2.2.1 PHYSIOLOGY OF MENSTRUATION

Menstruation is the cyclical flow of blood and tissue from the uterus in women between puberty and menopause.

Menarche is the onset of menstruation which typically begins between the ages of 12-13 years. It occurs 2-3 years after initial breast development.  Factors like race, environment, and nutrition can affects menarche. 

The menstrual cycle of a woman follows a monthly pattern which has influence on her life. It occur in about every 26-30days throughout the childbearing age (puberty to menopause) unless interrupted by pregnant or fertility control. It is govern by negative feedback mechanism originating from the brain.

The hypothalamus is the ultimate source of control and it governs the anterior pituitary gland by hormonal pathways. The anterior pituitary in turn governs the ovary by hormonal. The ovary produces hormones which control changes in the uterus. All the changes occur simultaneously and in harmony.

Menstrual Cycle

The average cycle is 28days long and recurs regularly from puberty to menopause unless pregnancy intervenes. There are 3 main phases and they affects the tissue structure of the endometrium.

The hypothalamus releases Gonadotrophic releasing hormone (GnRH) or Luteinising hormone releasing hormones (LHRH) which stimulates the anterior pituitary gland to secretes the Gonadotrophic hormones (FSH and LH).

• FSH (Follicle Stimulating Hormone) stimulates the growth of the ovarian follicle and the secretion of oestrogen from the lining of the follicle by the granulosa cells. The level of FSH rises during the first half of the cycle and when the oestrogen level reaches a certain point its production is stopped.

• LH (Luitenising hormone) triggers ovulation and stimulates the development of corpus luteum and the secretion of progesterone. The oestrogen level which keeps rising causes both FSH and LH level to rise once ovulation occurs and progresterone is released, it inhibits any new rise, in LH inspite of high oestrogen level, but if no pregnancy after 14days, the corpus luteum degenerates and negative feedback effect of progesterone ceases and FSH and LH level rises again to begin a new cycle.

The 3 phases of the cycle

Menstrual Phase: It is characterized by vaginal bleeding lasting for 3-5days. Physiologically this is the terminal phase of the menstrual cycle when the endometrium is shed down to the basal layer along with blood from the capillaries and the unfertilized ovum. This happens due to the degeneration of the corpus luteum which lowers the level of progesterone and oestrogen.

The Proliferative Phase: It follows menstruation and lasted until ovulation. Sometime the first few days while the endometrium is reforming are described as regenerative phase. FSH, stimulates the growth of ovarian follicle which secretes oestrogen, which in turn stimulates proliferation of the endometrium in preparation for a zygote. The endometrium thickens becoming soft and vascular and contains mucus secreting glands. This phase terminates when ovulation occurs and oestrogen production is declined. It lasted for 9-10days.

The Secretory Phase: It follows ovulation. The LH stimulates the corpus luteum to produce progresterone and some oestrogen. The endometrium thickens to 3.5mm and becomes spongy, increasing the production of mucus by the secretory glands. There is increase secretion of the mucus in the uterine tube as well as the cervical glands to lubricate the vagina. This is believed to assist the passage of spermatozoa for fertilization. But when it fails to occur, menstruation occurs making the beginning of a new cycle. It lasted about 14 days.

Hypothalamus

       Secretes

LHRH or GnRH

             Stimulates

Anterior Pituitary Gland

Secretes

             Gonadotrophic hormones

FSH LH

                                                Ovaries 

Oestrogen Progesterone

Ovarian Follicle Corpus Luteum

Test item – 

• Identify the components of male reproductive system

• Identify the components of female reproductive systen

• Describe the phases of the menstrual cycle

STUDENTS’ ACTIVITY

Topic: Anatomy and Physiology of the Male and Female System

Learning outcome: The student will be able to

• Describe the male reproductive system

• Discuss the process of sperm formation

• Describe the female reproductive system

• Describe the menstrual cycle

Task: In line, the students describe the various organs that constitutes the male and female reproductive system

UNIT 3.0