Anatomy 2: Chapter 21- Blood Vessels and Circulation ep9-6

Intro

Blood circulates throughout the body, moving from the heart through the tissues and back to the heart, in blood vessels

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capillary exchange plays a key role in homeostasis. the most important processes that move materials across typical capillary walls are diffusion, filtration, and reabsorption

special circulation

the vascular supply through organs in which blood flow is controlled by separate mechanisms

Total peripheral resistance

total peripheral resistance of the cardiovascular system reflects a combination of factors: vascular resistance, blood viscosity, and turbulence

Systemic arteries

-several large arteries are called trunks, including pulmonary, brachiocephalic thyrocervical and celiac trunks -most major arteries are paired, with one artery of each pair on either side of the body.

Venous return from the upper limbs

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CNS activities and cardiovascular center

- A general sympathetic activation stimulates the cardio acceleratory and vasomotor centers(cardiac output and bp increase) - When the parasympathetic division is activated , the cardioinhibitory center is stimulated (decrease in cardiac output) -Parasympathetic activity does not directly affect the vasomotor center, but vasodilation takes place as sympathetic activity declines -The higher brain centers can also affect blood pressure. Our thought processes and emotional states can produce significant changes in blood pressure by influencing cardiac output and vasomotor tone

The superior vena cavae

- All the body's systemic veins(except cardiac veins) drain into either the superior vena cavae or inferior vena cava. Superior vena cava receives blood from the tissues and organs of the head, neck, chest, and shoulders and upper limbs -numerous veins drain the cerebral hemispheres. The largest, superior sagittal sinus, is in the falx cerebri. -Most of the inferior cerebral veins converge within the brain to form the great cerebral vein. It delivers blood from the interior of the cerebral hemispheres and the choroid plexus to the straight sinus. Other cerebral veins drain into the cavernous sinus with numerous small veins from the orbit. -Each transverse sinus drains into a sigmoid sinus, which penetrates the jugular foramen and leaves the skull as the internal jugular vein -vertebral veins drain the cervical spinal cord and the posterior surface of the skull. these vessels descend within the transverse foramina of the cervical vertebrae, along with the vertebral arteries

Blood flow to lungs

- An extensive capillary network surrounds each alveolus. Local responses to oxygen levels within individual alveoli regulate blood flow through the lungs -When an alveolus contains plenty of oxygen, its blood vessels dilate -Blood flow then increases, promoting reabsorption of oxygen air from side the alveolus. When the oxygen content of the air is very low, the vessels constrict. They shunt blood to other alveoli that contain more oxygen - This mechanism is precisely the opposite of that in other tissues, where a decline is oxygen levels causes local vasodilation rather than vasoconstriction -Blood pressure in pulmonary capillaries is lower than that in systemic capillaries - If the blood pressure in the pulomonary capillaries rises above 25 mm Hg, fluid enters the alveoli, causing pulmonary edema

Arterial Blood pressure

- Arterial pressure is important because it maintains blood flow through capillary beds. -Arterial pressure is not constant. Rather it rises during ventricular systole and falls during ventricular diastole. -Peak blood pressure is systolic-measured during ventricular systole -Minimum blood pressure at the end of ventricular diastole is called diastolic pressure -The difference between the systolic and diastolic pressures is the pulse pressure -To report a single blood pressure value we use the mean arterial pressure. It is calculated by adding one third of the pulse pressure to the diastolic pressure. MAP= diastolic pressure + pulse pressure/ 3 -Hypertension- abnormally high blood pressure is termed hypertension. Abnormally low blood pressure is hypotension -Stage 1 hypertension in adults is systolic blood pressure range of 140-159 and a diastolic pressure range of 90-99 -Hypertension significantly increases the workload on the heart and the left ventricle gradually enlarges. More muscle mass means a greater demand for oxygen -Increased arterial pressures also place a physical stress on the walls of the blood vessels throughout the body. -This stress promotes or accelerates the development of arteriosclerosis. It also increases the risk of aneurysms, heart attacks, and strokes

Five general classes of blood vessels

- Arteries: carry blood away from the heart. As they enter peripheral tissues, arteries branch repeatedly and the branches decrease in diameter - Arterioles: smallest arterial branches -capillaries: blood moves in these from arterioles, where diffusion takes pace between blood and interstitial fluid. - From the capillaries, blood enters small venules, which unite to form larger veins that return blood to the heart

Heavy exercise

- At higher levels of exertion, other physiological adjustments take place as the cardiac and vasomotor centers activate the sympathetic nervous system -Cardiac output increases toward maximal levels -Under massive sympathetic stimulation, the cardioacceleratory center can increase cardiac output to levels as high as 20-25 liters per minute -restrict blood flow to non essential organs like digestive system -Only blood supply to brain remains unaffected

Arteries of the foot

- At the ankle, the anterior tibial artery becomes the dorsalis pedis artery - At the ankle, the posterior tibial artery divdies to form the medial and lateral plantar arteries, they supply blood to the plantar surface of the foot - these arteries are conneceted to the dorsalis pedis through a pair of anastosomes. the arrangement produces a dorsal arch and a plantar arch. small arteries branching off these arches supply the distal portions of the foot and the toes

The respiratory pump

-As you inhale, your thoracic cavity expands, reducing pressure within pleural cavities. This drop in pressure pulls air into your lungs. At the same time it also pulls blood into the inferior vena cava and right atrium from the smaller veins of your abdominal cavity and lower body. -As you exhale, your thoracic cavity decreases in size. Internal pressure then rises, forcing air out of your lungs and pushing venous blood into the right atrium. This mechanism is called the respiratory pump

Venous valves

-The arterial system is a high pressure system - Blood pressure in a peripheral venule is only about 10 percent of that in the ascending aorta, and pressures continue to fall along the venous system -Venous valves prevent blood from moving back toward capillaries -As long as the valves function normally, any movement that distorts or compresses a vein pushes blood toward the heart. This effect improves venous return * If the walls of the veins near the valves weaken or become stretched and distorted , the valves may not work properly. Blood then pools in the veins, and the vessels become grossly distended. The effects range from mild discomfort and a cosmetic problem, as in superficial varicose veins, in the thighs and legs, to painful distortion of adjacent tissues, as in hemorrhoids

