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Mammalian Reproduction Part II – Process

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Mammalian Reproduction Part II – Process. The Placenta. Physically anchors fetus to uterus Transport nutrients O 2 /waste to/from fetus Synthesizes hormones for maintaining pregnancy Maternal/fetal blood separate Fetus is a foreign object to mother Fetus carries ½ father proteins

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the placenta
The Placenta
  • Physically anchors fetus to uterus
  • Transport nutrients O2/waste to/from fetus
  • Synthesizes hormones for maintaining pregnancy
  • Maternal/fetal blood separate
    • Fetus is a foreign object to mother
    • Fetus carries ½ father proteins
    • Different self-recognition proteins
the placenta3
The Placenta
  • Protects fetus from bacteria and larger molecules
  • Eutherian placenta composed of fetal/maternal tissue
  • Eutherian placenta produces some nutrients
  • All mammals have a placenta of some type. Best developed in eutherians.
placental types choriovitelline
Placental Types - Choriovitelline
  • Yolk-sac placenta
  • Most primitive
  • Monotremes/Marsupials (except peramelidae)
  • Vascularization between chorion and large yolk sac
  • Yolk sac enlarged and passes nutrients
placental types choriovitelline6
Placental Types - Choriovitelline
  • Monotremes:
    • Fetus receives nutrients from “uterine milk”
    • Once egg forms, it is laid (platypus) or transferred to pouch (Echidna)
    • Young hatch at undeveloped stage (altricial)
placental types choriovitelline7
Placental Types - Choriovitelline
  • Platypus
    • Eggs incubated for 11-12 days
    • Hatchlings are ~11mm long
    • Platypus do not have nipples, but have milk producing areas with hair tufts
    • Weaning at 21 days
placental types choriovitelline8
Placental Types - Choriovitelline
  • Echidnas:
    • Egg retained in pouch
    • Young ~1.5mm long
    • Nurse ~100 days
    • Ejected from pouch 50-60 days because spines form
    • Weaning at 140-150 days
placental types choriovitelline9
Placental Types - Choriovitelline
  • Marsupials:
    • Blastocyst sinks into depression in uterine mucosa
    • Contact strengthened by folding of blastocyst wall in contact with uterus
    • Embryo nourished by “uterine milk” secreted by uterine mucosa
    • Limited diffusion across placenta
placental types choriovitelline10
Placental Types - Choriovitelline

Marsupial Peramelid Placental

placental types chorioallantoic
Placental Types - Chorioallantoic
  • Peramelids (bandicoots) and all eutherians
  • Fusion involves chorion and allantois
  • Greater degree of intimacy between fetus and mother
  • Six tissue layers potentially involved:
    • M. endothelium F. epithelium
    • M. connective tissue F. connective tissue
    • Uterine epithelium F. endothelium
placental types chorioallantoic12
Placental Types - Chorioallantoic
  • Peramelid Design:
    • Less effective than eutherian
    • Blastocyst rests on uterus on side with allantois
    • Large, vascularized allantois
    • Lacks villi between fetal/maternal tissue
    • Uterus becomes vascularized at contact point
placental types chorioallantoic14
Placental Types - Chorioallantoic
  • Eutherian Design:
    • Blastocyst adheres, then sinks into uterus
    • Villi form and uterus becomes vascularized
    • Tissue may be eroded during implantation leading to different degrees of intimacy
    • Fetal contribution to placenta must be expelled from mother
      • Deciduous: afterbirth of fetal/maternal placenta
      • Non-deciduous: maternal placenta retained
placental types chorioallantoic placental types
Placental Types – ChorioallantoicPlacental Types

