Gametogenesis

Question 1

What are the phases of male gametogenesis?

Answer 1

1. Spermatogenesis
   1a. Spermatogonial
   1b. Spermatocyte
   1c. Spermatid
2. Spermiation
3. Maturation

Question 2

Describe the first step of spermatogonial spermatogenesis.

Answer 2

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.

Question 3

What are type A (dark) spermatogonia cells named for? What is a special function of these cells?

Answer 3

Type A (dark) spermatogonia were named for intensely basophilic nucleus containing finely granular chromatin (diffuse)

These cells are stem cells for male reproduction.

Question 4

What is the type A dark spermatogonia doing while sitting on the basal lamina of the seminiferous tubules?

Answer 4

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.

Question 5

What is the difference between Type A dark and Type A light spermatogonia

Answer 5

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.

Question 6

What do Type A light Spermatogonia differentiate into?

Answer 6

Type A light spermatogonia differentiate into Type B spermatogonia while on the basal lamina of the seminiferous tubules.

Question 7

Describe Type B Spermatogonia.

Answer 7

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

Question 8

What do Type B spermatogonia differentiate into? Where do these differentiated cells then go?

Answer 8

Type B spermatogonia mitotically divide into primary spermatocytes.

The primary spermatocytes then move apocalyptic through the junction all complex of the Sertoli cells.

Question 9

What marks the transition from spermatogonia phase of spermatogenesis to the spermatocyte phase?

Answer 9

When Type B spermatogonia mitotically divide into primary spermatocytes

Question 10

Describe the spermatocyte portion of spermatogenesis.

Answer 10

1. The primary spermatocyte is moving apically in the through the junctional complex of Sertoli cells.
2. The primary spermatocyte begins prophase I (longest) to become (2N, 4C) then completes the first meiotic division creating the secondary spermatocyte (N, 2C)
3. Continually moving apically the secondary spermatocyte undergoes a second meiotic division resulting in (N,C) spermatids

Question 11

What marks the transition to the spermatid phase of spermatogenesis?

Answer 11

When the secondary spermatocyte meiotically divides to form spermatids. These are then located apically in close contact with cell membrane of Sertoli cells.

Question 12

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?

Answer 12

Sertoli cells

1. Golgi phase
2. Cap phase
3. Acrosome phase
4. Maturation phase

Question 13

Describe what happens during the golgi phase of differentiation of the spermatid into spermatozoan.

Answer 13

1. Proacrosomal granules accumulate in golgi complex and combine to form the acrosomal vesicle.
2. The acrosomal vesicle approaches nucleus and defines anterior pole
3. Centrioles migrate to posterior pole to begin organizing the atonement of the sperm tail

Question 14

Describe the cap phase of differentiation of spermatids to spermatozoan.

Answer 14

1. Acrosomal vesicle spreads over anterior surface of nucleus forming the acrosomal cap
2. Nuclear envelope under the cap thickens and loses nuclear pores
3. Nuclear content condenses

Question 15

Describe the acrosome phase of differentiation of the spermatid to the spermatozoan.

Answer 15

1. Cytoplasm between acrosome and cell membrane reduces
2. Nucleus elongates posteriorly
3. Microtubules coalesce to form manchette
4. Manchette will elongate to form the “head” and transports material into flagellum
5. Centrioles form connecting piece attaching flagellum to posterior surface of nucleus

Question 16

Describe the maturation phase of differentiation of spermatid into spermatozoan.

Answer 16

1. Mitochondria form sheath around flagellum - forming “middle piece”
2. Excess cytoplasm is expelled forming the “residual body” -this is phagocytosis by Sertoli cell
3. Now is spermatozoan

Question 17

Describe what occurs during Spermiation.

Answer 17

1. Sertoli-to-Spermatid junctional complex breaks down
2. Immature spermatozoan are released into lumen of seminiferous tubule
   - they are released in clumps because cytoplasmic bridges from spermatogonia persist

Question 18

What chemical would you expect to increase in concentration within Sertoli cells during spermiation? Why?

Answer 18

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

Question 19

Where can final maturation occur?

Answer 19

Lumen of seminiferous tubule

Efferent ductule

Epididymis

Question 20

What occurs during maturation of spermatozoans?

