test 3

Question 1

Vascular Development occurs in what two mechanisms

Answer 1

 Vasculogenesis
- making of new blood vessels
 Angiogenesis
- vessels sprout from existing vessels

Question 2

3 weeks of development

Answer 2

 1st blood islands appear in mesoderm
 Surrounding wall of yolk sac
 Arise from mesoderm cells
 Induced for form hemangioblasts
 Precursor to vessels and blood formation

Question 3

Hematopoietic stem cells

Answer 3

 Come from mesoderm surrounding aorta near kidney
 Colonize liver (source of first blood cells
 Becomes hematopoietic organ of the embryo and fetus
 2-7 months gestation
 Stem cells from liver colonize bone marrow (@ 7th month bones start to form)
 Liver loses RBC making function.

Question 4

Major vessels (Dorsal aorta, cardinal vein) for via

Answer 4

 Form via Vasculogensis

- making of new blood vessels

Question 5

Remainder of vascular system other than the major vessels form via

Answer 5

 Angiogensis

 Sprout off existing blood vessels

Question 6

The major arterial conduits in the early embryo

Answer 6

 dorsal aortas
 Simply a continuation of the endocardial tubes.
 Arise from the Aortic Sac (Distal most part of the truncus arteriosus)

Question 7

Cranial portions of the Dorsal aortas become

Answer 7

 first pair of aortic

arches.

Question 8

How many aortic arch systems are there

Answer 8

 There are six pairs of aortic arches present at some point during development, but the 5th aortic arch is only transient.
 5th Aortic Arch never forms or forms incompletely and regresses
 Arches are numbered I, II, III, IV, and VI
 As they develop, some become modified and other regress

Question 9

3 mm Embryo

Answer 9

• The first pair of arches is large
• Second pair is just forming
• All the other arches develop from the region of the aortic sac.
• Distally (not shown here), the dorsal aortas fuse to form a single vessel.

Question 10

4 mm Embryo – Day 27

Answer 10

• Aortic arch I has largely disappeared
  * Part of it remains - becomes the Maxillary Artery. (goes to the front of your face)
• Aortic arch II is regressing.
  * Remnants of arch II – becomes the Stapedial Artery. (to your ear)
• Aortic arch III is already large and well developed.
• Aortic arches IV and VI are being formed as ventral and dorsal sprouts.
  * aortic arch VI already has a sprouting branch of the primitive pulmonary artery

Question 11

10mm Embryo – Day 29

Answer 11

• The first two aortic arches have disappeared
• Aortic arches III, IV, and VI are quite large.
• The truncoaortic sac has been divided
  * Arch VI is now continuous with the pulmonary trunk.
• Starting to lose symmetry
• The intersegmental arteries will be important in the formation of the subclavian arteries.

Question 12

14mm Embryo

Answer 12

• The symmetrical pattern is largely gone.
• There is further division of the aorta and pulmonary artery.
• Arch III forms the common carotid artery and first part of the internal carotid artery
• Arch IV stays on each side but becomes different structures.
• Left Arch IV – part of Aortic arch between LCC and L. Subclavian
• Right Arch IV – Proximal R. Subclavian
• Intersegmental arteries have migrated upward to become the subclavian arteries.
• **Remember the Arch V never forms
• Arch VI (aka. Pulmonary Arch)
  * Gives off branches that grows toward the developing lung buds
  * The dorsal portion of the right arch VI has disappeared and the left arch VI will become the ductus arteriosus.

Question 13

17mm Embryo

Answer 13

• A portion of the vessel that was formerly the right dorsal aorta disappears.
• Proximal portion persists and becomes the right subclavian artery.

Question 14

At Birth

Answer 14

• At birth, the distal part of the left sixth aortic arch (the ductus arteriosus) normally obliterates
  * ligamentum arteriosum.
• The adult aortic arch system is now established.

