Flashcards in Lecture 34: Reproductive Histology Deck (14)
Structure of Testis
* Tunica albuginea:
- CT capsule surrounding testis
- Thickened posterior part of capsule = mediastinum testis:
-- Extends CT septa that divide testis into lobules
* Seminiferous tubules:
- Highly convoluted
- 30-70 mm long
- Site of spermatogenesis
* Intratesticular ducts (convey sperm to surface of testis):
- Tubuli recti: Simple columnar epithelium
- Rete testis: Simple cuboidal epithelium
* Extratesticular ducts (conduct spermatozoa outside the body):
- Seminal vesicles
- Prostate gland
- Bulbourethral (Cowper’s) glands
* Functions of testis:
- Produces spermatozoa
- Endocrine functions:
-- Leydig cells: Produce testosterone
-- Sertoli cells: Major role in controlling spermatogenesis
* Primordial germ cells (2N)
* Spermatogonia (2N)
- Type A (stem cells)
- Type B:
- Leave mitotic cycle and enter meiotic cycle under influence of retinoic acid
* Primary Spermatocytes (2N)
- First maturation division (meiosis I)
* Secondary spermatocytes (N) x2 cells
- Second maturation division (meiosis II)
* Spermatids (N) x4 cells
- See Slides 7-14
Pathway for Sperm Transport: From Tubuli Recti --> Epididymis
* Tubuli recti
* Rete testis
* Efferent ductules:
- CT and smooth muscles surround each ductule
- Lined by simple columnar cells lying on a basement membrane.
- Tall columnar cell groups alternate with short cell groups, giving the lumen an irregular bore.
- Each cell type may bear cilia, the only motile cilia in the entire duct system.
- Tortuous and surrounded by CT
- Pseudostratified columnar epithelium with basal and tall columnar cells which may bear stereocilia
- Basement membrane surrounded by smooth muscle cells.
- See Slide 16-28 (?)
Pathway For Sperm Transport: From Vans Deferens to Ejaculatory Duct
* Vas deferens:
- Mucosa consists of pseudostratified columnar epithelium
- Lamina propria contains elastic fibers
- Submucosa consists of vascular connective tissue.
- Muscularis externa consists of an outer longitudinal, middle circular, and inner longitudinal layer.
- Adventitia is fibrous.
* Ejaculatory duct:
- Passes through the prostate gland
- Opens into the urethra on a thickened part of the urethral mucosa called the colliculus seminalis
- Lined by simple columnar or pseudostratified columnar epithelium
Follicular Structure During Oogenesis: After Puberty
* After puberty:
- Diploid primary oocyte;
- Secondary follicle with multiple layers of follicle cells and beginning of antrum formation
- Membranagranulosa surrounds outside of follicle cells.
- 2 chromatids/chromosome
- Haploid secondary oocyte + haploid polar body
- Tertiary follicle with multiple layers of follicle cells, corona radiata and large antrum:
-- Cells between membrana granulosa and antrum = mural granulosa cells.
-- Cells between zona pellucida and antrum = cumulus cells
- 2 chromatids/chromosome
Follicular Structure During Oogenesis: Ovulation
* Haploid secondary oocyte with corona radiata and thecal cells + haploid polar body:
- Granulosa cells develop FSH receptors and LH receptors
- Circulating FSH stimulates granulosa cells to produce estrogen
* 2 chromatids/chromosome
* Meiosis resumes and is arrested at metaphase II:
- Due to LH surge which shuts down gap junctions between granulosa cells and oocyte.
- Reduces transfer of cAMP and cGMP from cumulus cells to oocyte
- cAMPconcentration is reduced, allowing activation of MPF.
Tertiary (Graafian) Follicle
* Components (external to internal):
- Theca externa:
-- Produce angiogenesis factor
- Theca interna:
-- With LH receptors
-- Secrete testosterone
- Membrana granulosa
- Mural granulosa cells:
-- Develop FSH receptors
-- Synthesize aromatase in response to FSH
-- Aromatase converts testosterone into 17β-estradiol.
-- Estrogens stimulate formation of LH receptors on granulosa cells.
