Building A Human Flashcards
Definition of embryogenesis
Process by which the embryo forms and develops..
Fundamentals of anatomy are laid down within the 1st 2 months
Definition of cleavage
Splitting of the cell into double the no without growth
Definition of morula
Solid ball of cells resulting from division of a fertilised ovum and from which a blastula forms
Definition of blastocyst
Where some differentiated cells are present in the blastula
Definition of gastrulation
Process through which cells sort out to generate the body plan
This involves the inward movement of the epiblast
Definition of germ layer
Group of cells in an embryo that interact with each other as the embryo develops and contribute to the formation of all organs and tissues
Definition of anterior
Embryological anterior = anatomical superior
Definition of posterior
Embryological posterior = anatomical inferior
Definition of neurulation
Formation of neural tube
Starts anteriorly, ceases posteriorly
Results in formation of brain, spinal cord
Definition of secondary neurulation
De novo formation of lumen in solid mass
Definition of somites
Each of a no of body segments containing same internal structures
Form vertebral column, associated musculature, peripheral nerves and order
Definition of preformation
Everything in the embryo is preformed and simply gets bigger during development
Definition of epigenesis
Structures of the adult form arise progressively during development
Definition of homeosis
Replacement of part of 1 segment of an insect/segmented animal by a structure characteristic of a different segment through mutation
Definition of collinearity
Independent variables are high correlated
Definition of homeotic
Genes that regulate development of anatomical structures
Definition of morphogenetic
Molecules that give form and shape to cells
When do the key events in human development occur
At the very earliest stages of embryogenesis
First 2 months
Describe the human development timeline
1st trimester
2nd, 3rd trimester
1st, embryonic period
2nd, 3rd, foetal period
What happens in the first 9 days of development
0, fertilisation in Fallopian tube 1, first cleavage 2, 2 cell stage, 4 cell stage 3-4, 8 cell uncompacted morula 4-8, cell compacted morula 5, formation of early blastocyst 6-7, formation of late stage blastocyst 8-9, implantation of blastocyst in endometrium
Describe cleavage
Follows immediately after fertilisation
Series of rapid cell divisions, no growth, increase no of cells => blastocyst
Describe the structure of the blastocyst
Layer of cells on the perimeter, trophoblast
Inner cell mass, deep to the trophoblast
Blastocyst cavity, deep to trophoblast
Describe the purpose of the inner cell mass
Form all the cells in our body
Embryo derived from inner cell mass
Describe the purpose of the trophoblast
Interacts with the uterus
Provides support for the embryo
How are the cells in a blastocyst rearranged
The inner cell mass differentiates to form the epiblast and the hypoblast
Both these cell layers form 2 flat sheets of cells
Blastocytic cavity becomes the umbilical vesicles
Epiblast between amniotic sac and hypoblast
2 flat cell sheets form the blastodisc
Prochordal plate forms between the epiblast and hypoblast
Umbilical vesicle surrounded by extraembryonic coelom
Describe the cell structure before gastrulation
Bilayered embryonic disc between the amnion and yolk sac
Describe the superior view of the bilayered embryonic disc
Leaf shaped
Cut edge of yolk sac
Cut edge of amnion
Hensens node and primitive streak towards the posterior side
What happens during gastrulation
Cells move into the primitive streak
Displace hypoblast from epiblast to form the endoderm, mesoderm and ectoderm
What forms from the endoderm
Alveolar cells
Thyroid cells
Digestive/pancreatic cells
What forms from the mesoderm
Cardiac muscle cells Skeletal muscle cells Tubule cells of kidney RBC Smooth muscle cells in gut
What forms from the ectoderm
Skin cells of epidermis
Neurones in brain
Pigment cells
Describe the development of development
Proceeds from anterior to posterior
Describe the process of primary neurulation
Driven by intrinsic and extrinsic cellular forces
