What is the normal volume of ejaculate?
List the compositon of the ejaculate and the contributions which part of the male reproductive system contribute
Testis and epidiymis (5%): sperm, testosterone, antixodant (motility)
Seminal vesicles (50-80%): Secretion rich in fructose, proteins and semen clotting factors, ILs, Prostaglandin E
Prostate (13-33%): PO4-, bicarbonate buffers, PSA, zinc, spermine
Bulbourethral and urethral glands (2-5%): lubrication of male reproductive tract
Name 4 essential requirements for successful fertilisation of an egg by sperm
Timing: sperm viable for up to 3 days, oocyte viable for 36-72hrs
Motility: sperm required to swim against action of tubal cilia and to penetrate the cervical mucus
Quantity: 40-100 million sperm, but only 1 egg
Capacitation: changes to outer glycoprotein coat of sperm to allow fertilisation
Acrosome reaction: required for sperm to penetrate zona pellucida
Male fertility treatments
Correct hormonal imbalances/blockages or psychological problems
Obtain the best possible sample from ejaculate/surgically retreive sperm for use in artifical insemination, intrauterine insemination, IVF, or ICSI
Causes of male infertility
Impotence (psychosexual, drug induced)
Azoospermia (primary or secondary testicular failure, obstructive, retrograde ejaculation)
Not enough sperm - oliogozoospermia < 20million/ml
Poorly motile sperm
Sperm don't bind to or ertilise the egg
Causes of female infertility
Tubal disease or blockage
Anovulation (priamry or secondary ovarian failure, polycystic ovarian disease)
IVF diagnosis: anti-sperm antibodies, egg anomaly, fertilisation failure, abnormal embryo development, implantation problem
Failure to conceive after 1-2 years of trying
84% of couples conceive within 1 year, 92% in two years if having regular sex and no contraception
Fertility in women declines from ~30years, rapidly from 37years
Describe the events of coitus
Involves four stages: Excitement, plateau, orgasmic, resolution
Male orgasm results in ejaculation and sperm emission.
Sperm deposited in upper vagina and enter cervix. Sperm become motile once they are ejaculated.
Sperm supported by mucus components and form reservoir in cervical crypts
Sperm swim or are transported into the uterus to the uterine tubes
A few spem reach the amulla, which is the site of fertilisation.
What is the importance of the acrosome reaction?
The acrosome is the cap-structure over the anterior half of the sperm's head which contains enymes.
As the sperm approaches the zona pellucida the membrane surrounding the acrosome fuses with the plasma membrane of the oocyte, exposing the contents of the acrosome. Enzymes digests to zona pellucida and the membrane of the oocyte.
Part of the sperm's cell membrane then fuses with the cell membrane of the egg, This activates the oocyte to undergo its secondary meiotic division, and the two haploid nuclei fuse to form a zygote.
No acrosome reaction - no fertilisation
Describe the events of fertilisation
Fertilistion occurs in the ampulla of the oviduct.
Mature sperm meets the oocyte (which is in metaphase II). The membrane of the perm fuses with the membrane of the oocyte and it enters the egg.
Fusion of the egg and spem membrane cause an increase in intracellular calcium. The egg cell depolarises, preventing fusion of other sperm. Cortical granules that lie beneath the cell membrane of the egg are released, which harden the zona pellucida.
The egg is stimulated to complete the second meiotic division. A second polar body is formed and extruded, making it haploid.
When the sperm enters the egg, the parental chromosomes mix forming a zygote and mitosis begins.
What are the 5 stages of early embryo development?
Pronucleate phase: 6-20hrs
Cleavage: 18hrs - 3 days
Compaction 3-4 days
Blastocyst: 5-7 days
Hatching: 6-7 days
What is the importance of genome activation of the embryo?
Large amounts of mRNA are inherited from the oocyte which support the development of the embryo through fertiisation and early cleavage.
Onset of mRNA production from the embryonic genome begins at the 4-8cell stage. Activation of the male genome is required for the compaction stage of development which forms the inner cell mass and trophoectoderm.
The inner cell mass becomes the embryo, while the trophoectoderm beomes the placenta. The male genome controls the development of the trophoectoderm which invades the uterus. Female imprinting controls the growth rate and invasion of the embryo.
Implantation of the blastocyts
The blastocyst consists of an inner cell mass which becomes the embryo, and an outershell of trophoblast which becomes the placenta.
The trophoblast differentiates into an inner cytotrophoblast and an inner synctiotrphoblast.
The syncytiotrophoblast is phagocytic and invades endometrium. By 12-14 days the blastocyts is completely embedded within the endometrium and the epithelium grows over it.
What are the risks involved in fertility treatment?
Describe the basic mechanism of an erection
Physical or psychological stimulus activates the parasympathetic nervous system
Parasympathetic stimulaton by the cavernous nerves causes dilation of the arteries in the penis. Veins of the corpus cavernosa are compressed, reducing venous return.
Describe the basic mechanism of ejaculation
Urethra fills with semen from the ductus deferens which is mixed with prostatic and seminal fluid (emission)
The internal urethral spincter contracts. (sympathetic)
Contraction of bulbospongious muscles at the base of the penis creates pressure that forces semen through urethra (pudendal nerve, somatic)
What are the four stages of coitus?
Describe the events that occur in sperm after ejaculation
- Semen is deposited in the upper vagina
- Semen coagulates immediately after ejaculation due to clotting factors. This prevents sperm from being physically lost from the vagina
- Liquefaction occurs by the action of enzymes and sperm enter the cervix.
- Sperm that enter the uterus are tranported to the uterine tube by propulsion (swimming) and fluid currents created by the cilliated cells in the uterine tract.
- sperm under go maturational changes (capacitation and the acrosome reaction) that enable them to fertilise the ovum when they reach the ampulla
What are the maturational changes that spem complete to enable fertilisation?
Capacitance: loss of surface glycoprotein from the sperm . Caused by proteolytic enzymes secreted from the uterine endometrium.
Acrosome reaction: occurs in the acrosome of the sperm as it approaches the egg. As the sperm approaches teh zona pellucida of the egg the acrosome fuses the with plasma membrane of the oocyte releasing enzymes which digest the cumulus around the oocyte and allows the sperm to fuse with the egg.