Reproductive L3 Flashcards
Seminiferous tubule structure
basement membrane on the outside
in the lumen- mature sperm
different cells around
Ladig cells outside in ECM
Blood vessels in ECM
Blood testicular barrier- separate sperm from immune system
What are the cells inside the seminiferous tubule?
-spermatogonium( stem cells lead to cells that become sperm in the process of spermatogenesis). Have 2n chromosome number
-Spermatocytes ( primary -> secondary) -> Spermatids-> sperm
Sertoli cell (supporting cells)- help the spermatozoa precursor cells to turn into spermatozoa. Create the blood-testes barrier.
When and where does Spermatogenesis occurs?
-only after puberty and only in the seminiferous tubules of the testes
What is the average rate of sperm production?
~300-600 sperm/grams of testis tissue/second
~20 g per testis = 40 g overall
3 phases of spermatogenesis
- mitotic division
- meiotic division
- Cytodifferentiation
what cells are reactivated in puberty?
spermatogonial stem cells
how do spermatogonia divide?
by mitosis. 1 daughter cell remains undifferentiated -to
maintain the stem cell population.
– The other daughter cell continues to divide by
meiosis, forming spermatogonia. The
spermatogonia continue to divide by meiosis.
where do the mitotic divisions occur?
basal compartment of the seminiferous tubule
close to the basement membrane
how many chromosomes do spermatogonia have?
46
how are sertoli cells connected?
tight junctions
Spermatogenesis
At puberty, the primary gem cells are reactivated
– spermatogonial stem cells.
• The spermatogonia divide by mitosis.
– 1 daughter cell remains undifferentiated -to
maintain the stem cell population.
– The other daughter cell continues to divide by
mitosis, forming spermatogonia. The
spermatogonia continue to divide by mitosis.
When the mitotic divisions are complete, the spermatogonia
move between adjacent sertoli to the adluminal
compartment of the seminiferous tubules.
• In the adluminal compartment, the cells are called primary
spermatocytes –they undergo meiosis
• Each of these primary spermatocytes starts with n-46
– The primary spermatocytes undergo meiosis I
– the DNA content doubles - each of the spermatocytes still has
46 chromosomes. (meiosis I). The primary spermatocytes then
divide to produce secondary spermatocytes
• Secondary spermatocytes have 23 chromosomes, each
the chromosome has two chromatids.
• Secondary spermatocytes divide very rapidly - meiosis II
- to give four spermatids, each with 23 chromosomes.
• Spermatids are still round cells and have a round
morphology. Round spermatids.
• The final process in spermatogenesis is
spermiogenesis in which the round spermatids
differentiate their shape and become
spermatozoa (Sperm).
• Sperm move into the lumen of the seminiferous
tubules
• The round spermatids form a tail, a mid piece, and a head
• The midpiece is packed with mitochondria to produce energy
• The head contains the DNA and is covered by the acrosome a
a compartment filled with enzymes that are required for egg
penetration.
• The excess cytoplasm of the spermatid is also lost into a structure
called the residual body that is phagocytosed by the Sertoli cells
after the sperm leaves
what are the cells that undergo myosis called?
primary spermatocytes
where do the spermatogonia move to after mitotic division?
they move between adjacent Sertoli cells to the adluminal compartment of seminiferous tubules
sperm structure
• The midpiece is packed with mitochondria to produce energy
• The head contains the DNA and is covered by the acrosome a
compartment filled with enzymes that are required for egg
penetration.
• The excess cytoplasm of the spermatid is also lost into a structure
called the residual body that is phagocytosed by the Sertoli cells
after the sperm leaves
Hormonal control of spermatogenesis
Hypothalamus produces GnRH( gonadotropin releasing hormone) after puberty. GnRH travels down the portal blood system to the anterior pituitary. Gonadotrophs cells in the anterior pituitary produce hormones gonadotropins- FSH and LH( luteinizing hormone).
LH is released from the pituitary-> travels through peripheral blood down to the testis and binds to the Leydig cells in the interstitial fluid. These cells then produce testosterone ( one of the androgens)
Some of the testosterone(dihydrotestosterone) travels through blood and causes secondary sexual characteristics.
FSH from the pituitary travels down the blood to the testes, and binds to the sertoli cells. Sertoli cells produce androgen binding protein- helps androgen disperse around the body. It also traps some testosterone in the seminiferous tubules so it cannot diffuse out through the lipid membrane. This testosterone helps sperm develop. WITHOUT TESTOSTERONE, SPERMATOGONIA DO NOT DEVELOP INTO SPERM.
As testosterone lvls increase they feedback to the cells in the hypothalamus and reduce GnRH production. Testosteron also feeds back on the level of gonadotrophs in the anterior pituitary- turns down the production of FSH and LH.
FSH also causes protein inhibin to be produced. Inhibin feeds back to anterior pituitary to reduce the production of FSH.
Kisspeptin
A hormone controls the release of GnRH
