Developmental Biology Flashcards
What is the role of the superior laryngeal nerve?
It innervates the top third of the oesophagus (including the larynx).
What is the role of the recurrent/inferior laryngeal nerve?
It innervates the lower third of the oesophagus.
What are the pharyngeal arches?
Projections that appear on either side of the developing pharynx in humans in the fourth week of human development. In humans, the fifth arch is not present.
Which laryngeal branch innervates the fourth pharyngeal arch?
The superior laryngeal branch of the vagus nerve.
Which laryngeal branch innervates the sixth pharyngeal arch?
The recurrent/inferior laryngeal branch of the vagus nerve.
What happens to the recurrent nerves as the vasculature of the thorax develops?
They become trapped behind the subclavian artery (on the right side) and the aortic arch (on the left side) and, instead of the previously direct route, have to take a circuitous route into the thorax and back up to the larynx.
What are the statistics for congenital defects in the UK?
Occur in 1/5 of pregnancies
1-2% of live births
Around 60% have no known cause
What are the six research organisms commonly used as human models?
Mouse Chicken Frog Zebrafish Nematode worm Fruit fly
Why is the fruit fly (drosophila melanogaster) a good model for humans?
50% of its genome has homologous genes in the human genome.
Of human disease genes, 75% have Drosophila homologues e.g. Pax6 ‘eyeless’ transcription factor in Drosophila is almost identical to Pax6 factor in humans.
What effect does the expression of Pax6 mutations have in humans, mice and Drosophila respectively? What does this show about Pax6?
Humans: heterozygous mutations cause aniridia (no iris).
Mice: heterozygous mutations cause aniridia & homozygous mutations cause craniofacial defects and complete absence of eyes.
Drosophila: heterozygous mutations have no effect & homozygous mutations cause complete absence of eyes.
These show that, across organisms, the Pax6 gene is essential for the development of light-sensitive organs. (This is further shown by the fact that when Pax6 mRNA is injected into Xenopus frog and Drosophila embryos it causes ectopic eye formation. This demonstrates that the same gene initiates eye development in both insects and vertebrates.)
What are the steps of human embryonic development?
Fertilisation Cleavage (5-9 days after fertilisation (a.f.)) Implantation (6-9 days a.f.) Gastrulation (3-4 weeks a.f.) Body plan (4 weeks a.f.) Organogenesis (4-8 weeks a.f.) Foetal development (8-40 weeks a.f.) Birth
For how long do males produce sperm?
Throughout adult life after puberty (at a rate of around 1000 spermatozoa per second)
Describe the process of fertilisation.
Sperm penetrates a layer of somatic follicle cells and the zona pellucida.
Contact with zona pellucida causes bursting of the acrosome, enabling it to penetrate the zone pellucida and reach the membrane of the egg cell.
Immediately after the first sperm cell has fused with the egg cell membrane, cortical granules release their contents via exocytosis, causing the zona pellucida to harden and preventing polyspermy.
What is the process of cleavage?
A large cell divides into smaller cells without growth (due to lack of nutrients). The cells become progressively smaller in size.
What are the stages of development from embryo onwards?
ZYGOTE — cleavage — MORULA — blastulation — BLASTULA — gastrulation — GASTRULA