Baroreceptor Reflexes

- Baroreceptors are specialized receptors that monitor the degree of stretch in the walls of expandable organs - The baroreceptors involved in cardiovascular regulation are found in the walls of 1) the carotid sinuses(expanded chambers near the bases of the internal carotid arteries of the neck) 2) aortic sinuses, pockets in the walls of the ascending aorta adjacent to the heart and 3) wall of right atrium -Aortic baroreceptors monitor blood pressure within the ascending aorta. Any changes trigger the aortic reflex, which adjusts blood pressure to maintain adequate blood pressure and blood flow through the systemic circuit - When blood pressure rises, the increased output from the baroreceptors alters activity in the CV center and produces two major effects 1.A decrease in cardiac output, due to parasympathetic stimulation and the inhibition of sympathetic activity 2. Widespread peripheral vasodilation, due to inhibition of excitatory neurons in the vasomotor center * the decrease in cardiac output reflects primarily a reduction in heart raye due to the release of ACh at the SA node. * The widespread vasodilation lowers peripheral resistance, and this effect combined with a reduction in cardiac output leads to a fall in blood pressure to normal levels -When blood pressure falls below normal, baroreceptor output is reduced accordingly. This change has two major effects to raise blood pressure 1. An increase in cardiac output, through stimulation of sympathetic innervation to the heart. This results from the stimulation of the cardioacceleratory center and is accompanied by an inhibitory center 2. Widespread peripheral vasodilation, caused by the stimulation of sympathetic vasoconstrictor neurons by the vasomotor center -Atrial baroreceptors monitor blood pressure at the end of the systemic circuit - at the vena cavae and the right atrium

Natriuretic Peptides

- Cardiac muscle cells in the wall of the right atrium of the heart produce atrial natriuretic peptide in response to excessive stretching during diastole -Ventricular muscle cells produce related hormone called brain natriuretic peptide -These peptide hormones reduce blood volume and blood pressure. They do so by 1) increasing sodium ion excretion by the kidneys 2) promoting water losses by increasing the volume of urine produced 3) reducing thirst 4) blocking the release of ADH, aldosterone, epinephrine, and noepinephrine and 5) stimulating peripheral vasodilation -As blood volume and blood pressure decrease, the stresses on the walls of the heart are removed, and natriuretic peptide production ceases

Diffusion

- Different substances diffuse across capillary walls by different routes 1. Water, ions, and small organic molecules such as glucose, amino acids, and urea can usually enter or leave the bloodstream by diffusion between adjacent endothelial cells or through channels in plasma membranes 2. Large water soluble compounds are unable to enter or leave the blood stream except at fenestrated capillaries, such as those of the hypothalamus, the kidneys, many endocrine organs, and the intestinal tract 3. Large water soluble compounds are unable to enter or leave the bloodstream except at fenestrated capillaries, such as those of the hypothalamus, the kidneys, many endocrine organs, and the intestinal tract 4. lipids, such as fatty acids and steroids and lipid soluble materials including soluble gases such as oxygen and carbon dioxide can cross capillary walls by diffusion through the endothelial plasma membranes 5. Plasma proteins are normally unable to cross the endothelial lining anywhere except in sinusoids, such as those of the liver, where plasma proteins enter the bloodstream

arteries of the thigh and leg

- Each external iliac artery crosses the surface of an iliopsoas muscle and penetrates the abdominal wall midway between the anterior superior iliac spine and the pubic symphsis on that side. It emerges on the anterior, medial surface of the thigh as the femoral artery -The deep femoral artery branches off its lateral surface. The deep femoral artery supplies blood to the ventral and lateral regions of the skin and deep muscles of the thigh. It gives rise to the femoral circumflex arteries -The femoral artery become popliteal artery at the knee and then posterior and anterior tibial arteries then fibular artery -The anterior tibial artery provides blood to the skin and muscles of the anterior portion of the leg

Vasomotion

- Each precapillary sphincter alternately contracts and relaxes a dozen times a minute. These rhythmic changes in vessel diameter are called vasomotion -Vasomotion is controlled locally by changes in concentrations of chemicals and dissolved gases in the interstitial fluids. For example, when dissolved oxygen concentrations decrease within a tissue, the capillary sphincters relax, so blood flows to the area increase. -When you are at rest, blood flows through 25 percent of the vessels within a typical capillary bed in your body -When many tissues become active, the blood flow through capillary beds must be coordinated.

vessel length

- Increasing the length of a blood vessel increases friction: The longer the vessel, the greater the surface area in contact with blood

The distribution of blood

- Our total blood volume is unevenly distributed among arteries, veins, and capillaries -The heart, arteries, and capillaries in the pulmonary and systemic circuits normally contain 30-35 percent blood volume. The venous system contains the rest -About 1/3 of the blood in the venous system is circulating within the liver, bone marrow, and skin -Veins are much more distensible, or expandable than arteries -Veins which expand easily are called capacitance vessels -If serious hemorrhaging occurs, the vasomotor center of the medulla oblongata stimulates sympathetic nerves that innervate smooth muscle cells in the walls of the medium sized veins. This activity has two major effects: 1. Systemic veins constrict: this process is called venoconstriction-it decreases the amount of blood within the venous system, increasing the volume within the arterial system and capillaries 2. The constriction of veins in the liver, skin, and lungs redistributes a significant proportion of the total blood volume. As a result, blood flow to delicate organs (such as the brain) and to active skeletal muscles can be increased or maintained after blood loss. The amount of blood can be shifted from veins in the liver, skin, and the lungs to the general circulation is called the venous reserve. It is normally about 20% of total blood volume

Antidiuretic hormone

- Released at posterior lobe of pituitary gland in response to a decrease in blood volume, increase in osmotic concentration of plasma, or to circulating angiotensin II. -It brings peripheral vasoconstriction that elevates blood pressure -this hormone also stimulates water conservation by the kidneys, thus preventing a reduction in blood volume that would further reduce blood pressure

medium sized veins

-similar in size to muscular arteries -thin tunica media, thick tunica externa

venules

-smallest venous vessels -collect blood from capillary beds -They vary widely in size and structure -smallest ones resemble expanded capillaries

