Circulatory system
Department of Histology & Embryology
Sichuan University
I. The components of the
Circulatory system
Cardiovascular System
Lymphatic vascular system
Arteries
Heart
Capillaries
Tissues
Veins
Lymphatic
Lymphatic
Thoracic duct
←
←
Right lymphatic duct vessels
capillaries
function:
transport nutrient,oxygen,carbon dioxide
and waste metabolic product
II. General Structure of the Blood Vessels
tunica intima
tunica media
tunica adventitia
III. Arteries

Large artery

Medium-sized artery

Small artery

Arteriole
Medium-sized artery
Muscular A.
Medium-sized artery
Muscular A.

Structural characters
1. Very much (10~40 layers) smooth muscle cells
intermingled with collagenous F., elastic F.
2. Very evident internal and external elastic lamina
3. Very defined 3 layers

Function
regulate blood flow to various organs
Large artery
elastic A.
Large artery
elastic A.

Structural characters
1. tunica media consists of elastic membranes mainly
abundant (40~70 layers) elastic laminas
and a few smooth muscle cells in media
2. internal and external elastic membranes
are not prominent
3. three layers are not distinguished
Functions of large A.
1.transport blood from heart
2.store blood during ventricle contraction
3.elastic recoil keep continuous blood flow
Small artery and arteriole
muscular A.
Structural characters
1.Diameter<1mm
2. Present internal elastic lamina
3. A few layers of smooth muscle F.
4. No external elastic lamina
5.Arteriole: diameter < 0.3mm
1~2layers of smooth muscle F.
Functions
1. regulate blood flow to organs and tissues
2. regulate blood pressure
Comparison
LA
MA
SA
Internal elastic lamina
not evident
evident
present
media
elastic laminas
S.M.F.
S.M.F.
external elastic lamina
not evident
evident
another name
function
elastic A.
absent
muscular A.
Capillary
A diffuse network of thin tubules between A. and V.
the main place for substance interchange
Characters
1. distribution (everywhere) -----very wide
total length (60,000 km) ------very long
total area(6000 m2 )------------very large
2. lumen (6~8μm) ------------very narrow
3. blood current-----------------very slow
?
4. wall ---------------------------very thin
Structure of the wall
-Endothelium
-Basal membrane
-Pericyte周细胞
3 Types Of Capillaries in EM

Continuous capillary 连续性毛细血管

Fenestrated capillary有孔毛细血管

Sinusoid血窦
 endothelium
 basal membrane
 cell junction
Continuous capillary
connective T.,muscle
T.,nervous T.
Fenestrated capillary
kidney, intestine,
endocrine gland
Sinusoid
liver, spleen, bone marrow
Continuous capillary
Fenestrated capillary
Sinusoid
Heart

endocardium—L. C.T.
endothelium: simple squamous epi.
subendothelium: L.C.T.
subendocardium: L.C.T.
Purkinje fiber

