Body Fluids and Circulation

 Chapter 3

Body Fluids and Circulation Introduction Different types of fluids are present in different cavities in human body. There are two types of fluids present in human body: 1. Intracellular fluid 2. Extracellular fluid 1. Intracellular fluid: The fluid which is present inside cells is called as intracellular fluid (ICF). 2. Extracellular fluid: The fluid which is present outside cells is called as extracellular fluid (ECF). The ECF fluid which is present in small spaces between cells of tissues is known as interstitial fluid. ECF differs depending on its location in the body: (a) Blood plasma: It is the ECF within blood vessels. (b) Lymph: It is the ECF present in within lymphatic vessels. (c) Cerebrospinal fluid: It is the ECF present in and around the brain and spinal cord. (d) Synovial fluid: It is the ECF in joints. Cardiovascular system All cells of our body require continuous supply of nutrients and oxygen for cellular activities. They also require system to remove waste products formed during various activities. Most of the body cells are located at some distance from the nutrient sources such as the digestive tract and sites of waste disposal such as kidneys. Cardiovascular system plays an important role in these activities. It connects different systems in body through network of blood vessels and blood. The cardiovascular system which consists of: 1. Blood 2. The heart 3. Blood vessels Blood Blood is a connective tissue composed of a blood plasma and different types of cells and cell fragments. Composition of Blood: Blood is composed of two components: 1. Blood plasma 2. Formed elements 1. Blood plasma: • Blood plasma is a liquid extracellular matrix mainly consisting of water and dissolved substances. • Blood consists of 55% blood plasma. • Blood plasma is composed of about 91.5% water and 8.5% solutes. • The solutes are mainly proteins (7%) and others like gases, nutrients, waste products, electrolytes (1.5%). 2. Formed elements: • Formed elements are various types of cells and cell fragments. • Blood contains about 45% formed elements. • Normally, more than 99% of the formed elements are cells named for their red color, red blood cells (RBCs) and Pale, colorless white blood cells (WBCs) and platelets which are cell fragments and occupy less than 1% of the formed elements. Process of Blood (Clotting) Coagulation: Blood clotting is a complex cascade of enzymatic reactions in which each clotting factor activates many molecules of the next one in a fixed sequence. Finally, a large quantity of product (the insoluble protein fibrin) is formed. 1. Two pathways, called the extrinsic pathway and the intrinsic pathway, lead to the formation of prothrombinase. 2. Once prothrombinase is formed, the steps involved in the next two stages of clotting are the same for both the extrinsic and intrinsic pathways, and together these two stages are referred to as the common pathway. Prothrombinase converts prothrombin (a plasma protein formed by the liver) into the enzyme thrombin. 3. Thrombin converts soluble fibrin open (another plasma protein formed by the liver) into insoluble fibrin. Fibrin forms the threads of the clot. Structure of Human Heart Heart is an important organ of cardiovascular system. It acts like a pump, which is responsible for circulating blood to all body parts. The shape of heart is just like our closed fist. Dimensions of heart are as follows: • Length: 12 cm • Width: 9 cm at its broadest point, and • Thickness: 6 cm Weight: 250 g in adult females and 300 p in adult males. • Location: The heart is located in a space between two lungs of thoracic cavity called mediastinum. The heart is surrounded by its own cavity called as pericardial cavity. Human Circulatory System: • Heart circulates blood in two circuits called pulmonary and systemic circulations. • The left side of heart is for systemic circulation and right side for pulmonary circulation. • The rapt atrium receives systemic blood relatively low in oxygen (deoxygenated) from various body parts. • This deoxygenated in right atrium is transferred to the right ventricle, which pumps it into the lungs for addition of oxygen and removal of carbon dioxide. • Exchange of oxygen and carbon dioxide occurs in the lungs, and blood high in oxygen (oxygenated) returns to the left atrium. This oxygenated blood is transferred to left ventricle, which in turn pumps it into the aorta and to all body parts Blood Vessels Blood vessels have important function of distributing blood from heart to different tissues and also returns it to heart. There are five main types of blood vessels: 1. Arteries 2. Arterioles 3. Capillaries 4. Venules 5. Veins • The blood vessels which carry blood away from the heart to other orphans are called as arteries. They leave the heart and divide into medium sized, muscular arteries that branch out into the various regions of the body. • Medium sized arteries then split into small arteries, which in turn split into still smaller arteries called arterioles. • As the arterioles enter a tissue, they branch into numerous minute vessels called capillaries. • Groups of capillaries within a tissue reunite to form small veins called venules. • These in turn merge to form progressively larger blood vessels called veins. • Veins are the blood vessels that convey blood from the tissues back to the heart. Structure: The wall of a blood vessel consists of three layers, also called as tunics. The three structural layers are: 1. The innermost layer is called as tunica interna. It is made up of epithelial tissue. 2. The middle layer is called as tunica media. It is made up of smooth muscles. CARDIAC CYCLE • The period of time that begins with contraction of the atria and ends with ventricular relaxation is known as the cardiac cycle. • The phase of contraction that the heart undergoes while it pumps blood into circulation is called systole. Cardiac Output (CO) Cardiac output is the volume of blood ejected from the left ventricle (or the right ventricle) into the aorta (or pulmonary trunk) each minute. Cardiac output equals the stroke volume (SV), the volume of blood ejected by the ventricle during each contraction, multiplied by the heart rate (HR), the number of heart beats per minute: 1. The P wave, 2. The QRS complex, and 3. The T wave. • The small P wave represents the depolarization of the atria. • The atria begin contracting approximately 25 MS after the start of the P wave. • The large QRS complex represents the depolarization of the ventricles, which requires a much stronger electrical signal because of the larger size of the ventricular cardiac muscle. The ventricles begin to contract as the QRS reaches the peak of the R wave. • Lastly, the T wave represents the repolarization of the ventricles. • The repolarization of the atria occurs during the QRS complex, which masks it on an ECG.