Human Physiology Test 4 Notes PDF

CHAPTER 14-BLOOD VESSELS, BLOOD PRESSURE AND BLOOD FLOW I. PHYSICAL LAWS GOVERNING BLOOD FLOW AND BLOOD PRESSURE A. The rate of blood movement through the cardiovascular system is related the pressure gradient across the vessel and inversely related to resistance of the v...

CHAPTER 14-BLOOD VESSELS, BLOOD PRESSURE AND BLOOD FLOW I. PHYSICAL LAWS GOVERNING BLOOD FLOW AND BLOOD PRESSURE A. The rate of blood movement through the cardiovascular system is related the pressure gradient across the vessel and inversely related to resistance of the vessel. 1. Flow=Pressure gradient/Resistance ( P/R) 2. Pressure refers to the driving force that pushes/moves blood through the vessels from high to low pressure. 3. Resistance refers to all of the factors that work to inhibit the flow of blood. a. The general rule is as follows: 1) Increased resistance, decreased flow rate. 2) Decreased resistance, increased flow rate. B. Pressure Gradient Differences 1. Whenever there is a pressure difference between two locations, the pressure gradient drives the flow from a region of higher pressure to one of lower pressure (or down the pressure gradient) 2. The Role of Pressure Gradients in Driving Blood Flow: a. As we discussed in the previous chapter, the Heart is the primary pump in the cardiovascular system. The heart serves to generate the pressure that drives blood through the vessels of the human body. b. By pumping blood into the arteries of the body, the heart creates a pressure gradient between the arteries and the veins that drives blood flow. 3. Pressure Gradients Across the Systemic and Pulmonary Circulation Circuits: a. Mean Arterial Pressure (MAP)-the average pressure in the aorta throughout the cardiac cycle. MAP is approximately 85mm Hg. b. Central Venous Pressure (CVP)-the pressure in the large veins returning to the heart (Superior and Inferior Vena Cava). CVP is approximately 2-8mmHg. c. The difference between MAP and CVP is the pressure gradient that drives blood flow through the systemic circulation. Since CVP is so small, the pressure gradient driving blood flow through the systemic circulation is equated to the Mean Arterial Pressure. d. If the pressure gradient used to drive blood flow through the circulation circuits is low, then resistance must be low as well. C. Resistance in the Cardiovascular System 1. Resistance refers to any condition or situation that reduces blood flow through the blood vessels of the human body. 2. Factors that influence resistance of blood vessels to blood flow: a. Vessel Radius 1) Generally, a decrease in vessel radius increases resistance (this is known as vasoconstriction), whereas an increase in  vessel radius tends to decrease resistance (this is known as (vasodilation). b. Vessel Length 1) Typically, longer vessels have greater resistance; however, this is not a major factor in terms of resistance since vessels are not growing in adults. c. Blood Viscosity 1) Viscosity refers to the thickness of blood. Resistance increases as viscosity increases. 3. The primary determinant of velocity is the total cross-sectional area of the vessel. II. OVERVIEW OF THE BLOOD VESSELS OF THE HUMAN BODY A. Blood vessels are classified according to whether they carry blood away from or to the heart and according to the size. B. Arteries and Arterioles carry oxygenated blood away from the heart to the body. Specifically, these vessels carry oxygenated blood to capillaries which are drained by venules and then larger veins (which carry deoxygenated blood). III. ARTERIES A. Structure of the Wall of Arteries: 1. 3 Layers in arterial walls (are also known as tunics): a. Tunica interna-innermost layer. Also known as the tunica intima. 1) Surrounds a central blood-containing space known as the lumen. 2) Lined with endothelium (simple squamous epithelium). This tissue reduces friction as blood moves through the lumen. b. Tunica media-composed primarily of smooth muscle tissue and elastic connective tissue. 1) This smooth muscle is regulated by the autonomic nervous system and various chemicals. 2) Vasoconstriction (reduction in lumen diameter due to smooth muscle contraction) and Vasodilation (widening of the lumen due to smooth muscle relaxation) both occur in the tunica media. 3) This layer is typically the thickest layer in the walls of arteries. This layer also helps to regulate blood pressure and blood flow. c. Tunica externa (tunica adventitia)-outermost layer of the arterial wall. 1) Is primarily connective tissue in structure. 2) Vasa vasorum-tiny blood vessels that carry blood into the outer layers of the arterial walls (into the tunica externa). 2. Since the walls of arteries contain large supplies of elastic and connective tissue, they are able to withstand the relatively high-pressure present in these vessels. a. This organization allows for expansion of arteries during systole (contraction). Recoil during diastole functions to pump blood forward. b. This creates the pulse in the radial artery. c. That said, arteries are known as “Pressure Reservoirs.  d. Blood pressure in arteries can be measured with a sphygmomanometer. e. Normal Blood Pressure is measured as systolic/diastolic. Healthy blood pressure is measured at 120/80 (however, there is a wide variation around this value). 3. The Aorta is the largest human artery (12.5mm internal diameter and 2mm thick wall). Other arteries range in size from a 2-6mm internal diameter and a 1mm thick wall. B. Arterioles-lead into capillaries. 1. Their walls contain large supplies of smooth muscle that encircle the endothelium. The action of this smooth muscle functions to regulate the flow of blood into capillaries. a. The action of this smooth muscle acts to control resistance in arterioles. 2. Due to their decreased lumen diameter, arterioles have the greatest resistance to blood when compared to other blood vessels. 3. Arterioles serve two major functions: a. Controlling blood flow into capillary beds. b. Regulating Mean Arterial Pressure (MAP). 4. Arteriolar Tone-refers to a partial contraction of smooth muscle in arterioles without stimulation. This ensures that at least a minimal pressure is maintained in arterioles. C. Distribution of Blood Flow to Organs 1. Blood does not flow equally to all organs, but it gets distributed among organs based on need. 2. Blood flow to organs is regulated by the smooth muscle in arterioles. 3. In many cases, blood flow to organs is locally regulated by nerve cells in the specific organ. This local regulation is referred to as Intrinsic Control. 4. Perfusion Pressure-the pressure gradient that drives blood flow through a given organ or tissue. This is essentially equal to Median Arterial Pressure (MAP). 5. Hyperemia-refers to a higher-than-normal rate of blood flow. D. Intrinsic Control of Blood Flow and Pressure to Organs is carried out in the following ways: 1. Regulation Based on Metabolic Activity: Active Hyperemia a. In general, increased metabolic activity associated with a particular organ stimulates vasodilation in the organ; thus, increasing blood flow to the organ. The reverse is true is well-that is, decreased metabolic activity in an organ stimulates vasoconstriction, thus reducing blood flow to the organ. b. Active Hyperemia-refers to an increase in blood flow following an increase in metabolic activity. 1) Events here: a) Increased metabolic activity in an organ leads to a decline in Oxygen levels. Along with this, Carbon dioxide levels increase in the tissues of the organ. This triggers an increase in blood flow to the tissues to bring in oxygen and  remove the extra carbon dioxide. b) When oxygen levels return to normal levels, and carbon dioxide levels drop, a negative feedback system triggers the vasoconstriction of arterioles; thus, reducing blood flow to the tissues of the organs. c) At this point, oxygen and carbon dioxide levels are at a normal level. 2. Regulation Based on Blood Flow: Reactive Hyperemia a. Reactive Hyperemia-refers to an increase in blood flow in response to a previous reduction in blood flow. This can be caused by the blockage of a blood vessel. The events to restore blood flow is identical to the events listed for active hyperemia. In both types of hyperemia, the results are the same, but the cause is different. 3. Regulation in response to Stretch of Arteriolar Smooth Muscle: The Myogenic Response a. Stretch-Sensitive Fibers are associated with smooth muscle in arterioles. When these fibers are stretched, they respond by contracting. This leads to a greater vascular resistance in the arteriole. 1) An increase in perfusion pressure can stimulate these fibers to initiate muscle contractions of vascular smooth muscle which increases resistance in the vessel. b. Myogenic Response-refers to a change in vascular resistance that occurs in response to stretch of blood vessels. This helps to establish Flow Autoregulation-local organ regulation that tends to keep blood flow constant. 