The abdominal aorta

- The abdominal aorta is a continuation of the thoracic aorta. -At the level of vertebra L4, the abdominal aorta splits into two major arteries- the left and right common iliac arteries- that supply deep pelvic structures and the lower limbs -The abdominal aorta delivers blood to all the abdominopelvic organs and structures. The major branches to visceral organs are unpaired -By contrast, branches to the body wall, the kidneys, the urinary bladder, and other structures outside the peritoneal cavity are paired - The abdominal aorta gives rise to three unpaired arteries: 1) The celiac trunk: delivers blood to the liver, stomach, and spleen. The celiac trunk divides into three branches a) the left gastric artery supplies the stomach and the inferior portion of the esophagus b) splenic artery supplies the spleen and arteries to the stomach and pancreas. c) common hepatic artery supplies arteries to the liver, stomach, gallbladder, and duodenal area 2) superior mesenteric artery: supplies arteries to the pancreas and duodenum, small intestine, and most of the large intestine 3)inferior mesenteric artery delivers blood to the terminal portions of the colon The abdominal aorta also gives rise to five paired arteries 1. Inferior phrenic arteries supply the inferior surface of the diaphragm and the inferior portion of the esophagus 2. Adrenal arteries each supply one adrenal gland, which caps the superior part of a kidney 3. renal arteries travel posterior to the peritoneal lining to reach the adrenal glands and kidneys 4. The gonadal arteries originate between the superior mesenteric arteries. In males, they are called testicular arteries and are long, thin arteries that supply blood to the testes and scrotum. In females they are termed ovarian arteries and supply blood to the ovaries, uterine tubes and uterus. The distribution of gonadal vessels differs by gender

Blood flow to the brain

- The brain has a very high demand for oxygen and receives a substantial supply of blood -12 % of the cardiac output goes to the brain -Neurons do not have significant energy reserves and in functional terms the cardiovascular system treats blood flow to the brain as a top priority - Even during a cardiovascular crisis, blood flow through the brain remains as near normal as possible -Total blood flow to the brain remains relatively constant, but blood flow to specific regions of the brain changes from moment to moment. These changes occur in response to local changes in the composition of the interstitial fluid that accompany neural activity -These changes ensure that the active neurons will receive the oxygen and nutrients they require - The brain receives arterial blood through four arteries . An interruption of flow in any one of these large vessels does not significantly reduce blood flow to the brain as a whole because these arteries form anastomoses inside the cranium

Blood flow to the heart

- The coronary arteries arise at the base of the ascending aorta, where systemic pressures are highest. Each time the heart contracts, it squeezes the coronary vessels so blood flow is reduced - When you are at rest, coronary blood flow is about 250 mL/min. When the workload on your heart increases local factors, such as reduced O2 levels are increased lactic acid, dilate the coronary vessels and increase blood flow. Epinephrine released during sympathetic stimulation promotes the vasodilation of coronary vessels -For reasons that are not clear, some people have coronary spasms. These spasms can temporarily restrict coronary circulation ad produce symptoms of angina - When the cardiac workload increases much above resting levels, individuals with these conditions experience signs and symptoms of heart failure

vessel diameter

- The effects of friction on blood act in a narrow zone closest to the vessel wall. In a small-diameter vessel, friction with the walls slows nearly all the blood. resistance is therefore relatively high. blood near the center of a large diameter vessel does not encounter friction with the walls, so the resistance is large vessels is fairly low. -differences in diameter have much more significant effects on resistance than do differences in length -There's no way to control vessel length, but vessel diameter can change quickly through vasoconstriction or vasodilation. -Because a small change in diameter produces a large change in resistance, mechanisms that alter the diameters of arterioles provide control over peripheral resistance and blood flow.

Hormones and cardiovascular regulation

- The endocrine system regulates cardiovascular performance in both short term and the long term. - Other hormones important in regulating cardiovascular function include 1) antidiuretic hormone 2)angiotensin II 3) erythropoietin (EPO) 4) the natriuretic peptides (ANP and BNP) -All four are concerned primarily with the long term regulation of blood volume

Pressures in small arteries and arterioles

- The mean arterial pressure and the pulse pressure become smaller as the distance from the heart increases -In essence, blood pressure decreases as it overcomes friction and produces blood flow - The pulse pressure lessens due to the cumulative effects of elastic rebound along the arterial system - By the time blood reaches a precapillary sphincter, no pressure fluctuations remain, and the blood pressure is steady at approximately 35 mm Hg

Subclavian arteries

- The subclavian arteries supply blood to the arms, chest wall, shoulders, back, and CNS - Three major branches arise before a subclavian artery leaves the thoracic cavity: 1) internal thoracic artery- supplying the pericardium and the anterior wall of the chest 2) vertebral artery- provides blood to the brain and spinal cord 3) thyrocervical trunk- provides blood to muscles and other tissues of the neck, shoulder, and upper back(becomes axillary artery then humeral circumflex arteries then brachial artey then deep brachial artery, then divides into radial and ulnar artery, then radial and ulnar arteries fuse to form the superficial and deep palmar arches

Systemic veins

- Veins collect blood from tissues and organs of the body by means of elaborate venous network that drains into the right atrium of the heart by the superior and inferior venae cavae - One significant difference between the arterial and venous systems involves the distribution of major veins in the neck and limbs -Arteries in these areas are deep beneath the skin, protected by the bones and soft tissue. Veins have two sets-peripheral and deep.During warm weather peripheral are used and during cold weather deep are used

