Lec.12 DEV'T OF CARDIOVASCULAR SYSTEM

Question 1

During the early phases of development, the embryo is nourished through diffusion from the fluid secreted by the ____ into the uterine cavity.

However, as the size and complexity of the embryo increases, it soon needs a circulatory system to distribute nutrients and oxygen and to remove carbon dioxide and metabolites.

Answer 1

uterine glands

Question 2

The circulatory system, including the heart, arteries, veins and blood, begins to develop as early as the ____ week of gestation to meet the embryo’s needs.

The circulatory system is the first functional organ system.

Answer 2

third week

Question 3

*Blood Cells
The formation of blood cells, ____, occurs in three overlapping periods.

The first, or mesoblastic period of blood- formation, occurs in the ____.

Answer 3

hematopoiesis’

yolk sac

Question 4

*Mesoblastic Period
The first blood cells appear in the _____ of the yolk-sac wall very early in development.

At first, blood islands are formed, these are spaces in the mesoderm occupied with clusters of ____.

Outer cells differentiate into ____, forming endothelial cells, and the inner cells into ____.

Answer 4

visceral mesoderm

haemangioblasts

angioblasts

primitive blood cells

Question 5

*Blood Cells
In the second period of hematopoiesis, ____, the liver and the spleen become the major blood-forming organs.

In the third period, ____, the bone marrow takes over as the major blood-forming organ.

Answer 5

hepato-lineal period

medullary period

Question 6

*Mesoblastic Period
The blood islands coalesce and the endothelial cells form tubes establishing the first vessels.

This process of spontaneous blood- vessel formation is referred to as ____.

Vessels forms new vessels by sprouting – a process referred to as ____.

Answer 6

vasculogenesis

angiogenesis

Question 7

*Mesoblastic Period
The first blood cells to be formed are ____.

Primitive erythropoiesis evolves within a few days into mature erythropoiesis resulting in erythrocytes without nuclei.

Answer 7

primitive nucleated erythrocytes

Question 8

*Hepato-lineal Period
This period starts at a crown-rump length of 8 mm in what animal?.

In the liver, erythropoietic stem cells as well as megakaryocytes can be seen.

By 12 mm, _____ are also formed.

The liver becomes the most prominent hematopoietic organ in cattle embryos up to the ____ month of pregnancy.

Answer 8

cattle

neutrophils

5th month

Question 9

*Hepato-lineal Period
During the ____ month, the liver’s blood-forming activity declines and at birth it has ceased.

The ____ is active in hematopoiesis from the third to the seventh month of pregnancy in cattle.

Answer 9

sixth month

spleen

Question 10

*Medullary Period
The bone marrow begins its hematopoietic activity at a crown-rump length of about 18 cm during the month ____ of pregnancy in cattle.

This will be the main source of blood cells in adult animals.

Answer 10

4th month

Question 11

*Heart
The heart develops from the ____ shaped cardiac tube after embryonic folding has repositioned it within the pericardial cavity ventral to the embryonic disc.

Embryonic heart beats begin at:
Day __ of pregnancy in the pig
Day __ in the dog and cattle
Day __ in the horse

Answer 11

horseshoe-shaped

Day 22 of pregnancy in the pig
Day 23 in the dog and cattle
Day 24 in the horse

Question 12

*Loop Formation
To develop into the four-chambered mammalian heart, the cardiac tube undergoes first a loop formation and then an internal division.

The cardiac tube will become U-shaped with the loop of pointing ____.

Answer 12

ventrally

Question 13

*Loop Formation
Throughout this process, the developing heart is beating at a rhythm set by pacemakers in the ____.

At first, this and the atrium are not enclosed within the pericardial cavity, but they gradually become enveloped by the ____.

Answer 13

sinus venosus

pericardium

Question 14

*Loop Formation
During the enclosure, the atrium becomes positioned dorsal to the ventricle, and the loop takes on the shape of an S.

The curved portion of the ventricle develops into the ____ whereas the curved portion of the bulbus cordis develops into the ____.

Answer 14

future left ventricle

future right ventricle

Question 15

Steps for formation of heart chamber:

Incorporation of the____ into the atrium

Division of the ____

Division of the ____

Division of the ____ and the ____

Division of the ____ and ____

Answer 15

sinus venosus

atrioventricular channel

atrium

ventricle and the bulbus cordis

conus cordis and truncus arteriosus

Question 16

*Heart Chambers
At the atrioventricular channel, the inner cardiac wall develops anterior and posterior thickenings, the ____.

The cushions will grow until they meet and fuse in the midline of the canal, forming the ____.

This divides the channel into right and left _____.

Answer 16

endocardial cushions

septum intermedium

atrioventricular channels

Question 17

*Heart Chambers
As the septum intermedium develops, a crescent-shaped fold, the ____ begins to form.

This separates the atrium into right and left components connected through a minor opening, the ostium primum

Answer 17

septum primum

Question 18

*Heart Chambers
As the endocardial cushions grow towards the midline, the septum primum also grows, gradually closing the ____.

Before this closure, however, programmed cell death in the septum primum results in formation of the ____.

This allows continued blood flow from the developing right atrium to the left.

A second crescent-shaped fold, the ____, develops to the left of the ____.

Answer 18

ostium primum

ostium secundum

septum secundum

septum primum

Question 19

*Heart Chambers
The transition between the ventricle and the bulbus cordis is marked externally by a ____ and internally by a muscular fold that develops into the muscular part of the interventricular septum, which grows towards the septum intermedium.

