Lecture 26: Female Reproductive Physiology

Question 1

Trace the steps followed by a primordial germ cell through the process of meiosis and oogenesis and compare with spermatogenesis

Answer 1

• Primordial germ cells:
  
  • Develop from the germinal epithelium of the indifferent gonad early in embryonic development
  • They migrate into the future ovaries and become:
    
    • Oogonia
• Oogonia:
  
  • Are surrounded by a single layer of nongerminal granulosa cells.
  • The oogonium plus granulosa is called a:
    
    • Primordial Follicle
  • The ovum is a primary Oocyte
• The primary Oocyte:
  
  • Begins the process of meiosis:
  • Becomes arrested during the diplotene stage of prophase I
  • All primary oocytes are arrested during the diplotene stage of meiosis I during embryonic development
  • Most of the primary oocytes will become atretic before birth
  • After birth, only about 500,000 primary oocytes remain out an initial number of oogonia cells of about 7 million
  • Beginning at puberty, one of these primary oocytes will complete the first stage of meiosis to become:
    
    • A secondary Oocyte + Polar body
• Secondary oocytes:
  
  • Complete the second half of meiosis and become:
    
    • Ootid + Polar body
  • Fertilization occurs at the second metaphase stage of oogenesis:
    
    • Therefore, an immature egg is fertalized
    • Meiosis is not completed unless fertilization occurs
• Comparision with spermatogenesis:
  *

Question 2

Describe the time intervals of the Uterine phases based on a 28-day cycle

Answer 2

• Uterine phases:
  
  • Days 01-05:
    
    • Menstruation
  • Days 04-14:
    
    • Proliferation
  • Days 14-28:
    
    • Secretion

Question 3

Describe the time intervals of the Ovarian phases based on a 28-day cycle

Answer 3

• Ovarian phases:
  
  • Days 05-14:
    
    • Follicular Growth
  • Day 14:
    
    • Ovulation
  • Days 14-23:
    
    • Development of corpus luteum
  • Days 24-28:
    
    • Regression of corpus luteum

Question 4

Describe the relationship between the release of anterior pituitary hormones and ovarian hormones in relation to the phases of the menstrual cycle

Answer 4

• Anterior pituitary sex hormones:
  
  • FSH
  • LH
  • peak at ovulation
• Ovarian hormones
  
  • Estrogen and progesterone
  • Estrogen peaks just before ovulation
  • Progesterone begins to rise right before ovulation and peaks after

Question 5

Describe changes in the ovary that occur during the menstrual cycle and relate to hormonal cycles

Answer 5

• The first stage of follicular growth is moderate enlargement of the ovum itself, which increases in diameter 2-3x
• Followed by growth of additional layers of granulosa cells in some of these follicles –> secondary follicles
• Concentrations of both FSH and LH increase slighlty during first few days of cycle:
  
  • Increase in FSH is slightly greater than that in LH
  • FSH increase precedes increase in LH
  • increase in FSH and LH → growth of multiple follicles:
    
    • Follicles add multiple layers of granulosa cells
    • Spindle-shaped cells around follicles form multiple layers around each follicle → Theca (interna and externa)
    • Early growth of follicle is stimulated by FSH

Question 6

Describe the interactions between the granulosa and theca cells in estrogen production and relate to LH and FSH

Answer 6

• Theca:
  
  • The theca interna:
    
    • Cells become epitheloid and develop the ability to secrete estrogen and progesterone
  • The theca externa:
    
    • Will become the protective capsule of the developing follicle
• Granulosa cells:
  
  • Secrete a follicular fluid containing a high concentration of estrogen
  • This causes an antrum to appear

Question 7

Describe the role of enzymes and hormones postulated to be involved in ovulation

Question 8

Describe changes that occur in the uterus during each phase of the menstrual cycle

Answer 8

• Proliferative stage:
  
  • Estrogen phase
  • occurs before ovulation
  • most of the endometrium has been desquamated at beginning of phase
  • The only epithelial cells left are those in the deeper portions of the glands and crypts
  • Estrogen causes stromal and epithelial cells to rapidly proliferate
  • Endometrial surface is re-epithelialized within 4-7 days after the beginning of menstruation
  • There is progressive thickening of the endometrium due to increasing number of stromal cells and growth of endometrial glands
  • Endometrial glands, especially in cervical region, secrete a thin, stringy mucous
• Secretory stage:
  
  • Progesterone phase
  • progesterone and estrogen are secreted in large quantities by corpus luteum
  • Progesterone causes marked swelling and secretory development of the endometrium
  • Glands increase in tortuosity
  • Excess of secretory substances accumulates in glandular epithelial cells
  • Results are a highly secretory endometrium that contains large amounts of stored nutrients
  • These uterine secretions (“uterine milk”) provide nourishment for the early dividing ovum
• Menstruation:
  
  • If ovum is not fertilized, corpus luteum suddenly involutes about 2 days before the end of the cycle and decreases secretion level
  • Reduction in estrogens and progesterones (especially progesterone) causes menstruation
  • Decreased stimulation of endometrial cells is followed by involuation of endometrium itself
  • 24 hours before the beginning of the onset of menstruation, tortuous blood vessels leading to the mucosal layers become vasospastic, leading to necrosis of the endometrium.

Question 9

Describe the effects of estrogen and progesterone on various structures and physiological pathways