Spermatogenesis Flashcards
Name 6 main functions of testes and the structural characteristic of testes
- Site of sperm production and storage
- Produces hormones that regulate spermatogenesis and produce secondary sexual characteristics
- Lie in the scrotum outside body as 1.5-2.5 degrees lower than body temp is optimum for sperm production
- Overheating of testes reduces sperm count
5.Well vascularised and well innervated - Normal volume of testes is approx. 15-25ml each
STRUCTURAL CHARACTERISTICS
- 90% of testis is made up of seminiferous tubules
- Separates lobules with seminiferous tubules separated by septa
- All of the seminiferous tubules leads to rete testis
- Eventually leads to epididymis, store the spermicide and ejaculation moves along vas deferens
Explain the control during erection and ejaculation
Spongy tissue is called the CORPUS CAVERNOSUM
During erection :
- Vasodilation of arterial supply into corpus cavernosum
- Partial vasoconstriction of the venous return
- Dilating arteries lead to penis and constricting veins lead out of penis
- Creates a hydraulic pressure
- Vasodilation and vasoconstriction is controlled by the AUTONOMIC nervous system
—> not under conscious control
—> causes coordinated smooth muscle contractions of the vas deferens, glands and urethra
- PARASYMPATHETIC CONTROL:
The erection - dilation of arteries and constriction of the veins - SYMPATHETIC CONTROL:
Ejaculatory process
Movement of sperm into epididymis, vas deferens, penile urethra (emission)
Is smooth muscle contraction under sympathetic nervous system control - Sympathetic nervous system control but with some somatic nervous system involvement
Still not under conscious control
Expulsion of the glandular secretion and evacuation of urethra
REMEMBER: Point Shoot and Score
Parasympathetic control, sympathetic control and somatic control
What are the main characteristics and structures involved in seminal fluid?
-
Seminal vesicles involved in ejaculation
- As sperm comes past the seminal vesicles will contract and add its secretions
- Comprises of 50-70% of ejaculat
- Contains : proteins, mucus, Vit C, prostaglandins, high fructose conc provide energy source and high pH protects against acid environment in vagina -
Bulbo - urethral gland not part of ejaculatory process
- During sexual arousal these glands produce clear viscous secretion high in salt known as pre-ejaculate
- Fluid helps lubricate urethra for spermatozoa to pass through
- As sperm propelled at high speed
- Neutralises traces of acidic urine -
Prostrate
- Secretes white or milky fluid roughly 30%
- Protein content less than 1%
- Includes proteolytic enzymes, prostatic acid, phosphatase and prostate specific antigen - ivolved in liquefaction
- High zinc conc x500-1000 that in the blood is antibacterial
Describe the structure of a sperm
Nucleus :
Contains all the DNA (haploid)
No cytoplasm
Acrosome:
Contains enzymes - hylurodinase and a rosin - that cut through outer layers of egg and allow for adhesion molecules to bind to the egg
Midpiece:
Full of mitochondria - mitochondria sheath
Supply energy for the tail of the sperm
Sperm tail :
Arrangement of 9 pairs of binges and pair in the idle
Same as villi structure called the axoneme
Fibres use ATP from mitochondria to slide against each other making tail move in whiplash motion driving sperm forward
Describe the effects of anabolic steroids on males
Anabolic steroids feedback on pituitary and hypothalamus to reduce FSH and LH
Sertoli cell population drops due to reduced FSH/LH from pituitary
Leads to testicular atrophy
Compare the oogonia and spermatogonia
FEMALES
- Oogonia all laid down in foetus
- Begin meiosis to make oocyte before birth
- Cannot make more oogonia by mitosis
- Limited supply
MALES
- Spermatogonia laid down in foetus
- Begin meiosis to make spermatocyte after puberty or …
- Divide mitotically to make more spermatogonia
- Lifetime supply
What are the main characteristic of ejaculation
- 300m sperm produced per day
Approx 120m spermatogonia in average ejaculate - Normal ejacualate volume : 1.5-6ml
- Initial portion of the ejaculate most sperm rich
99.9% lost before reaching ampulla of the uterine then - Seminal fluid consists of secretions from :
Seminal vesicle, prostate, bulbo-urethral gland combined with epididymal fluid
Describe the stages of spermatogenesis
- Spermatogonia
There are primary germ cells, or spermatogonia on the basement membrane. - Primary spermatocytes
Move into adluminal compartment and duplicate their DNA
So chromosomes replicate but don’t separate and stay together - sister chromatids
2 homologous pairs will come together and crossing over occurs - genetic material exchange
46XY diploid - Secondary spermatocytes
Undergo meiosis 1 to give 23X and 23Y haploid number of chromosomes and arranged as s
Inter chromatic - Spermatids
Meiosis 2 gives 4 haploid spermatids
Round spermatid > elongated spermatid differentiation
Loose cytoplasm grow tail - Spermatozoa
Mature sperm extruded into the lumen
Describe process of sperm moving from testes to urethral opening
- Spermatogenesis occurs in the testis
- Spermatozoa is stored temporary in the epididymis for a few days
3.In ejaculation it moves via smooth muscle contraction along the vas deferens - During ejaculation the seminal vesicles secrete some fluid into the ejaculate
- The 2 vas deferens meet and join the urethra at the ejaculatory duct
- The prostate also contributes some fluid to the ejaculate
- Sperm move out the urethra vis the same path as the urine
- Sperm emerges from the urethral opening
How is the male HPG axis different to female
- Cyclical process in females whereas it is non-cyclical in males
- Same hormones work on the gonad in males - testosterone negatively feeds back like steroid in females
- Males always have some pituitary LH and FSH stimulating the testes and always have testosterone which feeds back to limit its own production
- This is steady state
What are the main characteristics of the spermatogenesis?
New cycle every 16 days and entire process is approx. 74 days
3 KEY MOMENTS:
1. Mitotic proliferation of spermatogonia
2. Meiosis and development of spermatocytes
3. Spermatogenesis, becoming spermatids : elongation ,loss of cytoplasm, movement of cellular contents
Each cell division from a spermatogonia m to spermatid is incomplete
The cells remain connected to one another by cytoplasmic bridges
Forms a syncytium - allows for synchronous development
Get syncytia at various stages of development giving continuous supply of sperm
