The Cardiovascular System

The Cardiovascular System

Heart is the master of the cardiovascular system. It pumps out blood all over the body to circulate and supply oxygen, electrolytes, nutrients and hormones. Blood circulation controls the body temperature, the PH or acid base balance of the body. Circulation fights against infection, helps in clotting of blood during injury and eliminates waste products such as carbon dioxide.

Position

The heart lies in the thoracic cavity at the mediastinum [the space between the lungs]. It lies obliquely a little more to the left than the right. The apex is about 9cm to the left of the midline at the level of the 5th intercostal space and the base extends to the level of the 2nd rib.

Organs associated with the heart

Inferiorly- The apex rest on the central tendon of the diaphragm .

Superiorly- The great vessels in the aorta, superior venacava, pulmonary artery and pulmonary veins.

Posteriorly- Oesophagus ,trachea, left and right bronchus, decending aorta, inferior venacava, and thoracic vertebrae.

Lateraly- The left lung overlaps the left side of the heart.

Anteriorly- The sternum, rib, and intercostal muscles.

Structure

The heart wall is composed of three layers of tissues. Namely

·              Pericardium

·              Myocardium

·              Endocardium.

Pericardium

The pericardium is the outmost layer and is made up of two sacs. The outer sac and inner side

1. Fibrous pericardium –consists of fibrous tissue.

2. Serous pericardium- double layer of serous membrane.

The Fibrous Pericardium continues with the tunica adventitia of the great blood vessels above and is adherent to the diaphragm. It consists of two layers.

·              The outer layer of the serous pericardium is the parietal pericardium

·              The inner layer is visceral pericardium adherent to the heart muscles.

It secretes serous fluid called pericardial fluid. Pericardial fluid present in the space between the visceral and parietal layer, which allow smooth movement of the heart.

Myocardium

The myocardium is composed of specialized cardiac muscles found only in the heart. The Muscle arrangement of the myocardium enable the atria and ventricles to contract in a coordinated and efficient manner. It is also important for electrical activity of the heart.

Endocardium

It lines chambers and valves of the heart. It is a thin, smooth membrane to ensure smooth flow of blood through the heart. It consists of flattened epithelial cells, and it is continuous with the endothelium lining of blood vessels.

The cardiovascular [cardio-heart, vascular-blood vessels] system is divided for descriptive purpose into two main parts.

·               The heart pumping action ensures constant circulation of the blood.

·               The blood vessels which form a lengthy network through which the blood flows.

The lymphatic system is closely connected by both structurally and functionally with a cardiovascular system.

The heart pumps blood in to three anatomically separate systems of blood vessels.

·              The pulmonary circulation

·              The systemic circulation

·              The coronary circulation.

Pulmonary Circulation

The portion of the circulatory system which carries deoxygenated blood away from the right ventricle of the heart, to the lungs and returns oxygenated blood to the left atrium and ventricle of the heart.

Systemic Circulation

Systemic circulation carries oxygenated blood from the left ventricle, through the arteries to the capillaries in the tissues of the body. From the tissue capillaries the deoxygenated blood returns through a system of veins to the right atrium of the heart.

Coronary Circulation

Coronary Circulation is the circulation of blood in the blood vessels that supplies the heart muscles.

The cardiovascular system ensures a continuous flow of blood to all body cells. Heart plays a major role in continual physiological adjustment to maintain an adequate blood supply.

Interior of the heart

The heart is divided into a right and left side by the septum, partition consisting of myocardium covered by endocardium. It subdivided into 4 chambers they are

·              Left atrium.

·              Right atrium

·              Left ventricle

·              Right ventricle.

Right Atrium

Right atrial chamber is located in the upper portion of the right side of the heart which receives blood from all parts of the body by superior and inferior venacava. They are thin less muscular walls and smaller than ventricles.

Left Atrium

Left atrium receives oxygenated blood from the lungs and pumps it down into the left ventricle.

The lower portion of the heart left side of is left ventricle.

Right Ventricle

Deoxygenated blood flows in the right atrium, passes through the tricuspid valve and in to the right ventricle, which pumps the blood up to the lungs by pulmonary artery, through the pulmonary valve.

Left Ventricle

It is larger and more muscular chamber. It pumps and delivers the blood to all parts of the body by a larger artery [aorta] for systemic circulation.

Flow Of Blood Through The Heart

·               The right atrium receives deoxygenated blood from all over the body by superior and inferior venacava.

·               Deoxygenated blood from right atrium passes through right atrioventricular valve to right ventricle.

·               Pulmonary artery collects deoxygenated blood from right ventricle to lungs through pulmonary valve or semilunarvalve.

·              Pulmonary artery is divided in to left and right carries either side of the lungs.

·              In lungs exchange of gases takes place.

·              Oxygenated blood passes through pulmonary veins to the left atrium.

·              In left atrium blood passes through left atrioventricular valve to the left ventricles carries blood from left ventricles through aortic valves.

·              Arteries-Oxygenated blood passes through all parts of the body.

