The beginning of puberty is marked by the progressive increase in the production of sex hormones.

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2 Puberty is characterized by the changes that prepare the human body for the ability to reproduce. This stage generally occurs between the ages of 10 and 14 years old. The beginning of puberty is marked by the progressive increase in the production of sex hormones. A hormone is a chemical substance secreted by a gland.

3 Hormones are secreted by one part of the body to control one or more organs. The organs which the hormones control could be directly next to the gland which releases them or in a completely different part of the body. A hormone will only work on an organ which is sensitive to that hormone.

4 A small list of hormones in the human body Testosterone Estrogen Adrenaline (epinephrine) HGH (human growth hormone) Insulin Etc.

5 Two hormones play a major role in puberty secreted by the pituitary gland. Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) These hormones stimulate the maturation of the ova and the production of sperm. They also stimulate the ovaries and testicles to produce the male and female sex hormones (estrogen and progesterone (female) and testosterone (male)

6 The sex hormones initiate significant physical and psychological changes. These are more commonly referred to as primary and secondary sexual characteristics. We will list the primary and secondary changes in men and women.

7 Oogenesis is the process of an ovum production by meiosis. Puberty is the beginning of the fertile phase of a woman s life. A woman has all of her oocytes (precursor to an ovum) at birth. At puberty, a girl has approximately 700,000 oocytes.

8 The oocytes are diploid cells, meaning that they have 23 pairs of chromosomes each. Typically there is 1 ovum produced for each cycle of the menstrual system. During a woman s life, approximately 400 oocytes change into ova (plural of ovum)

9 The diploid oocyte undergoes a process call meiosis where the diploid cells become two haploid cells Haploid means that their only have one set of chromosomes, so 23 chomosomes. The oocyte does not split into two equal cells, one gets all the nutrients and the second dies quickly after.

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11 Each oocyte gives rise to one ovum. If this ovum is not fertilized, it is then expelled by the body during menstruation If the ovum is fertilized, the zygote forms and implants itself into the wall of the uterus to develop into a embryo.

12 The ovarian cycle is the process where a single ovarian follicle matures to produce an ovum and changes into a corpus luteum. At the beginning of the cycle, the pituitary gland secretes FSH which stimulates the development and growth of the ovarian follicle. As the follicle develops, it secretes more and more estrogen.

13 The increased estrogen leads to an increase of LH. This causes the ovum to be released from the follicle. The follicle then turns into a corpus luteum which then secretes progesterone. This hormone prepares the body for implantation of the zygote.

14 If there is no zygote present, then the lining of the endometrium is shed through menstruation. If the zygote does implant then the progesterone levels are maintained. The corpus keeps secreting progesterone until the placenta takes over.

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16 The menstrual cycle represents all of the periodic changes in the uterine endometrium. The menstrual cycle begins on the first day of menstruation. If a zygote is not implanted, then the drop of progesterone triggers menstruation.

17 After menstruation, the body begins the proliferation phase until ovulation occurs. The endometrium thickens again due to stimulation of estrogen. The final phase is the secretory phase which is marked by the thickening of the endometrium further.

18 An ovum lives for between hours and a spermatozoan lives for hours which means that a woman s fertile period is roughly 4 days. Hormone levels fluctuates throughout the ovarian and menstrual cycles.

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20 When a boy reaches puberty, the pituitary gland releases FSH, which stimulates spermatogenesis. Cells called spermatogonia cover the walls of the seminiferous tubules. These cells undergo meiosis to form spermatozoan (sperm) Each spermatogonia gives rise to four sperm. Men produce 120 million sperm per day.

21 As we saw, an erection is the process by which blood collects and is trapped in the penis. After spermatogenesis, the sperm collect in the vas deferens until ready to be expelled. When the erect penis is stimulated, the sperm are pushed through the ejaculatory duct towards the urethra.

22 Urine and sperm are enemies and urine will kill sperm on contact. To ensure that the urethra is clean, a man s body produces a pre-ejaculatory fluid to clean out the urethra. For ejaculation, the sperm is mixed with seminal fluid to create semen.

23 Semen then collects in the bulge of the urethra near the prostate. At the moment of ejaculation, the muscles around the urethra as well as the contraction of the penis serve to project the semen. The average ejaculation contains 3.5 ml of fluid and 350 million sperm.