Obgyn - Physiology Of Menstrual Cycle

Front 1

What causes follicles to develop?
Where?

Back 1

Hypothalamus releases GnRH to anterior pituitary in a pulsatile manner via Pituitary Portal Vein...
Ant Pit releases LH and FSH...
These hormones cause follicles to grow in BOTH OVARIES

Front 2

What does a pre-ovulatory follicle consist of?

Back 2

Germ cell (oocyte) surrounded by granulosa and theca cells; antral fluid

Front 3

In which follicle does the oocyte mature and how?
What is this process called?
When does this occur?
What occurs due to maturation?

Back 3

- One follicle becomes dominant (unknown how)
- All other follicles go through atresia via apoptosis
= RECRUITMENT
- Occurs day 3-4 of cycle
- FSH and LH continue to stimulate the dominant follicle --> oocyte matures; granulosa cells secrete rapidly increasing amounts of estradiol into circ

Front 4

The maturing follicle releases what hormone?
What part of the follicle releases it?
What does it do?
How long does it last?

Back 4

Granulocytes release increasing amounts of Estradiol into circulation -->
- effects on cervical mucus and endometrium --> facilitate sperm migration and blastocyst implantation

Normally, estradiol has negative feedback on pituitary...
Estradiol continues to increase until reaches critical level for sustained length of time --> begins POSITIVE FEEDBACK on pituitary ---> LH/FSH SURGEEEEEEEE

Front 5

What are the effects of the mid-cycle surge of FSH and LH?

Back 5

1. Ovulation - cause rupture of dominant follicle with release of oocyte

2. Change primary product of steroidogenesis from estradiol to progesterone

-------> Follicle thus changes to the Corpus Luteum

Front 6

Describe the appearance of the follicle
Describe the appearance of the corpus luteum

When does the follicle become the CL?

Back 6

Follicle = thin-walled cystic structure
CL = solid yellow body

Follicle becomes CL after LH/FSH surge

Front 7

What are the phases of the menstrual cycle and, on average, on what days do they occur?

Back 7

Follicular/Proliferative Phase = 0-14 days
- Straight, narrow glands with pseudostratification and mitosis
- Uncoiled spiral arteries
- Expansion of stroma
- Proliferation of all components to max thickness of 5mm

Ovulation = ~14

Luteal/Secretory Phase = 15-28
- No further increase in thickness
- Progressive glandular tortuosity and secretion
- Coiling of spiral arteries; engorged blood vessels
- Stromal edema
- Changes are maximal at time of implantation!

Late Secretory Phase
- decidualization of stromal cells (form mucous membrane) -- important for endometrial hemostasis

Front 8

What does the Corpus Luteum do?

Back 8

Secretes both estradiol and progesterone --> stimulate glandular and stromal elements (and spiral arteries) of endometrium to create an optimal environment for implantation of blastocyst

Front 9

When does implantation occur (if conception takes place)?
What else is occurring right then?

Back 9

6-7 days after ovulation
= peak hormone secretion by CL

Front 10

What happens to the CL if conception does not occur?

Back 10

CL regresses --> estradiol and progesterone levels in circ decline -->
- endometrium degenerates
- arteries constrict rhythmically - progressive ischemia and necrosis; release of proteolytic enzs, PGs, tissue factors ---> vaginal bleeding and sloughing off of tissue... = period
- relieve inhibitory effects on pituitary, so FSH and LH increase --> stim new group of ovarin follicles (during late luteal phase - before menstruation occurs)

Front 11

What happens to the blastocyst after implantation?

Back 11

Blastocyst forms trophoblastic cells (outer layer) --> secrete chorionic gonadotropin

Front 12

What is the trophoblast?
- Function?

Back 12

Outer layer of the blastocyst that forms after it implants
- Secretes chorionic gonadotropin --> prevents regression of the CL
...Thus, CL continues to secrete estradiol and progesterone until fetoplacental unit acquires the ability to sustain itself (~6 wks gestation)

Front 13

When can the fetus sustain itself without the corpus luteum?

Back 13

6 weeks gestation

Front 14

Where does GnRH get secreted from?
When is it secreted?

Back 14

ARCUATE NUCLEUS of the hypothalamus

- arcuate nucleus acquires ability to secrete GnRH at puberty - secreted in pulsatile fashion

Front 15

What is the normal range of GnRH pulsatile frequency?
- What controls/modulates this?
- How does the GnRH frequency change at the LH/FSH surge?

Back 15

~ 60-100 minutes (varies among ppl and with phase of menstrual cycle)
- controlled by steroid hormones, catecholamines, endorphins, other (poorly understood)
- no marked change in GnRH pulse freq during surge

Front 16

Specifically, where do LH and FSH come from?

Back 16

- synthesized by gonadotrophs, specialized cells in the anterior pituitary, in response to GnRH from the hypothal
- 2 pools of gonadotropins stored in pituitary under stim of GnRH:
--- Releasable Pool = source of midcycle surge
--- Reserve Pool

Front 17

What is the hypothalamus' role in the midcycle surge of LH/FSH?

Back 17

None.

Front 18

What are theca cells?
- Shape?
- What do they produce?

Back 18

= Spindle-shaped cells of the follicle; modified ovarian stromal cells separated from the granulosa cells by a basement lamina; highly vascularized
- Have LH receptors
- Produce androstenedione and testosterone
....--> androstenedione diffuses across basement lamina to the granulosa cells

Front 19

What are granulosa cells?
- What do they produce?

Back 19

= Cells of the follicle
- Have FSH receptors
- FSH converts androstenedione (diffused across basement lamina fro theca cells) into estradiol
- Produce Estradiol and Estrone

Front 20

What is Luteinization?

Back 20

When the dominant follicle becomes the corpus luteum after the FSH/LH surge

Front 21

How long is the CL's lifespan in the absence of pregnancy?

Back 21

~2 weeks

Front 22

Endometrium
- layers?
- components?

Back 22

Layers: Basal and Functional

Components: vascular, glandular, stromal
**Components change continuously throughout menstrual cycle under influence of ovarian steroid hormones

Front 23

During sloughing off of the endometrium, what is the difference in the two layers?

Back 23

Basal layer does not slough off!!! (functional layer does)
... Basal layer immediately begins to regenerate a new functional layer

Front 24

Normal age of onset of menstruation
- racial exception?

Back 24

13 (11-13)
- a little earlier in African Americans

Front 25

Normal frequency of menstruation?
Normal duration of menstruation?
Normal blood loss during on cycle?

Back 25

Frequency: 28 days (25-33)
Duration: 5 days (3-7)
Blood Loss: 45 ml/cycle (30-100)

Front 26

What is Molimina?

Back 26

PMS!!!
- due to progesterone (secreted by CL)

(technically, "PMS" is molimina to a "pathological" degree)

Front 27

What is the only source of progesterone in a non-pregnant woman?

Back 27

CORPUS LUTEUM

Front 28

What is dysmenorrhea?
- cause?

Back 28

= Painful periods

- large role of Prostaglandins - breakdown of endometrium and uterine contraction

Front 29

What is Diapedesis?

Back 29

Movement of blood cells (esp WBCs) from within the vessel out into the surrounding tissue

Front 30

What physical event occurs WITHIN the follicle to allow ovulation?

Back 30

Myoepithelial cells (smooth muscle) contract due to PGs stimulated by LH and FSH