Act. 22: VERTEBRATES UROGENITAL SYSTEM AND DEVELOPMENT

• Animals exhibit a diplontic life cycle.
• gametes (sex cells) as the only haploid cells
• Reproductive cells are produced in the gonads (the reproductive organs) in the process called gametogenesis.
• Spermatozoa or sperm cells, the male sex cells, are produced in the testes of the male animals through spermatogenesis.
• The ova or egg cells, the female sex cells, are formed in the ovaries of the female animals through oogenesis.
• the urogenital system is referred as the combination of the excretory and reproductive systems.
• In vertebrates, the principal excretory organs are the pairs of kidneys.
• ureters are paired ducts connecting the kidneys to the urinary bladders.
• The urine may be stored in a thin-walled, bilobed urinary bladder
• Cleavage is the process of cell growth and division such that the zygote turns into a multicellular morula embryo which eventually forms a cavity (blastocoel) and become a blastula embryo.
• Gastrulation is the process of cellular movement within the gastrula embryo so the three germ layers (endoderm, mesoderm, and ectoderm) are formed and the individual cells of the embryo start to undergo differentiation or the attainment of a cell’s specialized function.
• Anamniotes include birds and reptiles which have enough amount of yolk in the egg to support the development of the young
• amniotes such as mammals evolve the use of placenta to support their young within the uterus to adapt to the lack of yolk in their embryos.
• yolk small amounts (microlecithal),
• yolk moderate amounts (mesolecithal)
• large amounts of yolk (macrolecithal)
• yolk distributions: centrally-placed (centrolecithal)
• yolk distributions: at one end or pole (telolecithal)
• yolk distribution: evenly distributed (isolecithal/homolecithal).
• an egg that can be partially cleaved is said to be meroblastic
• egg that is totally cleaved is said to be holoblastic.
• The pigmented region is the animal pole or animal hemisphere.
• non-pigmented region is the vegetal pole or vegetal hemisphere.
• A morula may have cells composed of cells (blastomeres)