Chapter 21 Lecture Outline* Rod R. Seeley Idaho State University Trent D. Stephens Idaho State University Philip Tate Phoenix College *See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Cardiovascular System Chapter 21 The Cardiovascular System Peripheral Circulation and Regulation

Functions of the Peripheral Circulation Carry blood Exchange nutrients, waste products, and gases Transport of hormones, components of the immune system, molecules required for coagulation, enzymes, nutrients, gases, waste products, etc. Regulate blood pressure Direct blood flow

Types of Blood Vessels Arteries Elastic Muscular Arterioles Capillaries: site of exchange with tissues Veins: thinner walls than arteries, contain less elastic tissue and fewer smooth muscle cells Venules Small veins Medium or large veins

Capillaries Capillary wall consists of endothelial cells (simple squamous epithelium), basement membrane and a delicate layer of loose C.T. Scattered pericapillary cells that are fibroblasts, macrophages or undifferentiated smooth muscle cells. Substances move through capillaries by diffusion through Lipid-soluble and small water-soluble molecules through plasma membrane Larger water-soluble molecules pass through fenestrae or gaps between endothelial cells.

Types of Capillaries Continuous. No gaps between endothelial cells. No fenestrae. Less permeable to large molecules than other capillary types. E.g., muscle, nervous tissue. Fenestrated. Have pores. Endothelial cells have numerous fenestrae. Fenestrae are areas where cytoplasm is absent and plasma membrane is made of a thin, porous diaphragm. Highly permeable. E.g., intestinal villi, ciliary process of eye, choroid plexus, glomeruli of kidney Sinusoidal. Large diameter with large fenestrae. Less basement membrane. E.g., endocrine glands (large molecules cross their walls). Sinusoids. Large diameter sinusoidal capillaries. Sparse basement membrane. E.g., liver, bone marrow.Venous sinuses are similar in structure but even larger. E.g., spleen

Structure of Capillary Walls

Capillary Network Blood flows from arterioles through metarterioles, then through capillary network Flow through thoroughfare channel fairly consistent while flow through arterial capillaries is intermittent Smooth muscle in arterioles, metarterioles, precapillary sphincters regulates blood flow

Structure of Arteries and Veins Tunica intima Endothelium Basement membrane Lamina propria (C.T. layer) Internal elastic membrane. Fenestrated layer of elastic fibers. Tunica media: smooth muscle cells arranged circularly around the blood vessel. Vasoconstriction: smooth muscles contract, decrease in blood flow Vasodilation: smooth muscles relax, increase in blood flow Tunica externa (adventitia): connective tissue, varies from dense regular near the vessel to loose that merges with the surrounding C.T.

Photomicrograph of Artery and Vein

Elastic Artery Elastic or conducting arteries Largest diameters, pressure high and fluctuates between systolic and diastolic. More elastic tissue than muscle. Relatively thick tunica intima, thin tunica intima

Muscular Artery Muscular or medium arteries Smaller muscular arteries Smooth muscle allows vessels to regulate blood supply by constricting or dilating Most of the smaller unnamed arteries Thick walls due to 25-40 layers of smooth muscle. Also called distributing arteries because smooth muscle allows vessels to partially regulate blood supply to different regions of the body. Smaller muscular arteries Adapted for vasodilation and vasoconstriction.

Arterioles Transport blood from small arteries to capillaries Smallest arteries where the three tunics can be differentiated Like small arteries, capable of vasoconstriction and dilation

Venules and Small Veins Venules drain capillary network. Endothelial cells and basement membrane with a few smooth muscle cells. As diameter of venules increases, amount of smooth muscle increases. Small veins. Smooth muscle cells form a continuous layer. Addition of tunica adventitia made of collagenous connective tissue

Medium and Large Veins Medium veins. Go-between between small veins and large veins. Large veins. Tunica intima is thin: endothelial cells, relatively thin layer of C.T and a few scattered elastic fibers. Tunica media has circularly arranged smooth muscle cells. Adventitia is predominant layer.

Valves Valves found in all veins greater than 2 mm in diameter. Folds in intima form two flaps that overlap. More valves in veins of lower extremities than in veins of upper extremities.

Other Vessel Types Vasa vasorum: blood vessels that supply the walls of arteries and veins. Penetrate vessel walls from the exterior. Branches of arteries. Arteriovenous anastomoses. Vessels allow blood to flow from arterioles to small veins without going through capillaries. If arranged in a convoluted fashion and surrounded by collagenous connective tissue, referred to as a glomus. Portal veins: veins that begin in a primary capillary network, extend some distance and end in a secondary capillary network without a pumping mechanism, such as the heart, between.

