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Cardiovascular system > Lecture 6- Embryology part I > Flashcards

Lecture 6- Embryology part I Flashcards

1
Q

primitive atrium

A

forms the atria

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1
Q

Achievements of early embryonic development

A
  1. First two weeks created tissues of the future embryo and future placenta
  2. The third week created the three germ layers
    1. Ectoderm, mesoderm and endoderm – primordia of all tissue
  3. Fourth week created recognisable body form and the mesoderm begins to organise
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2
Q

when does the CVS begin development

A

10th day after fertilisation- first functional organ to develop

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3
Q

when can the heart be heard

A
  • Can be heard beating on a sonography by week 6
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4
Q

outline the key 5 stages of embryonic development of the CVS

A

(1) Formation of the primitive heart tube
(2) Cardiac looping
(3) Development of the atria
(4) Formation of the Great vessels
(5) Septation

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5
Q

At the start of this development the CVS system exists as two regions

A

near the cranial (head end) end of the embryo- cardiogenic fields (derived from the mesoderm)

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6
Q

Cardiogenic fields consist

A

consists of blood islands which are primitive tissue and mark the beginning of blood, vessel and heart development

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7
Q

Blood islands develop further and

A

fuse to form two tubes which are called endocardial tubes – one on each side of the embryo

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8
Q

how are the two endocardail tubes brough together

A

Folding

In the 4th week the embryo begins to folding which puts the heart tissue in the correct position to form the primitive heart tube surrounded by the pericardial sac

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9
Q

how many ways does folding occur

A

2

  1. Cephalo-caudal folding
  2. Lateral folding
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10
Q

Cephalo-caudal folding

A

Brings cardiogenic filed from cranial entre towards the centre of the embryo to sit in the thoracic region where the heart will be

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11
Q

Lateral folding

A
  1. Fuses the two lateral sides of the embryo
  2. Brings two cardiogenic fields into the midline so they can fuse and form the primitive heart tube
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12
Q

what day is the ptimitive ehart tube form

A

day 25

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13
Q

characteristics of the primitive heart tube

A
  • 6 parts
  • no valves
  • no barriers between structure
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14
Q

name the 6 parts of the primitive heart tube

A
  • Aortic roots- forms arteries of the aortic arch
  • Truncus arteriosus- outflow of blood
    • Involved in the formation of the pulmonary trunk and aorta
  • Bulbus cordis- Involved in the formation of the pulmonary trunk and aorta
  • Primitive ventricle- forms ventricles
  • Primitive atrium- forms the atria
  • Sinus venosus- forms part of the right atrium and vena cave
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15
Q

aortic roots

A

formed at the top of the primitive heart tube

  • forms arteries of the aortic arch
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16
Q

Truncus arteriosus

A

outflow of blood

involved in the formation of the pulmonary trunk and aorta

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17
Q

bulbus cordis

A
  • Involved in the formation of the pulmonary trunk and aorta
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18
Q

primitive ventricles

A

forms ventricles

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19
Q

sinus venosis

A
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20
Q

acronymn to learn parts of the primitive heart tube

A

All The Best Vaccums Are Silver

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21
Q

what happens after the primitive heart tube is formed

A

(2) Cardiac looping

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22
Q

why must the heart loop

A

The newly formed heart tube is surrounded by the pericardial sac- as the heart tube grows and elongates, it gets too long for the sac. This means that to fit, it must loop

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23
Q

outline cardiac looping

A
  1. The primitive ventricle moves ventrally (coming forward) and to the right
  2. The primitive node moves dorsally (behind) and to the left
  3. This puts the inflow portion of the heart (veins and atria) behind the outflow portion (ventricles and arteries)  the same shape and orientation as mature hearts
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24
Q

the looping creates a space behind the arteries (aorta and pulmonary trunk) and in front of the superior vena cava called the

A

transverse pericardial sinus

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25
Q

at the end of the looping what has happened to inflow and outflow

A

in the correct orientation with respect to eachother

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26
Q

what occurs after (2) cardiac looping

A

(3) development of the atria)

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27
Q

after looping the atria are a

A

single space

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28
Q

(3) Development of the atria: develoment of the sinus venosus

A
  • Right and left sinus horns are equal size
  • Then venous return shifts to the right sinus horn
  • Left sinus horn recedes
  • Right sinus horn is absorbed by the enlarging right atrium becoming the vena cava
29
Q

(3) Development of the right atria

A
  • Develops mostly from the primitive atrium and sinus venosus
  • Receives venous drainage from the body (vena cava) and the heart (coronary sinus)
30
Q

