development Flashcards
(15 cards)
Vascular system early development
the vascular system and the heart begin to development during WEEK 3
Blood vessel formation begins within MESENCHYME associated with the extraembryonic membrane (CHORION), wall of umbilical vesicle, and amnion
Mesenchyme around the umbilical vesicle is where the first blood vessels- VASCULAR PROGENITOR CELLS/ ANGIOBLASTS
Angioblasts clumps– BLOOD ISLANDS- inside angioblasts transform into flat endothelial CELLS
Hematopoietic Stem Cells- in blood islands in the umbilical vesicle, differentiated endothelial cells
Blood vessels form within the embryo during the middle of week 3
Vasculogenesis (directly from vascular precursor cells)– includes the aorta, the vitelline and cardinal veins and endocardium of the heart.
When new vessels sprout from existing vessels–Angiogenesis (used to expand and remodel the primitive vascular network formed by vasculogenesis)- Most vessel formation via angiogenesis
Developmental fate of the systemic venous channels
Early in the 4th week, heart is tubular structure- vessels in the caudal (venous) end, The systemic venous channels of the embryo, the Pharyngeal Arch arteries (aortic arches at the cranial end)
3 pairs of veins connect to the Systemic Venous Sinus
The vitiline veins originate from the wall of the umbilical vesicle (yolk sac)
Umbilical Veins come from the chorion- surrounds the embryo and contributes to the formation of the placenta- these veins contain well oxyygenated blood
Common cardinal veins (anterior and posterior) venous drainage from the body of the embryo
Vitelline Veins
originate from Umbilicle vesicle Wall circulation
They pass thru the Transverse Septum
Remodeled– Venous duct forms
Becomes the main drainage channel for the liver draining directly into the IVC
Where are the primitive heart fields located
After passing thru primative streak, cardiac progenitor cells are a part of the intraembryonic mesoderm. They migrate cranially to form bilateral aggregates in cranial part of disc.
What mesoderm layer are cardiac angioblasts located
Cardiac progenitors located in splanchnic mesoderm
Embryonic coelom is U shaped with transverse portion of U located at the caranial end
What is the primary heart field and secondary heart field
The bilateral heart field expand and merge at the cranial end of trilaminar embryo form a crescent of mesenchyme known as the cardiogenic crescent or the primary heart field
PHF is part of the splanchnic mesoderm and is accosiated with the cranial part of the intraembryonic coelom, the primitive pericardial cavity
Cells of the PHF express the gene Nkx2.5, mesenchyme cells located medial and dorsal to the PHF are designated as the secondary heart field these cells express Islet 2
How and where does the primary (primitive) heart tube form
Day 18, cells from the PHF form a plexus of endothelial tubes adjacent to the foregut, as the embro folds in the transverse plane, the endothelial plexus on each side of the embryo approach each other and fuse to form a single endothelial lined tube called the endo cardium
The surrounding splanchnic mesoderm of the PHF forms an outer layer around the endothelim called myocardium
Dorsally in the midline the myocardium is connected with the ventral surface of the forgut by a mesentery, the dorsal mesocardium
What are the layers of the primitive heart tube
Endocardium: the endothelial (an epithelium) lining of the lumen of the primary tubular heart
Myocardium: the outer epithelial tube of the primary heart tube
Cardiac jelly: an accumulation of extracellular matrix between the endocardium and the myocardium. The cardiac jelly is essentially the fused basement membrane of the 2 epithelia
Epicardium: becomes the visceral pericardium of the heart. The epicardium is derived from the proepicardial organ an outgrowth of coelomic epthelium- give rise to cornoary vessels
What vessels enter and leave the tubular heart
The inflow vessels: caudal end of the primary heart tube and represent the systemic venous inflow from the embryo (2 ubilical veins, 2 vitelline veins from the yolk sac, and 2 common cardinal veins from head, trunk and limbs)
Outflow: cranial end5 pharyngeal arch arteries from the aortic sac
chambers (components) present within the initial primitive heart tube
Primary heart tube forms, only heart comonent present is the left ventricle
Looping
primary heart tube is initially straight and contains one heart segment or component added
Apex of the loop is between the developing left and right ventricles
Direction of loop is programed into the cardiac precursor cells as they migrate. During gastrulation (signaling from the primitive node and left lateral mesoderm impose sidedness or laterally on the forming embryo disc)
Heart loops to the right forcing apex to the left–> dextrocardia
The primary atrium and the systemic venoussinus ascend to a postition
How are additional components added to the primitive heart tube
the developing right ventricle, the atrioventricular AV canal , the primary atrium (PA) the systemic venous sinus and the outflow tract/region all originated from the secondary heart field
how does looping and early septation affect cardiac blood flow
pulsation begins day 21-22
Flow of blood thru the looped heart becomes physiologically separated before its anatomically separated
What portion of each definitive atria is formed from the systemic venous sinus, primitive atria, the pulmonary veins
Right atrium: Smooth portion of the right atrium is derived from the absorption of the right SVS, additional structures of the right sinoatrial valve, these include the valve of the inferior caval vein, the valve of the coronary sinus and the terminal crista. The trabeculated portion is contained within the appendage
Left atrium: Much smooth portion is absorption of the 2 generations of pulmonary veins, trabeculates portion of the left atrium is restricted to the appendage
