Reproductive Systems and Fertility - 1 and 2 Flashcards
How many chromosomes are involved in mitosis and what offspring is produced?
1 maternal and 1 paternal chromosome
–> 2 genetically identical daughter cells
produced
How many chromosomes are involved in meiosis and what offspring is produced?
1 maternal and 1 paternal chromosome
Meiosis 1 = crossing over of chromosomes
Meiosis 2 = 4 genetically different
chromosomes produced
= 4 genetically different offspring cells
produced
What causes differences between siblings?
= Meiosis - crossing over = independent assortment of chromosomes
What is a gonad?
The organ where gametes are produced
They also produce hormones that control secondary sexual characteristics.
What is the female gonad and what is the male gonad?
Ovary in female
Testes in male
What are germ cells?
Any cell in the series of the germ line that eventually become gametes
Often indicate the cells before meiosis
What are the germ cells called found in the testis and in the ovary?
Spermatogonia in the testis
Oogonia in the ovary
What is the origin of germ cells?
Germ cells originate from primordial germ cells (PGCs)
How are primordial germ cells (PGCs) formed?
PGC arises in the posterior yolk sac and stay there until gonads are formed
Gonads form from the genital ridge and become testis or ovary
PGCs migrate into the gonad and then reside as germ cells
What is spermatogenesis?
The production of sperm from the primordial germ cells.
When are primordial germ cells formed?
- 3-6 weeks of embryogenesis - PGCs are
formed - 2-3 months of embryogenesis PGCs migrate
into the gonad (future testis) becoming
dormant
What happens at puberty in males ?
Testosterone causes maturation of seminiferous tubules in the testis.
Allowing spermatogonia to proliferate and enter meiosis. = commencement of meiosis in a wave
Some spermatogonia remain - functioning as stem cells
What is the testis made out of ?
= Seminiferous tubules
What is the order of spermatogenesis?
Primordial germ cell (PGC) enters gonad –> Spermatogonium (puberty) –> diploid spermatogonia proliferate by mitotic cell division inside testis –> Primary spermatocyte –> Meiotic division 1 = Secondary spermatocyte –> Meiotic division 2 = Spermatids —> differentiation => Spermatozoa = Sperm
Where does spermatogenesis take place?
In the seminiferous tubule
- In close relation to Sertoli cells
Where are Sertoli cells located?
Span from the basement membrane to the lumen, surrounding differentiating spermatogonia
What is the function of Sertoli cells?
Produce enzymes and growth factors required for spermatogenesis
Also a function as a phagocyte to clean up residual cytoplasm of sperm
What are Leydig cells?
Interstitial cells
Secrete testosterone in response to LH
Where are Leydig cells located?
Reside outside of seminiferous tubules
When do sperm undergo most of their differentiation?
= after the completion of meiosis
How do sperm share the cytoplasm?
via cytoplasmic bridges
How is sperm sharing the cytoplasm via cytoplasmic bridges during spermatogenesis beneficial?
After meiosis some cells only have Y chromosomes and no X chromosomes.
By sharing the cytoplasm until the last stage of differentiation, sperm with Y chromosomes can be supplies with essential proteins encoded by genes on the X chromosomes.
What is spermiogenesis?
= differentiation step of spermatids becoming a highly specialised spermatozoa
Where does spermiogenesis occur?
In the seminiferous tubules
What are the 5 key stages of spermiogenesis?
- Nucleus condense
- Formation of acrosome
- Formation of flagellum
- Mitochondria gathered at the midpiece –>
generate ATP for movement of cilia - Removal of excess cytoplasm
After spermiogenesis where do sperm go?
Sperms are released to the lumen and then transferred to the epididymis
What is spermiation?
The process of sperm being released from the Sertoli cells to the lumen.
Sperms are not motile (cant move) when released
What is the epididymis?
A long single duct with peristaltic contraction
What is the function of the epididymis?
Serves as a reservoir for sperm - their passage takes 1-21 days
Concentrates the fluid x100
Sperm undergo further maturation, acquiring mobility, increasing dependence on fructose for energy production
What is the path of the sperm?
Testis –> Epididymis –> Ductus deferens = Vas deferens –> Vesicular gland = Seminal vesicle –> prostate –> Bulbourethral gland –> Urethra
What is capacitation?
The final stage of maturation of sperm
Where does capacitation take place?
In the female’s genital tract for ~ 7 hrs