The Cardiovascular System: Blood Vessels

2 factors that influence blood flow

1) PRESSURE DIFFERENCES The greater the pressure difference, the greater the blood flow. Blood flows from areas of high pressure to areas of low pressure. 2) RESISTANCE The higher the resistance, the smaller the blood flow

Describe three factors that affect vascular resistance

1) SIZE OF THE LUMEN • Vascular Resistance increases when diameter of lumen decreases 2) BLOOD VISCOSITY (thickness) • Vascular Resistance increases when blood viscosity increases 3) TOTAL BLOOD VESSEL LENGTH • Vascular Resistance increases when total blood vessel length increases

Defining pulse

A traveling pressure wave caused by left ventricular contractions that cause alternating expansion and recoil of arteries.

Defining collateral circulation

Alternative route of blood flow through an anastomosis

Tunica Interna

Innermost covering of a blood vessel lining the lumen • Endothelium attached to a basement membrane • Smooth endothelium reduces surface friction to blood flow, secretes chemical mediators that influence vessel contraction, and assists with capillary permeability

Venous Valves

LOW BLOOD PRESSURE IN VEINS ALLOWS BLOOD RETURNING TO THE HEART TO SLOW AND EVEN BACK UP; THE valves aid in venous return by preventing the backflow of blood.

Define varicose veins

Leaky venous valves can cause veins to become dilated and twisted in appearance

State which vein is commonly used for administration of medication, transfusions, or obtaining blood samples

Median cubital vein

Tunica Media

Middle layer of a blood vessel • Smooth muscle REGULATES DIAMETER OF LUMEN (INNERVATED BY THE SYMPATHETIC AXON OF ANS) WHICH REGULATES BLOOD FLOW THROUGH DIFFERENT PARTS OF THE BODY AND BP • ELASTIC FIBERS ALLOW VESSEL TO STRETCH/RECOIL

Tunica Externa

Outermost covering of a blood vessel • Elastic and collagen fibers; contains numerous nerves • ANCHORS VESSEL TO SURROUNDING TISSUES

Describing precapillary sphincters

The distal-most muscle fiber (cell) at the metarteriol—capillary junction that regulates blood flow into capillaries.

The function and mechanism of capillary exchange

The mission of the entire cardiovascular system is to keep blood flowing through capillaries through: • Capillary exchange = Movement of substances between the blood and the interstitial fluid • Mainly occurs via diffusion -Molecules travel down their concentration gradients -O2, CO2, glucose • Also occurs via transcytosis -Large, lipid-insoluble molecules (certain proteins) -Substances in plasma become enclosed in vesicles that are endocytosed (taken up) by epithelial cells, followed by exocytosis into the interstitial fluid

Stating the function and structure of venules

Within a tissue, groups of capillaries unite to form venules • Tiny veins with thin walls and loose intracellular junctions (near capillaries) FUNCTION: Drain capillary blood and begin the flow of blood back toward the heart -Serve as additional exchange sites and allow movement of WBCs into tissues (initially- capillary end) -Progressively become thicker-walled, eliminating exchange function toward vein end

Stating the purpose of venous valves

aid in preventing backflow of blood as it returns to the heart

Explain how the cardiovascular center regulate blood pressure

cardiovascular center located in medulla oblongata; help regulate heart rate and SV, it also controls the neural and hormonal feedback systems that regulate blood pressure and blood flow to specific tissues. Output from the cardiovascular center flows along sympathetic and Parasympathetic neurons of the ANS; opposing sympathetic (stimulatory) and parsympathetic (inhibitory) innervation controls the heart.

Describing blood pressure in various vessels of the cardiovascular system

see chart 20.10

Explain the damaging effects of untreated hypertension

• Angina pectoralis • Heart attack (69% of 1st time victims have HTN) • Congestive heart failure (74% have HTN) • Atherosclerosis • Peripheral artery disease • Stroke (77% of 1st time victims have HTN) • Kidney damage • Loss of vision • Erectile dysfunction

Stating the function and structure of arteries

Arteries carry blood away from the heart Walls of arteries have a thickened tunica media (compared to veins) • More smooth muscle assists in vasoconstriction and vasodilation Walls of arteries have many elastic fibers • Allows artery walls to stretch easily without tearing when there are small increases in blood pressure Types: Elastic, muscular, arterioles (baby arteries)

Explain how baroreceptors regulate blood pressure

Baroreceptors monitor changes in pressure and stretch in the walls of blood vessels; they send impulses to the cardiovascular center to help regulate blood pressure. Ex: When blood pressure rises, it stretches the wall of the carotid sinus, stimulating the baroreceptors. The stretched baroreceptors increase their transmission of nerve impulses to the cardiovascular center, which initiates reflex activity to lower blood pressure to the brain.