Cardiovascular response to hemorrhaging

- When hemostasis fails to prevent significant blood loss, the entire cardiovascular system makes adjustments - The immediate problem is to maintain adequate blood pressure and peripheral blood flow. The long term problem is to restore normal blood volume

capillary beds

- capillaries function not as individual units but rather as part of an interconnected network called a capillary bed or capillary plexus - A single arteriole generally gives rise to dozens of capillaries. They empty into several venules, the smallest vessels of the venous system - A precapillary sphincter guards the entrance to each capillary. Contraction of the smooth muscle cells of this sphincter narrows the capillary entrance, reducing or stopping the flow of blood - a capillary bed contains several direct connections between arterioles and venules. The wall in the first part of such a passageway contains smooth muscle that can change its diameter. This segment is called a metarteriole. The rest of the passageway resembles a typical capillary in structure and is called a thoroughfare channel - More than one artery may supply blood to a capillary bed. the multiple arteries are called collaterals. They fuse before giving rise to arterioles. The fusion of two collateral arteries that supply a capillary bed is an example of an arterial anastomosis -An arterial anastomosis acts like an insurance policy: If one artery is compressed or blocked, capillary circulation will continue. -Arteriovenous anastomoses are direct connections between arterioles and venules - The pattern of blood flow through an arteriovenous anastomosis is regulated primarily by sympathetic innervation under the control of the cardiovascular center of the medulla oblongata - Angiogenesis is the formation of new blood vessels from pre-existing vessels and occurs under the direction of vascular endothelial growth factor.

Exercise, cardiovascular fitness and health

- cardiovascular performance improves significantly with training. -Trained athletes have larger hearts and greater stroke volumes than do non-athletes, and these are important functional differences - An athelete at rest can maintain normal blood flow to peripheral tissues at a heart rate as low as 32 bpm. When necessary, the athlete's cardiac output can increase to levels 50 percent higher than those of non-athletes

thoracic aorta

- diaphragm divides the descending aorta into a superior thoracic aorta and an inferior abdominal aorta -Thoracic aorta starts at T5 and penetrates diaphragm at vertebra T12 -This vessel supplies blood to branches that service the tissues and organs of the mediastinum, the muscles of the chest and the diaphragm and the thoracic spinal cord - We group the branches of the thoracic aorta as either visceral or somatic -visceral branches supply the organs of the chest -Visceral branches supply the organs of the chest. The bronchial arteries supply the tissue of the lungs not involved in gas exchange -The pericardial arteries supply the pericardium -The esophageal arteries supply the esophagus arteries supply the esophagus, and the mediastinal arteries supply the tissues of the mediastinum - Somatic branches supply the chest wall. The intercostal arteries supply the chest muscles and the vertebral column area. The superior phrenic arteries deliver blood to the superior surface of the diaphragm, which separates the thoracic and abdominoplevic cavities

Muscular arteries

- medium sized arteries/distribution arteries - distribute blood to the body's skeletal muscles and internal organs -characterized by a thick tunica media -The external carotid arteries of the neck, the brachial arteries of the arms, the mesenteric arteries of the abdomen, and the femoral arteries of the thighs are examples of muscular arteries -Major arterial pressure points(press them against bone to control severe bleeding) are the common carotid, radial, brachial, femoral, popliteal, posterior tibial. and dorsal pedal

Capillaries

- radiate through connective tissues and branch beneath the basement membrane of the epithelia -Capillaries are the only blood vessels whose walls permit exchange between the blood and surrounding interstitial fluids -Blood flows through capillaries relatively slowly, allowing sufficient time for diffusion or active transport of materials across the capillary walls. In this way, the histological structure of capillaries permits a two-way exchange of substances between blood and interstitial fluid - A typical capillary consists of an endothelial tube inside a thin basement membrane. No tunica media or tunica externa -two types of continuous capillaries and fenestrated capillaries

Vascular resistance

- the forces that oppose blood flow in the blood vessels -largest component of total peripheral resistance -The most important factor in vascular resistance is friction between blood and the vessel walls. The amount of friction depends on two factors: vessel length and vessel diameter.

Blood Viscosity

- the resistance to flow caused by interactions among molecules and suspended materials in a liquid. -Liquids of low viscosity such as water flow at low pressures, like water -Whole blood has a viscosity about five times that of water, due to its plasma proteins and blood cells

The structure of vessel walls

- the walls of arteries and veins have three distinct layers- the tunica intima, tunica media, and tunica externa 1. Tunica intima(interna) is the inner layer of a blood vessel. In arteries, the outer margin of the tunica intima contains a thick layer of elastic fibers called the internal elastic membrane 2. The tunica media is the middle layer of a blood vessel. It contains concentric sheets of smooth muscle tissue in a framework of loose connective tissue. thickest layer. 3. Tunica externa is the outer layer of a blood vessel. -Their layered walls give arteries and veins considerable strength. The muscular and elastic components also permit controlled changes in diameter as blood pressure or blood volume changes vasa vasorum= supply arteries and veins

Elastic Rebound

-As systolic pressure climbs, the arterial walls stretch -Thus expansion allows the arterial system to accommodate some of the blood provided by ventricular systole -When diastole begins and blood pressures fall, the arteries recoil to their original dimensions. This phenomenon is called elastic rebound. -However, most of the push from elastic rebound forces blood flow along the arterial network while the left ventricle is in diastole

Light exercise

-As you begin light exercise, three interrelated changes take place -Extensive vasodilation occurs as skeletal muscles consume oxygen more quickly. peripheral resistance decreases, blood flow through capillaries increases, and blood enters the venous system at a faster rate -The venous return increases as skeletal muscle contractions squeeze blood along the peripheral veins and faster breathing pulls blood into the vena cavae by the respiratory pump -Cardiac output rises, primarily in response to 1) the rise in venous return and 2) atrial stretching -This regulation by venous feedback produces a gradual increase in cardiac output to about double resting levels. The increase supports accelerated blood flow to skeletal muscles, cardiac muscle, and the skin

In the pulmonary circuit, deoxygenated blood enters the lungs in arteries and oxygenated bloodleaves the lungs by veins

-Blood entering the right atrium has just returned from the peripheral capillary beds, where it released oxygen and absorbed carbon dioxide -At the lungs, oxygen is replenished and carbon dioxide is released - The arteries of the pulmonary circuit differ from those of the systemic circuit in that they carry deoxygenated blood -The smallest branches of the arteries are called pulmonary arterioles. They provide blood to capillary networks that surround alveoli -As oxygenated blood leaves the alveolar capillaries, it enters venules that in turn unite to form larger vessels carrying blood toward the pulmonary veins -these four veins, two from each lung, empty into the left atrium, to complete the pulmonary circuit * at any moment, the systemic circuit contains about 84% of total blood volume

pressure in vessels

-Blood vessels must be resilient enough to withstand changes in pressure, and flexible enough to move with underlying tissues and organs - The pressures inside vessels may vary with distance from the heart

