MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Y.I. Fedoniuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

CHAPTER 9. REPRODUCTIVE PROCESS

ANATOMY OF THE REPRODUCTIVE ORGANS

THE FEMALE REPRODUCTIVE CYCLE

The Development of Female Germ Cells begins during Puberty (ages 13–16). With the onset of puberty, girls experience periodic fluctuations in Blood and urine estrogen levels, corresponding to the cyclic activity of the Gonads, which regulates the female reproductive cycle. During one of the regular estrogen surges, ovulation occurs—the rupture of an ovarian follicle and the release of the most mature oocyte. The first menstruation begins a few days later. In adolescent girls, reproductive cycles are irregular. Full sexual maturity is attained only when these cycles become regular and ovulatory.

The average duration of the female reproductive cycle is 27–28 days. During this period, a follicle matures, culminating in ovulation towards the end of the cycle. The oocyte travels through the Fallopian tubes into the Uterus. If Fertilization has taken place, the zygote implants in the uterine wall; if not, it is expelled from the body.

A corpus luteum develops at the site of the ruptured follicle, producing the hormone progesterone, which counteracts the stimulatory effect of estrogens on the contractions of the uterine and tubal musculature. If fertilization and Pregnancy occur, the corpus luteum persists and enlarges; otherwise, it regresses. The regression of the corpus luteum creates the conditions necessary for the maturation of the next follicle.

Menstruation—the periodic discharge of blood from the uterus—is directly linked to follicular maturation and ovulation. It occurs cyclically every 27–28 days if fertilization does not take place. Menstruation is associated with structural Changes in the endometrium (the uterine mucosa). The endometrium thickens and becomes edematous in preparation for the reception of a fertilized egg; if fertilization fails to occur, the mucosal lining breaks down and is shed from the uterus. This shedding is accompanied by bleeding. Menstruation typically lasts 3 to 5 days, resulting in a blood loss ranging from 50 to 250 ml. The onset of menstruation is triggered by a decline in ovarian hormone concentrations in the blood during this period, which leads to tonic contractions of the myometrium. Following menstruation, the endometrium regenerates, and the entire cycle repeats.

Around the age of 50, women enter the Climacteric period (menopause), which is characterized by the gradual cessation of reproductive Functions. The reproductive cycles become irregular and anovulatory, eventually leading to Amenorrhea—the permanent cessation of menstruation.

In men, the climacteric phase typically begins after the age of 60 and is characterized by a decline in sperm motility, loss of fertilizing capacity, and impaired ejaculation.

The onset of the climacteric is highly individual and depends on lifestyle, past illnesses, climate, and Nutrition.