AP2 Chapter 20 Blood Vessels and Circulation Buie Steele

Aldosterone

"salt retaining" hormone promoting Na+ retention by the kidneys - water follows salt/sodium osmotically --- Na+ retention promotes water retention thereby promoting high blood volume and BP

Arteriovenous Anastomosis

(shunt) blood flows from an artery directly into a vein and bypasses the capillaries - occurs in fingers, palms, toes, and ears --- where they reduce heat loss in cold weath by allowing warm blood to bypass these exposed surfaces (hence why your ears are so cold) --- makes these poorly perfused areas more susceptible to frostbite

Capillary Leak Syndrome

- AKA "Clarkson's Disease" - rare medical condition characterized by endothelial cells in the lining of the capillaries separating and allowing for a leakage of fluid from the circulatory system to the interstitial space, resulting in markedly dangerous hypotension, hemoceoncentration and hypoalbuminemia - life threatening because each episode has the potential to cause damage to/failure of vital organs due to limited perfusion

Sinusoids

- AKA "Discontinuous capillaries" - irregular blood-filled spacces in the liver, bone marrow, spleen, some other organs - endothelial cells are separated by wide gaps with no basal lamina and frequently have larger fenestration through them - these spaces are twisted tortuous passageways (30-40 microm wide) that conform to the shape of the surrounding tissue - proteins and blood cells can pass through the pores --- this is how albumin, clotting factors, and other proteins synthesized by the liver enter the blood, and how newly formed blood cells enter the circulation from the bone marrow and lymphatic organs

Hypertension Risk Factors

- Obestity: each extra pound of fat requires miles of additional blood vessels to serve it and all of this added vessels length increases peripheral resistance and BP --- just carrying around extra weight increases workload of the heart also --- sedentary behavior is also another risk factor --- diets high in cholesterol and saturate fat contribute to arteriosclerosis --- K and Mg reduce BP - Smoking: nicotine is a terrible contributor to hypertension because it stimulates the myocardium to beat faster and harder while it stimulates vasoconstriction and increases the afterload against which the myocardium must work --- just when the heart needs extra oxygen, nicotine causes coronary vasoconstriction and promotes myocaridal ischemia - Race, herediry, sex: person whose parents or siblings have hypertension is ~30% more likely than average to develop it --- incidence of strokes is 2x as high among blacks than whites --- 18-54 yo more common in men --- >65 yo more common in women

Arterioles

- the smallest of the resistance arteries - contain only 1-3 layers of smooth musccle --- contain very little tunica externa - the most significant point of control over peripheral resistance and blood flow

Brain

- total blood flow to the brain fluctuates less than that of any other organ (~700 mL/min at rest) --- this consistency is important because even a few seconds of oxygen deprivation can cause loss of consciousness --- 4-5 min of oxygen deprivation is enough to cause irreversible damage --- although total cerebral perfusion is fairly stable, blood flow can be shifted from one part to another in a matter of seconds - the brain regulates its own blood flow in response to changes in BP and chemistry --- cerebral arteries dilate when system BP drops and constrict when it rises >> minimizes fluctuations in cerebral BP --- cerebral blood flow remains quite stable even when MAP fluctuates from 60-140 mmHg, however an MAP <60 mmHg produces syncope and >60 mmHg causes cerebral edema - main chemical stimulus for cerebral autoregulation is pH --- poor perfusion alows CO2 to accumulate inthe brain >> lowering pH of the tissue fluid and triggering local vasodilation >> improves perfusion --- extreme hypercapnia (excess CO2) depresses neural activity --- hypocapnia (lack of CO2) raises pH and stimulates vasoconstriction >> reducing perfusion and giving CO2 a chance to rise to a normal level --- hyperventilation (exhaling CO2 faster than body produces it0 induces hypocapnia >> cerebral vasoconstriction, ischemia, dizziness, and sometimes syncope

Capillary Exchange

- two way movement of fluid in the capillary walls between the blood and surrounding tissues --- the exchange occurs between the blood and connective tissue, leaving the capillaries at one point and entering at another --- significant exchange also occurs across the walls of the venules, but capillaries are the most important exchange site because they greatly outnumber the venules - chemicals given off by the capillary blood to the perivascular tissues include: oxygen, glucose, and other nutrients, antibodies, and hormones --- chemicals taken up by the capillaries include: CO2 and other wastes, and many of the same substances that they give off (glucose, fatty acids released from storage in the liver, adipose tissue, calcium and other minerals released from bone, antibodies secreted by immune cells, and hormones secreted by the endocrine glands - there is substantial movement of water into and out of the bloodstream across the capillary walls - chemicals pass through capillary wall by one of three routes

Venous Sinuses

- veins with especially thin walls, large lumens, and no smooth muscle - not capable of vasomotion Ex) coronary sinus of the heart & dural sinuses of the brain

Antidiuretic Hormone

Primarily promotes water retention - at pathologically high concentrations it is a vasoconstrictor --- aka vasopressin >> both effects raise BP

Neurogenic Shock

a form of vascular shock that results from a sudden loss of vasomotor tone, allowing the vessels to dilate - can result from something severe like brainstem shock or something slight as emotional shock

Autoregulation

ability of tissues to regulate their own blood supply

Net Filtration Pressure (NFP)

created by opposing forces - prevailing force is inward at venous end because osmotic pressure overrides filtration pressure (at arterial end)

Oncotic Pressure (OP)

difference between COP of blood and tissue fluid --- draw water into the capillary by osmosis, opposing HP - typical COP of blood is ~28 mmHg at arterial end, due mainly to albumin --- tissue fluid has less than 1/3 protein concentration of blood plasma and has COP of ~8 mmHg --- thus OP is 20 in

Pulse Pressure

difference between systolic and diastolic - important measure of the maximum stress exerted on small arteries by the pressure surges generated by the heart - dont confuse with pulse rate

Perfusion

flow per given volume or mass of tissue (mL/min/g) Ex) large organ such as a femur could have greater flow but less perfusion than a small organ such as the ovary, because the ovary receives much more blood per gram of tissue

Reactive Hyperemia

increase above the normal level of flow - seen when the skin flushes after a person comes in from the cold - if a tissue's blood supply is cut off for a time and then restored, it often exhibits reactive hyperemia --- may be due to the accumulation of metabolites during a period of ischemia (inadequate blood supply to an organ or part of the body , especially the heart) --- can also be seen in the forearm of a person who's BP cuff is inflated for too long and then loosened