The carotid and the blood supply to the brain

-Each common carotid artery divides into an external carotid artery and an internal carotid artery - The carotid sinus, located at the base of the internal carotid artery may extend along a portion of the common carotid - The external carotid arteries supply blood to the structures of the neck, esophagus, pharynx, larynx, lower jaw, and face - The internal carotid arteries enter the skull through the carotid canals of the temporal bones, delivering blood to the brain -internal carotid artery branches into 1) opthalamic artery, which supplies the eyes 2) anterior cerebral artery, which supplies the frontal and parietal lobes of the brain 3) a middle cerebral artery, which supplies the midbrain and lateral surfaces of the cerebral hemispheres -The brain is extremely sensitive to changes in blood supply. An interruption of blood flow for several seconds produces unconsciousness. After four minutes some permanent neural damage can occur -The vertebral arteries enter the cranium at the foramen magnum, where they fuse along the ventral surface of the medulla oblongata to form the basilar artery - the vertebral artery and the basilar artery supply blood to the spinal cord, medulla oblongata, pons, and cerebellum. -They then divide into the posterior cerebral arteries which in turn branch off into the posterior communicating arteries -internal carotid and basilar artery are interconnected . They form a ring shaped anastomosis called the cerebral arterial circle which encircles the infundibulum of the pituitary gland. WIth this arrangement the brain can receive blood from either the carotid or the vertebral arteries, reducing the likelihood of a serious interruption of circulation -Strokes or cerebrovascular accidents (CVAs), are interruptions of the vascular supply to a portion of the brain . The middle cerebral artery, a major branch of the cerebral arterial circle is the most common site of a stroke -Strokes affecting vessels that supply the brain stem also produce distinctive symptoms. Strokes affecting the lower brain stem are commonly fatal

Elastic arteries

-Elastic arteries are known as conducting arteries because they carry large volumes of blood away from the heart. Include pulmonary trunk and aorta as well are their major branches -Walls are extremely resilient b/c a lot of elastic fibers and few smooth muscle cells in tunica media. As a result, elastic arteries can tolerate the pressure changes of the cardiac cycle - Their expansion cushions the sudden rise in pressure during ventricular systole, and their recoil slows the drop in pressure during ventricular diastole. In this way, elastic arteries help to make blood flow continuous - The elasticity of the arterial system dampens the pressure peaks and valleys that accompany the heartbeat. by the time the blood reaches the arterioles, the pressure fluctuations have disappeared, and blood flow is continuous

Exercise and cardiovascular disease

-Exercise lowers cholesterol levels by stimulating enzymes that help move low-density lipoproteins(LDLs) from the blood to the liver. -Exercise also increases the size of the lipoprotein particles that carry cholesterol, making it harder for small proteins to lodge in the vessel walls. -exercise also reduces blood pressure and slows the formation of plaques -Regular moderate exercise may cut the incidence of heart attacks almost in half -exercise also speeds recovery after heart attack -intense athletic training can have adverse effects on the body

Filtration

-Filtration is the removal of solutes as a solution flows across a porous membrane -Solutes too large to pass through the pores are filtered out of the solution -The driving force for filtration is hydrostatic pressure -In capillary filtration, water and small solutes are forced across a capillary wall, leaving larger solutes and suspended proteins in the bloodstream -Filtration takes place primarily at the arterial end of the capillary , where capillary hydrostatic pressure is the highest

Cardiovascular regulatory mechanisms

-Homeostatic mechanisms regulate cardiovascular activity to ensure that blood flow through tissues, called tissue perfusion meets the demands for oxygen and nutrients. The factors that affect tissue perforation are 1) cardiac output 2) peripheral resistance and 3) blood pressure -The purpose of cardiovascular regulation is to ensure that these blood flow changes occur 1) at an appropriate time 2) in the right area 3) without drastically changing blood pressure and blood flow to vital organs -The regulatory mechanisms focus on controlling cardiac output and blood pressure to restore adequate blood flow after blood pressure decreases. We can group these mechanisms as follows: -Autoregulation: local factors change the pattern of blood flow within capillary beds a precapillary sphincters open and close in response to chemical changes in interstitial fluids -Autoregulation causes immediate localized homeostatic adjustments. If autoregulaion fails to normalize conditions at the tissue level, neural mechanisms and endocrine factors are activated -Neural mechanisms: they respond to changes in arterial pressure or blood gas levels sensed at specific sites -endocrine mechanisms: the endocrine system releases hormones that enhance short-term adjustments and that direct long-term changes in cardiovascular performance

Arteries of the Pelvis and lower limbs

-Near the level of vertebra L4, the terminal segment of the abdominal aorta divides to form a pair of elastic arteries- the right and left common iliac arteries-plus the small median sacral artery - At the level of the lumbosacral joint, each common iliac divides to form an internal iliac artery and an external iliac artery -internal iliac artery supplies the pelvic cavity -external iliac artery supply lower limb, larger in diameter

Reabsorption

-Reabsorption occurs as a result of osmosis - The osmotic pressure (OP) of a solution is an indication of the force of osmotic water movement. It represents the pressure that must be applied to prevent osmotic movement across a membrane. - The presence of suspended proteins that cannot cross capillary walls creates an osmotic pressure called blood colloid osmotic pressure(oncotic pressure) -Osmotic water movement continues until either the solute concentrations are equalized or an opposing hydrostatic pressure prevents the movement -Remember that hydrostatic pressure forces water out of a solution and osmotic pressure draws water into a solutionv

Reflex Control of Cardiovascular system

-The cardiovascular center detects changes in tissue demand by monitoring arterial blood, especially its blood pressure, pH, and concentrations of dissolved gases. -The baroreceptor reflexes respond to changes in blood pressure and the chemoreceptor reflexes monitor changes in the chemical composition of arterial blood - These reflexes are regulated through a negative feedback loop: The stimulation of a receptor by an abnormal condition leads to a response that counteracts the stimulus and restores normal conditions

