Embryology 1 Flashcards
Embryology - achiemvents of early embryonic development
The first two weeks created tissues of the future embryo and future placenta
The third week created the three germ layers -
ectoderm, mesoderm and endoderm - which are the primordia of all tissues
The fourth week created a recognisable body form and the mesoderm began to organise
What effect does folding of the embryo have on the early development of the heart
Lateral folding - Creates a heart tube
Cephalocaudal folding - Brings theirs heart tube into the thoracic region
Formation of the primitive heart
To get to fullly mature heart from first development of heart we need to -
The primitive heart tube must be divided to create the 4 chambers
The inflow vessels and the outflow vessels must be remodelled
Thus creating the familiar configuration of vessels returning blood from the systemic circulation and the great vessels taking blood away from the heart
Pericardial cavity
Even during development the heart is suspended in the pericardial cavity
Structure and zones of the primitive heart tubes
No physical barriers between these sections - but recognisable different in terms of the derivatives that derive from them
Inflow comes through collection of vessels called sinus venosus, blood pushed into atrium then to primitive ventricle
The structure then begins to narrow down into structure called Bulbus cordis, which feeds into the truncus arteriosus and then into the aortic roots
However things run out of room, therefore
So looping occurs
The tube elongates and runs out of room, so….
It twists and folds up (this normal, regular and predictable)
Then places the inflow and outflow in the correct orientation with respect to each other
Large expansion of the ventricles and the atrium
After cardiac looping - we’ve got a complete folding of our primitive heart tube
Tissues contributing to the development of the atria
Development of the sinus venosus -
R and L sinus horns equal in size then gradual remodelling occurs leading to -
The venous return shifts to the RHS and the L sinus horn recedes back
The right sinus horn is absorbed by the enlarging RA
Development of the atria - RA develops from -
Most of the primitive atrium and the sinus venosus
It receives venous drainage from the body (venae cava) and the heart (coronary sinus)
LA develops from -
a small portion of the primitive atrium ( a very smooth walled structured compared to the RA (which has a large amount of trabecular present
Absorbs proximal parts of pulmonary veins
Revceives oxygenated blood from the lungs
Oblique sinus - oblique pericardial sinus is formed as left atrium and expands to absorb the proximal part of the pulmonary veins
Conflicting circulatory requirements
Mature circulation that needs to develop =
Deoxygentated blood collected from the body
Pumped to the lungs for re-oxygenation and removal of CO2
Reoxygenated blood return from the lungs to the hear and pumped around the body
However in the fetus - lungs don’t work
Oxygenation and removal of CO2 occur at the placenta
So shunts are required to maintain fetal life (e.g. foramen ovale allowing blood to flow between R and L atria - shuts during new borns first breath)
And these shunts must be reversible at birth
(As the Blood arrives at the wrong side of the heart)
The fetal circulatory shunts
3 of them
Foramen ovale
Ductus Arteriosus
Ductus Venosus
Need to build a vessel that bypasses the liver as all the oxygenated liver would be used up if it went there
So it goes to the Inferior vena, and from here to the right atrium
Most of this blood will bypass right ventricle and lungs and go straight to left atrium (some of this blood will go to RV and lungs
From the LA —> LV—> aorta which travels around the body as normal and is taken to the placental surface for gas and nutrient exchange
Oxygenated blood to IVC (bypassing liver) = Ductus venosus
Foramen ovale - connects RA and LA
Pulmonary trunk to the aorta = Ductus arteriosus
At birth respiration begins - causing the LA. Pressure to increase, so the foramen ovale closes, the DA contracts and as the placental support is removed the DV closes
The Great vessels
Which major arteries?
head & upper limb
route blood to lungs for oxygenation
ascending, arch and descending thoracic aorta
The aortic arches
Early arterial system begins as a bilaterally symmetrical system of arched vessels
Undergo extensive remodelling to create the major arteries leaving the heart
Some species of animals have a 5th arch present - not in humans
Aortic arch derivatives:
4th arch - R= proximal part of the R subclavian artery
L = arch of aorta
6th arch = pulmonary arch
R= R pulmonary artery
L=L pulmonary artery and Ductus Arteriosus
The aortic arches are remodelled to create the mature disposition
As the heart “descends” the nerve hooks around the aortic arch and “turns back on itself”
The left recurrent laryngeal nerve (innervates larynx) becomes hooked around the shunt between the PT & aorta - so it distends down a lot further down than the right laryngeal nerve
Patent ductus Arteriosus
Failure of physiological closure of the Ductus arteriosus
Which direction will the blood shunt? L—> R (blood flows form aorta to the R pulmonary artery
Is viable with life - but could experience lethargy and tiredness during extensive exercise
