Blood (Chapter 16)

Components of Blood

Blood is a specialized connective tissue composed of plasma and formed elements. Understanding its composition is essential for grasping its functions in transport, regulation, and protection.

• Plasma: The liquid matrix of blood, making up about 55% of total blood volume. It consists of water (90%), proteins (albumin, globulins, fibrinogen), electrolytes, nutrients, gases, hormones, and waste products.

• Functions of Plasma: Maintains osmotic balance, transports substances, and aids in clotting and immune responses.

• Formed Elements: Cellular components including erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets).

• Hematocrit: The percentage of blood volume occupied by erythrocytes; normal range is 40-45%.

• Buffy Coat: Thin layer between plasma and erythrocytes containing leukocytes and platelets.

Erythrocytes (Red Blood Cells)

Erythrocytes are the most numerous formed elements, specialized for oxygen transport.

• Shape: Biconcave discs, increasing surface area for gas exchange and flexibility for passage through capillaries.

• Function: Transport oxygen via hemoglobin and assist in carbon dioxide transport.

• Hemoglobin: A protein with four heme groups, each binding one O2 molecule. Chemical structure allows reversible binding of oxygen.

• Erythropoiesis: Formation of erythrocytes, stimulated by erythropoietin (EPO) from the kidneys in response to hypoxia. Occurs in red bone marrow.

• Breakdown/Recycling: RBCs are broken down in the spleen and liver. Iron is recycled, globin is broken into amino acids, and heme is converted to bilirubin.

• Abnormal Conditions: Anemias (low RBCs or hemoglobin), polycythemia (excess RBCs), hypoxia (low oxygen).

Blood Types

Blood types are determined by antigens on RBC surfaces and corresponding antibodies in plasma.

• ABO Blood Types: Type A (A antigen, anti-B antibody), Type B (B antigen, anti-A antibody), Type AB (A and B antigens, no antibodies), Type O (no antigens, both anti-A and anti-B antibodies).

• Rh Factor: Presence (+) or absence (−) of Rh antigen. Concern arises in pregnancy if mother is Rh− and fetus is Rh+.

Leukocytes (White Blood Cells)

Leukocytes are immune cells with diverse functions and characteristics.

• Overall Function: Defend against pathogens, remove debris, and mediate immune responses.

• Shared Characteristics: Nucleated, capable of diapedesis (movement through vessel walls).

• Granular Leukocytes: Neutrophils (most numerous, phagocytosis), Eosinophils (combat parasites, allergies), Basophils (release histamine, rarest).

• Agranular Leukocytes: Lymphocytes (B and T cells, immune response, mature in lymphoid tissues), Monocytes (phagocytosis, become macrophages), Additional info: Dendritic cells are also derived from monocytes.

Thrombocytes (Platelets)

Platelets are cell fragments essential for blood clotting.

• Function: Initiate clot formation by adhering to damaged vessels.

• Precursor Cell: Megakaryocyte breaks apart to form platelets.

Hemostasis and Coagulation

Hemostasis is the process of stopping bleeding, involving three phases and a complex cascade.

• Three Phases: 1. Vascular spasm (vasoconstriction), 2. Platelet plug formation, 3. Coagulation (clotting).

• Coagulation Cascade: Two pathways (intrinsic and extrinsic) converge at the common pathway, leading to fibrin formation.

• Clot Resolution: Plasmin enzyme dissolves fibrin, restoring vessel patency.

Blood Disorder Terminology

Common disorders include anemia, polycythemia, thrombocytopenia, and leukopenia.

• Anemia: Reduced oxygen-carrying capacity.

• Polycythemia: Excess RBCs, increasing viscosity.

• Thrombocytopenia: Low platelet count, risk of bleeding.

• Leukopenia: Low WBC count, risk of infection.

The Heart (Chapter 17)

Structure and Layers of the Heart

The heart is a muscular organ with distinct layers and chambers, responsible for pumping blood throughout the body.

• Layers: Epicardium (outer), Myocardium (muscle), Endocardium (inner).

• Base vs Apex: Base is superior, apex is inferior and points left.

• Interventricular Septum: Separates right and left ventricles.

• Coverings: Pericardium (fibrous and serous layers).

Chambers and Valves

The heart has four chambers and four valves, each with specific functions in circulation.

• Chambers: Right atrium (receives O2-poor blood), right ventricle (pumps O2-poor blood to lungs), left atrium (receives O2-rich blood), left ventricle (pumps O2-rich blood to body).

• Valves: Tricuspid (right AV), Pulmonary (right semilunar), Mitral (left AV), Aortic (left semilunar).

Heart Sounds and Murmurs

Heart sounds are produced by valve actions; murmurs indicate abnormal flow.

• Lub-dup: Lub (AV valves close), Dup (semilunar valves close).

• Murmur: Caused by turbulent blood flow, often due to valve defects.

