Circulatory system Zhong Jie Li （李仲杰）, Ph. D School of Medicine, Zhejiang University 20151023

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.

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

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.

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

The wall of heart epicardium myocardium endocardium

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

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

Endocardium Endothelium Subendothelial layer Subendocardial layer: Purkinje fiber

Myocardium

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.

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

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.

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.

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

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

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

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

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 40-70 concentrically- arranged elastic laminae internal and external elastic lamina are not distinguished tunica adventitia are thinner, abundant vasa vasorum

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

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

Smooth muscle regulates blood flow and pressure.

Medium-sized artery Tunica Adventitia Media intima

Medium-sized artery

Muscular artery Elastic artery

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

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

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

large veins

Medium-sized vein

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.

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.

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

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

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

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

(stripe)

Continuous capillary

Pinocytotic vesicles

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

Fenestrated capillary

Perforated pores

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

Sinusoid

Sinusoid

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

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