Spermatogenesis and Oogenesis Flashcards
Spermatogenesis
Process of formation of sperm
- begins at puberty
- rarely totally ceases
Where is the site of sperm formation?
Seminiferous tubule of the testicle
Events of spermatogenesis
Start with 2n chromosome (spermatogonium) –> mitotic division = primary spermatocyte (2n) –> at end of meiosis 1 = secondary spermatocyte (2 1n chromosomes) –> meiosis 2 = early spermatids (4 n chromosomes) –> differentiation, seroli cells provide nutrients –> sperm cells (spermatozoa)
Spermatogenesis progress from the cortex of the semineferous tubule and ends in the _____
Lumen
- where fully formed sperm cells are released
Each spermatogonia produces _____
4 sperm cells
- 1:4 ratio
Events of oogonium
Begin with primary oocyte (2n) –> meiosis 1 = secondary oocyte and first polar body –> secondary ooctye undergoes meiosis 2 = ootid and second polar body –> ootid differentiates into 1 ovum
Females only produce _____ from an oogonium
1 ovum
- do not undergo mitosis!!!
Seasonality’s effect on spermatogenesis
Produce sperm throughout the year, but may produce more during the species’ season of breeding
- high vs low production
Meiosis 1
2 haploid cells form
- chromosomes are still double
- telophase and cytokinesis with cleavage furrow
Meiosis 2
Sister chromatids separated
- 4 haploid daughter cells result
- contains single chromosomes
- prophase 2 - telophase 2
Epididymis
Storage of produced sperm
Blood flow of the testicle
Enters testicular artery
- artery and venous return are intertwined = pampiniform plexus
- acts to cool the blood entering the testis
Testosterone secreted by Leydig cells has a _______ feedback
Negative
LH stimulates Leydig cells to secrete ______
Testosterone
FSH stimulates Sertoli cells to produce _____
Inhibin
- also converts testosterone to estrogen
- helps with spermiogenesis
Males: LH released from AP in a ______ fashion
Pulsatile
- only have a tonic center, no surge
- prevents refractoriness to sustained LH
Testosterone secretion is ______ and ______
Short; pulsatile
- elevated testosterone in testis is essential for spermatogenesis
Pampiniform plexus helps maintain high levels of ______ in the testis
Testosterone
Large spikes of _____ has a negative feedback and ______ LH production
Testosterone; downregulates
Is peripheral blood a good indicator of the testicular environment?
No, 500x dilution of testosterone, estrogen, and DHT by systemic circulation
What are the 3 biological events involved in spermatogenesis?
- mitosis
- meiosis
- spermiogenesis
Mitosis
Proliferation phase which allows for continual supply of germ cells
Meiosis
- allows for diploid to haploid
- allows for crossing over
- assures genetic diversity
Spermiogenesis
Dramatic morphological changes from spermatids to spermatozoa
The proliferation phase of spermatogenesis occurs in the ______ area of the seminiferous tubules
Basal
Meiosis and differentiation of spermatogenesis occurs in the ______ area of the seminiferous tubules
Adluminal
______ envelop the developing spermatogonia
Seroli cells
What process of spermatogenesis is very heat sensitive?
Maturation of spermatogonia into primary spermatocytes
- mitosis
Primary spermatocytes undergo _____ and form ______
Meiosis 1; secondary spermatocytes
- haploid!
Secondary spermatocytes undergo ____ and become ______
Meiosis 2; spermatids
What is one cycle of the seminiferous tubule?
Progression through all stages at one location along a seminiferous tubule
- cycle length is unique to each species
What are the approx days to complete spermatogenesis for the bull and stallion?
- bull: 61 days
- stallion: 55 days
Stages of cycle
Arbirtarily defined cellular associations that transition one to the next at predictable intervals
Breakdown of spermatogenesis in the bull
8 stages in the bull
- takes 13.5 days to transition thu all 8 stages (or 1 cycle)
- complete spermatogenesis takes 4.5 cycles
- 4.5 cycles x 13.5 days = 61 days
Spermatogenesis must occur _____ cooler than body temperature
3-7 degrees C
What structures are involved in temperature control of the testicles?
- scrotal sweating
- tunica dartos muscle
- cremaster muscle
- pampiniform plexus
Blood testis barrier
Sertoli cells are joined by tight junctions which effectively create a barrier from the immune system
- allows metabolism of developing sperm to occur in a controlled environment
- developing sperm are not allowed access to the interstitial space where the immune system will recognize them as foreign
Sex determination
One pair of chromosomes determines sex of the animal
Females can only contribute an ____
X
Males contribute an ____ or a _____
X; Y
Sex of the offspring is determined by whether an __________ fertilizes the oocyte
X or Y bearing sperm
Chromosomal sex
Determined at fertilization
Gonadal sex
Determined by presence of XY chromosome
Phenotypic sex
Determined by secretion of testosterone to suppress estrogen
Head
Contains the DNA
- acrosome cap contains enzymes which aid in fertilization
Midpiece
Contains mitochondria which produce power for the tail action
Tail
Flagellum like action provides movement
- 1-4 mm/minute in fluid environment
Semen
Name given for the sperm and associated fluids which are ejaculated
- all spermatozoa plus fluid from accessory sex glands
Accessory sex glands
- ampulla
- prostate
- seminal vesicles
- bulbourethral glands
Oogenesis
Development of the oocyte
When do oogonia undergo mitosis?
During prenatal growth
Oogonia enter meiosis near the time of _______
Birth
- remain in resting prophase until puberty
- meiosis then resumes in a few cells each cycle
Following oogenesis, ____ ovum and _____ polar bodies are produced
1; 3
A secondary oocyte is capable of fertilization ________
Immediately
- exception: dogs ovulate a primary ooctye that is not capable of fertilization for 2 days
Differences in germ cell production
- males constantly replenish germ cells thru ongoing mitosis
- females are born with all they will ever have and slowly deplete their supply
- great increase in number of sperm by mitosis in the male
- oogenesis involves limited number of oogonia each cycle
