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18. The serous membranes are found lining the compartments of the ventral cavity of the body. They consist of a parietal layer lining the inside of the body wall and a visceral layer covering internal organs. In between the two membranes is a potential space, the serous cavity, which contains serous fluid. 19. A homeostatic system consists of a receptor that detects an internal or external stimulus, a control system that integrates the input from the receptor, and an effector such as a muscle or a gland that causes changes in response to the stimulus. 20. Negative feedback systems involve responses that are in opposition to the stimulus, thereby maintaining the environment near the set point or normal level. Conversely, positive feedback systems entail a series of responses, each increasing in intensity until a climax event is reached, at which point the system will return to homeostasis.

Answers to “Can You Apply What You’ve Learned?” 1. B Feedback: The pain is coming from a region below the umbilicus, hence it is in the lower portion of the abdomen and it is located on the right side. It is therefore in the right lower quadrant. 2. D Feedback: The right iliac region is located just medial to the pelvic bones. 3. B Feedback: X-rays are not absorbed by soft tissue such as the appendix. They are usually used to visualize dense structures. 4. B Feedback: Sweat glands release heat at the surface of the skin. 5. B Feedback: Serotonin is a neurotransmitter responsible for regulating both pathways associated with depression in the brain and gastric motility in the stomach. Drugs such as SSRIs are used to treat depression in individuals with low levels of serotonin in the brain by inhibiting its reuptake by neurons. Because the SSRI drugs cannot specifically target the brain, they also have an effect within the digestive system, causing nausea and diarrhea.

Answers to “Can You Synthesize What You’ve Learned?” 1. Lynn has broken the bones within her forearm, the radius and ulna. She has an abrasion on her chin as well as bruising on her buttocks and thigh. 2. The epinephrine counteracted the effect of the bee sting, acting in opposition to the stimulus; it was therefore an example of negative feedback. 3. X-rays and CT scans are optimal for visualizing dense tissues such as tumors. An MRI or ultrasound would be better suited for examining soft tissues.

Chapter 2 Answers to “What Did You Learn?” 1. The mass of an atom is determined by the combined number of protons and neutrons within its nucleus. The charge is a function of the ratio of protons to electrons. 2. The nucleus of a chlorine atom consists of 17 protons and 17 neutrons. The electrons are arranged into three separate shells; the first shell closest to the nucleus contains two electrons, the second shell contains eight electrons, and the third outer shell contains seven electrons for a total of 17 electrons. 3. Isotopes are atoms of the same element that differ in their number of neutrons. In a radioisotope the extra neutrons will decay and be released as radiation. 4. Elements such as the noble gases have satisfied the octet rule by having a complete outer electron shell and are therefore not reactive. Other elements may form bonds in order to satisfy the octet rule and fill their outer shells. 5. Common cations of the human body include sodium ions (Na+), potassium ions (K+), calcium ions (Ca2+), magnesium ions (Mg2+), and hydrogen ions (H+). Common anions include chloride ions (Cl-), bicarbonate ions (HCO3-), and phosphate ions (PO43-). 6. Hydrogen (H), sodium (Na), magnesium (Mg), potassium (K), and chloride (Cl) 7. In order to satisfy the octet rule, atoms with only one electron in their outer shell may give up the electron, resulting in a slightly positive cation with a full outer shell. Conversely, atoms with seven electrons in their outer shell may accept an electron from another atom, becoming a slightly negative anion but with a full outer shell. 8. Ionic bonds are formed due to an attraction between ions with different charges; therefore, two positive cations cannot form an ionic bond with each other, nor can two negatively charged anions. 9. The molecular formula exhibits the type and number of atoms in a molecule; the structural formula also provides information on how the atoms are arranged. 10. Isomers are molecules composed of the same type and number of elements, but are arranged differently. 11. A covalent bond is formed when atoms share electrons in their outer orbitals in order to satisfy the octet rule. 12. Oxygen atoms each contain six electrons in their outer orbitals and each have room for two more. In a double bond they share two pairs of electrons and thereby each satisfies the octet rule. 13. A covalent bond between atoms of the same element will result in an equal distribution of electrons across the molecule since both atoms are equally electronegative, resulting in a nonpolar molecule. Molecules composed of different atoms result in an unequal distribution of charge across the molecule, where more electronegative atoms have a slightly negative charge and less electronegative atoms are slightly less negative. Since oxygen and hydrogen atoms are nearly equal in terms of electronegativity, atoms of these two different elements can also form nonpolar covalent bonds. 14. Both molecular oxygen (O2) and carbon dioxide (CO2) are nonpolar molecules. 15. A hydrogen bond is an intermolecular attraction between a slightly positive hydrogen atom and another slightly negative atom. 16. Hydrogen bonding is an important factor behind many of the properties of water molecules. 17. Surfactant is required to break cohesive attraction between water molecules in the alveoli of the lungs. The high heat of vaporization of water molecules makes them an effective mechanism for dissipating heat at the surface of the skin. 18. Nonelectrolytic molecules such as glucose do not dissociate in water. Electrolytes such as sodium chloride (NaCl) disassociate into constituent ions in an aqueous environment, forming a solution capable of conducting electricity. 19. In an aqueous environment, amphipathic molecules such as phospholipids will orient themselves so that their hydrophobic domains face each other while the hydrophilic domains are exposed to water. This is the basis behind the arrangement of phospholipids within a phospholipid bilayer.

20. Each water molecule can disassociate into one negatively charged hydroxyl ion and one positively charged hydrogen ion, leaving it with an equal distribution of positive and negative charges, which is considered neutral. 21. An acid is capable of releasing hydrogen ions in an aqueous environment. 22. pH is the relative measure of hydrogen ions in a solution. 23. Buffers maintain the pH of physiologic solutions within a normal range by absorbing hydrogen ions when an acid is added or hydroxyls when a base is added to the solution. 24. Blood is a suspension of formed elements that settle out of solution when a sample is left standing. 25. Blood is also considered a colloid because it contains numerous proteins and a solution because of its numerous dissolved solutes, such as ions and sugars. 26. The concentration of a solution may be expressed as either the mass of solute/volume of solution, percent of mass of solute in 100 milliliters of solution, moles of solute/liter of solution (molarity), or the moles of solute/kilogram of solvent (molality). 27. Biological molecules typically contain carbon (C), hydrogen (H), and oxygen (O) and in some cases may also contain nitrogen (N), phosphorus (P), and sulfur (S). Of these, hydrogen is the only one capable of forming a common biological ion. 28. Carboxylic acids and phosphates are capable of acting as acids. 29. A polymer is composed of repeating monomer subunits. Proteins are composed of amino acids, carbohydrates are composed of simple sugars, and nucleic acids are composed nucleotides. 30. Lipids are hydrophobic molecules and do not typically dissolve in water. 31. Phospholipids contain both a hydrophilic head group and a pair of hydrophobic fatty acid tails, making them ideally suited for forming cellular membranes. 32. Glycogen can be found within the liver and muscle tissue of animals and is composed of repeating glucose subunits. 33. Fructose, glucose, and galactose are monosaccharides. Sucrose, maltose, and galactose are disaccharides. Glycogen and starch are polysaccharides. 34. Nucleic acids store and transfer genetic information within cells. 35. RNA molecules contain a ribose sugar rather than the deoxyribose sugar of DNA. The nucleotide thymine is present in DNA. In its place, RNA contains the nucleotide uracil. 36. Amino acids are the monomers of a protein and are held together by peptide bonds. 37. A dipeptide consists of 2 amino acids, an oligopeptide contains 3 to 20 amino acids, a polypeptide contains 21 to 199 amino acids, and a protein consists of 200 or more amino acids. The term protein is generally used to refer to any of these molecules. 38. The R group of leucine is a short nonpolar hydrocarbon, making it a nonpolar amino acid. 39. The tertiary structure of a protein is its three-dimensional shape. The quaternary structure describes the interaction of two or more polypeptide chains within a functional protein. 40. Denaturing a protein changes its conformation and often affects its activity. Exposure of a protein to hydrogen ions can denature a protein by disrupting electrostatic interactions such as ionic bonds within the molecule.

