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Animal Reproduction (ch. 46-47)
Asexual vs. sexual reproduction
Slipper Shell (Slippery Limpet)

Reproduction is broken up into two general catagories, asexual and sexual. Sexual reproduction is characterized by the fusion of male and female haploid gametes, to create a single diploid zygote. This zygote possesses a mixture of genetic material from the two parents, but it is genetically unique. Asexual reproduction is facilitated by some kind of replication such as fission, budding, fragmentation with regeneration and parthogenesis.

Apart from these two methods of reproduction, there is hermaphoditism, which allows certain organisms to switch sex at will for reproduction. This is primarily used in invertebrates such as slipper-shells

Gamete production and delivery

Male gametes, sperm, are created in the testes. Starting with a primary spermatocyte, it divides into two secondary spermatocytes. Then each of the secondary spermatocytes divide into two spermatids, which then morph into mature sperm cells.
Female gametes, eggs, begin as a primary oocyte. The primary oocyte then divides into two secondary oocytes, but only one of these secondary oocytes become an egg. The other secondary oocyte becomes a polar body.

These gametes then fuse together to create a zygote. This fusion can take place externally and internally. External fertilization occurs when organisms release their gametes into a medium, such as air or water. This type is random and the gametes must be ready to face varying conditions and is generally practiced by fish and insects. Internal fertilization occurs inside the the female. This type of fertilization is generally practiced by mammals. Internal reproduction has a much higher success rate than external.

Female human reproductive anatomy

The female reproductive anatomy consists of the labia, glans, and clitoris externally.
Internally the female reproductive anatomy consists of the vagina, uterus, oviducts, and ovaries.
The vagina is a muscular but elastic chamber that is purposed as a sperm depository .
The uterus, or womb, is a muscular organ that is capable of expanding enough to accommodate a 4 kg fetus.
When eggs leave the ovaries, they move down the oviducts and stop in the uterus. Inside the uterus,
there are cilia to catch the egg as it moves through.
The oviducts, or fallopian tubes, receive eggs from the ovaries and carry them to the uterus.
The ovaries are the site that eggs are created.

Male human reproductive anatomy

The male reproductive anatomy consists of the testes, scrotum, and penis.
The testes produce sperm in tightly coiled tubes known as seminiferous tubules.
The scrotum is a sac that holds the testes. Human sperm can not survive at human body temperature
so the scrotum keeps the testes 2 degrees (Celsius) colder than the rest of the body.
The penis is a organ that is designed to engorge upon arousal. It contains urethra, tubes for the purpose
of transporting sperm.

Human fetal development

Soon after conception (about 24 hours) the zygote begins to divide. This process is called cleavage.
After 2-3 days of this process the egg arrives at the uterus. At the 5 day mark, it forms a blastocyst,
or a colony of cells to small to be considered a fetus, but to large to be considered an egg. After
this phase, it enters a gestation period of about 266 days. In this period, the cells divide many times
and begin to look like a fetus.

Animal development

The animal fetal development is broken into four sections, fertilization, cleavage, gastrulation, and organogenesis.
Fertilization works similarly in animals as it does in humans.
Cleavage works similarly in animals as it does in humans.
Gastrulation is the process that turns the blastocyst into a two or three layered embryo called a gastrula. These
extra layers are called germ layers. Each of these layers of cells are responsible for developing certain parts of
the organism.
In organogenesis, the germ layers develop into rudimentary organs