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  • 胎盘哺乳动物

    Kangaroo running on grass, illustrating characteristics of marsupials, not placental mammals.

    Is this kangaroo a placental mammal?
    ::袋鼠是胎盘哺乳动物吗?

    You know that female kangaroos have a pouch for the final of their babies. So, no, kangaroos are not placental mammals. What is a placental mammal?
    ::你知道雌性袋鼠有一个邮袋 用来最后的婴儿。所以,不,袋鼠不是胎盘哺乳动物。什么是胎盘哺乳动物?

    Therian Mammals
    ::Therian 哺乳动物

    Like other female vertebrates , all female mammals have ovaries . These are the organs that produce eggs (see Figure ). Therian mammals also have two additional female reproductive structures that are not found in other vertebrates. They are the uterus and vagina .
    ::与其他雌脊椎动物一样,所有雌性哺乳动物都有卵巢,这些是产卵的器官(见图 ) 。 雄性哺乳动物还有另外两种女性生殖结构,在其他脊椎动物中找不到,它们是子宫和阴道。

    • The uterus (plural, uteri) is a pouch-like, muscular organ. The embryo or fetus develops inside the uterus. Muscular contractions of the uterus push the offspring out during birth.
      ::子宫(多胞胎、子宫)是一种象邮袋一样的肌肉器官,胚胎或胎儿在子宫内发育,子宫的肌肉收缩将子孙在分娩期间推出。
    • The vagina is a tubular passageway through which the embryo or fetus leaves the mother’s body during birth. The vagina is also where the male deposits during mating .
      ::阴道是胚胎或胎儿在分娩期间离开母亲身体的管状通道,阴道也是男方在交配期间沉积的地方。

    The female reproductive system of a therian mammal with labeled structures.

    Female Reproductive System of a Therian Mammal (Human). Therian mammals are viviparous , giving birth to an embryo or infant rather than laying eggs. The female reproductive system of all therian mammals is similar to that of humans.
    ::女性哺乳动物生殖系统(人类):遗传哺乳动物具有活力,生育胚胎或婴儿,而不是产卵;所有遗传哺乳动物的女性生殖系统与人类相似。

    Therian mammals are divided into two groups: placental mammals and mammals. Each group has a somewhat different reproductive strategy.
    ::遗传哺乳动物分为两组:胎盘哺乳动物和哺乳动物,各组的生殖战略略有不同。

    Placental Mammals
    ::胎盘哺乳动物

    Placental mammals are therian mammals in which a placenta develops during . sustains the fetus while it grows inside the mother’s uterus. Placental mammals give birth to relatively large and mature infants . Most mammals are placental mammals.
    ::胎盘哺乳动物是一种胎盘在...期间发育的胎盘哺乳动物,在母亲的子宫内生长时,胎盘哺乳动物会维持胎儿的生长。胎盘哺乳动物生育的婴儿数量相对较大,而且较成熟。大多数胎盘哺乳动物都是胎盘哺乳动物。

    The Placenta
    ::胎盘

    The placenta is a spongy structure. It consists of membranes and from both mother and embryo (see Figure ). The placenta passes oxygen, nutrients , and other useful substances from the mother to the fetus. It also passes carbon dioxide and other wastes from the fetus to the mother. The placenta lets from the fetus and mother exchange substances without actually mixing. Thus, it protects the fetus from being attacked by the mother’s immune system as a “foreign parasite .”
    ::胎盘是一种海绵结构,由膜和母子和胚胎组成(见图 ) 。胎盘将氧、养分和其他有用物质从母亲传给胎儿。胎盘还将二氧化碳和其他废物从胎儿传给母亲。胎盘让胎儿和母子相互交换物质而不实际混合。 因此,胎盘保护胎儿免受母亲作为“外国寄生虫”的免疫系统攻击。

    A human placenta showing structure and fetus for educational purposes.

    Placenta of a Placental Mammal (Human). The placenta allows the exchange of gases, nutrients, and other substances between the fetus and mother.
    ::胎盘允许胎儿和母亲之间交换气体、营养物质和其他物质。

    Pros and Cons of Placental Reproduction
    ::原产地和原产地的有利和有利

    The placenta permits a long period of fetal growth in the uterus. As a result, the fetus can become large and mature before birth. This increases its chances of surviving.
    ::胎盘允许子宫胎儿长时期生长,因此胎儿在出生前可以长大成熟,增加存活的机会。

    On the other hand, supporting a growing fetus is very draining and risky for the mother. The mother has to eat more food to nourish the fetus. She also becomes heavier and less mobile as the fetus gets larger. As a result, she may be less able to escape from predators . Because the fetus is inside her, she can’t abandon it to save her own life if she is pursued or if food is scarce. Giving birth to a large infant is also risky. It may even result in the mother’s death.
    ::另一方面,抚养一个成长中的胎儿对母亲来说是非常耗尽和危险的。 母亲必须吃更多的食物来养育胎儿。 随着胎儿长大,她也会变的更重、流动性更小。 结果,她可能更没有能力逃离食肉动物。 由于胎儿在她体内,如果追求胎儿,或者食物短缺,她不能为了拯救自己的生命而放弃它。 生一个大的婴儿也是危险的。 这甚至可能导致母亲死亡。

      

     

    Summary
    ::摘要

    • Therian mammals are viviparous. They give birth to an embryo or infant rather than laying eggs.
      ::动物哺乳动物是活生生的,它们产下胚胎或婴儿,而不是产卵。
    • The female reproductive system of a therian mammal includes a uterus and a vagina.
      ::哺乳动物的雌性生殖系统包括子宫和阴道。
    • There are two groups of therian mammals: placental mammals and marsupials.
      ::有两组哺乳动物:胎盘哺乳动物和哺乳动物。
    • Placental mammals give birth to a relatively large and mature fetus. This is possible because they have a placenta to nourish the fetus and protect it from the mother’s immune system. This allows for a long period of growth and development before birth.
      ::胎盘哺乳动物生下相对较大和成熟的胎儿。 这是可能的,因为他们有一个胎盘来养活胎儿,保护胎儿免受母亲免疫系统的伤害。 这使得胎儿在出生前可以长时期发育发育。
    • Because the offspring of placental mammals is relatively large and mature at birth, it has a good chance of surviving. However, carrying and giving birth to a large fetus is risky for the mother. It also requires her to eat more food.
      ::由于胎盘哺乳动物的后代在出生时相对较大和成熟,它有存活的良好机会,然而,携带和生下大胎儿对母亲来说是危险的,还需要她多吃点食物。

    Review
    ::回顾

    1. What are therian mammals? What structures are found in these mammals that are absent in other vertebrates?
      ::动物哺乳动物是什么?在这些哺乳动物中发现了其他脊椎动物所缺少的哪些结构?
    2. What are the functions of the uterus and vagina in therian mammals?
      ::子宫和阴道在哺乳动物体内的功能是什么?
    3. What is the placenta?
      ::什么是胎盘?
    4. Describe how the placenta functions?
      ::描述胎盘的功能吗 ?
    5. Placental mammals greatly outnumber the other two groups of mammals. Infer why placental mammals have been so successful.
      ::胎盘哺乳动物的数量大大超过另外两组哺乳动物,因此,胎盘哺乳动物为什么如此成功。