The Topography and Structure of the Heart

THE HEART - Location

3rd to 6th Rib (3rd to 5th ICS)

More or less obliquely oriented

Apex slightly to the left side

Canine heart

Cow heart

More vertical orientation – Small and large Ruminant and Horse

Sternopericardiac ligament

Horse heart

Species differentiation of the heart location

Ruminants - 3rd to 6th Rib, Horse: 2 to 6, Pig 2 to 5 (smaller

The heart: relations

The heart is located within the?

mediastinum

Any pleura that is not covering the lung is…?

is the parietal pleura

The plurae

Visceral pericardium(Epicardium)(2)

is the layer which covers the heart wall

Pericardial cavity(3)

The space between visceral and parietal pericardium, which is essentially a potential space containing small amount of serous fluid

Parietal pericardium(4)

The outer layer which is attached to the mediastinum

Fibrous pericardium(5)

is the third layer, fibrous connective tissue(Modified CT of the mediastinum),

which attaches the parietal pericardium to the mediastinal pleura (mediastinum).

Mediastinal pleura (6)

The outermost layer in this region, note that the fibrous pericardium connects the parietal

pericardium and the mediastinal pleura

Phrenicopericardiac / sternopericardiac ligament (7)

The fibrous pericardium continues as tunica adventitia of the great vessels as they pass through the mediastinum after arising from the base of the heart. It also forms Phrenicopericardiac / sternopericardiac ligament (7) at the apex of the heart

layers of the heart labeled

Function of the pericardium

provides an isolated environment to the heart

The pericardial fluid, though very little, functions as a lubricant

The pericardium prevents overdilation of the heart

The Auricle

a blind sac extended from each atrium is called auricle

The Atrium

Thin-walled chamber that receives blood. Located dorsal

The ventricle

Thick-walled chamber located ventrally that pumps the blood away from the heart

Outer anatomy of the heart

The conus arteriosus

The cone shaped part of the right ventricle where the pulmonary trunk arises from the right ventricle

The Interventricular Grooves

The grooves that demarcate ventricles from each other

Great arteries: Pulmonary trunk

Carries deoxygenated blood to the lungs

Great arteries: Aorta

Oxygenated blood supply to the body

Great veins: Cranial and Caudal vena cava

Collect deoxygenated blood from the body

Great veins: Azygos vein

Collects deoxygenated blood from most of the thoracic wall

Heart wall: Myocardium

Arrangement of the cardiac muscles

Overall reduction in the size of heart and the chambers

Pumping action: Atria → to ventricles, Rt. Ventricle → Lungs, Lt. Ventricle → Body

The cardiac cycle - Rhythmic contractions

Systole (Contraction) of the atria/ventricles.

Diastole (Dilation/ relaxation) of the atria/ventricles.

Unidirectional flow

The right AV Opening

guarded by the tricuspid valve

The Cusps

A roughly triangular leaf or flap of a heart valve

The left Atrium and Ventricle

The Mitral Valve/Left AV Valve

The Aorta and Aortic Valve

The Heart valves and their relationship with the body wall

Coronary arteries - Right (Smaller) and Left

Arise from the bulb (dilated origin) of the aorta

Located in the coronary and interventricular grooves of the heart

Left coronary artery is large in what species?

Canine and ruminants

Right coronary artery is larger in what species?

Horses

Blood supply to the heart

Blood supply to the heart: Arterial supply

Great Coronary Vein(Cardiac Vein)

Venous return/drainage

Major Venous drainage from the heart

coronary sinus is the terminal dilated part

Opens into the right atrium

Sympathetic cardiac nerves

Sympathetic innervation

Stellate (Cervico-thoracic) and Middle cervical ganglia

Parasympathetic cardiac nerves

Parasympathetic innervation Right and left Vagus nerves

Nerve supply to the heart

Vector of heartworm disease

Mosquitoes of Aedes, Anopheles, and Culex are the most common genera acting as vectors

Common species that get heartworm?

Dogs, cats and ferrets are susceptible

Dirofilaria immitis

Where do heartworms reside in the heart?

The adult worms occlude the right side of the heart and the pulmonary trunk/arteries

General implications of heartworm infestation:

Inflammation of the pulmonary vasculature as Live, adult heartworms cause direct mechanical trauma

Dead heartworms leads to more severe vascular reactions and subsequent pathologic changes

Symptoms of heartworm disease

Coughing after exercise

Refusing to exercise or play

Seeming lethargic or weak

Loss of appetite

Unintentional weight loss