Hypertension Treatment

key: weight loss, diet, and drugs - diuretics lower blood volume and pressure by promoting urination - ACE inhibitors block the formation of AGII (vasoconstrictor) - Beta-blockers (propranolol) also lowers AGII levels but do so by inhibiting secretion of renin - Calcium channel blockers ( verapamil and nifedipine) inhibit the inflow of calcium into cardiac and smooth muscle >> inhibiting their contractions and promoting vasodilation and reducing cardiac workload

Hypovolemic Shock

loss of blood volume as a result of hemorrhage, trauma, bleeding ulcers, burns, or dehydration --- dehydration: in hot weather the body excretes 1.5L sweat/hr >> water transfers from the bloodstream to replace tissue fluid lost in the sweat >> blood volume drops too low to maintain adequate circulation - most common

Mean Arterial Pressure (MAP)

mean pressure you would obtain if you took measurements at several intervals throughout the cardiac cycle (because the low pressure --- not simply a mean of systolic and diastolic because the low pressure diastole lasts longer than the high pressure systole - varies with the influence of gravity - most influences disorders such as syncope, atherosclerosis, kidney failure, edema, and aneurysms - close estimate isobtained by adding diastolic and 1/3 of the pulse pressure (difference between systolic and diastolic) --- so for a BP of 120/75, MAP is 75 + (1/3) 45 = 90 mmHg (typical for vessesls at the level of the heart)

Diastolic

minimum arterial BP occurring during *ventricular relaxation* between heartbeats

Medium Veins

most veins with individual names Ex) radial and ulnar veins, small and great saphenous veins - contain a tunica interna with an endothelium, basement membrane, loose connective tissue, and sometimes a thin internal elastic lamina --- the tunica media is much thinner than it is in medium arteries --- exhibits bundles of smooth muscle but not a continuous muscular layer as seen in arteries - in limbs, infoldings of the tunica interna that meet in the middle of the lumen form *venous valves* directed towards the heart - pressure in the veins is not high enough to push all of the blood upward against the pull of gravity in a standing or sitting position --- the upward flow of blood in these vessels depends partly on the messaging action of skeletal muscles and the ability of these valves to keep the blood from dropping down again when the muscles relax

Mitral Valve Stenosis

narrowing >> blood may back up into the pulmonary circuit, raising capillary hydrostatic pressure and causing pulmonary edema, congestion, and hypoxemia

Vasoconstriction

narrowing of the vessel - occurs when the smooth muscle of the tunica media contracts

Net Reabsorption Pressure (NRP)

net HP - OP

Venous Anastomosis

one vein empties directly into another - most common - provides several alternative routes of drainage from an organ, so blockage of avein is rarely as life-threatening as blockage of an artery

Internal Carotid Artery

passes medial to the angle of the mandible and enters the cranial cavity through the carotid canal of the temporal bone - it supplies the orbits and ~80% of the cerebrum - compressing the internal carotid arteries near the mandible can therefore cause loss of consciousness - gives rise to following branches: opthalmic, anterior cerebral, middle cerebral

Systolic

peak arterial BP attained during *ventricular contraction*

Valves

serve to ensure a one-way flow of blood toward the heart

Compensated Shock

several homeostatic mechanisms bring about spontaneous recovery - hypotension resulting from low CO triggers baroreflex and production of AGII, both of which counteract shock by stimulating vasoconstriction - if a person faints and falls to a horizontal position gravity restores blood flow to the brain --- quicker recovery is achieved if the person's feet are elevated to promote drainage of blood from the legs

Angiogenesis and Cancer

several malignant tumors secrete growth factors that stimulate a dense network of vessels to grow into them and provide nourishment to cancer cells - holy grail of cancer = STOP ANGIOGENESIS

Responses to Circulatory Shock

shock is described according to severity as compensated or decompensated

Metarterioles

short vessels that link arterioles and capillaries - instead of a continuous tunica media, they have individual muscle cells spaced a short distance apart, each forming a precapillary sphinctor

Vasa vasorum

small vessels that nourish the outer half of all the larger vessel --- the inner wall is thought to be nourished by diffusion from the blood in the lumen

Arterial Pressure Points

some major arteries come close to the body surface to be palpated - these places can be used to take a pulse (Ex carotid, femoral, brachial, radial) - these can also serve as emergency pressure points where firm pressure can be applied to reduce arterial bleeding

Viscosity

thickness - erythrocyte count and albumin concentration are critical in determining blood viscosity - defiiencies in erythrocytes (anemia) or albumin (hypoproteinemia) reduces viscosity and speeds up blood flow - viscosity increases and flow declines with conditions such as polycythemia (increased hemoglobin concentration) and dehydration

Arterial Anastomosis

two arteries merge and provide collateral (alternative) routes of blood supply to a tissue - common in coronary circulation as well as around joints where movement may tmeporarily compress an artery and obstruct one pathway

Circulatory Routes

heart >> arteries >> capillaries >> veins >> heart - blood usually passes through only one network of capillaries from the time it leaves the heart until the time it returns (exceptions: portal systems and anastomoses)

Decompensated Shock

if mechanisms of compensated shock fail, several life threatening positive feedback loops occur - poor CO results in myocardial infarctions/ischemia, which further weakens the heart and reduces output - slow circulation of the blood can lead to diseminated intravascular coagulation (DIC) (as vessels become congested with clotted blood, venous return decreases drastically) - ischemia and acidosis of the brainstem depresses the vasomotor and cardiac centers >> loss of vasomotor tone, further vasodilation >> and further drop in BP and CO

Cardiogenic Shock

inadequate pumping by the heart - usually a result of a MI

Hypertension

resting BP > 140/90 - can potentially weaken small arteries, cause aneurysms, and promote the development of atherosclerosis

Anaphylactic Shock

results from exposure to an antigen to which a person is allergic - antigen-antibody complexes trigger the release of histamine, causing generalized vasodilation and increased capillary permeability

Capillary Beds

- a network of 10-100 capillaries supplied by a single metarteriole --- the metarteriole serves as a thoroughfare channel leading directly to a venule --- capillaries empty into the distal end of the thoroughfare channel or directly into the venule - precapillary sphinctors open >> capillaries are well perfused with blood and engage in exchanges with tissue fluid - precapillary sphinctor closed >> blood bypasses capillaries, flows through thoroughfare channel to a venule and engages in little fluid exchange - in skeletal muscle, about 90% of the capillaries have little or no blood flow during periods or rest --- however during exercise they receive an abundance of blood flow, while capillary beds in the skin and intestines shut down to compensate for this (feedback relationship)