Describing systolic and diastolic blood pressure

Blood pressure (BP) is the pressure exerted by blood on the walls of a blood vessel. It is generated by ventricular contraction. SYSTOLIC BLOOD PRESSURE: The highest pressure in the arteries during systole (~110 mm Hg) DIASTOLIC BLOOD PRESSURE: The lowest pressure in the arteries during diastole (~70 mm Hg) Arterioles: ~35 mm Hg Venules: ~16 mm Hg Blood arriving at the R. atrium: ~0 mm Hg Blood pressure is determined by cardiac output, blood volume, and vascular resistance

Describe the mechanism for measuring systolic and diastolic blood pressure including which blood vessel is commonly used for blood pressure measurements.

Clinical BP refers to the pressure in arteries due to left ventricular systole and the pressure remaining in arteries during left ventricular diastole Use a sphygmomanometer (blood pressure cuff) to compress the brachial artery Measured as systolic pressure/diastolic pressure

Explain how the azygos system provides collateral circulation.

Composed of the azygos, hemiazygos, and accessory hemiazygos veins • ultimately drain into the superior vena cava Drains most thoracic structures + abdominal wall COLLATERAL CIRCULATION: Serves as a bypass to the inferior vena cava due to links (venous anastomoses) between the azygos system veins and large veins draining the lower limbs and abdomen. • If the inferior vena cava becomes obstructed, blood from the lower body can bypass through the azygos system to the superior vena cava

Define vasoconstriction

Decrease in lumen diameter of a blood vessel

Define vasodilation

Increase in lumen diameter of a blood vessel

Define hypertension

Persistently high blood pressure; systolic BP 140 mm Hg or greater, OR diastolic BP of 90 mm Hg or greater Sometimes called the "silent killer" - It can damage your arteries, heart, and organs without showing symptoms - the only way to diagnose Hypertension is to have your BP checked Damages the walls of the arteries - Damaged arteries trap more plaque as well as harden (lose elasticity) more quickly • Lowers blood supply to organs (including the heart) • Increases risk for developing blood clots • Increases the workload of the heart • Increases the risk of blood vessel rupture

Describing the function of anastomoses

Provide alternative routes for blood flow TO AN ORGAN OR TISSUE IN THE EVENT THAT A CERTAIN ROUTE IS DISRUPTED • Vessels can become compressed, BLOCKED, or injured

Stating generally where on the body the pulse may be felt

Pulse can be felt anywhere in the body that one can palpate an artery that can be compressed up against a bone (or another firm structure)

Describe structure and function of muscular arteries

STRUCTURE: Tunica media contains more smooth muscle and less elastic fibers than elastic arteries • Not able to recoil and propel blood like elastic arteries • Increased smooth muscle allows greater vasoconstriction/vasodilation capabilities Relatively thick walls compared to the overall size of the vessel FUNCTION: Vasoconstriction and vasodilation to adjust blood flow rate to tissues Ex: brachial artery, radial artery, femoral artery

Describe structure and function of elastic arteries

STRUCTURE: • Have the largest diameter of all arteries • Have relatively thin walls compared to the overall size of the vessel • Many elastic fibers in the tunica media FUNCTION: Help propel blood forward while the ventricles are relaxing • Elastic walls stretch easily to accommodate surges of blood pumped from ventricles • Recoil as ventricles relax forcing blood onward to smaller arteries (muscular arteries) Ex: Aorta, Pulmonary trunk, branches of aorta (brachiocephalic trunk, subclavian, common carotid, common iliac)

Describe structure and function of arterioles

STRUCTURE: • Small arteries that blood flows through prior to entering capillary beds • Wall thickness is about 50% of total vessel diameter • Distal end is called the metarteriole which tapers toward the capillary junction -Distal-most muscle cell forms a precapillary sphincter, which monitors blood flow into the capillaries • Tunica externa is rich in ANS nerves to adjust vessel diameter FUNCTION: Adjust and regulate the flow of blood into capillary networks of the body's tissues

The function and structure of capillaries

STRUCTURE: As arterioles enter tissues they branch into numerous tiny vessels called capillaries • Capillaries: smallest blood vessels • Form the "U-turns" that connect arterial outflow to venous return of blood • Walls are only endothelium- single cell thick -no tunica media or tunica externa FUNCTION: Allow for exchange of substances between the blood and the interstitial fluid that bathes body cells (capillary exchange)

Stating the function and structure of veins

STRUCTURE: thin walls with smooth muscle and elastic fibers with valves FUNCTION: return blood to the heart

Describe the distribution of blood in the body.