Nerve Supply Unmyelinated sympathetic nerve fibers form plexi in tunica adventitia: vasoconstriction Small arteries and arterioles innervated to greatest extent Vessels of penis and clitoris innervated by parasympathetic Some blood vessels innervated by myelinated fibers and act as baroreceptors that monitor stretch and detect changes in blood pressure

Aging of the Arteries Arteriosclerosis: general term for degeneration changes in arteries making them less elastic Atherosclerosis: deposition of plaque on walls

Pulmonary Circulation From right ventricle into pulmonary trunk Pulmonary trunk divides into left and right pulmonary arteries. Two pulmonary veins exit each lung and enter left atrium

Systemic Circulation Aorta: exits left ventricle and is divided into three parts Ascending aorta: right and left coronary arteries branch from here Aortic arch: arching posteriorly and to the left and has three branches Brachiocephalic artery Left common carotid Left subclavian artery Descending aorta Thoracic aorta: portion in thorax Abdominal aorta: inferior to diaphragm. Ends as two common iliac arteries

Branches of the Aorta

Major Arteries

Head and Neck Arteries

Major Arteries of the Head and Thorax

Arteries of Upper Limb and Shoulder

Arteries of Abdomen

Arteries of Abdomen and Pelvis

Arteries of Pelvis and Lower Limb

Arteries of Lower Limb

Systemic Circulation: Veins Return blood from body to right atrium Major veins Coronary sinus (heart) Superior vena cava (head, neck, thorax, upper limbs) Inferior vena cava (abdomen, pelvis, lower limbs) Types of veins Superficial, deep, sinuses

Major Veins

Venous Sinuses Associated with the Brain

Veins of Head and Neck

Head and Thorax Veins

Veins of Shoulder and Upper Limb

Veins of Thorax

Inferior Vena Cava and Its Tributaries

Hepatic Portal System Portal system: vascular system that begins and ends at a capillary bed with no pumping mechanism in between. Hepatic portal- liver; renal portal- kidney; hypothalamohypophyseal portal between hypothalamus and pituitary. Blood entering the hepatic portal vein is rich with nutrients collected from the intestines, but may also contain toxic substances. Both nutrients and toxic substances will be regulated by the liver Nutrients: either taken up and stored or modified chemically and used by other parts of the body Biotransformation: Toxic substances can be broken down by hepatocytes or can be made water soluble. To be transported in blood and excreted by the kidneys.

Veins of Abdomen and Pelvis

Veins of Pelvis and Lower Limb

Veins of Lower Limb

Dynamics of Blood Circulation Interrelationships between Pressure Flow Resistance Control mechanisms that regulate blood pressure and blood flow

Laminar and Turbulent Flow Laminar flow Streamlined; interior of blood vessel is smooth and of equal diameter along its length Outermost layer moving slowest and center moving fastest Turbulent flow Interrupted Rate of flow exceeds critical velocity Fluid passes a constriction, sharp turn, rough surface Partially responsible for heart sounds Sounds due to turbulence not normal in arteries and is probably due to some constriction; increases the probability of thrombosis

Blood Pressure Measure of force exerted by blood against the wall Blood moves through vessels because of blood pressure Measured by listening for Korotkoff sounds produced by turbulent flow in arteries as pressure released from blood pressure cuff

Blood Flow Rate of flow through a tube is expressed as the volume that passes a specific point per unit of time. E.g.; cardiac output at rest is 5L/min, thus blood flow through the aorta is 5L/min Flow = (P1 – P2/R) P1 and P2 are pressures in the vessel at points one and two; R is the resistance to flow Directly proportional to pressure differences, inversely proportional to resistance Resistance = 8vl/r4 v is viscosity, l = length of the vessel, r is the radius of the vessel

Poiseuille’s Law Flow decreases when resistance increases and vice versa. Since resistance is proportional to blood vessel diameter, constriction of a blood vessel increases resistance and thus decreases flow Flow =(P1 –P2)/R - (P1 –P2)r4/8vl During exercise, heart beats with greater force increasing pressure in the aorta. Capillaries to skeletal muscle increase in diameter decreasing resistance and increasing flow. Increased flow in aorta can go from 5L/min to 5 times that amount

Viscosity Measure of resistance of liquid to flow Resistance proportionate to flow As viscosity increases, pressure required to flow increases Viscosity influenced largely by hematocrit (percentage of the total blood volume composed of red blood cells). Dehydration and/or uncontrolled production of RBCs can lead to increased viscosity which increases the workload on the heart.

