Reproduction

I. Some comparisons of mammalian infraclasses

  1. Similarities in reproduction between mammalian infraclasses:

    1. Internal fertilization
    2. Nourish young with milk from mammary glands
  1. Differences: mode of reproduction

    Prototheria Metatheria Eutheria
    Lay eggs Give birth to live, partially developed young Give birth to well developed young
    Epipubic bones Epipubic bones in most No epipubic bones
    Young left in nest or pouch-like abdominal groove Young carried on teats, often in pouch Young usually not carried attached to teats
    No placenta Usually a simple placenta, but some species more complex than others Complex placenta
    Altricial young Highly altricial young Altricial or precocial young

    II. Basic anatomy and physiology

    1. Female

      1. Structures of eutherian mammals(Fig. 10.4)

        1. ovary (2) - produce ova (singular= ovum)
        2. oviducts or fallopian tubes (2) - through which ovum travels
        3. uterus (1 or 2) - in which ovum implants and develops
        4. cervix (1 or 2) - seals uterus from external environment during fetal development and through which neonate passes at birth
        5. vagina (1) - connects internal reproductive tract with the external world

      1. Contrast with monotremes and marsupials (Fig. 11.1)

        1. Monotremes
          possess a cloaca
        2. Marsupials
          Dual vaginal canals; ureters join reproductive tract to form urogenital sinus
          Medial vaginal canal           (usually temporary)

      1. Types of eutherian reproductive systems (Fig. 10.8)

      Duplex

      Bipartite

      Bicornuate

      Simplex
      Uterus 2 2 separate uterine horns 1 uterus with 2 horns + body 1
      Cervix 2 1, but has 2 separate openings (one to each uterine horn) 1 1
      Vagina 1 1 1 1
      Examples rodents, rabbits pigs, carnivores insectivores, most ungulates, bats, some primates edentates, primates

      1. Neural and hormonal control of the estrous cycle (Fig. 10.6)


        FSH=follicle stimulating hormone
        E=estrogen
        LH=luteinizing hormone
        P=progesterone
        1. Development of uterine tissue and ovum within a follicle (FSH, E)
        2. Ovulation (LH)

          1). Spontaneous
          2). Induced

        1. Ruptured follicle becomes corpus luteum, secretes P
        2. If conception occurs, P maintains pregnancy
        3. If conception doesn't occur

          1). Corpus luteum regresses
          2). Uterine lining regresses
          3). Cycle starts over

      1. Contrast with primate menstrual cycle

    1. Male

      1. Structures (Fig. 10.2)

        1. Testes (2) - produce sperm

          1) Scrotal
          2) Abdominal (held entirely within the body cavity)
          ex. monotremes, edentates, elephants, cetaceans
          3) May be seasonal

        1. Epididymis (2) - in which sperm are stored
        2. Vas deferens (2) - through which sperm pass
        3. Urethra (1) - connects to outside, also carries urine
        4. Accessory glands - add secretions to sperm to make semen

        1) Prostate
        2) Bulbo-urethral (Cowper's)
        3) Vesicular (seminal vesicles)
        4) Function of secretions

        1. Penis - may contain a bone ( baculum, Fig. 10.3)
    1. Placenta = fusion of maternal and fetal tissues

      1. Functions

        1. Transfer of nutrients from mother to fetus
        2. Gas exchange
        3. Production of hormones

      1. Types (Fig. 10.10)

        1. Choriovitelline
        2. Chorioallantoic
        3. Membranes

          1) Chorion
          2) Allantois
          3) Amnion
        4. patterns of attachment and layers between maternal and fetal blood in eutherians

    1. Lactation
      1. Endocrine control
      2. Milk composition
        1. fat
        2. protein
        3. carbohydrate (lactose)
        4. colostrum

    III. Interesting mammalian reproductive strategies

    1. Usual sequence
      copulation -> ovulation-> fertilization -> implantation + pregnancy -> birth

    2. Variants

      1. Delayed fertilization
        copulation -> females store sperm -> fertilization

      2. Delayed implantation
        copulation -> ovulation -> fertilization-> early development -> dormancy -> implants and finishes development

      3. Delayed development
        copulation -> fertilization -> implantation -> dormancy -> resumption of development

      4. Embryonic diapause
      5. Spontaneous abortion