Question 15

Sinus Venosus

Answer 15

• The sinus venosus is the major point of entry into the common atria.
  * Remains paired until the embryo is 4mm
  * Even after the endocardial tubes fuse.

Question 16

In a 4 mm embryo, there is a

distinguishable (venous)

Answer 16

• Central (unpaired) portion,
• Transverse portion
• Right and left sinus horns.

Question 17

Mid 4th week (venous)

Answer 17

 Sinus venosus receives blood from the right and left sinus horns.
 Each horn receives blood from 3 veins
 Vitelline vein
 Umbilical vein
 Common Cardinal vein
 Communication between sinus and atrium is wide open
 Communication will eventually shift to the right
 Caused by shift in blood in venous system
 Occurs at about 4-5 weeks.

Question 18

5th week (venous)

Answer 18

 Obliteration of the right umbilical vein and left vitelline vein
 Left sinus horn loses importance

Question 19

week 10 (venous)

Answer 19

 Left common cardinal vein become obliterated

 All that remains of the left sinus horn is the oblique vein of the left atrium and the coronary sinus.

Question 20

Right Sinus horn

Answer 20

 Shunt of blood left to right enlarges right sinus horn
 Right horn and vein are the only communication between the original sinus venosus and the atrium
 Forms the smooth walled part of the right atrium.

Question 21

Sinuatrial valves

Answer 21

 Sinuatrial orifice (entrance to the common atrium) is flanked on each side by valvular folds.
 Right and left venous valves
 Left venous valve fuses with the atrial septum
 Superior part of the right venous valve disappears
 Inferior part of the right venous valve becomes the valve of the inferior vena cava and the valve of the coronary sinus.
- held direct the flow

Question 22

The sinus venosus receives three pairs of veins

Answer 22

• Vitelline veins
• Carry blood from the yolk sac to the sinus venosus
- provides nutrients for the embryo
• Umbilical veins
• Goes to the placenta and gets blood to embryo
• Common cardinal veins
• Drain the body of the embryo

Question 23

Vitelline venous system

Answer 23

• Enters the sinus venosus

* Gives rise to the hepatic veins

Question 24

Umbilical venous system

Answer 24

• Enter the sinus venosus lateral to the vitelline veins.

* Persists as the umbilical vein in the term fetus.

Question 25

Cardinal venous system

Answer 25

* Enters the sinus venosus lateral/superior to the umbilical veins * Forms a large complex network of veins throughout the body.

Question 26

Embryonic Venous Systems – 10mm Embryo

Answer 26

* Left vitelline vein has disappeared * Right Vitelline vein is transforming into a structure that will eventually be the hepatic veins and all of the veins of the hepatic portal system. * The left umbilical vein has joined the hepatic system. * The left umbilical vein will persist in the fetus as the umbilical vein. * Inferior portion of the cardinal venous system is gaining complexity. * The left side and right side are migrating inward and joining. * Right umbilical vein turns into the subcardinohepatic anastomosis

Question 27

Embryonic Venous Systems – 14mm Embryo

Answer 27

* The left sinus horn has separated from the right * Will eventually become the coronary sinus. * The right side of the subcardinal venous system is developing into the principle venous channels to the heart from the lower body.

Question 28

Embryonic Venous Systems – 17mm Embryo

Answer 28

* The upper limbs are now drained by veins which empty into the anterior cardinal veins. * The major portions of the posterior cardinal veins have disappeared * There is even greater demand on the right subcardinal vein.

Question 29

Embryonic Venous Systems – 24mm Embryo

Answer 29

* The anterior cardinal veins now have a channel between them (the left brachiocephalic vein). * These cardinal veins will drain the entire head and upper extremities. * The subcardinal veins have completely fused * Make up a large portion of what will become the inferior vena cava. * There are now clear venous channels to the kidneys and adrenal glands.

Question 30

Embryonic Venous Systems – Term Embryo

Answer 30

* Further development leads to the complete venous system. * Notice that the umbilical vein still persists and enters the portal vein. * Notice the ductus venosus.