Fertilisation and Embryo Development
• It is normal to have 20 million-300 million sperm per ml of semen
o 100-1000 of these sperm reach the ampulla
• The vagina is acidic
o Sperm are lost here by leakage or destruction by leukocytes
o Cervix- filters poor quality sperm
▪ Not all species have cervixes
o Uterine Tubal Junction (UTJ)- used in sperm selection
▪ Different mechanisms between species
o Isthmus – stores sperm
▪ Preserves motility and viability until ovulation
▪ Sperm that reach this point are protected
o Ampulla- holds oocytes
▪ Site of fertilisation
o Infundibulum- the opening of the oviduct
▪ Oocyte picked up by fimbriae and swept into here
o
• When sperm reach the UTJ they undergo a series of selective events
o Knockout mice used to identify 13 genes that are important for sperm getting
through the UTJ
▪ 11 of genes interact with the gene Adam3
▪ Adam3 has to be located in the right area of the sperm
• Adam3 believed to be involved with sperm binding to the lining of
the UTJ
• The isthmus has a thicker wall
o Has a thinner lumen
o Contains cilia
o Sperm are shielded from leukocytes in the isthmus
o Sperm can bind to the isthmus for up to 24 hours to rest
▪ Sperm are released from walls in waves
• Believed to be related to ovulation
• This limits the number of sperm around the egg at one time
o Decreases the chance of polyspermy
, o
• Sperm’s journey to the ampulla
o Sperm move due to thermotaxis
▪ Sperm swim towards the warmer environment of the ampulla
▪ Human sperm can detect temperature changes as small as 0.006
degrees C
o Sperm also move due to chemotaxis
▪ Sperm swim towards progesterone released from cumulus cells around
oocyte
o Sperm also move by rheotaxis
▪ Rheotaxis is the movement of sperm against a current
▪ Current is created by tubal fluid stretching from the ampulla to the
isthmus
▪ Sperm must become hyperactivated (capacitated) to do this
o
o Capacitation- occurs in the isthmus
▪ Gives the sperm the capacity to fertilise egg
▪ Membrane of the sperm head changes to become more fluid
• Cholesterol, phospholipids and glycoproteins on the surface are
lost
▪ Capacitation can only occur when the sperm is in the oviduct because it
makes it more unstable
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller alexgpegg. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £4.49. You're not tied to anything after your purchase.
