MENSTRUAL CYCLE & PUBERTY
Puberty
Puberty is the stage of human growth and development in which a person becomes physically mature.
Puberty usually begins at the age of about 11 for females, and 14 for males.
During puberty, the reproductive system of a young person begins to function. The sex organs mature and begin to produce gametes. Changes also appear in a young person's body - these changes are called secondary sexual characteristics. These changes are caused by sex hormones (estrogen and progesterone in females, and testosterone in males).
The Menstrual Cycle
For a female, the first sign of puberty is usually the monthly discharge of blood or menses from the uterus via the vagina. This is called menstruation. The menstrual period or time of menstruating usually lasts for about five days. However, the length of the menstrual period and the amount of blood lost vary from female to female.
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NATURAL VARIATION
The average menstrual cycle for a female adult is 28 days long. However menstrual cycles can range from about 21 to 33 days due to natural variation. Natural variation depends on various factors including stress, tiredness, illness, unbalanced diet or malnutrition.
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As a female ages, the ovaries will eventually stop releasing mature eggs and the menstrual cycle will stop. This is called menopause. Menopause usually takes place between 45 and 55 years of age.
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CHANGES IN A FOLLICLE DURING THE MENSTRUAL CYCLE
The ovaries contain many developing follicles. The diagram shows the development of one follicle during the menstrual cycle (not that there are other follicles at different stages of development, but are not shown in the diagram for ease of understanding)
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1. Primary follicles
- Young follicles are called primary follicles
- Each primary follicle consists of a potential egg cell surrounded
by a layer of smaller cells known as follicle cells.
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2. Graafian follicle
- A primary follicle may develop into a Graafian follicle
- The Graafian follicle contains an egg surrounded by
follicle cells and a fluid filled space. The egg has a haploid
number of chromosomes.
- Usually, only one egg is released every month. The ovaries
take turns to release an egg
3. Ovulation
- On day 14 of the 28-day cycle, the Graafian follicle
ruptures and releases the egg into the oviduct
through the funnel like opening.
- The release of the egg from the ovary is called
ovulation.
4. Corpus lutem
- After ovulation, the Graafian follicle develops into
a corpus lutem
- The corpus lutem produces hormones that prepare the
body for pregnancy.
5. Corpus lutem breaks down
- If no fertilization occurs, the corpus lutem will persist
for some time and then eventually break down.
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The cycle of events taking place in the ovaries is controlled by hormones secreted by the pituitary gland. The follicles in the ovaries and the corpus lutem in turn secrete hormones that control the changes taking place in the uterus. Thus the menstrual cycle is controlled by hormones.
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Figure 1. Follicular development in the ovaries
Stages in the menstrual cycle
MENSTRUAL FLOW STAGE (Day 1 - 5)
- The first day of menstruation is the first day of the menstrual cycle. The uterine lining (endometrium) breaks down and flows from the uterus out of the body through the vagina
- The pituitary gland secretes follicle-stimulating hormone (FSH) into the bloodstream
OVULATION (Day 14)
Effects of LH:
- LH causes ovulation
- Also causes the formation of the corpus lutem from the remains of the Graafian follicle
- The corpus lutem secretes progesterone and some estrogen
CORPUS LUTEM (Day 15 - 28)
Effects of Progesterone:
- Progesterone maintains the uterine lining by causing it to thicken further and be richly supplied with blood capillaries, preparing it for the implantation of the embryo.
- Inhibits ovulation
- Inhibits FSH production
Fertilization is possible from around day 11 to day 16 (6 days). This is known as the fertile period of the menstrual cycle.
An egg is released around day 14 and can approximately survive till day 16.
Sperm can live for approximately 3-4 days in the female reproductive system. This means that sperm released in the vagina on day 11 can still fertilize the ovum and bring about pregnancy.
WHAT HAPPENS IF NO FERTILIZATION OCCURS?
1. The egg will break down
2. Eventually, LH production is inhibited by high concentration of progesterone in the blood. The drop in LH level in the blood causes the corpus lutem to break down.
3. When the corpus lutem breaks down, progesterone is not secreted.
4. Without progesterone, the thickened uterine lining cannot be maintained, so it breaks down.
5. The lining flows from the uterus together with some blood through the vagina. This marks the beginning of menstruation. It occurs around the 28th day from the beginning of the previous menstruation.
6. FSH is again produced by the pituitary gland and the whole cycle is repeated.
FOLLICLE STAGE (Day 6 - 13)
Effects of FSH:
- FSH stimulates the development of the follicles in the ovaries. Usually, one follicle will develop into a Graafian follicle in one of the ovaries during each cycle.
- It stimulates the follicles in the ovaries to secrete estrogen.
Effects of Estrogen:
- Causes the repair and growth of the uterine lining. The uterine lining becomes thick and spongy with blood vessels.
