ECR L27
SPERMATOGENESIS
13/01/2000
PROF FRASER

Cryptorchidism - hidden testes (non-descent), either unilateral or bilateral. They need to be brought down by the age of about 5 years otherwise it can have an effect on fertility.

Spermatogenesis is similar to oogenesis - you have to go through meiosis.

MEIOSIS:

reduces chromosome number
so haploid (23) number of chromosomes
mixes up genes - genetic variation

MITOSIS:
DNA synthesis - cell division - two exact copies

MEIOSIS:
DNA synthesis - pairing of homologues (crossing over - variation) - meiosis I (2 cells produced) - meiosis II (each new cell splits to produce 4 new gametes, all haploid)

Doesn’t always occur correctly - some missing gamete chromosomes.

DEFECT	RESULT
22 + 23 = 45	not viable
45, X O	female - Turner’s syndrome
47, XXY	male, sterile - Kleinfelter’s syndrome
47, XXX	reasonably normal
47, XYY	reasonably normal
extra autosome	trisomy 21 - Down’s syndrome

Chromosome 21 is also linked with Alzheimer’s disease, so if a Down’s syndrome person lives a long time (after about 45), they usually get Alzheimer’s as they are genetically a lot more susceptible to it.

Sertoli cells are nurse cells - somatic. Cells are allowed through the tight junctions by an air-lock type system. In tight junctions, there are usually 6-12 points of adherence.

STEM CELLS - spermatogonia:

Mitotic proliferation - produces more cells. Mitosis ceases and cells then enter meiosis:

CYTOPLASMIC BRIDGES:

The sperm can sometimes be released too early when they are immature. This is quite serious because only the mature sperm cells can really function properly. The time taken from the start of mitosis to the production of the sperm is about 64 days.

RECAP:

mitotic proliferation: stem cells divide every 16 days (testis)
meiosis (testis)
spermiogenesis (testis)
maturation (epididymis)

Sertoli cell numbers decrease after puberty. The number of cells times 4 is the maximum number of sperm cells that can be produced at one time.

Endocrine disrupters - oestrogen look-alikes.