Chapter 21 biology Alison

Four different types of shock

(1) hypovolemic shock due to decreased blood volume (2) cardiogenic shock due to poor heart function, (3) vascular shock due to inappropriate vasodilation (4) obstructive shock due to obstruction of blood flow.

Vascular resistance is the opposition to blood flow due to friction between blood and the walls of blood vessels. Vascular resistance depends on _________________________________________________;

(1) size of the blood vessel lumen, (2) blood viscosity, and (3) total blood vessel length. (R is the opposition to blood flow due to friction between blood and the walls of blood vessels The higher the R, the smaller the blood flow)

In most parts of the body, blood can flow through a capillary network from an arteriole into a venule as follows:

1. Capillaries. In this route, blood flows from an arteriole into capillaries and then into venules (postcapillary venules). As noted earlier, at the junctions between the metarteriole and the capillaries are rings of smooth muscle fibers called precapillary sphincters that control the flow of blood through the capillaries. When the precapillary sphincters are relaxed (open), blood flows into the capillaries; when precapillary sphincters contract (close or partially close), blood flow through the capillaries ceases or decreases. Typically, blood flows intermittently through capillaries due to alternating contraction and relaxation of the smooth muscle of metarterioles and the precapillary sphincters. This intermittent contraction and relaxation, which may occur 5 to 10 times per minute, is called vasomotion. In part, vasomotion is due to chemicals released by the endothelial cells; nitric oxide is one example. At any given time, blood flows through only about 25% of the capillaries. 2. Thoroughfare channel. The proximal end of a metarteriole is surrounded by scattered smooth muscle fibers whose contraction and relaxation help regulate blood flow. The distal end of the vessel has no smooth muscle; it resembles a capillary and is called a thoroughfare channel. Such a channel provides a direct route for blood from an arteriole to a venule, thus bypassing capillaries.

Two general types of stimuli cause autoregulatory changes in blood flow:

1. Physical changes. 2. Vasodilating and vasoconstricting chemicals. .

Several hormones help regulate blood pressure and blood flow by altering cardiac output, changing systemic vascular resistance, or adjusting the total blood volume:

1. Renin-angiotensin-aldosterone (RAA) 2. Epinephrine and norepinephrine. 3. Antidiuretic hormone (ADH). 4. Atrial natriuretic peptide (ANP)

After birth, when pulmonary (lung), renal (kidney), and digestive functions begin, the following vascular changes occur:

1. When the umbilical cord is tied off, blood no longer flows through the umbilical arteries, they fill with connective tissue, 2. The umbilical vein collapses but remains as the ligamentumteres (round ligament), a structure that attaches the umbilicus to the liver. 3. The ductus venosus collapses but remains as the ligamentum venosum, a fibrous cord on the inferior surface of the liver. 4. The placenta is expelled as the afterbirth. 5. The foramen ovale normally closes shortly after birth to become the fossa ovalis, a depression in the interatrial septum. When an infant takes its first breath, the lungs expand and blood flow to the lungs increases. Blood returning from the lungs to the heart increases pressure in the left atrium. This closes the foramen ovale by pushing the valve that guards it against the interatrial septum. Permanent closure occurs in about a year. 6. The ductus arteriosus closes by vasoconstriction almost immediately after birth and becomes the ligamentum arteriosum. Complete anatomical obliteration of the lumen takes 1 to 3 months.

hypovolemic shock

A common cause of _______________ is acute (sudden) hemorrhage. The blood loss may be external, as occurs in trauma, or internal, as in rupture of an aortic aneurysm. Loss of body fluids through excessive sweating, diarrhea, or vomiting also can cause _________________. Other conditions—for instance, diabetes mellitus—may cause excessive loss of fluid in the urine. Sometimes, _____________ is due to inadequate intake of fluid. Whatever the cause, when the volume of body fluids falls, venous return to the heart declines, filling of the heart lessens, stroke volume decreases, and cardiac output decreases. Replacing fluid volume as quickly as possible is essential in managing _____________.