4. Regulation by Locally Secreted Chemical Messengers a. A number of chemical substances, many of which are secreted by cells in the walls of blood vessels, can affect the contractile activity of vascular smooth muscle. b. Specific chemicals that regulate vascular smooth muscle 1) Nitric Oxide-released continually by endothelial cells. This chemical stimulates vasodilation. Histamine is secreted by inflamed tissue and stimulates nitric oxide synthesis. 2) Adenosine-released in cells of the coronary arteries in response to reduced oxygen supplies (hypoxia). Adenosine causes vasodilation. 3) Prostacyclin-is another vasodilator that functions in preventing blood clots. E. Extrinsic Control of Blood Flow and Pressure to Organs 1. Extrinsic Control of Blood Flow is carried out by factors external to the cells of the arteriole. 2. Neurons from the sympathetic division of the ANS innervate the smooth muscle of arterioles. The smooth muscle in arterioles have both Alpha and Beta receptor sites on their sarcolemma (plasma membrane). The neurotransmitter  epinephrine can bind to both sites, depending on the situation. 3. Epinephrine-released by the adrenal medulla typically binds to Alpha receptors on arteriolar smooth muscle which leads to vasoconstriction. However, epinephrine binds to Beta receptors on cardiac muscle to promote vasodilation. a. This situation is associated with Fight or Flight Reponses-blood flow is diverted from the organs to the heart and skeletal muscle. 4. Vasopressin (Antidiuretic Hormone)-secreted by the posterior pituitary gland. This hormone promotes vasoconstriction of blood vessels in the kidneys in an effort to promote water reabsorption into the blood. 5. Angiotensin II-hormone that promotes vasoconstriction. IV. CAPILLARIES-are the primary site where exchange of nutrients and waste products occurs between blood and human tissues. A. Features of Capillaries 1. They are the smallest blood vessels (1mm long, 5-10 micrometers in diameter). 2. They are only one cell layer thick. Due to this, materials can easily diffuse through the capillary wall to either enter or exit tissues. 3. Often times, capillaries are highly branched which provides a great surface area for exchanges between the blood and tissues. This branching often forms Capillary Beds. Due to the formation of these branched capillaries, almost all cells within the body are within 1mm of a capillary. 4. The extensive branching of capillaries gives them a greater cross-sectional area compared to other blood vessels. Due to this, when blood enters a capillary bed, its velocity of flow decreases. Think of a series of rivers emptying into a lake-the velocity of water flow slows dramatically in the lake, which has a greater cross-sectional area compared to the rivers. a. The reduced blood flow in capillaries allows time for the exchange of materials between the blood and body tissues. 5. The density of capillaries in an organ or body structure is related to the metabolic activity of the structure. B. Types of Capillaries-based on their degree of leakiness. 1. Continuous Capillaries-the most common type of capillary. a. These are highly permeable to small, water-soluble substances. b. Since the endothelial cells of these capillaries are held tightly together, it is difficult for large materials to pass through them. 2. Fenestrated Capillaries-contain large pores through which water-soluble materials can pass through. These are common in the kidneys. 3. Sinusoidal capillaries-large blood-filled spaces that function in the exchange of substances between blood and tissues. Sinusoids are found in the liver and spleen. 4. Discontinuous Capillaries-connect fenestrated capillaries to sinusoids. C. Local Control of Blood Fow Through Capillary Beds 1. Blood flow through capillaries is controlled by smooth muscles and metarterioles. 2. Smooth muscle surrounds capillaries on the arteriole end of the capillary to  form Precapillary Sphincters. Contractions of these sphincters constrict the capillaries which increases their resistance to flow. Precapillary sphincters are only affected by local controls (by oxygen, carbon dioxide levels, etc.). a. When precapillary sphincters are relaxed, blood flows through all capillaries in the bed. b. If precapillary sphincters constrict, blood flow bypasses capillaries and flows through metarterioles. Metarterioles carry blood directly from arterioles to venules, bypassing capillaries. D. Exchange of Materials Across Capillary Walls-occurs in three ways: 1. Simple Diffusion a. Most small solutes move through capillary walls via simple diffusion. b. Remember that molecules will diffuse from greater to lesser concentrations. 2. Bulk Flow-the movement of fluids and solutes together from greater to lesser concentration. a. Filtration-movement of the fluid from blood to interstitial fluid. b. Absorption-movement of the fluid from interstitial fluid to the blood. c. The purpose of bulk flow is to maintain fluid balance between fluid compartments in the body. 1) A shift in fluid from plasma to interstitial fluid causes a condition known as edema (swelling). 3. Mediated Transport-movement of molecules via protein carriers in plasma membranes. 4. Transcytosis-movement of molecules through cell membranes via vesicles. E. Starling Forces-forces that drive the movement of fluid into and out of capillaries. 1. This is impacted by the following forces: a. Capillary Hydrostatic Pressure (PCAP)-fluid pressure in the capillary. This is essentially capillary blood pressure. b. Interstitial Fluid Hydrostatic Pressure (PIF)-fluid pressure outside of a capillary. c. Colloid Osmotic Pressure-is created by proteins. 2. Net Filtration Pressure (NFP)-this is the difference between the filtration pressures and absorption pressures. a. If NFP is positive, filtration occurs; when it is negative, absorption occurs. b. General Rule: At the arteriole end of a capillary, filtration occurs while absorption occurs at the venule end of a capillary. 3. Factors that Affect Filtration and Absorption Across Capillaries a. Changes in either capillary or interstitial fluid hydrostatic pressure. b. Pathological conditions (disease). 1) Kidney disease, liver disease and cardiovascular disease can all play major roles in affecting fluid levels in tissues. V. VENULES A. Characteristics: 1. Are slightly smaller than arterioles.  2. They have very thin walls that do not contain smooth muscle. 3. The smallest venules can function in the same way as capillaries. VI. VEINS-formed by venules that join together. A. Characteristics: 1. Have a slightly larger diameter (5mm) in their lumen than arteries. 2. Their walls are very thin (.5mm) compared to the walls of arteries. The walls of veins are structured in a similar fashion to that of arteries. 3. The blood pressure in veins is significantly less than that of arteries. 4. Veins are the only vessels that contain valves as part of their internal structure. The valves ensure that blood moves in a forward direction. 5. Veins are referred to as having a high compliance. This mean that they stretch easily. This ability to stretch occurs due to the thin walls of veins. 6. This high compliance leads to a low pressure in veins. In short, veins hold more blood than arteries and at a lower pressure. Because of this, veins are described as “Volume Reservoirs.” Recall that arteries are “Pressure Reservoirs.” a. The blood stored in veins can quickly be shifted to arterial side in times of need. This occurs when the brain signals the heart to increase the rate of its pumping action. B. The return of blood to the heart via venous return is driven by a pressure gradient between the peripheral veins and the right atrium. This gradient is approximately 15mm Hg. C. Factors That Influence Venous Pressure and Venous Return to the Heart 1. The Skeletal Muscle Pump a. Veins have one-way valves to promote blood flow to the heart. b. When skeletal muscles contract, they compress veins which promotes the movement of blood towards the heart. Contraction opens proximal valves and closes distal valves. Alternating this activity “pumps” blood toward the heart. 2. The Respiratory Pump-respiratory movements, including action of the diaphragm, creates a vacuum in the thoracic cavity which helps to push blood towards the heart. 3. Blood Volume-a large blood volume creates a pressure in veins which helps to move blood towards the heart. 4. Venomotor Tone a. The sympathetic nervous system can trigger contraction of the smooth muscle in veins. This contraction acts to push blood back towards the heart. This type of movement is known as venomotor tone. VI. REGULATORY PROCESSES RELATED TO BLOOD VESSELS A. Cardiac Output-can have a large impact on blood pressure which directly affects the flow of blood through arteries and veins. B. Cardiovascular Center of the Medulla-makes adjustments in heart activity based on the body’s demand for oxygen. C. The Baroreceptor Reflex  1. Baroreceptors are special nerve cells located in the largest blood vessels of the body. These can create action potentials that stimulate the sympathetic division of the autonomic nervous system to increase heart activity under times of increased metabolic activity. D. Hormonal Control 1. Numerous hormones can affect heart activity. For example, epinephrine, vasopressin and angiotensin II can all increase the action of the heart which impacts the action of blood vessels. VII. DISORDERS RELATED TO BLOOD VESSELS AND BLOOD FLOW 1. Hypertension-persistently high blood pressure above 120/80. This can be caused by atherosclerosis, genetics, poor diet. How is this treated? 