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

    1. Prototheria (subclass): eggs
    2. Metatheria: partly developed live-born neonates and simple placenta
    3. Eutheria: well developed neonates and complex placenta

Metatheria Eutheria
Small braincase Large braincase
Poorly developed auditory bullae Well developed auditory bullae
Small cerebral hemispheres Large cerebral hemispheres
Epipubic bones in most No epipubic bones
Young carried on teats, often in pouch Young usually not carried attached to teats
Simple placenta Complex placenta
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