Transcytosis

A small quantity of material crosses capillary walls by _____________. In this process, substances in blood plasma become enclosed within tiny pinocytic vesicles that first enter endothelial cells by endocytosis, then move across the cell and exit on the other side by exocytosis. This method of transport is important mainly for large, lipid-insoluble molecules that cannot cross capillary walls in any other way. For example, the hormone insulin (a small protein) enters the bloodstream by transcytosis, and certain antibodies (also proteins) pass from the maternal circulation into the fetal circulation by transcytosis.

Pulmonary Arteries

After birth, the _____________________ are the only arteries that carry deoxygenated blood. On entering the lungs, the branches divide and subdivide until finally they form capillaries around the air sacs (alveoli) within the lungs. CO2 passes from the blood into the air sacs and is exhaled. Inhaled O2 passes from the air within the lungs into the blood. The pulmonary capillaries unite to form venules and eventually pulmonary veins, which exit the lungs and carry the oxygenated blood to the left

Visceral Branches

Along its course, the thoracic aorta sends off numerous small arteries, ______________ to viscera, and parietal branches to body wall structures.

The Deep Veins

Along their course, the superficial veins form small connections (anastomoses) with ______________ that travel between the skeletal muscles. These connections allow communication between the deep and superficial flow of blood. The amount of blood flow through superficial veins varies from location to location within the body.

azygos system

Although the brachiocephalic veins drain some portions of the thorax, most thoracic structures are drained by a network of veins, called the ________ that runs on either side of the vertebral column. The system consists of three veins—the azygos, hemiazygos, and accessory hemiazygos veins—that show considerable variation in origin, course, tributaries, anastomoses, and termination. Ultimately they empty into the superior vena cava.

The tunica interna of veins, the tunica media of veins, The tunica externa of veins

Although veins are composed of essentially the same three layers as arteries, the relative thicknesses of the layers are different. ________________________ is thinner than that of arteries; __________________________ is much thinner than in arteries, with relatively little smooth muscle and elastic fibers. _____________________ is the thickest layer and consists of collagen and elastic fibers. Veins lack the internal or external elastic laminae found in arteries. They are distensible enough to adapt to variations in the volume and pressure of blood passing through them, but are not designed to withstand high pressure. The lumen of a vein is larger than that of a comparable artery, and veins often appear collapsed (flattened) when sectioned.

changes in O2 level

An important difference between the pulmonary and systemic circulations is their autoregulatory response to _________________. The walls of blood vessels in the systemic circulation dilate in response to low O2. With vasodilation, O2 delivery increases, which restores the normal O2 level. By contrast, the walls of blood vessels in the pulmonary circulation constrict in response to low levels of O2. This response ensures that blood mostly bypasses those alveoli (air sacs) in the lungs that are poorly ventilated by fresh air. Thus, most blood flows to better-ventilated areas of the lung.

end arteries

Anastomoses may also occur between veins and between arterioles and venules. Arteries that do not anastomose are known as ___________. Obstruction of an ____________ interrupts the blood supply to a whole segment of an organ, producing necrosis (death) of that segment. Alternative blood routes may also be provided by nonanastomosing vessels that supply the same region of the body.

The Fetal Circulation

Another major route—____________________—exists only in the fetus and contains special structures that allow the developing fetus to exchange materials with its mother

Veins

Are the blood vessels that convey blood from the tissues back to the heart.

coronary arteries

Arise from the ascending aorta just superior to the aortic valve.

vena cava

Arteries usually follow definite pathways; veins are more difficult to follow because they connect in irregular networks in which many tributaries merge to form a large vein. Although only one systemic artery, the aorta, takes oxygenated blood away from the heart (left ventricle), three systemic veins, the coronary sinus, superior _______________ (SVC) and inferior vena cava (IVC), return deoxygenated blood to the heart (right atrium)

circulatory routes

Arteries, arterioles, capillaries, venules, and veins are organized into _____________ that deliver blood throughout the body.Now that you understand the structures of each of these vessel types, we can look at the basic routes the blood takes as it is transported throughout the body.

