Reproductive System - AP Biology

Sperm cells are stored and mature in the epididymis until they are transported to the urethra through the vas deferens. The testes are the site of sperm production, while the seminal vesicles produce fluids that are later incorporated into semen.

The seminal vesicles secrete seminal fluid to promote and nourish sperm as they are released. The bulbourethral glands secrete a component of seminal fluid, while the prostate gland secretes alkaline fluid.

"Germ cells" is simply another term for gametes, and thus refers to either sperm or ovum.

Ovum are produced in the ovaries. After production, the fallopian tubes propel ovum to the uterus using the movement of cilia. The endometrium is the lining of the uterus, and allows for implantation of a fertilized ovum.

In the majority of cases, fertilization occurs in the fallopian tubes of the female. The egg is released from the ovary and travels into the fallopian tube during ovulation. Sperm travel to the fallopian tube to fertilize the egg, creating a zygote. The zygote begins to divide, forming a blastocyst before it reaches the uterus where it becomes embedded in the endometrium via the process of implantation. Certain pregnancy complications can arise if the blastocyst implants while still in the fallopian tube, resulting in ectopic pregnancy.

Sperm is created in the seminiferous tubules of the testes. It is then transported to the epididymis, where it will mature and be stored prior to ejaculation.

The male reproductive system consists of a series of ducts, which includes the epididymis, vas deferens, and urethra. The epididymis is a coiled tube attached to the testis, which receives sperm from the seminiferous tubules. The vas deferens connects the epididymis with the urethra, which in turn conducts sperm to the tip of the penis.

In female mammals, the fimbriae are finger-like projections that sweep the ovulated egg from the ovary into the oviduct.

Villi are found in the digestive tract and work to increase surface area for more efficient absorption of nutrients. Flagella are threadlike structures that provide motility for sperm. Microtubules are composed of the protein tubulin, and are used in the construction of cilia and flagella. The endoderm is the innermost embryonic tissue layer, which develops to form the lining of the respiratory and digestive tracts.

The blastula is defined as beginning following the cleavage stages. Following seven cleavages 128 cells have formed, and will later begin to form the differentiated layers of endoderm, mesoderm and ectoderm before going into the gastrula stage.

During gastrulation, the ectoderm begins to fold in on itself following the primitive streak. These neural folds form the basis of the neural tube, later developing into the adult nervous system.

Somites go on to form skeletal muscle, vertebrae, and the dermis.

The corpus luteum is a structure in the ovary that secretes progesterone, and is preserved during pregnancy with the help of human chorionic gonadotropin (HCG). If fertilization does not take place, the corpus luteum will degenerate into the corpus albicans. As a result, corpus albicans formation only takes place if the woman is not pregnant.

Blastocyst implantation is considered the first event of pregnancy, and the placenta will later form in order to secrete hormones crucial for embryonic development.

The ectoderm is generally credited with the formation of the skin, teeth, nervous system, and sense organs. The lining of the digestive tract is formed from the endoderm.

The fusion of haploid gametes (sperm and egg) produces a zygote. The addition of the chromosomes from sperm and egg restores the diploid state of the cell and gives rise to a diploid organism.

An embryo refers to the developing organism after the first cellular division, following formation of the zygote. A blastocyst forms during the first stages of embryogenesis, and is defined by cellular replication without cellular growth.

The first stage after fertilization is the single-celled zygote, which quickly begins to divide. These divisions, however, do not increase the overall size of the embryo and are known as cleavage divisions. As the mass of cells divides, it is considered a morula.

Eventually, the morula develops an inner cell mass and associated trophoblast. At this stage, it is considered a blastula or blastocyst. It is during this stage that implantation occurs. After implantation, the cell develops the three germ layers through the process of gastrulation. Once the endoderm, mesoderm, and ectoderm have been established, the embryo is considered a gastrula.

Mitosis is the process by which diploid cells duplicate and divide to ensure all cells have the same number of chromosomes and genetic material. Meiosis is the process by which haploid gametes are produced by the primary sex organs.

The term “zygote” is sued to describe a fertilized egg. The zygote is diploid and formed by the fusion of the sperm and egg gametes. The developing organism is called the zygote until it is composed of 16 cells during cleavage, when it is called the “morula.”

Developing embryos exhibit an asymmetry; the zygote can be described as having two hemispheres. These two poles are called the animal and vegetal poles. The vegetal pole contains more yolk and will become the endoderm. The animal pole contains less yolk and will become the ectoderm and mesoderm.

Holoblastic cleavage is the type of cleavage found in developing embryos with a low yolk concentration. This allows for the complete cleavage that forms planes that extend through the entirety of the zygote. Different cleavage patterns in holoblastic cleavage include bilateral, radial, rotational, and spiral. Animals whose zygotes undergo holoblastic cleavage include placental mammals, amphibians, and annelids.

Meroblastic cleavage is partial cleavage in zygotes with a high concentration of yolk. In developing embryos that undergo this process, cell divisions do not penetrate the yolk. Two types of meroblastic cleavage are discoidal and superficial cleavage. This process occurs in insects, some fish, and some types of birds.