Lecture 34 - Embryo Blood Vessels

What does the cardinal venous system drain?

Drains the body of the embryo

What are some possible symptoms associated with aberrant origin of the right subclavian artery?

Dyspnea and dysphagia

Define postductal coarctation

Postductual coarctation occurs when the constriction is located distal to the ductus arteriosis.

Define preductal coarctation

Preductual coarctation occurs when the constriction is located distal to the left subclavian artery but proximal to the ductus arteriosis.

What substance keeps the ductus venosus open until birth?

Prostaglandins - the same stuff that keeps the ductus arteriosis open until birth.

In the fetus/embryo, what substance keeps the ductus arteriosis open?

Prostaglandins act as a vasodilator to keep the ductus arteriosis open

At birth, the distal portion of the umbilical arteries are obliterated (boom!) and become what?

The medial umbilical ligaments

The inferior portions of the vitelline veins give rise to which vessels?

The portal vein, superior and inferior mesenteric vein, and the splenic vein.

Define the primitive system of blood vessels

The primitive system of blood vessels just refers to the development of the aortic sac and the 6 pairs of aortic arches

What is the purpose of the ductus venosus?

The purpose of the ductus arteriosis is to allow the majority of oxygenated placental blood to bypass the hepatic sinusoids into the inferior vena cava.

Which two aortic arches combine to form the brachiocephalic trunk?

The right 3rd and 4th aortic arches

What is the fate of the right 7th cervical intersegmental artery?

The right 7th intersegmental artery becomes PART of the right subclavian artery. (The rest comes from the 4th aortic arch and part of the dorsal aorta).

True or false: the aortic arches are formed by both vasculogenesis and angiogenesis

True. They arise from both de novo vasculogenesis and sprouting/budding of existing vessels (angiogenesis).

Coarctation of the aorta is frequently associated with which syndrome?

Turner's syndrome. This syndrome is caused by monosomy X (therefore females only).

By what process do intersegmental arteries arise? (vasculogenesis or angiogenesis)

Vasculogenesis

The anterior and posterior cardinal veins join to form the _____ ______ veins before entering the sinus horn.

common cardinal

How many umbilical veins are in the umbilical cord?

1 - this carries oxygenated blood from the placenta towards the heart

What 4 structures contribute to the final aortic arch? List them from proximal to distal.

1. Aortic sac 2. Left aortic arch IV 3. Left dorsal aorta proximal to the 7th intersegmental artery 4. Left dorsal aorta distal to the 7th intersegmental artery

An interrupted aortic arch is sometimes associated with which two disorders?

1. DiGeorge syndrome 2. Severe VSDs

After birth, prostaglandin levels drop. This leads to the closure of two embryologic vessels. What are they?

1. Ductus arteriosis 2. Ductus venosus

Describe the 3 basic ways that the primitive blood vessel system alters to eventually achieve the adult pattern.

1. Hypertrophy of aortic arches 3, 4, and 6. (The 3rd aortic arch pair gives rise to the carotid arteries, the R 4th gives rise to part of the R subclavian, the left 4th gives rise to the final aortic arch, the 6th pair gives rise to the pulmonary arteries) 2. Addition of new vessels (e.g., external carotid grows off of the 3rd aortic arch) 3. Disintegration of some vessel segments

List the negative effects that patent ductus arteriosis has on the heart in chronological order.

1. Left ventricular hypertrophy - the LV has to work 2-3 times as hard to push blood into systemic circulation because so much blood is needlessly recycled into pulmonary circulation. 2. Pulmonary hypertension - extra blood is traveling to lungs 3. Right ventricular hypertrophy - RV receives and has to push this extra blood This will lead to congestive heart failure

What three things do the subcardinal veins give rise to?

1. Renal veins 2. Gonadal veins 3. Contributes to abdominal part of IVC

What 3 structures contribute to the formation of the right subclavian artery? List them from proximal to distal.

1. Right 4th aortic arch 2. Right dorsal aorta 3. Right 7th intersegmental artery

After birth, what 3 things to the closing of the ductus arteriosis?