Resistance Vessel

Arterioles play a key role in regulating blood flow from arteries into capillaries by regulating resistance, the opposition to blood flow due to friction between blood and the walls of blood vessels. Because of this they are known as ______________. In a blood vessel, resistance is due mainly to friction between blood and the inner walls of blood vessels. When the blood vessel diameter is smaller, the friction is greater, so there is more resistance.

35 mmHg

As blood leaves the aorta and flows through the systemic circulation, its pressure falls progressively as the distance from the left ventricle increases. Blood pressure decreases to about ___________ as blood passes from systemic arteries through systemic arterioles and into capillaries, where the pressure fluctuations disappear. At the venous end of capillaries, blood pressure has dropped to about 16 mmHg. Blood pressure continues to drop as blood enters systemic venules and then veins because these vessels are farthest from the left ventricle. Finally, blood pressure reaches 0 mmHg as blood flows into the right ventricle.

Homeostasis response to shock 3: Activation of the sympathetic division of the ANS.

As blood pressure decreases, aortic and carotid baroreceptors initiate powerful sympathetic responses throughout the body. One result is marked vasoconstriction of arterioles and veins of the skin, kidneys, and other abdominal viscera (Vasoconstriction does not occur in the brain or heart.) Constriction of arterioles increases systemic vascular resistance, and constriction of veins increases venous return. Both effects help maintain an adequate blood pressure. Sympathetic stimulation also increases heart rate and contractility and increases secretion of epinephrine and norepinephrine by the adrenal medulla. These hormones intensify vasoconstriction and increase heart rate and contractility, all of which help raise blood pressure.

The thoracic aorta

As the aorta continues to descend, it lies close to the vertebral bodies and is called __________. ______________ s about 20 cm (8 in.) long and is a continuation of the arch of the aorta. It begins at the level of the intervertebral disc between the fourth and fifth thoracic vertebrae, where it lies to the left of the vertebral column. As it descends, it moves closer to the midline and extends through an opening in the diaphragm (aortic hiatus), which is located anterior to the vertebral column at the level of the intervertebral disc between the twelfth thoracic and first lumbar vertebrae.

Capillaries

As the arterioles enter a tissue, they branch into numerous tiny vessels are called?

Muscular Venules

As the postcapillary venules move away from capillaries, they acquire one or two layers of circularly arranged smooth muscle cells. These ________________ (50 m to 200 m) have thicker walls across which exchanges with the interstitial fluid can no longer occur. The thin walls of the postcapillary and __________________ are the most distensible elements of the vascular system; this allows them to expand and serve as excellent reservoirs for accumulating large volumes of blood. Blood volume increases of 360% have been measured in the postcapillary and _____________________.

Pressure reservoir

As they stretch, the elastic fibers momentarily store mechanical energy, functioning as a _______________.

Blood Pressure (BP)

As you have just learned, blood flows from regions of higher pressure to regions of lower pressure; the greater the pressure difference, the greater the blood flow. Contraction of the ventricles generates _________________, the hydrostatic pressure exerted by blood on the walls of a blood vessel. _____________ is determined by cardiac output, blood volume, and vascular resistance (described shortly). ______________ is highest in the aorta and large systemic arteries; in a resting, young adult,__________ rises to about 110 mmHg during systole (ventricular contraction) and drops to about 70 mmHg during diastole (ventricular relaxation).

Precapillary Sphincter

At the metarteriole-capillary junction, the distalmost muscle cell forms the _______________, which monitors the blood flow into the capillary; the other muscle cells in the arteriole regulate the resistance (opposition) to blood flow.

the hepatic portal vein

At the same time the liver is receiving nutrient-rich but deoxygenated blood via _________________________, it is also receiving oxygenated blood via the hepatic artery, a branch of the celiac trunk. The oxygenated blood mixes with the deoxygenated blood in sinusoids. Eventually, blood leaves the sinusoids of the liver through the hepatic veins, which drain into the inferior vena cava.

interstitial fluid hydrostatic pressure (IFHP)

BHP "pushes" fluid out of capillaries into interstitial fluid. The opposing pressure of the interstitial fluid, called _______________, "pushes" fluid from interstitial spaces back into capillaries.

carotid sinus reflex

Baroreceptors in the wall of the carotid sinuses initiate the _______________, which helps regulate blood pressure in the brain.