2. Venous Pooling-occurs when blood accumulates in veins. Instead of moving to the heart, the blood remains in veins. This can cause “light-headedness.” 3. Hypotension-reduced blood pressure. This may make a person feel dizzy because of a reduced blood flow to the brain. Under normal conditions, reflex mechanisms typically compensate for this effect. CHAPTER 15-THE CARDIOVASCULAR SYSTEM: BLOOD I. BLOOD A. Is the only fluid tissue in the human body. It contains living cells and fluid. B. Blood is pushed through the body by the pumping action of the heart. 1. Arteries-carry blood away from the heart. These branch until they become microscopic capillaries. Carbon dioxide and wastes can pass into capillaries by diffusion. Nutrients diffuse out of capillaries into body tissues. 2. Capillaries lead to Veins, which carry deoxygenated blood back to the heart. a. This blood is then pumped to the lungs where it picks up oxygen. The oxygenated blood is then returned to the heart for dispersal to the body. II. CHARACTERISTICS/FEATURES OF BLOOD A. It is classified as being a type of connective tissue since blood contains the 3 elements of connective tissue: 1. Cells 2. Matrix-the liquid portion of blood. 3. Fibers-mostly protein fibers such as fibrin. These provide support to blood. These a also play a role in blood clotting. B. It has a salty, metallic taste. This is due to the presence of iron. C. Blood’s color depends on the amount of oxygen it is carrying. 1. Scarlet red blood is oxygen rich; whereas, dark red blood is low in oxygen. D. Blood has a greater density than water. In other words, blood is more viscous than water. Blood viscosity is established by erythrocytes. E. Blood is slightly alkaline, with a pH between 7.35 and 7.45. F. It maintains a temperature around 100.4-degrees F (38 degrees C). This is slightly higher than normal body temperature. G. Blood makes up about 8% of total body weight. H. Average blood volume is 5-6L in males and 4-5L in females. III. FUNCTIONS OF BLOOD A. Distribution/Transport-this includes: 1. Carrying oxygen from the lungs to body tissues. 2. Delivering nutrients and water to body tissues. 3. Transporting metabolic wastes from body tissues to sites of elimination. a. CO2 is carried to the lungs and nitrogen wastes to the kidneys. 4. Transporting endocrine hormones to their target organs. B. Regulation-The regulatory functions of blood include: 1. Maintaining normal body temperature a. Blood does this by absorbing and distributing heat throughout the body and to the skin where heat loss can occur. 2. Maintaining normal pH in body tissues a. Many blood proteins and solutes act as buffers. These buffers prevent sudden pH changes. b. Blood stores bicarbonate ions, which serve as the primary buffer in body tissues. 3. Maintaining normal fluid volume in the circulatory system C. Protection-this includes: 1. Preventing blood loss-platelets and blood proteins aid in clot formation which stops blood loss. 2. Fighting and preventing infection-antibodies and leukocytes are involved in fighting and preventing infection. IV. COMPOSITION OF BLOOD A. Blood is composed of 2 Primary Components: 1. Plasma-the liquid matrix of blood. 2. Formed Elements-blood cells and cell fragments. These are suspended in plasma. a. The Formed Elements in Human Blood: 1) Erythrocytes-red blood cells. 2) Leukocytes-white blood cells. 3) Thrombocytes-platelets. B. Blood is the most commonly examined tissue in the body. It is used to determine what illness a patient has. 1. In a lab, blood is spun in a centrifuge. This pushes the heavier formed elements to the bottom of the tube and the less dense plasma remains at the top. a. Erythrocytes settle at the bottom of the tube; thus, producing a red mass at the base of the tube. Hematocrit-the percentage of erythrocytes to total blood volume. Red blood cells account for 45% of the total blood volume. b. Buffy Coat-a thin, white layer at the top of the erythrocyte layer. The buffy coat contains leukocytes and platelets. These components make up less than 1% of total blood volume. c. Plasma-sits above the buffy coat and it makes up about 55% of blood volume. V. BLOOD PLASMA-the liquid portion of blood. A. Plasma is a straw-colored, sticky fluid. B. Plasma is Composed of: 1. Water-accounts for over 90% of total plasma volume. Water serves as a dissolving and suspending medium for blood solutes. a. Water is also involved in absorbing heat and heat transfers. 2. Plasma Proteins-account for 8% of total plasma volume. Plasma Proteins Include: a. Albumin-accounts for 60% of plasma proteins. 1) This protein is produced by the human liver. 2) Functions of Albumin include: a) Carrying hydrophobic molecules (steroids, lipids) through the body. b) Acting as a blood buffer. c) Creating osmotic pressure, which acts to maintain water balance between blood and tissues. b. Globulins-account for 36% of plasma proteins. 1) Types of Globulins in the Body: a) Alpha, Beta Globulins-produced by the liver. 1) These are transport proteins that attach to and transport lipids, metal ions and fat-soluble vitamins. b) Gamma Globulins-antibodies released primarily by plasma cells during an immune response. c) Clotting Proteins-make up 4% of plasma proteins. 1) This includes fibrinogen and prothrombin which are involved in blood clotting. Both of these proteins are produced in the liver. c. Fibrinogen-helps to form the threads of blood clots to prevent blood loss. d. Metabolic enzymes e. Antibacterial proteins 3. Non-protein Nitrogenous Substances-this includes by-products of cellular metabolism such as lactic acid, urea, uric acid, creatinine and ammonium salts. 4. Nutrients-this includes materials absorbed in the digestive tract. Some of these materials include glucose and other simple sugars, amino acids, fatty acids, cholesterol and vitamins. 5. Electrolytes-this includes ions such as potassium, calcium, sodium and phosphate. a. Bicarbonate is also an electrolyte. Recall, that bicarbonate is a major buffer. b. Many electrolytes help maintain proper blood osmotic pressure. 6. Respiratory Gases-including oxygen and carbon dioxide. a. Most oxygen is bound to hemoglobin in erythrocytes. Some oxygen is dissolved in plasma. b. Carbon dioxide is transported attached to hemoglobin in erythrocytes and as bicarbonate dissolved in plasma. C. The Lymphatic System-removes approximately 3L of liquid that moves from the blood  into the tissues of the body on a daily basis. This material collects in lymphatic vessels and moves through lymph nodes for cleansing. This fluid (known as Lymph) is exchanged between the lymphatic system and the cardiovascular system via blood capillaries and lymphatic capillaries. Once in the bloodstream, this fluid becomes part of the plasma. 1. Failure of the lymphatic system to function properly can lead to edema (swelling). VI. FORMED ELEMENTS-cells and cell fragments in blood. A. 3 Formed Elements in Human Blood: 1. Erythrocytes 2. Leukocytes 3. Thrombocytes B. Erythrocytes-Red Blood Cells 1. Erythrocytes are small (7.5 micrometers in diameter), biconcave discs with depressed centers. 2. Cellular Structure of Erythrocytes: a. Are bound by a true cellular membrane. b. They lack a nucleus, and they do not contain cellular organelles. Internally, they are essentially hollow. c. Erythrocytes contain Hemoglobin (Hb). What is this compound? 3. Erythrocytes contribute greatly to blood viscosity. a. Women contain 4.3-5.2 million cells per mm3 and Men contain 5.1-5.8 cells per mm3. This leads to about 2.5 trillion erythrocytes in a healthy adult. b. An increase in erythrocyte number increases blood viscosity; thus, blood flow slows. The opposite is true as well. 4. Erythrocytes transport oxygen and carbon dioxide through the body. Much of the oxygen is carried by hemoglobin which is stored in erythrocytes. 3 Features that allow erythrocytes to transport large supplies of gases through the body: a. Their small size and shape increases their surface area to volume ratio. Due to this, oxygen is always close to the surface of the erythrocyte. b. They are primarily composed of hemoglobin (97%) and very little else. c. Erythrocytes generate their energy via anabolic methods, therefore, they do not contain mitochondria. Due to this, erythrocytes do not use the oxygen that they carry. 5. Hemoglobin-transports most of the oxygen through the body. It can also carry carbon dioxide. a. Males usually contain 13-18 g of hemoglobin per 100 ml of blood; females contain slightly less than this. b. Hemoglobin is composed of: 1) Globin-a complex protein with 2 alpha chains and 2 beta chains. 