Gametogenesis Flashcards
What are the phases of male gametogenesis?
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Spermatogenesis
1a. Spermatogonial
1b. Spermatocyte
1c. Spermatid - Spermiation
- Maturation
Describe the first step of spermatogonial spermatogenesis.
The primordial germ cell migrates from the extra-embryonic mesoderm to the seminiferous tubules. At the seminiferous tubules the germ cell settles into the basal lamina where the names changes to Type A (dark) spermatogonia.
What are type A (dark) spermatogonia cells named for? What is a special function of these cells?
Type A (dark) spermatogonia were named for intensely basophilic nucleus containing finely granular chromatin (diffuse)
These cells are stem cells for male reproduction.
What is the type A dark spermatogonia doing while sitting on the basal lamina of the seminiferous tubules?
While on the basal lamina the type A dark spermatogonia is undergoing mitotic replication into more type A dark spermatogonia as well as Type A light spermatogonia.
What is the difference between Type A dark and Type A light spermatogonia
Type A dark spermatogonia consists of intensely basophilic nucleus. Type A light spermatogonia has a pale nucleus and daughter cells are connected by cytoplasmic bridges.
What do Type A light Spermatogonia differentiate into?
Type A light spermatogonia differentiate into Type B spermatogonia while on the basal lamina of the seminiferous tubules.
Describe Type B Spermatogonia.
Heterochromatic with condensed chromatin in periphery of nucleus
prominent nucleolus
maintained cytoplasmic bridges from type A light
still located at the basal lamina of the seminiferous tubules
What do Type B spermatogonia differentiate into? Where do these differentiated cells then go?
Type B spermatogonia mitotically divide into primary spermatocytes.
The primary spermatocytes then move apocalyptic through the junction all complex of the Sertoli cells.
What marks the transition from spermatogonia phase of spermatogenesis to the spermatocyte phase?
When Type B spermatogonia mitotically divide into primary spermatocytes
Describe the spermatocyte portion of spermatogenesis.
- The primary spermatocyte is moving apically in the through the junctional complex of Sertoli cells.
- The primary spermatocyte begins prophase I (longest) to become (2N, 4C) then completes the first meiotic division creating the secondary spermatocyte (N, 2C)
- Continually moving apically the secondary spermatocyte undergoes a second meiotic division resulting in (N,C) spermatids
What marks the transition to the spermatid phase of spermatogenesis?
When the secondary spermatocyte meiotically divides to form spermatids. These are then located apically in close contact with cell membrane of Sertoli cells.
Which cell influences the spermatid to differentiate into a specialized cell. What are the steps of this differentiation from a spermatid to a mature sperm?
Sertoli cells
- Golgi phase
- Cap phase
- Acrosome phase
- Maturation phase
Describe what happens during the golgi phase of differentiation of the spermatid into spermatozoan.
- Proacrosomal granules accumulate in golgi complex and combine to form the acrosomal vesicle.
- The acrosomal vesicle approaches nucleus and defines anterior pole
- Centrioles migrate to posterior pole to begin organizing the atonement of the sperm tail
Describe the cap phase of differentiation of spermatids to spermatozoan.
- Acrosomal vesicle spreads over anterior surface of nucleus forming the acrosomal cap
- Nuclear envelope under the cap thickens and loses nuclear pores
- Nuclear content condenses
Describe the acrosome phase of differentiation of the spermatid to the spermatozoan.
- Cytoplasm between acrosome and cell membrane reduces
- Nucleus elongates posteriorly
- Microtubules coalesce to form manchette
- Manchette will elongate to form the “head” and transports material into flagellum
- Centrioles form connecting piece attaching flagellum to posterior surface of nucleus
Describe the maturation phase of differentiation of spermatid into spermatozoan.
- Mitochondria form sheath around flagellum - forming “middle piece”
- Excess cytoplasm is expelled forming the “residual body” -this is phagocytosis by Sertoli cell
- Now is spermatozoan
Describe what occurs during Spermiation.
- Sertoli-to-Spermatid junctional complex breaks down
- Immature spermatozoan are released into lumen of seminiferous tubule
- they are released in clumps because cytoplasmic bridges from spermatogonia persist
What chemical would you expect to increase in concentration within Sertoli cells during spermiation? Why?
Integrin-linked kinase
the sertoli-to-spermatid junctional complex was formed on beta1-integrins so when this breaks down you see an increase in this chemical
Where can final maturation occur?
Lumen of seminiferous tubule
Efferent ductule
Epididymis
What occurs during maturation of spermatozoans?
- Head of sperm decreases in size, DNA further condenses
- Sperm is more slender, cytoplasm further removed
- Lipid, protein, and glycosylation of sperm membrane changes (to promote fusion)
- Decapitation - alters outer surface of acrosomal membrane facilitating rupture
- cAMP, Ca2+, and pH shift to increase phosphorylation resulting in increased flagella and sperm motility
What is the embryonic ovary a mix of?