- Cumulus (oophorus) cells:
-- Will facilitate release of ovum at ovulation
-- Involved in fertilization
* Usually projects from the surface of the ovary like a blister.
* Takes about 9 days to develop from primordial follicle in humans.
* Note: meiosis will only resume if the egg is fertilized.
* At the end of meiosis II, the egg will have given off a second haploid polar body, and the first polar body may also divide (theoretically).
- See Slides 33-35
Ovarian Cycle: Ovulation
* Ovulation occurs on day 14 of the cycle.
* The stimulus for ovulation is a rise in levels of FSH and a sharp rise in LH (also from the anterior pituitary).
* During ovulation, an egg is released from the Graafian follicle.
- The egg is surrounded by a layer of follicle cells (the corona radiata).
- The egg is arrested in the second half of meiosis (metaphase II).
- The egg will not complete meiosis unless fertilized.
- The egg is accompanied by a very small, nucleated sister cell (product of the first meiotic division) called a polar body.
* The outer part of the Graafian follicle remains behind and is made up of thecal cells, which secrete progesterone.
Ovarian Cycle: Luteal Phase
* During this phase the residual thecal and granulosa cells of the follicle, left over after ovulation, secrete estrogen and progesterone.
* The residual theca and granulosa cells proliferate and form a large glandular structure called the corpus luteum.
* The progesterone and estradiol are necessary to maintain the implantation of the fertilized oocyte.
* If fertilization does not occur:
- The corpus luteum regresses and levels of progesterone and estradiol decrease, resulting in the beginning of the next menstrual phase.
- Inhibin, released by the granulosa cells, inhibits secretion of gonadotropins, especially FSH, resulting in regression of the corpus luteum
- See Slide 38-42
* Layers of the wall of the uterus:
--- Columnar surface epithelium
--- Uterine glands
--- Connective tissue stroma
--- Spiral arterioles
--- Functional layer
--- Basal layer
- Mucosal surface is characterized by numerous crypts.
- Epithelium produces a glycoprotein-rich cervical mucous:
-- Mucous composition varies throughout uterine cycle, being thinnest around the time of ovulation.
- Lined with stratified, non-keratinized squamous epithelium
- Epithelium secretes glycogen throughout menstrual cycle:
-- Glycogen breakdown products contribute to low pH of vaginal fluids
- See Slides 46-48
Endometrial Cycle Overview
* The endometrial cycle refers to the cyclic changes in the endometrium and lasts, on average, 28 days.
* The cycle begins with the first day of menstruation and ends 28 days later.
* The endometrial cycle can be divided into three phases:
- Menstrual phase (Days 1-4 or 5)
- Proliferation phase (Days 4-14)
- Secretory phase (Days 15-28)
* The endometrial cycle essentially prepares the lining of the uterus to receive the fertilized egg.
* Implantation of the fertilized egg occurs about seven days after ovulation.
* Ovulation occurs on day 14 of the menstrual cycle.
* If fertilization does not occur, then decreasing levels of estradiol and progesterone result in the vasoconstriction of the spiral arterioles supplying the endometrium followed by the sloughing off of the endometrium at the beginning of the next cycle.
Endometrial Cycle: Proliferation Phase
* Endometrial growth increases the endometrial thickness from 1-2 mm to 8-10 mm by day 14.
* Blood vessels and glands grow with the expanding endometrium.
* Cells that initiate the growth come from the bases of the glands that formed in the previous endometrium that were deep enough to survive the loss of the previous endometrium.
* The proliferation phase is due to an increase in levels of estradiol secreted by the granulosa cells of the developing ovarian follicle.
* Near the end of this phase there is a sharp rise in estradiol levels.
Endometrial Cycle: Menstrual Phase
* During this phase the endometrial build-up from the previous cycle sloughs off, resulting in the menstrual flow.
* Menstruation begins with vasoconstriction of the spiral arteries that have been supplying the endometrium, followed by local ischemia.
- This vasoconstriction is mediated by prostaglandins.
- Inflammatory cells invade the area and continue the process of endometrial breakdown.
- Factors that inactivate the clotting process maintain bleeding until the lining is sloughed off.
- See Slide 52