Answers to “Do You Know the Basics?” 1. C Feedback: Isotopes are atoms of the same element that differ in the number of neutrons.

2. A Feedback: Lipids are hydrophobic molecules and are not soluble in water. 3. C Feedback: Water has a high specific heat, allowing it to absorb energy without changing temperature. Conversely, the high heat of vaporization for water allows it to dissipate a large amount of energy during evaporative cooling of the skin. 4. D Feedback: A pH less than 7.0 is acidic and a pH greater than 7.0 is basic. 5. D Feedback: The formed elements of blood act as a suspension. Dissolved proteins in the plasma act as a colloid. The numerous dissolved solutes also make it a solution. 6. A Feedback: Triglycerides are not considered polymers because they are not composed of repeating monomer subunits. 7. C Feedback: Glucose is stored in animal tissues as glycogen. 8. B Feedback: Although phosphates which contain phosphorus are common ions in the body, phosphorus itself is not a common ion. 9. B Feedback: A hydrogen bond is an intermolecular attraction between a slightly positive hydrogen atom and another slightly negative atom. 10. B Feedback: Denaturing a protein changes its conformation. Excessive denaturation can permanently affect protein structure and possibly its function as well. 11. Common cations of the human body include sodium ions (Na+), potassium ions (K+), calcium ions (Ca2+), magnesium ions (Mg2+), and hydrogen ions (H+). Common anions include chloride ions (Cl-), bicarbonate ions (HCO3-), and phosphate ions (PO43-). 12. A polar molecule such as water results from an unequal distribution of electrons between covalently bonded atoms. Oxygen, the more electronegative of the atoms, will have a stronger pull on the electrons and will thus have a slightly more negative charge around it. The hydrogen atom will be relatively more positive (or less negative). Two water molecules can form a hydrogen bond between their opposite poles, whereby relatively positive hydrogen will be attracted to relatively negative oxygen on the other molecule. 13.

14. Covalently bonded compounds such as glucose will not dissociate when dissolved in water; however, they will remain in solution after the mixture is no longer agitated. Ionic compounds such as sodium chloride (NaCl) will disassociate in water. The polar water molecules will disrupt the electrostatic interactions between sodium and chloride ions, thereby separating them. 15. An acid contributes hydrogen ions to a solution, making it more acidic; a base absorbs hydrogen ions from a solution, making it more basic. pH is the measure of hydrogen ions in a solution. A buffer is a solution capable of absorbing either hydrogen or hydroxyl ions, thereby maintaining its pH when acids or bases are added.

16. The concentration of a solution may be expressed as either the ratio of the mass of solute compared to the volume of the solution, as the percent of mass of solute in 100 milliliters of solution, as the number of moles of solute per liter of solution (molarity), or the number of moles of solute per kilogram of solvent (molality). 17. Proteins are composed of amino acids; carbohydrates are composed of simple sugars; nucleic acids are composed of nucleotides; and lipids consist of fatty acids. 18. The catabolism of either the nitrogenous bases present in nucleotides or the amine groups of amino acids may result in nitrogenous waste that must be removed from the body by the kidneys. 19. In an aqueous environment, amphipathic molecules such as phospholipids will orient themselves so that their hydrophobic domains face each other while the hydrophilic domains are exposed to water. This is the basis behind the arrangement of phospholipids within a phospholipid bilayer. 20. Denaturing a protein changes its conformation and often affects its activity. Exposure of a protein to a pH outside of its norm or an increase in temperature can denature a protein by disrupting electrostatic interactions such as ionic bonds within the molecule.

Answers to “Can You Apply What You’ve Learned?” 1. C Feedback: Surfactant is a detergent that prevents hydrostatic interactions between water molecules, thereby preventing the lungs from collapsing. Premature babies often lack the ability to produce surfactant and are at risk for respiratory problems. 2. B Feedback: Electrolytes such as sodium chloride (NaCl) dissociate into constituent ions in an aqueous environment, forming a solution capable of conducting electricity. Nonelectrolytic molecules such as glucose do not dissociate in water. 3. B Feedback: Isotopes are atoms of the same element that differ in their number of neutrons. In a radioisotope the extra neutrons will decay and be released as radiation, which may be measured or visualized during a diagnostic test. 4. D Feedback: Calcium ions are an important structural component of bone tissue. 5. C Feedback: Proteins consist of covalently bonded amino acids held together by peptide bond.

Answers to “Can You Synthesize What You’ve Learned?” 1. High-energy radiation can affect bonds within nucleotides, thereby damaging DNA. 2. Acidosis is an increase in the number of hydrogen ions in the blood, resulting in a lower pH. The increasing number of hydrogen ions may start to damage the hydrostatic interactions holding proteins together, destroying tertiary structure and denaturing the proteins. 3. The drug would regulate the levels of the monosaccharide glucose within the blood.

