there are three major types of blood vessels in the human body arteries which conduct oxygenated blood away from the heart veins which conduct deoxygenated blood towards the heart and capillaries which connect the arterial system to the Venus system capillaries serve as sites of gas exchange allowing oxygen to diffuse from blood into body tissues and carbon dioxide to diffuse from body tissues into blood here we see that arteries will Branch into smaller versions of themselves called arteriales and it's the arterials that have a direct connection to the capillary beds the capillaries then merge with smaller versions of veins called vules which then branch in into larger sized veins there are three layers or tunics comprising the wall of blood vessels these three layers are known as the tuna intima Tunica Media and tuna externa the tuna intima represents the innermost layer of a blood vessel wall it is comprised of end iial cells which is a single layer of simple squamous cells the tuna media represents the middle or intermediate layer this layer is comprised of a mixture of both smooth muscle and dense elastic connective tissue the tuna externa represents the outermost layer it is comprised of dense elastic connective tissue only the three tunicas will appear in the same order or sequence in arteries as well as veins however the thickness of the tuna media and tuna externa differ in arteries versus veins in arteries the tuna media which is the smooth muscle layer is thick while the tuna externa is thin in arteries the reverse holds true for veins in veins the tuna media is thin while the tuna externa is thick now blood capillaries which connect arterials to venules are microscopic and not visible to the naked eye because capillary walls only contain a tuna intima layer comprised of endophilic media nor tuna external layer in blood capillaries hence their microscopic size in cross-section we can see that the tuna Media or smooth muscle layer of the artery is noticeably thicker compared to the Tunica Media layer of the vein conversely the tuna external layer of the artery is thinner compared to the tuna externa of the vein another major difference between arteries and veins is the discrepancy in the size of their relative lumens or cavities because arteries have a more narrow or constricted Lumin for blood flow blood coursing through arteries will exert greater pressure against arterial walls because this arterial blood encounters more resistance being driven through such a confined space now the pressure exerted by Blood against blood vessel walls is defined as blood pressure so we can establish that arteries exhibit higher blood pressure compared to veins here we see that veins have much larger lumens or cavities compared to arteries therefore blood coursing through the spacious Lumin of veins will exert less pressure against Venus walls Venus blood encounters less resistance being driven through a larger Lumen or cavity therefore veins will exhibit lower blood pressure compared to arteries now another reason for arteries exhibiting higher blood pressure than veins is the thicker Tunica Media or smooth muscle layer found in arteries with more smooth muscle comes more powerful or forceful contractions to propel blood along this is another reason why arterial blood exerts greater pressure against arterial walls than Venus blood against Venus walls in fact the pressure exerted by arterial blood is so strong or forceful that each time we palpate or feel for pulse near one of our superficial veins for instance The Superficial radial Vein on our wrist we're actually feeling the rhythmic pulsation of the deeper radial artery through the more superficial radial vein this illust illustrates the extent to which arterial blood pressure is greater than Venus blood pressure going from interior to exterior the layers of the arterial or Venus wall are tuna intima tuna media then the tuna externa here we can again note the smaller size of the lumen in the cross-section of of the artery compared to the lumen in this cross-section of the vein also the tuna media in the cross-section of the artery is noticeably thicker than its tuna externa the Tunica externa in the cross-section of the vein is noticeably thicker than its Tunica Media here is a long itudinal as well as a cross-sectional view of an artery displaying the disorder known as aerosis AO is derived from the term aoma which translates to a degeneration of the inner arterial wall known as the tuna intima due to plaque buildup now sclerosis translates to Hardon which refers to the loss of elasticity in arterial walls a number of reasons including hypertension elevated ldls diabetes or toxins such as tobacco can damage the inner endothelial layer of the artery wall known as the tuna intima once the tuna intima is damage fatty or plaque deposits made out of cholesterol can also Lodge themselves into the blood vessel lining and build up at the injured site this induces an inflammatory response that attracts white blood cells to the injury site this accumulation of both white blood cells as well as plaque can cause the arterial wall to to harden which Narrows or constricts arteries sometimes even completely obstructing blood flow altogether this leads to poor circulation in that artery in the photo micrograph on the right we can see a grossly thickened tuna intima resulting from atherosclerosis now the Lumen or cavity of the artery is severely narrowed here are a few more images of inflamed and thickened tuna intimas resulting from atherosclerosis the lumens or cavities of these arteries are constricted to varying degrees from partial to almost complete obstruction atherosclerosis can increase the risk of stroke heart attack and and also developing a blood clot which is known as a thrombus this brings us to the first checkpoint question