Flashcards in 37 - Female Reproduction I Deck (104):
Where is gonadotropin-releasing hormone (Gn-RH) secreted from?
The hypothalamus via neurosecretory cells
Describe the process of Gn-RH secretion
Gn-RH is packaged into vesicles which then flow down the axons of neurosecretory cells and to the axon terminals
There are three routes that Gn-RH can take in order to be delivered to the anterior lobe of the pituitary gland. What are they?
1 - Primary capillary plexus
2 - Hypophyseal portal veins
3 - Secondary capillary plexus
What happens when the Gn-RH reaches the pituitary gland?
- Gn-RH enters the parenchyma (cellular part) of the pituitary
- It then stimulates basophilic gonadotropes
What happens when basophilic gonadotropes of the pituitary are stimulated by Gn-RH?
They release follicle stimulating hormone (FSH) and luteinizing hormone (LH)
From the pituitary gland, where do FSH and LH travel? How?
FSH and LH travel through the local capillary network and then through the general circulation to get to the ovaries
What do FSH and LH do in the ovaries?
- Follicle maturation
- Formation of corpus luteum
What is the corpus luteum?
A temporary endocrine gland
How long is a typical female cycle?
Will the levels of FSH and LH be high or low during the first half of the cycle?
What happens at mid-cycle (day 13)?
- Small spike in FSH which stimulates follicle maturation and oocyte release
- Large spike in LH which helps to release the oocyte from the ovary (ovulation)
Does each follicle contain an oocyte?
What is the other name for follicle cells?
What do follicle (granulosa) cells do?
Produce and release estrogen and progesterone
What do estrogen and progesterone influence?
The endometrial lining of the uterus
There are three layers of the uterus. What are they?
1 - Outer perimetrium
2 - Myometrium
3 - Endometrium (innermost)
Describe the endometrium
There are two layers...
- Basal layer which is deeper and is connected to the myometrium
- Functional layer which is reformed each menstrual cycle in response to estrogen and progesterone
What does estrogen do specifically?
Stimulates the thickening and proliferation of connective tissue in the functional layer
What does progesterone do specifically?
Stimulates glands in the functional layer to produce and release secretory products
When do estrogen and progesterone increase during the cycle?
Just before mid-cycle (before FSH and LH)
Why do estrogen and progesterone increase during this time?
In order to prepare the endometrium for possible implantation
Describe the development of an oocyte before implantation
What layer of the endometrium does the blastocyst implant into?
What happens if there is no implantation?
The functional layer sheds
What prompts the functional layer to shed?
A drop in estrogen and progesterone
What is an ovary?
An almond-shaped structure that is covered by mesothelium
What type of cells will you find in the mesothelium of an ovary?
simple squamous or cuboidal epithelium
What is the purpose of the mesothelium?
Provides a thin layer of fluid on the outer surface of the ovary (single layer of cells)
What do you find immediately deep to the epithelium of the ovary?
The tunica albuginea or "white coat"
What is the purpose of the tunica albuginea or "white coat"?
A protective envelope that completely covers the ovary
What is the tunica albuginea or "white coat" composed of?
Dense irregular connective tissue
What do you find deep to the tunica albuginea or "white coat"
Cortical (outer region) of the ovary
What would you find in the cortical region of the ovary?
- Follicles of different development stages
- Follicles of embedded in dense CT
- Follicle (granulosa) cells that surround the oocyte while it matures
What process takes place in the cortical region of the ovary?
Oogenesis: creation of an ovum (egg cell)
What process will occur just before an oocyte is ready to undergo ovulation?
Granulosa cells around the mature oocyte produce estrogen and progesterone which prepares the endometrial lining of the uterus
What is the center region of the ovary?
What is found in the medullary region?
Blood vessels, lymphatic vessels, nerve fibers
Describe the structure and function of the blood vessels in the medullary region
- Dilated capillaries bring in nutrients and remove waste
- Vessels are embedded in loose connective tissue
What happens to an ovary after having many oocytes released?
It becomes dimpled because ovulation disrupts the epithelium and forms scar tissue
This dimpling increases with age
Where do most ovarian cancers arise from?
Germinal epithelium that covers the ovary - 70%
What are primordial follicles?
The most immature follicles found in the ovary
When do we develop primordial follicles?
Present since before birth
What happens to primordial follicles during puberty?
Each month during puberty a few primordial follicles undergo maturation
What eventually happens to the oocyte that is inside of primordial follicles?
After maturation, the oocyte that is inside is released from the ovary during ovulation
Describe a single chromatid chromosome
- Centromere in center
Describe a double chromatid chromosome
- Sister chromatids
What does haploid mean?
"single set" - 23 chromosomes
What does diploid mean?
"double set" - 46 chromosomes
How do we abbreviate the chromosome number?
haploid = 1 n
diploid = 2 n
Do sex cells (i.e. egg, sperm) contain 23 or 46 chromosomes each?
23 - they are haploid (1 n)
Do somatic (body) cells contain 23 or 46 chromosomes each?
46 - they are diploid (2 n)
How do we abbreviate the amount of DNA content?
What does "1 d" mean?
The amount of DNA in 23 SINGLE-chromatid chromosomes
What does "2 d" mean?
The amount of DNA in 23 DOUBLE-chromatid chromosomes
The amount of DNA in 46 SINGLE-chromatid chromosomes
What does "4 d" mean?
The amount of DNA in 46 SINGLE-chromatid chromosomes
When does oogenesis begin?
What is oogenesis?