2) Heme-a ring-shaped structure that binds to the globin molecule. a) There are 4 heme groups in every hemoglobin molecule. b) Each of the heme groups contains an iron atom. 1) Iron easily combines with oxygen. Therefore, each hemoglobin molecule can transport 4  oxygen molecules. c) A single red blood cell contains 250 million hemoglobin molecules, so each erythrocyte can carry about 1 billion oxygen molecules. c. Hemoglobin picks up oxygen in the lungs. 1) The oxygen is then transported to body tissues where it is released for use by tissue cells. 2) When oxygen binds to iron, the hemoglobin is known as oxyhemoglobin. The oxygen changes the shape of hemoglobin which now becomes bright red. 3) When oxygen releases from iron, hemoglobin returns to its original shape. At this point, the hemoglobin is known as deoxyhemoglobin and it becomes dark red in color. d. About 20% of the carbon dioxide transported in blood combines with hemoglobin. Carbon dioxide attaches to the globin portion of hemoglobin to form carbaminohemoglobin which is a dark red color. 1) Carbon dioxide uptake occurs in body tissues. a) The carbon dioxide is carried to the lungs where it is eliminated from the body. 2) Erythrocytes do contain the enzymes carbonic anhydrase which catalyzes the reaction between carbon dioxide and water to produce carbonic acid (a very weak acid) which can dissolve to produce bicarbonate buffer. 6. Erythrocyte Production a. Hemopoiesis/Hematopoiesis-blood cell formation. 1) This occurs in red bone marrow. Recall that red bone marrow is in irregular bones and in the epiphyses of long bones. b. Erythropoiesis-red blood cell formation. Erythrocytes do not have the ability to divide. c. Hemocytoblasts (Hematopoietic Stem Cells)-located in red bone marrow. 1) These mature into all types of blood cells. 2) Once these start developing into a particular type of blood cell, they cannot stop. d. Events in Erythropoiesis 1) Hemocytoblasts develop into myeloid stem cells which are then transformed into proerythroblasts. 2) The proerythroblasts then develop into erythroblasts. 3) Erythroblasts produce huge numbers of ribosomes which are involved in protein production. a) Hemoglobin formation and iron accumulation also occurs in the erythroblast. 4) Next, the erythroblast develops into a normoblast. a) A normoblast begins to turn pink-red in color as more hemoglobin is produced. A normoblast also loses all  cellular organelles. It also begins to assume the typical biconcave shape. 5) Normoblasts develop into reticulocytes which are essentially young erythrocytes. Reticulocytes enter the bloodstream to begin transporting oxygen and carbon dioxide. Reticulocytes become mature erythrocytes within about two days. a) Reticulocytes account for 2-3% of all erythrocytes in a healthy human. b) Reticulocyte counts are used clinically as an index of the rate of erythrocyte formation. e. The body must maintain a constant number of erythrocytes. 1) Too few erythrocytes can lead to hypoxia (oxygen deprivation) and too many erythrocytes increases blood viscosity. 2) Healthy individuals produce about 2 million new erythrocytes every second. f. Hormonal Control of Erythropoiesis: 1) Erythropoietin (EPO)-hormone produced primarily by the kidneys. a) Some can be produced by the liver. b) This hormone directly regulates erythropoiesis. c) When cells in the kidney become hypoxic, they increase their erythropoietin production. What causes this hypoxia? 1) Reduced number of erythrocytes due to blood loss. 2) Reduced oxygen availability. 3) Increased tissue demand for oxygen-as would occur during exercise. d) Excess oxygen in the bloodstream or too many erythrocytes depresses erythropoietin production. e) Oxygen availability regulates erythropoietin production-not the number of erythrocytes. f) Renal dialysis patients are often given genetically engineered erythropoietin to regulate erythrocyte formation. 1) Some athletes have illegally used this product to improve their stamina and performance; however, this may increase blood viscosity and lead to dehydration (Homeostatic Imbalance 17:1). g) Testosterone can also increase EPO production. g. Dietary Requirements for Erythopoiesis: 1) Iron-needed for hemoglobin production. Free iron is toxic in the body, so iron is stored in other forms (ferritin or hemosiderin). 2) B Complex Vitamins-including B12 and folic acid. 7. Erythrocyte destruction and removal a. Since erythrocytes cannot divide, they become old and lose their ability to carry oxygen. They have a useful life span of about 120 days. b. Old erythrocytes are often trapped in the spleen where they are destroyed  by macrophages. 1) The heme is pulled off of globin. The iron in the heme is stored in the body for future use. The remainder of the heme molecule is broken down into bilirubin which is a yellow pigment that leaves the body via feces. 2) The globin portion of hemoglobin is broken down into amino acids that are used by the body to produce other proteins. This is an example of internal recycling. 8. Erythrocyte Disorders: a. Anemias-condition in which the blood has an abnormally low oxygen- carrying capacity. In anemia, blood oxygen levels are inadequate to support normal metabolism. 1) Characteristics of anemia include shortness of breath, pale skin, fatigue. 2) Causes of Anemia: a) Insufficient Numbers of Erythrocyte-caused by blood loss, bone marrow failure and erythrocyte destruction. 1) Hemorrhagic anemias-result from blood loss. 2) Hemolytic anemias-erythrocytes rupture prematurely. Some infections cause this. 3) Aplastic anemia-results from damage to bone marrow. b) Decreased Hemoglobin Content-often results from poor nutrition. 1) Iron-deficiency anemia-low iron content. 2) Pernicious anemia-caused by a vitamin B-12 deficiency. c) Abnormal Hemoglobin-usually genetic in nature. 3 Examples of this include: 1) Thalassemias-occur when one of the globin chains is faulty or absent. 2) Sickle-cell anemia-occurs when erythrocytes are sickle-shaped. These blood cells rupture easily; thus, reducing their capacity to carry oxygen. Is often treated with a blood transfusion. 3) Polycythemia-an abnormally high number of erythrocytes. This increases blood viscosity which causes the blood to flow sluggishly. a) Polycythemia vera-common in patients who have bone marrow cancer. The erythrocyte count is exceptionally high. b) Severe polycythemia is treated by blood dilution-that is, removing some blood and replacing it with saline.  c) Blood doping is an artificially induced polycythemia practiced by some athletes. C. Leukocytes-white blood cells. 1. General Features of Leukocytes: a. They are complete cells-leukocytes contain a nucleus and organelles. b. They can divide to reproduce. c. On average, there are 4000-11,000 leukocytes per mm3 of blood. They account for less than 1% of total blood volume. d. Leukocytes help fight disease and they protect us from damage by bacteria, viruses, parasites, toxins and tumor cells. 1) To carry out this function, leukocytes can leave capillaries and enter tissues (a process known as diapedesis). Leukocytes move through tissues by amoeboid motion. a) Leukocytes can follow chemical trails secreted by damaged cells. This is known as positive chemotaxis. b) Whenever an infection occurs, the body increases its leukocyte production. Leukocytosis-a leukocyte count greater than 11,000 cells per mm3. This is common during bacterial and viral infection. 2. Leukocytes are Classified into 2 Major Categories a. Granulocytes-contain membrane-bound cytoplasmic granules. b. Agranulocytes-do not contain membrane-bound cytoplasmic granules. 3. Granulocytes a. Characteristics: 1) Are spherical in shape and contain lobed nuclei. 2) Stain with Wright’s Stain. 3) All granulocytes are phagocytic. b. Types of Granulocytes: 1) Neutrophils-most numerous leukocyte in the body. a) Are twice as large as erythrocytes. b) Are referred to as neutrophils because their granules take up basic (blue) and acidic (red) dyes. c) Their granules have a lilac color. d) The granules of neutrophils contain defensins which are antibiotic type proteins and enzymes. e) Neutrophil nuclei contain 3 to 6 lobes. f) Neutrophils are chemically attracted to sites of inflammation. g) Neutrophils are involved in: 1) Attacking bacteria and fungi via phagocytosis. 2) Producing defensins which “spear” bacteria. 3) Using oxygen to produce hydrogen peroxide which kills bacteria. h) Neutrophil numbers increase greatly during bacterial  infection. 2) Eosinophils-account for 1-4% of all leukocytes and are similar in size to neutrophils. a) Their nuclei stain red and they contain 2 lobes that are connected by a thin band of nuclear material. b) Eosinophils contain large granules that are filled with a variety of digestive enzymes. c) Functions of Eosinophils: 1) Fight parasitic worms (roundworms, flatworms). a) Eosinophils accomplish this by secreting enzymes that digest the covering around the worm. 2) Inactivate/phagocytize chemicals or molecules that lead to allergies. 3) Basophils-account for 0.5% of all leukocytes (are the rarest of all leukocytes). They are similar in size to neutrophils. a) They contain large granules that stain purple to black. b) Their granules contain histamine. 