1 The Cardiovascular system

2  The cardiovascular system includes: - heart - blood vessels  Performs the function of pumping and carrying blood to the rest of the body. The cardiovascular system

3 The Heart -The heart is the central organ of the thorax - In the dog, the heart lies caudoventrally between the third and seventh ribs and slightly to the left. - In the horse, the heart lies dorsalventraly between the third and sixth ribs and slightly to the left.

4 Pericardium- the fibroserous sac enclosing the heart, composed of: A. fibrous pericardium B. serous pericardium - and covered by the pericardial mediastinal pleura

5 A. Fibrous pericardium- tough, fibrous sac surrounding the serous pericardium, the heart and pericardial cavity

6 B. Serous pericardium - a serous membrane forming a closed cavity, composed of : 1. Parietal layer of Serous pericardium - lines the inner surface of the fibrous pericardium

7 B. Serous pericardium- cont. 2. Visceral layer of Serous pericardium - covers the myocardium of heart also called: epicardium

8 C. pericardial cavity: potential space between the visceral and parietal layers of serous pericardium contains ~ 1 ml of serous fluid that acts as a lubricant

9 the pericardial mediastinal pleura covers the fibrous pericardium

11 Structure  The heart is roughly conical with the base being dorsal and the apex close to the sternum opposite the sixth costal cartilage.

12 Structure - The base is formed by the thin walled atria which are clearly separated from the ventricles by an encircling coronary groove - coronary groove contains the main coronary vessels.

13 General anatomy of the heart In the adult it consists of four chambers: 1.Right atrium 2.Left atrium 3.Right ventricle 4.Left ventricle

14 - The ventricles constitute a much larger part of the heart which is much firmer than the atria due to muscular walls - The left being much thicker than the right. - The right ventricle lies as much cranially as to the right of the left ventricle. Structure

15 Right atrium The caudal vena cava enters the chamber above the opening of the coronary sinus. The cranial vena cava opens at the terminal crest. The intervenous tubercle separates the two caval openings preventing confrontation between the two streams. - The right azygous vein enters dorsally.

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17 Caudal to the tubercle lies the fossa ovalis which corresponds to the foramen ovale of fetal life. Caudal to the tubercle lies the fossa ovalis which corresponds to the foramen ovale of fetal life. The right auricle is a blind-ended sac extending to the cranial face of the pulmonary trunk. The right auricle is a blind-ended sac extending to the cranial face of the pulmonary trunk. Pectinate muscles within the auricle branch from the terminal crest which marks the boundary between the auricle and the main atrium. Pectinate muscles within the auricle branch from the terminal crest which marks the boundary between the auricle and the main atrium. Right atrium

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19 Left atrium Similar form to the right atrium. Receives pulmonary veins which enter at two or three sites. Auricle similar to right.

20 Right ventricle Receives blood from right atrium through right atrioventricular valve (tricuspid). Cusps are joined by fibrous Chordae Tendinae which attach to papillary muscles on ventricular wall.

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22  Lumen of ventricle crossed by septomarginalis trabecula (muscle band extend from septum to lateral wall).  Blood flows through semilunar pulmonary valve to pulmonary trunk. Right ventricle

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24 Left ventricle  Left atrioventricular valve is bicuspid and much larger and stronger than the right.  The ventricular wall is much thicker than on the right due to high resistance of the systemic circulation.  Blood leaves the ventricle via the semilunar aortic valve into the aorta.

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27 Cardiac vessels The heart tissue receives 15% of the cardiac output from the left ventricle. This travels in two arteries from sinuses just above the aortic valve.

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29 The coronary veins –Blood returns to the heart via the cardiac vein. –This opens into the the right atrium via the coronary sinus just below the entrance of the caudal vena cava.

30 Systemic circulation The systemic arteries: The aortic arch The origin of the aorta is similar to that of the pulmonary trunk but is from the left ventricle.

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Arteries and Veins Cranial to the Heart 1. Brachiocephalic trunk- 1st branch from the aortic arch, gives rise to: (2) left common carotid artery and terminates as the (3)right common carotid artery and (4) right subclavian artery 5. left subclavian artery- originates from aortic arch beyond the brachiocephalic trunk dog-dorsal view Cow Horse I. Arteries- Branches of the Aortic Arch B. Horse and Ruminant: 1. Brachiocephalic trunk- only branch from the aortic arch. (2) left and (3) right common carotid arteries do not arise separately as in dog, but from a (6)common bicarotid trunk A. Dog heart Dog-ventral view

33  The common carotid arteries supply structures of the head.  The subclavian artery supplies blood to the forelimb and to structures of the neck and cerviocothoracic junction.  It winds around the cranial border of the first rib to enter the limb through the axilla,it changes its name to axillary at this point.

34 The subclavin detaches four branches in its intrathoracic course: 1.The vertebral artery 1.The costocervical trunk 1.The internal thoracic artery 1.The superficial cervical artery

35 The thoracic aorta The thoracic aorta runs caudally below the roof of the thorax to enter the abdomen by the aortic hiatus of the diaphragm. It continues as the abdominal aorta in company with the azygous vein and thoracic duct.

36 The systemic veins  The systemic veins return blood to the heart through the cranial vena cava, caudal vena cava and coronary sinus.  The cranial vena cava : - is formed close to the entrance to the chest by the union of the external jugular and subclavian veins.

37  The caudal vena cava: - is formed on the abdomen near the pelvic inlet, by the union of right and left common iliac veins. The systemic veins

Diaphragm Diaphragm consists of contractile skeletal muscle, innervated by phrenic nerve Openings in Diaphragm: 1. Aortic hiatus-(hiatus- term for gap, cleft, or opening)- dorsal part of diaphragm, passage of aorta, azygos, and thoracic duct 2. Esophageal hiatus- centrally located and ventral to aortic hiatus, passage of esophagus 3. Caval foramen- to right\ventral of esophageal hiatus, passage of caudal vena cava dog