Circulatory system

Shiping Ding (丁世萍 ), Ph. D

School of Medicine, Zhejiang University

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.

Concepts of organs and systems

Organ: composed of four kinds of the tissues in a particular way

TypesHollow organs: studied from inside to outside

Substantial organs:

System: composed of many organs which have relationship with each other in structure and function.

parenchyma

interstitium

General outline

•Blood vascular system (cardiovascular system)

•Lymphatic vascular system

---Closed tubular system

According to the circulating

fluid in the tubes, blood or lymph:

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.

The blood vessels include three major divisions:

Arteries – deliver blood from heart to capillariesCapillaries – the smallest blood vessels and closest to body cells, the interchanges between blood and tissues occur thereVeins – carry blood from body to the heart

Histological Structure of Blood Vessels

Structural feature 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

Artery 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

• 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.

Structure features of artery

Tunica intimaeTunica intimae

• is the inner coat and it consists of

1)inner endothelial layer

2)subendothelial layer: a layer of loose connective tissue

3)internal elastic membrane (often very distinct)

• This layer is relatively constant within different size arteries.

Tunica mediaTunica 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.

Tunica adventitiaTunica 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.

Medium-sized artery (Muscular artery):Medium-sized artery (Muscular artery):

muscular artery: diameter larger than 1mmdiameter larger than 1mm

Tunica intimaTunica intima

EndotheliumEndothelium

Subendothelial layer: LCTSubendothelial layer: LCT

Internal elastic laminaInternal elastic lamina: clear: clear

Tunica media: contain Tunica media: contain 10~40 layers10~40 layers of circular of circular

smooth musclesmooth muscle

Tunica adventitiaTunica adventitiaExternal elastic laminaExternal elastic lamina

LCT: contain vasa vasorumLCT: contain vasa vasorum

TunicaTunicaAdventitiaAdventitia

TunicaTunicaMediaMedia

Tunica Tunica intimaintima

Medium-sized artery

Classic muscular artery- elastic stain

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 lamina

internal and external elastic lamina are not distinguished

tunica adventitia are thinner, abundant vasa vasorum

PTPT stain stain

Elastic arteryElastic artery Muscular arteryMuscular artery

Small artery: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

Arterioles:Arterioles:

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

Vein 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)

some veins have valves

Large veins D>10mmLarge veins D>10mm

Medium-sized vein D=2~9mmMedium-sized vein D=2~9mm

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

A Comparison of a Typical Artery and a Typical Vein

elastic tissue is colored dark purple, cytoplasm (in smooth muscle and nerve) is lighter purple, and collagen is pale pink.

Artery, vein, nerve, elastin stain

Artery, vein, nerve, elastin stain

elastic tissue is colored dark brown, collagen is pale pink and cytoplasm

(in smooth muscle and nerve) is purple.

Artery, vein, nerve, trichrome stain

collagen is colored blue and smooth muscle is red.  Red blood cells

in the venous lumen are brighter red.

CapillariesCapillaries• 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.

CapillariesCapillaries

1) L/M: • A single layer of endothelial

cells• Pericyte• A basement membrane

Pericyte:

long cytoplasmic processes

have a contractile function, participating in the repair process

Capillary - pericyte

The types of Capillaries

Continuous C.Continuous C.

Fenestrated C.Fenestrated C.

SinusoidSinusoid

E/ME/M

Continuous capillary

Fenestrated capillary Sinusoid

Structure endothelial cell: large number of pinocytotic vesicles

cell junctions between the endothelia (tight junction)

no pores, no gaps

basement membrane: integrity

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

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

Location distributed in muscle tissue, brain, lung and connective tissue, etc.

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

distributed in tissues where interchange of substance in big size occurs, as in the liver, spleen, and some endocrine glands

The types of Capillaries

Continuous capillary Fenestrated capillary Sinusoid

Heart Heart

a hollow muscular organ that contracts rhythmically

pump blood through the circulatory system

The wall of heartThe wall of heart

endocardiumendocardium

myocardiummyocardium

epicardiumepicardium

The wall of heartThe wall of heart

ESE

subendocardial layer

endocardium

myocardium

epicardium

Purkinje fibers

endocardium

EndotheliumEndothelium

Subendothelial layer: fined CTSubendothelial layer: fined CT

SubendocardialSubendocardial layer: LCT, blood vessels, nerves and layer: LCT, blood vessels, nerves and the impulse-conducting system of the heartthe impulse-conducting system of the heart

闰盘 线粒体

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

构成心包脏层

心包受损 影响心脏功能

epicardiumLCT: contain adipose cells, blood vessels and

nerves

MethotheliumMethothelium

Conducting SystemConducting Systemcomponents: components:

sinoatrial node (SA node): sinoatrial node (SA node): the primary pacemaker of the heartthe primary pacemaker of the heart

located in epicardium of right atriumlocated in epicardium of right atrium

atrioventricular node( AV node)atrioventricular node( AV node)

bundles( AV bundles) located in bundles( AV bundles) located in subendocardial layer. subendocardial layer.

network of Purkinje fibernetwork of Purkinje fiber

Impulse generating and conducting Impulse generating and conducting system of the heart:system of the heart:

Pacemarker cell

Transitional cell Purkinje cell

Location SA / AV SA / AV /AV bundle

AV bundle / branches

Structure small, fusiform or polygonal in shaped

less myofibril

thinner and shorter than caridac muscle

more myofibril than P cell

shorter, boarder than caridac muscle, with 1-2 centrally located nuclei

rich in mitochondria, glycogen, less myofibril

well-developed intercalated disks

Function heartbeat heartbeat generatinggenerating

transmit impulsetransmit impulse Transmit impulse into the Transmit impulse into the ventricle quicklyventricle quickly

transitional cell Purkinje cell

Purkinje cellPurkinje cell Cardiac cellCardiac cell

Purkinje cells Purkinje cells both broader and shorter than both broader and shorter than ordinary cardiac muscle fibers, rich in ordinary cardiac muscle fibers, rich in sarcoplasm, two nuclei can be found,sarcoplasm, two nuclei can be found, well-well-developeddeveloped intercalatedintercalated disks.disks.

Purkinje fiber

Purkinje fibers

cardic valveThe core of dense connective tissueThe core of dense connective tissue

endotheliumendothelium prevent the back flow of bloodprevent the back flow of blood

Question1. To describe the difference between large artery and medium-sized artery.2. To describe the types of capillary.

Good-bye!

Thank you for your attention!