Chapter 3 Answers to “What Did You Learn?” 1. Kinetic energy represents a change in position. Movement of sodium ions along a concentration gradient or the movement of electrons from higher to lower energy state are both examples of kinetic energy. 2. The movement of muscle is an example of mechanical energy, a form of kinetic energy. 3. Even though energy can neither be created nor destroyed, it can change forms. Such transformations are rarely completely efficient, resulting in the release of some of the energy as heat, the least organized form of energy. 4. Reactants are the substrates prior to a reaction. The reactants are converted to products during the reaction. 5. This synthesis reaction would be anabolic, because it would result in a more complicated structure. It would also be endergonic, since it would require an input of energy. 6. ATP is produced by exergonic reactions. It is often used to couple exergonic reactions to endergonic reactions that require an input of energy. 7. When equilibrium is disturbed in a reversible reaction, the system will adjust driving the reaction toward either the reactants or the products, until equilibrium is reestablished. 8. Although raising the temperature of a reaction increases the kinetic energy of molecules, in a biological system this can decrease the rate of the reaction by denaturing the enzymes involved. 9. Enzymes lower the energy of activation required for a reaction. 10. The active site of an enzyme is the temporary binding site of the substrate on the enzyme. 11. Enzymes are proteins that catalyze metabolic reaction by lowering the activation energy necessary for the reaction. The structure of the protein directly affects its affinity for its specific substrate. Inorganic cofactors are often associated with enzymes facilitating their actions. Organic cofactors (coenzymes not attached to the protein) such as NAD+ and FAD+ may also be required to complete enzymatic reactions. 12. The name of an enzyme usually describes its action and usually contains the suffix -ase. 13. The rate of an enzyme-catalyzed reaction will increase as the concentration of substrate is increased, until all of the enzyme molecules are saturated. Decreasing temperature from an enzyme’s optimum range will gradually decrease activity by decreasing the kinetic energy of the system. Increasing temperature will have a more sudden negative effect on enzyme function as the molecule is denatured. Changing pH of an enzymatic reaction will readily denature the protein as the excessive hydrogen or hydroxyl ions interfere with electrostatic interactions within the enzyme, denaturing it. 14. Competitive inhibitors affect enzyme activity by competing with substrates at the active site. Noncompetitive inhibitors modulate the shape of the enzyme by binding to an allosteric binding site, outside of the active site, thereby affecting the overall shape of the enzyme and its function. 15. A metabolic pathway consists of a series of enzyme-catalyzed reactions. Often the final product of the pathway serves as an allosteric inhibitor of enzymes within the pathway, providing for negative feedback within the system. 16. Phosphorylation and dephosphorylation entail the addition or removal of phosphates, respectively. Addition of a phosphate to an enzyme affects the shape, and therefore the function, of the enzyme. 17. C6H12O2 + 6 O2 → 6 CO2 + 6 H2O. The catabolism of glucose, an exergonic reaction, results in the production of six molecules of carbon dioxide. Oxygen acts as the final electron acceptor in the process which involves the energy from the release of CO2 to synthesize ATP. 18. Cellular oxidation begins with glycolysis in the cytosol of the cell. The remaining steps are the intermediate reactions, the citric acid cycle, and the electron transport chain which occur within the mitochondria.

19. Glycolysis is an anaerobic process that occurs in the cytosol of a cell. The net reaction entails the synthesis of two 3-carbon pyruvate molecules from one 6-carbon molecule of glucose. The reaction involves the initial input of two molecules of ATP and yields four, for a net yield of two molecules of ATP. Two molecules of NAD+ are also reduced to form NADH + H+ from electrons and protons released during the oxidation of glucose. 20. Under aerobic conditions, in the presence of oxygen, pyruvate enters the mitochondria to complete oxidation. Under anaerobic conditions pyruvate will be converted to lactate. 21. The intermediate stage of cellular respiration is an aerobic process that links glycolysis with the citric acid cycle. It is catalyzed by pyruvate dehydrogenase and involves the decarboxylation of pyruvate to yield carbon dioxide. The remainder of the molecule is combined with coenzyme A to form the acetyl CoA complex. Two molecules of NAD+ are reduced to form NADH + H+ from electrons and protons released during the oxidation of pyruvate to acetyl CoA. 22. The citric acid cycle is an aerobic process that occurs within the matrix of mitochondria. Assuming one molecule of glucose, the process entails the catabolism of one acetyl CoA molecule, yielding one oxaloacetate and two molecules of carbon dioxide. The oxidation of acetyl CoA also yields three molecules of NADH + H+, one molecule of FADH2, and one molecule of ATP. 23. Cellular respiration of one molecule of glucose yields two molecules of ATP and two molecules of NAHD during glycolysis, and two molecules of NADH during the intermediate stage. The citric acid cycle yields six more molecules of NADH + H+, two molecules of FADH2, and two more molecules of ATP. 24. NADH and FADH2 couple the oxidation of glucose and subsequently pyruvate to the electron transport chain. 25. Oxidative phosphorylation entails the transfer of electrons from NADH and FADH2 to the electron transport chain, the establishment of a proton gradient through the use of energy from electron passed along the chain, and finally the diffusion of the proton gradient through the ATP synthetase to form bonds between ADP and Pi. 26. Glycolysis yields two molecules of ATP for every one molecule of glucose. Under aerobic conditions the complete oxidation of one molecule of glucose yields 36 molecules of ATP. 27. Under anaerobic conditions pyruvate is converted to lactate in the cytosol. This facilitates the regeneration of two molecules of NAD+ which can then be utilized to continue with the glycolysis of more glucose, yielding ATP. 28. The beta-oxidation of fatty acids converts them to acetyl CoA, which can only be consumed during the aerobic stage of cellular respiration.

Answers to “Do You Know the Basics?” 1. A Feedback: Energy from the hydrolysis of ATP (a chemical reaction) is used to power the sliding of filaments during a muscle contraction (a mechanical process). 2. A Feedback: Oxidation-reduction reactions involve the exchange of electrons between the oxidizing and the reducing agent. 3. B Feedback: Increasing pH interferes with electrostatic interactions within the enzyme, causing denaturation of the molecule. 4. C Feedback: Since ATP does not bind to the active site of phosphofructokinase, it is not a competitive inhibitor. It is an example of an allosteric/noncompetitive inhibitor. 5. D Feedback: Enzymes are very specific for their substrate and are therefore only involved in very particular reactions. 6. A Feedback: Glycolysis yields two molecules of pyruvate from one molecule of glucose.

7. D Feedback: NAD+ and FAD+ are coenzymes involved in oxidation-reduction reactions where they shuttle electrons away from the substrate. 8. A Feedback: Glycolysis is able to continue under anaerobic conditions, yielding two molecules of ATP, two molecules of NADH, and one molecule of lactate. 9. C Feedback: One molecule of glucose may yield 2 molecules of ATP under anaerobic conditions and 36 molecules of ATP if oxygen is present. 10. D Feedback: Oxidative phosphorylation entails the transfer of electrons from NADH and FADH2 to the electron transport chain, the establishment of a proton gradient through the use of energy from electrons passed along the chain, and finally the diffusion of the proton gradient through the ATP synthase to form bonds between ADP and Pi. 11. Energy stored in glycogen or triglycerides represents chemical energy, a form of potential energy. Electrical energy such as the propagation of an impulse along a neuron, the mechanical energy of a muscle contraction, or sound energy vibrating either the tympanic membrane in the ear or the vocal folds of the larynx are all examples of kinetic energy. 12. Chemical reactions are classified as either reactions that cause a structural change to a molecule, reactions that change the chemical energy of a molecule, or reactions that are either reversible or irreversible. An oxidation-reduction reaction is an exchange reaction and would therefore be an example of a change in chemical structure. 13. ATP is oxidized to ADP and Pi, releasing energy which is used to do work in the cell. The regeneration ATP from ADP and Pi is then coupled to the oxidation of hydrocarbons during cellular respiration. 14. Enzymes are globular proteins that catalyze metabolic reaction by lowering the activation energy necessary for the reaction. The structure of the protein directly affects its affinity for its specific substrate. Thus the slightest conformational change due to a change in temperature or pH can readily affect enzyme function. 15. A metabolic pathway consists of a series of enzyme-catalyzed reactions. Often the final product of the pathway serves as an allosteric inhibitor of enzymes within the pathway, causing a conformation change in the protein. This rearrangement may affect the affinity for the substrate at the enzymes' active site, thereby providing for negative feedback within the system. 16. Glycolysis is an anaerobic process that occurs in the cytosol of a cell. The net reaction entails the synthesis of two 3-carbon pyruvate molecules from one 6-carbon molecule of glucose. The reaction involves the initial input of two molecules of ATP and yields four, for a net yield of two molecules of ATP. Two molecules of NAD+ are also reduced to form NADH + H+ from electrons and protons released during the oxidation of glucose. 17. Under aerobic conditions, in the presence of oxygen, pyruvate enters the mitochondria to complete oxidation. Under anaerobic conditions pyruvate will be converted to lactate. 18. Oxygen serves as the final electron acceptor of the electron transport chain during oxidative phosphorylation. Molecular oxygen (O2) in the mitochondrial matrix is split and each oxygen atom along with electrons from the electron transport chain combine with two hydrogen ions, yielding a molecule of water. 19. The carbon in carbon dioxide is liberated from the hydrocarbon backbone of sugars or other organic molecules used to fuel cellular respiration. 20. Healthy respiratory and cardiovascular systems provide metabolically active tissues with adequate oxygen to drive efficient aerobic respiration. Tissues deprived of oxygen will not be able to burn fuels efficiently nor produce adequate amounts of ATP.