Edema

- accumulation of excess fluid in a tissue - edema occurs when fluid filters into a tissue faster than it is reabsorbed - as tissues become congested with fluid, oxygen delivery and waste removal are impaired and the tissues may begin to die - often shows as swelling of the face, fingers, abdomen, or ankles but also occurs in internal organs where its effects are hidden - pulmonary edema presents a threat of suffocation as fluid replaces air in the lungs - cerebral edema can produce headaches, nausea, and sometimes delirium, seizures, and coma - in severe edema, so much fluid may transfer from the blood vessels to the tissue spaces that blood volume and pressure drop low enough to cause circulatory shock

Veins

- afferent vessels of heart --- carry blood back to the heart - "capacitance vessels" of the circulatory system --- thin walled and flaccid --- expand easily to accomodate an increased volume of blood >> have a greater capacity for blood containment than arteries do --- at rest about 65% of blood is found in the systemic veins as compared with only 13% in the systemic arteries - blood flow through veins is steady, rather than pulsating with the heartbeat (as in arteries) - veins merge to form larger and larger ones as they approach the heart --- smaller veins = *tributaries* - 5 levels of veins - blood in veins is under low pressure which allows blood to easily drain out of the capillaries --- low pressure because so distant from the ventricles of the heart - BP averages around 11mmHg

Thoracic Respiratory Pump

- aids flow of venous blood from the abdominal to the thoracic cavity - IVC is the main vein governing this pump - if abdominal pressure on the IVC rises while thoracic pressure on it drops, then blood is squeezed upward toward the heart --- remember it is not squeezed down/distally (your valves prevent this) - central venous pressure fluctuates from 2 mmHg when you inhale to 6 mmHg when you exhale --- blood flows faster when you inhale --- when you inhale, your thoracic cavity expands and its internal pressure drops, while downward movement of the diaphragm raises the pressure in your abdominal cavity

Carotid Bodies

- also located near the bifurcation of the common carotid arteries - chemoreceptors that monitor changes in blood composition/chemistry - oval receptors 3 x 5mm in size innervated by sensory fibers of the vagus and glossopharyngeal nerves - primarily transmit signals to the brainstem respiratory centers, which adjust breathing to stabilize the bloos pG and its CO2 and O2 levels

Baroreflexes

- autonomic, negative feedback response to changes in BP --- important in short term regulation of BP Ex) adapting to changes in posture - detected by baroreceptors of the carotid sinus --- glossopharyngeal nerve fibers from these sinuses transmit signal continually to the brainstem --- when BP rises their signaling rate increases >> inhibits the sympathetic cardiac and vasomotor neurons and reduces sympathetic tone and excites the vagal fibers to the heart >> reduces heart rate and CO, dilates arteries and veins, and reduces BP --- when BP drops below normal, the opposite reaction occurs and BP rises back to normal Ex) jumping quickly out of bed and feeling dizzy --- gravity draws blood into larger veins of the abdomen and lower limbs when you stand >> reduces venous return to the heart and cardiac output to the brain --- normally baroreceptors respond quickly to this drop in pressure and restore cerebral profusion

Local Control

- autoregulation - platelets, endothelieal cells, and perivascular tissue secrete a variety of vasoactive chemicals - according to the metabolic theory of autoregulation, if a tissue is adequately perfused, it becomes hypoxic and its metabolites (CO2, H+, K+, lactic acid, adenosine, etc.) accumulate >> these factors stimulate vasodilation >> increases perfusion --- as the bloodstream delivers oxygen and carries away the metabolites, the vessels constrict >> homeostatic dynamic eq is established that adjusts perfusion to the tissue's metabolic needs - examples of vasoconstrictive chemicals: histamine, bradykinin, prostaglandins all stimulate under conditions such as trauma, inflammation, and exercise - blood rubbing against the endothelial cells creates a shear stress (like rubbing palms together) that stimulates them to secrete prostacyclin and nitric oxide (vasodilators)

Carotid Sinus

- baroreceptors - have a relatively thin tunica media and an abundance of glossopharyngeal nerve fibers in the tunica externa - located in the wall of the internal carotid artery just above the branching point - a rise in BP easily stretches the thin media and stimulates these nerve fibers --- the glossopharyngeal nerve then transmits signals to the vasomotor and cardiac centers of the brainstem and the brainstem responds by lowering the HR and dilating the blood vessels, thereby lowering the BP

Pulmonary Circuit

- begins with pulmonary trunk branching into L/R pulmonary arteries - R pulmonary artery branches into 2 , both branches enter lung at the hilum --- upper branch is the superior lobar artery (serving superior lobe of the lung) --- lower branch divides again within the lung to form the middle lobar and inferior lobar arteries (serving the two lower lobes) - L pulmonary artery is always more variable --- gives off several lobar arteries to the superior lobe before entering the hilum, then enters the lung and gives off a variable number of inferior lobar arteries to the inferior lobe - in both lungs, these arteries lead ultimately to small basket-like capillary beds that surround the pulmonary alveoli (air sacs) --- this is where blood unloads CO2 and picks up O2 - L atrium of the heart receives 2 pulmonary veins on each side - main goal of pulmonary circuit is to exchange CO2 for O2 - lungs also receive a separate systemic blood supply by way of the bronchial arteries

Tunica Media

- the middle layer and usually the thickest - consists of smooth muscle, collagen, and sometimes elastic tissue - strengthens the vessels and prevents blood pressure from rupturing them - produces vasomotion

Conducting Arteries

- biggest of the three types of artery - AKA "Elastic Arteries" - contain a layer of elastic tissue --- *internal elastic lamina* at the border between the interna and the media - expand during ventricular systole to receive blood, and recoil during diastole Ex) aorta, common carotid arteries, subclavian arteries, pulmonary trunk, common iliac arteries - lacking tunica externa - expansion of the artery takes some of the pressure off the blood so that smaller arteries downstream are subjected to less systolic stress --- the recoil between heartbeats prevents the blood pressure from dropping too low while heart is relaxing and refilling

Blood Flow in Different Vessels

- blood flow in arteries is pulsatile - in the aorta, blood rushes forward at about 120 cm/s during systole and has an average speed of 40 cm.s over the cardiac cycle --- when measured further away from the heart, systolic and diastolic pressures are lower and there is less difference between them - because of arterial elasticity and the effect of friction against the vessel wall, all measures of BP decline with distance (systolic, diastolic, pulse, and mean arterial) --- there is no pulse pressure beyond the arterioles, but there are slight pressure osciliations in the vena cava caused by the respiratory pump - in capillaries and veins the blood flows at a steady speed without pulsation becuase the pressure surgers have been damped out by the distance traveled and the ellasticity of the arteries --- this is why injured veins exhibit relatively slow, steady bleeding, whereas blood gushes out intermittently from a severed artery

