Spermatogenesis Flashcards
What is the main reproductive organ in the male?
Testis
What is the function of the testis
-To produce sperm
-To produce hormones (androgens, oestrogens, inhibin, activin, relaxin-like factor)
Which cells live in the semimiferous tubules?
- Sertoli cells
-Germ cells
(myoid cells)
Where do myoid cells live in the testis?
They surround the seminiferous tubules in a thin layer
What is present in the interstitial compartment?
- Leydig cells
- capillaries and lymphatic vessels
When does the blood testis barrier develop
During puberty
What is the function of the BTB?
- Avoids sperm passing into the interstitum
- protects sperm from the immune system
-retains hormones within the ST
What makes up the BTB?
Sertoli cells with tight gap junctions
What is spermatogeneis?
The whole process going from an undifferentiated germ cell to spermatozoa. The process takes 74 days.
What are the 3 phases in spermatogenesis?
-Mitosis
-meiosis
-Spermiogenesis
What is spermiogenesis?
where spermatids acquire the morphology of specialised cells
Where do primordial germ cells originate?
They originate in the yolk sac during the first few weeks of gestation
Where do primordial germ cells migrate to?
They migrate to the genital ridges, and once they are here they are called gonocytes. They proliferate by mitosis
Initially there is no sex differentiation in primordial germ cells/ gonocytes. Describe the sex differentiation process
In XY embryos, around week 5/6 pre-sertoli cells enter the genital ridges. They express SRY genes which drives the differentiation of the male gonads.
What are seminiferous cords?
Pre-sertoli cells surround the gonocytes and produce cords. Until a lumen is formed they are described as seminiferous cords.
When are gonocytes called stem cells
When they move to the basement membrane of the seminiferous cords
Why is the stem cell niche important
Because it keeps the stem cells in an undifferentiated state so that men can produce sperm their whole life
how many germ cells can a sertoli cell support and why is this important
30-50 germ cells
If a sertoli cell is damaged then there are less germ cells and so less spermatogenesis can occur
What is the first step of of spermatogenesis?
Stem cells undergo mitosis to produce spermatogonia, and these undergo several rounds of mitosis to produce more spermatogonia (one spermatogonia A1 can produce 16 spermatogonia B)
What is the second step of spermatogenesis?
Spermatogonia undergo mitosis to produce primary spermatocytes.
What is the third step of spermatogeneis?
Primary spermatocytes undergo meiosis I to produce secondary spermatocytes.
This process involves crossing over, random assortment and produces 2 haploid cells from one progenitor cell.
CHECK W STEVE
What is the fourth step of spermatogenesis?
Secondary spermatocytes undergo meiosis II to produce spermatids
CHECK W STEVE
What is the fifth step of spermatogenesis
round spermatids become spermatozoa through cytodifferentiation (spermiogenesis)
Note: round spermatids develop into elongated spermatids during this process before becoming spermatozoa
what are myoid cells?
Contractile cells that help release sperm into the lumen
Describe the formation of the acrosomal vescile
the golgi apparatus produces lysosomes that will form the acrosomal vescile.
The spermatocyte rotates so that this is facing down the way - and so the tail will grow out of the other end.
Cytoplasm is removed and droplets phagocyted by sertoli cells
What is spermiation
The final release of sperm into the lumen of the seminiferous tubules
Why would we use a machine to determine whether X or Y sperm (X is bigger)
- avoid genetic sex linked diseases
-large animal production
-endangered species
-risk of shifting sex ratio - e.g. china
What is the spermatogenic wave?
The process by which a stem cells starts division and differentiation occurs every six days - this is controlled by sertoli cells.
What stimulates Leydig cells?
LH
What stimulates Sertoli cells?
FSH
What do leydig cells produce?
-Testosterone
-oestrogen
-Oxytocin
What do sertoli cells produce?
-Anti-mullarin hormone
-Inhibin B
- Androgen binding protein
What effect does Testosterone have on sertoli cells?
-helps them maintain BTB
-Helps them support meiosis
- helps then support spermatid elongation
-Essential for spermiation
What stimulates myoid cells
-Testosterone
-oestrogen
-oxytocin
What is azoospermia?
Absence of any sperm in the ejaculate
What are the two classifications of Non-obstructive azoospermia?
- Pre-testicular (secondary hypogonadism)
-testicular (primary hypogonadism)
What histological feature is seen in NOA
Sertoli cell only syndrome
Name some causes of pre-testicular NOA
-Kallman’s syndrome
- pituitary tumours
Name some causes of testicular NOA
- Infection (mumps)
- Klinefelters syndrome
-Iatrogenic (cancer treatments)
-Ischaemic - testicular torsion
-Idiopathic
Describe causes of obstructive azoospermia
- Vasectomy
- Congenital anomalies
-iatrogenic injury
-Infection
What requirements are necessary for a man to be classed as fertile
- 1.5ml of ejaculate
- 15 million sperm per ml of semen
- 32% of the sperm need to swim forwards
-4% need to be morphologically normal
Define the classification of olgiospermia
Mild: 10-15 million
Moderate: 5-10 million
Severe: <5 million
List some environmental and lifestyle causes of reduced spermatogenesis
- Obesity
- Diabetes
- Temperature
- Alcohol
- Smoking
- Chemo/radiotherapy
- Endocrine distributors
- Cadmium
- Dioxin
