histology, lecture 13, circulatory system (lecture notes)

histology10-11-2010 bashar alameen


The Circulatory System

Today I will talk about The first part of the circulatory system only which is the heart…

The circulatory system includes both the blood and lymphatic vascular system .

@ The blood vascular system consist of the

1 - heart

2 - arteries

3 - capillaries

4 - veins.

The heart :

@ is the pump ,that is composed of cardiac fibers. it is involved in contraction and through it`s rhythmic contraction the blood is

circulated through the body .

@has a fibers skeleton that maintains the form of the heart serve as attachment for the muscles fiber. You already learn about cardiac muscles so you already know about the different characteristic of the cardiac muscles.

@has four chambers (two atria R , L) and (two ventricles R,L) you have to know that atrial walls are thinner than the ventricular once due to the thicker myocardium presents in the ventricles.

@has three layers from inside to outside they are:

endocardium ,myocardium, epicardium , (epicardium also known as visceral pericardial ).

endocardial layer is the internal layer , myocardial layer is the middle , you have a myo so it is a muscle so it is a layer where a cardiac muscle cells are ,then you have the epicardial layer which is the external layer . so this is longitudinal view of the heart , you can see the different chamber 1-2-3-4


The two upper small chamber are the atria right and left , and the lower big one are a ventricle right and left , now if you look at the walls of the atria chamber they are much thinner than in the ventricle and then the wall of the left ventricle it`s much thicker than the right one .

The yellow things in the figure are the part of the conducting system which you will know more about in few minutes .

@Now the conducting system is composed of two nodes :

1 - the upper one called the sinoatrial node

2 -the lower one called the atriovantricular node .

You have a bundles (yellow line punched out the atriovantricular node ) that originate from the atriovenrical node having it`s same name ,so the atrioventricular bundles that branchs into right and left bundles those bundles further branch where the mostly cells branch are called purkinje fibers and you will know the characteristic of the purkinje fibers later today in this lecture

So there are many layers or components of the endocardium, again, the endocardium is the internal layer of the heart you have three component from inside to outside the most internal layer is the lining of endothelial cells , so if you have the heart we said this is the heart here, then inside of the heart it`s covered by this


endothelium cells lining , then to supporting this endothelium lining you have a layer of loose connective tissue called subendothelial layer. (sub=below endothelium lining =

subendothelial layer ) .

Another layer of connective tissue is even below the subendothelail layer ,since it`s below the whole endocardium it`s

called the sub endocardial layer.

the difference between the sub endothelial layer and subendocardial layer is : the subendocardium layer contains elastic fibers,veins.nerves and part of the conducting system such as purkinje fibers.

@ The endocardium consist of endothelial cells which serve as lining and supporting layer of loose connective tissue and the subendothelial layer of loose connective tissue containing for example a part of the conducting system such as purkinje fibers.s

So the next layer , the middle layer of the heart ,the myocardiam , so in the myocardium you have cardiac muscles in

layer that are arrange in spiral fashion .

@ the myocardium again as I mentioned before is the thinner in the atria and thicker in the ventricle being thicker in

the left ventricle .

the myocardium contains two types of muscle cells the first one is the regular cardiac muscle cells and the second one is the specialized on conduction which are called conducting cell.

Now the last layer of the heart , the one that is external to the heart is called

@ The epicardium and there are two layers component in the epicardium:

1 - the outermost which it`s simple layer or squamous epithelium covering loose connective tissue and similar to the endocardium you have 2 - another layer that is below the epicardiam which is called the subepicardil layer which contain these snaps and ganglia

What is the meaning of the gangilion!!?

You Have to be specific , the ganglion is the universal definition of aggregations or accumulation of cells bodies of neurons outside of the CNS , so never say ganglions is inside of the CNS because this is


referred to the nucleus , but when you say outside the CNS is referred as ganglion .

This is an image of stained section of the heart where you can see those layers of simple sequamus epithelial cell supported by a layer of connective tissue and then here is the subepicardium layer containing the nerves and other structures , usually they are fat cells or adipocytes in the subepicardial layer and you can recognize

these fat cells here .

This here the myocardium where you can recognize the transverse ends of the cardiac muscles cell

@ The conducting system :

Is composed of modified cardiac muscles cells which are specialized for conduction , so they are not for contraction but for conduction and they are functionally integrated by gap junctions , now the conducting system is composed again of two nodes which are sinoatrial node , atrioventricular node and then a bundles that is called atrioventricular bundles ,or bundles of hiss

The sinoatrial node : it is a small mass of modified cardiac muscle cells , these cells characterized by being fussiform form , they are smaller than other cardiac muscles cells , they have pure myofibrils than the other ones adjacent to them ( the regular cardiac muscle cells ) , now the atrioventricular node has cells that are similar to the sinoatrial node however they have cytoplasmic projections that

extends in many direction for made network .

The atrioventricular bundles again is the one that originates from the atrioventricular node and it has a structure that is similar to the node from which they originate , so it has a structure similar to the atrioventricular node , it branches to left and right bundles branches which farther branch distinctly producing the purkenje

fibers.

The purkinje fibers have a distinctive appearance , they are larger than regular cardiac muscle cell , they have either one or two central nuclei , they have abundant glycogen and mitochondria due to the abundance of glycogen in these cells , the myofibrils are displaced peripherally , therefore myofibrils are usually located


peripherally or in the periphery of these purkenji fibers or cells and these myofibrils are restricted or reduced in number , finally the purkinji fibers are joined by intercalated discs , now you know about intercalated discs which are the interfaced or which are in the interface between the cardiac muscle cells where you can find the junctional complexes between these cells ,now there are no intercalated cells between the cells in the nodes however there are once between the purkenji fibers , so here you have on the left this an image of staind section view of heart , you saw this earlier , you can see the endocardium here , all of this endocardium with the subendocardial layer and then you have the myocardium , now in this subendocardial layer you can see those fibers or cells , you can see that those cells are much bigger or larger than the other cardiac cells , these are the purkenje cells another difference that you can see in these cells from the other cells , is those lightly stained areas inside the purkinje cells which are indicating the area where the glycogen is present , so you can distinguish purkenji cells by there large size and by the presence of light area which are lightly stained due to presence of glycogen , this purkenje fibers here are in the subendocardial layer however , this image in the right , you can see here is the myocardium , this is longitudinal , so you can see the branching that characterizes the cardiac muscles cell and the

intercalated discs .

Figure 11.4 (please refer to the figures in order to understand the pictures )

If you compare these cells to these one , the first one are much larger and they have lightly stanind area where large amount of

glycogen are.

Forgive me for any mistake ,,

I wish u successes in your exam's,,

Special hi to saleh 3eeni , 7azem mish 7ayah , muhamed wallahee ,,,

The little Love-god lying once asleep,


Laid by his side his heart-inflaming brand,

Whilst many nymphs that vowed chaste life to keep

Came tripping by; but in her maiden hand

The fairest votary took up that fire

Which many legions of true hearts had warmed;

And so the General of hot desire

Was, sleeping, by a virgin hand disarmed.

This brand she quenched in a cool well by,

Which from Love's fire took heat perpetual,

Growing a bath and healthful remedy,

For men diseased; but I, my mistress' thrall,

Came there for cure and this by that I prove,

Love's fire heats water, water cools not love

William Shakespeare

histology, lecture 13, circulatory system (lecture notes)

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