Ovary, Hypothalamus/hypophysis Flashcards
Ovary functions
- Production of oocytes
-
Production of hormones
- Sex steroids - estradiol & progesterone
- Protein hormones - relaxin, inhibin, activin
Ovarian cycle
- Follicular phase (day1-14)
- Ovulation (day 14-15)
-
Luteal phase (day 15-28)
- Luteal regression begins ~day 24
How does follicle number change from birth to menopause?
You’re birthed with ~1 million primordial follicles, but you lose them through atresia nad through ovulation.
At menopause, you only have about 1000 primordial follicles, but they can’t develop –> loss of estrogens & progestins
What’s the average length of the ovarian cycle?
What is day 1 of the cycle represent?
What is menarche? What is menopause?
28 days
Day 1 of cycle = Day 1 of menses
Menarche: initiation of menses; ~12yo
Menopause: cessation of menses; ~50yo
Cycles vary from 21-35 days. What phase is the variation occuring in?
Follicular phase
Luteal phase is always 14 days
What happens in the follicular phase vs the luteal phase of the ovarian cycle? (general)
What happens in the ovarian cycle vs the uterine cycle?
What are the 4 stages of follicular development?
What are the cell types that make up follicles?
Primordial -> Primary -> Secondary (antral) -> Mature (Graafian)
Cell types: oocyte, granulosa cells, theca
What is the chromosome number of the oocyte in each follicular stage?
Primary oocyte (4N) until it meiosis makes it a secondary oocyte (2N) in the graafian follicle
Describe how the structure of the primordial follicle changes in maturation to the primary follicle
-
Primordial follicle (inner to outer)
- Primary oocyte
- > basement membrane
- > follicular (squamous) cells
- > stroma
Follicular cells become granulosa cells & zona pellucida forms
-
Primary follicle:
- Primary oocyte
- > zona pellucida
- > granulosa cells (w gap junctions)
- > basement membrane
- > theca from fibroblast cells
What are the white bubbles at the edge of this ovary?
Primordial follicles
The majority of ovarian cancer arises from what cells?
The germinal epithelium at the cortex
What is the “PO”?
Primary oocyte
you can see how its wrapped by granulosa cells
What are the arrows pointing at?
At the edge by primordial follicles, so it’s germinal epithelium
Label these as primordial or primary follicles
Both are primary follicles because they have those granulosa cells and you can see the theca outside the basement membrane
Describe the structure of the secondary (antral) follicle
- Inner to outer:
- oocyte
- zona pellucida
- Granulosa cells & fluid-filled antrum
- basement membrane
- theca interna, theca externa - fibroblast-like cells differentiating into hormone-producing cells
What is this?
A secondary follicle because you can see the fluid filled antrum forming (white arrows)
TI= theca interna
Zona pellucida
gel-like, proteinrich layer secreted by oocyte
As the secondary (antral) follicle matures, what grows larger?
The antrum
Corona radiata
First layer of granulosa cells directly adjacent to the zona pellucida (mouse arrow).
- Remains at ovulation
- Sends cell processes through teh zona pellucida to communicate with the oocyte
What is the white arrow poitning to?
Basement membrane (usually stained a little pinker or darker red than this), but you know it’s between the granulosa and the theca
Cumulus oophorus (CO)
all the granulosa cells that surround the oocyte, including that first layer - the corona radiata
Structure of the mature Graafian follicle
Whats the difference between it and the secondary follicle histologically?
Very similar to the mature secondary follicle.
The only difference is its location - it’s gonna be closer to the edge because it was chosen to be ovulated
Name the differentiation that occurs in follicle development
Squamous cells
–> Granulosa cells: secrete estrogens, has FSH receptors
Fibroblasts
–> theca interna: secrete androgens, has LH receptors
–> theca externa: fibrous & vascualr
Follicular atresia
Happens to the majority of follicles; occurs via apoptosis
- Starts during fetal life, continues a few years past menopause
- Occurs at any stage during follicular development
What does follicular atresia look like histologically?
The cumulus oophorus separates from the oocyte
Nuclei of granulosa cells look fucked up and squiggly
Hormones involved in ovarian follicle development
GnRH (hypothalamus) goes to pituitary gonadotrophs
FSH & LH (pituitary) goes to granulosa & theca cell FSH & LH receptors to cause follicle development
Estradiol & inhibin B (ovary)
Estrogen & progesterone-
Which one peaks before ovulation? Which one peaks after?
Why can’t FSH ever be as high as LH?
It has inhibin suppressing it
GnRH
Describe its path and its funciton
- Decapeptide synthesized by neuroendocrine cells whose cell bodies are in the arcuate & preoptic nuclei
- Released into primary capillary plexus in median eminence
- Hypothalamohypophysial portal system
- Pars distalis, where it binds GnRH receptors on gonadotrophs to synthesize and release FSH & LH
Fxn: pulsatile secretion in men and women causes puberty onset
GnRH regulation during follicular phase
During the late follicular phase, positive feedback from estradiol –> increase the pulse frq of GnRH
GnRH regulation during the luteal phase
Negative feedback from progesterone –> decrease GnRH pulse frq
Other than estradiol (increase) and progesterone (decrease), what else influences GnRH pulse rate?
- Stimulates: norepinephrine
- Inhibits: dopamine, endorphins, melatonin, CRF
What phase is the follicle in when estrogen reaches its peak?
What happens at peak estrogen?
Late secondary follicle- lots of granulosa cells producing estrogen
Low estrogen was negative feedbacking and suppressing GnRH, FSH, and LH.
But at these high levels, it then positive feedbacks and increases GnRH, FSH, & LH
What is teh follicle in when progesterone reaches its peak?
What happens?
Progesterone is released from the corpus luteum
It negative feedbacks GnRH, FSH, and LH
What causes the LH surge?
The peak of estradiol!
Estradiol positive feedback does not result in an FSH surge due to inhibin secreted by the granulosa cells suppresses FSH.
Why doesnt estradiol positive feedback also result in an FSH surge?
Inhibin B secreted by granulosa cells selectively suppresses gonadotrophs secreted FSH
Targets pituitary and theca interna!
What happens after the LH surge?
All that LH binds the LH receptors on theca cells
–> suppression of LH-induced synthesis of androgen precursors
–> no androgen precursors, so decreased estradiol synthesis.
Do FSH & LH increase or decrease with age?
How do their relative proportions change in age?
Increase.
Reproductive period: more LH than FSH
Menopause: more FSH
What kind of follicle is this
Squamous lining so it’s not granulosa cells - it’s a primordial follicle
What are the light-staining cells surrounding the tip of the arrow?
granulosa lutein cells are paler
Theca interna cells
Only way you can differentiate between theca interna & externa is just proximityt to the granulosa cells.
Coiled glands -> secretory phase of uterus
Progesterone
Primary oocyte
Late (multilaminar) primary follicle
(no antrum, so its not secondary)
Secretory phase because coiled glands
external os
Stratum granulosum
Cumulus oophorus is the granulosa cells connecting corona radiata to the rest of the granulosa cells; this is what will get degraded to release the oocyte
Menstrual uterus - you can see the endometrium sloughing off
B,D,A,C
A = epididymis due to stereocilia & smooth epithelial lining
B = seminiferous tubules in the testes
C = vas deferens due to 3 layers of smooth muscle
D = efferent ductules due to wavy epithelium
remember, SEVENUP
