Topic 2 Human Reproductive Anatomy: Differences in Development

Question 1

• Fish and amphibians have external fertilization (ovuliparity) in water, to prevent gametes from drying out, and to allow sperm to swim to the egg. This requires cooperative mating behaviors to ensure simultaneous egg and sperm release.
  a. There is no copulation in external fertilization!
  b. Ovuliparity - external fertilization

Answer 1

External Development

Question 2

• Reptiles, birds, and some mammals (monotremes) have internal fertilization, which requires cooperative behavior leading to copulation. These organisms then lay eggs (oviparous; if the egg hatches to live young internally or immediately after release, ovoviviparous). There are no placenta or tropic interactions between the zygote and parent.
  a. Viviparity - birth to live young that was given nutrients during development
  b. Oviparity - egg is laid and hatches later
  c. Ovoviviparous - eggs are internal and birthed as live young, but the egg is not nourished in any way by the parent

Answer 2

Internal development

Question 3

• Certain animals like marsupials and tropical fish spend a short time in the uterus as embryos, then crawl out and complete development attached to a mammary gland in the mother’s pouch! As the name suggests, there is no placenta, so there is limited exchange of food and oxygen between mother and young

Answer 3

Non-Placental Internal Development

Question 4

• Major components of this development in humans include the umbilical cord and placenta system. The oxygen is received directly from the mother (as fetal lungs are not functional until birth), as well as nutrients. CO2 and metabolic wastes are removed. The placenta and umbilical cord form from outgrowths of amnion, chorion, allantois, and the yolk sac. Amnion contains amniotic fluid as a shock absorber.
  i. Placenta formation - begins with chorion, and blood vessels of allantois wall enlarge and become umbilical vessels that connect the fetus with the developing placenta. The yolk sac becomes associated with umbilical vessels.

Answer 4

Placental Internal Development

Question 5

• Internal fertilization is typically associated with production of fewer games than external fertilization, but a higher % of survival of zygotes. This is because zygotes are sheltered from predators and have greater protection and care from mother. This is true even in oviparous animals (reptiles and birds lay eggs with shells and internal membranes that fish and amphibians lack).

Answer 5

Note

Question 6

• Group of tetrapods, four- limbed animals with backbones or spinal columns that have terrestrially adapted eggs that are supported by several extra embryonic membranes.
  i. Does not include amphibians or frogs

Answer 6

Amniotes

Question 7

• Mammals that lay leathery eggs, lack nipples, and are endothermic (but have an unusually low body temperature and metabolic rate compared to other mammals)
  i. Includes platypuses and echidnas

Answer 7

Monotremes