Sperm Structure and Transport

sperm head includes …

nucleus, acrosome, postnuclear cap

sperm tail includes …

middle piece, principal piece, terminal piece

sperm nucleus

oval, flattened

genetic material is nearly inert due to high degree of keratinization (disulfide cross-linking)

at fertilization→ disulfide cross-links are reduced by glutathione in cytoplasm of oocyte

head of sperm→ acrosome

covers the anterior 2/3 of the nucleus

membrane-bound lysosomes that contain hydrolytic enzymes (acrosin, hyaluronidase, zona lysin, esterases & acid hydrolases)

postnuclear cap on head of sperm

membrane component posterior to the acrosome

middle piece of sperm tail

mitochondria → arranged in a helical structure

laminated columns → flexibility for movement

9 coarse fibers

9 pairs of microtubules around 2 central filaments (9+9+2)

annulus→ tail of sperm

juncture between middle piece & principle piece

principle piece

majority of the tail

ATP usage in sperm

motility (60%)

substrate cycling (40%)→ production of different substrates involved in metabolism

maintenance of ionic gradients→ very small amount

transcription and translation → none after condensation of nucleus and loss of residual body

sperm metabolism

temperature dependant → ATP production increases as temp increases

ATP dependent processes are temp dependent → motility increases with increasing temps

as velocity increases…

temperature increases

caput, vas deferens, corpus, cauda roles in transport of sperm

contractions

rete testis role in sperm transport

fluid flow

RT secretion

seminiferous tubule role in sperm transport

bulk fluid flow

contractions of myoid cells

Vas Deferens role in sperm transport

fluid flow

cilia

epididymal function

maturation

• change in fertility

• develop motility

• nuclear condensation

• cytoplasmic droplet

• increase disulfide crosslinking

transport

components of sperm

water

sperm

substrates (fructose→ main source of energy, sorbitol, inositol, glycerol, phosphatidylcholine, citric acid)

inorganic salts (sodium, potassium, calcium, magnesium, chloride)

proteins

factors of evaluating semen → color

white to cream color - good

yellow - urine present

clear or thin in appearance - few sperm

factors of evaluating semen → volume

weight, 1 ml-1 gm

factors of evaluating semen → concentration

hemocytometer- gold standard

spectrophotometer, photometer, fluorometer (measure DNA)

factors of evaluating semen → motility

visual estimation - nearest 5% estimate

-total motility → all the moving sperm

-progressive motility → those sperm moving in a straight line

CASA- computer-aided sperm analysis

-tracts individual sperm and computes a variety of statistics on the sample

factors of evaluating semen → viability

dead (red) vs alive (green) sperm

factors of evaluating semen → morphology

there are numerous methods including staining, visual inspection, computer systems

morphology classification

primary classifications → head abnormalities

secondary classification → tail abnormalities

sperm challenges

transport, capacitation, hyperactivation, chemotaxis/recognition, sperm-zona binding, acrosome reaction, egg penetration, fertilization

barriers from sperm to oocyte → sperm

vagina/cervix/uterus

uterotubal junction

isthmus/sperm reservoir

barriers from sperm to oocyte → oocyte

follicle wall

infundibulum

ampulla

semen deposition in vagina (species)

cow, sheep, primates

semen deposition in cervix (species)

mouse

semen deposition in intrauterine (species)

sow, mare

challenges migrating the vagina, cervix, and uterus

vagina → acidic pH, retrograde flow of semen (loss from flow back)

cervix → migrate along walls and folds, not through the lumen

uterus → leukocytic infiltration of uterus, long uterine body and horns

solutions to migrating the vagina, cervix, and uterus

alkaline pH of seminal plasma

cervical mucus acts as a vehicle for sperm

uterine muscle contractions increase during late follicular phase

immune response is delayed → occurs only after copulation

rapid transport phase of sperm transport

within a few minutes, sperm can be found in oviduct

these sperm are non-viable and do not result in fertilization

sustained transport phase of sperm transport

“trickle-like” delivery over hours

these are the capacitated sperm that do result in fertilization

Cervical mucus of the cow

two types of mucus → sialomucin & sulfomucin

low viscosity (sialomucin mucus) environment in the valley of the cervix creates “privileged pathway” for healthy spermatozoa

sialomucin mucus

low viscosity and helps forward movement; “valley”

sulfomucin mucus

high viscosity and washed sperm out; “mountains”

uterotubal junction challenges

folds in mucosa = dead ends

viscous fluid

removal of seminal plasma

removal of defective/slow spermatozoa

uterotubal junction solution

waves of contractions

oviductal sperm reservoir

binding of spermatozoa to oviductal epithelium in utero-tubal junction of isthmus → carbohydrate recognition, oviductal mucosa protects spermatozoa against aging and damage

release → a change in the sperm surface, rather than a change in oviductal epithelium. Ony hyperactivated spermatozoa can detach

present in cows, pigs, hamsters, sheep, hares, and mares

oviductal sperm reservoir proposed functions

maintenance of spermatozoa between the onset of oestrus and ovulation

synchronization of Sperm & Egg transport in oviduct

prevention of polyspermy

capacitation and hyperactivation

capacitation

set of changes in the sperm plasma membrane that enables a cell to acquire fertilizing potential/undergo acrosome reaction

requires removal of seminal fluid → decapacitation activity

asynchronous and continuous → Only a % of spermatozoa are capacitated and are continuously replaced

state lasts 50-240 minutes → die unless they undergo acrosome reaction

initiated in cervix by seminal plasma removal, completed in isthmus during detachment from sperm reservoir by female-derived factors

sperm challenges during capacitation

cholesterol efflux increases intracellular pH, tyrosine phosphorylation, plasma sperm membrane fluidity, destabilization, and fusibility

acrosome is altered

increased intracellular Ca²⁺ levels and pH

hyperactivation

increase in flagellar bend amplitude and asymmetry, lateral head displacement, velocity observed in spermatozoa from oviductal ampulla

enhances release from sperm reservoir, progressive motility and sperm penetration of cumulus entracellular membrane

is accompanied by Ca²⁺ oscillations in sperm head and midpiece, regulated by cAMP and calmodulin

reversible

oocyte transport

capture by infundibulum → facilitated by expanded cumulus, fimbriae and mesosalpinx contractions

oviductal muscle contractions → low amplitude & high frequency during estrus

cilia have back-and-forth movement

occurs with estrogen being the primary hormone

both the isthmus and uterus have a lot of sympathetic nerves

stimulatory and inhibitory adrenergic receptors are present → estrogen = contractions, progesterone = relaxation

sperm-oocyte recognition

chemotaxis → chemo-attractants may be present in follicular fluid that accompanies the eggs

thermotaxis → 2 degrees C difference between isthmus and ampulla

spermatozoa acquire chemotactic responsiveness during capacitation

exposure to cumulus cells alters sperm motility