PHYSIOLOGY OF THE UTERINE CYCLE OR MENSTRUAL CYCLE

Menstruation is the cyclical discharge of blood, mucous and cellular debris from the uterine lining. The time of onset of the first period is termed as menarche. This cyclical (28-30 days) monthly process is by and large regular and predictable right from menarche until menopause except during pregnancy, lactation, anovulation or interference with medication. The highest incidence of anovulatory cycles is under age 20 and over age 40.

At age 25, over 40% of cycles are between 25 and 28 days in length; from 25 to 35, over 60% are between 25 and 28 days.

Although each woman has an individual cycle which varies in length, the average cycle is taken to be 28 days long and recurs regularly from puberty to menopause except when pregnancy intervenes.

The menstruation cycle begins from the first day of the menstruation to the next one. There are three main phases and they affect the tissue structure of the endometrium, controlled by the ovarian hormones.

Phases of menstrual cycle

Following are the three phases of the menstrual cycle

1. Proliferative Phase
2. Secretory Phase
3. Menstrual Phase

a) Proliferative Phase

• The proliferative phase begins at the end of menstruation and lasts until ovulation, which is about 10 days.
• In this time the anterior lobe of the pituitary gland produces an increased amount of FSH.
• This hormone plays a major role in the maturation of the single ovum but sometimes two or more may do
  SO.
• Once the primordial follicle is ripe by the influence of
  FSH, it is known as Grafian. While the FSH prepares the ovum to become mature, in the meantime, another female hormone oestrogen secreted by the ovary affects the lining of the endometrium.

• This hormone passes directly into the bloodstream and has its effect on the endometrium, stimulating the columnar cells to reproduce the endometrium more rapidly forming a thicker lining and increasing the number of glands and blood capillaries causing more vascular and spongy.
• In this phase, the endometrium becomes 2-3mm thick to receive the fertilized ovum.
• Rising blood levels of estradiol exert negative feedback on FSH secretion and positive feedback on
  LH secretion. As a result of a surge in the LH level, ovulation occurs.
• Ovulation is a process whereby a secondary oocyte is released from the ovary following the rupture of a mature Graafian follicle and becomes available for conception.
• The ovum remains viable for 24-72 hours.
• After ovulation this phase is complete.

b) Secretary Phase

• This phase begins just after ovulation and lasts for about two weeks.
• In this phase, there is an increase in the secretion of
  LH by anterior pituitary gland, a temporary endocrine gland called corpus luteum is formed from the ruptured follicle.
• The ruptured follicle is filled with a yellow substance known as luteum.
• Under the influence of LH, the corpus luteum produces the second ovarian hormone, especially the progesterone hormone.
• This hormone is directly absorbed into the bloodstream and causes the further thickening of the endometrium lining, so the endometrium becomes highly
  the fertilized ovum.
  vascularized, thick and spongy for the reception of
• The endometrial glands become enlarged and secrete glycogen and mucin, which is essential for the nourishment of the ovum if fertilized.
• However, if the ovum is not fertilized the size of the corpus luteum shrinks and the progesterone level in blood is decreased. Because of this, the endometrium ceases to grow further and the menstrual phase begins again.
  In fertilized, there is no menstrual flow and now the endometrium is called decidua where the fertilized ovum embeds.

• Then it produces the human chorionic gonadotrophin hormone, which keeps corpus luteum intact and thus allows it to continue secreting progesterone.
• If the ovum is not fertilized, then menstrual bleeding begins.

c) Menstrual Phase

• If the ovum is not fertilized, the progesterone level in blood is decreased which causes shrinkage and degeneration of the corpus luteum.
• As a result of decreased oestrogen and progesterone levels in the blood, the superficial layer of the endometrium is shed and the blood discharge from the vagina follows.
• This lasts for about 4-6 days.
• The normal amount of blood flow at each cycle is approximately 60-90ml.
• When the progesterone level in the blood falls to a certain level the pituitary gland again starts to secrete

Hormonal control on menstrual cycle

The FSH and immediately the whole cycle is repeated again.

1. FSH -Follicular Stimulating Hormone - Causes growth of follicles in the ovaries prior to ovulation and promotes the formation of sperm in the testes.

2. LH - Leutinizing Hormone - Plays an important role in causing ovulation and also promotes secretion of female sex hormones by the ovaries and testosterone by the testes.

1. HCG - Human Chorionic Gonadotrophin - Promotes growth of the corpus luteum and secretion of estrogen and progesterone by the same.
2. Estrogen (Estradiol) - Stimulates the development of female sex organs, the breasts and other secondary sexual characteristics.
3. Progesterone (Progestin) - Stimulates secretion by uterine endometrial glands in preparation for implantation, otherwise known as Decidual reaction.
   It also helps to promote the development of the secretory apparatus of breasts.

The regulation of the menstrual cycle is due to the normal integrated functioning of the hypothalamo-pituitary-ovarian axis. The hypothalamus and the pituitary are situated in the human brain and affect the production of releasing hormones which induce the end organ - ovaries to release the primary female hormones namely estrogen and progesterone. This is called positive feedback. When the levels of these hormones have reached an adequate level to perform their respective functions, they suppress the releasing effect in the brain. This is called negative feedback.

HUMAN SEXUALITY

The term sexuality refers to a person's perceptions, thoughts, feelings and behaviour related to sexual identity and sexual interaction with others.

Sexual health is the integration of the romantic, emotional, intellectual and social aspects of sexual being in ways that enhances personality, love and communication. Every person has a right to receive information and to consider accepting sexual relationships for pleasure as well as procreation. WHO(1975)

Adult sexuality has been broadly " classified as procreative and non-procreative

Components of human sexuality

Sexuality is a dynamic force that is active throughout each persons life. The components of sexual system are

1. Biologic sex : Chromosome, hormones, primary and secondary sex characteristics
2. Sexual identity or core gender identity : Sense of maleness and femaleness
3. Gender identity: sense of masculinity and feminity
4. Gender role behaviour or sex behaviour : Behaviour motivated by desire for sexual pleasure ultimately
   orgasm( physical sex)

Development of human sexuality

Sexual cycle

Each person experiences sexual desire in a way unique to him or herself and many different stimuli can trigger the feeling .Both the male and the female respond to any sexual stimulation by experiencing a cycle of events.Masters and Johnson (1966) were sexologists were the first to explain in detail how human beings respond to sexuality.Sexual cycle describes the physical changes that body experience at different level of arousal. It includes four stages.

• Exictement

In their theory, after an initial period of desire mene and women go through 4 phases.

• Plateau
• Orgasm
• Resolution