Reproduction Samples

(last update - 10/14/02)

- click on images to see animations -

At the time of conception, it is not known whether the fertilized egg will evolve into a male or a female. Sex differentiation occurs 8 weeks after conception and is based upon the influence of specific hormones.
During puberty a girl’s breasts will begin to grow and continue to develop until full maturity is reached.
Also during this period, hair will begin to grow under the arms, on the legs and in the pubic area.
Growth spurts occur between the ages of 10 and 14.
As the female grows her hips and thighs become round and full.
The external sexual organs: the labia and clitoris begin to grown and develop.
The female internal organs which are the vagina,uterus, fallopian and ovaries increase in size.
As mentioned earlier, the female internal organs consist of the vagina, the uterus, two fallopian tubes and two ovaries.
Contained within each ovary are thousands of immature eggs- a girl is born with between 300,000 and 500,000 eggs- all of the eggs she will have throughout her lifetime.
hormonal activity begins to mature the eggs.
The hypothalamus is a gland in the brain that is responsible for regulating thirst, hunger, sexual drive, sleep patterns and endocrine functioning.
Around the time of puberty, the hypothalamus begins to secrete a neuro-hormone known as GnRH(gonadotropins releasing hormone). This hormone is secreted in a pulsatile fashion every 60 to 90 seconds. The job of the GnRH is to stimulate cells in the anterior pituitary in the brain which produces FSH, (follicle stimulating hormone), and LH (luteinzing hormone).
FSH stimulates the follicles(the cell complex that surrounds and matures the egg) to maturity enabling them to produce estrogen. These follicles develop during the first half of the menstrual cycle but only one dominant follicle will emerge. This dominant follicle will expel an egg during ovulation.
The menstrual cycle begins with Day one of bleeding and lasts until the bleeding has stopped.

The next phase of the cycle is known as the follicular or proliferative phase. During this period which is variable in length , FSH stimulates follicular development. Estrogen is dominant and the uterine lining begins to thicken in preparation for the implantation of the fertilized egg.
The mature egg is expelled from the follicle and is captured by the cillia-the hair like projections of the fallopian tubes.
The ruptured follicle then closes and forms the corpus luteum -a yellowish body that secretes the progesterone and helps maintain a pregnancy.
Fertilization occurs in the fallopian tubes and it takes 3-4 days for the fertilized egg to travel down the tube and implant in the uterine lining.

The uterine lining continues to grow. If fertilization does not occur, the corpus luteum disintegrates and the levels of estrogen and progesterone fall dramatically. The menstrual cycle then starts again.

The male body becomes angular and muscular and muscle mass increases, most notably in the upper chest and shoulders
Hair begins to grow on the face, abdomen, chest, arms, buttocks, legs and in the pubic area.
The male reproductive system consists of the penis, testicles, scrotum, seminal vesicles, epididymis, vas deferens and prostate glands. While the penis and testes are external organs , the other structures are internal and are contained within the body.
The scrotum is a pouch of skin located behind the penis and contains and protects the testes.
Under the influence of testosterone, immature sperm cells develop in the testicles and mature
The penis is made up of two parts, the shaft and the glans. The shaft is the main part of the penis, while the glans also known as the head is the tip. All men are born with a foreskin, a fold of skin that covers the glans.
The inside of the penis is comprised of spongy tissue, which can expand and contract. When blood rushes into the veins and spongy tissue in the penis it becomes engorged and the penis becomes erect.
The epididymis are long coiled tubes that sit on top of and behind each testicle. Sperm are continuously being transported away from the testicles and through the epididymis.
The sperm then reaches the vas deferens which are known as the “storehouse.” The vas deferens extend from the epididymis to the urethra
Prior to ejaculation the seminal vesicles and the prostate glands produce fluids that mix with the sperm to create semen. Semen is the fluid that is ejaculated from the penis, and each ejaculation can contain up to 500 million sperm.