1) Histamine acts as a vasodilator during an inflammatory response. Histamine also attracts leukocytes to an inflamed site. c) The nucleus of basophils is generally U or S-shaped with two or three constrictions. 4. Agranulocytes a. Characteristics 1) These lack visable cytoplasmic granules. 2) Their nuclei are spherical or kidney shaped. b. Types of Agranulocytes 1) Lymphocytes-2nd most abundant type of leukocyte. a) They have a large nucleus that stains deep purple. 1) The nucleus almost fills the entire cell. b) Most lymphocytes are found in lymphoid tissues (such as the spleen and lymph nodes). Only a few lymphocytes are actually in the bloodstream. c) Types of Lymphocytes: 1) T Lymphocytes-involved in immune responses. Specifically, T lymphocytes act directly against viruses and tumor cells. 2) B Lymphocytes-give rise to plasma cells which can produce antibodies that are released into the blood. 2) Monocytes-account for 4-8% of all leukocytes in the body. a) Their nucleus stains dark purple and it has a distinct U or kidney shape.  b) Monocytes can differentiate into Macrophages which are phagocytic cells on viruses and bacteria. 5. Leukopoiesis-production of leukocytes. a. This process is regulated by hormones known as colony-stimulating factors (CSF’s). These stimulate the formation of new leukocytes. Can be given to some patients in an effort to increase the functioning of the immune system. b. Granulocyte Formation: 1) Hemocytoblast → Myeloid Stem Cell → Myeloblast → Precursor cells → Neutrophils Eosinophils Basophils c. Agranulocyte Formation 1) Hemocytoblast ↓ Myeloid Stem Cell Lymphoid Stem Cell ↓ ↓ Monoblast Lymphoblast ↓ ↓ Monocyte Lymphocyte ↓ Plasma Cells 6. Leukocyte disorders: a. Leukopenia-abnormally low white blood cell count. This can be induced by some drugs (such as steroids) and cancer treatments. b. Leukemia-refers to a group of cancerous conditions involving leukocytes. 1) Normally, the leukocytes remain unspecialized and impair bone marrow function. 2) Treatments include radiation, drug therapy, bone marrow transplants 3) Leukemias are often named for the type of cell that is involved. c. Infectious mononucleosis-caused by the Epstein-Barr virus. 1) Signs/Symptoms include fatigue, aches, sore throat, low-grade fever. 2) Characterized by an excessive number of agranulocytes. 3) There is no cure at present-it usually runs its course in a few weeks. D. Thrombocytes (Platelets)-are cell fragments, not true cells. 1. Platelets contain many small, purple-staining granules. a. These granules contain chemicals that are involved in blood clotting. The chemicals include serotonin, Ca+, ATP, enzymes, clot factors.  2. Platelets begin forming clots when blood vessels are broken. They stick to the damaged site to form a plug which stops blood loss. 3. They live for only about 10 days if they are not involved in clot formation. 4. Platelet formation-is regulated by the hormone thrombopoietin. a. Steps in this process: 1) Hemocytoblast  Megakaryoblast  Megakaryocyte  Fragments to form thrombocytes VII. HEMOSTASIS-“stoppage of bleeding” A. This is the process of clot formation. Hemostasis prevents blood loss. This is a rapid, localized response to damaged blood vessels. B. 3 Phases in Hemostasis: 1. Vascular spasm 2. Platelet plug formation 3. Coagulation (blood clotting) C. Events in Hemostasis: 1. Vascular Spasm a. Immediately after an injury, damaged blood vessels constrict (vasoconstrict). b. This constriction is known as vascular spasm. Vascular spasm is an attempt to reduce blood loss so that platelet plug formation and blood clotting can occur. c. Factors that lead to vascular spasm: 1) Injury to vascular smooth muscle 2) Chemicals released by endothelial cells of blood vessels 3) Platelets 4) Reflexes associated with pain receptors. 2. Platelet Plug Formation a. Platelets form a plug that temporarily seals the break in the vessel wall. b. Normally, platelets do not stick together. However, this changes when a blood vessel is broken. When a blood vessel is damaged, underlying collagen fibers are exposed. This forces platelets to undergo the following changes: 1) Platelets swell and from spiked processes. 2) Platelets become sticky and attach to the exposed collagen. 3) Once attached, the platelets begin to release: a) Serotonin-enhances vascular spasm. b) Adenosine diphosphate-attracts more platelets to the injury site and it makes platelets sticky. 4) Within minutes a platelet plug is formed.  5) Prostacyclin-produced by endothelial cells. This chemical prevents platelets from attaching to each other outside the injury site. 6) Finally, the platelet plug is reinforced with fibrin (protein) threads. 3. Coagulation-blood clotting; occurs when blood is converted from a liquid to a gel. a) Coagulation occurs through 3 distinct phases: 1) Phase 1-Formation of Prothrombin Activator-can occur through 1 of 2 pathways: a) Intrinsic Pathway-occurs immediately after an injury. 1) Is a very slow process and it involves several intermediate compounds. 2) This process uses compounds in the blood to produce prothrombin activator. b) Extrinsic Pathway-is initiated by a compound known as tissue thromboplastin (which is released by damaged cells). 2) Phase II-Prothrombin activator converts prothrombin into thrombin a) Prothrombin activator converts the protein prothrombin into the active enzyme thrombin. 3) Phase III-Formation of the Fibrin mesh a) Thrombin (from above) converts the protein fibrinogen into long protein threads known as fibrin. b) Fibrin-a long, fibrous protein. 1) Fibrin threads function by: a) Providing a surface for platelets to attach to. This helps form the bulk of a clot. b) Forcing plasma to become gel-like. This traps formed elements and other blood components. b) Clot Retraction and Repair 1) Clot retraction helps to stabilize newly formed clots. 2) Platelets contain the contractile proteins actin and myosin. a) These two proteins contract and pull on the fibrin threads. b) This tightening pulls broken blood vessels closer together and it forces serum (plasma) from the forming clot. c) Fibrinolysis-process that removes unneeded blood clots when healing has occurred. This process also helps to remove small clots that form in blood vessels. This is an important process for body homeostasis. 1) Plasmin-enzyme that can digest blood clots. It is activated by the protein plasminogen which is in all clots. 2) Fibrinolysis begins about 2 days after clot formation. d) Several mechanisms in the body prevent clots from becoming too large. These include: 1) Removal of clot factors by the body 2) Absorption of thrombin by the body (slows clot formation) 3) Heparin-anticoagulant contained in the granules of basophils and  mast cells. Heparin inhibits the activity of thrombin. D. Disorders of Hemostasis-can be classified into 2 Major Categories: 1. Thromboembolytic conditions-these result from conditions that cause undesirable clot formation. a. Thrombus-clot that develops and persists in an unbroken blood vessel. 1) A large thrombus may block circulation, causing blockage or death. b. Embolus-a free floating molecule in the blood. A thrombus can break apart to form an embolus. The embolus can form an embolism when the molecule reaches a blood vessel that is too small for passage. 1) Problems arise when an embolus reaches a blood vessel that is too narrow for the embolus to pass through. Again, this is deadly. 2) Heparin, Coumadin, Warfarin and aspirin can serve as anticoagulants. 2. Bleeding disorders-occur when clotting is affected. Examples include: a. Thrombocytopenia-condition in which the number of circulating platelets is deficient. This can cause widespread hemorrhage. This often results from bone marrow damage. Small purple patches on the skin are a sign of this. Typically, a platelet count less than 50,000/mm3 is used to diagnose this. b. Hemophilia-this refers to several disorders in which the blood does not clot properly. In most cases, it is the result of a deficiency of clot factors. It is genetic in nature. Hemophilia is treated with transfusions of plasma and clot factors. c. Thromboembolic Disorders-cause undesirable clots in the body. d. Disseminated intravascular coagulation-involves widespread clotting and severe bleeding. VIII. TRANSFUSION AND BLOOD REPLACEMENT A. A loss of 30% of blood volume can be fatal. Transfusions are now done to prevent problems when blood is lost. B. Human erythrocytes are covered by special identity proteins. 1. Humans must be given blood that contains similar proteins to their own. If blood is detected as being foreign, then the transfused cells will agglutinate (clump) and be destroyed. C. ABO Blood Groups 1. Agglutinogens-proteins found on the cell membranes of erythrocytes. These can lead to immune responses. Human blood groups are based on the two presence/absence of agglutinogens (A and B). 2. Agglutinins-preformed antibodies in human blood. These act against erythrocytes carrying agglutinogens that are not present on a person’s own erythrocytes. 