- When present in high concentrations, estrogen inhibits FSH production, preventing the maturation and development of more follicles.
- At high concentrations, estrogen also stimulates the pituitary gland to secrete lutenising hormone (LH).
WHAT HAPPENS FERTILIZATION OCCURS?
1. The fertilized egg becomes a zygote. The zygote develops into an embryo.
2. The embryo embeds itself into the uterine lining.
3. The embryo secretes a hormone which prevents the corpus lutem from breaking down until a structure called the placenta is formed.
4. The corpus lutem continues to secrete progesterone and estrogen until the placenta is able to take over the production of progesterone and estrogen.
Development of an embryo
IMPLANTATION
- The cilia lining the inner surface of the oviduct sweep the fertilized egg or zygote along the oviduct. Peristaltic movements in the wall of the oviduct also help move the zygote to the uterus.
- The zygote divides by mitosis to form a ball of cells called the embryo.
- It takes about five days for the embryo for the embryo the reach the uterus.
- The embryo may float freely in the uterus for about two days.
- Eventually, the embryo sinks in or becomes embedded in the uterine lining. This is called implantation. Implantation usually occurs about seven days after fertilization
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DEVELOPMENT OF THE PLACENTA
- Soon after implantation, finger-like projections called villi begin to grow from the embryo into the uterine lining. They contain blood capillaries of the embryo.
- The villi and the uterine lining in which the villi are embedded make up the placenta. Thus the placenta is formed partly from the embryonic tissue and partly from the uterine lining.
- a tube known as the umbilical cord attaches to embryo to the placenta.
DEVELOPMENT OF THE AMNIOTIC SAC
- A membrane called the amniotic sac or amnion begins to develop at about the same time as the placenta
- The amniotic sac encloses the embryo in a fluid-filled space known as the amniotic cavity
- The fluid in the amniotic cavity is called the amniotic fluid
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10-12 weeks after fertilization, all major organs are formed and the embryo is hence forth known as a fetus.
Figure 4. Early stages of development of embryo
Figure 5. Development of amniotic sac and placenta
Sexually Transmitted Infection (STIs)
Some diseases may be spread through sexual intercourse. A disease spread or transmitted in this way is called a sexually transmitted infection (STI). STIs can result in irreversible physical damage or even death.
STIs are caused by bacteria or viruses. The bacteria or viruses are transferred from an infected person to an uninfected person in the following ways:
- Through semen when it comes into contact with the mucous membrane in the vagina
- Through fluid in the vagina when it comes into contact with the mucous membrane of the urethra
- When blood from an infected person gets into the bloodstream of an uninfected person
Acquired Immune Deficiency Syndrome (AIDS)
The most widely known STI caused by a virus called Human Immunodeficiency Virus (HIV). The term AIDS refers to the most advanced stages of HIV infection. HIV destroys the body's immune system - the system that protects a person against infection. HIV destroys a persons immune system by destroying the lymphocytes (WBCs that identify and then produce specific antibodies against bacteria and viruses).
Thus, in this way normally mild infections may prove to be fatal for a person with AIDS.
Signs and Symptoms of AIDS
It may take months and years before HIV develops into AIDS. Signs of AIDS include:
- Chronic or persistent fever
- Severe diarrhea lasting for months
- Pneumonia
- Cancer of blood vesels (Kaposi's Sarcoma)
- Brain Infection
- Widespread tuberculosis affecting many organs at the same time
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Modes of Transmission
HIV is usally transmitted via the following:
- Sexual intercourse with an infected person
- Sharing hypodermic needles with an infected person (for example for doing drugs, tattooing, acupuncture or ear-piercing)
- Blood transfusion with blood from an infected person
- During pregnancy, the virus may pass down from an infected mother to the fetus.
HIV is not spread through toilet seats, doorknobs, coughs, swimming pools, or mosquitos.
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PREVENTION AND CONTROL OF STIs
These are some ways to reduce the risk of getting infected with STIs like HIV:
- Keep to one sex partner or do not have sex.
- Be fully open with your sexual partner about STIs (inquire if they have an STI before intercourse)
- Males should wear a condom of they or their partners are not sure whether they are infected.
- Drug addicts tend to share needles. Do not share needles or abuse drugs.
- Do not share instruments that are likely to break the skin and be contaminated with blood (e.g. razors and toothbrushes)
- Go to reliable operators for treatments that require needles or break the skin (e.g. acupuncture, tattoos etc.). Make sure that all equipment being used is either properly sterilized or is disposable after use.
- If you are getting a transfusion, make sure that the blood has been tested (advisable to get blood transfusions from reliable networks and hospitals)
- Known that there are after sex options of preventing HIV and some STIs as well, so in case you do have unprotected sex take the proper medication or pills in the limited time frame (usually 72 hours).