Chemoreceptor Reflexes

-The chemoreceptor reflexes respond to changes in carbon dioxide, oxygen, or pH levels in blood and CSF - The chemoreceptors involved are sensory neurons. they are located in the carotid bodies, situated in the neck near the carotid sinus, and the aortic bodies near the arch of the aorta -When chemoreceptors in the carotid bodies or aortic bodies detect either an increase in the carbon dioxide content or a decrease in the pH of the arterial blood, the cradioacceleratory and vasomotor centers are stimulated. At the same time, the cardio inhibitory center is inhibited. This dual effect causes an increase in cardiac output, peripheral vasoconstriction, and an increase in blood pressure -Strong stimulation of the carotid or aortic chemoreceptors causes widespread sympathetic activation, with more dramatic increases in heart rate and cardiac output -The chemoreceptors of the medulla oblongata are involved primarily with the control of respiratory function and secondarily with regulating blood flow to the brain -Coordination of cardiovascular and respiratory activities is vital, because accelerating blood flow in the tissues is useful only if the circulating blood contains an adequate amount of oxygen

Muscular Compression

-The contractions of skeletal muscles near a vein compress it, helping to push blood toward the heart -The valves ensure that blood flows in only one direction -Contraction while walking is enough. -However if standing still with knees locked contraction cant occur, blood flow to brain decreases and can result in fainting. -horizontal position from fainting restores blood flow

Erythropoietin

-The kidneys release EPO if blood pressure falls or if -the oxygen content of the blood becomes abnormally low. -EPO acts directly on blood vessels, causing vasoconstriction, thereby increasing blood pressure. -EPO also stimulates the production and maturation of red blood cells -These cells increase the volume and viscosity of the blood and improve its oxygen-carrying capacity

Neural mechanisms

-The nervous system adjusts cardiac output and peripheral resistance to maintain adequate blood flow to vital organs. centers responsible for these regulatory activities include the cardiac centers and the vasomotor center of the medulla oblongata - cardiovascular center, composed of the cardioinhibitory center, cardioacceleratory center and vasomotor center -The cardio acceleratory center increases cardiac output through sympathetic innervation -The cardioinhibitory center decreases cardiac output through parasympathetic innervation - The vasomotor center contains two populations of neurons: 1) A very large group responsible for widespread vasoconstriction and a smaller group responsible for vasodilation of arterioles in skeletal muscles and the brain. The vasomotor center controls the activity of sympathetic motor neurons 1. Control of vasoconstriction: the neurons innervating peripheral blood vessels in most tissues are adregenic(release NE). NE causes vasoconstriction 2. Control of vasodilation: Vasodilator neurons innervate blood vessels in skeletal muscles in the brain. The stimulation of these neurons causes vasodilation. This relaxation is triggered by the appearance of NO in the surroundings. the most common vasodilator synapses are cholinergic-relase ACh. Other vasodilator synapses are nitroxidergic-their axon terminals release NO as a neurotransmitter

Pulmonary and systemic circuits

-The pulmonary circuit consists of arteries and veins that transport blood between the heart and the lungs -This circuit begins at the right ventricles and ends at the left atrium -From the left ventricle, the arteries of the systemic circuit transport oxygenated blood and nutrients to all organs and tissues -Veins of the systemic circuit ultimately return deoxygenated blood to the right atrium - Three major patterns of blood vessel organization are worth noting: 1. The peripheral distributions of arteries and veins on the body's left and right sides are generally identicaexcept near the heart, where the largest vessels connect to the atria or the ventricles. Corresponding arteries and veins usually follow the same path. For example, the left and right subclavian arteries parallel the left and right sublavian arteries 2. A single vessel may have several names as it crosses specific anatomical boundaries. 3. Several arteries and veins usually service tissues and organs. often anastosomes between adjacent arteries or veins reduce the impact of a temporary or event permanent blockage or occulusion, in a single blood vessel

Superficial veins of the head and neck

-The superficial veins of the head converge to form the temporal , facial, and maxillary veins. -The temporal vein and the maxillary vein drain into the external jugular vein -In healthy individuals, the external jugular vein is easily palpable

Vasomotor tone

-The sympathetic vasoconstrictor nerves are always active, producing a significant vasomotor tone -Constriction has a large effect on resistance -The resistance of a maximally constricted arteriole is roughly 80 times that of a fully dilated arteriole. -Because blood pressure varies directly with peripheral resistance, the vasomotor center can control arterial blood pressure very effectively by making modest adjustments in vessel diameters

Arteries

-Their relatively thick, muscular walls make arteries elastic and contractile. Elasticity permits the vessel diameter to change passively in response to changes in blood pressure - When stimulated, arterial smooth muscles contract, constricting the artery- a process called vasoconstriction. When these smooth muscles relax the diameter of the lumen increases- a process called vasodilation Vasocontriction and vasodilation affect the afterload on the heart, peripheral blood pressure and capillary flow In traveling from the heart to peripheral capillaries, blood passes through elastic arteries, muscular arteries, and arterioles

Arterioles

-poorly defined tunica externa -The diamters of smaller muscular arteries and arterioles change in response to local conditions or to sympathetic or endocrine stimulation. For example, arterioles in most tissues vasodilate when oxygen levels are low - Arterioles vasoconstrict under sympathetic stimulation. -The force opposing blood flow is called resistance so arterioles are also called resistance vessels -Occasionally, local arterial pressure exceeds the capacity of the elastic components of the tunics. The result is an aneurysm or bulge in the weakened wall of an artery

Pressure and Resistance determine blood flow and affect rayes of capillary exchange

-Under normal circumstances, blood flow is equal to cardiac output -Capillary blood flow is determined by the interplay between (P) and resistance (R) in the cardiovascular network. To keep blood moving, the heart must generate enough pressure to overcome the resistance to blood flow in the pulmonary and systemic circuits -increased pressure means increased flow -pressure gradient: difference in pressure from one end of the vessel to the other -The largest pressure gradient is found between the base of the aorta and the proximal ends of peripheral capillary beds -Blood leaving the peripheral capillaries enters the venous system. The pressure gradient across the venous system is relatively small, but venous resistance is very low. -The low venous blood pressure-aided by valves, skeletal muscle contraction, gravity, and other factors-is enough to return the blood to the heart

