chapter 9circulatory systemjcyxy.ahmu.edu.cn/_upload/article/files/7d/9e/e5bb... ·...

Anhui Medical University


Chapter 9 Circulatory System

Xue-mei [email protected] of Histology and EmbryologyAnhui Medical University



• 1. General description• 2. Heart• 3. Arteries• 4. Capillaries• 5. Veins• 6. Key points• 7. Homework



We study microstructures at three structural levels: cells,tissues,organs Cells ---is the smallest structure and

functional unit of living organisms.Tissues---groups of cells and intercellular

substances make up the body tissues. Organs---several different kinds of tissue are further

organised to form organsSystem---several organs with related functions

together form systems

review

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OrgansSeveral different kinds of tissues areorganised in particular ways to formorgans.From the structure view, there are twokinds of organs in human body

1) cavity organs 2) parenchyma organs



1) Cavity organsThe wall of cavity

organs can be divided into three or four layers.

The wall of blood vessels is made up of three layers: ① tunica intima② tunica media③ tunica adventitia


Anhui Medical University2) Parenchyma organs① capsule: connective tissue② parenchyma: functional cell③interstitial substance: connective tissue, blood

vessels,lymphatic vessels and nervous fibers.

LM: thymus LM: lymph node



1 General description



Our body need the nutrition to grow, we need a system to transport

the nutrition and the oxygen to the tissues andcells

the waste products of metabolism and carbondioxide out of tissues and cells



Which systemwill completethis function inhuman body ?



Circulatory system

1)Cardiovascular system

heart, arteries, capillaries , veins

2)Lymphatic vascular system

lymphatic capillaries, lymphatic vessels, lymphatic ducts



1)Cardiovascular systemis the major circulatory systemconsists of the heart and blood vessels the heart as a pump propels the blood into arteries the arteries take blood from the heart to capillaries



1)Cardiovascular system

exchanges of substances between the blood and the tissues take place through the walls of capillaries blood from capillaries is collected by veins---return to the heart.



2)Lymphatic vascular systemis the assistant circulatory system.

begins in the lymphatic capillaries which are closed-ended tubules

collected to form lymphatic vessels,lymphatic ducts which terminate in the large vein.



Circulatory system is a closed tubular systemarteries

heart capillaries

veins

lymphatic capillaries（ closed-ended tubules ）

lymphatic ductslymphatic vessels



2. Heart(1) The heart wall ★(2) Cardiac valve

(3) Conducting system of the heart



is a muscular pump that contracts rhythmicallypumping the blood through the circulatory system. three layers in the wall of the heart.

Heart



(1) The heart wall

endocardiumendotheliumsubendothelial layersubendocardial layer

myocardium: thickest layer

consists of cardiac muscle

epicardium LCTmethothelium



Subendothelial layer a thinlayer of connective tissue

Subendocardial layera layer of connective tissue containing branches of conducting system of the heart (Purkinje cells).

Endocardium

Endothelium simple squamous epithelium

LM: the wall of heart



is the thickest of thetunics of the heart

consists of cardiac muscle cells

arranged in the inner longitudinal layer, the middle circular layer,outer oblique layer

small amount of LCT

Myocardium




is the visceral layer of pericardium (serous membrane)

consists of a layer of connective tissue and a layer of flattened mesothelial cells

Epicardium




endotheliumsubendothelial layersubendocardial layer

Myocardium:

Epicardium:

LCT methothelium

Endocardium: Review


Purkinje cells



formed by infolding ofendocardium

consists of endothelium +DCT

prevent the back flow of blood

(2) Cardiac valve

cardiac valve

LM: cardiac valve

endothelium

DCT



Have you ever considered this：Why does people’s heart keeps beating continuously and rhythmically ？



(3) Conducting system of the heart

① Definition

--- consists of the special cardiac musclecells

--- to generate and conduct a rhythmicimpulses that is spread to the entiremyocardium， in order to coordinate theheart beat.


Anhui Medical University② composition---sinoatriol node (SA node):

located in epicardium of right atrium

---atrioventricular node (AV node):

located in subendocardial layer

--- atrioventricular bundles (AV bundles):

located in subendocardial layer

Conducting system of the heart


Anhui Medical University③ three types of cells---pacemaker cells (P cells)

• mainly distributed in SA nodeand AV node

• small, ovoid or polygonal in shaped• heartbeat generating -----It is because of

this fact that the heart keeps beating rhythmically



• If the pacemaker cells are damaged, the heart will stop beating.

• and in practice, in order to save patients’ life, cardiac pacemaker sometimes are planted.

• consists of pulse generator and a conducting wire connected to cardiac muscle

• pacemaker inventor ： Wilson Greatbatch



--- transitional cells

• mainly distributed in periphery of SA nodeor AV node

• thinner and shorter than cardiac musclecells

• to transmit impulses



--Purkinje cells (bundle cells)

• distributed in subendocardial layer

• ---larger diameter, shorter than typical cardiac muscle cells

---clear cytoplasm

---well-developed intercalated disks

• to conduct impulses to cardiac muscle cells



Purkinje cellscardiac myocytes

LM：larger，shorter，clear cytoplasm，distincter intercalated disks than cardiac myocytes



3. Arteries

（1） Medium-sized arteries ★（2） Large arteries（3） Small arteries and arterioles



Arteries

transport blood from heart to capillaries

according to their size, structure and function

Large artery (elastic artery)Medium-sized artery(muscular artery)Small artery(muscular artery)

are classified


Anhui Medical University（1）Medium-sized arteries

---Structure

Tunica intimaendotheliumsubendothelial layer internal elastic membrane

Tunica media contain 10~40 layers of circular smooth muscle

Tunica adventitia external elastic membraneLCT

Medium-sized artery



----Tunica intima• endothelium• subendothelial layer• internal elastic membrane

- prominent- wave-liked- pink-colored band- elastin

LM:Medium-sized artery



----Tunica media

• thickest layer

• smooth muscle: 10-40 layers, arranged circularly

• collagenous fibres， elastic fibres， produced by smooth muscle

Medium-sized arteries



----Tunica adventitia

• external elastic membranenot prominent

• LCT

Medium-sized arteries



intima

media

adventitia

Diagram HE staining Weigert staining

cross section of the medium-sized arteryReviewendothelium

subendotheliallayer

internal elasticmembrane



• The human body is very wonderful, when there is certain structure, there is certain function related

• Medium-sized arterycontains a lot of smooth muscle

• what function does this artery have ?