Answer 20

1. Head of sperm decreases in size, DNA further condenses
2. Sperm is more slender, cytoplasm further removed
3. Lipid, protein, and glycosylation of sperm membrane changes (to promote fusion)
4. Decapitation - alters outer surface of acrosomal membrane facilitating rupture
5. cAMP, Ca2+, and pH shift to increase phosphorylation resulting in increased flagella and sperm motility

Question 21

What is the embryonic ovary a mix of?

Answer 21

Connective tissue and stroma cells

Question 22

During early oogenesis where do the primordial germ cells migrate to from the extra-embryonic mesoderm?

When does this occur?

Answer 22

Migrates to the periphery of the ovary

during the third month of development

Question 23

What are the division of the ovary?

Where are the primordial germ cells located?

Answer 23

Outer cortex - where primordial germ cells divid and oogenesis occurs

Inner medulla

Question 24

When do primordial germ cells switch to Oogonia?

Answer 24

When the cells reach the ovarian cortex

Question 25

What is a syncytium?

Answer 25

Oogonia performing rapid mitotically proliferation without full cell division

Question 26

Describe the formation of the primordial follicle.

Answer 26

1. After the primordial germ cell reaches the ovarian cortex it is then referred to a as an Oogonia.
2. The Oogonia begins mitotically dividing rapidly, without full cell division forming a syncytium.
3. 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.
4. Squamous cells are termed follicular cells, and are surrounded by a basal lamina.

Question 27

Before the syncytia break down, what phase of meiosis will the oogonia enter?

Answer 27

The oogonia enters interphase of Meiosis I before forming the primordial follicle.

Resulting in (2N/4C) and prominent chromatin/chromosomes in the nucleus

Question 28

What are atretic follicles? What is their fate? How many atretic follicles typically occur?

Answer 28

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.

Question 29

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?

Answer 29

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

Question 30

Label this image. What stage is this of oogenesis?

Answer 30

Primary follicle

Question 31

What occurs during maturation of a primary follicle?

Answer 31

1. Cortical granules, special secretory vesicles produced by primary oocytes, amass at the periphery of the cell
2. Oocyte develops microvilli that push through zona pellucida, between granulosa cells
3. Granulosa produces cytoplasmic processes that extends between cells toward zona pelucida
4. Thecal cells differentiate into theca externa and theca interna
5. Granulosa cells secrete hyaluronic acid rich fluid called the liquor folliculi
6. Liquor folliculi disrupts granulosa which has been weakened by cytoplasmic extensions
7. Disrupted granulosa evacuate a liquor folliculi filled space called the antrum

presence of antrum signals maturation from primary follicle to secondary follicle

Question 32

What is the difference between the theca externa and the theca interna? At which stage do these form?

Answer 32

Theca externa - mostly collagen and smooth muscle

Theca interna - highly vascularized cuboidal secretory cells

these differentiate during maturation of the primary follicle

Question 33

Label this image of a follicle.

At what stage is this? How do you know?

Answer 33

This is a secondary follicle, you can tell this because of the antrum.

Question 34

Describe the maturation of the secondary follicle.

Answer 34

1. Quantity of liquor folliculi increases, increasing size of antrum
2. 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

Question 35

Label this. What stage of follicle is this? How do you know?

Answer 35

This is a mature/Graafian follicle

presence of corona radiata and cumulus oophorus

Question 36

When does the primary oocyte become a secondary oocyte?

What occurs during this maturation?

Answer 36

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.

Question 37

What stage of meiosis does the secondary oocyte arrest in until fertilization?

Answer 37

The secondary oocyte enters meiosis 2, but arrests in metaphase 2 until fertilization

Question 38

Describe ovulation.

Answer 38

1. Liquor folliculi increases, increasing antrum size and pressure within follicle
2. Proteolysis degrades thecal wall nearest surface of ovary
3. Glycosaminoglycans are deposited in cumulus oophorus, weakening the tether to secondary oocyte
4. Smooth muscle cells in theca externa contract
5. Theca ruptures, releasing liquor folliculi
6. Cumulus oophorus is broken down so fluid release carries the cumulus mass (secondary oocyte surrounded by zona pellucida and corona radiata)