It refers to the series of events which regularly occurs in female after every 26-30 days. It occurs throughout the childbearing period between menarche and menopause. The cycle leads to the changes which takes place regularly in ovaries and uterine lining; these are stimulated by the changes in blood concentration of hormones. The hormones secreted during the cycle is regulated by negative feedback system.
The hypothalamus secretes luteinizing hormone releasing hormone(LHRH). this hormone stimulated the anterior pituitary to secrete-
- Follicle stimulating hormone(FSH)- this promotes maturation of ovarian follicles and secretion of Oestrogen, which leads to ovulation.
- Luteinizing hormone(LH)- it triggers ovulation and also stimulates the development of corpus luteum and secretion of progesterone.
The hypothalamus is stimulated by oestrogen alone and inhibited by both oestrogen and progesterone.
The average length of cycle is 28 days and it occurs in 3 phases-
1. Menstrual Phase
When the ovum is not fertilized, the corpus luteum starts to degenerate. This has 2 effects-
- falling of the level of oestrogen and progesterone
- the functional layer of endometrium starts to shed during menstruation; because they depend on high level of ovarian hormones.
The menstrual flow consist of secretions from endometrial glands, endometrial cells, unfertilized ovum etc.
During this phase, the hypothalamus and anterior pituitary resumes their cycle activity and level of FSH rises which in turn initiates new cycle.
This Figure is taken for education Purpose from Mero.medium.com
2. Proliferative Phase
At this stage, the ovarian follicles which are stimulated by FSH grows and becomes mature. After maturity they produce oestrogen which stimulates the proliferation of functional layer of endometrium. The endometrium becomes very vascular and the concentration of mucous secreting glands also increases. The rising level of oestrogen is responsible for stimulation of LH. The LH triggers ovulation; this marks the end of proliferative phase.
3. Secretory phase
After ovulation, LH stimulates the development of corpus luteum from the ruptured ovarian follicle. The corpus luteum produces oestrogen, progesterone and inhibin. The progesterone influences the secretory glands to produce increased amount of watery mucous. . This assist the passing of spermatozoa through the uterus to the uterine tube where the ovum is usually fertilized. The concentration of watery mucous also increases in the uterus by the cervical glands which lubricated the vagina
The ovum survives in the fertilized form for a very short duration, about 8 ours. The spermatozoa may be capable for fertilizing the ovum for only 24 hours. Certain changes occurs in a female during ovulation like-
- cervical mucous which is thick and dry now becomes thin, elastic and watery.
- body temp rises by 1 degree just during ovulation
- abdominal discomfort during middle of cycle.
After ovulation, the combination of oestrogen, progesterone and inhibin together works to inhibit the hypothalamus and anterior pituitary; so the level of FSH and LH fall. Low level of FSH in the second half prevents further follicular development. If the ovum is not fertilized, the LH level falls which leads to degeneration and death of corpus luteum. This in turn leads to falling the level of oestrogen, progesterone and inhibin. Thus inhibition of new cycle. If the ovum is fertilized, there is no breakdown of endometrium and no menstruation.
The menopause is a period which occurs between 45-55 years, the period which marks the end of childbearing period. It is caused by progressive reduction in oestrogen levels because the no. of ovarian follicles becomes less with age. The ovaries further becomes less reactive to FSH and LH; ovulation and menstrual cycle becomes irregular and ultimately ends. Several other changes also takes place during this period like-
- short term vasodilation, and discomfort and disturbance in sleep pattern
- shrinking of breasts
- atrophy of sex organs
- skin gradually becomes thin
- increase in blood cholesterol level which leads to cardiovascular diseases.
PUBERTY IN FEMALES
Puberty is the age at which the internal reproductive organ becomes mature. It occurs at age between 12-14 years; this period is called menarche also marks the beginning of childbearing period. The changes takes place at puberty are-
- the uterus, uterine tubes and ovaries becomes mature
- the menstrual cycle begins
- the breast develop and enlarge
- pubic and axillary hair grows
- increase in height and widening of pelvis
PUBERTY IN MALES
In males puberty occurs between 10-14 years. The changes that occurs in males are-
- growth of muscle and bones and also increase in height and weight
- enlargement of larynx and deepening of voice
- hair starts growing on the face, axillae, chest, abdomen and pubis
- enlargement of penis, scrotum and prostrate glands
- maturation of the seminiferous tubules and also the production of spermatozoa
- the skin becomes thick and oilier.
Multiple choice questions(MCQs)
1. How many phases are present in the reproductive cycle?
A. 3 B. 5
C. 2 D. 4
2. The hormones secreted during reproductive cycle are regulated by?
A. negative feedback system B. positive feedback system
C. sympathetic system D. parasympathetic system
3. What is the main cause of menopause?
A. Reduction in the level of oestrogen
B. reduction in the level of progesterone
C. increase in the level of oestrogen
D. increase in the level of progesterone
4. Match the following changes occurring at different events-
a. menopause 1. Enlargement of larynx
b. puberty in female 2. Cervical mucus becomes thin
C. ovulation 3. Uterine tubes becomes mature
D. puberty in male 4. Increase in blood cholesterol level
5. What physiological changes takes place during puberty in males?
A. deepening of voice B. enlargement of scrotum
C. hair growth on axillae D. all of the above
6. Which of the following change does not occur during ovulation?
A. cervical mucus becomes watery B. increase body temp
C. atrophy of sex organ D. abdominal discomfort
7. Which of the following statement is NOT true?
A. the reproductive cycle occurs after every 26-30 days
B. during ovulation, body temp falls
C. proliferative phase ends when ovulation begins
D. FSH promotes maturation of ovarian follicles.
8. Which hormone stimulates the anterior pituitary for the secretion of FSH and LH?
A. LHRH B. GH
C. adrenal gland D. thyroid gland
9. What changes occur during menopause?
A. breasts develop and enlarge B. widening of pelvis
C. pubic hair growth D. none of the above
10. What suppresses the hypothalamus to control its regulation?
A. oestrogen B. progesterone
C. FSH D. both A and B
2. negative feedback system
3. reduction in level of oestrogen
4. a – 4 b – 3 c – 2 d – 1
5. all of the above
6. atrophy of sex organs
7. during ovulation, body temp falls
9. none of the above
10. both A and B
REFERENCE: 1. Ross and Wilson-Anatomy and physiology in health and illness; 12th edition; page no.-: 456-458, 463.