Critical Closing Pressure, Laplace’s Law and Compliance Critical closing pressure: Pressure at which a blood vessel collapses and blood flow stops Laplace’s Law Force acting on blood vessel wall is proportional to diameter of the vessel times blood pressure F= D X P; thus as diameter of a vessel increases, force on the wall increases. Weakened part of a vessel wall bulges out and is an aneurysm. Vascular compliance: Tendency for blood vessel volume to increase as blood pressure increases Compliance = increase in volume/Increase in pressure More easily the vessel wall stretches, the greater its compliance Venous system has a large compliance (24 times greater than that of arteries) and acts as a blood reservoir

Physiology of Systemic Circulation Determined by Anatomy of circulatory system Dynamics of blood flow Regulatory mechanisms that control heart and blood vessels Blood volume Most in the veins (greater compliance) Smaller volumes in arteries and capillaries

Cross-Sectional Area As diameter of vessels decreases, the total cross-sectional area increases and velocity of blood flow decreases. Only one aorta with a cross-sectional area of 5 cm2. Total cross-sectional area of the millions of capillaries is 2500 cm2. Much like a stream that flows rapidly through a narrow gorge but flows slowly through a broad plane

Pressure and Resistance Blood pressure averages 100 mm Hg in aorta and drops to 0 mm Hg by the time the blood gets to the right atrium. Due to decreased resistance to flow as cross-sectional area increases. Greatest drop in pressure occurs in arterioles which regulate blood flow through tissues No large fluctuations in capillaries and veins Muscular arteries and arterioles are capable of constricting or dilating in response to autonomic and hormonal stimulation. Muscular arteries regulate flow into a region of the body; arterioles regulate flow into a specific tissue.

Pulse Pressure Difference between systolic and diastolic pressures Increases when stroke volume increases or vascular compliance decreases. Compliance tends to decrease with age (arteriosclerosis) and pressure rises. Pulse pressure can be used to take a pulse to determine heart rate and rhythmicity Most frequent site used to measure pulse rate is in the carpus with the radial artery- the radial pulse.

Capillary Exchange and Regulation of Interstitial Fluid Volume Capillary exchange: the movement of substances into and out of capillaries Most important means of exchange: diffusion. Lipid soluble cross capillary walls diffusing through plasma membrane. E.g., O2, CO2, steroid hormones, fatty acids. Water soluble diffuse through intercellular spaces or through fenestrations of capillaries. E.g., glucose, amino acids. Blood pressure, capillary permeability, and osmosis affect movement of fluid from capillaries Fluid moves out of capillaries at arterial end and most but not all returns to capillaries at venous end. That which remains in tissues is picked up by the lymphatic system then returned to venous circulation.

Fluid Exchange Across Capillary Walls Net filtration pressure (NFP)- force responsible for moving fluid across capillary walls. Two forces affect pressure Hydrostatic pressure: physical pressure of blood flowing through the vessels or of fluid in interstitial spaces Osmotic pressure: movement of solutes (plasma or tissue fluid) through a membrane (plasma membrane) in the presence of a non-diffusible solute (large proteins). Large proteins do not freely pass through the capillary walls and the difference in protein concentrations between the blood and interstitial fluid is responsible for osmosis

Pressures Involved NFP = Net hydrostatic pressure minus net osmotic pressure Net hydrostatic pressure = BP-IFP Net osmotic pressure = BCOP-ICOP where BP = blood pressure IFP = interstitial fluid pressure= (lymphatic vessels are pulling in tissue fluid) BCOP = blood colloid osmotic pressure ICOP = interstitial fluid colloid osmotic pressure

Fluid Exchange Across the Walls of Capillaries

Edema and Capillary Exchange If capillaries become more permeable, proteins can leak into the interstitial fluid increasing ICOP. More fluid moves from the capillaries into the interstitial fluid: edema. Chemicals of inflammation increase permeability Decreases in plasma concentration of protein reduces BCOP; more fluid moves into interstitial fluid Liver disease resulting in fewer plasma proteins Loss of plasma proteins through the kidneys Protein starvation Blockage of veins increases capillary BP; reduced venous return due to gravity Blockage or removal of lymphatic vessels (blockage: elephantiasis; removal: cancer)

Characteristics of Veins Venous return to heart increases due to increase in blood volume, venous tone, and arteriole dilation Venous tone: continual state of partial contraction of the veins as a result of sympathetic stimulation

Effect of Gravity on Blood Pressure In a standing position, hydrostatic pressure caused by gravity increases blood pressure below the heart and decreases pressure above the heart. Muscular movement improves venous return.

