MENSTRUAL CYCLE & MONOPAUSE

STD-12      UNIT-6     CHA-3

HUMAN REPRODUCTION

MENSTRUAL CYCLE & MONOPAUSE

MENSTRUAL CYCLE

• Menarche ( Gr . men - month , arche - beginning ) Beginning of menstruation or first menstruation is called menarche .
• The beginning of menstruation varies . It usually occurs between 12 and 15 years .
• Menstruation occurs in humans , apes and old world monkeys . 
• Menstruation is bleeding from the uterus of adult females at intervals of one lunar month . 
• In human females , the menstruation is repeated at an average interval of about 28/29 days and the cycle of events starting from one menstruation till the next one is called the menstrual cycle . 
• One ovum is released ( ovulation ) during the middle of each menstrual cycle . 
• As stated above menstrual cycle generally starts between 12 and 15 years and continues until about 45-50 years . 
• It is regulated by certain hormones , some of which are secreted by the pituitary gland . 
• The pituitary gland is stimulated by releasing factors produced in the hypothalamus . 
• The hormones produced by the pituitary gland influence the ovaries .
• The hormones secreted by the ovaries affect the walls of the uterus .

The menstrual cycle consists of four phases :

• menstrual phase 
• proliferative phase 
• ovulatory phase 
• secretory phase . 

Menstrual Phase ( Bleeding phase or menses ) . 

• In a 28 day menstrual cycle , the menses takes place on cycle days 3-5 . 
• The production of LH from the anterior lobe of the pituitary gland is considerably reduced . 
• The withdrawal of this hormone causes degeneration of the corpus luteum and , therefore , progesterone production is reduced . 
• Production of oestrogens is also reduced in this phase . 
• The endometrium of the uterus breaks down and menstruation begins . 
• The cells of endometrium secretions , blood and the unfertilized ovum constitute the menstrual flow . 

Follicular Phase ( Proliferative Phase ) . 

• This phase usually includes cycle days 6-13 or 14 in a 28 day cycle . The follicle stimulating hormone ( FSH ) secreted by the anterior lobe of the pituitary gland stimulates the ovarian follicle to secrete oestrogens.
• Oestrogens stimulate the proliferation of the endometrium of the uterine wall The endometrium becomes thicker by rapid cell multiplication and this is accompanied by an increase of uterine glands and blood vessels.  

Ovulatory Phase.  

• Both LH und FSH attain a peak level in the middle of the cycle (about 14th day).  
• Rapid secretion of LH induces rupturing of Graafian follicle and thereby the release of ovum in human beings secondary oocyte is released).  
• This is called ovulation.  
• In fact LH causes ovulation. 

Luteal Phase (Secretary Phase).  

• This phase usually includes cycle days 15 to 28 in a 28 day cycle. 
• The lateinising hormone (LH) is secreted by the anterior lobe of the pituitary gland.  LH causes ovulation. 
• The remaining cells of the ovarian follicles are stimulated by the LH to develop corpus luteum.  
• The corpus luteum secretes large amounts of progesterone.  
• Progesterone stimulates the uterine glands to produce increased amounts of watery mucus.  
• During the secretory phase, there is also a similar increase in the secretion of watery mucus by the vaginal glands and by the glands of the Fallopian tubes.  
• Progesterone is also essential for the maintenance of the endothelium.  Such an endothelium is necessary for implantation of the fertilized ovum and other events of pregnancy.  
• In the absence of fertilization, the corpus luteum degenerates. 
• This causes disintegration of the endothelium leading to menstruation marking a new cycle.  
• Thus increase production progesterone cause secretory phase.
• Thus after the secretory phase, the menstrual phase begins.  
• Menstruation often described as "hosting of uterus for lost ovum". 

Hormonal Control of Menstrual Cycle.  

• Gonadotropin releasing hormone (GnRH) also called Gonadotropin releasing factor (GnRF), is secreted by the hypothalamus of the brain which stimulates the release of follicle stimulating hormone (FSH) and luteinizing hormone (LH).  
• FSH stimulates the ovarian follicles to produce oestrogens during the proliferative phase.  
• LH stimulates the corpus luteum of the ovary to secrete progesterone. 
• Menstrual phase is caused by the reduction of progesterone and oestrogens.  
• Proliferative phase is caused by the increased production of oestrogens.
• LH causes ovulation.  
• Secretory phase is caused by increased production of progesterone.

MENOPAUSE ( Gr . men = month , pausis = cessation ) 

• It is a phase in woman's life when ovulation and menstruation stop . 
• It occurs between 45 to 55 years of age . 
• Some women have irregular cycles for months or years prior to menopause . 
• Others simply stop menstruating abruptly . 
• Cause . One theory is that menopause is a result of changes in pituitary gland and the nearby hypothalamus . 
• Another theory suggests that menopause may begin when no follicles are left in the ovaries . 
• In fact decline in oestrogen and progesterone level leads to menopause .

Symptoms . 

• The uterus and the vagina gradually become atrophic (decreased work ) . 
• Women may suffer temporarily depression , hot flashes , and other physiological and psychological problems in menopause . 
• Most of these symptoms can be relieved by taking hormones prescribed by a physician . 
• But this replacement of hormones is not encouraged due to some side effects 

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