Describe the Menstrual Cycle – Class 10

MENSTRUAL CYCLE

The reproductive period of the human female continues from about the age of 13 years to 45-50 years.

In females, ovaries release ovum or egg once every 28 days from the age of puberty. The uterus prepares itself every month to receive a fertilized egg. 

Thus, its lining becomes thick and spongy. If the egg is not fertilized it lives for about a day. Afterwards this lining of the uterus is no longer required and Menstruation Occurs.

This period is marked by a characteristic event repeated almost every month (28 days with minor variation) in the form of a menstrual flow. 

Also Check – Why does Menstruation occur ?

It may be temporarily stopped only by pregnancy.

The period of a menstrual cycle is counted from the day of the onset of the flow to the next onset after 28 days .

Menstural Cycle has 4 phases

1. Menstrual phase 
2. Follicular phase
3. Ovulatory phase
4. Luteal phase

 Menstrual phase : 

• It lasts for 3-5 days during which blood is discharged. 
• The bleeding is caused due to the shedding and rupturing of the blood vessels that make up the thickened innermost lining of the uterus, called the endometrium.
• Starting from the onset of the menstruation flow, the ovary begins to form a new egg in a follicle.

Also Check – Reproduction In Human Beings

Follicular phase :

•  It continues from days 5-12.
• As the follicle grows, the amount of oestrogens produced by the ovary increases.
• This hormone then acts on the uterus and causes its lining to become thicker and develop more blood vessels.
• This change is a kind of preparation of the uterus to receive the fertilized egg and assist in the early implantation of the embryo and its subsequent development.

Ovulatory phase : 

• On about the 13th or 14th day, the follicle ruptures (ovulation) and the released egg travels down the oviduct.
• The two hormones produced by the pituitary gland, follicle stimulating hormone (FSH) and
• luteinizing hormone (LH), promotes the maturation and release of the ovum.

Luteal phase :

•  It lasts from days 15-28. 
• Uterus lining thickens further and after the release ofthe ovum, the emptied follicle in the ovary turns into a hormone-producing tissue called corpus luteum .
• If the ovum is fertilized, the corpus luteum continues to release progesterone and so keeps the uterus in a state suitable for implantation.
• However, if on the other hand there is no fertilization, the ovum disintegrates and the corpus luteum stops producing progesterone.
• As a result, the thickened lining of the uterus (endometrium) restarts shedding on the 28th day and loses blood which escapes through the cervix and vagina.