Lecture Notes in Human Anatomy - Hryhorieva O.A., Svitlytskyi A.O. 2020

The Study of Viscera (splanchnologia)
Anatomy of Internal Organs
The vascular system. Vessel classification. The heart and arteries, developmental variants and anomalies. Veins. Portocaval and cavacaval anastomoses. Structure of the lymphatic system. Structure and functions of immune system organs. Modern instrumental methods for cardiovascular system research

Lecture Outline:

1. General structural plan of The Cardiovascular system.

2. Circulatory system.

3. Anatomy of the Heart.

4. Structure of Blood vessels.

5. Anatomy of The Lymphatic system.

The circulatory system consists of a central organ—The Heart—and connected Blood Vessels. Blood travels to the body's Tissues and Organs through blood vessels, which form a single closed system. Blood movement through the vessels is driven by heart contractions; the heart, through its rhythmic contractions, forces blood to circulate.

The heart is a four-chambered, hollow muscular organ of conical shape, weighing 250-300 g. It is located between the Lungs in the so-called Mediastinum. It lies asymmetrically: 2/3 of its mass is situated to the left and 1/3 to the right of the anterior median line. The longitudinal axis of the heart runs from top to bottom, from right to left, and from back to front. The upper border of the heart extends along the cartilages of the third Ribs; the right border runs from the middle of the Cartilage of the 3rd right rib to the middle of the cartilage of the 5th right rib; the left border extends from the middle of the cartilage of the 3rd left rib to the 6th left rib; and the lower border runs from the middle of the cartilage of the 5th right rib to the 6th left rib. The heart features a base facing upward, backward, and to the right; a rounded apex directed downward, forward, and to the left of the anterior median line; and three surfaces: sternocostal, pulmonary, and diaphragmatic. Externally, the heart is covered by the Pericardium, a serous sac that forms a closed enclosure. It consists of two layers: an outer fibrous layer and an inner serous layer. The fibrous layer transitions into the outer Sheath of the great Vessels of the heart and forms Connective Tissue strands that anchor the pericardium to the inner surface of the Sternum. The inner serous layer is divided into two leaves: the visceral leaf (epicardium) and the parietal leaf, which is closely fused with the inner surface of the outer fibrous layer and lines it from within. Between the visceral and parietal leaves lies a slit-like serous pericardial cavity filled with a small amount of serous fluid, which reduces friction during heart activity. The Middle layer of the heart wall is the muscular layer, or myocardium. The myocardium is a network of mononuclear Cells known as cardiomyocytes. The third (inner) layer of the heart lines the inner surface of the heart chambers and is called the endocardium; it consists of a layer of Connective tissue with elastic fibers and smooth Muscle cells.

The human heart is divided by a longitudinal septum into left and right halves. The right half receives deoxygenated blood, while the left receives oxygenated blood; this septum has no openings, and under normal conditions, oxygenated and deoxygenated blood do not mix. Each half is subdivided into an atrium (upper chamber) and a ventricle (lower chamber). The atrium and ventricle of each heart half communicate through the atrioventricular opening. The endocardium forms folds in the region of these openings, known as Valves. The right atrioventricular valve has three cusps (tricuspid valve), and the left atrioventricular valve has two cusps, known as the mitral valve.

The right atrium receives the SUPERIOR VENA CAVA, the INFERIOR VENA CAVA, the coronary sinus (which collects blood from the heart wall), and small cardiac Veins. Its anterosuperior wall features an additional pouch called the right auricle. During systole, blood flows from the right atrium through the atrioventricular opening into the right ventricle. The tricuspid (right) atrioventricular valve directs blood flow and prevents its backflow during ventricular systole.

On the inner surface of the right ventricle, there are cone-shaped projections called papillary Muscles, to which the free margin of the tricuspid valve attaches, preventing it from everting toward the atrium during systole. The pulmonary trunk emerges from the right ventricle, carrying deoxygenated blood from the heart to the lungs. At the Water/144.html">Origin of the pulmonary trunk lies a semilunar tricuspid valve formed like pocket-like cusps, which prevents the backflow of blood into the ventricle.

The left atrium receives four Pulmonary veins, which bring oxygenated blood from the lungs. Its anterosuperior wall features an additional pouch called the left auricle.

The structure of the left ventricle is similar to that of the right; it also contains papillary muscles to which the free margin of the bicuspid (mitral) valve attaches, preventing it from everting toward the atrium during systole. The aorta emerges from the left ventricle, and its opening is similarly guarded by a semilunar tricuspid valve.

An essential role in the rhythmic activity of the heart is played by the cardiac conduction system, which generates the heart's rhythm and distributes it throughout the heart; it consists of two nodes and two bundles. The nodes include: the sinoatrial node, located between the superior vena cava and the right auricle, which is responsible for the synchronous contraction of the atria; and the atrioventricular node, located near the septal cusp, which is responsible for the synchronous contraction of the ventricles. The bundles include: the sinoatrial bundle, which transmits impulses from the sinoatrial node to the atrioventricular node; and the atrioventricular bundle (bundle of His), which runs along the interventricular septum and divides into right and left branches that course beneath the endocardium into the ventricular myocardium, ensuring their rhythmic contraction.

