spermatogenesis and semen

3 goals of spermatogenesis

produce spermatozoa - cells capable of fertilization

replenish supply of primordial stem cells

create genetic diversity

3 phases of spermatogenesis

proliferation phase (mitosis) - spermatocytogeneis - begins with spermatogonia and finishes with spermatocytes

meiotic phase - spermatidogenesis - begins with primary spermatocytes and finish with haploid spermatids

differentiation phase - spermiogenesis - spherical shaped spermatid finishes with spermatozoa

label testis - gross anatomy 

spermatizoa produced in seminiferous tubules of testes

seminiferous tubules and spermatogenesis

occurs across the wall of tubules

sertoli cells - structurally support other cells involvedin producing spermatozoa - give them nutrition, produce fluid and mop things up, span from basement membrane to lumen, connect at tight junctions creating the sperm-testis barrier which created the basal compartment and adlumenal compartment 

meiotic divisions

prophase of 1st division = relatively long process - lifespan of primary spermatocyte is longer than any other germ cell found on seminiferous epithelium 

primary spermatocytes divide by meiosis to form secondary spematocytes in phase 1

in pahse 2 become spherical spermatids

lifespan of spermatocytes in bull

primary = 18-19 days

secondary = 1-1.7 days

total duration of spermatogenesis = 61 days 

differentiation phase

aims to produce a sophisticated self propelled package of enzymes and DNA  

• golgi phase, cap phase, acrosomal phase and maturation phase 

each cell is genetically unique

then released into lumen = spermiation 

head of spermatozoa

nucleus and acrosome and post nuclear cap

shape varies across species

acrosome contains hydrolytic enzymes required for penetration of zona pellucida 

tail of spermatozoa

self powered flagellum

composed of - middle piece, principle piece and terminal piece

cycle of seminiferous epithelium

across species - length of cycle varies 4-9 weeks

spermatogenic wave - differences at any given instant in time along semiferous tubule 

stage of cycle differs in adjacent regions of tubule 

finite region of tubules releasing sperm at given time 

time for completion of spermatogenesis

spermatozoa production

produced in testes

mature in head and body of epidiymis - move here via fluid produced by sertoli cells

stored in tail of epididymis until ejaculation 

epididymis 

transport through it takes 1-2 weeks 

spermatozoa mature and develop motile capacity

epididyis stores 10-50 × 10^9 cells - enough for several ejaculations 

copulation frequency - no effect on time spermatozoa in 1st part of epididymis - frequency copn → density of spermatozoa in epididymal tail and therefore decrease ejaculate 

semen evalution 

record volume, colour, appearance 

NB EEJ sample cf. natural service = more dilute accessory gland secretion 

live:dead ratio

mass motility/wave motion

density

mass motility or wave motion

score 0-5

5  very good - billowing clouds

4 has clouds - good 

3 fair

2 poor

1 very poor

0 dead 

general appearance of ram semen

colour correlates to density

be careful with presence of infection as it will affect colour

head abnormalities

would have implication for ability to get in and fertilise egg

tail abnormalities

would have difficulties of it getting places

spermatozoa sensitive to what

temp - keep sample, glassware, dilution and staioning fluids warm

water

bright light, blood, detergents, cigarette smoke, rubber bung in syringes 

mitotic division 

diploid

synchronised

occurs in basal compartment 

do get cell nicrosis and death 

endocrine regulation

hypothalamus produces GnRH and causes anterior pituitary to produce LH and FSH

LH acts on leydig cells which live between seminifeous tubules and produce testosterone which acts on sertoli cells and get -ve feedback at level of anteiror pituitary and hypothalamus 

FSH acts on sertoli cells and produces inhibin and -ve feedback at level of anterior pituitary 

sperm-testis barrier

immune system recognises spermatids as foreign divides semiferinous tubules into 2 compartments to prevent imune cells from breajing down spermatozoa - immune cells to large to fit through barrier

some viruses hide in testes and then can be passed to another animal in semen

morphology

primary vs secondary defects

compensable vs non-compensable defects