of this lecture [Music] recording while capillary beds and smaller blood vessels such as arterials and venules may vary in number and pattern between individuals the major arteries and veins are actually conserved between individuals here is a figure illustrating the major arteries of the body here is a figure illustrating the major veins of the body we do want to note many of the arteries and veins in the body will share the same names but not every artery has a vein counterpart and vice versa for instance the great sainis vein located in the femoral or thigh region has no arterial counterpart in the image on the right we have the median pubal vein also known as the median basilic vein it is a superficial vein located in the front of the elbow which is known as the anti- cubital region this is why the median cubital vein is also termed the anti-al vein abbreviated ACV this vein is quite clinically relevant as it is routinely used for veny puncture in other words the common site of blood drops now pulse is defined as the traveling pressure wave created by arteries expanding and recoiling as blood is being pushed away from the heart through the aorta and arteries with each systolic or contraction event of the left ventricle we can manually palpate or feel pulse now there are seven major pulse points named after arteries over which they can be felt here we have the superficial temporal artery located near the Temple of the head the paraded artery located in the neck the brachial artery in the upper arm the radial artery in the wrist the femoral artery in the thigh the poil artery behind the knee and the dorsalis petus artery located on the top of the foot recall that we can feel or Pate pulse from a deeper artery through a more superficial vein now while pulse is a close approximation of your true heart rate pulse is not a precise nor an exact measurement of your true heart rate heart rate measures how quickly the heart is Contracting in other words how many times the heart contracts or beats per minute heart rate like pulse is measured in units of beats per minute or BPM now unlike pulse heart rate must be measured using medical devices such as a heart rate or ECG monitor blood pressure is defined as the force that blood exerts against the walls of vessels through which it flows pulse is not an indicator for high or low blood pressure in other words measuring pulse is not a substitute for measuring blood pressure now pulse and blood pressure do have a positive correlation but they do not share a perfect correlation for instance during exercise or physical activity heart rate can even safely double so that blood is delivered to our working muscles but blood pressure May respond to exercise by only increasing by a small or slight amount this is because healthy blood vessels will dilate or widen to accommodate increase in blood flow therefore blood pressure will increase at a lower rate compared to heart rate here is a graph displaying blood flow velocity or speed in each type of blood vessel as a function of the total cross-sectional area of that blood vessel type although blood velocity is not the same value as blood pressure both values do have a positive correlation with one another the more quickly blood flows through a vessel the more pressure or Force force that blood exerts against the vessel walls the more quickly blood flows through a vessel the more force or pressure that blood exerts against those vessel walls now the total cross-sectional area of each blood vessel type refers to the overall combined area after adding together all the individual diameters belonging to every blood vessel of that same type owing to their microscopic size capillaries are the smallest blood vessel and therefore also the most numerous blood vessel in the human body this is why Blood capillaries have the largest total crosssectional area larger than any other blood vessel type adding together the individual diameters of the billions of capillaries will sum to be a huge area you can liken this large area to a very spacious Lumen or cavity now because there's only a single aorta present in the entire body the aorta will therefore have the smallest total cross-sectional area of any blood vessel type the larger the total cross-sectional area of a blood vessel the lower its blood flow velocity in other words the larger the total cross-sectional area of a blood vessel the more slowly blood flows through that type of blood vessel and since blood capillaries have the largest total cross-sectional area capillaries will therefore exhibit the lowest blood flow velocity this makes sense as capillaries serve as the sites of gas exchange where low blood flow velocity ensures that gases have adequate time to diffuse by the same token the smaller the total cross-sectional area of a blood vessel the greater or higher its blood flow velocity in other words the smaller the total cross-sectional area of a blood vessel the more quickly blood flows through a blood vessel of that type and since the aorta has the smallest total cross-sectional area the aorta will exhibit the highest blood flow velocity this makes sense as the aorta is responsible for Distributing oxygenated blood to the entire systemic circulation high blood flow velocity ensures that blood will sufficiently reach body tissues comparatively since arterials are smaller in size compared to arteries the diameters of all the arterials in the body added together will therefore sum to be a larger total cross-sectional area than that of the less numerous arteries therefore arterials will exhibit lower blood flow velocity compared to arteries the term blood pressure as a standalone term without any proceeding descriptors generally refers to the pressure exerted by blood inside arteries against arterial walls there are several types of blood pressure