Human Anatomy and Physiology BIOL3306 Fall 2024 PDF

Human Anatomy and Physiology BIOL3306 Fall 2024 Week 9: The Cardiovascular System The Blood Vessels Professor: Nour Nissan The Blood Vessels The Vasculature consists of billions of blood vessels that transport blood to the tissues, where gases, nutrients, a...

Human Anatomy and Physiology BIOL3306 Fall 2024 Week 9: The Cardiovascular System The Blood Vessels Professor: Nour Nissan The Blood Vessels The Vasculature consists of billions of blood vessels that transport blood to the tissues, where gases, nutrients, and wastes are exchanged, and then transport it back to the heart Collectively, they measure over 96,000 km long Other functions: – Regulate blood flow to tissues – Control blood pressure – Secrete a variety of chemicals Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved Blood Vessels Transport Blood Arteries –................................................... – Transport blood under high pressure – Are thick-walled Veins –............................................. – Are thin-walled Capillaries –.......................................................................... – Are microscopic Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.1 Overview of Arteries and Veins Arteries—Distribution System of the vasculature; Travel away from the heart, branching into vessels of progressively smaller diameter Arteries in the pulmonary circuit carry deoxygenated blood, while those in the systemic circuit carry oxygenated blood Capillaries—Exchange System of the vasculature; Smallest diameter; Form branching networks of Capillary Beds Gases, nutrients, wastes, and other substances are exchanged between the cells and the blood through the capillary walls Veins—Collection System of the vasculature; Drain blood from capillary beds and return it to the heart; Small veins merge with others to become progressively larger In the pulmonary circuit, veins transport oxygenated blood; In the systemic circuit, veins transport deoxygenated blood Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.1 Arteries and Veins Arteries: comprised of elastic tissue Arterioles—Smallest arteries, all contain smooth muscle Veins Outnumber arteries; Less elastic. Thin walls Venules—Smallest veins; Drain blood from capillary beds.............................. —Endothelial flaps. Prevent backflow in the veins; Numerous in the legs Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart Pumps Blood through the Vessels Pump composed entirely of living cells and cellular materials Output can vary from 5 liters to 25 liters of blood/minute Heart rate at rest: 75 beats/minute Heart rate can accelerate to over 200 beats/minute with exertion Heart can beat on its own, yet heart rate can be modified by the nervous system Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.2 Blood Pressure in Different Portions of the Circulation Blood Pressure in the Table 18.2 Pressures in pulmonary circuit is the Pulmonary and much............ (about 15 m Systemic Circuits m Hg) than in the systemic circuit (about 95 mm Hg) Circuit Pulmonary Circuit Pressure Blank Cardiac Outputs (how Pulmonary arteries 15 mm Hg much blood is being Pulmonary veins 5 mm Hg ejected from the Systemic Circuit Blank Arteries 120 mm Hg ventricles) the right and (systolic), 80 mm Hg (diastolic) left ventricles are equal Arterioles 80–35 mm Hg even though the right Capillaries 35–15 mm Hg ventricle has thinner walls Venules 15–5 mm Hg than the left ventricle Veins 5–0 mm Hg Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.2 Blood Pressure in Different Portions of the Circulation Systemic Arterial Pressure Highest in the aorta and the elastic arteries and declines slightly as it spreads through the muscular arteries Systolic Pressure—Pressure during ventricular systole; Averages about 110–120 mm Hg Diastolic Pressure—Pressure during ventricular diastole; Averages about 70–80 mm Hg........................................ (.................... )—Average pressure in the systemic arteries during an entire cardiac cycle; Generally measures around 95 mm Hg (ensuring effective organ perfusion and tissue oxygenation.) Pulse Pressure—Difference between pressures; About 40 mm Hg (this reflects the force the heart generates with each contraction). Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.2 Blood Pressure in Different Portions of the Circulation Calculating the.................................................... Use measured systolic and diastolic pressures to estimate MA P; Heart spends more time in diastole than systole MAP = diastolic pressure + 1 (systolic pressure – diastolic pressure) 3 So the MA P is approximately equal to the diastolic pressure plus one- third of the pulse pressure; For a normal blood pressure of 120 80 : 1 MAP = 80 mm Hg + (120 mm Hg  80 mm Hg) 3 = 93mm Hg This is close to the average MA P of about 95 mm Hg Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.2 Blood Pressure in Different Portions of the Circulation Systemic Arterial Pressure (continued) Pressure in the systemic circuit declines sharply in the arterioles; About 80 mm Hg in large arterioles to about 30 mm Hg in small arterioles; Due to increased peripheral resistance Measuring the Arterial Blood Pressure Typically measured in the arm using a Sphygmomanometer and a Stethoscope.................... Pressure—When the sounds are first heard.................... Pressure—When the sounds almost stop Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.2 Blood Pressure in Different Portions of the Circulation Systemic Capillary Pressure Pressure continues to decline throughout the remainder of the systemic circuit At the arterial end of a capillary bed, the pressure is about 35 mm Hg At the venular end of the capillary bed, the pressure has decreased to about 15 mm Hg This decrease is largely due to the reduction in blood volume that takes place in capillaries Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.2 Blood Pressure in Different Portions of the Circulation Systemic Venous Pressure Pressure declines further in the venules and veins, dropping to only about 4 mm Hg in the inferior vena cava and as low as 0 mm Hg in the right atrium Due largely to the high compliance of veins and declining resistance as these vessels merge and become larger Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.2 Blood Pressure in Different Portions of the Circulation Mechanisms of Venous Return 1) Venous Valves—Prevent backflow in the veins 2) Smooth Muscle in the Walls of Veins—May contract under sympathetic nervous system stimulation to increase the rate of venous return 3) Skeletal Muscle Pump—Skeletal muscles surrounding the deeper veins of the upper and lower limbs squeeze the blood in the veins and propel it toward the heart as they contract and relax 4) Respiratory Pump—Similar mechanism for veins of the thoracic and abdominopelvic cavities; Driven by the rhythmic changes in pressure in the cavities that occur with ventilation; During inspiration, high pressure in the abdominopelvic cavity pushes blood in the abdominal veins upward Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.2 Blood Pressure in Different Portions of the Circulation Figure 18.6 The skeletal muscle pump. Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.3 Disorders of Blood Pressure: Hypertension and Hypotension........................—An abnormally high blood pressure; May be acute (short-term) or chronic (long-term) Estimated 20% of the world’s population has chronic hypertension; Associated with coronary artery disease (leading cause of death in North America); stroke (fifth leading cause of death), heart failure, certain types of dementia, kidney disease, and vascular disease Classified based on the average of two or more readings recorded on two or more successive visits to a healthcare provider Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.3 Disorders of Blood Pressure: Hypertension and Hypotension Hypertension (continued) Normal (Normotensive): systolic less than 120 mm Hg and diastolic less than 80 mm Hg Pre-Hypertension: systolic 120–139 mm Hg, diastolic 80– 89 mm Hg Stage 1 Hypertension: systolic 140–159 mm Hg, diastolic 90–99 mm Hg Stage 2 Hypertension: systolic greater than or equal to 160 mm Hg, diastolic greater than or equal to 100 mm Hg Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.3 Disorders of Blood Pressure: Hypertension and Hypotension Hypertension (continued) Two key areas in treatment are lifestyle modifications, including smoking cessation, weight loss if needed, limited alcohol intake, increased physical activity, dietary modifications including decreased salt, cholesterol, and saturated fat intake Drug therapy targets cardiac output, blood volume, and peripheral resistance. Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.3 Disorders of Blood Pressure: Hypertension and Hypotension...........................