Reproductive System Flashcards
Describe the Ovary.
The ovary contains a cortex and a medulla, and a tunica albuginea (not as fibrous as that of the testis) just under its surface epithelium.
The ovary has both an endocrine function (produce hormones) and an exocrine function (produce oocytes).
Hormones are produced by developing follicles
Follicles are transformed after ovulation to corpora lutea (to produce a different set of hormones).
The ovary responds to pituitary hormones, including FSH and LH.
Describe the Ovarian Cortex.
The cortex contains the developing follicles.
The cortex is peripherally located except in mare.
The mare ovary has the cortex in the center, and an ovulation fossa on one edge.
The ovary contains follicles of many stages of development and regression.
Tissues between the follicles is referred to as stroma; stromal cells are fibroblast-like, with lipid droplets.
Describe the Tunica Albuginea and Serosa.
The tubica albuginea is connective tissue around the outer edge of the cortex, but it is not as fibrous as in the male.
The tunica serosa covering the ovary (also called mesovarium) has simple cuboidal epithelium (with age it gets more squamous).
Describe the Ovarina Medulla.
Contains the blood vessles for the ovary.
The medulla and/or cortex also contains a system of channels lined by cuboidal epithelium, called the rete ovarii (a developmental equivalent of the rete testis). These can form cysts or tumors.
Describe the Oogenesis.
Oogonia (the stem cell) divide mitotically until birth or shortly thereafter, and give rise to primary oocytes, which become arrested in meiotic prophase I.
When stiumlated to divide, the primary oocyte completes meiosis I, dividing to form the secondary oocyte and the 1st polar body. There is unequal division of cytoplasm between daughter cells, and the secondary oocyte is much larger than the polar body.
The secondary oocyte is formed just prior to ovulation in most species (although the bitch & mare ovulate the pirmary oocyte, before it divides.
Therefore ‘all’ observable follicles on slides of postnatal ovaries contain primary oocytes arrested in prophase I, regardless of the stage of development of the follicle.
The secondary oocyte undergoes the 2nd meiotic division right after fertilization (usually), to form the ovum and the 2nd polar body.
Describe Ovarina Follicles
The oocytes are indside follicles, surrounded by capsule-like structure called the zona pellucida, and a layer of epithelial cells called follicular epithelial cells, or granulosa cells.
The zona pellucida is a thick glycoprotein layer secreted by both the oocyte and the granulosa cells.
There is a basement membrane around the follicular epithelial cells, and a theca (theca interna and theca externa) around the follicle outside the basement membrane.
Stages or follicle development are describe based on their appearance: primordial, primary, secondary, and tertiary (or Graafian).
Describe a Primordial follicle.
Ooctye is surrounded by a single layer of squamous cells. These follicles are quiescent. There is a basement membrance between the follicle and the ovarina stroma.
Describe Primary Follicle.
Primary follicle - the oocyte is surrounded by cuboidal granulosa cells
Some texts say it has to be a single layer of granulosa cells.
“Late Primary”: is a term sometimes used to refer to primary follicle with more than one layer of granulosa cells.
For the purpose of this class, the follicle is primary until fluid begins to accumulate between the granulosa cells.
The zona pelludia forms around oocyte (not seen in this image).
The theca may also be forming.
Describe secondary follicle.
Small pockets of follicular fluid appear between granulosa cells.
The pockets have not yet coalesced into one large fluid cavity (the antrum).
The theca becomes obvious.
Tertiary Follicle
This has one large fluid-filled cavity (antrum), with a layer of granulosa cells around the periphery (stratum granulosum, ZG)
The oocyte is surrounded by granulosa cells called the cumulus oophorus.
The corona radiata (CR) is the layer of granulosa cells immediately in contact with the zona pellucida.
The cumulus oophorus is attached to the wall of the follicle by a mass of granulosa cells called the hilus.
Ovarian Follicles
The granulosa cells of more advanced follicles are divided in to specific areas, including cumulus oophorus, corona radiata, and stratum granulosum.
Atretic follicles are follicles that are degenerating, and this can happen at any stage.
Describe an Atretic follicle.
Follicular atresia - many follicles degenerate to become atretic. This can happen at any stage of the follicle development.
Depending on the species, 50-75% of antral follicles (follicles with an antrum) will be atretic at any given time.
Interstitial Cells
Interstitial cells in the cat and dog are formed from theca interna cells which persist.
Ovarian Cycle Overview.
Ovarian cycles can be divided into 5 groups, with differences in physiology:
Primate menstrual cycle
Domestic animal cycles - cows, sheep, goat, pig, horse, ginea pig (because its cycle is like these others)
Labratory rodent cycles - need copulation to form a fully functional CL
Reflex (induced) ovulators - rabbit, cat, mink, ferret, camelids - need copulation to cause ovulation
Canine cycle - dog and wolf, CL persists for a period approximating normal pregnancy in unmated animals, or after a non-fertile mating (pseudopregnancy).
There are generally two phases to the ovarian cycle: follicular and luteal
Luteal Phase
The Corpus Luteaum (CL) is a transient endocrine gland, derived from an ovulated follicule, that produces progesterone to play a critical role in the establishment and maintenance of pregnancy.
Eventually it undergoes regression, loses the capacity to produce progesterone, and involutes to become a connective tissue scar.
It’s duration varies widely between species, and can be affected by mating and/or pregnancy.
CL regression is an example of apoptosis. PGF2a is involved in most species, and probably oxytocin pulses from the hypothalamus, and large or small amounts of oxytocin produced by the CL itself.
Define Apoptosis
A genetically determined process of cell self-destruction that is marked by the fragmentation of nuclear DNA, is activated wither by the presence of a stimulus or by the removal of stimulus or suppressing agent, is a normal physiological process eliminating DNA-damaged, superfluous, or unwanted cells (as immune cells targed against the self in the evelopment of self-tolerance or larval cells in amphibians undergoing metamorphosis), and when halted (as by genetic mutation) may result in uncontrolled cell growth and tumor formation - called also programmed cell death.
Define Necrosis
Death of living tissue; speficically : death of a portion of tissue differentially affected by local injury (as loss of blood supply, corrosion, burning, or the local lesion of a disease)
Follicular Phase
The previous CL is degenerating/regressing.
The follicle is maturing toward ovulation
Estrogen is being produced by the granulosa cells in response to FSH.
Estrogen and FSH cause the expression of LH receptors on the granulosa cells; FSH recepotrs decline.
Rising estrogen in the late follicular phase initiates the LH surge, which triggers ovulation.
In the uterus: the endometrium is proliferating.
Theca cells have LH receptors, and are stimulated by LH to produce androgens that diffuse into the follicle.
Describe Granulosa cells in Follicular Phase.
Have FSH receptors intially, and are stimulated by FSH to produce estrogen from the androgens. Estrogen has a postive feedback on granulosa cells, stimulating proliferation of more granulosa cells.
Granulosa cells develop LH receptor (in response to FSH and estrogen) late in the follicular phase, to make them sensitive to the LH surge that precedes ovulation. FSH recepotrs decrease.
Pre-ovulatory LH Surge
Rising estrogen levels during the follicular phase stimulate release of LH from pituitary - the high estrong at the end of the follicular phase causes an LH surge, which:
Stimulates primary oocyte to complete meiosis I.
Starts process of ovulation
Induces formation of the corpus luteum (CL) in the ovulated follicle.