Autoregulation of Blood flow within tissues

-Under normal resting conditions, cardiac output remains stable and perioheral resustance within individual tissues is adjusted to control local blood flow -factors that promote the dilation of precapillary sphincters are called vasodilators. local vasodilators act at the tissue level to accelerate blood flow through their tissue of origin. Examples of local vasodilators include the following: - decreased tissue oxygen levels or increased CO2 levels -Lactic acid or other acids generated by tissue cells -nitric oxide released from endothelial cells -rising concentrations of potassium ions or hydrogen ions in the interstitial fluid -chemicals released during local inflammation, including histamine and NO -Elevated local temperature -These factors work by relaxing the smooth muscle cells of the pre-capillary sphincters -Local vasoconstrictors include prostaglandins and thromboxanes released by activated platelets and white blood cells and the endothelins released by damaged endothelial cells -Local vasodilators and vasoconstrictors control blood flow within a single capillary bed -In high concentrations, these factors also affect arterioles increasing or decreasing blood flow to all capillary beds in a given area

Veins

-Veins collect blood from all tissues and organs and return it to the heart -Blood pressure in veins is lower than in arteries -In general veins are larger than their corresponding arteries

Venous Pressure and Venous Return

-Venous pressure, although low, determines venous return-the amount of blood arriving at the right atrium each minute -Venous return has a direct impact of the cardiac output. Blood pressure at the start of the venous system is only about 1/10 that at the start of the arterial system - Pressures at the entrance to the right atrium fluctuate, but they average about 2 mm Hg. -The effective pressure in the venous system is roughly 16 mm Hg -This pressure compares with 65 mm Hg in the arterial system -Although venous pressures are low, veins offer comparatively little resistance, so pressure declines very slowly as blood moves through the venous sytem. -As blood moves toward the heart, the veins become larger, resistance drops, and the velocity of blood flow increases -Two factors assist the low venous pressures in propelling blood toward your heart: muscular compression of peripheral veins and the respiratory pump during inhalation

Differences between arteries and veins

-Walls of arteries are thicker than those of veins. The tunica media of an artery contains more smooth muscle and elastic fibers than does that of a vein -The lumen of an artery often looks smaller than that of the corresponding vein. Because the walls of the arteries are relatively thick and strong , they keep their shape when sectioned. cut veins tend to collapse -The endothelial lining of an artery cannot contract, so when an artery constricts, its endothelium becomes folded and the sectioned arteries have a pleated appearance. The lining of a vein lacks these folds

Angiotensin II

-appears in the blood when specialized kidney cells called juxtaglomerular cells, release the enzyme renin in response to a fall in renal blood pressure -Renin starts an enzymatic chain reaction. It converts angiotensinogen, a plasma protein produced by the liver to angiotensin I. In the capillaries of the lungs, angiotensin-converting enzyme then modifies angiotensin I to angiotensin II - Angiotensin II has four important functions: 1)It stimulates the adrenal production of aldosterone-causing Na retention and K loss by the kidneys 2) It stimulates the secretion of ADH in turn stimulating water reabsorption by the kidneys and complementing the effects of aldosterone 3) It stimulates thirst, resulting in increased fluid consumption(presence of ADH and aldosterone makes sure that the additional water consumed will be retained) and 4) stimulates cardiac output and triggers the constriction of arterioles

Ascending aorta

-begins at the aortic valve of the left ventricle -The left and right coronary arteries originate in the aortic sinus at the base of the ascending aorta, just superior to the aortic valve.

Fenestrated capillaries

-contain pores that penetrate the endothelial lining. The pores allow rapid exchange of water and solutes between blood and interstitial fluid. -Examples of fenestrated capillaries include the choroid plexus of the brain and the blood vessels in a variety of endocrine organs, such as the hypothalamus and the pituitary, pineal, and thyroid glands. -Fenestrated capillaries are also found along absorptive areas of the intestinal tract and at filtration sites in the kidneys. Both the number of pores and their permeability characteristics may vary from one region of the capillary to another -sinusoids are fenestrated and commonly have gaps between adjacent endothelial cells and the basement membrane is either thinner or absent. As a result, sinusoids permit the free exchange of water and solutes as large as plasma proteins between blood and interstitial fluid - Blood moves through sinusoids relatively slowly, maximizing the time available for exchange across the sinusoidal walls. SInusoids occur in the liver, bone marrow, spleen, and many endocrine organs, including pituitary and adrenal glands -Along sinusoids of the liver, spleen, and bone marrow, phagocytic cells monitor the passing blood, engulfing damaged red blood cells, pathogens, and cellular debris

Turbulence

-high flow rates, irregular surfaces, and sudden changes in vessel diameter upset the smooth flow of blood, creating eddies and swirls. -increases resistance and slows blood flow -Turbulence normally occurs when blood flows between the atria and the ventricles and between and the ventricles and the aortic and pulmonary trunks - Turbulence seldom occurs in smaller vessels unless their walls are damaged.

large veins

-include the superior and inferior venae cavae and their branches within the abdominopelvic and thoracic cavities. - All large veins have three layers

Continous capillaries

-supply most regions of the body -the endothelium is a complete lining -continuous capillaries are located in all tissues except epithelia and cartilage -allow water, small solutes, and lipid soluble materials to diffuse into the interstitial fluid and at the same time prevent loss of blood cells and plasma proteins. -Some exchange may occur between blood and interstitial fluid by bulk transport- the movement of materials by endocytosis - in specialized continuous capillaries in most of the central nervous system and in the thymus, the endothelial cells are bound together by tight junctions. These capillaries have very restricted permeability

aortic arch

-three elastic arteries originate along the aortic arch and deliver blood to the head, neck, shoulders, and upper limbs: brachiocephalic trunk, left common carotid artery, and left subclavian artery - brachiocephalic trunl( innominate artery) ascends for a short distance before branching to form the right subclavian artery and the right common carotid artery -

An Overview of Cardiovascular Pressures

-vessel diameters decrease as you get further away from the heart and increase as you get closer -Total cross-sectional areas: your blood moves from one big pipe(aorta, cross sectional area 4.5 cm2) into countless tiny ones (peripheral capillaries, total cross section area of 5000 cm2) and then blood travels back to the heart through two large pipes (the venae cavae) - Pressures: As arteries branch, their total cross-sectional area increases and blood pressure falls rapidly -Velocity of Blood Flow: As the total cross-sectional area of the vessels increases from the aorta toward the capillaries the velocity of blood flow decreases -Systemic pressures are highest in the aorta, peaking at about 120 mm Hg. pressures reach a minimum of 2 mm Hg at the entrance to the right atrium.