1. Sudden change in blood oxygen tension 2. Sudden drop in prostaglandins (vasodilators) 3. An increase in endothelin production (a growth factor produced by endothelial cells) These three things lead to contraction of vascular smooth muscle in the ductus arteriosis, leading it to close off.

Within the umbilical cord, there is only one umbilical vein - but in the developing embryo there are two (L and R) umbilical veins that drain into the sinus venosus. Describe the process at the primordial liver by which these two early veins lead to one final umbilical vein.

1. The L and R umbilical veins pass laterally to the primordial liver 2. They sprout into the hepatic sinusoids 3. The proximal part of both umbilical veins is obliterated 4. The rest of the right umbilical vein is obliterated 5. The distal portion of the left umbilical vein is now the only vein carrying oxygenated blood from the liver and it connects directly to the hepatocardiac channel.

Which two structures contribute to the pulmonary arteries?

1. The aortic sac 2. The left and right 6th aortic arches

Describe the two types of abnormal superior vena cava development.

1. The right anterior cardinal vein does not give rise to the SVC, so a left sided SVC develops and blood enters the R atrium via the coronary sinus 2, The formation of both a left (enters R atrium via coronary sinus) and right SVC.

What are the 3 main systems of veinous development?

1. Vitelline system 2. Umbilical system 3. Cardinal system

In patent ductus arteriosis, what fraction of blood leaves the aorta into pulmonary circulation rather than into systemic circulation?

1/3 to 1/2. This means that blood is circulated through the lungs 2-3 times for every one time that it enters systemic circulation.

How many hours after birth does it take for the ductus arteriosis to close?

10-15 hours

How many thoracic intersegmental arteries are there?

12

How many umbilical arteries are in the umbilical cord?

2 - these carry deoxygenated blood away from heart towards the placenta

The common carotid artery is derived which aortic arch?

3rd

How many lumbar intersegmental arteries are there?

5

How many cervical intersegmental arteries are there?

7

What causes a right aortic arch?

A right aortic arch results when the left 4th aortic arch and the left dorsal aorta are obliterated. The right side then forms the arch. Dyspnea and dysphagia may result as vessels pass to the left side.

In patent ductus arteriosis, why does blood travel through the aorta, then ductus arteriosis, then pulmonary arteries to the lung? Why doesn't blood travel the other way?

After birth, systemic circulation pressure is much higher than pulmonary pressure. A patent ductus arteriosis makes an easy route for blood to exit systemic circulation into the low pressure environment of the pulmonary vessels.

What is an intersegmental artery?

An artery that arises within paraxial mesoderm travels between somites and connects to the dorsal aorta

What does the umbilical venous system do?

Carries O2 rich blood from placenta to sinus venosus

What does the vitelline venous system drain?

Carries blood from yolk sac to sinus venosus

Define coarctation of the aorta.

Coarctation of the aorta is caused by an abnormal thickening of the aortic wall which leads to its constriction.

True or false: intersegmental arteries remain separate from one another

False! The intersegmental arteries connect via a long anastamoses that parallels the dorsal aorta

What is the fate of the anastamoses between the 12 thoracic intersegmental arteries?

Gives rise to the internal thoracic arteries

What medication is used to close a patent ductus arteriosis?

Indomethacin - a prostaglandin inhibitor. Connection to MCB: indomethacin is a cyclooxygenase inhibitor. This prevents the conversion of arachadonic acid into prostaglandins. If this doesn't work, then surgery should do the trick.

What is the embryologic remnant of the left umbilical vein (in the liver)?

The ligamentum teres hepatis. Also known as the round ligament of the liver.

What is the fate of the left dorsal aorta distal to the left 7th cervical intersegmental artery?

It becomes the descending thoracic and abdominal aorta

What is the fate of the distal portion of the left 6th aortic arch?

It becomes the ductus arteriosis (and later the ligamentum arteriosum)

What is the fate of the 1st aortic arch?

It breaks up but may contribute to the maxillary arteries

What is the fate of the 2nd aortic arch?

It breaks up but may contribute to the stapedial and hyoidal arteries

Once the connections between the 5th lumbar intersegmental arteries are made with the umbilical arteries, what is the fate of the proximal portion of the umbilical arteries (the region between the connection and the the abdominal aorta).

