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Flashcards in Embryology Deck (40):

On what wall of the embryo do limb buds initially develop?



Approximately what week do limb buds begin to appear?

4 weeks


Where does the tissue for limb bud development originate from?

Lateral mesoderm, derived from the somatic layer of the lateral plate mesoderm.


What does the remnant of the notochord become in an adult?
What condition is associated with it?

Nucleus pulposus
Slipped disc - herniated


What is the differing function of the lateral plate mesoderm and somites in limb development?

Lateral plate mesoderm - limb skeleton

Somites - muscles


Describe the three degress of asymmetry in limbs

Proximodistal axis - shoulder to fingers

Dorsovental axis - no hairy palms

Anteroposterior axis - left/right hands are mirror images


What is the core of the limb bud made from?



What is the function of the apical ectodermal ridge?

Orchestrates limb development from proximal to distal. Stops differentiation of the mesenchyme directly below it, final stage is the appearance of paddles before it regresses.


What is the function of the zone of polarising activity?

Allows the generation of asymmetry in the limbs. (anteroposterior axis determination_
Is a signalling centre located at the posterior base of the limb bud.
Controls patterning and maintains the AER.


Describe how digital rays form.

Mesenchyme condensation within the plates which become cartilagenous models of the digital bones.


What portion of the spine does the upper and lower limb bud appear opposite?

Upper - caudal cervical spine segments

Lower - Lumbar and sacral spinal segments


Describe how development of the brachial plexus determines innervation of specific muscles.

Muscles are compartmentalised and nerves grow into common muscle masses.

Anterior divisions regroup to form medial and lateral cords so flexors are derived from these.

Posterior divisions regroup to form the posterior cord so extensors are supplied by this.


Describe the difference between a dermatome and myotome.

Dermatome - strip of skin supplied by a single spinal nerve

Myotome - muscle or group of muscles supplied by a single spinal nerve


What does the cardiovascular system derive from?



Describe the folding that leads to the final position of the heart.

Lateral folding creates the heart tube. A pair of primitive vessels forms and predominate either side. Early vessels pushed together to make one large tube at the same time as the gut.
Cephalocaudal folding brings it to the thoracic region.


What are blood islands?

A composite of primitive blood cells and capillaries. Found either side of the midline.


From cephalic to caudal, name the regions of the primitive heart tube.

Aortic roots
Truncus arteriosus
Bulbus cordis
Sinus venosus


What role does the pericardium play in heart development?

Forces the tube to bend as the size of the pericardium doesn't increase in proportion to the heart. Causes the cephalic end to move ventrally and caudally to the right. Caudal end moves dorsally and cranially to the left.


Describe development of the sinus venosus

Right and left sinus horns are equal in size. Venous return shifts to the right and the left sinus horn recedes. The right sinus horn is absorbed by enlargement of the right atrium.


What does the right atrium develop from?

Most of the primitive atrium
Sinus venosus


What does the left atrium develop from?

Small proportion of the primitive atrium
Absorbs the proximal pulmonary veins


What causes the oblique pericardial sinus to form?

The left atrium expands, absorbing the pulmonary veins


Explain why the right atrium has trabeculae and the left atrium is smooth.

The left atrium absorbs the primordial pulmonary veins.


What allows foetal circulation to bypass the lungs?

Ductus arteriosus


Describe the fate of the 4th and 6th arch in development of the great vessels.

4th - right to proximal part of right subclavian artery. Left to arch of aorta.

6th - right to right pulmonary artery. Left to left pulmonary artery and ductus arteriosus


Describe the recurrent laryngeal nerves

A branch of the vagus.
Innervates the intrinsic laryngeal muscle, affecting speech.

Right branch drops to T1/T2
Left drops to T4/T5 then turns back up.


Explain why the recurrent laryngeal nerves drop to the thoracic vertebrae then turn back up.

As the heart descends the nerve hooks around the 6th aortic arch and turns back on itself.


Describe the atrioventricular canal

Point of constriction so the atria can communicate with the ventricle after looping


State the structures formed during septation.

Interatrial septum
Interventricular septum
Septation of the ventricular outflow tract to form the pulmonary trunk and aorta.


Describe the first step of septation.

Endocardial cushions develop in the atrioventricular region. Divides the developing heart into right and left channels. Grow into the lumen then connect in the centre.


Describe the steps of atrial septation.

Septum primum grows down towards the fused endocardial cushions.
The ostium primum is present before the septum primum fuses with the endocardial cushions.
Before the ostium primum closes, the ostium secondum appears in the septum primum.
A second crescent-shaped septum (septum secondum) grows. The hole in this is the foramen ovale.


What component of the left and right atrium is derived from the primitive atrium?



What part of the primitive heart tube is absorbed by the right atrium?

Sinus venosus


What is the adult remnant of the foramen ovale?

Fossa ovalis


What is the shunt in the heart allowing it to bypass the lungs?

Foramen ovale


Describe the septation of the outflow tract.

Endocardial cushions form in the truncus arteriosus.
Grow towards and twist around each other, forming a spiral septum.
Creates the root of the aorta and pulmonary trunk.


What structure allows the umbilical vein to bypass the liver?

Ductus venosus


Describe the change in circulation at birth.

Respiration beginning causes a change in pressure so it's greater in the left atrium than the right.
The foramen ovale shuts because the septum primum is pushed against the septum secondum, sealing the holes which fuse over time.
The smooth muscle in the ductus arteriosus closes and becomes fibrous over time.
Ductus venosus closes as the placental support is removed.


State the fates of the foetal shunts

Foramen ovale - fossa ovalis
Ductus arteriosus - ligamentum arteriosum
Ductus venosus - ligamentum venosum
Umbilical vein - ligamentum teres (hepatis)


State the fates of the regions of the primitive heart tube

Sinus venosus - right atrium
Atrium - auricles of atria
Ventricle - left ventricle
Bulboventricular sulcus - primary interventricular foramen
Bulmus cordis
(proximal third) - right ventricle
(conus cordis) - outflow tract of L/R ventricles
(truncus arteriosus) - roots, proximal aorta and pulmonary trunk