Systemic veins and venules hold 64% of blood volume = they function as BLOOD RESEVOIRS • blood can be diverted quickly if the need arises • Ex: veins constrict during muscular activity -Reduces blood volume in reservoirs, and increases the flow to skeletal muscles • Principle blood reservoirs -Veins of abdominal organs (liver and spleen!) -Veins of the skin

Influences on capillary exchange

TWO OPPOSING PRESSURES: 1) CAPILLARY BLOOD PRESSURE: drives fluid and solutes out of vessels • The pressure of blood against the walls of the capillaries pushes fluid out of the blood and into the interstitial space 2) BLOOD COLLOID OSMOTIC PRESSURE: drives fluid and solutes into vessels • Presence of proteins in plasma and their virtual absence in the interstitial fluid gives blood a higher osmotic pressure • Drives fluid into the blood from the insterstitial space -Osmotic pressure: pressure of a fluid due to its concentration of solutes If capillary blood pressure is GREATER than blood colloid osmotic pressure • Fluid moves OUT of capillaries and INTO interstitial space --> called filtration • Occurs at arteriole end of a capillary: water and solutes are filtered out of blood If blood colloid osmotic pressure is GREATER than capillary blood pressure • Fluid moves INTO capillaries and OUT of interstitial space --> called reabsorption • Occurs at venous end of a capillary: water and solutes are reabsorbed into blood

Distinguishing between tachycardia and bradycardia

Tachycardia: rapid resting pulse (>100 bpm) Bradycardia: slow resting pulse (<50 bpm)

Autoregulation of capillary blood flow

The ability of a tissue to automatically adjust blood flow to match its metabolic demands Tissues can adjust blood flow to match their own metabolic demands • Tissue cells release vasodilators -Arterioles dilate, precapillary sphincters relax -BLOOD FLOW INCREASES & O2 DELIVERY TO TISSUE RISES • Tissue cells release vasoconstrictors -Arterioles constrict, precapillary sphincters constrict -BLOOD FLOW DECREASES & O2 DELIVERY TO TISSUE DECREASE • Some tissues oxygen/nutrient demands increase drastically during physical activity, making autoregulation crucial in maintaining blood supply -e.g. Skeletal muscles, heart

Define blood flow

The volume of blood that flows through any tissue in a given time period Measured in mL/min

Venous Return

The volume of blood flowing back to the heart THROUGH SYSTEMIC VEINS • PRIMARILY DRIVEN BY PRESSURE FROM CONTRACTIONS OF THE LEFT VENTRICLE

Describe blood vessel walls

Transport/distribute BLOOD THROUGHOUT THE BODY to deliver materials (such as nutrients, oxygen, and hormones) and carry away wastes; form a closed system of tubes that carry blood away from the heart, TRANSPORTS IT TO THE TISSUES OF THE BODY WHERE NUTRIENTS AND WASTES ARE EXCHANGE, and then return it to the heart.

Define hemorrhoids

Varicose veins in the anal canal

Explain how venous valves, skeletal muscle contractions, and breathing help return venous blood to the heart

mechanisms help boost venous return: 1. THE SKELETAL MUSCLE PUMP - Contraction of muscles compress veins, pushing some blood towards heart. Some blood also backflows but valves close to stop it. - Relaxation of muscles causes pressure to fall dramatically in previously compressed areas of vein. - Blood moves up from inferior regions and valves prevent backflow from superior regions. 2. THE RESPIRATORY PUMP - During inhalation the diaphragm moves down, thoracic cavity pressure decreases and abdominal cavity pressure increases. - Abdominal veins are compressed, and blood moves from abdominal veins upwards into thoracic veins. - Exhalation: reversed, but valves prevent backflow from thoracic veins into abdominal veins

Describe the function of the hepatic portal circulation

• Venous blood from the GI tract (stomach + intestines), spleen, pancreas, and gallbladder does not drain directly into the inferior vena cava. • Blood from the splenic, superior and inferior mesenteric veins passes into the hepatic portal vein and travels to the liver for processing before exiting via the hepatic vein and into the inferior vena cava. - Blood from GI tract is rich in nutrients that must travel to the liver for storage and processing before distribution to body tissues - Alcohol from GI tract travels to liver for detoxification - Bacteria are destroyed by phagocytosis in liver