Hy Embryology 05 Part 3

Front 1

Describe the umbilical cord

Back 1

1. A patent opening called the primitive umbilical ring exists on the ventral surface of the developing embryo through which three structures pass: the yolk sac (vitelline duct), connecting stalk, and allantois
2. As the amnion expands, it pushes the vitelline duct, connecting stalkm and allantois together to form the primitive umbilical cord
3. The definitive umbilical cord at term is pearl-white, 1-2 cm in diameter, 50-60cm long, eccentrically positions, and contains the R and L umbilical arteries, left umbilical vein, and mucus connective tissue (Wharton's jelly)
4. The right and left umbilical arteries carry deoxygenated blood from the fetus to the placenta. The left umbilical vein carries oxygenated blood from the placenta to the fetus

Front 2

What carries deoxygenated blood from the fetus to the placenta?

Back 2

R and L umbilical arteries

Front 3

What carries oxygenated blood from the placenta to the fetus?

Back 3

L umbilical vein

Front 4

What does the definitive umbilical cord contain?

Back 4

-R and L umbilical arteries
-L umbilical vein
-Mucus connective tissue (Wharton's jelly)

Front 5

Describe the allantois

Back 5

1. Passes through the primitive umbilical ring that exists on the ventral surface of the developing embryo
2. Nonfunctional in humans and degenerates to form the median umbilical ligament in adults

Front 6

What forms the medial umbilical ligament in adults?

Back 6

Allantois

Front 7

Describe the clinical significance of the presence of only one umbilical artery within the umbilical cord

Back 7

An abnormal finding that suggests CV abnormalities

Front 8

What may physical inspection of the umbilicus in a newborn infant reveal?

Back 8

1. A light-gray, shiny sac indicting an omphalocele
2. A fecal (meconium) discharge indicated a vitalline fistula
3. A urine discharge indicating a urachal fistula

Front 9

What is the significance of a light-gray, shiny sac on the umbilicus of a newborn infant?

Back 9

Indicated an omphalocele

Front 10

What indicates an omphalocele on a newborn infant?

Back 10

The presence of a light-gray, shiny sac on the umbilicus

Front 11

What is the significance of a fecal (meconium) discharge on the umbilicus of a newborn infant?

Back 11

Indicated a vitalline fistula

Front 12

What indicates a vitalline fistola on a newborn infant?

Back 12

Fecal (meconium) discharge on the umbilicus

Front 13

What is the significance of a urine discharge on the umbilicus of a newborn infant?

Back 13

Indicated a urachal fistula

Front 14

What is indicates a urachal fistula on a newborn infant?

Back 14

Urine discharge on the umbilicus

Front 15

Describe vasculogenesis in the extraembryonic mesoderm

Back 15

1. Occurs first within the extraembryonic visceral mesoderm around the yolk sac on day 17
2. By day 21, vasculogenesis extends into the extraembryonic somatic mesoderm located around the connecting stalk to form the umbilical vessles and in secondary villi to form tertiary chorionic villi
3. Vasculogenesis occurs by the same mechanism as intraembryonic mesoderm
4. Blood vessles formed in the extraembryonic mesoderm become continuous with blood vessels within the embryo, thereby establishing a blood vascular system between the embryo and placenta

Front 16

Describe the mechanism of vasculogenesis

Back 16

1. Vasculogenesis occurs by a process in which the extraembryonic and intraembryonic mesoderms differentiate into angioblasts, which form clusters known as angionic cell clusters
2. The angioblasts located in the periphery of angiogenic cell clusters give rise to endotrhelial cells, which fuse with each other to form small blood vessels

Front 17

Describe vasculogenesis in the intraembryonic mesoderm

Back 17

1. Blood vessels form within the embryo by the same mechanism as in extraembryonic mesoderm
2. Blood vessels formed in the extraembryonic mesoderm become continuous with blood vessels within the embryo, thereby establishing a blood vascular system between the embryo and placenta

Front 18

Describe hematopoiesis

Back 18

1. Blood cell formation first occurs within the extraembryonic visceral mesoderm around the yolk sac during week 3 of development
2. During this process, angioblasts within the center of the angiogenic cell clusters give rise to primitive blood cells
3. Beginning at week 5, hematopoisis is taken over by a sequence of embryonic organs: liver, spleen, thymus, and bone marrow

Front 19

Where does blood cell formation first occur?

Back 19

Extraembryonic visceral mesoderm around the yolk sac during week 3 of development

Front 20

What is the first type of hemoglobic produces?

Back 20

During the period of yolk sac hematopoiesis, the earliest embryonic form of hemoglobin (hemoglobin ζ2ε2) is synthesized

Front 21

What type of hemoglobin is produced during liver hematopoiesis?

Back 21

-Fetal form of hemoglobin(HbF) called hemoglobin a2γ2
-Hemoglobin a2γ2 is the predominant form of hemoglobin during pregnancy because it has a high affinity for oxygen than the adult form of hemoglobin (HbA, hemoglobin a2ß2) and therefore "pulls" oxygen fromt he maternal blood into fetal blood

Front 22

What is the predominant form of hemoglobin during pregnancy?

Back 22

Hemoglobin a2γ2

Front 23

What type of hemoglobin is produced during the period of bone marrow hematopoiesis?

Back 23

The adult form of hemoglobin, called hemoglobin a2ß2, is synthesized and gradually replaces hemoglobin a2γ2

Front 24

When does bone marrow hematopoeisis occur?

Back 24

About week 30

Front 25

Describe Thalassemia syndromes

Back 25

A heterogenous group of genetic defects characterized by the lack or decreased synthesis of either the a-globulin chain (a-thalassemia) or ß-globulin (ß-thalassemia) of hemoglobin a2ß2

Front 26

Describe hydrops fetalis

Back 26

1. The most severe form of a-thalassemia
2. Causes severe pallor, generalized edema, and massive hepatosplenomegaly
3. Invariably leads to intrauterine fetal death

Front 27

What is the most severe form of a-thalassemia?

Back 27

Hydrops fetalis

Front 28

Describe ß-thalassemia major (Cooley anemia)

Back 28

1. The most severe form of ß-thalassemia
2. Causes severe, transfusion-dependent anemia
3. Most common in Mediterranean counties and parts of Africa and SE Asia

Front 29

What is the most severe form of ß-thalassemia?

Back 29

ß-thalassemia major (Cooley anemia)

Front 30

Describe Hydroxyurea

Back 30

1. A cytotoxic drug
2. has been shown to promote HbF production by the reactivation of ?-chain synthesis
3. Useful in treatment of sickle cell disease, in which the presence of HbF counteracts the low oxygen affinity of sickle Hb (HbS) and inhibits the sickling process

Front 31

Describe the order of progression of sites of fetal hematopoiesis

Back 31

1. Yolk Sac (Hb ?2e2, Weeks 3-10)
2. Liver (Hb a2?2, Week 6-Birth)
3. Thymus and Spleen (Week 12-Birth, Thymus>Spleen)
4. Bone Marrow (Hb a2ß2, Starts Week 12, but really piks up at Week 20)