It disappears

What is the fate of the carotid duct?

It disappears

What is the fate of the right dorsal aorta between the right 7th cervical intersegmental artery and its junction with the left dorsal aorta (near T4)

It disappears

What is the fate of the distal portion of the right 6th aortic arch?

It disappears!

How does the body compensate for preductal coarctation?

It does not compensate very well at all because collateral circulation does not form well at all. This results in very little oxygenated blood being delivered to the body and legs. This can be fatal if not surgically corrected. One way that the body may try to compensate is to keep the ductus arteriosis patent so that O2-poor blood can enter systemic circulation. Deoxygenated blood is better than no blood.

Which maternal infection may cause patent ductus arteriosis?

Maternal rubella

What causes a double aortic arch?

Persistance of the right dorsal aorta distal to the right 7th intersegmental artery. Also leads to dyspnea and dysphagia, but often more symptomatic than an aberrant right subclavian.

What is the embryologic remnant of the ductus venosus?

The ligamentum venosum

What structures do the 5th aortic arches contribute to?

Nothing! Ha! The fifth aortic arches never actually form.

From what embryological tissue (be specific) do intersegmental arteries arise?

Paraxial mesoderm. Most intraembryonic vasculogenesis occurs in the intraembryonic splanchnopleuric mesoderm, but some angioblasts form in the paraxial mesoderm.

The internal carotid artery is derived from which embryonic vessels (there are two)?

Part of the 3rd aortic arch and the dorsal aorta

What is patent ductus arteriosis?

Patent ductus arteriosis is a disorder that occurs when the ductus arteriosis does not close. This leads to an increased amount oxygenated blood being sent back to the lungs.

Early in embryologic development, the dorsal aorta arises as a pair and later fuses to form one tube. At what vertebral level does this fusion begin and proceed caudally?

T4

How many pairs of aortic arches are there?

Technically 6, although the 5th pair never really forms.

What is the fate of the 3rd aortic arch?

The 3rd aortic arches are considered the main "feeders" to the head. They give rise to the carotid arteries.

What does the aortic sac give rise to?

The aortic sac gives rise to the aortic arches

What is the aortic sac?

The aortic sac is a distal outpocketing on the truncus arteriosis

What is the carotid duct?

The carotid duct is just a fancy name for the area of dorsal aorta that connects the 3rd and 4th aortic arches.

What is the fate of the left sinus horn?

The left sinus horn (and it's corresponding inlets - cardinal, umbilical, and vitelline veins) reduce in size and gradually their functions are entirely overtaken by the veins of the right side. The only thing that it gives rise to is the coronary sinus.

Which umbilical vein (L or R) gives rise to the final umbilical vein?

The left umbilical vein.

What portion of the heart does the 4th aortic arch connect to?

The left ventricle

What causes an interrupted aortic arch?

The cause is very similar to the aberrant subclavian artery with one additional thing missing. 1. The right 4th aortic arch is obliterated 2. The proximal portion of the dorsal aorta (proximal to the 7th cervical intersegmental artery) is obliterated 3. AND the left 4th aortic arch is obliterated The result: 1. The right subclavian forms from the distal portion of the dorsal aorta (distal to the 7th cervical intersegmental artery), and the right 7th cervical intersegmental artery - BUT it comes off of the pulmonary trunk. 2. The aortic arch only gives rise to the carotid arteries 3. The ductus arteriosis is patent and massive 4. The subclavian arteries come off of the pulmonary trunk (low O2)

What does the proximal part of the left anterior cardinal give rise to?

The coronary sinus. (this forms from the left sinous horn and the left anterior cardinal vein)

How does the body compensate for postductal coarctation?

The development of collateral circulation. The descending thoracic/abdominal aorta will still receive adequate blood through anatomoses with the intercostal, and internal thoracic arteries, among others.

What is the name of the vein that directly connects the umbilical vein to the hepatocardiac channel

The ductus venosus

How/where does the external carotid artery arise?

The external carotid artery is a sprout from the 3rd aortic arch

What is the fate of the 7 cervical intersegmental arteries?