---Function

have the ability to alter the size of their lumen by contraction or relaxation of smooth muscle

regulate the amount of blood flowing into the organs or tissues



（2） Large arteries

• ---Structural features

• subendothelial layer: thicker

• internal elastic membrane : not prominent

• tunica media: ---- 40-70 layers of elastic membrane



LM:cross section of large arteries

What is the function for many layers of elastic membrane ?



---Function// assistant pump // to keep blood flows continuously

Why



When the left ventricle of the heart contracts, and blood enters the large arteries with considerable force

The large arteriesdistend significantly because of much elastic tissue in their walls



This recoil acts as an additional force that pushes the blood into smaller arteries

It is because of this fact that blood flows continuously through arteries

During diastole, the arteries walls come back to their original size, because of the elastic recoil of their walls



Small arteries---Structural features• diameter less than 1mm• internal elastic membrane is present.• 3 --- 4 layers smooth muscle• no external elastic membrane

（3） Small arteries and arterioles

LM: small artery



• ---Structural features

• diameter less than 0.3 mm

• no internal elastic membrane

• 1 --- 2 layers of smooth muscle

Arterioles

LM: arteriole



• --- Function • regulate the amount of blood flowing• regulate the blood pressure

LM:small artery LM:arteriole

peripheral resistance vessels



during treatment of hypertension ，some antihypertensive drugs can be used to relax smooth muscle of small arteries and arterioles

therefore making blood pressure drop by reducing peripheral resistance

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4. Capillaries

（1） General description（2） LM structure of capillaries（3） EM classification and structure ★（4） Function of capillaries ★



the most thin vessels in the body---- average diameter about 8 um

（1） General description



the most widely distributed vessels in the body

---- the total length of capillaries in human body: 10000 km

EM：the capillary plexusLM：the capillary plexus



the simplest structure• a layer of endothelial cells• basement membrane• pericytes

（2） LM structure of capillaries

cross section

longitudinal section

LM capillaries

RBC pass through the capillaries in a single-file fashion, benefitting oxygen and carbon dioxide exchange


Anhui Medical UniversityPericyte• flattened with processes• located outside of cap. • function

-- supporting-- contraction

scanning electron microscope

Pericyte

transmission electron microscope

Pericyte



Continuous capillaryFenestrated capillary

Sinusoid capillary

（3） EM classification and structure



Structure-- endothelial cells：continuou

more pinocytotic vesiclestight junctions

-- basement membrane: continuouDistribution --CT, muscles, lungs and CNS ……

Continuous capillaries



Exchange of substance--through pinocytotic vesicles--low capillary permeability

EM : Continuous capillary

continuou pinocytotic vesicles

tight junctions


Anhui Medical UniversityFenestrated capillariesStructure--endothelial cells： have fenestrae or pores

have or haven’t diaphragm tight junction

-- basement membrane: continuouDistribution --gastrointestinal tract, endocrine glandand renal glomerulus.


Anhui Medical UniversityEM : fenestrated capillarypores / diaphragm / tight junctions

Exchange of substanceSome big molecular substance canpass the wall of capillaries more easily.high capillary permeability



sinusoid capillariesStructure--endothelial cells: have pores without diaphragm

wide gaps between the cells--basement membrane : incomplete or absent

Distribution ---liver, spleen, bone marrow ….

.

LM: irregular luminawider diameter



Exchange of substancebetween blood and tissue is greatly facilitatedby the structure of this type of capillaries.highest capillary permeability

EM : spleen sinusoid

poreswide gaps



capillary permeability means theability of substances which passthrough the walls of the capillaries

selected permeability and exchangeof material

（4） Function of capillaries



5. Veins



The veins can also be divided into large veins,medium-sized veins, small veins.

The basic structure of veins is similar to thatof arteries.

The structure of veins differs from that ofarteries in the following respects

Veins



larger diameter, thinner walls，irregular lumenthe boundaries between three tunica not clearmore CT, less smooth muscle （in bundles）with vein valve

//infolding of tunica intima//semilunar-liked//prevent back flow of blood

Structural features

SEM : vein valve



Function of vein valve

-----prevent back flow of blood

varicose veinsOpen when blood flow return to the

heart ，close when blood backflow



LM: A : small regular lumen, thick wallV : large irregular lumen, thin wall

Can you tell the differencebetween arteries and veins ?



• Origin of connective tissues.• Classification of connective tissues.• Loose connective tissue: the cells( fibroblast,

macrophage, mast cell and plasma cell), fibers ( collagenous fiber, elastic fiber, and reticular fiber) and ground substance (molecular sieve and tissue fluid) of

• Dense connective tissue.• Adipose tissue.• Reticular tissue

6.Key points



7.homework

1.What are the structure of the heart wall ？2.Compare the structure and function of large

artery 、medium-sized artery and small artery.3.Describe the type and structure of capillaries

under EM .4.What are the structural differences between

the arteries and veins?5. explanation of nouns： internal elastic membrane

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