Lecture 32: The Menstrual Cycle and Ovulation Flashcards
(35 cards)
Be able to draw the process of oogenesis (up to fertilization of ovum)
Be able to draw the LH, FSH, Inhibin, Estradiol and Progesterone throughout the menstrual cycle on the slides
Ok
What is active in oocytes at these stages?
Arrest at Prophase I
Arrest at Metaphase II
Resumption of Meiosis II after fertilization
- elevated cAMP
- elevated MAPK
- degeneration of MAPK
What are the characteristics of the primordial follicle?
- arrested at prophase I
- single layer of pregranulosa cells
- most will degenerate, only dominant ones reach ovulation
What are the characteristics of the primary follicle?
What proteins are produced?
- primary oocyte
- cuboidal layer of granulosa cells
-produces Z proteins (1 - 4)
What are the characteristics of the secondary follicle?
- 3-6 layers of cuboidal granulosa cells
- preantral, minimal endocrine function
Describe the changes that occur in the oocyte as it develops from pirmary to secondary follicle
- secrete paracrine factors that induce stromal cells to differentiate into thecal cells
- increased vascularization
- zona pellucida develops binding sites for sperm
How does the primary follicle increase vascularization?
- migrate from outer cortex to inner cortex to be closer to ovarian vasculature
- release angiogenic factors to induce the development of arterioles
What is the difference between thecal and granulosa cells at the secondary follicle level?
Thecal: analogous to Leydig > has LH receptors
Granulosa: analogous to Sertoli > has FSH receptors, produces minimal androstenedione
How does the antrum develop in secondary follicles?
-follicular fluid (antrum) grows around egg along with granulosa proliferation > forms the cumulus oophorus/corona radiata
What are the two types of granulosa cells found in the antral phase and how are they different?
Mural granulosa/stratum granulosum: outer wall, steroidogenic
Cumulus granulosa: form gap and adhesion junctions with the oocyte and released with it
What happens to the thecal and granulosa cells during the antral phase?
Thecal: responds to LH - forms androstenedione (from acetate and cholesterol) which diffuses to granulosa
Granulosa: responds to FSH (and LH later) creates aromatase to convert androstenedione to estradiol
Describe the growth of the follicles during the antral phase
- grows rapidly, slows as it gets larger
- have the ability to complete meiosis, but are all arrested at prophase I (elevated cAMP)
How is the dominant follicle selected?
Candidates: large antral follicles
Mural granulosa secretes low estrogen and inhibin B > FSH levels decline > the large antral follicle with the most FSH receptors becomes the dominant follicle > becomes the Graffian follicle
What is the periovulatory period and what happens to the oocyte during this time?
- time from LH surge onset to ovulation (about 32-36 hours)
- structure changes to prepare for ovulation. thecal and mural granulosa will prepare for luteinization (increase production of progesterone and form the corpus luteum)
What are the effects of the LH surge on the thecal cells?
LH receptors increase, makes more androstenedione
What are the effects of the LH surge on granulosa cells?
Strructural: differentiation to granulosa lutein, expression of more LH receptors and increased vascularization
Cellular:
- aromatase inhibition leadingt to androstenedione accumulation that feedbacks to LH
- increased vascularization > increased cholesterol availability for progesterone production
What major structural effects does the LH surge have?
- Theca and granulosa release cytokines and hydrolytic enzymes to break down follicular wall
- cumulus ocyte complex detaches (free floating oocyte)
- basal lamina of mural granulosa degrades > release of angiogenic factors that increase follicle vascularization (corpus hemorrhagicum)
What are the major events of the luteal phase
Antral cavity filled with stuff to form the corpus luteum
- corpus hemorrhagicum forms at the antral cavity, debris removed by macrophages
- granulosa lutein (yellow) cells with cholesterol esters collapse into the antral cavity as well as theca, blood vessels and WBCs
What happens to the corpus luteum after formation?
No fertilization: remains for about 14 days and becomes scar like collagen filled body called corpus albicans
Fertilization: hCG rescues it and stays viable throughout the pregnancy
During pregnancy, what is the role of the corpus luteum?
-hCG > produces more progesterone that prepares the uterine lining for implantation
What happens to the levels of these hormones after the LH surge?
Estrogen
Progesterone
LH
- transient decrease shortly after LH surge, but rebounds and peaks at the luteal phase, decrease as menses phase approaches so there is only 1 ovulation
- increases and peaks at the luteal phase, decrease as menses phase approaches (if pregnant, hCG compensates via the corpus luteum)
- decrease rapidly and suppressed by progesterone and estrogen until menses
What happens during follicular atresia?
- apoptosis of the granulosa cells and occytes of non-dominant follicles
- thecal cells repopulate the ovarian stroma. retain LH receptors and still produce androstenedione
Be able to draw the HP-Ovarian axis along with feedback mechanisms
Ok
What causes the LH surge?
Pulsatile release of GnRH
LH release gets more responsive each pulsatile surge of GnRH > eventually leading to LH surge