Valves

These are the fibrous flaps of tissues that are present in cardiac chamber, between the arteries chambers and veins. They ensure unidirectional flow and prevent backflow of blood.

They are

Arterioventricular Valve

It is present in every ventricle and atrium.

Tricuspid Valve

The valve lies between the right ventricle and right atrium.

Mitral Valve

It is present between left atrium and left [bicuspid valve] ventricle.

Semilunar Valve

It is present between arteries and ventricles.

Aortic Valve

An aortic valve is present between the aorta and left ventricle.

Pulmonary Valve

Pulmonary valve exists between the pulmonary artery and right ventricle.

Functions of heart

The structure of the heart is primarily responsible for transportation of blood and to supply nutrients to all parts of the body. This continuous activity uplifts the role of the heart as a vital organ.

Blood pumping cycle of the heart is called as cardiac cycle, which ensure that the blood is distributed throughout the body. The oxygen distribution process begins when oxygen –free blood (impure) enters in to the heart through the right atrium goes in to the right ventricle, enters the lungs for oxygenation and release of carbondi-oxide and transfers in to left atrial chambers, ready for re-distribution. About 5-6 liters of blood circulates in the body and cardiac cycles are completed per minute.

Oxygen reloading process occur in two phase. The systole is a short period that occurs, when the tricuspid and mitral valve close.

The diastole is a relatively longer period when the aortic and pulmonary valve close. The systole –disastole relationship is the mean blood pressure. Other ways of physically determining the regular functioning of the heart is through examining the pulse rate.

Circulatory System

In the fig - 1.6 shows Red color indicates oxygenated blood carried in arteries. Blue indicates deoxygenated blood carried in veins.

The relationship between the heart and different types of blood vessels.

Heart

·              Aorta

·              Arteries

·              Arterioles

·              Capillaries

·              Venules

·              Veins

·              Venacava

·              Heart

Arteries

Arteries are the blood vessels that carries oxygenated blood through out the body. Arteries consists of several layers and smooth muscles that enable them to pump blood throughout the body after it leaves the heart.

ARTERIES - It has three layers

·              Tunica adventica

·              Tunica media

·              Tunica intima

Arterioles

Blood valve that receives blood from the arteries. Those are present next to the arteries and before the capillaries. Arterioles also have smooth muscles.

Capillaries

These are the smallest structure of the circulatory system. The point at which the exchange of oxygen and corbon di-oxide occurs through the thin walls of the capillaries.

Venules

Blood vessels that receive blood from the capillaries and transport deoxygenated blood to the veins.

Veins

Veins are blood vessels that carry blood towards the heart. Blood vessels receive blood from the venules and transport blood back to the heart. Like arteries, veins, have three layers.

Blood Components

Blood is a body fluid that consists of:

·              Plasma

·              Red Blood Cells

·              White Blood Cells

·              Platelets

Plasma

Plasma in blood is over 50% of the volume of blood and over 90% of plasma is water. The main component of plasma is plasma albumin which is a protein that enables and controls the osmotic pressure of the blood.

Red Blood Cells (RBC)

Red blood cells or erythrocytes are disc like in shape. RBCs are enucleated, do not contain a nucleus. The red blood cells contain iron laden haemoglobin which carries oxygen to the cells. Red blood cells also contain glycoproteins which determine the blood group of an individual. The blood types are type A, type B, type AB and type O.

White Blood Cells

White blood cells or leukocytes are part of the immune system which fights against infections from pathogens. When the white blood cell count rises, it is a sign of infection. All leukocytes have a distinct nucleus.

The various types of white blood cells are:

·              Eosinophils

·              Basophils

·              Neutrophils

·              Lymphocytes

·              Monocytes

Platelets

Platelets or thrombocytes(do not have nucleus) maintain haemostasis (clotting). Haemostasis is enabled by the coagulation or thickening of blood by production of fibrin from the clotting factors found within the platelets to prevent blood loss, when a blood vessel has been broken due to injury.

Lymphatic system

The lymphatic subsystem, a part of the circulatory system, is closely aligned with the body’s immune system and removes excessive fluid from the body. The lymphatic vessels contain lymph including lymphocytes. Lymphatic system also consists of lymph nodes and lymphatic organs. These organs include the thymus gland, spleen, bone marrow and tonsils. Nodes are found throughout the lymphatic system and they serve to filter the blood as it travels throughout the body. Swollen lymph nodes are a signal of a disease or an infection. Many lymph nodes are found in the neck area, under the arms and in the groin area, although there are hundreds of them throughout the body.

Spleen

Spleen is an organ present in the upper left part of the abdomen and to the left side of the stomach. The spleen plays multiple supporting roles in the body. It acts as a filter for blood as part of the immune system. Old red blood cells are recycled in the spleen, platelets and white bloods are stored.

Diseases related to blood and blood vessels

·              Phlebitis

·              Deep Vein Thrombosis (DVT)

·              Anaemia, including pernicious anaemia and sickle cell anaemia

·              Leukaemia

·              Lymphoma

·               Thrombocytopenia.