Human Reproduction

• Sperm is produced in the seminiferous tubules, within the testes. 
• It then collects in the vasa efferentia, and then the epididymus, where they mature fully. 
• Sperm then travel through the vas deferens to the urethra.
•  The VD combines with seminal vesicle via the ejaculatory ducts. These secrete mucus which aids mobility, and the prostate secrets an alkaline fluid that neutralises the acidity of urine in the urethra.

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• Occurs in germinal epithelium of seminiferous tubules.
• The spermatogonium is first to be produced, and they undergo mitosis to make >>>
• Diploid spermocytes undergo mitosis to produce primary spermatocytes.
• Primary spermatocyes undergo meiosis 1 and form haploid secondary spermatocytes.
•  Second spermocytes undero meiosis 2 into haploid spermatids, that mature into ??
• Spermatozoa.
• Sertoli cells provide nutrients and protection for this process, and the mature spermatozoa.

DIAGRAM

Described using the journey of a ovum.

• Oocytes are produced in the germinal epithelium of an ovary.
• After maturation, they move into the fallopian tube/oviduct, and are wafted along by ciliated cells.
• They tehn pass into the uterus, which has thick muscular wall. For each menstrual cycle, the uterus becomes lined with the endometrium.
• If the ovum is not fertilised, the ovum and endometrium are passed through the cervix and vagina, during a woman's 'period'.

DIAGRAM

• Oogonia are formed before birth, an undergo mitosis to form primary oocytes.
• Oocytes begin meiosis one, but pause at Prophase 1.
• Germinal epithelium cells divide into follicle cells whoch then surround the primary oocytes, and are called primary follicles.
• Primary oocytes complete meoisis 1 and  to form secondary oocytes and a polar body.
• The mature Graafian follicle migrates to the surface of the ovary and bursts, releasing secondary oocyte = OVULATION.
• Secondry oocyte's second meiotic division is paused until fertilisation.
• Upon fertilisation,  large ovum and a second polar body are formed.
• After this division, the ovum nucleus fuses with sperm nucleus to form an zygote.
• The graafian follicle becomes the coorpus luteum, which releases progesterone during pregnancy.

SECONDARY OOCYTE STRUCTURE:

• corona radiata =follicle cells
• zona pellucida = behind follcile cells

• *********** propels semen through cervix and into uterus.
• Sperm travels from epididymus to oviduct of female.
• Conipers glands and prostate glands secrete fluids to create semen.
• Only a few sperm reach fertilisation site.

• Sperm uses flagella to swim from the uterus and into the oviduct.
• Viable for 48 hours.
• The oocyte is surrounded by follicle cells and a membrane called the zona pellucida.
• CAPACITATION = changes in the membrane over the acrosome of a sperm cap, allowing fertilisation.
• When the acrosome touches the zona pellucida, it ruptures and releases proteases,  which digest the layers of cells surrounding oocyte.
• Inversion of acrosome= thin needle filament to pierce softened membrane.
• This causes the zona pellucida to harden, and become the fertilisation membrane, stopping any more sperm from entering.
• It also stimulates second meiotic divison of primary oocyte, to become a mature ovum.
• ovum nucleus and sperm nucleus fuse and form diploid zygote.

Cleavage

The rapid cell division in early embryo, with little growth, but many new cells created.

Blastocyst

Hollow ball of cells with trophoblast layer- amnion and chlorion.

Implantation

Attachment of fertilised egg to the endometrium and uterus wall.

• Zygote divides by mitosis to become a blastocyst, which embeds into the endometrium.
• A blastocyst has a two-layer wall around it called the trophoblast, made from the amnion (on the inside) and the chlorion (on the outside.)
• The Chlorion has villi to absorb nutrients from the endometrium, and also secretes Human chlorionic gonadotropin (hCG) which stops the corpus luteum from degenerating.

Sub fertility: difficulty in concieving naturally.

• absence of/a irregular menstrual cycle: 95% treated with drug clomiphene.
• blockage of fallopian tube, maybe by infection: microsurgery

Pregnancy testing

Most use monoclonal antibodies (copies of one type of antibody) to test for hCG (human chlorionic gondotropin), which acts as an antigen.

High levels of hCG in urine indicates pregnancy. Antibodies bound to latex beads react with hCG causing them to bind together and change colour..

IVF:

• Hormones are used to develop many follicles at ones.
• Oocytes collected using a tube and ultrasound.
• semen is collected and put onto a dish with nutrients.
• sperm added to oocyte.
• fertilised eggs are implanted