3. Human Blood Type Agglutinogen Agglutinins Type A A b Type B B a Type O None a and b Type AB A and B None  4. Type AB individuals-do not produce agglutinins; therefore, they can receive blood from anyone-safely. They are known as Universal Recipients. 5. Type O Individuals-do not contain agglutinogens; therefore, their blood will not cause an immune response. They are known as Universal Donors for this reason. D. Rh Blood Groups 1. Rh Factors-Rh agglutinogens (are at least 8 of these). This is named for the Rhesus monkey (where it was first discovered). a. Most Americans are Rh+-they contain the Rh antigen. 2. If an Rh negative person is given Rh+ blood; they will begin to produce Rh antibodies. a. However, a transfusion reaction does not occur in the first event. Reactions occur in later events when Rh+ blood is given to the Rh- person. 3. Problems can arise when a pregnant Rh- mother is carrying an Rh+ baby. In this case, Rh+ agglutinogens will pass into the mother’s bloodstream via the placenta. The mother will then build antibodies against the Rh+ blood. This does not harm the first pregnancy; however, if the same situation develops again, problems can arise. a. In this case, a second baby can become anemic and hypoxic. Brain damage and even death can occur. This is known as Hemolytic Disease of the Newborn or Erythroblastosis fetalis. This is treated with RhoGAM which prevents an immune response by the mother. E. Transfusion Reactions-occurs from mismatched blood. In these, foreign erythrocytes clump (agglutinate). This is treatable. F. Blood Typing-is done by adding a or b agglutinins to a blood sample. G. Specific Tests on Blood Samples: 1. Microscopic studies-to observe shape/size of erythrocytes. 2. Differential White Blood Cell Count-to determine what type of infection a person has. 3. Complete Blood Count-gives full blood chemistry. 4. Platelet count 5. Comprehensive Metabolic Panel-used to measure electrolyte, nutrient and hormone levels in the blood. CHAPTER 16-THE RESPIRATORY SYSTEM: PULMONARY VENTILATION I. THE RESPIRATORY SYSTEM-functions by supplying the body with oxygen and disposing of carbon dioxide. To accomplish this, four processes, collectively known as respiration, must occur: A. Pulmonary Ventilation-movement of air into and out of the lungs so that the gases there are continuously changed and refreshed (breathing). B. External Respiration-movement of oxygen from the lungs to the blood and of carbon dioxide from the blood to the lungs. C. Transport of Respiratory Gases-movement of oxygen from the lungs to the tissue cells of the body and of carbon dioxide from the tissue cells to the lungs. This is carried out by blood in the cardiovascular system.  D. Internal Respiration-movement of oxygen from blood to the tissue cells and of carbon dioxide from tissue cells to blood. 1. The first two processes are carried out by the respiratory system and the last two processes are the responsibility of the cardiovascular system. Therefore, both the respiratory and cardiovascular systems must work together to ensure that body cells receive their oxygen, and that carbon dioxide is removed from the body. 2. The respiratory system is also involved in smell and speech. II. GENERAL ANATOMY OF THE RESPIRATORY SYSTEM A. The Major Structures that make up the Respiratory System Include: 1. The Nose, and Nasal Cavity 5. Bronchi and their smaller branches 2. The Larynx 6. The Lungs with their alveoli 3. The Pharynx 7. The Paranasal sinuses 4. The Trachea B. Overall the Respiratory System is composed of two zones: 1. The Respiratory Zone-the actual site of gas exchange, includes the bronchioles, alveoli and the alveolar ducts. 2. The Conducting Zone-includes all other passageways that serve as areas for air to reach exchange zones. These areas include the nasal cavity, pharynx, larynx and trachea. These areas serve as a conduit for gas to enter the respiratory zone. No gas exchange occurs in these structures. However, these structures do warm air to approximately 37 degrees Celsius and they ensure that the air is 100% humidified to ensure that cells in the respiratory zone do not dry out. III. THE NOSE AND PARANASAL SINUSES A. The nose is the only visible portion of the Respiratory System. The nose provides an airway for respiration, moistens and warms air, filters and cleans inspired air, serves as a resonating chamber for speech and houses the olfactory receptors. B. Respiratory mucosa-also lines much of the nasal cavity. This mucosa is made up of pseudostratified ciliated columnar epithelial tissue. 1. Goblet cells are also abundant in the respiratory mucosa. What do goblet cells do? 2. Lysozyme is an antibiotic secreted by the respiratory mucosa. 3. Capillaries and thin-walled veins are abundant beneath these mucosa layers. These vessels act to warm incoming air as it flows over the mucosa. a. Epistaxis-nosebleeds, often caused by an increased blood flow to the nasal cavity. 4. Paranasal Sinuses-surround the nasal cavity. These lighten the skull and aid in warming and moistening incoming air. These also produce mucus that flows into the nasal cavity. The paranasal cavities are located in the frontal, sphenoid, ethmoid, and maxillary bones. 5. What is rhinitis? Sinusitis? What can happen if the adenoids are enlarged? IV. THE PHARYNX-the throat; a funnel-shaped tube that connects the nasal cavity and mouth superiorly to the larynx and esophagus inferiorly.  A. The Pharynx is divided into three major regions: 1. The Nasopharynx-posterior to the nasal cavity, this serves only as an air passageway. a. During swallowing, the uvula moves to close off the nasopharynx; thus preventing food from moving into the nasal cavity. b. Pharyngeal tonsil (Adenoid)-located on the posterior wall of the nasopharynx. These trap and destroy pathogens entering the nasopharynx via air. If these become enlarged, they can block the flow of air through the nose and into the throat. As a result, the air is not properly warmed before it enters the lungs. The person may breathe with their mouth open. c. 4 Openings into the Nasopharynx 1) 2 Internal Nares 2) 2 Auditory (Eustachian) Tubes-these drain the middle ear cavity to equalize pressure in the ear with atmospheric pressure. 2. The Oropharynx-posterior to the oral cavity, opens into the mouth through the fauces. 3. The Laryngopharynx-opens into the larynx. Is also a passageway for food and air. a. This structure is continuous with the esophagus (tube that carries food to the stomach). V. THE LARYNX-the voice box, lies at the upper end of the trachea, just below the pharynx. A. This structure connects the pharynx and trachea. It is held in place by the hyoid bone. B. 3 Functions of the Larynx: 1. Serves as an open airway 2. Routes food and air into the proper channels 3. Voice production C. The larynx is lined by stratified squamous epithelium and pseudostratified columnar epithelium (which is capable of producing mucus that acts to filter dust from incoming air). D. The larynx is composed of 9 cartilages that form a box-like structure. Most of these are hyaline cartilage. The 9 major cartilages that make up the Larynx include: 1. The Thyroid Cartilage-large, formed by 2 attached cartilage plates, gives a triangular shape to the anterior portion of the larynx. This structure is often referred to as the Adam’s Apple. 2. The Cricoid Cartilage-lower cartilage, sits atop and is anchored to the trachea. 3. Arytenoid Cartilages-paired, very small. 4. Cuneiform Cartilages-paired. 5. Corniculate Cartilages-paired. 6. Epiglottis-flexible, composed of elastic cartilage and is covered by taste buds. a. This cartilage attaches to the superior edge of the thyroid cartilage and the epiglottis is free on its other borders b. When air passes into the larynx, the epiglottis remains open. However, during swallowing, the larynx pulls the epiglottis superiorly to cover the glottis (the hollow opening between the vocal cords).  Why is this action important? c. The cough reflex acts to expel any materials that slip pass the epiglottis. E. The Vocal Cords 1. True Vocal Cords-folds of elastic fibers which are stretched across the opening of the larynx. These appear white because they are avascular. These folds vibrate as air rushes up from the lungs; thus producing sound. The glottis is the opening between the true vocal cords. 2. False Vocal Cords-superior to the true vocal cords. These do not produce sound. These are only involving in helping to close the glottis during swallowing. VI. THE TRACHEA (Windpipe)-cylindrical tube that connects the larynx and the 2 primary bronchi. A. It is approximately 4 inches long and 2.5 cm in diameter. The wall of the trachea consists of 3 distinct layers: the mucosa (which is lined with pseudostratified columnar epithelial tissue that contains cilia and goblet cells), the submucosa and adventitita. 