Variations in Capillary Filtration and Reabsorption

- capillary activity can vary from place to place --- capillaries usually absorb most of the fluid they filter but this is not always the case - kidneys have glomeruli in which there is little or no reabsorption --- they are entirely devoted to filtration - alveolar capillaries of the lungs are solely dedicated to absorption so fluid does not fill the air spaces - in resting tissue, most precapillary sphinctors are constricted and the capillaries are collapsed - when a tissue becomes metabolically active, capillary flow increases --- in active muscles, capillary pressure rises to the point that filtration overrides reabsorption along the entire length of the capillary --- fluid accumulates in the muscle and increases muscular bulk by as much as 25% - capillary permeability is also subject to chemical influences - traumatized tissure releases chemicals such as substance P, bradykinin, and histamine which increases permeability and filtration

Arterial Sense Organs

- certain major arteries above the heart that have sensory structure in their walls that monitor blood pressure and chemisty - these receptors transmit info to the brainstem that serves to regulate the heartbeat, vasomotion, and respiration

Large Veins

- contains smooth muscle in all 3 tunics - have thin tunica media with only moderate amount of smooth muscle - tunica externa is thickest layer - diameter of ~10 mm Ex) SVC/IVC, pulmonary veins, internal jugular veins, and renal veins

Reduced Capillary Reabsorption

- depends on oncotic pressure, which is proportional to the concentration of blood albumin - deficiency of albumin (hypoproteinemia) produces edema by reducing the reabsorption of tissue fluid --- since albumin is produced in the liver, liver disease such as cirrhosis tend to lead to hyperproteinemia and edema - dietary protein deficiency - burns can also cause hyperproteinemia is severe because loss of protein from body surfaces no longer covered with skin - kidney disease allows proteins to escape in the urine

3 Classes of Arteries

- divided by size 1. Conducting Arteries 2. Distributing Arterties 3. Resistance Arteries

Cardiac Suction

- dring ventricular systole, the tendinous cords pull the AV valve cusps downward >> expanding the atrial space - expansion creates a suction that draws blood into the atria from the vena cava and the pulmonary veins

Artery

- efferent vessels of heart --- carry blood away from the heart - contain relatively strong, resilient tissue >> resistance vessels --- each beat of the heart creates a surge of pressure in the arteries as blood is ejected into them and arteries are built to withstand these surges - more muscular that veins, thus they retain their round shape even when empty, and appear relatively circcular in tissue sections - divided into 3 classes by size - thicker than veins since they must withstand greater pressures/adapt to rapidly changing pressures without breaking --- the role of arteries is to regulate blood distribution by adjusting their diameter via this expansion --- expanding reduces the BP so it is important for the artery to spring back into shape, hence the presence of greater elastic tissue - in large arteries, BP averages 90-100mmHg and surges to 120 mmHg during systole

Precapillary Sphincters

- encircles the entrance of one capillary - constriction of these sphinctors reduces or shuts off blood flow through their respective capillaries and diverts blood to tissues or organs elsewhere - dilation >> capillaries are well perfused - closing >> most blood bypasses the capillaries

Laminar Flow

- flow in layers - faster near the center of a vessel where it encounters less friction - slower near the walls where it drags the vessel - blood normally exhibits smooth, silent, laminar flow --- when a blood vessel dilates, a greater portion of the blood is in the middle of the stream and average flow may be quite swift --- when the vessel constricts more of the blood is close to the wall and average flow is slower (why plaque on the walls creates blockage.slower blood flow (heart has to work extra hard to pump through that

Blood Pressure

- force that the blood exerts against a vessel wall - clinically the most important measurement is the systemic arterial BP at a point close to the heart - the combination of expansion and recoil maintain a steady flow of blood downstream, in the capillaries, throughout the cardiac cycle - can be measured within a blood vessel or the heart by inserting a catheter or needle connected to a manometer (pressure measuring device) --- BP customarily measured with a sphyg, connected to an inflatable cuff wrapped around the arm, brachial artery is most commonly used (given that it is sufficiently close to the heart) and the BP recorded here approximates the maximum arterial BP found anywhere else in the body

Fenestrated Capillaries

- have endothelial cells riddles with patches of filtration pores >> "fenestrations"--- pores are about 20-100 nanom in diamete and are spane by glycoprotein membrane that is much thinner than the cell's plasma membrane - allow for the rapid passage of small molecules, but still retain most proteins and larger particles in the bloodstream - important in organs that engage in rapid absorption or filtration (kidneys, endocrine glands, small intestine, choroid plexus of the brain)

Venous Return and Physical Activity

- heart beats faster and harder >> increasing cardiac output and BP - blood vessels of the skeletal muscles, lungs, and coronary circulation dilate - increase in respiratory rate and depth enhances action of the thoracic pump - muscle contractions increase venous return via the skeletal muscle pump increased venous return >> increases cardiac output >> critical in perfusion of muscles

Varicose Veins

- in people who stant for extended periods of time, blood tends to pool in the lower limbs and stretch the veins, especially true of superficial veins, which are not surrounded by supportive tissue >> stretching pulls the cusps of the venous valves farther apart until the valves become less incapable of sealing the vessel and preventing the backfloe of blood >> as the veins beceome further distended, their walls gorw weak and they develop into varicose veins with irregular dilations and twisted pathways - obesity and pregnancy promote development of varicose veins by putting pressure on large veins of the pelvic region and obstructing drainage from the limbs --- with less drainage of blood, tissures of the left and foot may become edematous and painful - hemorrhoids are varicose veins of the anal canal

Skeletal Muscle Pump

- in the limbs veins are surrounded and massages by the muscles - contracting muscle squeezes the blood out of the compressed part of a vein and the valves ensure that this blood can go only to the heart

Increased Capillary Filtration

- kidney failure leads to water retention and hypertension >> raising capillary BP and filtration rate --- histamine dilates arterioles and raises capillary pressure and makes the capillary wall more permeable - old age --- capillary walls are more permeable in old age, putting elderly people at risk for edema - poor venous return causes capillary BP to rise (the flow of blood from the capillaries back to the heart) >> thus edema is a common problem among people confined to bed or a wheelchair - failure of the right ventricle if the heart tends to cause pressure to back up in the systemic veins and capillaries, thus resulting in systemic edema --- failure of the left ventricle causes pressure to back up in the lungs causing pulmonary edema

