Reproduction and embryology

• what is fertilisation?

  fertilisation is a series of processes which culminate with the union of the male gamete(the sperm) and the female gamete(the oocyte) to form a diploid zygote
• where do sperm develop?

  seminiferous tubules of the testes
• What is azoospermia?

  no sperm present within the ejaculate. caused by primary testicular failure, blockage to the vas deferent - infection/trauma.
• What is oligozoospermia?

  reduced number of sperm in the ejaculate (Low sperm count). Caused by gonadotrophin insufficiency, drugs(social and medical, alcohol)
• what is idiopathic oligozoospermia?

  Low sperm count but physiological parameters normal - this is unexplained.
• What is teratozoospermia?

  abnormal morphology of the sperm(Giant head, double tail, bent tail) caused by genetics, toxins and viral infections.
• what is asthenospermia?

  reduced or lack of sperm motility. caused by toxins and viral infections
• what is sperm agglutination?

  sperm clump together in groups. caused by infection/ autoimmune response.
• what changes happen to sperm in the uterus in readiness for fertilisation?

  capacitation
• What is the corona radiata?

  the first barrier preventing access of sperm to the oocyte. Is an outer layer of cumulus cells that is embedded in an intercellular matrix of carbohydrates, protein and hyaluronic acid
• What is the oocyte surrounded by?

  zona pellucida
• how does the sperm bind to the zona pellucida?

  The zona pellucida is 15-15 um thick. It has sperm receptors. At first the capacitated sperm loosely and reversibly adhere to the surface of the zona pellucida. Then, the sperm become strongly and irreversibly bound to the zona pellucida. Many sperm bind to the zona pellucida but usually only a few sperm penetrate into the perivitelline space and only one will fuse with the oocyte plasma membrane
• what happens during the acrosome reaction?

  The outer acrosome membrane fuses with the covering membrane of the oocyte. Small vesicles containing acrosomal enzymes such as across are pinched off and their contents are released. The inner acrosomal membrane is exposed. A tunnel is digested through the zona pellucida by across. The lurching movements from the sperm propel it through the zona pellucida and the perivitelline space so that the head is in contact with the oocyte surface membrane. Penetration through the zona pellucida requires both hyper activated sperm and lysis of the zona pellucida.
• What is polyspermy?

  fertilization by more than one sperm. this is usually fatal and often detected in spontaneous miscarriage.
• what is the cortisol reaction?

  Its a reaction that occurs when the sperm fuses with the egg to preent polyspermy (multiple sperm penetrating the egg) to occur. The fast-block is a quick release of calcium followed by the gradual production of an impenetrable envelope from cortical granules (slow-block)
• What happens before the first mitotic cell division?

  prior to fertilisation, the chromosomes of the oocyte had been arrested in metaphase of meiosis II. Once fertilisation occurs, meiosis II of the oocyte is completed and the second polar body is extruded.
• What happens when the decondensation of sperm nucleus occurs

  The chromatin of the mature sperm is transcriptionally compacted tightly in the head. After the head of the sperm enters the cytoplasm of the oocyte, it is affected by cytoplasmic factors that cause the chromatin threads of DNA to decondense and become transcriptionally competent.
• first mitotic division

  the membranes of both pronuclei break down, and the haploid chromosomes from the male and female gamete become organised around a mitotic spindle. The combination of the male and female chromosomes is called syngamy. Fertilisation is complete 18-24 hours after fusion. The fertilised oocyte is known as a zygote. this restores the number of chromosomes to diploid.
• what is an embryo?

  a zygote is called an embryo after 2 days of fertilisation
• what is a foetus?

  term used after 8 weeks of fertilisation
• development before implantation

  day 0 - fertilisation occurs, cell begins to divide - has a cleavage. Day 1 - becomes a 2 celled embryo. Day 2 - becomes a 4 cell embryoday 3 - known as a morula as the cell divides. Day 5 - known as a blastocyst. Days 6-8 - start of implantation, known as a trophoblast.
• What is 'cleavage'?

  division of cells in the early embryo
• what happens in week 2 of embryonic development?

  The inner cell mass becomes flattened into a bilaminar embryonic disc, the cells form 2 distinct layers. The epiblast becomes the floor of the amniotic cavity, and the hypoblast becomes the embryonic yolk sac. at this stage the beginnings of uteroplacental circulation develop
• what happens in week 3 of embryonic development?

  Gastrulation. the bilaminar embryonic disc becomes the trilaminar.
• what is the ectoderm?


  the germ layer covering the embryo's surface - will give rise to the skin. In contact with the amniotic cavity very early on.
• what is the mesoderm?

  middle layer. develops the connective tissue, smother muscle, blood, skeleton, reproductive and endocrine systems.
• What is the endoderm?


  The hypoblast becomes the endoderm. Epithelial linings and some glandular structures will form.
• what are the functions of the notocord?

  the axial skeleton(bones of head and spinal cord)the neural plate(gives rise to the primitive nervous system)
• what happens during weeks 4-8 of embryonic development?


  the trilaminar disc folds into a C shaped cylindrical embryo and all the major structures and organs are established although few are functional.
• define organogenesis


  the development of the organ systems
• human development: growth

  hyperplasia: cell division and hypertrophy: increase in cell size.
• human development: morphogenesis

  development of form - involves movement of sheers + masses of cells
• human development: differentiation

  maturation of cells forming tissues and organs capable of specialised function
• How does the heart form?

  the primitive heart develops from the mesodermal germ layer. By 21 days post fertilisation, cells surrounding the heart have become differentiated as myocardial cells capable of eliciting an organised response, so the heart begins beating.
• What are somites?

  prominent paired blocks of tissue - the number of somites indicates the age of the embryo
• What is neurulation?

  the process by which the neural plate becomes the neural tube
• what development has occurred by week 5?


  upper limb buds become paddle-shaped. CRL is 7-9mm. Lower limb buds are flipper like. rapid brain development and head enlargement. facial prominences develop. Mesonephric ridges denote position of mesonephric kidneys
• what development has occurred by week 6?

  head very large, projects over heart dominance. joints of upper limbs differentiate. digital rays of upper limbs evident. retinal pigment formed so eye is obvious. external ear canal and auricle formed. reflex responses to touch. CRL 11-14mm
• what development has occurred by week 7?


  notches between digital rays partially separate future fingers. CRL 16-18 mm. Liver prominent
• what development has occurred by week 8?


  digits of hands separated but still webbed. earth characteristic shape but still low set. CRL 27-31mm. purposeful limb movements occur. Eye lids closing. notches visible between digital rays of feet. head still disproportionately large(half of total embryo length). external genitalia evident(not enough for sex determination. ossification begins in lower limbs.