1. Smoking inhibits the activity of and often destroys cilia in the trachea; thus coughing becomes the only means to remove mucus from the trachea B. The walls of the adventitia are reinforced internally by 16-20 C-shaped rings of hyaline cartilage. This structure provides the trachea with its great flexibility which allows the esophagus to expand during swallowing and it provides the trachea the ability to stretch during respiration. VII. THE BRONCHI AND THE BRONCHIAL TREE-this is the area where respiratory structures are first encountered. The bronchial tree refers to the branched airways leading from the trachea to microscopic air sacs in the interior of the lungs. A. The Primary Bronchi (Right and Left) are formed where the Trachea branches (near C7). 1. One primary bronchus runs into each lung. The right primary bronchus is wider, shorter and more vertical than the left; thus, it is a more common site for objects to become lodged. B. Once inside the lungs, the primary bronchi branch to form Secondary Bronchi. 1. There are three of these in the right lung and two in the left lung. 2. Secondary Bronchi branch into smaller Tertiary Bronchi which branch repeatedly into smaller and smaller bronchi. There are about 23 orders of branching in the bronchi. This branching is often known as the Bronchial Tree. C. Passageways smaller than 1 mm are known as Bronchioles. The smallest of these are known as Terminal Bronchioles which terminate in tubes known as Alveolar Ducts. 1. Alveoli-air sacs at the ends of alveolar ducts. Alveoli form clusters known as alveolar sacs. The walls of the alveoli are covered by a thin layer of simple squamous epithelial tissue (Type I Cells). a. Type II Cells-scattered among the squamous epithelial cells, secrete surfactant which reduces the surface tension of the alveolar fluids and prevents the walls of the alveoli from sticking together and collapsing. b. Externally, the alveoli are covered by pulmonary capillaries. THE ALVEOLI ARE THE SITES OF EXCHANGE OF GASES BETWEEN THE AIR AND BLOOD. There are about 3 million alveoli per lung. D. The tissue composition of the walls of the primary bronchi resembles that of the trachea, but as the tubes become smaller, several differences are observed:  1. Cartilage rings are replaced by smaller plates of cartilage. There is no cartilage in the smaller bronchioles. 2. The amount of smooth muscle increases in the walls of the smaller passageways. VIII. THE LUNGS AND PLEURA-paired structures occupying much of the thoracic cavity. A. Each cone-shaped lung occupies its own pleural cavity. The lungs are surrounded by the rib cage externally and the diaphragm inferiorly. The right and left lungs are separated from each other by the mediastinum.The intercostal muscles are located between the ribs. 1. Just deep to the clavicle is the apex (pointed tip) of the lung. The base of the lung sits on the diaphragm. 2. Hilum-located on the medial surface of the lung. Pulmonary blood vessels and primary bronchi enter the lung through this opening. B. The left lung is slightly smaller than the right lung. 1. The Left Lung-has an upper and lower lobe that are separated by an oblique fissure. 2. The Right Lung-has 3 lobes-an upper lobe, middle lobe and lower lobe. The horizontal fissure divides the upper and middle lobes, while the oblique fissure divides the middle and lower lobes. 3. Each lobe of the lung contains a number of bronchopulmonary segments that are separated from each other by connective tissue walls (septa). a. Each segment is served by its own artery and vein. D. The lungs are highly innervated with nerve fibers. These include sensory fibers and parasympathetic and sympathetic motor fibers. Parasympathetic fibers typically constrict the air tubes and sympathetic fibers dilate them. E. The Pleura-form a thin, protective, double layered serous membrane around each lung. 1. 2 Layers makeup the Pleural Membranes: a. The Parietal Pleura-covers the thoracic wall and superior portion of the diaphragm. b. The Visceral Pleura-covers the external surfaces of the lungs. 1) The space between these two membranes is referred to as the pleural cavity and it is filled with pleural fluid. What is the function of this fluid? 2) What is pleurisy? IX. PULMONARY VENTILATION (BREATHING) A. Breathing consists of two phases: inspiration (the period when air flows into the lungs) and expiration (the period when gases exit the lungs). B. Pressures Associated with Breathing 1. Atmospheric Pressure(Patm)-the pressure exerted by the air (gases) surrounding the body. At sea level, atmospheric pressure is 760 mm Hg (or 1 atm). a. A negative respiratory pressure indicates that the pressure in that area is less than atmospheric pressure. The opposite is also true. 2. Intrapulmonary Pressure (Ppul) is the pressure in the alveoli. It rises and falls with the phases of breathing but it always eventually equalizes with atmospheric pressure.  3. Intrapleural Pressure (Pip)-pressure in the pleural cavity. This is always about 4 mm Hg less than Ppul; therefore, Pip is always negative relative to Ppul. a. How is this negative pressure established? 1) By the natural recoil of the lungs-the lungs are elastic, so they tend to assume the smallest size possible. 2) Due to the surface tension of the alveolar fluid-alveolar fluid surface tension draws the alveoli to their smallest size. b. However, the above 2 forces are countered by the natural elasticity of the chest wall which acts to pull the thorax outward and to enlarge the lungs. 4. Transpulmonary Pressure-the difference between Ppul and Pip (Ppul-Pip). The greater this pressure is the larger the lungs are. This pressure directly prevents the lungs from collapsing. a. Atelectasis-collapsed lung. b. Pneumothorax-air in the thoracic cavity. C. Pulmonary Ventilation-the process of breathing (inspiration and expiration). 1. In the lungs, volume changes lead to pressure changes and pressure changes lead to the flow of gases to equalize the pressure. 2. Boyle’s Law-at constant temperature, the pressure of a gas varies inversely with its volume. In other words: P1V1=P2V2 where: P is the pressure of the gas in mm Hg V is its volume in mm3 1 and 2 represent the initial and resulting condition a. Gases always fill their container. Thus, in a large container, the molecules in a given amount of gas will be far apart and the pressure will be low but if the volume of the container is reduced, then the gas molecules will be forced closer together and the pressure will rise. This principle can also be applied to the thoracic cavity. When the volume of the thoracic cavity increases, then the gas pressure in the cavity decreases; thus, allowing air to rush into the thoracic cavity from the atmosphere. 3. Inspiration-period when air flows into the lungs. a. Quiet Inspiration-normal inspiration. Quiet Inspiration is produced by: 1) The Diaphragm-as this muscle contracts, it moves inferiorly and flattens out. This increases the height (volume) of the thoracic cavity. 2) Action of the Intercostal Muscles a) As the external intercostals contract, they lift the rib cage and pull the sternum superiorly, thus increasing the volume of the thorax. b) These two activities increase the size of the thoracic cavity by only a few millimeters, however, this is enough to increase thoracic cavity volume by about 500 ml. c) As volume increases in the thoracic cavity, the lungs are  stretched and intrapulmonary volume increases. As a result, Ppul drops about 1mm Hg relative to atmospheric pressure. d) When Ppul is less than Patm, then air rushes into the lungs. e) Inspiration ends when Ppul = Patm. b. During Deep or Forced Inspiration that occurs during exercise and related events, the thoracic volume is further increased by the activity of accessory muscles (including the scalene, the sternocleidomastoid and the pectoralis). 4. Expiration-period when air flows out of the lungs. a. This is a passive process that depends more on lung elasticity than on muscle contraction. b. As the inspiratory muscles relax and resume their resting state, the rib cage descends and the lungs recoil. Thus, both the thoracic and intrapulmonary volumes decrease. This compresses the alveoli and P pul rises to about 1 mm Patm. This creates a pressure gradient in which air then flows out of the lungs. c. Forced Expiration is an active process produced by contraction of abdominal wall muscles (primarily the oblique and transverses muscles). These contractions depress the rib cage and force the internal organs against the diaphragm. Controlling forced expiration is important for regulating precise air flow out of the lungs. 5. Gas Exchange Between the Blood and the Alveoli a. Oxygen and carbon dioxide movements are always by simple diffusion through very thin membranes. b. Typically, oxygen concentrations are greater in the alveoli than in the blood; whereas carbon dioxide concentrations are greater in the alveoli compared to the blood. c. The rate of gas movement is proportional to the gradient difference between the alveoli and blood. d. Recall that the majority of oxygen is transported to tissues by hemoglobin. The release of oxygen from hemoglobin is triggered by the presence of carbon dioxide in the blood near tissue cells. This carbon dioxide makes the blood more acidic which increases oxygen release from hemoglobin. X. FACTORS THAT INFLUENCE PULMONARY VENTILATION A. Airway Resistance-this includes friction or drag encountered in the respiratory passageways. 