Gravity

- large veins of the neck are normally collapses with their venous pressure close to 0 - dural sinuses of the brain have more rigid walls and cannot collapse --- pressure is ~-10 mmHg --- creates a risk of air embolism when punctured - when you are sitting or standing, blood from your head and neck returns to the heart simply by flowing "downhill" through the large veins above the heart

Tunica Inerna (Intima)

- lines the inside of the vessel and is exposed to the blood - consists of simple squamous epithelium >> endothelium - overlies a basement membrane and a sparse layer of loose connective tissue --- continuous with the endocardium of the heart - acts as a selectively permeable barrier to material entering or leaving the bloodstream --- it secretes chemicals that stimulate dilation or constriction of the vessel - normally repels blood cells and platelets so that they flow freely without sticking to the vessel wall --- but when there is damage to the endothelium, platelets may adhere to it and form a blood clot

Obstructed Lymphatic Drainage

- lymphatic system is a network of one-way vessels that collect fluid from tissues and return it to the bloodstream - obstruction of these vessels can interfere with fluid drainage and lead to the accumulation of tissue fluid distal to the obstruction

Capillaries

- microscopic (.2-.4 micom), thin walled vessels connecting the smallest veins and arteries - a place where materials such as nutrients, wastes, hormones, and leukocytes must pass between the blood and tissue fluids, through the walls of the vessels >> the "exchange vessels" of the cardiovascular system - composed of only an endothelium and basal lamina - ends of capillaries differ in size --- average ~5 microm in diameter at the proximal end where they receive arterial blood and widen to ~9 microm at the distal end where they empty into a small vein --- often branch along the way - scarce in tendons and ligaments, barely found in cartilage, and absent from epithelia and the cornea and lens of the eye - 3 types - dubbed the "business end" of the cardiovascular system , because all the rest of the system exists to serve the exchange processes that occur here --- compared to venules, capillaries greatly outnumber venules, thus deemed more important of the two - must accomodate erythrocytes - about 1 billion ---scarcely any cell in the body is more than 60-80 microm in diameter away from the nearest capillary

Hypertension

- most common cardiovascular disease --- ~30% of americans >50 yo and 50% by 74 yo - damages the heart because it increases afterload, making the ventricles work harder to expel blood >> myocardium enlarges up to a point (hypertrophic response) but eventually it becomes excessively stretched and less efficient --- strains blood vessels and tears the endothelium >> creates lesions that become focal points of atherosclerosis >> worsens the hypertension and establishes a terrible positive feedback cycle - major cause of heart failure, stroke, and kidney failure - in the kidneys, the arterioles thicken in response to the stress, their lumens become narrower and renal blood flow declines --- in response to the resulting drop in BP, kidneys release renin >> leads to formation of vasoconstrictor AGII and release of aldosterone (promoting salt retention) >> worsens hypertension - primary hypertension accounts for ~90% of cases --- primary hypertension can result from a complex web of behavioral, hereditary, and other factors - many risk factors - many treatments - secondary hypertension very bad --- accounts for ~ 10& of cases --- secondary to other identifiable disorders (including kidney disease which may cause renin hypersecretion, atherosclerosis, hyperthyroidism, Cushing Syndrome, and polycythemia)

Thorax

- supplied by several arteries arising directly from the aorta and from the subclavian and axillary arteries - thoracic aorta begins distal to the arch and ends at the aortic hiatus (passageway through diaphragm) - azygous system of the thoracic wall provides venous drainage from the wall and viscera of the thorax

Diffusion

- most important mechanism of exchange - glucose and oxygen (being the most cencentrated in systemic blood) diffuse *out* of the blood - CO2 and other wastes (being more concentrated in the tissue fluid), diffuse *into* the blood - diffusion is only possible if the solute can either permeate the plasma membrane or the endothelial cells or find passages large enough to pass through (namely the filtration pores or intercellular clefts) - lipid soluble substances such as steroid hormones, O2, CO2, diffuse easily through the plasma membranes --- substances insoluble in lipids, such as glucose, electrolytes, must pass through membrane channels, filtration pores, or intercellular clefts

Distributing Arteries

- muscular/medium arteries - smaller branches that distribute blood to specific organs --- stem from conducting arteries - both the internal and external elastic lamina are thick and can be clearly seen --- smooth muscle is more evident than elastic tissue - most arteries that have specific anatomical names are either conducting arteries or distributing arteries Ex) brachial, femoral, renal , and splenic arteries - typically have up to 40 layers of smooth muscle constituting about 3/4 of the wall thickness

Continuous Capillaries

- occur in most tissue, such as skeletal muscle - basal lamina (thin protein carbohydrate layer) surrounds the endothelium and separates it from the adjacent connectice tissues - endothelial cells are separated by narrow intercellular clefts >> small solutes such as glucose can pass through these clefts but most plasma proteins, other large molecules, and platelets/blood cells cannot --- CC of brain lack these and have more complete tight junctions that form the blood brain barrier - endothelial cells held together by tight junctions >> form a continuous tube - pericytes lie external to the endothelium ---

Aortic Bodies

- one of the three chemoreceptors located in the aortic arch near the arteries of the head and upper extremeties - structurally similar to the carotid bodies and carry out the same function

Tunica Externa (Adventitia)

- outermost layer - consists of loose, connective tissue that often merges with neighboring blood vessels, nerves, or other organs - anchors the vessel and provides passage for small nerces, lymphatic vessels and smaller blood vessels that supply the tissues of the larger vessel

Mechanisms of Venous Return

- pressure gradient - gravity - skeletal muscle pump - thoracic (respiratory) pump - cardiac suction

Transcytosis

- process in which endothelial cells pick up material on one side of the plasma membrane by pinocytosis or receptor mediated endocytosis, transport vesicles across the cell, and discharge the material on the other side by exocytosis - accounts for only a small fraction of solute exchange across the capillary wall, but fatty acids, albumin, and some hormones such as insulin move across the endothelium by this mechanism

Lungs

- pulmonary circuit is the only route in which arteries carry oxygen poor blood and veins carry oxygen rich blood - pulmonary arteries have thin distensible walls with less elastic tissue than systemic arteries --- pulmonary arteries have a BP of 25/10 --- capillary hydrostatic pressure is about 10 mmHg if the pulmonary circuit as compared to 17 mHg in systemic capillaries - blood flows more slowly through pulmonary capillaries >> thus having more time for gas exchange - oncotic pressure overrides hydrostatic pressure so capillaries are engaged almost entirely in absorption >> prevents fluid accumulation in the alveolar walls and lumens which could compromise gas exchange - pulmonary arteries constrict in response to hypoxia --- systemic arteries dilate in response to local hypoxemia (want to get to the oxygen-deprived area) --- pulmonary hypoxemia indicates that part of the lung is not being ventilated well (mucous congestion of airway or degenerative lung disease) --- vasoconstriction in poorly ventilated regions of the lung redirects blood flow to better ventilated regions

