AP® Biology - Endocrine and Development Part 3

Glucagon would make this boy's condition worse. ## Footnote Type I diabetes involves a lack of insulin, a hormone that reduces plasma glucose levels. Thus, this boy would likely have high blood sugar. Glucagon, the hormone with the opposite function of insulin, would raise his blood glucose levels further.

The reproductive system generates new offspring from parent organisms, facilitating the survival of the species.

Some reproductive methods also increase genetic variation. This allows a species to adapt to changes in its environment.

Sexual reproduction involves two organisms and results in offspring that genetically differs from both of them. Asexual reproduction is carried out by a single organism and produces genetically identical offspring.

All prokaryotes use asexual reproduction, though they have alternative methods of gene transfer. Eukaryotic species can reproduce sexually, asexually, or through both mechanisms.

A gamete is a haploid cell that combines with another gamete during sexual reproduction. Together, the fused cells form a zygote that develops into a new organism.

In humans, the male gamete is the sperm, while the female gamete is the egg or ovum.

The gonads are endocrine organs that produce gametes.

The female gonads are the ovaries; the male gonads are the testes.

The most important sex hormones are testosterone in males and estrogen and progesterone in females.

While these hormones are steroids, their production is closely related to that of the peptides FSH and LH.

An androgen is a general term for a hormone that influences male development.

The most important androgen to know is testosterone, a steroid hormone.

Oogenesis is the production of the female gametes, ova, in the ovaries.

Oogenesis begins before birth. Specifically, all of a female's oocytes are produced and arrested at prophase I by the time she is born.

The least mature cell is the oogonium, which is the original parent cell in oogenesis. It is followed by the primary oocyte, secondary oocyte, and ovum.

Both meiosis and mitosis are involved in this diffferentiation process.

All of a female's oocytes are primary and are arrested in prophase I of meiosis.

In oogenesis, meiosis I involves the division of a primary into a secondary oocyte.

Meiosis II, which is only completed if the egg is fertilized, involves the division of this secondary oocyte into a mature ovum.

Oogenesis produces three cells per primary oocyte: one ovum and two polar bodies.

In meiosis I, the primary oocyte divides into one secondary oocyte and one polar body. This first polar body generally does not divide further. If fertilized, the secondary oocyte undergoes meiosis II, where it divides into one ovum and a second polar body.

Spermatogenesis is the production of the male gametes, sperm, in the seminiferous tubules of the testes.

Spermatogenesis begins at puberty.

The least mature cell is the spermatogonium, which is the original parent cell in spermatogenesis. It is followed by the primary spermatocyte, secondary spermatocyte, and spermatid. A fully mature sperm cell is known as a spermatozoon.

Both meiosis and mitosis are involved in this differentiation process.

Spermatogenesis never ceases; it continues throughout a man's adult life.

In contrast, oogenesis does not occur as a steady process. Virtually all of a woman's eggs are partially differentiated by birth, and all differentiation ceases completely at menopause.

Spermatogenesis produces four equally functional gametes, while oogenesis produces one mature ovum and two nonfunctional polar bodies.

Spermatogenesis takes place continuously from puberty to death, while oogenesis begins before birth and ends at menopause.

Developing cells become haploid during meiosis I, which is the division from primary to secondary spermatocyte. After this transition, the gamete will be haploid but with replicated chromosomes.

Meiosis II, on the other hand, refers to the division from secondary spermatocyte to spermatid. After this step, the gamete will be haploid with only one copy of each chromosome, as in its final state.

Puberty is the period of the human lifespan during which the reproductive system becomes mature.

In females, this process is marked by menarche, or the first menstrual period. In males, spermatogenesis begins at puberty.

Male reproductive organs are mainly found outside of the body, while female organs are located internally.

In males, the urethra serves both reproductive and urinary purposes, while in females, it is only involved in urination.

The zygote implants in the endometrium (lining) of the uterus.

Immediately after ovulation, this lining begins to thicken to provide a favorable environment for the potential zygote.

The oviducts

Each Fallopian tube connects a single ovary to the uterus.

The scrotum, which holds the testes, sits outside the body. This keeps the testes at a temperature slightly lower than 37º C, facilitating spermatogenesis.