Short term elevation of blood pressure

Almost as soon as the pressures start to decrease, several short term responses appear - In the initial neural response carotid and aortic reflexes increase cardiac output and cause peripheral vasoconstriction With blood volume reduced an increase in heart rate, typically up to 180-200 bpm, maintains cardiac output - vasomotor tone is increased, which constricts the arterioles and raises the blood pressure. At the same time, venoconstriction mobilizes the venous reserve and quickly improves venous return -short term hormonal effects also occur. adrenal medulla secrete NE and E. These hormones increase cardiac output and extend peripheral vasoconstriction. In addition, the release of ADH by the posterior lobe of the pituitary gland and the production of angiotensin II enhance vasoconstriction as a part of the long term response -These short term responses restore normal arterial pressures and peripheral circulation after blood losses of up to 20% of total blood volume -If compensatory mechanisms fail, the individual develops signs of shock

Long term restoration of blood volume

Short term responses temporarily compensate for a reduction in blood volume. Long term responses are geared toward restoring normal blood volume. This process can take several days after a serious hemorrhage: -decrease in capillary blood pressure triggers a recall of fluids from the interstitial spaces - Aldosterone and ADH promote fluid retention and reabsorption at the kidneys, preventing further reductions blood volume -Thirst increases, and the digestive tracts absorbs additional water. This intake of fluids increases the blood volume and ultimately replaces the interstitial fluids "borrowed" at the capillaries -Erythropoietin targets the bone marrow. It stimulates the maturation of red blood cells, which increases blood volume and improves oxygen delivery to peripheral tissues

Interplay between Filtration and Reabsorption

The continuous movement of water out of the capillaries, through the peripheral tissues, and then back to the bloodstream by the way of the lymphatic system has four important functions: 1. Ensures that the plasma and interstitial fluid are in constant communication and mutual exchange 2. It accelerates the distribution of nutrients, hormones, and dissolved gases throughout tissues 3. It assists in the transport of insoluble lipids and tissue proteins that cannot enter the bloodstream by crossing the capillary walls 4. It has flushing action that carries bacterial toxins and other chemical stimuli to lymphatic tissues and organs responsible for providing immunity to disease -Capillary blood pressure is the difference between the pressure inside the capillary wall and the hydrostatic pressure outside the capillary wall of the hydrostatic pressure outside the capillary - The net capillary hydrostatic pressure tends to push water and solutes out of capillaries and into the interstitial fluid. Factors that contribute to the net hydrostatic pressure include: 1. The capillary hydrostatic pressure, which ranges from 35 mm Hg at the arterial end of a capillary to 18 mm Hg at the venous end and 2. The interstitial fluid hydrostatic pressure (IHP). Measurements of IHP have yielded very small values that differ from tissue to tissue A positive IHP opposes CHP and the tissue hydrostatic pressure must be overcome before fluid can move out of a capillary. A negative IHP assists CHP, and additional fluid will be pulled out of the capillary Plasma proteins in capillary blood create capillary colloid osmotic pressure. the net capillary colloid osmotic pressure tends to pull water and solutes into a capillary from the interstitial fluid. The net colloid osmotic pressure is the difference between: 1. The blood colloid osmotic pressure, which is about 25 mm Hg and 2. The interstitial fluid colloid osmotic pressure. Its as variable and low as the IHP because the interstitial fluid in most tissues contains negligible quantities of suspended proteins -The net filtration pressure is the difference between the net hydrostatic pressure and the net osmotic pressure At the arterial end of the capillary, the net filtration pressure is positive, so fluid will tend to move out of the capillary into the interstitial fluid If the net filration is negative, fluids tend to move into the capillary (reabsorption) -The transition between filtration and reabsorption occurs where the CHP id 25 mm Hg, because at that point the hydrostatic and osmotic forces are equal-that is NFP is 0 mm Hg -Of the nearly 24 liters of fluid that move out of the plasma and into the interstitial fluid, 20.4 liters are reabsorbed Any condition that affects hydrostatic or osmotic pressures in the blood or tissues will shift the balance between hydrostatic and osmotic forces - if hemorrhaging occurs, both blood volume and blood pressure decrease. this reduction in CHP lowers the NFP and increases the amount of reabsorption. The result is a decrease in the volume of interstitial fluid and an increase in the circulating plasma volume. This process is known as a recall of fluids - If dehydration occurs, the plasma volume decreases due to water loss, and the concentration of plasma proteins increases -If the CHP rises or the BCOP declines fluid moves out of the blood and builds up in peripheral tissues, a condition called edema

capillary importance

The vital functions of the cardiovascular system depend entirely on events at the capillary level: All chemical and gaseous exchange between blood and interstitial fluid takes place along capillary walls. -Cells rely on capillary diffusion to obtain nutrients and oxygen to remove metabolic wastes, such as carbon dioxide and urea

pressure

When talking about cardiovascular pressures, three values are important: 1. Blood pressure: refers to arterial pressure(reported in mm Hg). 2. Capillary hydrostatic pressure: hydrostatic pressure is the force exerted by a fluid pressing against a wall. Capillary hydrostatic pressure is the pressure within capillary walls 3. Venous pressure: pressure within the venous system -The difference in pressure (delta P) across the entire systemic circuit sometimes called the circulatory pressure, averages about 100 mm Hg. For circulation to occur, the circulatory pressure must overcome the total peripheral resistance- the resistance of the entire cardiovascular system