Answers to “Can You Apply What You’ve Learned?” 1. C Feedback: The enzyme tyrosinase is required to convert tyrosine to melanin.

2. The patient would be given O− blood. O− blood does not contain any antigens of the ABO blood group, nor the Rh D antigen. It is therefore the universal donor blood type. It has no surface antigens to trigger agglutination in a recipient, regardless of blood type. 3. An athlete involved in blood doping is trying to get a competitive advantage, by artificially increasing the number of red blood cells available to the body, thereby improving cardiovascular function. This can be accomplished in one of two ways. An athlete can remove a volume of his own blood, forcing his body to produce new blood cells, and then reintroduce the original blood back into his body, thereby increasing the number of red blood cells. Another option is to inject EPO, a synthetic hormone that stimulates red blood cell production. However, there is an inherent danger in increasing the number of formed elements in the blood, thereby increasing its viscosity. This increases total peripheral resistance that may result in blood vessels forcing the heart to work harder.

Chapter 19 Answers to “What Did You Learn?” 1. A failing cardiovascular system will result in tissues that are deprived of needed oxygen and nutrients, waste product accumulation, and possible cell death. 2. All arteries carry blood away from the heart. All veins carry blood toward the heart. 3. Blood returning from the systemic circuit enters the right atrium from the superior vena cava, inferior vena cava, and the coronary sinus. It flows into the right ventricle through the right atrioventricular valve and then into the left ventricle. From the left ventricle, blood flows through the pulmonary semilunar valve and into the pulmonary trunk, which is the start of the pulmonary circuit. Blood returns to the heart from the pulmonary circuit through the pulmonary veins, and enters the left atrium. From the left atrium blood will flow through the left atrioventricular valve, into the left ventricle. From the left ventricle blood will leave the heart, through the aortic semilunar valve, into the aorta, which is the start of the systemic circuit. 4. Sustained pumping of unequal amounts of blood from the ventricles may result in edema. 5. The heart is rotated such that its right side (right atrium and ventricle) is located more anteriorly, while its left side (left atrium and ventricle) is located more posteriorly. 6. The pericardium is composed of two layers: a fibrous pericardium attached to both the sternum and the diaphragm, and an inner serous pericardium. The serous pericardium has two layers: a parietal layer that lines the inner surface of the fibrous pericardium, and a visceral layer that covers the outside of the heart. The space between the parietal and visceral layers is the pericardial cavity. 7. A relatively deep coronary sulcus extends around the circumference of the heart and separates the atria from the ventricles externally. 8. The scalpel would first pass through the fibrous pericardium, followed by the parietal layer of the pericardium, the visceral layer of the pericardium, the myocardium, and finally the endocardium. 9. The interventricular septum separates the left and right ventricles. The septum lies just deep to the interventricular sulcus, which is visible on the superficial surface of the heart. 10. Chordae tendineae are thin strands of collagen fibers that anchor into papillary muscles and attach to the cusp of the atrioventricular valves, to prevent the valve from prolapsing (inverting and flipping into the atrium) when the ventricle is contracting. 11. Cardiac muscle has features that support its great demand for energy, including an extensive blood supply, numerous mitochondria, and other structures such as myoglobin and creatine kinase It is also versatile in being able to use numerous different molecules as fuel for aerobic respiration including fatty acids, glucose, lactic acid, amino acids, and ketone bodies. 12. The fibrous skeleton of the heart acts as an electric insulator because it does not conduct action potentials and thus prevents the atrial chambers from contracting at the same time as the ventricular chambers. 13. The posterior interventricular artery provides blood to the posterior surfaces of the right and left ventricles. Blockage of the posterior interventricular artery would deprive these regions of blood. 14. The coronary sinus collects venous blood and drains deoxygenated blood from the heart wall directly into the right atrium of the heart. 15. The cells of the sinoatrial node initiate the heartbeat, and are therefore commonly referred to as the “pacemaker” of the heart. 16. The cardioacceleratory center is the origin of sympathetic innervations for the heart. Stimulation by the sympathetic division increases both heart rate and the force of heart contraction. 17. Nodal cells have a resting membrane potential of –60 mV. 18. Autorhythmicity refers to a nodal cell’s capacity to depolarize and generate an action potential without any external influence. This process involves an initial influx of Na+ into the cell through slow voltage-gated channels, open from the previous action potential. The cell depolarizes from a resting membrane potential of –60 mV to a threshold of –40mV, triggering the opening of fast voltage-gated Ca2+ channels, allowing the cell to depolarize to just above 0 mV. As Ca2+ channels close, voltage-gated K+ channels

