1. 2006 clinical medicine
Circulatory System
Department of Histology and Embryology Li jinxin No

2. CIRCULATARY SYSTEM In this chapter, the following are examined:
1. Organisation of the heart , including the three-layered structure of the heart wall and the conducting system.

3. 2. Histological characteristics of the various segment of the arteries and veins.
3. Correlation between the structure of the three types of capillary and their major functions.

4. 1.General description
--- closed tubular
system consisting
of cardiovascular and
lymphatic vascular
system.

5. 1.1 The cardiovascular system includes the heart, arteries, capillaries and veins. They are hollow organs, wall of which is composed of 3 tunics and lined with endothelium.

6. 1.2 The lymphatic vascular system begins in blind-ended lymphatic capillaries, which anastomose in lymphatic vessels and then empty into the large veins near the heart by lymphatic ducts.

7. 2.Heart – a pump The wall of the heart – 3 layers: myocardium
endocardium
myocardium
epicardium

8. endocardium
myocardium
epicardium

9. 2.1 Endocardium – thin inner lining composed of 3 layers
a. Endothelium
b. Subendothelial layer is a thin sheet of connective tissue.
c. Subendocardial layer consists of loose connective tissue and the conducting system of the heart.

10. Endothelium
Subendothelial layer
Subendocardial layer

11. 2.2 Myocardium
a. Composed of cardiac muscle richly supplied with capillaries.
b. Thicker in ventricles than in atria, and thickest in the left ventricle.

12. c. Atrial myocardial fibers contain specific atrial granules secreting atrial natriuretic factor (ANF). This hormone increases excretion of water and sodium and potassium ions and decreases blood pressure.

13. 2.3 Epicardium – visceral layer of the pericardium
a. Consists of a thin layer of loose connective tissue covered by mesothelium ( 间皮 ).
b. Numerous adipose cells in the subepicardial layer.

14. 2.4 Conducting system of the heart
2.4.1 Composed of
the sinoaterial node (SA),
atrioventricular node (AV),
AV bundle and the network
Purkinje fibers.

15. 2.4.2 Three types of specialized cardiac muscle cells:
P-cells (pacemaker cells),
transitional cells
Purkinje fibers.

16. 2.4.3 Purkinje fibers – terminal branches of conducting system
a. Broader and shorter than ordinary cardiac muscle fibers.
b. Pale stained and rich in sarcoplasm. c. Few myofibrils.
d. Well-developed intercalated discs between Purkinje fibers.

17. 3.Arteries – inner tunic Tunica media – middle layer Tunica adventitia
General structure of blood vessels
---- three layers (except for capillaries)
Tunica intima
– inner tunic
 Tunica media
– middle layer
 Tunica adventitia
– outer layer

18. A. Tunica intima consisting of 3 layers
Endothelium :simple squamous epithelium.
Subendothelial layer is loose connective tissue.
Internal elastic membrane is made up of elastin.

19. B. Tunica media
Consists mainly of smooth muscle cells and fenestrated elastic membranes, among which variable amounts of fibers and matrix are interposed.
There are no fibroblasts. Smooth muscle cells are responsible for production of the fibers and matrix.

20. C. Tunica adventitia
Outer layer of loose connective tissue with vasa vasorum (营养血管)and nerve.
The external elastic membrane
may be found between media and adventitia.

21. (conducting arteries)
– classified according to size into 3 groups:
A. Large arteries
(conducting arteries)
B. Medium-sized arteries
( distributing arteries)
C. Small arteries
( resistance vessels)

22. 3.1 Large arteries
The large arteries include the aorta, the pulmonary trunk and their main branches.
40 –70 layers of elastic membranes in the tunica media. (elastic arteries)

23. Subendothelial layer
Endothelium
Tunica
intima
media
adventitia
vasa vasorum

24. Tunica media

25. Function
They carry the blood from the heart to the middle arteries.

26. 3.2 Medium-sized arteries
Thin tunica intima with distinct internal elastic membrane.
Tunica media is composed of layers of smooth muscle cells (muscular arteries).
Tunica adventitia is as thick as the tunica media. A definite external elastic membrane is situated between the tunica media and the tunica adventitia.

27. 1. Endothelium 2. internal elastic membrane 3. Tunica media 4
1.Endothelium 2.internal elastic membrane 3.Tunica media 4.Tunica adventitia

29. Function
These vessels regulate the distribution of the blood to various parts of the body. They are therefore also termed distributing arteries.

30. 3.3 Small arteries
With a diameter less than 1mm. Called arterioles if less than 300 µm.
The internal elastic membrane is prominent. When the diameter is less than 50µm, The internal elastic membrane disappears
The tunica media is mainly composed of layers of smooth muscle cells (muscular arteries).

31. Small arteries
Small vein
arteriole

32. Function
These vessels regulate the distribution of the blood to various parts of the body tissue.
Resistance vessels.

33. 4. Capillaries The smallest blood vessels with diameter of 5 -10 µm.
The thinnest wall composed of
endothelium resting on a basal lamina, within which pericytes are enclosed.
Distribute widely in the body and form a network with different density according to metabolism.
Great surface area (6000 m2) facilitates substance exchange.

34. 1. Basement
Membrane
2. Pericyte
3. Endothelial
cells 2 1 3

35. Classification based on ultrastructures Continuous capillaries
Fenestrated capillaries
Sinusoids (discontinous capillary)

36. 4.1 Continuous capillaries
A continuous layer of endothelial cells joined by tight junctions.
A continuous layer of basal lamina.
A large number of pinocytotic vesicles in the cytoplasm of endothelial cells.
Present in the muscular tissue, connective tissue, nervous tissue and lungs.

37. tight junction
pinocytotic vesicles

38. 4.2 Fenestrated capillaries
The continuous endothelium and basal lamina is the same as that of the continuous type.
Characterized by pores, usually closed by a diaphragm.
Present in tissues in which rapid exchange of substances occurs between the tissues and the blood, such as in the renal glomerulus, submucosa of stomach and intestine, and some endocrine glands.

39. pore

40. 4.3 Sinusoids (discontinous capillary)
An enlarged and irregular lumen (diameter of µm).
Wide gaps (discontinuous) between endothelial cells.
The basal lamina may be incomplete or lack at all.
Found in the liver, spleen, bone marrow, and certain endocrine glands.

42. 5.Veins – capacitance vessels
Larger diameter, thinner wall and fewer smooth muscles than accompanying arteries.
Internal and external elastic membranes are absent.
The adventitia is the thickest consisting of longitudinally oriented smooth muscle cells, collagenous and elastic fibers.
Lumen frequently appears irregular, with valves (folds of intima) in small and medium-sized veins to prevent blood flow in reverse direction.

43. Exercise: 1.Describe the structure and function of the heart wall.
2.Compare the structure features and
function of the three sizes of artery.
3. Describe the general structure of the
capillaries and the features of three
types of capillary.
4.What are the structural features of
veins compared with arteries?