What is Angiology ? | Gross Anatomy | Anjani Mishra

                                                                                               Written By Anjani Mishra

Angiology

Angiology is the description of the organs of circulation of the blood and lymph- the heart and vessels including spleen and thymus.

• Cardio-vascular system
•  Lymphatic system

Cardio-vascular system

The cardiovascular system consists of;

1. The heart,
2. The arteries, which convey blood from the heart to the tissues,
3. The capillaries, microscopic tubes in the tissues, which permit the necessary interchange     between the blood and the tissue, and
4. The veins, which convey the blood back to the heart.

1.      Heart

·        The heart is the central hollow muscular organ which functions as a suction and force pump.

·        It is situated in the ventral half of the middle mediastinal space of the thorax and is enclosed in a fibro-serous sac called pericardium.

·        The size, shape and position of the heart vary between and within species. Commonly its shape is that of an irregular and somewhat flattened cone.

·        It is asymmetrical in position. The long axis (from the middle of the base to the apex) is directed ventrally and caudally.

·        The base is directed dorsally from 3^rd to 6^th rib and is placed about 10-12 cm below the spine.

·        The apex is directed ventrally and caudally and lies centrally dorsal to the sternum and is attached to the 6^th chondro-sternal joint by pericardiaco-sternal ligament and is very close to the diaphragm.

·        About 5/7 portion of the heart lies on the left side of the median plane, because right lung is conciderably larger in size. 

The heart is considered to have an apex, base, two surfaces and two borders;

Borders:

A. Cranial (right) border

B. Caudal (left) border

           A.  Cranial (right) border:

·        This border is strongly convex and curves ventrally and caudally.

·        The greater part is parallel with the sternum.

B. Caudal (left) border:

·        This border is much shorter and is nearly verticle

Surfaces:

A.    A.   Atrial(right, diaphragmatic) surface

B.    B.  Auricular (left, sterno-costal) surface

• These surfaces are convex and marked by grooves (transverse and longitudinal) which indicate the division of the heart into four chambers, the two atria dorsally and two     ventricles ventrally.

•  The transverse groove which encircles the heart at the base of ventricles demarcates the   separation between the atrium and ventricles.

•  The longitudinal grooves are mainly two in number (left and right) which extends from   the base of the ventricles to the apex. The left one is cranial and the right one is caudal in   position. Both these grooves meet with each other, a little above the apex.

• The left and right longitudinal grooves mark the margin of the interventricular septum.

• There is a small intermediate longitudinal groove which descends from the transverse   groove along the posterior border of the heart.

•  Internally the atria are separated by the interatrial septum.

• The interventricular septum is the partition which separates the cavities of the two  ventricles. It is placed obliquely, so that one surface which is convex, faces craniad and to  the right and bulges into the right ventricle; the other surface, which faces into the left   ventricle, is concave and looks caudad and to the left.

Pericardium

The pericardium is the fibro-serous sac which encloses the heart and in part, the great vessels connected with it. It consists of two layers;

A.    Fibrous layer

B.    Serous layer 

A.       A.  Fibrous layer:

·        Relatively thin, but strong and inelastic.

·        It is attached dorsally to the large vessels at the base of the heart and is continued in part upto the longus coli muscle.

·        It is firmly attached ventrally to the middle of the caudal half of the thoracic surface of the sternum.

B.          B.  Serous layer:

·        It is a close sac, surrounded by the fibrous pericardium and invaginated by the heart.

·        It is smooth and glistening and contains small amount of clear serous fluid, the liquor pericardii, in the pericardial cavity.

It may be regarded as consisting of two parts, parietal and visceral layer;

a.      Parietal layer

b.      Visceral layer

a.      Parietal layer:

·        Lines the fibrous layer, to which it is closely attached. 

b.      Visceral layer:

·        Covers the heart and parts of the great vessels and is, therefore also termed the epicardium.

Structure of the heart

The heart wall consists mainly of peculiar striated muscle, the myocardium, which is covered externally by the visceral part of the serous pericardium, or epicardium, and is lined internally by the endocardium.

1.      The epicardium

2.      The myocardium

3.      The endocardium

1.      The epicardium:

·        The epicardium is, in general, closely associated/attached to the muscular wall, but is loosely attached over the coronary vessels and the associated sub-epicardial fat. 

2.      The myocardium:

·        Consists of planes of fibers arranged in a somewhat complicated manner. The muscular tissue of the atria is almost completely separated from that of the ventricles by the fibrous rings around the atrio-ventricular orifices.

·        In the atria, the muscle bands fall naturally into two groups- superficial and deep. The superficial are common to both atria and the deep are special to each.

·        The superficial or common fibers for the most part begin and end at the atrioventricular rings, but some enter the interatrial septum.

·        The deep or special bundles also forms two sets. Looped fibers pass over the atria from ring to ring, while spiral fibers surround the ends of the veins which open into the atria, the auricles and the oval fossa.

·        The muscular wall of the ventricles is much stronger than that of the atria. The left ventricle is, in general, about three times as thick as that of the right one, but is thin at the apex.

·        The superficial fibers are attached above to the atrioventricular fibrous ring and pass in a spiral towards the apex.

·        The fibers, although they appear to be proper to each ventricle, have almost all been shown to be, in reality, common to both. Their arrangement is scroll-like. They begin on one side, curve around in the wall of that ventricle, then pass in the septum to the opposite side, and curve around the other ventricle. 

3.      The endocardium:

·        Lines the cavities of the heart and is continuous with the internal coat   of the vessels which enter and leave the organ.

·        Its free surface is smooth and glistening and is formed by a layer of endothelial cells.

·        The other surface is thin layer of fibro-elastic tissue, which is connected with the myocardium by a subendocardial elastic tissue containing vessels and nerves.

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