Blood supply to the heart is provided by Branches of the right and left coronary Arteries, which arise from the aorta immediately distal to the semilunar valve.

The pathway through which blood leaves the heart via arterial vessels and returns to the heart via venous vessels is called a circuit of Blood Circulation.

There are two main circuits:

- The systemic (greater) circulation, which supplies blood to all organs and Tissues of the body. The systemic circulation begins in the left ventricle of the heart, from which blood enters the aorta, branching successively into arteries, arterioles, and capillaries. Through the capillary walls, metabolic exchange takes place between the blood and body tissues—oxygen and nutrients pass into the tissues, while carbon dioxide and Metabolic waste products enter the blood;

- The pulmonary (lesser) circulation, in which gas exchange occurs between alveolar air and deoxygenated blood. The Pulmonary Circulation begins in the right ventricle; deoxygenated blood flows from it into the pulmonary trunk, which divides into the right and left pulmonary arteries, each carrying blood to the corresponding lung and branching into arterioles and capillaries that form a dense network around the alveoli. Gas exchange takes place between the capillary deoxygenated blood and alveolar air: carbon dioxide diffuses from the pulmonary capillaries into the alveoli, and oxygen passes from the alveoli into the blood. The pulmonary capillaries converge into veins—two pulmonary veins emerge from each lung and empty into the left atrium.

Blood vessels are classified into arteries, arterioles, capillaries, and veins.

Arteries are vessels that carry blood away from the heart. The general distribution patterns of arteries in the body are as follows:

- arteries correspond to the Skeletal structure;

- arteries are located correspondingly (parallel) to nerve trunks, forming neurovascular bundles;

- arteries are accompanied by veins: large arteries by a single vein, and medium and small arteries by two veins (arterial pulsation assists venous blood flow);

- arteries are accompanied by lymphatic vessels.

The walls of the arteries consist of three layers: inner, middle, and outer. The inner layer is formed by flat endothelial cells and is smooth and even, which prevents blood clot formation. The middle layer is made up of smooth muscles and elastic fibers that form two sub-layers—an inner circular layer and an outer longitudinal layer. When these muscles contract under METABOLISM/18.html">The Influence of nerve impulses, the lumen of the blood vessel changes. The outer layer is built of fibrous and connective tissue, housing blood Vessels and nerves.

Veins are the vessels through which blood flows back to the heart; they act as transport conduits. The walls of veins have the same structure as arterial walls, but they are significantly thinner and almost completely lack elastic fibers, causing them to collapse easily. The inner lining of many veins features pocket-like valves that prevent the backward flow of blood. Blood movement through veins is driven by heart contractions, the suction action of The Heart and thoracic cavity (due to negative pressure in the chest), as well as the contractions of skeletal muscles.

Capillaries perform an exchange function: through their walls, oxygen and nutrients pass from the blood into the tissues, while waste products and carbon dioxide pass from the tissues into the blood. The Capillary Wall is extremely thin, consisting of a single layer of endothelial cells and a basement membrane. When an organ is in a relatively inactive state, a portion of the capillaries supplying it with blood remains dormant; however, during heightened organ activity, its blood supply increases.

The lymphatic system is an integral part of the Vascular System, serving as an auxiliary drainage pathway for fluid returning from organs and tissues. It consists of lymphatic pathways and lymphoid organs. The pathways through which Lymph moves include lymphatic capillaries, lymphatic vessels, lymphatic trunks, and lymphatic ducts. The lymphoid organs comprise lymphoid structures within the mucous membranes of Internal Organs, Lymph Nodes, and the Spleen. The lymphatic system is an open system, meaning lymph flows in only one direction—toward the heart. Lymphatic capillaries originate blindly in the tissues and empty into lymphatic vessels. Small lymphatic vessels merge into trunks, and subsequently into ducts, eventually converging into two main trunks: the Thoracic duct and the Right lymphatic duct. Lymph nodes are located along the course of lymphatic vessels, numbering around 400 in The Human Body. They are bean-shaped, pinkish-gray in color, and measure 1–22 mm in size. Each node is covered externally by a connective tissue capsule containing smooth muscle fibers, the contraction of which facilitates lymph drainage and regulates its flow. Trabeculae extend inward from the capsule, carrying blood vessels and nerves. The framework of the node consists of lymphoid tissue permeated by a network of spaces known as lymph sinuses. Lymph nodes are sites of lymphocyte production and act as mechanical and biological barriers for the body, filtering out and destroying 99% of all microbes. While some lymph nodes are solitary, they typically occur in groups draining specific body regions or organs; such nodes are referred to as regional.

All lymph nodes are classified into superficial and deep groups. Deep nodes are generally located along major blood vessels or near internal organs, whereas superficial nodes lie subcutaneously and are named according to their anatomical Location (e.g., axillary nodes).