1. School of Medicine, Zhejiang University
Circulatory system
Shiping Ding (丁世萍), Ph. D
School of Medicine, Zhejiang University

2. Learning Objectives To be familiar with the type of capillary.
To be familiar with the type of artery and vein.
To distinguish with all the types of blood vessels. 2

3. 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.

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

5. Cardiovascular System
The histological study of the 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.
--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

6. Histological Structure of Blood Vessels6

7. Composition of Arteries and Veins:
Tunica intimae
1. Endothelium
2. Subendothelial layer
3. Internal elastic membrane
Tunica media
Mainly smooth muscle
Tunica adventitia
external elastic membrane
Mainly connective tissue
medium-sized A

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

9. Structure features of artery
The wall of Arteries consist of three layers or “coats” often referred to as tunics.
Tunica intimae – is the inner coat
Tunica media – is the middle layer
Tunica adventitia or tunica externa is the outer layer of the wall of the blood vessel
Layers of arteries wall differ in different size blood vessels. The structure and function of arteries change as their diameter decreases.

10. Tunica intimae It is the inner coat and it consists of
--inner endothelial layer
--subendothelial layer: a layer of loose connective tissue
--internal elastic membrane (often very distinct)
This layer is relatively constant within different size arteries.

11. Tunica media
This layer makes up the greatest part of the wall of the artery.
It is comprised primarily of smooth muscle.
In small arteries or arterioles it may be only 1-3 cells thick but in larger arteries may comprise hundreds of layers of muscle cells.
In large arteries, there in increased amounts of elastin fibers.

12. Tunica adventitia This is the outer layer of the wall of the artery.
It consists primarily of connective tissue and serves to attach the blood vessel into the surrounding connective tissue.
Often contains adipose tissue and often contains blood vessels (vasa vasorum) that supply the walls of the blood vessels.

13. Medium-sized artery (Muscular artery):
muscular artery: diameter larger 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
Classic muscular artery- elastic stain
Tunica adventitia

14. 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 lamina
internal and external elastic lamina are not distinguished
tunica adventitia are thinner, abundant vasa vasorum
Elastic artery
Muscular artery

15. 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

16. Arterioles:
Less than 0.3mm in diameter. Have similar and simpler structure as that of muscular artery.
Several layers of smooth muscle in tunica media.
Responsible for the presence of blood pressure.

17. 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 (well-developed)
some veins have valves

18. Large veins D>10mm

19. Medium-sized vein D=2~9mm

21. Vein valves: Bag-like protrusion of tunica intima, which prevents the blood flow from running to opposite direction. Exists only in the vein that has low position or far away from heart.
Vein with valve

22. Artery, vein, nerve, elastin stain
elastic tissue is colored dark brown, collagen is pale pink and cytoplasm (in smooth muscle and nerve) is purple.

23. Capillaries
Capillaries are the site where materials carried in the blood are unloaded and other materials are loaded into the blood.
In many organs the capillaries form a network.
Consist of a single layer of simple squamous epithelium. the average diameter about 8um.
Stomach, vascular injection of mucosa

24. Capillaries 1) L/M: A single layer of endothelial cells
A basement membrane
pericyte:
Capillary(b) and venule (a)
Capillary - pericyte

25. E/M
According to the appearance of the endothelium and basement membrane:
Continuous capillary
Fenestrated capillary
Sinusoid

26. Continuous capillary:
distributed in muscle tissue, brain, lung and connective tissue, etc.
endothelial cell: large number of pinocytotic vesicles, cell junctions between the endothelia (tight junction), no pores, no gaps
basement membrane: integrity
permeable

27. 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
basement membrane: continuous
Fenestrated capillary (kidney)

28. 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

29. Heart a hollow muscular organ that contracts rhythmically
pump blood through the circulatory system
epicardium
myocardium
endocardium

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

31. endocardium Endothelium Subendothelial layer: fined CT
Subendocardial layer: LCT, blood vessels, nerves and the impulse-conducting system of the heart

32. Shown in yellow are parts of the cardiac conducting system
The endocardium consists of the endothelium, a thin layer of connective tissue with smooth muscle cells, and a layer of variable thickness lacking smooth muscle called the subendocardial layer.
(a) Below the endothelium (En) and myoelastic layer, the subendocardial layer (SEn) in the ventricles contains the conducting (Purkinje) fibers (P) of the heart's impulse conducting network. These fibers are cardiac muscle cells joined by intercalated disks but specialized for impulse conduction rather than contraction. With glycogen filling much of the cytoplasm and displacing myofibrils to the periphery, Purkinje fibers typically are more pale staining than contractile cardiac muscle fibers (M).
(b) In the atria Purkinje fibers (P) are often closer to the endothelium (En) and intermingle with the contractile fibers within the myocardium (M). Both X200. H&E.
Shown in yellow are parts of the cardiac conducting system
the cardiac conducting system

33. Purkinje fibers
Structure --specialised conducting fibers, --larger than cardiomyocytes --Fewer myofibrils --a large number of mitochondria and glycogen --intercalated disc Function: conduct cardiac action potentials more quickly and efficiently than any other cells in the heart
The endocardium consists of the endothelium, a thin layer of connective tissue with smooth muscle cells, and a layer of variable thickness lacking smooth muscle called the subendocardial layer.
(a) Below the endothelium (En) and myoelastic layer, the subendocardial layer (SEn) in the ventricles contains the conducting (Purkinje) fibers (P) of the heart's impulse conducting network. These fibers are cardiac muscle cells joined by intercalated disks but specialized for impulse conduction rather than contraction. With glycogen filling much of the cytoplasm and displacing myofibrils to the periphery, Purkinje fibers typically are more pale staining than contractile cardiac muscle fibers (M).
(b) In the atria Purkinje fibers (P) are often closer to the endothelium (En) and intermingle with the contractile fibers within the myocardium (M). Both X200. H&E.

34. myocardium
thickest layer, consists of cardiac muscle, is richly supplied with capillaries
three layers are divided roughly, cardiac muscle arrange spirally.
Cardiac muscle:HE×100

35. epicardium 构成心包脏层 LCT: contain adipose cells, blood vessels and nerves
Methothelium
epicardium
构成心包脏层
心包受损 影响心脏功能

36. 小结——心血管系统 1 心血管系统 心脏 心内膜 内皮 单层扁平上皮 内皮下层 内膜下层 浦肯野纤维 心肌膜 心肌纤维 心外膜 浆膜
动脉、静脉 内膜
内弹性膜 中膜 外膜
毛细血管
连续毛细血管
有孔毛细血管
内皮细胞有窗孔
窦状毛细血管
基膜不完整，内皮细胞空隙大

37. 小结——心血管系统 2 动脉 静脉 大 内膜厚、内弹性膜不明显 中膜：40-70层平滑肌，弹性膜多 外膜：营养血管 内膜、中膜薄
外膜纵行平滑肌多
弹性纤维少
管径不同 中
内膜：内弹性膜明显
中膜：10-40层平滑肌，纤维少
外膜纵行平滑肌少 小
中膜：3-10层平滑肌
内皮外几层环行平滑肌 微
内皮+1-3层平滑肌
内皮外为结缔组织

38. Question 1. To describe the difference between large artery and medium-sized artery. 2. To describe the types of capillary.