1. F = P/R where F is airflow, P is pressure and R is resistance. 2. On average, we move about 55 ml of air in and out of the lungs with each breath. 3. Normally, airway resistance is reasonably low because: a. Airway diameters are large (relatively speaking). b. Gas flow stops at the terminal bronchioles and diffusion takes over as the force that controls gas movement B. Alveolar Surface Tension-created where air meets blood. This is produced due to the stronger attraction of liquid molecules for each other compared to the attraction between  the gas and air. 1. This leads to cohesion between the liquid molecules and it increases the surface area of the liquid. This cohesion between water molecules can create enough stress to collapse alveoli. 2. Surfactant-molecule composed of lipids and proteins that is produced by alveolar cells. This compound reduces the cohesiveness of water molecules in the blood, thus, allowing expansion of the lungs. C. Lung Compliance-refers to the “stretchability” of the lungs. 1. Know the equation for lung compliance from textbook. 2. The more a lung expands, the greater its compliance. High compliance leads to more efficient ventilation. 3. Lung Compliance is determined by two factors: a. Distensibility of lung tissue and of the thoracic cage around the lungs. b. Alveolar surface tension. XI. RESPIRATORY VOLUMES AND PULMONARY FUNCTION TESTS A. There are four major respiratory volumes that influence the lungs: tidal volume, inspiratory reserve volume, expiratory reserve volume and residual volume. 1. Tidal Volume (TV)-refers to the 500 ml. of air that moves into and out of the lungs during normal, quiet breathing. 2. Inspiratory Reserve Volume (IRV)-the amount of air that can be inspired forcibly beyond the tidal volume (2100 ml to 3200 ml). 3. Expiratory Reserve Volume (ERV)-the amount of air that can be evacuated from the lungs after a tidal expiration (1000 ml to 1200 ml). Even after a strenuous expiration, about 1200 ml of air remains in the lungs-this volume of air is referred to as the Residual Volume (RV). B. Respiratory Capacities-are created by two or more lung volumes. The major respiratory capacities include: 1. Inspiratory Capacity (IC)-the total amount of air that can be inspired after a tidal expiration. It is TV + IRV. 2. Functional Residual Capacity (FRC)-the combined RV and ERV values. This represents the amount of air remaining in the lungs after a tidal expiration. 3. Vital Capacity (VC)-the total amount of exchangeable air. It is: TV + IRV + ERV. VC is approximately 4800 ml. 4. Total Lung Capacity (TLC)-sum of all the lung volumes and is normally 6000 ml in males and slightly less in women. C. Anatomical Dead Space-refers to air that fills respiratory passageways but never contributes to gas exchange in the alveoli (usually about 150 ml). D. Pulmonary Function Tests-breathing is measured by a spirometer. These tests are used to identify various pulmonary related disorders (such as obstructive pulmonary disease). 1. Minute Ventilation-the total amount of gas that flows into or out of the respiratory tract in 1 minute. This is normally 6L/min in quiet breathing. 2. Forced Vital Capacity (FVC)-measures the amount of gas expelled when a subject takes a deep breath and then forcefully exhales as rapidly as possible. 3. Forced Expiratory Volume (FEV)-determines the amount of air expelled during  specific time intervals of the FVC Test. CHAPTER 17-THE RESPIRATORY SYSTEM: GAS EXCHANGE I. BASIC PROPERTIES OF GASES A. Gas exchange in the body occurs by bulk flow or diffusion of gas into tissues. B. Dalton’s Law of Partial Pressure-the total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture. The pressure exerted by each gas (its partial pressure) is proportional to the percentage of that gas in the mixture. C. Henry’s Law-when a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure. In other words, the greater concentration of a gas in the gas phase, the more and the faster that gas will move into solution in the liquid. II. EXTERNAL RESPIRATION-refers to the movement of oxygen from the lungs into the blood. Three Factors Influence this Process: A. Partial Pressure Gradients and Gas Solubilities 1. PO2 in the alveoli is approximately 104mm Hg compared to P O2 in the blood which is about 40mm Hg. What does this mean? 2. PCO2 is about 5mm Hg in the alveoli and 40mm Hg in the blood. This carbon dioxide is expelled from the lungs during expiration. Again, what happens in this case? 3. Even though the gradients are different, equal amounts of oxygen and carbon dioxide are exchanged with each other since carbon dioxide is much more soluble in liquid than oxygen. 4. Pulmonary edema-the accumulation of excess fluid in the lungs. This can impact oxygen and carbon dioxide movements into and out of the body and alveoli. B. Ventilation-Perfusion Coupling-for gas exchange to work efficiently, ventilation (the amount of gas reaching the alveoli) must be coupled with perfusion (blood flow in pulmonary capillaries). 1. When PO2 is high in alveoli, pulmonary arterioles dilate, thus increasing blood flow into the associated pulmonary capillaries. This is an attempt to empty the oxygen into the blood. a. When PO2 is low in alveoli, pulmonary arterioles constrict, reducing the amount of blood flowing into the pulmonary capillaries. Notice that PO2 influences pulmonary arterioles. 2. Alveolar PCO2 influences the bronchioles, not arterioles. a. When alveolar PCO2 levels are high, bronchioles dilate. This helps remove  remove carbon dioxide from tissues. b. When PCO2 levels are low, bronchioles constrict. This increases carbon dioxide levels in the alveoli, which creates a concentration gradient for the appropriate removal of carbon dioxide. C. Thickness and Surface Area of the Respiratory Membranes-the respiratory membrane is.5 to 1 micrometer thick. Gas exchange is very efficient through this thin surface. 1. The Respiratory Membrane is composed of three single layered membranes: a. Endothelial cells in the Capillary Wall b. The Capillary Basement Membrane c. The Alveolar Membrane III. INTERNAL RESPIRATION (CAPILLARY GAS EXCHANGE)-movement of oxygen from blood to the tissue cells and of carbon dioxide from tissue cells to blood. A. In this case the partial pressures and diffusion gradients are reversed from the above situation. B. PO2 is always lower in tissues than in the surrounding systemic arterial blood; thus, oxygen moves from the _______________ to the ______________. The case is reversed for carbon dioxide. Its partial pressure is greater in tissues compared to the surrounding blood supply, therefore, carbon dioxide moves from ____________ to ______________. C. In summary, gas exchanges occur between the blood and alveoli and the blood and tissues based on partial pressure gradients. These exchanges are the result of simple diffusion across respiratory membranes. IV. TRANSPORT OF OXYGEN AND CARBON DIOXIDE BY THE BLOOD A. Oxygen Transport 1. Oxygen is carried in the blood in 2 ways: a. Attached to the red pigment hemoglobin within erythrocytes. b. Dissolved in plasma. Only a small fraction of oxygen is carried in this manner since oxygen is poorly soluble in water. 2. Hemoglobin (Hb)- a. Oxyhemoglobin (HbO2)-refers to the combination of oxygen and hemoglobin. b. Reduced hemoglobin vs. Deoxyhemoglobin c. Four oxygen molecules can attach to hemoglobin. Uptake of oxygen molecules are increased dramatically after the first oxygen attaches to the hemoglobin. d. The influence of PO2 on Hemoglobin Saturation 1) Oxygen-hemoglobin dissociation curve a) Arterial blood is almost completely saturated with oxygen. b) Hb is almost completely saturated with oxygen at 70mm Hg. Due to this, O2 delivery to tissues can still be adequate when inspired air is well below regular O2 levels (as might occur in high altitudes).  c) Only 25% of bound oxygen is released during one systemic circuit, thus O2 is still available in venous blood. Due to this, oxygen can be released from Hb during periods of heavy exercise without any major changes in respiratory or cardiac output. e. Temperature, blood pH, and PCO2 can all influence hemoglobin saturation rates. How might these factors influence O2 release? 1) The Bohr Effect-occurs due to the fact that certain amino acids release hydrogen ions when oxygen binds to hemoglobin. This can lead to a slight decrease in blood pH (more acidic) which stimulates the release of oxygen from hemoglobin near tissues. f. Nitric Oxide (NO)-secreted by the lungs, is a well-known vasodilator that plays a role in regulating blood pressure. 1) Hb is a vasoconstrictor and acts to destroy nitric oxide. To prevent this from leading to problems, NO attaches to Hb in a fashion that prevents it from being destroyed. B. Carbon Dioxide Transport 1. Normal body cells produce about 200 ml of CO2 every minute-exactly the amount excreted by the lungs. Blood transports CO2 from the tissue cells to the lungs in three forms: a. Diss