Anatomy and Function of the Heart and Blood Vessels, Study notes of Cardiology

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The Heart & Blood Vessels

Dr. Ali Ebneshahidi

Functions of Heart and blood Vessels

1. The heart is an essential pumping organ in the cardiovascular system where the right heart pumps deoxygenated blood (returned from body tissues) to the lungs for gas exchange, while the left heart pumps oxygenated blood (returned from the lungs) to tissue cells for sustaining cellular respiration.
2. Attached to the heart is blood vessels that transport blood in various circulation pathways:

Pulmonary blood vessels transport blood between the heart and the lungs.

Systemic blood vessels transport blood between the heart and body tissues.

4. Pericardium: membranous sacs that surround the heart and hold

it in the mediastinum. It consists of an outer layer called fibrous pericardium (made of fibrous connective tissue) and an inner layer called serous pericardium (serous membrane). serous pericardium is subdivided into a parietal pericardium (lining the wall of mediastinum) and a visceral pericardium (covering the surface of the heart). Between these two layers is a space called pericardial cavity which is filled with the pericardial fluid to reduce friction.

5. Heart wall

a) Three layers of tissues forming the walls of heart and creating the heart chambers and heart valves inside.

b) Epicardium is the outermost layer, and is the same as the visceral pericardium (the innermost tissue of pericardium).

c) Myocardium is the middle, and thickest layer; composed of cardiac muscle which contains specialized structures such as intercalated disks that allow this layer to function a unit.

d) Endocardium is the innermost layer, made of endothelial and connective tissues that not only forms the inner lining of the heart chambers, also forms the heart valves and extends outward to become the endothelium tissue of blood vessels. It also contains specialized nerve like muscle fibers called purkinje fibers to activate heart actions.

6. Heart chambers: hollow cavities within the heart for containing blood.

• Two smaller chambers called atrium are near the base, and two larger chambers called ventricle are close to the apex.
• Right Atrium (RA) after receiving deoxygenated blood from body tissues through the superior and inferior vena cava, pumps the blood into the Right Ventricle (RV) via the tight atrioventricular orifice.

7. Heart valves : Extensions of endocardium for preventing back flow of blood into heart chambers.

• Two heart valves located between atria and ventricles are called atrio- ventricular valves (AV valves) which include the tricuspid valve between RA and RV, and bicuspid valve (mitral valve) between LA and LV.
• Two heart valves located at the exiting arteries are called semilunar valves (SL valves) which include the pulmonic semilunar valve at the base of pulmonary trunk, and the aortic semilunar valve at the base of aorta.
• Each AV valve consists of cusps (extensions of endocardium), chordae tendineae, and papillary muscles (the later two are designed to prevent eversion of the cusps into the atria).
• Each SL valve only consists of 3 half- moon shaped cusps extended directly from endocardium.

• Heart valves open and close in response to pressure changes in heart chambers - when the atria are full, AV valves open due to lesser pressure in ventricles; when the ventricles are full, AV valves close and SL valves open due to lesser pressure in atria and exiting arteries.
• AV valves prevent backflow into atria, while SL valves prevent backflow into ventricles.

Intrinsic Control

In extrinsic control, pressure receptors along the aorta and common carotid arteries detect changes in blood pressure and send nerve impulses to the cardiac centers in medulla oblongata, which in turn activates either sympathetic nerves (to increase heart rate and contractility) or parasympathetic nerves (to decrease heart rate and contractility). These nerves innervate the SA node, changing the basic rhythm in cardiac action. Hormones such as epinephrine and norepinephrine can also have the same stimulatory effect on the SA node. ebneshahidi