Flashcards in Histology: Female Reproductive System Deck (44):
Outline the process of oogenesis
1. Embryonic gonads contain primordial germ cells
2. PGCs undergo mitosis --> oogonia
3. 5th month of foetal development: oogonia enlarge and divide --> primary oocytes
4. Primary oocytes enter meiosis I
5. 7th month of foetal development primary oocytes surrounded by layer of flattened cells --> primordial follicles
6. Primordial follicle (encapsulation) blocks first meiotic division, keeping the follicle in prophase I
7. No further changes occur until puberty
What is atresia in the ovarian cycle?
When the remained of the follicles degenerate or regress in a cycle (only one matures enough to be ovulated)
What are the three phases in the ovarian cycle?
Follicular, ovulatory, luteal
Describe the primary follicle stage in the follicular phase
Stimulated primordial follicles --> increase in size, oocyte enlargers --> cells surrounding follicle multiple (change from simple squamous to simple cuboidal) --> granulosa cells now line follicle --> zona pellucida between oocyte and granulosa is formed
What is the zona pellucida?
A thick glycoprotein and acid proteoglycan layer between the oocyte and granulosa cells
What is stroma?
General term for the supporting tissue which is rich in fibroblast-like cells
What is the ovary surrounded by?
Cuboidal/columnar germinal epithelium
Where is the tunica albuginea located in women?
Fibrous layer beneath the germinal epithelial surrounding the ovary
Describe the growing follicle stage
Granulosa cells form multi-layered capsule around the oocyte (zona granulosa, ZG), the stroma around follicle starts to organise into theca folliculi (TF) and most follicles present are primordial
Describe the secondary (antral) follicular stage
Remaining follicles take up fluid to develop the follicular antrum; the oocyte is embedded on one side in the zona granulosa cells ( cumulus oophorous cells) and the surrounding theca organises into the theca interna and theca externa
What is the cumulus oophorous?
Group of granulosa cells that connect the primary oocyte to the rest of the granulosa cells (appears to form a stem-like structure)
What does the theca interna do?
Secretes androgen precursors
Describe the Graafian follicle stage
First meiotic division completed just prior to ovulation (secondary oocyte and first polar body) --> antrum enlarges, secondary oocyte is attached to the side by bridges of granulosa (corona radiata) and the follicle begins to bulge from the side of the ovary in preparation for rupture --> ovulation
What does the ovum consist of?
Secondary oocyte, zona pellucida and corona radiata of granulosa cells
When does the second meiotic division of the secondary oocyte complete?
At fertilisation --> fertilised egg (zygote) and second polar body
Describe the ovulatory phase
Ovarian wall thins next to Graafian follicle, and ruptures in order to expel the ovum (secondary oocyte) into the peritoneal cavity
What is the role of progesterone?
Prepares endometrium for implantation
Describe the luteal phase
After ovulation, the granulosa cells and theca cells, of the ruptured Graafian follicle remnants, proliferate and form a highly vascularised endocrine structure known as the corpus luteum (yellow body) which secreted progesterone and oestrogens
What happens in the luteal phase if fertilisation/implantation doesn't occur?
If fertilisation/implantation doesn’t occur, corpus luteum degenerates and leaves a fibrous scar known as the corpus albicans (white body)
What happens in the luteal phase if fertilisation/implantation does occur?
If implantation occurs, the developing placenta secretes hCG in order to maintain the corpus luteum and its secretion of progesterone
What is the function of the oestrogen produced by the corpus luteum?
Oestrogen maintains the uterine mucosa still
What is the function of the progesterone produced by the corpus luteum?