open, allowing an influx of K+ into the nodal cell, resetting the resting membrane potential, and once again triggering the opening of slow voltage-gated Na+ channels. 19. Starting with the sinoatrial node the action potential will travel through the myocardium of the atria. It will trigger the atrioventricular node, which will in turn pass the action potential to the AV bundle, the left and right bundle branches, Purkinje fibers, and finally the myocardium of the ventricles. 20. AV nodal cells have both smaller fiber diameters and fewer numbers of gap junctions, which serve to slow down the conduction of the action potential from the atria to the ventricles. 21. Voltage-gated Ca2+ channels allow calcium to enter cardiac muscle cells. 22. (1) Depolarization of cardiac muscle cells occurs as a result of fast voltage-gated Na+ channels opening. (2) Even though slow voltage-gated K+ channels open to depolarize the cell, Ca2+ channels open, allowing an influx of Ca2+ to prolong the depolarization, producing the plateau phase of the action potential. (3) Finally, Ca2+ channels close, allowing repolarization of the cell through the continued influx of K+. 23. The plateau phase of a cardiac muscle cell contraction allows for a prolonged refractory period. This delay does not allow the summation of muscle contractions in the heart, preventing tetany. 24. The P wave reflects electrical changes of atrial depolarization. The QRS complex represents the electrical changes associated with ventricular depolarization. The T wave is the electrical change associated with ventricular repolarization. The P-Q and S-T segments represent the atrial and ventricular plateau phases, respectively. 25. Pressure changes that occur during the cardiac cycle produce the unidirectional movement of blood through the heart chambers, as well as opening and closing of heart valves to ensure that blood continues to move in a “forward” direction without backflow. 26. During late ventricular systole, semilunar valves open and ventricular ejection occurs as blood leaves the heart and enters the trunks of the aorta and pulmonary artery. 27. Increased ventricular pressure during ventricular systole causes both the closing of the atrioventricular valves and opening of the semilunar valves. 28. The end-diastolic volume is the amount of blood in a relaxed ventricle, after atrial systole. Stroke volume is the amount of blood ejected from the heart during ventricular systole. Since not all of the blood is ejected from the heart during a ventricular contraction, the volume of blood remaining in ventricles after a contraction is the end-systolic volume. 29. Cardiac output is a function of stroke volume and heart rate. 30. The resting cardiac output would be (75 beats/min × 70 mL/beat) 5.25 L/min. The cardiac output during exercise would be (150 beats/min × 100 mL/beat) 15.0 L/min. The cardiac reserve would be (15.0 L/min – 5.25 L/min) 9.75 L/min. 31. A positive chronotropic agent such as caffeine or cocaine will increase heart rate. A negative chronotropic agent such as β-blocker will decrease heart rate. 32. Entry of calcium ions into a cell brings it closer to threshold, whereas the efflux of potassium ions from a cell will hyperpolarize the cell, making it more difficult for the cell to reach threshold. 33. Increased venous return causes stretching of the heart walls, causing an increased preload, which increases the force of the subsequent contraction, and therefore increases stroke volume. Increased calcium in the sarcoplasm increases the number of ions available to bind to troponin, also increasing the force of contraction. 34. Stroke volume and heart rate have a direct relationship; therefore, as both variables increase, so does cardiac output. 35. Blood from the systemic circuit would flow from the right atrium to the left atrium through the foramen ovale, from where it would again enter into the systemic circuit, bypassing the pulmonary circuit.

Answers to “Do You Know the Basics?” 1. B Feedback: Blood returning from the systemic circuit enters the right atrium from the superior vena cava, inferior vena cava, and the coronary sinus. It flows into the right ventricle through the right atrioventricular valve and then into the left ventricle. From the left ventricle, blood flows through the pulmonary semilunar valve and into the pulmonary trunk, which is the start of the pulmonary circuit. 2. B Feedback: The pericardium is composed of two layers: a fibrous pericardium attached to both the sternum and the diaphragm, and an inner serous pericardium. The serous pericardium has two layers: a parietal layer that lines the inner surface of the fibrous pericardium, and a visceral layer, which covers the outside of the heart. The space between the parietal and visceral layers is the pericardial cavity. 3. D Feedback: The pulmonary semilunar valves prevent the backflow of blood from the pulmonary trunk, back into the right ventricle. 4. A Feedback: Blood returning from the systemic circuit enters the right atrium from the superior vena cava, inferior vena cava. Blood returning from the coronary blood supply drains to the right atrium through the coronary sinus. 5. A Feedback: An influx of calcium ions into a nodal cell causes depolarization. 6. B Feedback: Gap junctions within intercalated discs allow calcium to flow across to adjacent cardiac muscle cells, thereby propagating the action potential. 7. B Feedback: Contraction of the papillary muscles puts tension on the AV valve flaps through the chordae tendineae, thereby preventing prolapse of the valves and the subsequent backflow of blood into the atria. 8. A Feedback: The preload is a function of the end-diastolic volume, and depends upon the amount of venous return of blood to the heart. 9. D Feedback: Blood from the pulmonary trunk travels to the lungs through the pulmonary arteries. Pulmonary veins then bring blood back to the left atrium. 10. D Feedback: During the atrial reflex, increased venous return to the atria triggers sympathetic pathways that increase both the heart rate and force of contraction. 11. The pulmonary circuit carries blood from the right ventricle to the lungs and then back to the left atrium. The systemic circuit carries blood from the left ventricle through systemic arteries to all regions of the body, and then back to the left atrium through systemic veins. 12. The parietal layer of serous pericardium is a serous membrane that lines the inner surface of the fibrous pericardium, which supports the heart in the mediastinum. The visceral layer of serous pericardium (also called the epicardium) is a serous membrane that covers the outside of the heart. Together, both layers produce serous fluid in the pericardial cavity to reduce friction as the heart moves during beating. 13. Chordae tendineae are thin strands of collagen fibers that anchor into papillary muscles and attach to the cusp of the atrioventricular valves to prevent the valve from prolapsing (inverting and flipping into the atrium) when the ventricle is contracting. 14. The atria are thin walled because they do not need to generate high pressure to push blood into the ventricles. Most of the filling of the ventricles is passive, and the ventricles are inferior to the atria so moving blood into the ventricles from the atria is relatively easy. The right ventricle wall is relatively thin with respect to the left ventricle wall because the right ventricle only has to pump blood through the pulmonary circuit to the lungs immediately lateral to the heart, whereas the left ventricle must generate enough pressure to drive blood through the entire systemic circuit.

15. Intercalated discs attach adjacent cardiac muscle cells. They also contain numerous gap junctions, which allow an action potential to move continuously along the sarcolemma of adjacent cells, resulting in synchronous contraction of the muscle. 16. The right coronary artery typically branches into a marginal artery (which supplies the right border of the heart) and the posterior interventricular artery (which supplies both left and right ventricles). The left coronary artery typically branches into the anterior interventricular artery (also called the left anterior descending artery), which supplies the anterior surface of both ventricles, most of the interventricular septum, and the circumflex artery (supplies left atrium and ventricle). 17. Sympathetic innervation increases heart rate and increases the force of the heart contractions. Parasympathetic innervation will decrease the heart rate. Parasympathetic innervation tends to have no effect on the force of contractions, except in special circumstances. 18. Spontaneous depolarization of cells within the sinoatrial node initiates an action potential that is propagated through gap junction across the cells of the left and right atria, causing atrial systole. As the atria are contracting, the action potential stimulates the atrioventricular node at the base of the right atrium, from where it travels along the AV bundle, the bundle branches, and finally the Purkinje fibers. The slow conduction through the AV node ensures that the signal does not reach the ventricles until atrial diastole, at which point the Purkinje fibers generate an action potential within the myocardium of the ventricles, causing ventricular systole. 19. The phases of the cardiac cycle are atrial systole, ventricular systole (early and late), and ventricular diastole (early and late). (1) During atrial systole, the atria contract to pump blood into the ventricles to finish their filling. The AV valves remain open and the ventricles are still in diastole from the previous cycle. The semilunar valves remain closed. (2) During early ventricular systole, the atria are now in diastole, the ventricles begin to contract, and the AV valves close. The semilunar valves remain closed for a short period of time and then they are forced open. (3) During late ventricular systole, the atria remain in diastole, the ventricles continue contracting, the AV valves remain closed, and the semilunar valves remain open. (4) During early ventricular diastole, the atria remain in diastole, the ventricles enter diastole, the semilunar valves close, and the AV valves remain closed for a short period of time and then they open. (5) During late ventricular diastole, the atria remain in diastole, the AV valves remain open, the ventricles passively fill with blood, and the semilunar valves remain closed. 20. Cardiac output is the amount of blood ejected from the heart in 1 minute. It is a function of the amount of blood ejected with each contraction (stroke volume) and the number of times that the heart contracts per minute (heart rate).