Answer 19

groove

Question 20

*Heart Chambers
The primitive ventricles expels its blood into the conus cordis which forwards it to the ventral aortae through the ____.

To complete the division of the cardiac tube into right and left halves, the bulbus cordis and the truncus arteriosus also need to be divided into two channels.

Answer 20

truncus arteriosus

Question 21

*Heart Chambers
Formation of two opposing cushions in the wall of these compartments will separate the flow of blood.

The cushions in the conus cordis fuse with those of the truncus arteriosus to form ____.

As they grow, the cushions fuse in the midline to form the ____ dividing the blood flow into two separate channels.

Answer 21

conu-truncal cushions

aorticopulmonary septum

Question 22

*Arterial System
When the pharyngeal or branchial arches form, each arch receives its own cranial nerve and its own artery.

This results in the formation of six ____ between the dorsal and ventral aortae on each side.

Answer 22

arterial arches (aortic arches)

Question 23

*Arterial System
All six aortic arches remain functional in fishes, while the ____ arches are largely rudimentary in mammals.

The ____ arch either remains rudimentary (as in the horse and pig) or never develops at all (as in cattle).

Only the ____ aortic arches form components of the developing circulatory system.

Answer 23

first and second arches

fifth arch

third, fourth and sixth aortic arches

Question 24

*Arterial System
The ventral aortae develop into the ____ and, in the cranial region, into the external carotid arteries.

The cranial portions of the dorsal aortae develop into the ____.

The first aortic arch largely degenerates, but a small portion remains and forms the ____.

Answer 24

common carotid arteries

internal carotid arteries

maxillary artery

Question 25

*Arterial System
The second aortic arch also degenerates but small portions of it do develop into the ____ and ____.

The third aortic arch forms the connection from the common carotid artery to the ____.

The fourth aortic arch is retained as the aortic arch on the left, while the right arch forms the ____.

The sixth aortic arch regresses on the right but, on the left, develops into the ____.

Answer 25

hyoid and stapedial arteries

internal carotid artery

right subclavian artery

pulmonary trunk

Question 26

*Arterial System
During pre-natal development, the pulmonary trunk remains connected to the aortic arch through the _____.

At birth, the lumen of the this is obliterated, but the non- patent structure persists as the ____.

Answer 26

ductus arteriosus

ligamentum arteriosum

Question 27

*Venous System
The venous system, for returning blood to the heart, forms in parallel with the arterial system.

Three major veins can be distinguished: the ____ veins carrying blood from the yolk sac the ____ veins carrying blood from the placenta the ____ veins carrying blood from the body of the developing embryo

Answer 27

omphalomesenteric or vitelline veins

umbilical veins

cardinal veins

Question 28

*Fetal Circulation
During fetal development, the ____ is where oxygen and nutrients are taken in and carbon dioxide and metabolites are excreted.

The oxygen-rich blood reaches the embryo and fetus through the ____ veins.

Answer 28

placenta

umbilical veins

Question 29

*Fetal Circulation
The left umbilical vein runs towards the liver where most of the blood flows through the ductus venosus into the ____.

Oxygenated blood in the ductus venosus receives deoxygenated blood from the liver and digestive tract through the ____ vein.

Answer 29

caudal vena cava

portal vein

Question 30

*Fetal Circulation
In the caudal vena cava, the relatively oxygenated blood mixes with the deoxygenated blood before it enters the ____.

Pressure in the right atrium causes most of the relatively oxygenated blood to pass through the _____ to the left atrium.

Answer 30

right atrium

foramen ovale

Question 31

*Fetal Circulation
A small fraction of the relatively oxygenated blood remains in the right atrium and is mixed with the deoxygenated blood from the ____.

The unoxygenated blood will continue into the right ventricle and to be pumped into the ____.

Answer 31

cranial vena cava

pulmonary trunk

Question 32

*Fetal Circulation
Relatively oxygenated blood from the left atrium enters the left ventricle and then the ____.

Blood for the heart musculature and brain comes from this relatively oxygenated source.

Answer 32

aorta

Question 33

*Fetal Circulation
The mixed blood in the pulmonary trunk is shunted through the ductus arteriosus into the aorta.

The blood mixes with the relatively oxygenated blood from the left ventricle. This mixture supplies the caudal portion of the fetus. The ____ will transport this blood mixture back to the placenta for oxygenation.

Answer 33

umbilical arteries

Question 34

*Circulation At Birth
Birth terminates the fetal-maternal association through the placenta.

As a result, carbon dioxide tension in the newborn is ____.

This stimulates receptors in the respiratory center in the ____ leading to respiration.

Answer 34

increased

medulla oblongata

Question 35

*Circulation At Birth
The first inspiration expands the lung volume considerably and thus stimulates ____.

The resulting increased blood flow through the pulmonary veins increases the pressure in the left atrium and closes the ____.

Answer 35

pulmonary blood circulation

foramen ovale

Question 36

*Circulation At Birth
Foramen ovale allows blood to cross the ____ and bypass pulmonary circulation during fetal development.

Thus, the blood that has been oxygenated in the lungs as a result of the first inspiration flows into the left ventricle (instead of the right side of the heart) and is expelled into the aorta.

Answer 36

atria

Question 37

*Circulation At Birth
The ____ closes, preventing deoxygenated blood from the pulmonary trunk from entering the aorta.

The blood flow from the placenta to the fetus is stopped by the ____ of the ductus venosus and left umbilical vein.

The blood flow to the placenta is stopped by contraction of the ____.

Answer 37

ductus arteriosus

contraction

umbilical arteries