The process by which primordial germ cells differentiate into mature ova or "eggs" and are prepared for fertilization
Can sperm fertilize a primordial germ cell?
No it must first become a mature ova
How many cell divisions occur prenatally in the process of ova maturation?
2 meiotic cell divisions
Where do primordial germ cells arise from?
The umbilical vesicle ("yolk sac")
During migration of the primordial germ cells to the ovaries, are they undergoing mitotic divisions?
Once the primordial germ cells reach the ovaries, do they stop undergoing mitotic divisions?
No, mitotic divisions continue within the ovaries
We have a special name for primordial germ cells that are found in the ovaries. What is it?
Describe an oogonia in terms of chromosomes and DNA
2n - diploid, 46 chromosomes
2d - 23 double or 46 single chromatid chromosomes
When does oogenesis begin?
Between the 3rd and 7th months of prenatal development
Do all oogonia begin oogenesis at the same time?
What happens during interphase of oogenesis before meiosis I?
46 double chromatid chromosomes are formed
What stage is oogenesis suspended in until puberty?
What stage is oogenesis in when a baby girl is born?
The ovary of a newborn will contain primary oocytes (2n-2d) which are suspended in prophase I of meiosis I
What happens every month starting at puberty?
Several follicles containing a primary oocyte that are suspended in prophase I will undergo maturation and usually only one is released
What period of the lifespan will primordial follicles be present in the ovary?
Prenatally and throughout reproductive years (until age 50-55)
What happens 12 hours before the oocyte is released from the ovary?
It completes meiosis I (metaphase, anaphase and telophase) then enters meiosis II
What happens during meiosis I?
- Homologous pairs of chromosomes split
- Each oocyte contains 23 double chromatid chromosomes
- Oocyte enters metaphase 2 and stops
When does meiosis II occur?
When the oocyte is contacted by a sperm
What type of chromosomes do mature oocytes contain?
23 single chromatid chromosomes
REVIEW of meiosis of oocytes
1. Meiosis I begins prenatally
2. Meiosis I stops at prophase I
3. Meiosis I resumes in puberty, 12-24 hours before ovulation for each individual oocyte
4. Meiosis I generates 23 double chromatid chromosomes
5. Meiosis II begins immediately after meiosis
6. Meiosis II stops at metaphase II
7. Ovulation occurs
8 Meiosis II resumes if/when the oocyte is fertilized in the fallopian tube or uterine tube
Describe the general structure of an ovarian follicle
An oocyte in the center surrounded by one layer of follicle cells and multiple layers of follicle (granulosa) cells
Describe a primordial follicle
- Primary oocyte suspended in prophase I
- Single layer of flat follicle cells
- Basal lamina found outside of follicle cells
- Outermost cells are part of the cortical stroma
What are the stages in a growing follicle?
1 - Unilaminar primary follicle
2 - Multilaminar primary follicle
3 - Secondary (antral) follicle
What phase is a unilaminar primary follicle in?
Primary in prophase I
What is the name of the acellular membrane that will surround the ovary of a unilaminar primary follicle?
What is the zona pellucida composed of?
Glycosaminoglycans (GAGs) and Glycoproteins
What is the function of the zona pellucida?
It isolates the oocyte from the surrounding cells and is protective in nature
What transition will the follicle cells of an unilaminar primary follicle undergo?
The single layer of follicle cells will become cuboidal
An oocyte in a unilaminar primary follicle will synthesize Activin. What does this do?
Stimulates stratification of follicle cells
What is the second stage of a growing follicle?
Multilaminar primary follicle
What happens to the single layer of follicle cells in a multilaminar primary follicle?
The single layer becomes a multilayer of granulosa cells
How do granulosa cells communicate?
via gap junctions
What will happen to the oocyte microvilli in the development of a multilaminar primary follicle?
The oocyte microvilli will extend outward through the zona pellucida so that the cytoplasmic processes of a granulosa cell will be able to contact the oocyte microvia by gap junctions
Describe the theca interna of follicles
Dense collagenous connective tissue that forms a basket around the follicle and has endocrine function
What are the cellular characteristics and components of theca interna of endocrine cells?
- Highly vascular
- Many mitochondria
- lipid droplets
When does the theca interna form?
Begins to form in the multilaminar primary follicle stage and is well developed by the secondary (antral) follicle stage
What is the third phase of a growing follicle?
Secondary (antral) follicle stage
What phase is the oocyte suspended in during the secondary follicle stage?
Still has a primary oocyte that is still suspended in prophase I and surrounded by a zona pellucida
What is a hallmark feature of the secondary (antral) follicle phase?
Bubbles in the granulosa cells called "antral spaces"
What is contained within the antral spaces or "bubbles" of the granulosa cells?
What do the most superficial antral spaces resemble?
What are the most superficial antral spaces called?
- Because of their membrane-like appearance
- Recall that the antral spaces are still deep to theca interna
Will the theca interna be well developed during the stage of secondary (antral) follicles?
Yes - the theca externa will also be well developed at this point
When will the follicle reach a stage of being a mature follicle?
Day 14 of the menstrual cycle
What happens to the small antral spaces during maturation?
They coalesce into a continuous antrum that still contains the liquour folliculi
What is the cumulus oophorus of a mature follicle?
The pedestal-like structures of the granulosa cells that function to join follicles to membrana granulosa (outer part of the granulosa cells that resembles a membrane)
What is a corona radiata of a mature follicle?
A layer of cells that surround the zona pellucida that resemble a "radiating crown" - hence the name