Blood Volume, Properties and Components

Blood Volume and Properties

• Males typically have a blood volume of 5-6 liters.
• Females typically have a blood volume of 4-5 liters.
• Blood temperature is about 38°C (100.4°F).
• The pH of blood is slightly alkaline (7.35-7.45).
• Blood is a liquid connective tissue that is thicker and slightly stickier than water.

Functions of Blood

• Blood transports oxygen, carbon dioxide, nutrients, hormones, and waste products.
• Blood regulates pH, body temperature, and osmotic pressure.
• Blood provides clotting mechanisms, immune cells and proteins for protection.

Components of Blood

• Blood plasma consists of 91.5% water and 8.5% solutes, including proteins like albumin and fibrinogen, which help maintain osmotic balance.
• Red blood cells (RBCs/Erythrocytes) have a biconcave disc shape to maximize surface area for oxygen exchange.
• Red blood cells lack a nucleus and mitochondria, and their lifespan is about 120 days.
• Males average 5.4 million RBCs/µL, while females average 4.8 million RBCs/µL.
• Red blood cells contain hemoglobin, which is a protein with four polypeptide chains, each with a heme group that binds oxygen.
• White blood cells (WBCs/Leukocytes) are divided into granular (neutrophils, eosinophils, basophils) and agranular (lymphocytes, monocytes) types.
• Neutrophils are common phagocytes.
• Lymphocytes include B cells (antibody production), T cells (cell-mediated immunity), and NK cells (tumor/infected cell destruction).
• Leukocytosis (increased WBC count) is a normal response to stress/infection, while leukopenia is harmful.
• Platelets (Thrombocytes) are small cell fragments produced by megakaryocyte fragmentation.
• Platelets are essential for hemostasis, aggregating to form plugs and initiating the clotting cascade with a short lifespan of only 5–9 days.

Additional Blood Concepts

• Polycythemia is an abnormally high percentage of RBCs, increasing blood viscosity and may impede flow.
• Erythropoietin (EPO) stimulates RBC production (erythropoiesis).
• Thrombopoietin (TPO) stimulates platelet production.
• Blood groups are based on A and B antigens (and the Rh factor).
• Type A blood has antigen A and contains anti-B antibodies.
• Type B blood has antigen B and contains anti-A antibodies.
• Type AB blood has both antigens, making it a universal recipient.
• Type O blood lacks both antigens, making it a universal donor.

Heart Anatomy and Orientation

• The heart resides in the mediastinum, between the lungs, extending from the sternum to the vertebral column.
• The apex is the inferior, leftward-pointing tip resting on the diaphragm.
• The base is the superior surface of the heart.
• The atria (upper chambers) receive blood.
• The ventricles (lower chambers) pump blood out.
• The interatrial and interventricular septa separate the left and right sides of the heart.
• Atrioventricular valves (Tricuspid on the right and Mitral/Bicuspid on the left) open during atrial contraction and close during ventricular systole.
• Semilunar valves (Pulmonary on the right and Aortic on the left) prevent backflow during ventricular relaxation.

Blood Flow and Circulatory Routes

• In systemic circulation, blood flows from the left atrium → Mitral valve → Left ventricle → Aortic valve → Aorta → Body tissues → Superior/Inferior vena cava → Right atrium.
• Systemic circulation transports oxygenated blood to the body.
• In pulmonary circulation, blood flows from the right atrium → Tricuspid valve → Right ventricle → Pulmonary valve → Pulmonary trunk → Pulmonary arteries → Lungs (oxygenation) → Pulmonary veins → Left atrium.
• Pulmonary circulation transports deoxygenated blood to the lungs and returns oxygenated blood.

Layers of the Heart Wall and Pericardium

• The heart wall layers include the epicardium (outermost protective layer), myocardium (thick, muscular middle layer, 95% cardiac muscle), and endocardium (smooth, innermost lining that minimizes friction).
• The pericardium is a double-layered membrane with a fibrous pericardium (outer, tough layer) and a serous pericardium (inner, with parietal and visceral layers).
• The pericardial cavity between pericardium layers contains lubricating fluid.

Cardiac Conduction and Regulation

• The conduction system starts at the Sinoatrial (SA) Node (the natural pacemaker in the right atrium), passes to the Atrioventricular (AV) Node, then through the Bundle of His, bundle branches, and finally through Purkinje fibers to stimulate ventricular contraction.
• The autonomic nervous system regulates heart function, with epinephrine increasing heart rate and contractility, and acetylcholine decreasing heart rate.
• Hormonal effects: Thyroid hormones modulate rate and strength of contraction.
• Cardiac output is calculated by the formula: Cardiac Output = Stroke Volume × Heart Rate.
• Regulation depends on preload (degree of stretch), contractility, and afterload (pressure to overcome).

Clinical Terms and Conditions

• Valve disorders include stenosis (narrowing of a valve restricting blood flow, e.g., mitral stenosis) and mitral valve prolapse (incomplete closure of the mitral valve).
• Congestive heart failure describes a loss of pumping efficiency.
• Left ventricle failure often leads to pulmonary edema, while right ventricle failure often leads to peripheral edema.
• Auscultation: Heart sounds ("Lubb" = closure of atrioventricular valves; "Dupp" = closure of semilunar valves) are used to assess valve function.
• Congenital defects, for example, a patent foramen ovale or Tetralogy of Fallot ("blue baby") affect normal blood flow.

Types and Structure of Blood Vessels

• Arteries carry blood away from the heart and typically have thick, muscular walls (tunica media) for withstanding high pressure.
• Veins return blood to the heart, and have thinner walls, larger lumens, and valves to prevent backflow.
• Capillaries are where the exchange of gases, nutrients, and waste occurs.

Hemodynamics and Vascular Resistance

• Vascular resistance factors include lumen size (vasoconstriction increases resistance), blood viscosity (thicker blood increases resistance), and vessel length (longer vessels create more friction).
• Blood pressure is measured typically at the brachial artery using a sphygmomanometer.

Korotkoff Sounds and Shock

• Korotkoff sounds: the first audible sound marks systolic pressure, and the disappearance of sound marks diastolic pressure.
• Shock is a state where the cardiovascular system fails to deliver sufficient oxygen and nutrients.
• Shock types include hypovolemic (low blood volume), cardiogenic (poor heart pump), vascular (excessive vasodilation), and obstructive (blockage in circulation).

Aorta Branches and Venous Circulation

• The ascending aorta gives off the coronary arteries.
• The arch of the aorta branches into the brachiocephalic trunk, common carotid, and subclavian arteries.
• Venous circulation involves the superior and inferior vena cava returning deoxygenated blood to the right atrium.
• Specific veins (e.g., coronary sinus, jugular veins) drain defined regions of the body.