Answers to “Can You Apply What You’ve Learned?” 1. D Feedback: Tachycardia may result in inefficient cardiac output because of a decreased ejection fraction, resulting in an increased endsystolic volume. 2. B Feedback: Blood pressure monitoring would give an indication of the state of the circulatory system, which although influenced by the heart, is not a good indicator of heart health. 3. C Feedback: Calcium channel blockers cause a negative ionotropic effect, decreasing the contractility of the heart, and subsequently decreasing cardiac output. 4. D Feedback: Decreased blood volume will cause decreased end-diastolic volume. Low end-diastolic volume will result in decreased stroke volume, and subsequent decreased cardiac output. The body will try to maintain cardiac output by increasing the heart rate. 5. B Feedback: Severing the vagus nerve will result in loss of vagal tone, allowing the SA node to increase the rate of contraction to either its own inherent pace or the pace set by any sympathetic stimulation.

Answers to “Can You Synthesize What You’ve Learned?” 1. Under normal conditions, in a fully developed heart, deoxygenated blood returning from the systemic circuit enters the right atrium from the superior vena cava, inferior vena cava, and the coronary sinus. It flows into the right ventricle through the right atrioventricular valve and then into the left ventricle. From the left ventricle, blood flows through the pulmonary semilunar valve and into the pulmonary trunk, which the start of the pulmonary circuit. Oxygenated blood returns to the heart from the pulmonary circuit through the pulmonary veins, and enters the left atrium. From the left atrium blood will flow through the left atrioventricular valve, into the left ventricle. From the left ventricle blood will leave the heart, through the aortic semilunar valve, into the aorta, which is the

start of the systemic circuit. With the foramen ovale open, deoxygenated blood from the systemic circuit would flow from the right atrium to the left atrium through the foramen ovale, from where it would again enter into the systemic circuit, bypassing the pulmonary circuit. 2. Angina pectoris results from diminished blood supply to the myocardium, usually caused by occlusion of blood flow through coronary arteries. It presents as pain on the left side of the body, usually the arm, jaw, or shoulder. This is an example of referred pain, which results from the merging of sensory stimuli originating due to lactic acid accumulation in the myocardium, with somatosensory stimuli from the left side of the body. 3. If the SA node is not functioning, the atria do not contract; fortunately, they only contribute a small fraction to the total enddiastolic volume. The ventricles would continue to contract because the AV node becomes the “default” pacemaker, and establishes the heart rate.

Chapter 20 Answers to “What Did You Learn?” 1. Arteries are usually thicker than companion veins. Arteries also have a predominant tunica media. Without a predominant layer of smooth muscle, by default, veins have a predominant tunica externa. Finally, veins have one-way valves, whereas arteries do not. 2. As arteries branch on to progressively smaller vessels their luminal diameter decreases. The composition of the tunics also changes, with a decrease in the amount of elastic fibers, and an increase in the amount of smooth muscle present in the walls of the arteries. 3. Sinusoids are the most permeable capillaries. They are located within bone marrow, liver, spleen, anterior pituitary gland, adrenal gland, and parathyroid glands. 4. Because veins contain over 55% of all of the blood within the body, they serve as reservoirs for blood. 5. There are four alternatives to a simple pathway of blood flow. The simple pattern involves blood flowing through an arteriole to a capillary bed, and out of the capillaries through a venule. An arterial anastomosis includes two or more arteries converging to supply the same body region. Similarly, a venous anastomosis includes two or more veins draining the same body region. An arteriovenous anastomosis is a shunt, bypassing a capillary bed by connecting an arteriole directly to a vein. Portal system blood flows through two capillary beds, with the two capillary beds separated by a portal vein. 6. Water-soluble substances such as carbon dioxide, oxygen, waste products, hormones, and nutrients enter or leave capillaries by diffusion. Lipid-soluble hormones and other molecules such as fatty acids utilize vesicular transport to enter or leave capillaries. 7. Hydrostatic pressure is the physical force exerted by a fluid on a structure. In contrast, osmotic pressure is the pull of water into an area by osmosis due to the higher relative concentration of solutes. 8. Blood hydrostatic pressure is greater at the arterial end of the capillary (35 mm Hg) and less at the venous end (16 mm Hg). In contrast, the net colloid osmotic pressures remain relatively constant (21 mm Hg). 9. The blood hydrostatic pressure is the greatest force at the arterial end of the capillary. This results in positive net filtration pressure, forcing fluids out of the capillary. At the venous end, the greatest force is due to the blood colloid osmotic pressure, resulting in a negative net filtration pressure, forcing fluids into the capillary. 10. Without functional lymphatic vessels, the excess 15% of fluid not reabsorbed by capillaries would accumulate within the tissue, causing edema. 11. Angiogenesis is stimulated in skeletal muscle in response to aerobic training, in adipose tissue. Angiogenesis occurs when an individual gains weight in the form of fat deposits. 12. Carbon dioxide, H+, K+, and lactic acids are by-products of cellular metabolism. As the metabolic rate increases, so do the levels of these by-products, which in turn act as local signals causing vasodilation, and increased blood flow to the tissue. 13. Total blood flow is a function of cardiac output. As total blood flow increases, so does the local blood flow to a tissue. 14. The pulse pressure is (155 mm Hg – 95 mm Hg) 60 mm Hg. The mean arterial pressure is (95 mm Hg + [1/3 × 60 mm Hg]) 115 mm Hg. 15. Capillary blood pressure must be sufficient for exchange of substances between the blood and surrounding tissue, but not be so high that it would damage the fragile vessels. 16. The relatively small pressure gradient (20 mm Hg) of veins is overcome by the respiratory pump and the skeletal muscle pump. The skeletal muscle pump entails movement of limbs, which compresses vessels in propelling blood. This movement is restricted to only one direction by one-way venous check valves. The respiratory pump carries out a similar role in the thoracic cavity, fluctuating intrathoracic pressure with each breath, and thereby compressing blood vessels. 17. The pressure gradient of systemic circulation is calculated by subtracting the mean arterial pressure in the vena cava from that of arteries near the aorta. This blood pressure gradient is the driving force to move blood through the vasculature. Changes in the blood pressure gradient are directly correlated with changes in total blood flow.

