Pangea 250 mya

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Mammalian ReproductionPart II Process
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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

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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.

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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

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Placental Types - Choriovitelline
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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)

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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

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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

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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

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Placental Types - Choriovitelline
Marsupial
Peramelid
Placental
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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

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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

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Placental Types - Chorioallantoic
V 20.3
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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

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Placental Types ChorioallantoicPlacental Types
Epitheliochorial
Endotheliochorial
Hemoendothelial
Syndesmochorial
Hemochorial
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Placental Types ChorioallantoicPlacental Types

• Epitheliochorial
• All 6 layers
• Least intimate
• Loose association between maternal/fetal tissues
• Non-deciduous
• Pigs, horse, lemurs, whales

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Placental Types ChorioallantoicPlacental Types

• Syndesmochorial
• Uterine epithelium eroded
• Deciduous
• Ruminants (goats, sheep, cows)

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Placental Types ChorioallantoicPlacental Types

• Endotheliochorial
• Erosion of maternal connective tissue and uterine
  epithelium
• Deciduous
• Carnivores

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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

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Placental Types ChorioallantoicPlacental Types

• Hemoendothelial
• All tissue eroded except fetal endothelium
• Surrounded by maternal blood
• Deciduous
• Lagomorpha, some rodents

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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

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Placental Types ChorioallantoicPlacental Types
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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)

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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

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Patterns of Reproduction Spontaneous Ovulation

• Spontaneous Ovulation (most mammals)
• Ovulation
• Copulation
• Fertilization
• Implantation
• Gestation
• Parturition
• Lactation

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Patterns of Reproduction Induced Ovulation

• hares/rabbits
• Copulation
• Ovulation
• Fertilization
• Implantation
• Gestation
• Parturition
• Lactation

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Patterns of Reproduction Delayed 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

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Patterns of Reproduction Delayed 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

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Patterns of Reproduction Delayed 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

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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

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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

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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

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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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