Control of Blood Flow in Tissues Local control: in most tissues, blood flow is proportional to metabolic needs of tissues Nervous System: responsible for routing blood flow and maintaining blood pressure Hormonal Control: sympathetic action potentials stimulate epinephrine and norepinephrine

Local Control of Blood Flow by Tissues

Local Control of Blood Flow Blood flow can increase 7-8 times as a result of vasodilation of metarterioles and precapillary sphincters in response to increased rate of metabolism Vasomotion: periodic contraction and relaxation of precapillary sphincters. Autoregulation. Long-term local control: capillaries become more dense in a region that regularly has an increased metabolic rate.

Nervous Regulation of Blood Vessels Important in minute-to-minute regulation of local circulation Provides a means by which blood can be shunted from one large area of the peripheral circulatory system to another area by increasing resistance Sympathetic division most important. Innervates all vessels except capillaries, precapillary sphincters, and most metarterioles. Vasomotor center in lower pons and upper medulla oblongata. Excitatory part is tonically active. Causes vasomotor tone. Norepinephrine Inhibitory part can cause vasodilation by decreasing sympathetic output Sympathetic stimulation of adrenal medulla causes output of norepinephrine and epinephrine into circulation. Causes vasoconstriction in vessels (α-adrenergic receptors) except in skeletal muscle where vasodilation takes place (ß-adrenergic receptors)

Regulation of Mean Arterial Pressure Mechanisms that maintain arterial blood pressure within a normal range of values Mean arterial pressure (MAP): slightly less than the average of systolic and diastolic pressures because diastole lasts longer than systole. 70 mmHg at birth, 100 mmHg from adolescence to middle age, 110 mmHg in healthy older individuals. MAP = CO(PR), MAP = HR(SV)(PR) MAP α HR, SV, and PR. If any of these go up, so does MAP. Two systems to regulate pressure: short-term and long-term

Short-Term Regulation of Blood Pressure Baroreceptor reflexes: change peripheral resistance, heart rate, and stroke volume in response to changes in blood pressure Chemoreceptor reflexes: sensory receptors sensitive to oxygen, carbon dioxide, and pH levels of blood Central nervous system ischemic response: results from high carbon dioxide or low pH levels in medulla and increases peripheral resistance

Baroreceptor Reflex Control

Adrenal Medullary Mechanism Activated when stimuli result in a substantial increase in sympathetic stimulation of heart and blood vessels (large decrease in blood pressure, sudden and substantial increase in physical activity, stress) Adrenal releases epinephrine and norepinephrine Hormones mimic sympathetic stimulation of heart and blood vessels.

Baroreceptor Effects

Chemoreceptor Reflex Control

Effects of pH and Gases

CNS Ischemic Response Elevation of BP in response to a lack of blood flow to the medulla oblongata. Functions in response to emergency situations and BP falls below 50 mmHg Neurons of vasomotor center strongly stimulated; increases blood flow to brain if vessels are intact but at the same time, decreases oxygenation of blood because blood does not go to lungs. Lack of oxygen causes vasomotor center to become inactive; extensive vasodilation follows with concomitant drop in BP. Death if CNS ischemic response lasts longer than a few minutes.

Long-Term Regulation of Blood Pressure Renin-angiotensin-aldosterone mechanism Vasopressin (ADH) mechanism Atrial natriuretic mechanism Fluid shift mechanism Stress-relaxation response

Renin-Angiotensin-Aldosterone Mechanism

Vasopressin (ADH) Mechanism

Long-Term Control of Blood Pressure

Long-term Mechanisms Atrial natriuretic hormone: released from cardiac muscle cells when atrial blood pressure increases, simulating an increase in urinary production, causing a decrease in blood volume and blood pressure Fluid shift: movement of fluid from interstitial spaces into capillaries in response to decrease in blood pressure to maintain blood volume and vice versa. Stress-relaxation response: adjustment of blood vessel smooth muscle to respond to change in blood volume. When blood volume suddenly declines and pressure drops, smooth muscles contract and vice versa.