Starts anteriorly, ends posteriorly Presumptive neural tissue proliferates, drives the formation of the folds Folds rise up and fuses Notochord drags tube down Epidermis fuses together
Neural crest forms under epidermis
Neural tube forms under neural crest
What is secondary neurulation
De novo formation of lumen from solid mass
Why is closure important in neurulation
Initiation of neural tube closure is discontinuous
Defects in neurulation result in
- Anencephaly (brains do not fuse at anterior neuropore)
- Craniorachiscisis (hind brain neuropore does not close)
- Spina bifida (posterior neuropore does not close)
Importance of the neural crest
Cells in the neural crest will migrate to form neurones and glia of PNS
Forms
- Pigment cells
- Schwann cells
- Satellite cells
- Unipolar and multipolar neurones in sympathetic ganglion
- Chromaffin cells in adrenal medulla
- Parasympathetic gut submucosal plexus
- Prevertebral plexus
Describe the structure of the mediolateral organisation of the body
Chordamesoderm below neural tube
Paraaxial mesoderm lateral to the neural tube
Intermediate mesoderm lateral to the paraaxial mesoderm
Lateral plate mesoderm lateral to the paraaxial mesoderm
What structures form from the intermediate mesoderm
Kidney
Gonads
What structures form from the chordamesoderm
Notachord
What structures form from the paraaxial mesoderm
Head
Somites
- Sclerotome
- Syndetome
- Myotome
- Dermatome
- Endothelial cells
What structures form from the lateral plate mesoderm
Splanchnic
Somatic
Extraembryonic
Function of the notachord
Contributes to the center of the invertebral discs, the nucleus pulposis
Lost in childhood
Function of somites
Blocks of mesoderm that form vertebral column and associated musculature
Order peripheral nerves, develop AP
Bud from anterior of presomitic mesoderm as embryo extends posteriorly
Describe the relationship between the neural crest and the somites
During neural crest migration, they meet the somites first
Somites organise neural crest so they only go into anterior half of each somite
This occurs as inhibitory molecules are released from the posterior half of each somite
Motor axons directed away from the nerve core through anterior half of somite
Defects in somite genesis
Results in scoliosis (abnormal curvature of the spine)
What develops from the endoderm
Foregut
Midgut
Hindgut
What structures form from the foregut
Oesophagus Thyroid Lung Liver Biliary tree Stomach Pancreas
What structures develop from the midgut
Small intestine
What develops from the hindgut
Colon
What develops in the first 44 days
Fingers form from cell death of webbing
Optic placode
Upper and lower limbs
Developing nose and umbilical cord
What develops in the first 55 days
Eyes, ears, nose
Upper, lower limbs
Umbilical cord
What develops between 13-26 weeks
Eyes, ears, mouth, nose
Upper, lower limbs
Umbilical cord
Describe the generative nature of development
Each step builds upon the previous step
Tissues communicate with each other to coordinate development
Spatial order required for successful cell differentiation
Possible locations of cells
Anteroposterior
Dorsoventral
Mediolateral
Left, Right
What are homeotic genes
Order of genes in chromosome = order of body parts
Exhibit collinearity
Transcription factors turn on and off different genes
Organisation of genes is v similar in humans and mammals
Describe the action of morphogens
Cells respond to threshold concs
Greater the distance from the source, receives v little
All based on position
Morphogens in spinal cord
Morphogens released from dorsal side of spinal cord => sensory neurone
Morphogens released from ventral side of spinal cord => motor function
Neural tube patterning, localised signals import identity
Importance of the notachord
Directs development of ventral spinal cord and motor neurons
Neural tube has a roof and floor plate, motor neurons form on either side of tube
Describe the importance of Sonic the Hedgehog
Highly expressed in notochord
Can diffuse from midline structures to generate different neuron types at different positions
Motor neurons received greatest [SHH]
Also patterns somite for sclerotome formation
The effects of mutations in SHH
Haloprosencephaly
Cyclopamine in some plants, have teratogenic effects = Cyclopia