18. Resistance is defined as the amount of friction the blood experiences as it travels through the blood vessels. 19. There is a direct relationship between the viscosity of blood and resistance. As viscosity increases, so does resistance. A similar relationship exists between vessel length and resistance. There is an inverse relationship between the diameter of blood vessels and resistance. As diameter decreases, resistance increases. 20. Individuals with sustained increased resistance generally exhibit elevated arterial blood pressure readings. This condition occurs because a greater pressure gradient must be produced to overcome the higher resistance and ensure normal blood flow and adequate perfusion of all tissues. 21. Short-term mechanisms for regulating blood pressure are important when a person arises from a sitting to a standing position. 22. As a person arises to a standing position her blood pressure will initially drop, but then be quickly reestablished to normal levels through the following mechanism: (1) Decreased stretch in the blood vessel wall is detected by baroreceptors in aortic arch baroreceptors and carotid sinuses. (2) The baroreceptors decrease their firing rate along the vagus and glossopharyngeal nerves, signaling the cardiovascular center in the medulla oblongata. (3) The cardioacceleratory center of the cardiac center increases stimulation to the SA and AV nodes, increasing cardiac output, while at the same time the cardioinhibitory center decreases parasympathetic stimulation. (4) Simultaneously, the vasomotor center stimulates vasoconstriction and an increase in peripheral resistance, along with shifting of blood from venous reservoirs. The resulting increase in cardiac output, increase in resistance, and larger circulating blood volume quickly elevate blood pressure. 23. Renin produced by the kidneys converts angiotensinogen into angiotensin I. Angiotensin I is then converted to angiotensin II by angiotensin-converting enzyme, found primarily within the endothelium of capillaries in the lungs. Angiotensin II raises blood pressure by causing vasoconstriction, causes a sensation of thirst, and induces the release of aldosterone and antidiuretic hormone. Since both of these hormones cause fluid retention in the kidneys, they increase blood volume and therefore raise blood pressure. 24. Atrial natriuretic peptide causes vasodilation, which lowers the total peripheral resistance, increases urine production, and ultimately decreases blood pressure. 25. Blood flow velocity decreases significantly in capillaries that have a decreased total cross-sectional area, a measurement that takes into consideration the total length of capillaries in the body, along with their diameters. 26. During exercise blood is diverted from the kidneys and digestive system to the coronary arteries, skeletal muscles, and skin. 27. All of the blood returning from the systemic circuit must eventually be pumped to the pulmonary circuit (accounting for endsystolic volume of the right ventricle). 28. Blood pressure is lower throughout the pulmonary circulation in comparison to the systemic circulation. 29. The brachiocephalic trunk supplies blood to the right arm, the right side of the face, and the brain. The left coronary artery supplies blood to the left side of the face and the brain, and the left subclavian artery provides blood to the left arm. 30. The superior vena cava drains the head, neck, upper limbs, and thoracic cavity. The inferior vena cava carries blood toward the heart from the lower limbs, pelvis, perineum, and abdomen. 31. The vertebral artery, thyrocervical trunk, and costocervical trunk branch off of the subclavian artery to provide blood supply to the head and neck. These regions are then drained by the vertebral, internal jugular, and external jugular veins. 32. Most of the venous blood of the cranium drains through the dural venous sinuses into the internal jugular veins. 33. The azygous system drains into the superior vena cava. 34. The bronchi, bronchioles, and connective tissue of the lungs are supplied with oxygenated blood by the bronchial arteries. 35. The celiac trunk branches into the common hepatic, left gastric, and splenic arteries. The common hepatic artery supplies blood to the liver, gallbladder, duodenum, as well as parts of the pancreas and stomach. The left gastric artery supplies blood to parts of the stomach and esophagus. The splenic artery supplies blood to the spleen, and part of the pancreas and stomach.

36. The splenic, inferior mesenteric, and superior mesenteric veins drain into the hepatic portal system. The hepatic portal system passes blood from organs of digestion and the spleen through the liver before entering the systemic circuit. 37. The kidneys receive blood through the renal arteries. The adrenal glands receive blood from the renal, middle suprarenal, and inferior phrenic arteries. The female uterus receives blood through the uterine artery. 38. From the subclavian artery blood will flow through the axillary artery, the brachial artery, then through either the ulnar or radial arteries, to the deep palmar arch, and finally to the digital arteries of the thumb. 39. The primary superficial veins of the upper limbs include the basilic, cephalic, and median cubital veins. 40. From the external iliac artery blood will flow into the femoral artery, through the popliteal artery, the anterior tibial artery, the dorsal pedis artery, the plantar arterial arch, and finally the digital arteries of the foot. 41. The great saphenous vein runs the length of the leg, and is significantly longer than the small saphenous vein, which joins the femoral vein within the popliteal region. 42. The umbilical vein delivers oxygenated blood from the placenta to the fetus. The ductus venosus shunts blood from the umbilical vein to the inferior vena cava, bypassing the fetal liver. Blood is shunted from the right atrium to the left atrium of the fetal heart through the foramen ovale, bypassing the pulmonary circuit. Any blood that does enter the fetal pulmonary circuit is shunted from the pulmonary trunk to the aorta by the ductus arteriosus. Blood returns to the placenta from the fetus through the umbilical arteries. 43. The ductus arteriosus and foramen ovale must close after birth in order to completely engage the pulmonary circuit of the neonate.

Answers to “Do You Know the Basics?” 1. B Feedback: Sinusoids are very unselective, and are not found in the brain. 2. C Feedback: Without a predominant layer of smooth muscle, by default, veins have a predominant tunica externa. 3. C Feedback: Vasa vasorum provide arterial blood to the tunica externa of a large vessel. 4. A Feedback: Decreased blood flow will decrease the amount of blood reaching a region, decreasing perfusion. Increased carbon dioxide, H+, or decreased O2 levels cause vasodilation, which ultimately improves perfusion of a tissue. Angiogenesis also provides more blood flow to a region, increasing perfusion. 5. B Feedback: The relatively small pressure gradient of veins is overcome by the respiratory pump and the skeletal muscle pump. 6. B Feedback: Increasing diameter will decrease resistance, increasing blood flow. 7. D Feedback: Total blood flow is important for maintaining adequate perfusion of a tissue. It increases with increasing pressure, but decreases against increasing resistance. 8. B Feedback: Blood flow velocity decreases significantly in capillaries which have a decreased total cross-sectional area, a measurement that takes into consideration the total length of capillaries in the body, along with their diameters. 9. D Feedback: Blood pressure is regulated by the cardiovascular center of the medulla oblongata, through the autonomic nervous system. It can also be adjusted by hormones such as epinephrine, antidiuretic hormone, aldosterone, atrial natriuretic peptide, or angiotensin.

