1.2 - Embryology + Anamolies Flashcards
What is an Embryo?
2
The first stage of development in utero
Between fertilization and 8 weeks
What is a Fetus?
How does it differ from an embryo? (2)
In utero - between 8 weeks gestation to birth
//
Organs begin functioning
Genitalia are visible on ultrasound
How large is an embryo at 4 weeks?
2.5 mm
What are Somites on an embryo?
2
Bilaterally paired blocks of mesoderm
Gives rise to the vertebrae, rib cage, and part of the occipital bone; skeletal muscle, cartilage, tendons, and skin (of the back).
How big is a fetus at 6 weeks?
8 mm
What are the 3 Germ Layers? on an embryo
Ectoderm
Mesoderm
Endoderm
What is the Ectoderm on an embryo?
2
Outer layer
Forms central nervous system, peripheral nervous system, + epidermis
What is the Mesoderm on an embryo?
2
Middle layer
Forms connective tissue, cartilage, bone, striated + smooth muscles, heart, blood + lymph vessels, kidneys, gonads, and other organs
What is the Endoderm on an embryo?
2
Inner layer
Forms epithelial lining of organs, parenchyma of the tonsils + other organs, epithelial lining of tympanic cavity, auditory tube, and other organs
What is the Neural Tube on an embryo?
3
Tube located in middle of embryo
Precursor to Central Nervous System
Rostral end will become brain
What structures can we see on an Embryo between 3-4 weeks?
7
Frontonasal Prominence
Heart
Umbilical Cord
Pharyngeal Arches 1 + 2
Mandibular Arch already formed
Lungs
Limb Buds
What is the Frontonasal Prominence of an embryo?
When does it appear?
Two areas of thickened ectoderm under the fore-brain, one on either side
///
3rd week
What is contained in the Frontonasal Prominence of an embryo?
(3)
Olfactory pits
Nasal pits (will become nostrils)
Upper lip
How do the nasal pits/nostrils form (Frontonasal Prominence) on an embryo?
When does it appear?
Fusion of median + lateral nasal prominences
4th week
How is the upper lip formed (Frontonasal Prominence) on an embryo? (2)
When does it appear?
Fusion of maxillary + median
Merging of median nasal
//
7th week
What is the Maxillary Processes on an embryo?
When does it appear
Embryological structure which gives rise to the upper jaw elements (e.g., maxillary bone) of the developing face
4th week
How is the Maxillary Processes formed on an embryo?
3
They enlarge and grow ventrally and medially, surrounding the future oral cavity.
Grow rapidly, first meeting the lateral nasal processes, and then the lower extension of the medial nasal processes.
The lower extension will give rise to the midstructure (philtrum) of the upper lip.
What are the Mandibular Process on an embryo? (2)
What are they the first to do?
When do they appear?
Forms the lateral wall and base of the primitive mouth
Give rise to the mandible and the lower part of the face and tongue.
//
First to merge with each other at the mid line
//
7th week
How do ears appear on an embryo?
Ears appear lateral + posteriorly as low set ears
What is the Hyoid Arch on an embryo?
When does it appear?
Almost complete ring of tissue around the external auditory meatus
4th week
What comes together to form the Hard Palate on an embryo?
2
Premaxillae
2 Palatine processes (vertical orientation)
Are the Oral and Nasal Cavities separated in a embryo at 7 weeks?
(2)
No
Tongue is in both cavities
What are the Pharyngeal Arches on an embryo?
When do they appear?
Series of externally visible anterior tissue bands lying under the early brain that give rise to the structures of the head and neck
4th week
What is the Mandibular Arch?
When does it form?
First of the bronchial arches
4th week