Progesterone promotes secretion from the mucosal glands to provide a suitable environment for a fertilised ovum to implant
Describe the formation of the corpus luteum
After ovulation, the granulosa cells of the Graafian follicle hypertrophy (called granulosa lutein cells), the theca lutein cells are derived from the theca interna cells and continue to produce mainly androgens and there is also connective tissue septa which carry blood vessels into the structure
Outline the hormonal control of the ovarian cycle
1. GnRH --> FSH and LH production
2. LH and FSH --> growth and development of ovarian follicles
3. Growing follicles produce oestrogen which, alongside inhibin production --> negative feedback to go to hypothalamus and pituitary --> inhibit LH and FSH release
4. Rising oestrogen levels --> positive feedback loop --> LH and FSH surge
5. This LH surge --> completion of meiosis I of the primary oocyte --> secondary oocyte --> production of enzymes that weaken the ovary wall, leading to ovulation
6. After ovulation, LH promotes the transformation of the ruptured Graafian follicle --> corpus luteum
7. The corpus luteum then produces progesterone, oestrogen and inhibin --> inhibits FSH and LH production as well as inhibit the development of any further follicles
8. Decrease in LH --> corpus luteum starts to degenerate --> oestrogen and progesterone levels fall --> allows FSH and LH to be produced again by the pituitary gland --> cycle starts again
What are the different parts of the uterus?
Fallopian tubes, fundus (body) of uterus and cervix
What is the stratum functionalis?
The stratum functionalis is a thick superficial layer of the endometrium that is sloughed off during menstruation and grows anew during each cycle
What is the stratum basalis?
Just superficial from the myometrium and this is not shed during menstruation and new glands develop from it
What is the fallopian tube covered by?
What is the endocervical canal?
Links the vagina to the body of the uterus
Describe the histology of the uterine cervix
Has folded mucosa, and is lined by simple columnar epithelial cells which make a mucous secretion
What is the function of the cervix?
Role of cervix is to admit spermatozoa to allow fertilisation of the ovum around time of ovulation, and to protect upper parts of tract from bacterial invasion
How does the cervix facilitate changes so that it's 'sperm-friendly' or 'sperm-hostile'?
Secretions of the glandular mucosa undergo cyclical change during the menstrual cycle to facilitate these roles (sperm-friendly, sperm-hostile)
What is the histology of the endocervical canal
By the external os, the endocervical mucosa epithelium is stratified squamous like that of the vagina due to exposure to more hostile, acidic environment
What is the vagina?
A fibromuscular canal
Describe the histology of the vagina
Lined by mucosal, stratified squamous epithelia, has dense lamina propria with many elastic fibres and a rich vasculature, lubrication of mucosa derived from cervical mucus and trans-epithelial exudate from thin-walled vessels in the lamina propria
What is the adventitia of the vagina continuous with?
This connective tissue merges with the adventitia of the bladder anteriorly and the rectum posteriorly
What is the myometrium?
Muscle layer of the uterus
Describe the histology of the myometrium
Fascicles of muscle fibres run in different directions forming ill-defined layers and it contains rich network of arteries and veins which are supported by dense fibrocollagenous tissue
How does the myometrium change during pregnancy?
Increases greatly in size in response to oestrogen and this increase in mass is mostly due to hypertrophy of the smooth muscle cells, but increased cell number (hyperplasia) also plays a role
What are the three phases of the menstrual cycle?
Menstrual phase (1-5), proliferative (6-14), secretory (15-28)
Describe the menstrual phase of the menstrual cycle
Days 1-5: functional layer of endometrium becomes detached from uterine wall and bleeding and detached tissue and blood passes through vagina as menstrual flow
Describe the proliferative phase of the menstrual cycle
Days 6-14: due to increased oestrogen levels, endometrium begins to proliferate and thicken, the tubular glands extend and spiral arteries form. The oestrogen produced stimulates the expression of endometrial progesterone receptors and ovulation occurs at the end of this phase
Describe the secretory phase of the menstrual cycle
Days 15-28: rising progesterone levels (from corpus luteum) act on endometrium to stimulate enlargement of endometrial glands and their secretion of mucus and glycogen in preparation for implantation of the fertilised ovum. If fertilisation doesn’t occur --> corpus luteum degenerates --> progesterone levels drop --> endometrium degenerates. Cycle then begins again