10. D Feedback: From the subclavian artery blood will flow through the axillary artery, the brachial artery, then through either the ulnar or radial arteries. 11. The tunica intima consists of an endothelium of simple squamous connective tissue, lined by a subendothelial layer of areolar connective tissue. The tunica media is composed predominantly of layers of smooth muscle. The tunica externa consists primarily of dense irregular connective tissue. 12. Arteries transport blood away from the heart. Veins return blood to the heart. Relative to veins, arteries have smaller luminal diameters and experience greater pressures. The tunica media is the predominant layer in arteries. Without a predominant layer of smooth muscle, by default, veins have a predominant tunica externa. 13. Hydrostatic pressure is the physical force exerted by a fluid on a structure. In contrast, osmotic pressure is the pull of water into an area by osmosis due to the higher relative concentration of solutes. Blood hydrostatic pressure is greater at the arterial end of the capillary (35 mm Hg) and less at the venous end (16 mm Hg). In contrast, the net colloid osmotic pressures remain relatively constant (21 mm Hg). 14. NFP = (HPb − HPif) − (COPb − COPif) 15. Blood flow decreases in longer vessels and increases in smaller vessels. However, since there are more smaller vessels than larger vessels, as the total cross-sectional area decreases so does blood flow. The viscosity of blood has inverse relationship with blood pressure. Increased blood viscosity decreases blood flow. Conversely, increased blood pressure increases blood flow. 16. Blood vessels containing α-adrenergic receptors contract in response to sympathetic stimulation, resulting in vasoconstriction; these include most vessels of the body. In contrast, blood vessels with β receptors relax in response to epinephrine, resulting in vasodilation; these include blood vessels in skeletal muscle and the coronary vessels. 17. Increased blood volume, increased cardiac output, and increased resistance will all raise blood pressure. 18. The cardiac center increases stroke volume and heart rate, thereby increasing cardiac output, and consequently raising blood pressure and blood flow. The vasomotor center regulates the degree of vasoconstriction, adjusting resistance in blood vessels, and subsequently adjusting blood pressure and blood flow. 19. In the systemic circuit arteries carry oxygenated blood away from the heart, to various parts of the body, and veins return deoxygenated blood back to the heart. In the pulmonary circuit arteries carry deoxygenated blood to the lungs, and pulmonary veins bring oxygenated blood back to the heart. 20. Postnatal changes to the circulatory system include constriction of the umbilical veins, umbilical arteries, and ductus venosus, so that they are no longer functional, and closure of the foramen ovale and ductus arteriosus. These changes are necessary in order to completely engage the neonate’s pulmonary circulation.

Answers to “Can You Apply What You’ve Learned?” 1. C Feedback: Albumin is the main plasma protein required for establishing the colloid osmotic pressure. Insufficient colloid osmotic pressure will not affect hydrostatic pressure, so blood will still leave capillaries, but it will not be drawn back in sufficiently, resulting in edema. 2. B Feedback: Exercise will cause an increase in blood pressure. Atrial natriuretic peptide lowers blood pressure by causing vasodilation. 3. D Feedback: Decreased blood supply to the brain can cause dizziness and possibly syncope (fainting). The carotid sinus detects changes in blood pressure en route to the brain and then signals the cardiovascular center in the medulla oblongata. The cardiovascular center adjusts cardiac output and vasoconstriction accordingly, to maintain adequate blood flow to the brain. 4. A Feedback: Storage of excess fat requires angiogenesis, increasing the overall length of the blood supply. Increasing length lowers blood flow, which must be compensated for by increasing other factors such as cardiac output, in order to restore blood flow. Losing fat reduces the blood flow necessary to maintain the adipose tissue, and therefore lowers blood pressure.

5. D Feedback: The popliteal artery is the origin of three collateral channels—the anterior tibial, posterior tibial and fibular arteries— which all anastamose at the foot.

Answers to “Can You Synthesize What You’ve Learned?” 1. Hypertension may cause damage to the endothelium of blood vessels. An inflammatory response to the damaged endothelium leads to a buildup of plaque within the walls of the artery. Low-density lipoproteins and very-low-density lipoproteins infiltrate and get trapped within the damaged tissue and become oxidized. These oxidized proteins, along with invading monocytes, turn lipids in the tunica intima into foam cells, which are then replaced by muscle tissue. This expanding mass of oxidized lipids and smooth muscle tissue is called an atheroma. As it expands, it can occlude the lumen of the artery, a condition called atherosclerosis. 2. Flexion at a joint can occlude blood flow through arteries in the region. Anastomoses at joints provide for alternative blood flow when vessels are occluded due to flexion. 3. Increased deposits of adipose tissue due to weight gain require angiogenesis to provide blood flow to the new tissue. This increases the total length of the vasculature, and subsequently increases resistance to cardiac output from the heart. As resistance increases, cardiac output must be increased, which raises blood pressure.

Chapter 21 Answers to “What Did You Learn?” 1. Lymphatic capillaries typically absorb water, dissolved solutes, and small amounts of protein. 2. The hydrostatic pressure of interstitial fluid separates the endothelial cells that form the lymphatic capillaries, allowing the interstitial fluid to enter the capillary. Once inside, the fluid exerts pressure on the endothelial cells, closing the gaps, and trapping the fluid in the vessel. 3. The lymphatic trunks drain lymph from various regions of the body. The trunks merge into one of two distinct lymphatic ducts. Each duct then returns the fluid back to the systemic circuit of the circulatory system. 4. The right lymphatic duct receives lymph from (1) the right side of the head and neck, (2) the right upper limb, and (3) the right side of the thorax. 5. Primary lymphatic structures, such as bone marrow and thymus, are involved in the formation and maturation of lymphocytes. Secondary lymphatic structures' immune cells follow their formation and provide the site where an immune response is initiated. The major secondary lymphatic structures include the lymph nodes, spleen, tonsils, lymphatic nodules, and MALT. 6. Red bone marrow is the site of production of all formed elements in the blood, including all lymphocytes; hence it is a primary lymphatic structure. 7. The cortex of the thymus contains immature T-lymphocytes (pre-T-lymphocytes), and the medulla contains mature T-lymphocytes. 8. Numerous lymphatic vessels will deliver lymphatic fluid to a lymph node. As the materials within the fluid percolate through the sinuses located in the medulla of the lymph node, they will be exposed to macrophages and lymphocytes. Macrophages will remove foreign particles from the lymphatic fluid. Lymphocytes will initiate an immune response upon exposure to the foreign particles. 9. The spleen is responsible for the filtration of blood. The white pulp of the spleen contains lymphocytes which monitor the blood for pathogens, and are capable of initiating an immune response. The red pulp within the sinusoids of the spleen contains macrophages, which remove foreign substances, pathogens, and either old or defective erythrocytes and platelets. 10. Lymph nodes filter lymph, whereas the spleen filters blood. 11. The three sets of tonsils are the pharyngeal, palatine, and lingual tonsils. Tonsils help protect against foreign substances that may be either inhaled or ingested. 12. The lymphatic cells in the MALT help defend against foreign substances that come in contact with mucosal membranes.

Answers to “Do You Know the Basics?” 1. B Feedback: The lymphatic system provides for an alternative route for the return of fluid toward the heart in the systemic circuit. It also provides an opportunity for lymphocytes and macrophages to filter and process body fluids. 2. A Feedback: The thoracic duct drains lymph from the right side of the head, neck, right arm, and the right side the thoracic cavity. 3. C Feedback: Lymphatic structures have an opening within their connective tissue coverings, which permit either lymphatic vessels or blood vessels to enter and leave the organs. 4. A Feedback: Although immature T-lymphocytes originate within red bone marrow, they complete maturation within the thymus. 5. B Feedback: Lymphatic capillaries are homologous with blood capillaries, in that they consist of a simple endothelial layer. Unlike blood capillaries, they also possess one-way flaps that allow interstitial fluid to enter the lymphatic system.