The walls of muscular arteries

Because of the reduced amount of elastic tissue in _______________________, these vessels do not have the ability to recoil and help propel the blood like the elastic arteries. Instead, the thick, muscular tunica media is primarily responsible for the functions of the muscular arteries. The ability of the muscle to contract and maintain a state of partial contraction is referred to as vascular tone. Vascular tone stiffens the vessel wall and is important in maintaining vessel pressure and efficient blood flow.

pluripotent stem cells

Blood cells develop from ________________ derived fromhemangioblasts. This development occurs in the walls of blood vessels in the yolk sac, chorion, and allantois at about 3 weeks after fertilization. Blood formation in the embryo itself begins at about the fifth week in the liver and the twelfth week in the spleen, red bone marrow, and thymus.

Velocity of Blood Flow

Blood flow is the volume of blood that flows through a tissue in a given period of time Blood flow is inversely related to the cross-sectional area of blood vessels

umbilical vein and ductus venosus

Blood passes from the fetus to the placenta via two umbilical arteries in the umbilical cord. These branches of the internal iliac (hypogastric) arteries are within the umbilical cord. At the placenta, fetal blood picks up O2 and nutrients and eliminates CO2 and wastes. The oxygenated blood returns from the placenta via a single _____________ in the umbilical cord.This vein ascends to the liver of the fetus, where it divides into two branches. Some blood flows through the branch that joins the hepatic portal vein and enters the liver, but most of the blood flows into the second branch, the ______________, which drains into the inferior vena cava.

5 liters

Blood pressure also depends on the total volume of blood in the cardiovascular system. The normal volume of blood in an adult is about _________ (5.3 qt). Any decrease in this volume, as from hemorrhage, decreases the amount of blood that is circulated through the arteries each minute. A modest decrease can be compensated for by homeostatic mechanisms that help maintain blood pressure , but if the decrease in blood volume is greater than 10% of the total, blood pressure drops. Conversely, anything that increases blood volume, such as water retention in the body, tends to increase blood pressure.

hemangioblast

Blood vessels and blood cells develop from the same precursor cell, called a _________. Once mesenchyme develops into hemangioblasts, they can give rise to cells that produce blood vessels (angioblasts) or cells that produce blood cells (pluripotent stem cells).

angioblasts

Blood vessels develop from ____________, which are derived from hemangioblasts. Angioblasts aggregate to form isolated masses and cords throughout the embryonic discs called blood islands.

Tunica externa

Consists of elastic and collagen fibers. The _______________contains numerous nerves and, especially in larger vessels, tiny blood vessels that supply the tissue of the vessel wall. (Outermost layer, adjacent to surrounding tissue)

The body contains three different types of capillaries:

Continuous capillaries, fenestrated capillaries, and sinusoids.

The skeletal muscle pump operates as follows 2:

Contraction of leg muscles, such as when you stand on tiptoes or take a step, compresses the vein. The compression pushes blood through the proximal valve, an action called milking. At the same time, the distal valve in the uncompressed segment of the vein closes as some blood is pushed against it. People who are immobilized through injury or disease lack these contractions of leg muscles. As a result, their venous return is slower and they may develop circulation problems.

Vasoconstriction

Contraction of the smooth muscle of an arteriole causes ______________, which increases resistance even more and decreases blood flow into capillaries supplied by that arteriole. By contrast, relaxation of the smooth muscle of an arteriole causes vasodilation, which decreases resistance and increases blood flow into capillaries. A change in arteriole diameter can also affect blood pressure: ___________ of arterioles increases blood pressure, and vasodilation of arterioles decreases blood pressure.

Homeostasis response to shock: 1. Activation of the renin-angiotensin-aldosterone system.