(3) Development of the left atria

A
  • Develops mostly from the primitive atrium and sinus venosus
  • Receives venous drainage from the body (vena cava) and the heart (coronary sinus)
31
Q

pulmonary veins begins as a

A

a single vein entering the left atrium

  • This vein is formed from four branches which converge to form one vein draining into the developing left atrium
  • As the left atrium grows, its absorbs the single pulmonary veins, absorbing all the way to the four branches
  • This means that when the left atrium has finished growing it is receiving blood from four pulmonary veins as seen in the mature heart
32
Q

absorption of the pulmonary vein

A

xThe proximal parts of the pulmonary veins become absorbed into the wall of the left atrium. The contribution of the pulmonary veins is shown in blue, and the primitive left atrium is shown in pink

33
Q

Oblique sinus

A

Oblique pericardial sinus formed as left atrium expands absorbing the pulmonary veins

34
Q

conflicting ciruclatory requires: in mature circulation:

A
  • Deoxygenated blood collected from the body
  • Pumped to the lungs for reoxygenation and removal of CO2
  • Reoxygenated blood returned from the lungs to the heart
  • Pumped around the body
35
Q

conflicting ciruclatory requires: in the foetus

A
  • Lungs don’t work
  • Oxygenation and removal of CO2 occur at the placenta
  • So Shunts are required to maintain foetal life
36
Q

shunts must be

A

reversible at birth….

as soon as the baby is born (first breath) the shunts MUST close

37
Q

Name the shunts in foetal circulation

A

ductus venosus

foramen ovale

ductruc arteriosus

38
Q

Outline foetal circulation (warning v long winded)

A
  1. Oxygenated bloods is carried from the placenta into the foetal circulation via the umbilical vein
  2. Oxygenated blood enter the inferior vena cava and mixes with deoxygenated blood- bypasses the developing liver via the ductus venosus
  3. The blood enter the right atrium and passes into the left atrium via the foramen ovale (when its closes become fossa ovalis) thereby bypassing the pulmonary circulation (not full developed yet so wouldn’t tolerate the pressure)
    • The blood can shunt from right to left side of the heart because the pressure in the right side of the heart is higher than the left in the foetus
      • The baby is not breathing and instead the foetus’ blood is being oxygenated by the mothers blood
      • Therefore blood doesn’t have to go to the alveoli for oxygenation- so pulmonary circulation can be btpassed
  4. The blood is pumped from the left ventricle into the aorta
  5. Blood that doesn’t pass through the foramen ovale, and instead is pumped into the pulmonary trunk from the right ventricle, enter systemic circulation at the arch of the aorta via the ductus arteriosus
39
Q

which shunt ensures blood bypasses the liver on the way from the placenta to the right atrium

A

ductus venosus

40
Q

why is the ductus venosus important

A

ensures the blood bypasses the deceloping liver and goes straight to the heart

  • the liver is very metabolically active- so bypassing it means that oxyegnated blood can maintain its oxygen saturatio for when it reaches the heart to be pumped around the body
41
Q

where is the foramen ovale found

A

between the right and left atria

42
Q

what is the foramen ovale called after it closes

A

fossa ovalis

43
Q

where is the ductus arteriosus found

A

in the pulmonary vein going into the aortic arch

44
Q

why is the ductus arteriosus important

A

by-pass the lungs

This system exists so that the right ventricle still has some blood to pump against. In the developing heart, the rule of ‘use it or lose it’ applies, so if the right ventricle has no blood passing though it, it will be underdeveloped in the mature heart. This is relevant in congenital heart defects such as tricuspid atresia.

45
Q

Simple diagram of shunts in the foetal heart

A
46
Q

shunts after birth

A
  1. Baby takes first breath and pO2 increases- Ductus arteriousus contracts
  2. More blood now flows through pulmonary circulation as blood in the pulmonary trunk cannot leave via the ductus arteriosus anymore
  3. This causes increased venous return to the left atrium, leading to an increase in left atrial pressure. When the pressure in the LA exceeds the RA the foramen ovale closes becomes fossa ovalis
  4. When the umbilical cord is cut, there is no longer blood flowing through the umbicilical vein, causing the ductus venosus to collapse
47
Q

normal clotting of the ductus arteriosus that occurs after nrith

A
  1. Baby takes first breath
  2. When exposed to higher pO2 the smooth muscle undergoes contraction and closes shunt
  3. Then becomes fibrotic
48
Q

what occurs after development of the atria and shunts

A

(4) formation of the great vessels

49
Q

(4) formation of the great vessels: where do vessels arise from

A

truncus arteriosus.