Connective tissue and stroma cells
During early oogenesis where do the primordial germ cells migrate to from the extra-embryonic mesoderm?
When does this occur?
Migrates to the periphery of the ovary
during the third month of development
What are the division of the ovary?
Where are the primordial germ cells located?
Outer cortex - where primordial germ cells divid and oogenesis occurs
Inner medulla
When do primordial germ cells switch to Oogonia?
When the cells reach the ovarian cortex
What is a syncytium?
Oogonia performing rapid mitotically proliferation without full cell division
Describe the formation of the primordial follicle.
- After the primordial germ cell reaches the ovarian cortex it is then referred to a as an Oogonia.
- The Oogonia begins mitotically dividing rapidly, without full cell division forming a syncytium.
- The syncytium is then invaded by stroma cells which subdivide. The resulting structure of an Oogonia surrounded by a single layer of squamous cells is called a primordial follicle.
- Squamous cells are termed follicular cells, and are surrounded by a basal lamina.
Before the syncytia break down, what phase of meiosis will the oogonia enter?
The oogonia enters interphase of Meiosis I before forming the primordial follicle.
Resulting in (2N/4C) and prominent chromatin/chromosomes in the nucleus
What are atretic follicles? What is their fate? How many atretic follicles typically occur?
Most follicles undergo atresia (spontaneous death and reabsorption)
Atretic follicles are absorbed and do not leave scar tissue.
By 7 months there are approximately 7 million follicles. About 2 million remain at birth. About 400,000 remain by puberty.
When is the oogonia referred to as a primary oocyte?
What name change occurs for the follicle?
How do the stroma cells differentiate at this stage?
What is secreted at this stage and what does that form?
When the oogonia enters metaphase I.
The follicle is now referred to as the primary follicle.
Stroma cells differentiate. Cells between basal lamina and the egg are now granulosa cells (more cuboidal/columnar and stratified). More stroma cells organize on outer surface of the basal lamina which are now theca cells.
The primary oocyte and granulosa cells secrete glycoproteins. This organizes into a coating called the zona pellucida. This contains three sperm receptors
Label this image. What stage is this of oogenesis?
Primary follicle
What occurs during maturation of a primary follicle?
- Cortical granules, special secretory vesicles produced by primary oocytes, amass at the periphery of the cell
- Oocyte develops microvilli that push through zona pellucida, between granulosa cells
- Granulosa produces cytoplasmic processes that extends between cells toward zona pelucida
- Thecal cells differentiate into theca externa and theca interna
- Granulosa cells secrete hyaluronic acid rich fluid called the liquor folliculi
- Liquor folliculi disrupts granulosa which has been weakened by cytoplasmic extensions
- Disrupted granulosa evacuate a liquor folliculi filled space called the antrum
presence of antrum signals maturation from primary follicle to secondary follicle
What is the difference between the theca externa and the theca interna? At which stage do these form?
Theca externa - mostly collagen and smooth muscle
Theca interna - highly vascularized cuboidal secretory cells
these differentiate during maturation of the primary follicle
Label this image of a follicle.
At what stage is this? How do you know?
This is a secondary follicle, you can tell this because of the antrum.
Describe the maturation of the secondary follicle.
- Quantity of liquor folliculi increases, increasing size of antrum
- Expansion of antrum subdivides granulosa cells - a)one layer remains on the basal lamina b) single-cell thick surrounds the primary oocyte called the corona radiata c) the cumulus oophorus connects the other two
the corona radiata and cumulus oophorus marks transition from secondary follicle to mature or Graafian follicle
Label this. What stage of follicle is this? How do you know?
This is a mature/Graafian follicle
presence of corona radiata and cumulus oophorus
When does the primary oocyte become a secondary oocyte?
What occurs during this maturation?
The primary oocyte becomes a secondary oocyte in the mature/Graafian follicle
The primary oocyte completes meiosis 1 producing two haploid (N/2C). One daughter cell has normal chromatin (N) but no cytoplasm and is termed a polar body. The other daughter cell has N chromatin and virtual all of the cytoplasm is termed the secondary oocyte.
What stage of meiosis does the secondary oocyte arrest in until fertilization?
The secondary oocyte enters meiosis 2, but arrests in metaphase 2 until fertilization
Describe ovulation.
- Liquor folliculi increases, increasing antrum size and pressure within follicle
- Proteolysis degrades thecal wall nearest surface of ovary
- Glycosaminoglycans are deposited in cumulus oophorus, weakening the tether to secondary oocyte
- Smooth muscle cells in theca externa contract
- Theca ruptures, releasing liquor folliculi
- Cumulus oophorus is broken down so fluid release carries the cumulus mass (secondary oocyte surrounded by zona pellucida and corona radiata)