Decreased blood flow to the kidneys causes the kidneys to secrete renin and initiates the renin-angiotensin-aldosterone system. Recall that angiotensin II causes vasoconstriction and stimulates the adrenal cortex to secrete aldosterone, a hormone that increases reabsorption of Na+ and water by the kidneys. The increases in systemic vascular resistance and blood volume help raise blood pressure.

Filtration

Diffusion is more important for solute exchange between blood and interstitial fluid, but bulk flow is more important for regulation of the relative volumes of blood and interstitial fluid. Pressure-driven movement of fluid and solutes from blood capillaries into interstitial fluid is called ___________. Pressure-driven movement from interstitial fluid into blood capillaries is called reabsorption. (________ is pressure-driven movement of fluid and solutes from blood capillaries into interstitial fluid Blood hydrostatic pressure (BHP) and interstitial fluid osmotic pressure (IFOP) promote filtration)

Reabsorption

Diffusion is more important for solute exchange between blood and interstitial fluid, but bulk flow is more important for regulation of the relative volumes of blood and interstitial fluid. Pressure-driven movement of fluid and solutes from blood capillaries into interstitial fluid is called filtration. Pressure-driven movement from interstitial fluid into blood capillaries is called ______________. (____________ is pressure-driven movement of fluid and solutes from interstitial fluid into blood capillaries Interstitial fluid hydrostatic pressure (IFHP) and blood colloid osmotic pressure (BCOP) promote ______________)

anaphylactic shock

Even with normal blood volume and cardiac output, shock may occur if blood pressure drops due to a decrease in systemic vascular resistance. A variety of conditions can cause inappropriate dilation of arterioles or venules. In ______________, a severe allergic reaction—for example, to a bee sting—releases histamine and other mediators that cause vasodilation. In neurogenic shock, vasodilation may occur following trauma to the head that causes malfunction of the cardiovascular center in the medulla. Shock stemming from certain bacterial toxins that produce vasodilation is termed septic shock. In the United States, septic shock causes more than 100,000 deaths per year and is the most common cause of death in hospital critical care units.

Tunica interna

Forms the inner lining of a blood vessel and is in direct contact with the blood as it flows through the lumen. (Innermost layer, adjacent to lumen)

Aging and the cardiovascular system

General changes in the cardiovascular system associated with aging include decreased compliance (distensibility) of the aorta, reduction in cardiac muscle fiber size, progressive loss of cardiac muscular strength, reduced cardiac output, a decline in maximum heart rate, and an increase in systolic blood pressure. Total blood cholesterol tends to increase with age, as does low-density lipoprotein (LDL); high-density lipoprotein (HDL) tends to decrease. There is an increase in the incidence of coronary artery disease (CAD), the major cause of heart disease and death in older Americans. Congestive heart failure (CHF), a set of symptoms associated with impaired pumping of the heart, is also prevalent in older individuals. Changes in blood vessels that serve brain tissue—for example, atherosclerosis—reduce nourishment to the brain and result in malfunction or death of brain cells. By age 80, cerebral blood flow is 20% less and renal blood flow is 50% less than in the same person at age 30 because of the effects of aging on blood vessels.

Zero.

However, IFHP is close to ________ (IFHP is difficult to measure, and its reported values vary from small positive values to small negative values.) For our discussion we assume that IFHP equals 0 mmHg all along the capillaries.

10-20%

If blood volume drops more than _______, or if the heart cannot bring blood pressure up sufficiently, compensatory mechanisms may fail to maintain adequate blood flow to tissues. At this point, shock becomes life-threatening as damaged cells start to die.

Blood Pressure

In clinical use, the term ______________ usually refers to the pressure in arteries generated by the left ventricle during systole and the pressure remaining in the arteries when the ventricle is in diastole. Blood pressure is usually measured in the brachial artery in the left arm.

