Gametogenesis: Amphibian & Mammalian Spermatogenesis Flashcards
Where does meiosis occur?
Only in the gonads—the ovary and testis—and more specifically, only in the germ cells that are lodged in the gonads.
the method of cell division that halves the number of chromosomes in the resulting egg and sperm cells
meiosis
Primordial germ cells arrive in the developing gonad after a long trip, often from the far reaches of the ________
yolk endoderm
General steps in gametogenesis:
- Extragonadal origin + migration of PGC
- Proliferation of germ cells
- Meiosis
- Maturation of gametes
The spermatids then go through a further differentiation process called ______ to become fully formed spermatozoa.
spermiogenesis
During the maturation of gametes, these are the 3 outcomes
- Blastula
- Tropoblast (forms the placenta)
- Inner cell mass (epiblast & hypoblast)
Which type of spermatogonia proceeds to become a stem cell and which one will enter meiosis
Type A = Stem cell
Type B = Enters meiosis
General steps of spermatogenesis
- Differentiation and proliferation
- Meiosis
- Spermiogenesis
What happens during spermiation
- Acrosome
- Flagellum formation
- Nuclear condensation
- Remove excess cytoplasm
- Specific mitochondrial arrangement (midline of sperm)
Streamlined to facilitate movement
Found in the acrosome is a hydrolytic enzyme (hyaluronidase) that digests zona pellucida
How long does the egg arrive from the fallopian tube to uterus
6 days
In humans, external fertilization is called ___________
ampullary-isthmic junction -> site of fertilization
ampulla & isthmus of the fallopian tube
a roundish structure surrounded by a tough sheath of connective tissue.
Protective connective tissue layer of testis
Tunica albuginea
These tubules should look like little doughnuts. It is in these _________ that the sperm are being produced.
Seminiferous tubules
secrete the male sex hormone,
testosterone
interstitial cells, or Leydig cells
The human male, for example, can
produce up to ______ sperm per day
300 million
a sperm count of less than _____ sperm per ml of ejaculate is tantamount to being sterile.
20 million
Other causes of sterility
tight jeans
hot baths,
fevers,
all of which raise the temperature of the testis.
Sperm development is extremely temperature-sensitive and can only occur in mammals at a temperature _____________
1.5–2.0°C cooler than normal body temperature
Different gonadal stages
- Recovery stage
- Growing stage -> maturing
- Mature stage
- Partly spawned -> little by little release
- Spent
tunica albuginea consists primarily of extracellular fibers of _______.
type I collagen
The cells that make collagen are called
fibroblasts
is the epithelium that produces sperm
seminiferous tubule
The _______for any epithelium is of major importance to the differentiation and maintenance of that epithelium. It is an acellular layer, made up primarily of type IV collagen, laminin, fibronectin, and heparan sulfate proteoglycan.
basement membrane
Nurse cells of spermatogenesis and is responsible for blood-testis barrier
Sertoli cells
The Sertoli cells are nondividing, tall, columnar cells that extend from the basement membrane to the lumen of the tubule. The nuclei of these cells are irregularly shaped and stain lightly, making them easy to identify.
As the cells progress through their differentiation, they move closer and closer to the lumen of the tubule. Spermatozoa sit with their tails sticking out into the lumen.
Sertoli cells function to support and nourish the germ cells throughout their development. Sertoli cells are also responsible for the translocation of the developing sperm toward the lumen and their eventual release.
The entire process of spermatogenesis (from spermatogonium to spermatozoan) takes 48 days in the rat and 64 days in humans.
The ____________, lying between the seminiferous tubules constitute the mesenchyme of the testis.
interstitial cells, or Leydig cells
In response to leutinizing hormone, LH, the Leydig cells secrete testosterone, which is required both for spermatogenesis and for development of secondary male characteristics.
male germ cells undergoing maturation division located inside the spermatocysts.
Spermatogenic Cells
small cells with irregular dense
nuclear materials.Their small spermatocyst is interspersed among the bigger spermatocysts. They are inactive in cell division and serve as the reserve cells for the next breeding period.
Residual Spermatogonia
large cells close to the periphery of seminiferous tubules. They are actively dividing cells with prominent nuclei and threadlike chromatin materials.
Active Spermatogonia
cluster of minute cells appearing as clumps of black rods
Spermatozoa
columnar or pyramidal cells that adhere to the basement membrane or lying among the germ cells.
Sertoli cells
functions of the Sertoli cells.
support and nourish the germ cells throughout their development.
translocation of the developing sperm towards the lumen
blood-testis barrier
