1. Circulatory system Zhong Jie Li （李仲杰）, Ph. D
School of Medicine, Zhejiang University

2. RENIEW: Concepts of organs and systems
Organ: composed of four kinds of the tissues in a particular way
Hollow organs: studied from inside to outside
Types
parenchyma
Substantial organs:
interstitium
System: composed of many organs which have relationship with each other in structure and function.

3. General outline Blood vascular system (cardiovascular system)
---Closed tubular system
According to the circulating
fluid in the tubes, blood or lymph
Blood vascular system (cardiovascular system)
Lymphatic vascular system

4. Cardiovascular System
includes two major components
Heart – mainly functions as a pump to move blood (and all the things blood carries) through the body.
Blood vessels – are the tubes that distribute the blood to the cells and then back to the heart.

5. Heart a hollow muscular organ that contracts rhythmically.
pump blood through the
circulatory system.

6. The wall of heart
epicardium
myocardium
endocardium

7. The wall of heart E SE endocardium subendocardial layer
Purkinje fibers
myocardium
epicardium

8. The wall of heart Endothelium Subendothelial layer: fined CT
Subendocardial layer: LCT, blood vessels, nerves and the cardiac conduction system of the heart
endocardium
myocardium: thickest layer, consists of cardiac muscle, is
richly supplied with capillaries
Atria and ventricle
LCT: contain adipose cells, blood vessels and
nerves
Methothelium
epicardium

9. Endocardium Endothelium Subendothelial layer Subendocardial layer:
Purkinje fiber

10. Myocardium

11. Purkinje cell Cardiac cell
Purkinje cells both broader and shorter than ordinary cardiac muscle fibres, rich in sarcoplasm, two nuclei can be found, well-developed intercalated disks.

12. Epicardium
1. Epicardium
2.Methothelium
3.Adipocyte
4.Cardiac muscle 1 2 3 4

13. Conducting System components: sinoatrial node (SA node): the primary pacemaker of the heart located in epicardium of right atrium atrioventricular node( AV node) bundles( AV bundles) located in subendocardial layer. network of Purkinje fiber: distributed in subendocardial layer.
The heart has a specialized system to generate a rhythmic stimulus that is spread to entir myocardium.

14. Impulse generating and conducting system of the heart:
Pacemaker cells: heart beat generating
Transitional cells: transmit impulse
Purkinje cells (bundle cell):
distributed in subendocardial layer.

15. The blood vessels include three major divisions: Arteries –
deliver blood from heart to capillaries
Capillaries –
the smallest blood vessels and closest to
body cells, the interchanges between blood
and tissues occur there
Veins –
carry blood from body to the heart

16. Structural features of blood vessel :
Tunica intima
Tunica media
Tunica adventitia

17. Artery transport blood from heart to capillaries
according to their size, structure and function
Large artery D>10mm
Medium-sized artery D>1~10mm
Small artery D>0.3~1mm
Arteriole D<0.3mm
Grade

18. Large artery: elastic artery: diameter larger than 10 mm Endothelium
Subendothelial layer: LCT
Internal elastic lamina:
Tunica intima
Tunica media: contain 40~70 layers of circular
elastic laminae
External elastic lamina
LCT: contain vasa vasorum
Tunica adventitia

19. Large(elastic) artery:
contains aorta, the pulmonary trunk and their main branches
With a large lumen relative to wall thickness
subendothelial layer is thicker with a few smooth muscles
tunica media is thick, contains a concentrically-
arranged elastic laminae
internal and external elastic lamina are not distinguished
tunica adventitia are thinner, abundant vasa vasorum

21. Large artery Tunica media PT stain
The abdominal aorta is an exception . It lacks vasa vasorum, which may explain its susceptibility dilation an aneurysm formation.
PT stain

22. Medium-sized artery: muscular artery: diameter more than 1mm
Endothelium
Subendothelial layer: LCT
Internal elastic lamina: clear
Tunica intima
Tunica media: contain 10~40 layers of circular
smooth muscle
External elastic lamina
LCT: contain vasa vasorum
Tunica adventitia

23. Smooth muscle regulates blood flow and pressure.

24. Medium-sized artery
Tunica
Adventitia
Media
intima

25. Medium-sized artery

26. Muscular artery
Elastic artery

27. Small artery: muscular artery: diameter more than 0.3mm Endothelium
Subendothelial layer: LCT
Internal elastic lamina: clear
Tunica intima
Tunica media: contain 3~9 layers of circular
smooth muscle
Tunica adventitia
LCT

28. Small artery: muscular artery and peripheral resistance vessel
internal elastic lamina is clear, while
external elastic lamina is not distinguished
the tunica media contains 3~9 layers of smooth
muscles

32. Vein large lumen, thin wall, irregular
internal and external elastic lamina are not clear
tunica media is thin, with a few elastic fibers and
smooth muscles
tunica adventitia is thick (best-developed)
many veins have valves

34. large veins

35. Medium-sized vein

38. Capillaries 1. In many organs the capillaries form a network.
2. Capillaries are the site where materials carried in the blood are unloaded and other materials are loaded into the blood.

39. 3.The structural bases of substance interchange of cap.：
（1）Larger square, thin vascular wall, short distance with surrounding cells （2）O2 、CO2 and lipid-soluble substances can penetrate the walls of cap. directly （3）liquid and macromolecule can pass through endothelial pores （4）pinocytotic vesicles can transport liquid （5）intercellular space facilitate more easily elements to pass through （6）basal membrane make small molecular substances filtrate readily , so disintegrate basal membrane or no is easier to material exchanges.
4. Capillary permeability: The ability of substances passing through capillary.

40. Capillaries LM: A single layer of endothelial cells basal lamina
pericyte:
The average diameter about 8um.

44. Pericyte: long cytoplasmic processes
2) EM:
Pericyte:
long cytoplasmic processes
have a contractile function, participating in the repair process

45. Classification
According to the appearance of the endothelium and basal lamina:
Continuous capillary
Fenestrated capillary
Sinusoid

46. Continuous capillary:
distributed in muscle tissue, brain, lung and
connective tissue, etc.
endothelial cell: large number of pinocytotic
vesicles, no pores, exist cell junctions
between the endothelia(tight juntion)
basal lamina: integrity
permeable

47. (stripe)

48. Continuous capillary

49. Pinocytotic vesicles

50. Fenestrated capillary:
distributed in tissues where rapid interchange of substances occurs between the tissue and the blood, as in the kidney glomerulus, mucosa of gastrointestine, some endocrine glands
endothelial cells: present abundant perforated pores(60-80nm in D, with 4-6 nm diaphragm), have or haven’t diaphragm on them
basal lamina: continuous

51. Fenestrated capillary

52. Perforated pores

53. Sinusoid:
distributed in tissues where interchange of substance in big size occurs, as in the liver, spleen, and some endocrine glands
a greatly enlarged diameter(30~40um)
endothelial cell: intercellular clefts are large between cells, many pores without diaphragm
absence of a continuous basement membrane
Macrophages are located either among or outside the cells of the endothelium

54. Sinusoid

55. Sinusoid

56. Lymphatic vascular system
(Study by yourself)
Lymphatic capillaries
Lymphatic vessel
Lymphatic ducts

57. Lymph vessels
Lymph vessels return fluid from tissues to circulatory system.
Depend upon muscles to move fluid
Very thin walled.