of an unfertilized egg
• honey bees
• drones males produced through parthenogenesis ?
  haploid
• workers queens females produced from
  fertilized eggs ? diploid

queen
worker
drone
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Reproductive Cycles and Patterns

• Most animals exhibit cycles in reproductive
  activity
• Often related to changing seasons
• Reproductive cycles
• Are controlled by hormones and environmental cues

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Fertilization

• Plays an important part in sexual reproduction
• Joining of egg sperm
• external
• usually aquatic animals
• internal
• usually land animals

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Patterns of Sexual Reproduction

• External fertilization, external development
• Internal Fertilization, External Development
• Internal Fertilization, Internal Development

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Hermaphrodites

• Certain Organisms seldom encounter a mate
• Solution ? hermaphroditism
• In which each individual has both male and female
  reproductive

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Sequential Hermaphroditism

• An individual reverses its sex during its lifetime

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Male Reproductive System
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Male Reproductive System

• Testicles
• produces sperm hormones
• Scrotum
• sac that holds testicles outside of body
• Epididymis
• where sperm mature
• Vas deferens
• tubes for sperm to travel from testes to penis
• Prostate, seminal vesicles, Cowpers
  (bulbourethal) glands
• nutrient rich fluid to feed protect sperm
• buffer to counteract acids in vagina

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Male reproductive system

• Sperm production
• over 100 million produced per day!
• 2.5 million released per drop!
• Testes epididymis
• sperm production maturation
• Glands
• seminal vesicles, prostate, bulbourethal
• produce seminal fluid nutrient-rich

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Spermatogenesis
Testis
Epididymis
Germ cell (diploid)
Coiled seminiferous tubules
1 spermatocyte (diploid)
MEIOSIS I
2 spermatocytes (haploid)
MEIOSIS II
Vas deferens
Spermatids (haploid)
Spermatozoa
Cross-section of seminiferous tubule
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Female Reproductive System
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Female Reproductive System

• Ovaries
• produces eggs hormones
• Uterus
• nurtures fetus lining builds up each month
• Fallopian tubes
• tubes for eggs to travel from ovaries to uterus
• Cervix
• opening to uterus, dilates 10cm (4 inches) for
  birthing baby
• Vagina
• birth canal for birthing baby

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Female Reproductive System
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Oogenesis

• What is the advantage of this development system?

Meiosis 1 completed during egg maturation
ovulation
Meiosis 2 completed triggered by fertilization
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The reproductive cycle of the human female

• The Ovarian Cycle
• The Uterine (Menstrual) Cycle
• Menopause

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Female Hormones

• FSH LH
• release from pituitary
• stimulates egg development hormone release
• peak release release of egg (ovulation)
• Estrogen
• released from ovary cells around developing egg
• stimulates growth of lining of uterus
• lowered levels menstruation
• Progesterone
• released from corpus luteum in ovaries
• cells that used to take care of developing egg
• stimulates blood supply to lining of uterus
• lowered levels menstruation

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The Ovarian Cycle

• In the ovarian cycle
• Hormones stimulate follicle growth, which results
  in ovulation
• Following ovulation
• The follicular tissue left behind transforms into
  the corpus luteum

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The Uterine (Menstrual) Cycle

• Occurs when the endometrium is shed
• Three Phases
• Mentrual Flow Phase? endometrium is shed and
  mentrual bleeding occurs
• Proliferative Phase? endometrium regenerates
  thickens
• Secretory Phase?endometrium thickens, if an
  embryo has not implanted by the end of this
  phase?A new menstrual flow commences

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Menopause

• After about 450 cycles, human females undergo
  menopause
• The cessation of ovulation and menstruation

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Fertilization
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Placental Mammals

• Human Chorionic Gonadotropin
• Secreted by embryo acts like LH to maintain the
  Corpus Luteum
• Excreted in urine
• Parturition
• Birth in late pregnancy estrogen increases
• This stimulates oxytocin receptors
• Oxytocin from fetus and mother stimulate
  contractions

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Hormonal Control of the Male Reproductive System

• Testosterone and other androgens
• Are directly responsible for the primary and
  secondary sex characteristics of the male

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Androgen secretion and sperm production?
controlled by hypothalamic and pituitary hormones
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Conception, Pregnancy and Birth

• Blastocyst
• Implants by burrowing endometrium grows over
• Provides nutrients first 2-4 weeks

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Placenta? Derived from both maternal and fetal
cells? produce progesterone

• Materials exchange across membranes

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Human fetal development

• The fetus just spends much of the 2nd 3rd
  trimesters just growing
• and doing various flip-turns kicks inside
  amniotic fluid

Week 20
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Human fetal development

• 24 weeks (6 months 2nd trimester)

fetus is covered with fine, downy hair called
lanugo. Its skin is protected by a waxy material
called vernix
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Human fetal development

• 30 weeks (7.5 months)

umbilical cord
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Getting crowded in there!!

• 32 weeks (8 months)

The fetus sleeps 90-95 of the day sometimes
experiences REM sleep, an indication of dreaming
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Birth
Hormone induction
positive feedback
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Birth (36 weeks)
Intestine
Placenta
Umbilical cord
Wall of uterus
Bladder
Cervix
Vagina
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The end of the journey!
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Mechanisms of some contraceptive methods
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RU486

• Progesterone analog
• Blocks progesterone receptors in uterus lining
  is shed
• Prostaglandins also taken

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Reproductive Technologies

• Ultrasound
• Amniocentesis
• Chorionic Villi Sampling (CVS)
• In Vitro Fertilization (IVF) or GIFT