Development of the vasculature: Venous system. Lymphatic system.

Question 1

Vitelline veins

Answer 1

return poorly oxygenated blood from the umbilical vesicle (yolk sac)

Question 2

Umbilical veins

Answer 2

carry well-oxygenated blood from the chorionic sac.

Question 3

Common cardinal veins

Answer 3

return poorly oxygenated blood from the body of the embryo

Question 4

Vitelline veins track

Answer 4

follow the omphaloenteric duct into the embryo;

• form a plexus around the
  duodenum;
• pass through the septum transversum and fall into sinus venosus

Question 5

the right vitelline vein

Answer 5

enlarges and forms the right hepatocardiac channel (hepatocardiac portion of the IVC);

• the proximal part of the left vitelline vein regresses;
• the right vitelline vein forms most of the hepatic portal system and the superior mesenteric vein;
• the distal portion of the left vitelline vein also disappears.

Question 6

Umbilical veins track

Answer 6

run on each side of the liver;

• carry well-oxygenated blood from the placenta to the sinus venosus;
• as the liver develops, the umbilical veins lose their connection with the heart and empty into the liver;
• the right umbilical vein disappears during the 7th week

Question 7

Umbilical veins

Answer 7

the cranial part of the left umbilical vein between the liver and the sinus venosus degenerates;

• the persistent caudal part of the left umbilical vein becomes the umbilical vein;
• a large venous shunt - the ductus venosus (DV) - develops within the liver;
• it connects the umbilical vein with the IVC.

Question 8

Cardinal veins track

Answer 8

or cardinal veins, the earliest veins to develop;

• drain cranial and caudal parts of the embryo, respectively;
• join the common cardinal veins, which enter the sinus venosus.

Question 9

Cardinal veins

Answer 9

the anterior cardinal veins become connected by an anastomosis (week 8

shunts blood from the left to the right anterior cardinal vein;

• shunt becomes the left brachiocephalic vein;
• the caudal part of the left anterior cardinal vein degenerates;
• the superior vena cava (SVC) forms from the right anterior cardinal vein and the right common cardinal vein.

Question 10

The posterior cardinal veins:

Answer 10

adult derivatives - the root of the azygos vein and the common iliac veins.

Question 11

The subcardinal veins:

Answer 11

form the stem of the left renal vein, the suprarenal veins, the gonadal veins, and a segment of the IVC

Question 12

The supracardinal veins:

Answer 12

form the adult azygos and hemiazygos veins;

caudal to the kidneys, the left vein degenerates, but the right vein becomes the inferior part of the IVC

Question 13

Inferior vena cava

Answer 13

The IVC is composed of 4 main segments:

1. A hepatic segment derived from the hepatic vein (proximal part of right vitelline vein) and hepatic sinusoids.
2. A prerenal segment derived from the right subcardinal vein.
3. A renal segment derived from the subcardinal– supracardinal anastomosis.
4. A postrenal segment derived from the right supracardinal vein.

Question 14

Anomalies of venae cavae

Answer 14

Persistent left SVC: develops because of persistence of the left anterior cardinal vein;

the abnormal left SVC opens into the right atrium through the coronary sinus.

Left SVC:
forms from the left anterior cardinal vein and common cardinal vein;
the right anterior cardinal vein and common cardinal vein degenerate

Question 15

Anomalies of venae cavae

Answer 15

Double IVC: inferior to the renal veins is represented by 2 vessels (usually the left one is much smaller);
the inferior part of the left supracardinal vein persists as a second IVC.

Interrupted abdominal course of the IVC: the most common anomaly of the IVC;
blood drains from the lower limbs, abdomen, and pelvis to the azygos system of veins;
the hepatic veins open separately into the right atrium

Question 16

Development of the lymphatic system

Answer 16

begins to develop at the end of the 6th week;

• a subset of venous endothelial cells migrate out from the cardinal veins to form the initial lymphatic vessels;
• endothelial cell precursors express the transcription factor, Prospero-related homeobox-1 (Prox1);
• later they start to express Nrp2 and Podoplanin;
• lymphatic vessels may also arise elsewhere from lymphangioblastic EPCs induced by the Vegfr and Prox1

Question 17

Development of the lymphatic system

Answer 17

6 primary lymph sacs present by 9th week:
2 jugular, 2 iliac, 1 retroperitoneal, 1 cisterna chyli.

