Mammalian Reproduction Part II – Process

1. Mammalian ReproductionPart II – Process

2. 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

3. 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.

4. 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

5. Placental Types - Choriovitelline

6. 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)

7. 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

8. 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

9. 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

10. Placental Types - Choriovitelline Marsupial Peramelid Placental

11. 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

12. 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

13. Placental Types - Chorioallantoic V 20.3

14. 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

15. Placental Types – ChorioallantoicPlacental Types Epitheliochorial Endotheliochorial Hemoendothelial Syndesmochorial Hemochorial

16. Placental Types – ChorioallantoicPlacental Types • Epitheliochorial: • All 6 layers • Least intimate • Loose association between maternal/fetal tissues • Non-deciduous • Pigs, horse, lemurs, whales

17. Placental Types – ChorioallantoicPlacental Types • Syndesmochorial: • Uterine epithelium eroded • Deciduous • Ruminants (goats, sheep, cows)

18. Placental Types – ChorioallantoicPlacental Types • Endotheliochorial: • Erosion of maternal connective tissue and uterine epithelium • Deciduous • Carnivores

19. 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

20. Placental Types – ChorioallantoicPlacental Types • Hemoendothelial: • All tissue eroded except fetal endothelium • Surrounded by maternal blood • Deciduous • Lagomorpha, some rodents

21. 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

22. Placental Types – ChorioallantoicPlacental Types

23. 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)

24. 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

25. Patterns of ReproductionSpontaneous Ovulation • Spontaneous Ovulation (most mammals): • Ovulation • Copulation • Fertilization • Implantation • Gestation • Parturition • Lactation

26. Patterns of ReproductionInduced Ovulation • hares/rabbits: • Copulation • Ovulation • Fertilization • Implantation • Gestation • Parturition • Lactation

27. 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

28. 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

29. 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

30. 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

32. 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

34. 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

37. 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