Major Vessels and Blood Flow

Blood enters and exits the heart through major vessels, following distinct circulatory paths.

• Vessels Returning Blood: Superior/inferior vena cava, pulmonary veins.

• Vessels Carrying Blood Away: Pulmonary artery, aorta.

• Path of Blood Flow: Right atrium → right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium → left ventricle → aorta → body.

• Coronary Circulation: Supplies heart muscle with oxygen and nutrients.

Heart Problems

• Angina Pectoris: Chest pain due to reduced blood flow to myocardium.

• Myocardial Infarction: Heart attack; death of heart muscle from prolonged ischemia.

Conduction System and Autorhythmicity

The heart's electrical system coordinates contraction and maintains rhythm.

• Autorhythmicity: Heart generates its own impulses via pacemaker cells.

• Sympathetic Influence: Increases heart rate (HR) and stroke volume (SV).

• Parasympathetic Influence: Decreases HR.

• Commands: Originate from medulla oblongata, reach heart via vagus (parasympathetic) and sympathetic nerves.

• Pacemaker Path: SA node → AV node → Bundle of His → bundle branches → Purkinje fibers.

• Contractile Cell Impulses: Depolarization (Na+ influx), plateau (Ca2+ influx), repolarization (K+ efflux).

• Functional Syncytium: Gap junctions allow coordinated contraction.

Cardiac Cycle and Output

The cardiac cycle consists of systole and diastole, with chamber actions and valve states changing accordingly.

• Systole: Contraction phase; blood ejected.

• Diastole: Relaxation phase; chambers fill.

• Valve States: AV valves open during diastole, closed during systole; semilunar valves opposite.

• Cardiac Output: Amount of blood pumped per minute. Calculated as:

• Factors Influencing CO: Heart rate, stroke volume, contractility, preload, afterload.

Blood Vessels (Chapter 18)

Structure of Blood Vessel Walls

Blood vessels have three layers, each with distinct tissue composition and function.

• Tunica Intima: Endothelial lining, reduces friction.

• Tunica Media: Smooth muscle and elastic fibers, controls diameter.

• Tunica Adventitia (Externa): Connective tissue, provides support.

Types of Blood Vessels

Blood vessels are classified by structure and function.

• Arteries: Carry blood away from heart; thick tunica media.

• Elastic Arteries: Large, near heart; withstand pressure.

• Muscular Arteries: Distribute blood to organs.

• Arterioles: Smallest arteries; "resistance vessels" due to control over blood flow.

• Capillaries: Site of exchange; types include:

  • Continuous: Tight junctions, most common.

  • Fenestrated: Pores for rapid exchange (kidneys, intestines).

• Veins: Carry blood to heart; thin walls, valves prevent backflow.

• Venules: Smallest veins, collect blood from capillaries.

Blood Flow, Resistance, and Pressure

Blood flow is influenced by vessel diameter, resistance, and pressure.

• Resistance: Affected by vessel diameter, blood viscosity, and vessel length.

• Vasoconstriction: Narrowing vessels; increases resistance, caused by chemicals like norepinephrine, angiotensin II.

• Vasodilation: Widening vessels; decreases resistance, caused by nitric oxide, histamine.

• Velocity: Highest in arteries, slowest in capillaries, increases in veins.

• Blood Pressure: Monitored by baroreceptors; regulated by vasomotor center, cardioacceleratory center, and cardioinhibitory center in the brainstem.

Venous Return and Blood Flow Regulation

Venous return is aided by muscle contractions, valves, and respiratory movements. Blood flow shifts to tissues based on metabolic needs.

• Factors Affecting Venous Return: Skeletal muscle pump, respiratory pump, venous valves.

• Factors Affecting Blood Flow Shift: Local vasodilation/constriction, sympathetic stimulation.

Blood Volume Regulation

Blood volume is controlled by hormones and kidney function.

• ANH (ANP): Atrial natriuretic peptide decreases blood volume by promoting sodium excretion.

• Aldosterone: Increases blood volume by promoting sodium retention.

• ADH: Antidiuretic hormone increases water reabsorption.

Capillary Exchange

Capillary exchange is governed by hydrostatic and osmotic pressures.

• NFP Equation: Net filtration pressure determines movement of fluid:

• CHP: Capillary hydrostatic pressure (pushes fluid out).

• BCOP: Blood colloid osmotic pressure (pulls fluid in).

• Positive NFP: Fluid moves out of capillary (filtration).

• Negative NFP: Fluid moves into capillary (reabsorption).

• Role of Plasma Proteins: Maintain BCOP, preventing excessive fluid loss.

Table: Comparison of Blood Vessel Types

Example: In the kidneys, fenestrated capillaries allow rapid filtration of blood plasma.

Additional info: The study guide covers essential concepts for exam preparation in Anatomy & Physiology, focusing on blood, heart, and blood vessels.