50
Q

how many pairs of arches

A
  • I,II,III,IV,VI (V arch doesn’t form in humans, so there are 5 arches numbered between I-VI without no.V)
51
Q

early arterial system

A

Early arterial system begins as a bilaterally symmetrical system of arched vessels–> undergo extensive remodelling to create the major arteries leaving the heart

52
Q

outline the formation of the great vessels

A
  • Truncus arteriosus: divided by the aorticopulmonary septum to form the pulmonary trunk and the aorta.
  • Sixth arch: goes on to form the right and left pulmonary (R VI and L VI) arteries arising from the pulmonary trunk. The left artery maintains its connection to the rest of the vessels via the ductus arteriosus, however the right artery loses this connection. When the baby is born and the ductus arteriosus closes, this separates the pulmonary circulation from the systemic circulation.
    • The sixth arch is also known as the pulmonary arch.
  • 4th arch: on the left side becomes the arch of the aorta, and on the right becomes the right subclavian.
  • 3rd arch: becomes the common carotids and the first part of the internal carotids.
  • Second and first arches: disappear.
53
Q
A
54
Q

Sixth arch

A

goes on to form the right and left pulmonary (R VI and L VI) arteries arising from the pulmonary trunk. The left artery maintains its connection to the rest of the vessels via the ductus arteriosus, however the right artery loses this connection. When the baby is born and the ductus arteriosus closes, this separates the pulmonary circulation from the systemic circulation.

  • The sixth arch is also known as the pulmonary arch.
55
Q

4th arch:

A

on the left side becomes the arch of the aorta, and on the right becomes the right subclavian.

56
Q

3rd arch

A

becomes the common carotids and the first part of the internal carotids.

57
Q

Second and first arches:

A

disappear

58
Q

what occurs after great vessel formation

A

(5) septation

59
Q

(septation)

A
  • After looping of the heart tube
  • Atrioventricular canal links atrium and ventricle
  • Don’t yet have ‘two pumps in series’ configuration
  • The primitive chambers must be divided
60
Q

Types of septation:

  1. Interatrial septum
  2. Interventricular septum
  3. Septation of ventricular outflow tract (pulmonary trunk and aorta)
A
61
Q

WHat are key to the separation of the left and right side of the heart?

A

Endocardial cushions

  1. The lining of dorsal and ventral aspects of the developing heart grow endocardial cushions.
  2. These grow to meet in the middle of the heart and are key in the separation of the left and right sides of the heart.
  3. They act as a target for the septa that develop as each septum will grow towards the cushions
62
Q

(5) Septation I- The Inter-atrial septum

A
  1. Septum of tissue grows from the top of developing atria towards the endocardial cushions. This is the septum primum, as it grows down the communicating hole between the atria is called the ostium primum
  2. Just before the septum primum meets the endocardial cushions and the ostium primum is closed, a hole forms in the middle of the septum- ostium secundum
  3. The septum primum meets the endocardial cushions, and the ostium secundum allows blood to continue to move from the right to left atrium
  4. Another septum grows down from the top of the atria called the septum secundum
  5. As the septum secundum grows down, it leaves another hole just below the ostium secundum
  6. These two septa, and two holes together form the foramen ovale - a right to left shuntallowing blood to flow from the right atrium into the left. This shunt will reverse and close after birth
63
Q
A
64
Q

outline inter-atrial septum septation simply

A
  1. formation of septum primum (above)
  2. formation of ostium primum (hole between septum primum and endocardial cushion)
  3. formation of ostium secundum
  4. septum secondum starts to form from the endocardial cushion
  5. hole in septum secundum called the ostium secundum
  6. these two septa and holes form the foramen ovale
65
Q

these two septa and holes form the foramen ovale forms a

A

right to left shunt

allowing blood to flow from the right atrium to the left (shunt closes after birth)

66
Q

Atria summary

A
  • Both left & right atria have components derived from the primitive atrium (i.e. auricles)
  • The right atrium absorbs the sinus venosus
  • The left atrium sprouts the pulmonary vein then grows to absorb it and its first 4 branches
  • Interatrial septum forms to divide the chamber into left and right chambers
  • The fossa ovalis is the adult remnant of the shunt used in utero to by- pass the lungs
67
Q

Ventricular septation

A

The formation of the ventricular septum take place in two steps:

  1. A muscular portion of the heart tissue grows upwards from the floor of the primitive ventricle towards the endocardial cushions. It doesn’t quite reach the cushions, forming the primary interventricular foramen
  2. A membranous portion then grows down from the endocardial cushions to meet the muscular portion and close the foramen (window)
68
Q

A defect in formation of the ………..portion is a common reason for ventricular septal defects

A

membranous

69
Q

Septation of the Outflow tract

A

The bulbis cordis and truncus arteriosus form one tube allowing outflow from the heart. This tube needs to be split in order to form the aorta and pulmonary trunk.

  1. In the beginning, there are two lines of proliferations of neural crest cells (these cells appear in the neural tube during neurulation and migrate to contribute to the development of a wide range of structures) on the walls of the outflow tract.
  2. This two lines of the cells spiral around and grow towards each other to meet in the middle
  3. This form a single spiral septum called the aorticopulmonary septum – consequently forming the aorta and pulmonary trunk.

Cardiovascular system (30 decks)

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