myocardium-- the thickest layer
abundant cardiac muscle cells

Epicardium--L. C.T.
coronary blood vessels, nerves
mesothelium
( visceral layer of the pericardium)
En endothelium
M muscle fibers
SEn subendocardial layer
P conducting (Purkinje) fibers
Mes mesothelium
N autonomic nerves
CT loose connective tissue
Ep epicardium
M myocardium
F fat
Development of Cardiovascular System
It derives from mesoderm 中胚层
 Establishment of
the early blood circulation
 Development of the heart *
 Congenital malformation *
1. Establishment of the
early blood circulation (3rd week)
blood islands
endothelium
blood stem cell
extraembryonic
embryonic
blood stem cells
these capillaries differentiate to:
arteries, veins & capillaries
2. Development of the heart★
• formation of endocardial heart tubes
• change of location of heart tube
• establishment of heart’s shape
• partition of the heart
• the congenital malformations
(1) Formation of endocardial heart tubes
cardiogenic area
生心区
*endocardial heart tubes
*paired tubes fuse into single
*heart tube link up with blood vessels
(embryo, connecting stalk, chorion & yolk sac)
－primitive cardiovascular system
(2) Change of location of heart tube
*ventral to the
foregut 前肠
*caudal to the
oropharyngeal
membrane
(3) Establishment of heart’s shape
① elongation
② dilatation
bulbus cordis
心球
Ventricle 心室
Atrium心房
sinus venosus 静脉窦
bulbus cordis － truncus arteriosus 动脉干
sinus venosus － veins
truncus arteriosus
bulbus cordis
ventricle
atrium
sinus venosus
veins
③ curvature formation
bulboventricular
loop 球室袢
( U-shaped )
bulbus cordis
*atrium
foregut
④ narrowing
atrium – ventricle
atrioventricular canal
房室管
(4) Partition of the heart *
primitive heart：one atrium
one ventricle
atrioventricular canal
partition of
atrium
ventricle
bulbus cordis
① partition of the
atrioventricular canal 房室管
dorsal endocardial cushion 心内膜垫
ventral endocardial cushion
② partition of the primitive atrium
septum primum
第一房间隔（原发隔）
foramen primum
第一房间孔（原发孔）
foramen secundum
第二房间孔（继发孔）
septum secundum
第二房间隔（继发隔）
foramen ovale
卵圆孔
* thin membrane from dorsocranial wall
* caudal free edge & the endocardial cushion
septum
primum
foramen
primum
* foramen secundum appears in the
cranial part of the septum primum
* foramen primum is closed
foramen
secundum
septum
secundum
foramen
ovale
*ventrocranial wall 腹颅侧壁
*thick membrane
*on the right side
*covers the foramen
secundum from the right side
心脏模型
foramen primum
septum primum :
(thin membrane)
(disappear)
foramen secundum
(cranial part)
septum secundum :
foramen ovale
(thick membrane)
(caudal part)
Before birth
blood in right
atrium
foramen ovale
left atrium
After birth
pulmonary blood
circulation starts
to work
- pressure in left
atrium increase
foramen ovale - close - by valve
valve fuses with the
septum secundum
- interatrial septum
③ Partition of the primitive ventricle
interventricular septum
室间隔
muscular interventricular septum
membranous interventricular septum
muscular interventricular septum
endocardial
cushions
interventricular
foramen 室间孔
apex
membranous interventricular septum
bulbar ridges 球嵴
(left & right)
muscular
interventricular
septum
endocardial
cushions
④ Partition of the bulbus cordis 心球
& the truncus arteriosus 动脉干
two large arteries: aorta
pulmonary trunk
two ridges － in the walls of the
bulbus cordis & truncus arteriosus
－bulbar ridges ( left & right )
aorta
pulmonary
trunk
two ridges grow & fuse together
－ aorticopulmonary septum
主肺动脉隔
ascending aorta & pulmonary
trunk twist around each other
aorticopulmonary septum is not coronal
but in
spiral
or sagittal
orientation
(5) The congenital malformations
① atrial septal defects 房间隔缺损
normally
§ The septum primum is absorbed excessively
§ The septum secundum developed poorly
§ The septum primum is fenestrated
* The septum primum can’t cover the
foramen ovale completely
* interatrial shunting of blood
blood
left → right
pulmonary circulation↑
body circulation↓
infection
development
② ventricular septal defects 室间隔缺损
muscular
*membranous
septal defects
③ Tetralogy of Follot 法乐四联症
a combination of four cardiac defects:
*pulmonary stenosis
肺动脉狭窄
*membranous ventricular septal defect
室间隔膜部缺损
*overriding aorta
主动脉骑跨
*hypertrophy of the right ventricle
右心室肥大
This malformation results from the right
of bulbus cordis partition
(aorticopulmonary septum)
right → left
blood diversion
Clinical symptom:
* Cyanosis of the lips and fingernails
“blue baby”
* Short of oxygen, easy to be tired.
* Poor growth and development
The end