Muscular Venules

- recieve blood from postcapillary venules - 1 mm in diameter - have a tunica media of one or two layers of smooth muscle and a thin tunica externa

Blood Flow

- since blood viscosity and vessel length do not change from moment to moment, vessel radius is the most adjustable of all variables that govern peripheral resistance - from capillaries to the vena cava, velocity rises again --- however blood in veins never regains the velocity it had in the large arteries because the veins are farther apart from the pressure head (the heart) --- because veins are larger that the capillaries, they create less resistance --- also because capillaries converge on one venule and many venules on a larger vein, a larger amount of blood is being forced into a progressively smaller channel - blood flows more slowly near the vessel wall than it does near the center of the vessel --- when the veddel dilates, radius is large, average velocity of flor is high --- when vessel constricts, radius is small, average velocity of flow is low because a larger portion of the blood is slowed down by friction against the vessel wall

Skeletal Muscles

- skeletal muscles receive a highly variable blood flow depending on their state of exertion - at rest, arterioles are constricted, most of the capillary beds are shut down, and total flow through the muscular system is ~ 1L/min - blood flow during exercise can increase more than 20 fold during strenuous exercise --- during exercise, arteriole dilate in response to E/NE from the adrenal medulla and sympathetic nerves --- precapillary sphinctors dilate in reponse to metabolites such as lactic acid, CO2, and adenosine --- this increase in blood flow requires blood to be diverted from other organs such as the digestive tract and kidneys to meet the needs of the working muscles - muscular contraction compresses blood vessels and impedes flow --- because of this muscular contraction, isometric contraction causes fatigue more quickly than intermittent isotonic contraction --- if you squeeze a rubber ball as hard as you can without relaxing your grip, you feel the muscles fatigue more quickly than if you intermittently squeeze and relax

Resistance Arteries

- small arteries - contain many layers of smooth muscle and relatively little elastic tissue - have much thicker tunica media in proportion to the lumen - small arteries are usually too variable in number and location to be given individual names

Postcapillary Venules

- smallest of the veins - receive blood from capillaries directly or by way of the distal ends of the throughfare channels - are even more porous than capillaries, therefore venules also exchange fluid with the surrounding tissues - 10-20 microm in diameter - contain tunica interna with only a few fibroblasts around it and no muscle --- surrounded by pericytes --- most leukocytes emigrate from the bloostream through the venule walls

BP Physiologically Governed by 3 Principal Variables:

1. Cardiac Output 2. Blood Volume (regulated by the kidneys --- have the greatest influence than any other organ on blood pressure) 3. Resistance to Flow - one of the body's main means of regulating BP/MAP is the ability of arteries to stretch and recoil during the cardiac cycle --- if the arteries were rigid pressure would rise much higher in systole and drop to nearly zero in diastole --- blood throughout the circulatory system would flow and stop, flow and stop, flow and stop... putting greater stress on small vessels --- but healthy conducting arteries expand with each systole and absorb some of the force of the ejected blood >> when the heart is in diastole, their eleastic recoil exerts pressure on the blood and prevents BP from dropping to zero >> elasti arteries smooth out the pressure fluctuations and reduce stress on the smaller arteries

3 Kinds of Arterial Sense Organs

1. Carotid Sinuses 2. Carotid Bodies 3. Aortic Bodies

3 Types of Capillaries

1. Continuous 2. Fenestrated 3. Sinusoids characterized by the ease with which the allow substances to pass through their walls and by structural differences that account for their greater or lesser permeability

3 Routes that Chemicals Pass Through Capillaries

1. Endothelial cell cytoplasm 2. Intercellular clefts between the endothelial cells 3. Filtration pores (fenestrations) of the fenestrated capillaries

3 Causes of Edema

1. Increased capillary filtration 2. Reduced capillary reabsorption 3. Obstruct lymphatic drainage

3 Ways of Controlling Vasomotion

1. Local Mechanisms 2. Neural Mechanisms 3. Hormonal Mechanisms

5 Levels of Veins

1. Postcapillary Venules 2. Muscular Venules 3. Medium Veins 4. Venous Sinuses 5. Large Veins

2 Physiological Purposes of Vasomotion

1. generalized raising or lowering of BP throughout the body --- requires centralized control --- an action on the part os the medullary vasomotor center or by hormones that circulate throughout the system, such as AGII or E --- widespread vasoconstriction raises overall BP because the whole "container" (blood vessel) squeezes on a fixed amount of blood --- this can be important in supporting cerebral perfusion in situations such as hemorrhaging or dehydration in which blood volume has significantly fallen 2. selective modifying the perfusion of a particular organ and rerouting the blood from one region of the body to another --- can be achieved by with central or local control --- Ex) during periods of exercise, sympathetic nervous system can selectively reduce flow to kidneys and digestive tract yet increase perfusion to skeletal muscles and metabolite accumulation in a tissue can stimulate local vasodilation and increase perfusion as well of that tissue without affecting circulation elsewhere in the body --- if a specific artery constricts, pressure downstream from the constriction drops and pressure upstream from it rises --- if blood can travel by either of the two routes and one route puts up more resistance than the other, most blood follows the path of least resistance --- this mechanism enables the body to redirect blood from one organ to another - after a meal, vasoconstriction shuts down blood flow to 90% or more of the capillaries in the muscles of your lower limbs (and muscles elsewhere) --- the intestines receive priority and the skeletal muscles receive receive relatively little flow -- this raises BP above the limbs, where the aorta gives off a branch (superior mesenteric artery) --- high resistance in the circulation of the limbs and low resistance in the superior mesenteric artery route blood to the small intestine where it is needed to absorb the nutrients you are digesting - during exercise muscles receive high priority --- to increase the circulation in these routes, vasoconstriction must occur elsewhere such as the kidneys and digestive tracts --- that reduces their perfusion for the time being, making more blood available to the organs important in exercise

3 Layers of Vessel Wall

1. tunica interna (tunica intima) 2. tunica media 3. tunica externa (tunica adventitia)

Cerebral Arterial Circle

AKA "Circle of Willis" composed of several arterial anastomoses - surrounds pituitary gland and optic chiasm - receives blood from internal carotid and basilar arteries - very variable among people --- most people lack one or more of the circle's components --- about 20% of the population has a complete arterial circle

Cerebral Vascular Accident (CVA)