• lymphatic vessels connect to the lymph sacs;
• vessels pass along main veins: to the head, neck, and upper limbs from the jugular lymph sacs;
• to the lower trunk and lower limbs from the iliac lymph sacs;
• to the gut from the retroperitoneal lymph sac and the cisterna chyli.

Question 18

the thoracic duct

Answer 18

develops from the caudal part of the right thoracic duct, the anastomosis between the left and right thoracic ducts, and the cranial part of the left thoracic duct;

Question 19

the right lymphatic duct

Answer 19

is derived from the cranial part of the right thoracic duct

Question 20

The spleen develops from

Answer 20

an aggregation of mesenchymal cells in the dorsal mesogastrium.

Question 21

The palatine tonsils develop from

Answer 21

the second pair of pharyngeal pouches and nearby mesenchyme.

Question 22

The tubal tonsils develop from

Answer 22

aggregations of lymph nodules around the pharyngeal openings of the pharyngotympanic tubes.

Question 23

The pharyngeal tonsils develop from

Answer 23

an aggregation of lymph nodules in the wall of the nasopharynx.

Question 24

The lingual tonsil develops from

Answer 24

an aggregation of lymph nodules in the root of the tongue.

Question 25

Lymph nodules also develop in

Answer 25

in the mucosa of the respiratory and alimentary systems

Question 26

Congenital lymphedema

Answer 26

diffuse swelling of a part of the body; may result from dilation of primordial lymphatic channels, or from congenital hypoplasia of lymphatic vessels; more rarely, involves widespread portions of the body

Question 27

``` Milroy disease (congenital familial lymphedema ```

Answer 27

a primary lymphedema syndrome; - linked to mutations in the Vegfr3 gene; - other, more rare forms of lymphedema have been linked to the FOXC2gene; - mutations in SOX18 (an SRY-related transcription factor) have also been associated with both dominant and recessive inherited forms of lymphedema; - typically bilateral, on the legs and feet; - in males may be associated with hydrocele; - other symptoms include prominent veins, upslanting toenails, papillomatosis, cellulitis, and urethral abnormalities in males; - infections significantly more likely in males than in females.

Question 28

Cystic hygroma (cystic lymphangioma):

Answer 28

large swellings usually appear in the inferolateral part of the neck; - consist of large single or multilocular, fluid-filled cavities; - may be present at birth, but they often enlarge and become evident during infancy; - most hygromas appear to be derived from abnormal transformation of the jugular lymph sacs. - those diagnosed in utero in the 1st trimester are associated with chromosomal abnormalities in about 50% of cases; - fetal outcome in these cases is poor.

Question 29

Fetal circulation

Answer 29

the lungs do not provide gas exchange; - the pulmonary vessels are constricted; - structures most important in the transitional circulation are the DV, oval foramen, and DA; - highly oxygenated blood returns from the placenta in the umbilical vein; - ≈ half of the blood passes directly into the DV, bypassing the liver; - the other half flows into the sinusoids; - blood flow through the DV is regulated by a sphincter; - it directs more blood to the portal vein and hepatic sinusoids and less to the DV; - most blood from the IVC is directed by the crista dividens through the oval foramen into the left atrium; - from the left atrium to the left ventricle and the ascending aorta

Question 30

Transitional neonatal circulation

Answer 30

DA constricts at birth; - controlled by oxygen directly or via its effects on PGE2 secretion; - mediated by bradykinin (released from the lungs during their initial inflation); - there is often a small shunt of blood via the DA from the aorta to the pulmonary trunk for 24 to 48 hours in a normal full-term infant; - in premature infants may remain open much longer; - inhibitors of PG synthesis (e.g., indomethacin) can cause constriction of a patent DA (PDA) in premature infants

Question 31

round ligament of liver (ligamentum teres

Answer 31

formed by intra-abdominal part of the umbilical vein; passes from the umbilicus to the porta hepatis; it is attached to the left branch of the portal vein

Question 32

Ligamentum venosum

Answer 32

persists as a remnant of the ductus venosus (DV); | passes through the liver from the left branch of the portal vein and attaches to the IVC.

Question 33

Medial umbilical ligaments:

Answer 33

the obliterated portions of the umbilical arteries

Question 34

Fossa ovalis:

Answer 34

formed after the closure of the oval foramen (usually closes functionally at birth); - anatomic closure occurs by the 3rd month; - the septum primum forms its floor; - the septum secundum forms the limbus fossae ovalis, which marks the former boundary of the oval foramen