—Abnormally low blood pressure; May be chronic, but most cases are acute; Defined as a systolic pressure lower than 90 mm Hg and/or a diastolic pressure lower than 60 mm Hg, but is generally diagnosed if an individual shows symptoms Mild hypotension may cause dizziness and lightheadedness Severe hypotension (Circulatory Shock) results in loss of consciousness and organ failure; Insufficient blood pressure to deliver oxygen and nutrients to cells, which can rapidly be fatal Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.4 Capillary Structure and Function Tissue Perfusion—Blood flow to a tissue through a capillary bed; Occurs in most tissues except cartilage, the sclera and cornea of the eye, and epithelial tissue Pericytes—Contractile fibers around some capillaries. Pericytes can contract and relax, which allows them to regulate the diameter of capillaries and control blood flow at the microvascular level. This is particularly important for matching blood supply with the metabolic needs of tissues. Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.4 Capillary Structure and Function Capillary Exchange—Movement of nutrients, gases, ions, and waste, between the blood in the capillary and the tissue cells; Three mechanisms: Diffusion through the membranes of endothelial cells – Lipid-soluble substances including oxygen, carbon dioxide, and some lipids move easily through the cells Diffusion and osmosis through gaps and fenestrations – Many capillaries have small gaps between endothelial cells and some have Fenestrations, or pores, within their cells; Water and small solutes, such as amino acids, can move through these pores........................ – Larger substances are taken into the cell by endocytosis and then leave the other side of the cell by exocytosis Ex. Proteins like insulin Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.4 Capillary Structure and Function Figure 18.12 Capillary exchange mechanisms. Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved  18.4 Capillary Structure and Function Types of Capillaries Tight Continuous Capillaries—Majority in the body; Located in muscles, skin, and most nervous and connective tissues; Least “leaky” with tight junctions; Most substances diffuse through the endothelial cells or move by transcytosis; Modified continuous capillaries in the brain form the blood brain barrier and have specialized tight junctions Fenestrated Capillaries—Endothelial cells contain fenestrations; Located in endocrine glands, small intestine, and kidneys; Much leakier than continuous capillaries; Pores allow for faster diffusion Sinusoidal Capillaries (Discontinuous)—Endothelial cells are a discontinuous sheet with an irregular basal lamina and very large pores; Three to four times larger in diameter than other capillaries; Located in liver, spleen, lymphoid organs, and bone marrow; Porous Transfer large substances such as blood cells and larger proteins Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.4 Tissue Perfusion in Special Circuits Heart—Size of a fist and weighs under one pound, which is less than 0.5% of the total body mass; Receives about 5% of the total cardiac output via the coronary circulation Perfusion pattern is opposite the rest of the systemic circuit; Heart perfusion decreases during systole because it actually squeezes its own arteries during ventricular systole; Perfusion increases during diastole One reason why extreme increases in heart rate are dangerous—the heart does not spend enough time in diastole to adequately perfuse its own myocardium Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.4 Tissue Perfusion in Special Circuits Brain—Accounts for only 2% of total body mass, but receives about 15% of total cardiac output; Most intolerant tissue in the body to ischemia (lack of blood supply); Sudden decrease in tissue perfusion will result in loss of consciousness within seconds Blood flow within the brain to different areas varies; Areas with higher activity require more oxygen; Certain neurotransmitters are direct vasodilators, whereas others act on astrocytes that are in contact with arterioles and they induce vasodilation to increase perfusion to active areas Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved 18.4 Tissue Perfusion in Special Circuits Skeletal Muscle—Blood flow can increase as much as 50-fold during exercise, known as..................... Mechanism behind hyperemia lies in the arterial structure Feed Arteries enter a skeletal muscle, branch into multiple arterioles and end in Terminal Arterioles that supply a capillary bed During resting conditions, resistance in feed arteries is high and many terminal arterioles are constricted During exercise, conditions around the skeletal muscle fiber dilate the terminal arterioles, which begins to increase tissue perfusion; As exercise continues, other arterioles also dilate; Continued exercise dilates the feed artery Copyright © 2025, 2019, 2016 Pearson Education, Inc. All Rights Reserved