your instruments digital monitors tend to be less accurate compared to manual meters now blood pressure is measured in units of millimeters of mercury and there are a number of factors influencing blood pressure salt content goes hand inand with water levels this is is because the greater the salt retention the greater the water retention and therefore the increased resistance or workload the heart must overcome in order to pump blood kidneys also help maintain salt and water homeostasis so the condition of the kidneys plays a major role with respect to blood pressure the kidneys also secrete a blood pressure regulating hormone called renin now blood viscosity also Bears a major influence on blood pressure as we have seen in our discussion of blood the greater the viscosity of blood the greater its resistance to flowing as a result the heart must contract more forcefully to overcome this resistance consequently blood pressure Rises with increased blood viscosity hormones such as aldosterone secreted by the adrenal gland also help regulate blood sodium levels the pressure exerted by blood inside veins against Venus walls will typically have the full descriptor Venus blood pressure this is because assessing Venus blood pressure is a more invasive procedure that requires inserting a central Venus catheter into a vein either a vein underneath the clavicle as is the case here or a vein in the arm for instance assessing Venus blood entails ing that catheter to end up in the superior venne Cava or the right atrium and ultimately connecting to a transducer and a monitor to measure Venus blood pressure that is the pressure exerted by Blood as it returns to the heart blood pressure is recorded as two numbers stolic blood pressure and diastolic blood pressure the top number known as systolic blood pressure is the pressure that blood exerts against arterial walls as the ventricles contract and Propel blood through arteries around the body diastolic blood pressure is the pressure exerted by Blood against arterial walls as the ventricles fill with with blood and relax in between beats when performing a manual blood pressure assessment of a subject we listen for two different sounds as the pressure in the cuff is gradually released the first sound or heartbeat heard is the sound of blood flow being restored in the subject's arteries this is because the subject blood has overcome the pressure applied to their arm to block off the circulation the value seen on the gauge or dial is the pressure apply to the cuff at that very moment when the first heart sound is heard this value on the gauge or dial corresponds to the greatest pressure that can be exerted by the subject's blood against their arterial walls we then listen for the last sound or the last heartbeat the value seen on the gauge or dial is the pressure applied to the cuff at that very moment the last sound is heard this value corresponds to the lowest pressure that is exerted by the subjects blood against their arterial walls taking a manual blood pressure reading illustrates how these two numbers systolic blood pressure and diastolic blood pressure actually represent a range where 80 mm of mercury represents a normal diastolic blood pressure value and 120 mm of mercury represents a normal systolic blood pressure value in the event an individual is suffering from elevated blood pressure or hypertension their heart will be pumping harder than normal whenever the heart contracts it must generate a pressure that exceeds the pressure inside arteries this is so the aortic semilunar valve will open effectively allowing blood to be pushed into the arteries now when the pressure within arteries known as arterial blood pressure increases this increases the resistance or opposing force that the heart must push against and overcome to eject blood as a result the heart must now work harder and consume more energy to generate a greater force to overcome this higher arterial pressure now recent research has found that systolic blood pressure steadily increases with advancing age this is due to increasing stiffness of arteries and long-term build up of plaque as we age therefore for individuals older than 50 years of age systolic blood pressure is a better indicator for risk of stroke mortality and overall cardiovascular health compared to diastolic blood pressure this is why more attention is given to the top number systolic blood pressure as a major risk factor for cardiovascular disease in individuals older than 50 years of age however the reverse is true for individuals younger than 50 years of age where diastolic blood pressure is actually a better indicator of cardiovascular health mortality and stroke risk than systolic blood pressure this is because diastolic blood pressure only increases until about age 50 and then proceeds to decline after age 50 this brings us to the next checkpoint question of this lecture recording we Define stroke volume as the volume of blood ejected from one ventricle either right or left per beat or contraction of the heart we will assign the the letters SV to represent stroke volume the value of cardiac output on the other hand is the volume of blood ejected from one ventricle either right or left per minute the average human cardiac output irrespective of gender is 5 L of blood per minute at rest we will assign the letter Q to represent cardiac output now Q or cardiac output is the product of heart rate multiplied by stroke volume heart rate is measured in units of beats per minute stroke volume is measured in units of lers of blood per beat cancelling like units beats is in the numerator we'll cancel out beats in the denominator and we will arrive at the final units of cardiac output which is measured in units of lers of blood per minute this brings us to the final checkpoint question of this lecture recording