Epitheliochorial Endotheliochorial Hemoendothelial

Syndesmochorial Hemochorial

placental types chorioallantoic placental types16
Placental Types – ChorioallantoicPlacental Types
  • Epitheliochorial:
    • All 6 layers
    • Least intimate
    • Loose association between maternal/fetal tissues
    • Non-deciduous
    • Pigs, horse, lemurs, whales
placental types chorioallantoic placental types17
Placental Types – ChorioallantoicPlacental Types
  • Syndesmochorial:
    • Uterine epithelium eroded
    • Deciduous
    • Ruminants (goats, sheep, cows)
placental types chorioallantoic placental types18
Placental Types – ChorioallantoicPlacental Types
  • Endotheliochorial:
    • Erosion of maternal connective tissue and uterine epithelium
    • Deciduous
    • Carnivores
placental types chorioallantoic placental types19
Placental Types – ChorioallantoicPlacental Types
  • Hemochorial:
    • Erosion of all maternal tissues
    • Fetal tissue in direct contact with maternal blood
    • Deciduous
    • Some insectivores, bats, higher primates, most rodents
placental types chorioallantoic placental types20
Placental Types – ChorioallantoicPlacental Types
  • Hemoendothelial:
    • All tissue eroded except fetal endothelium
    • Surrounded by maternal blood
    • Deciduous
    • Lagomorpha, some rodents
placental types chorioallantoic placental shape
Placental Types – ChorioallantoicPlacental Shape
  • Shape of the placenta determined by distribution of villi
    • Diffuse:
      • Villi over entire chorion
    • Cotylenodary:
      • Evenly spaced groups over entire chorion
    • Zonary:
      • Band of villi around equator of chorion
    • Discoidal:
      • Villi in one or two discs
birthing process
Birthing Process
  • Passage of embryo is difficult
  • Relaxin: hormone that relaxes pelvic ligaments and symphysis
  • Oxytocin: initiates contractions
  • Pelvic Passage:
    • Modifications to enlarge pelvis include resobtion of connective tissue joining pubic bones (gophers) or realignment of digestive tracts to be ventral to pelvis (moles)
birthing process24
Birthing Process
  • When placenta tears away it leaves scars on uterus
  • Counting scars gives indication of number of young produced
  • Nulliparous = 0 young
  • Multiparous = multiple litters
patterns of reproduction spontaneous ovulation
Patterns of ReproductionSpontaneous Ovulation
  • Spontaneous Ovulation (most mammals):
    • Ovulation
    • Copulation
    • Fertilization
    • Implantation
    • Gestation
    • Parturition
    • Lactation
patterns of reproduction induced ovulation
Patterns of ReproductionInduced Ovulation
  • hares/rabbits:
    • Copulation
    • Ovulation
    • Fertilization
    • Implantation
    • Gestation
    • Parturition
    • Lactation
patterns of reproduction delayed fertilization
Patterns of ReproductionDelayed Fertilization
  • Temperate bats:
    • Copulation
    • DELAY
    • Ovulation
    • Fertilization
    • Implantation
    • Gestation
    • Parturition
    • Lactation
  • Good for species with long dormancy
  • Viable sperm stored through winter/hibernation
    • Up tp 70-80 days
    • Sperm attach to uterine wall, receive nutrients
patterns of reproduction delayed implantation
Patterns of ReproductionDelayed Implantation
  • Insectivores, rodents, bears, mustelids, seals, armadillos, some bats:
    • Ovulation
    • Copulation
    • Fertilization
    • DELAY
    • Implantation
    • Gestation
    • Parturition
    • Lactation
  • Obligate (bears) or facultative
  • Embryo develops to blastocyst, remains in uterus until spring then continues to develop
patterns of reproduction delayed development
Patterns of ReproductionDelayed Development
  • Blastocyst implants, but delays development
  • Jamaican Fruit Bat example
    • March April: Birth 1st young, estrous
    • Apr/May: pregnant and nursing
    • Jul/Aug: birth to 2nd young, estrous, new blastocyst implants
    • Sep-Mar: implanted young delays then grows
embryonic diapause
Embryonic Diapause
  • Macropodid Marsupials
  • Mates and produces young (Joey)
  • If conditions good, reproduce again
  • Presence of joey causes 2nd embryo to arrest
  • 2nd young born when joey leaves pouch
  • Possible mating again to have 3 young
    • Joey outside pouch
    • Joey inside Pouch
    • Embryo arrested
special problems of reproduction
Special Problems of Reproduction
  • Cursiorial Species:
    • Predator exposure problems
    • Camouflaged young
    • Precocial young
  • Arboreal Species:
    • Less predator problems
    • Altricial young
    • More development may be needed for mental acuity
special problems of reproduction34
Special Problems of Reproduction
  • Aquatic Species:
    • Cetaceans:
      • Birthing as a breach to prevent drowning
      • Rich milk for fast growth of blubber
    • Pinnipeds:
      • Come on land to birth
      • Need to return to sea for forage
        • Short lactation, high fat, maternal body reserves
        • Longer lactation, foraging trips by female
special problems of reproduction37
Special Problems of Reproduction
  • Aerial Species:
    • Disproportionately large young
      • Up to 50% adult weight
    • Adult females larger than males, esp. wings
      • Some Females carry young
      • Others use nest
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