The first 6 (out of 7) cervical intersegmental arteries disintegrate. However, the anastomoses between them remains.

The left and right vitelline veins become surrounded by the primordial liver to form a vascular plexus. What is this plexus called?

The hepatic sinusoids

Initially, the left and right umbilical veins pass on either side of the primordial liver. What veins will the umbilical veins eventually grow into?

The hepatic sinusoids - derived from vitelline veins

What does the right vitelline vein give rise to?

The hepatocardiac channel. Initially, there is a left and right hepatocardiac channel, but left side disappears (just the proximal part disappears, the distal part will contribute to other veins) and the right vitelline vein becomes the final hepatocardiac channel.

The 5th lumbar intersegmental arteries and connection made with the umbilical arteries give rise to which arteries?

The iliac arteries and superior vesicular arteries

What is the fate of the left 7th cervical intersegmental artery?

The left 7th intersegmental artery becomes the left subclavian artery

An anastomoses forms between the left and right anterior cardinal veins. What vein does this anastamoses give rise to?

The left brachiocephalic vein

Anatomically speaking, where exactly does the left recurrent laryngeal nerve originate and why?

The left recurrent laryngeal nerve is a branch of the left vagus nerve (cranial nerve X). It can be found in an adult just lateral to the ligamentum arteriosum where it then it ascends to the larynx. As an embryo grows, the nerve is hooked by the 6th aortic arch/ductus arteriosis and must lengthen as the heart moves into the thorax with cranial/caudal folding.

What is the embryologic remnant of the ductus arteriosis?

The ligamentum arteriosum

Anatomically speaking, where exactly does the right recurrent laryngeal nerve originate and why?

The right recurrent laryngeal nerve is a branch of the right vagus nerve (cranial nerve X). It can be found in an adult looping beneath the proximal right subclavian artery where it then it ascends to the larynx. It is found in this region because the distal part of the right 6th aortic arch disintegrates, allowing the right nerve to originate higher than the left recurrent laryngeal nerve.

From what embryological vein is the hepatocardiac channel derived?

The right vitelline vein

What structure divides the truncus arteriosis into the ascending aorta and pulmonary trunk?

The spiraling conotruncal septum (see Embryo Heart II for more info)

The posterior cardinal veins will eventually connect to two parallel vein systems. What are they?

The subcardinal and supracardinal veins

What 2 vessels are derived from the right anterior cardinal vein?

The superior vena cava and right brachiocephalic vein

What major vessel does the hepatocardiac channel give rise to?

The terminal portion of the inferior vena cava

The 5th lumbar intersegmental arteries forms a connection with which embryologic arteries?

The umbilical arteries

What region of an embryo do the vitelline arteries supply?

The yolk sac (and eventually the GI tract)

True or false: the aortic arches connect the aortic sac to the dorsal aorta.

True

What is the fate of the 5 lumbar intersegmental arteries?

These contribute to the epigastic vessels. The 5th intersegmental artery will also form an attachment with the umbilical arteries to give rise to the superior vesicular arteries.

What is the fate of the 12 thoracic intersegmental arteries?

These give rise to the intercostal arteries (pretend that 12 are pictured here....)

What is aberrant origin of the right subclavian artery?

This is when the right subclavian artery develops just distal to the left subclavian artery, rather than coming off of the brachiocephalic trunk. This aberrant artery must travel posterior to the esophagus to reach the right side of the body.

What causes aberrant origin of the right subclavian artery?

This occurs when the right 4th aortic arch and proximal portion of the dorsal aorta (proximal to the 7th cervical intersegmental artery) are accidentally obliterated (these are two of the 3 components of the R subclavian). Instead, the right subclavian forms from the distal portion of the dorsal aorta (distal to the 7th cervical intersegmental artery), and the right 7th cervical intersegmental artery. The result is that the right subclavian artery originates distal to the left subclavian artery and passes posterior to the esophagus.

If the right anterior cardinal vein fails to give rise to the superior vena cava, how will blood enter the heart?

Through an abnormal left superior vena cava that empties into the coronary sinus

What is the purpose of the left and right anterior and posterior cardinal veins in the fetus?

To drain the body of the fetus