AKA "Stroke" sudden death (infarction) of brain tissue caused by ischemia --- cerebral ischemia can be produced by atherosclerosis, thrombosis, or a ruptured aneurysm - effects range from unnoticeable to fatal, depending on extent of tissue damage and function of the affected tissue --- blindness, paralysis, loss of sensation, and loss of speech are common - recovery depends on ability of neighboring neurons to take over loss of function and on the extent of collateral circulation to regions surrounding the cerebral infarction

Relation of Blood Pressure, Resistance, and Flow

F= (Pa - Pv) / R - the greater the pressure difference between two points, the greater the flow - the greater the resistance, the less the flow

Circulatory System

Key to life: must deliver oxygen and nutrients to the tissues, remove their wastes, at a rate that keeps pace with tissue matabolism - improper circulatory services to tissue can lead within minutes to tissue necrosis and death

Changes of BP with Age

Male @ 20: 123/76 Female @ 20: 116/72 Male @ 70: 145/82 Female @ 70: 159/85

Vasomotion

adjusting the diameter of the vessel - only significant way of controlling peripheral resistance from moment to moment

Flow

amount of blood flowing through an organ, tissue, or blood vessel in a given time (mL/min) - in average individual, total flow is constant and equal to cardiac output --- 5.25 L/min - flow through individual organs varies from minute to minute as blood is redirected from one organ to another Ex) digestion requires abundant flow to the intestines and the cardiovascular system makes this available by reducing flow through other organs such as the kidney (not super critical in digestion) --- when digestion and nutrient absorption are over, blood flow to the intestines declines and a higher priority is given to the kidneys and other organs postdigestion

Circulatory Shock

any state in which CO is insufficient to meet the body's metabolic needs - 2 categories: cardiogenic shock and low venous return shock - you can have cases where multiple forms of circulatory shock are in play

3 Reasons for Arteriole Control for Peripheral Resistance and Blood Flow

arterioles alone account for about half of the total peripheral resistance of the circulatory system 1. They are on the proximal side of the capillary beds --- so they are best positioned to regulat flow into the capillaries 2. They greatly outnumber any other class of arteries --- and thus provide the most numerous control points 3. They are more muscular in proportion to their diameters than any other class of blood vessels --- and thus are more capable of vasomotion

Natriuretic Peptides

atrial natriuretic peptide and brain natriuretic peptide antagonize aldosterone - secreted by the heart - increase Na+ excretion by the kidneys, thus reducing blood volume and BP --- also have a generalized vasodilator effect that helps to lower BP

Chemoreflexes

autonomic response to changes in blood chemistry, especially to pH and [O2] and [CO2] - initiated by chemoreceptors called aortic bodies and carotid bodies - primary role is to adjust respiration to changes in blood chemistry --- secondary role in stimulating vasomotion - hypoxemia (blood O2 deficiency), hypercapnia (excess CO2), and acidosis (low blood pH) stimulate chemoreceptors and act through the vasomotor center to include widespread vasoconstriction --- this increases overal BP, thus increasing perfusion of the lungs and rate of gas exchange - chemoreceptors also stimulate breathing, so increased ventilation of the lungs matches their increased perfusion

Medullary Ischemic Reflex

autonomic response to reduced perfusion to the brain --- the medulla oblongata monitors its own blood supply and activates corrective reflexes when it senses a state of ischemia - within seconds of a drop in perfusion, the cardiac and vasomotor centers of the medulla send sympathetic signals to the heart and blood vessels that accelerate the heart and constrict the vessels --- the actions raise the BP and ideally restore normal cerebral perfusion - cardiac and vasomote centers also receive input from other brain centers so stress, anger, and arousal can raise the BP - hypothalamus acts through the vasomotor center to redirect blood flow in response to exercise or changes in body temperature

Septic Shock

bacterial toxins trigger vasodilation and increased capillary permeability

Venous Pooling

blood accumulates in the limbs because venous pressure is not high enough to override the weight of blood and drive it upward - if enough blood accumulates in the limbs, CO may become so low that the brain is inadequately perfused and a person may experience dizziness or syncope (orthostatic hypotension) - this can be avoided by tensing the calf and other leg muscles (activating skeletal muscle pump)

Portal System

blood flows through two conseccutive capillary networks before returning to the heart - typicaly occur in the kidneys, connecting the hypothalamus and the anterior pituitary, and connecting the intestines to the liver

Venous Pooling (Vascular) Shock

body has normal total blood volume, but too much of it accumulates in the lower body - can result from long periods of standing, sitting, or from widespread vasodilation

Low Venous Return (LVR) Shock

cardiac output is low because too little blood is returning to the heart - 3 principal forms: hypovolemic, obstructed venous return, and venous pooling --- both venous pooling and hypovlemic shock are present in cases that involve both vasodilation and loss of fluid through abnormally permeable capillaries (septic and anaphylactic shock)

Solvent Drag

chemicals dissolved in the water that pass through the capillary wall if they are not too large - critical in kidney and intestinal function

Hypotension

chronic low resting BP - could be caused by blood loss, dehydrtaion or anemia

Filtration and Reabsorption

fluid filters out of arterial end of a capillary and osmotically reenters it at the venous end - fluid delivers materials to the cells and removes their metabolic wastes --- shifting balance between pH and osmotic forces is what allows a capillary to give off fluid at one point and reabsorb it at another - only pressure that changes significantly from the arterial end to the venous end is the capillary blood pressure, and this change is responsible for the shift from filtration to reabsorption --- With a reabsorb. pressure of 7 and a NFP of 13, it might appear that far more fluid would leave capillaries than reenter them but since capillaries branch along their length, there are more of them at the venous end than at the arterial end >> partially compensates for the difference between filtration and reabsorp. pressures --- also typically have twice the diameter at the venous end than they have at the arterial end >> more capillary surface area available to reabsorb fluid than give it off - *Consequently, capillaries reabsorb about 85% of fluid they filter; the other 15% is absorbed and returned to the blood by way of the lymphatic system*

Obstructed Venous Return Shock

growing tumor or aneurysm compresses a vein and impedes blood flow

Angiogenesis

growth of new blood vessels - controlled by growth factors and inhibitors - 3 critical instances when this is important--- over a longer time, a hypoxic tissue can inrease its own perfusion by angiogenesis 1. regrowth of uterine lining after each menstrual period 2. development of a higher density of blood capillaries in the muscles of well-conditioned athletes 3. growth of arterial bypass around obstructions in the coronary circulation

Pericytes

have elongated tendrils that wrap around the capillary containing the same contractile proteins as muscle - thought to contract and regulate blood flow through the capillaries themselves - have the potential to differentiate into endothelial and smooth muscle cells and thus contribute to vessel growth and repair

