T2 l9The testis and spermatogenesis Flashcards
what is the space outside the testis
Tunica vaginalis
what are the 2 main products from the testis
Spermatozoa
Hormones
where does spermatogenesis occur
Seminiferous tubules which are vascularised stroma containing Leydig cells
what is the process of spermatogenesis
(-some testosterone passes through to the seminiferous tubules
-converted to dihydrotestosterone by 5a-reductase in Sertoli cells )
Testosterone synthesised from acetate and cholesterol by Leydig cells
4 – 10 mg testosterone secreted daily
Principally into blood vessels but also lymph
- Androgens are required for spermatogenesis
-
anatomy look at slide 3
how was it
what is the pituitary control of androgen and spermatozoa production & Proof
Proof: Removal of pituitary (hypophysectomy) causes testes to shrink and spermatogenesis to arrest
At puberty, androgens rise and spermatogenesis commences
LH stimulates Leydig cells to produce androgens (which are required for spermatogenesis)
FSH stimulates Sertoli cells and is required for spermatogenesis
describe the seminiferous tubules
- surrounded by myoid cells
- then a layer of basement membrane
- Sertoli cells and spermatogenic cells within the tubules
- Physiological barrier formed by gap and tight junctioned complexes between Sertoli cells
- Creates a basal compartment containing spermatogonia
- whilst spermatocytes,spermatids and spermatazoa are in a separate adluminal compartment
what are the 3 processes that spermatogenesis occurs in
- Mitotic proliferation to produce lots of cells
- Meiotic division to generate genetic diversity
- Cell modelling to package chromosomes for delivery to the oocyte
describe the first phase of spermatogenesis
- Germ cells of immature testis (prospermatogonia) are reactivated at puberty to undergo rounds of mitosis in the basal compartment of the tubule
- From this self regenerating population emerge groups of cells called A1 spermatogonia which undergo a series of divisions to form a clone of cells
- Finally after the last round of division, the clone divide to form resting primary spermatocytes.
- Within this mitotic phase of division, although nuclear division is completed, cytoplasmic division is not, so all of the primary spermatocytes resulting from the division of a spermatogonium are linked by cytoplasmic bridges
describe the second stage of spermatogenesis
Meiosis:
Resting primary spermatocytes push through sertoli cell junctions into adluminal compartment
Enter meiotic prophase
Paired homologous chromosomes form contacts at pachytene, break, swap segments and rejoin
Very sensitive to damage at this time
First division ends with separation of homologous chromosomes to opposites ends of the meiotic spindle, cytoplasm divides forming short-lived secondary spermatocytes
These quickly divide to form haploid spermatids
Describe the third stage of spermatogenesis (look at pic for relevant number coord on slide 21)
3-Packaging
Cytoplasmic remodelling of spermatid
5: Tail for forward propulsion
4: Midpiece with mitochondria for energy
3: Nucleus with packaged chromosomes
2: Cap region forms for sperm-oocyte fusion
1: Acrosome forms to penetrate oocyte
A small residual body is the dustbin for unwanted cytoplasm, later eaten by sertoli cell
describe the spermatogenic cycle
We considered generation of sperm from a single spermatogonium
Once this process has started, new stem cells at the same location don’t start generation of clones again for a few days
The interval is constant at around 16 days, the process by which the stem cell population controls, or is controlled is unknown
The time for completion of spermatogenesis is 64 days, so there are four successive sets of clonal development (at four separate stages of the process) in one place at one time – and that’s what we see when we look down the microscope
describe the spermatogenic wave
If the seminiferous tubules are dissected longitudinally, adjacent synchronised clones of spermatogenesis are seen
What occurs after spermatogenesis
Spermatozoa wash into the rete
Through the vasa efferentia
Into the epididymis where fluid is absorbed and sperm concentrated
In the rete they can twitch: by the cauda epididymis they can swim
The process is dependent on androgen stimulation
What does spermatozoa mix with to form the components of semen
Spermatozoa mixed with secretions from seminiferous tubules, epididymis etc.
Addition of secretions from prostate, seminal vesicles and bulbourethral glands at time of ejaculation
what are the cellular components of the rete testis
Spermatozoa
Epithelial cells from tract
Spermatogenic cells
Leucocytes – risk of HIV etc
what is the function of the fluid components of semen and what is it made of
Can’t be essential for fertilisation
Provide a fluid vehicle for spermatozoa
- Nutrition (fructose, sorbitol)
- Buffer (to protect against vaginal acidity)
- Antioxidants (ascorbic acid, hypotaurine)
Describe the function of the endocervix in the female & what is it stimulated and inhibited by
Secretes mucus with cyclical variation
Macromolecular network of mucin fibrils ?guiding spermatozoa
Sperm can penetrate from day 9, peak at time of ovulation
- Oestrogen stimulates watery mucus
- Progesterone inhibits secretory activity
what does the endocervix offer the sperm
- Receptive to sperm at time of ovulation, interference at other times
- Protection from hostile vagina, and from being phagocytosed
- Supplementation of energy requirements
- Sperm selection by differential motility and morphology
- Short term reservoir within endocervical crypts
- Initiation of the next stage in sperm maturation: ‘capacitiation’
describe the process and function of capacitation
Sperm recovered at ejaculation don’t fertilise ova in vitro immediately
Those from the uterus will
Have undergone capacitiation
Stripping of glycoprotein from sperm surface which accumulates in the epididymis
Causes hyperactive motility – ‘whiplash’
And make sperm responsive to signals from oocyte where we end our journey
what 3 properties do you test in cervical mucus
- Consistency (watery or viscous)
- Spinnbarkeit (means elasticity, stickiness)
- Ferning (crystalisation on a glass surface)
How do you obtain sperm and what is the normal volume
Specimen is obtained by masturbation, collected in a clean container – (condoms often contain spermicide)
Normal ejaculated volume is 1.5 – 6 ml
Volume may be low in retrograde ejaculation, high volume may reflect abstinence or accessory gland inflammation
1.5 ml is the cut off (WHO 2010)
what are the factors analysed in semen
look at slide 51
concentration and vitality :
-Sperm concentration, or density, defined as the number of sperm per ml in the total ejaculate
Normal is over 15 million per ml
-Vitality: 58% or more live spermatozoa
3- Motility: Defined as percentage of progressively motile sperm in the ejaculate
Progressively motile means they go somewhere, rather than swim around in circles
WHO uses 32% as the cut off for the lower limit of normal for progressive motility
4- Morphology -visual assessment-Greater than 4% normal forms acceptable (WHO 2010
what is the nomenclature for describing Sperm
Normozoospermia
-Normal values
Oligozoospermia
-Low concentration
Asthenozoospermia-Too little motility
Teratozoospermia-Too many abnormals
Oligoasthenoterato-
zoospermia
-Mixture of the three
Azoospermia-No spermatozoa
Aspermia-No ejaculate
look at slide 54-55
how did it go