Hydrostatic Pressure (HP)

physical force exerted by a liquid against a surface such as a capillary wall (BP is a perfect example) - a typical blood capillary has blood HP of ~30 mmHg at arterial end --- HP of interstitial space around is -3 mmHg ( - indicates slight suction, which helps draw fluid out of capillary) --- positive HP within the capillary and negative interstitial pressure work in the same direction >> create a total outward force of ~33 mmHg

Hemodynamics

physical principles of blood flow - primarily based on pressure and resistance

Anastomosis

point where two blood vessels meet - shunts (atriovenous anastomosis) - venonus anastomosis - arterial anastomosis

Colloid Osmotic Pressure (COP)

portion of the osmotic pressure due to protein - OP

Air Embolism

presence of air in the bloodstream - if a deural sinus is punctured (remember negative pressure in these vessels), air can be sucked into the sinus and accumulate in the heart chambers >> blocks CO and causes sudden death - smaller air bubbles in the systemic circulation can cut off blood flow to the brain, lungs, myocardium, and other vital tissues

Central Venous Pressure

pressure at the point where inferior vena cava enters the heart = 4.6 mmHg (delta P = 7-13 mmHg)

Pressure Gradient

pressure generated by the heart is the most important force in venous flow even though it is substantially weaker in veins than in arteries - there is a venous pressure gradient in favor of flow of blood toward the heart - pressure gradient and venous return increase when blood volume increases - it also increases in the event of generalized, widespread vasoconstriction because this reduces the volume of the circulatory system and raises blood pressure and flow - pressure in venules ranges 12-18 mmHg

Baroreceptors

pressure sensors --- respond to changes in blood pressure

Transient Ischemic Attacks (TIA)

produced by brief episodes of cerebral ischemia - characterized by temporary dizziness, loss of vision or other senses, weakness, paralysis, headache, or aphasia - may result rom spasms of diseased cerebral arteries - lasts for just a moment to a few hours and is often an early warning of a impeding stroke

Hepatic Portal System

receives all of the blood draining from the abdominal digestive tract, as well as the pancreas, gallbladder, and spleen - called the portal system because it connects capillaries of the intestine and other digestive organs to modified capillaries (hepatic sinusoids) of the liver >> the blood passes through two capillary beds in series before it returns to the heart - intestinal blood is rich in nutrients for a few hours following a meal --- the hepatic portal system gives the liver the first claim to these nutrients before the blood is distributed to the rest of the body --- it also allows the blood to be cleansed of bacteria and toxins picked up from the intestines (an important function of the liver)

Arteriosclerosis

stiffening of the artery >> making the artery less able to expand and recoil freely - atherosclerosis is a form of arteriosclerosis--- *atherosclerosis*: growth of lipid deposits in the arterial walls >> these deposits can become calcified into complicated plaques >> give the arteries a hard, bonelike consistency - consequently the downstream vessels are subjected to greater stress and are more likely to develop aneurysms and rupture - primary cause: cumulative damage of free radicals --- cause gradual deterioration of the elastic and other tissues of the arterial walls Ex) old rubber bands less stretchy - as we get older, out arteries become less distentible and absorb less systolic force --- as a result of these degenerative changes, BP rises with age

Epinephrine/Norepinephrine

stimulate vasoconstriction and raises BP - adrenal and sympathetic catecholamines bind to alpha adrenergic recetros on the smooth muscle of most blood vessels --- in coronary blood vessels and blood vessels of skeletal muscle these chemicals bind to beta adrenergic receptors and cause vasodilation >> increasing blood flow to the myocardium and muscular system during exercise

Vasoactive chemicals

substances that stimulate vasomotion

Hormonal Control

these hormones influence BP either through vasoactive effects or other means such as regulating water balance - Angiotensin II - Aldosterone - Natriuretic Peptides - ADH - E/NE

Vessel Radius

the effect of the vessel radius on blood flow stems from the friction of the moving blood against vessel walls Blood Flow (F) is proportional to Radius (r)^4 --- makes vasomotion a very potent factor in the control of flow

Vessel Length

the farter a liquid travels in a tube, the more friciton it encounters - pressure and flow therefore decline with distance - if you were to measure MAP in a reclining person, you would obtain a higher value in the arm than in the ankle --- in a reclinging person a stronger pulse in the dorsal pedal artery of the foot is a good sign of adequate CO --- if perfusion is good at that distance from the heart, it is likely to be good elsewhere in the systemic circulation

Peripheral Resistance

the opposition of flow that the blood encounters in vessels away from the heart --- a moving fluid has no pressure unless it encounters at least some resistance >> thus pressure and resistance are not independent variables in blood flow - pressure is affected by resistance and flow is affected by both - resistance hinges on: blood viscosity, vessel length, vessel radius

Neural Control

the vasomotor center of the medulla oblongata exerts sympathetic control over blood vessels throughout the body - precapillary sphinctors have no innervation however and respond only to local and hormonal stimuli - sympathetic nerve fibers stimulate most blood vessels to constrict but they dilate the vessels of skeletal and cardiac muscle in order to meet the metabolic demands of exercise --- vasomotor center is an integrating center for 3 autonomic reflexes

Angiotensin II

vasoconstrictor --- raises BP - requires angiotensin-converting enzyme (ACE) --- hypertension is often treated with drugs called ACE inhibitors which block the action of this enzyme thus lowering AGII levels and BP

Aneursyms

weak point in an artery or in the heart wall - forms a thin-walled, bulging sac that pulsates with each beat of the heart and may eventually rupture - dissecting aneurysm: blood accumulates between the tunics of an artery and separates them, usually because of a degeneration in the tunica media --- most common sites are abdominal aorta, renal arteries, and the arterial circle of the brain (circle of willis) - even without hemorrhaging, aneurysms can cause pain or death by putting unrelenting pressure on brian tissue, nerves, adjacent vessels, pumonary air passages, or the esophagus --- other consequences include neurological disorders, difficulty in breathing or swallowing, chronic cough, or congestion of the tissues with blood - sometimes result from congenital weakness of the blood vessels and sometimes from trauma or bacterial infections such as syphilis - most common cause is the combo of arteriosclerosis and hypertension

Skeletal Muscle Pump

when the muscles surrounding a vein contract, they force blood through these valves - the propulsion of venous blood by muscular massaging aided by venous valves is the mechanism of blood flow

Vasodilation

widening of the vessel - brought about not by any muscular effort to widen a vessel, but rather by muscular passivity (relaxation of the smooth muscle, allowing BP to expand the vessel itself)