Blood-Brain Barrier

In contrast to sinusoids, the capillaries of the brain allow only a few substances to move across their walls. Most areas of the brain contain continuous capillaries; however, these capillaries are very "tight." The endothelial cells of most brain capillaries are sealed together by tight junctions. The resulting blockade to movement of materials into and out of brain capillaries is known as the ______________. In brain areas that lack the ____________, for example, the hypothalamus, pineal gland, and pituitary gland, materials undergo capillary exchange more freely.

autoregulation

In each capillary bed, local changes can regulate vasomotion. When vasodilators produce local dilation of arterioles and relaxation of precapillary sphincters, blood flow into capillary networks is increased, which increases O2 level. Vasoconstrictors have the opposite effect. The ability of a tissue to automatically adjust its blood flow to match its metabolic demands is called autoregulation. In tissues such as the heart and skeletal muscle, where the demand for O2 and nutrients and for the removal of wastes can increase as much as tenfold during physical activity, autoregulation is an important contributor to increased blood flow through the tissue. Autoregulation also controls regional blood flow in the brain; blood distribution to various parts of the brain changes dramatically for different mental and physical activities. During a conversation, for example, blood flow increases to your motor speech areas when you are talking and increases to the auditory areas when you are listening, mental and physical activities. During a conversation, for example, blood flow increases to your motor speech areas when you are talking and increases to the auditory areas when you are listening. (Autoregulation is the ability of a tissue to automatically adjust its own blood flow to match its metabolic demand for delivery of oxygen and nutrients and removal of wastes Physical and chemical stimuli can lead to autoregulation)

Metabolic

In most tissues, blood flows through only a small part of the capillary network when ___________ needs are low. However, when a tissue is active, such as contracting muscle, the entire capillary network fills with blood.

Homeostasis response to shock 2. Secretion of antidiuretic hormone.

In response to decreased blood pressure, the posterior pituitary releases more antidiuretic hormone (ADH). ADH enhances water reabsorption by the kidneys, which conserves remaining blood volume. It also causes vasoconstriction, which increases systemic vascular resistance.

Homeostasis response to shock 4. Release of local vasodilators.

In response to hypoxia, cells liberate vasodilators—including K+, H+, lactic acid, adenosine, and nitric oxide—that dilate arterioles and relax precapillary sphincters. Such vasodilation increases local blood flow and may restore O2 level to normal in part of the body. However, vasodilation also has the potentially harmful effect of decreasing systemic vascular resistance and thus lowering the blood pressure.

Epinephrine and norepinephrine

In response to sympathetic stimulation, the adrenal medulla releases epinephrine and norepinephrine. These hormones increase cardiac output by increasing the rate and force of heart contractions. They alsocause vasoconstriction of arterioles and veins in the skin and abdominal organs and vasodilation of arterioles in cardiac and skeletal muscle, which helps increase blood flow to muscle during exercise.

Sinusoids in diffusion

In sinusoids, however, the intercellular clefts are so large that they allow even proteins and blood cells to pass through their walls. For example, hepatocytes (liver cells) synthesize and release many plasma proteins, such as fibrinogen (the main clotting protein) and albumin, which then diffuse into the bloodstream through sinusoids. In red bone marrow, blood cells are formed (hemopoiesis) and then enter the bloodstream through sinusoids.

Superficial veins vs deep veins

In the upper limb, the superficial veins are much larger than the deep veins and serve as the major pathways from the capillaries of the upper limb back to the heart. In the lower limb, the opposite is true; the deep veins serve as the principal return pathways. In fact, one-way valves in small anastomosing vessels allow blood to pass from the superficial veins to the deep veins, but prevent the blood from passing in the reverse direction. This design has important implications in the development of varicose veins.

Lumen

Interior opening, of the vessel.

The skeletal muscle pump operates as follows 3:

Just after muscle relaxation, pressure falls in the previously compressed section of vein, which causes the proximal valve to close. The distal valve now opens because blood pressure in the foot is higher than in the leg, and the vein fills with blood from the foot. The proximal valve then reopens.

Arterioles defined

Literally meaning small arteries, _____________ are abundant microscopic vessels that regulate the flow of blood into the capillary networks of the body's tissues. The approximately The wall thickness of ________ is onehalf of the total vessel diameter. __________ have a thin tunica interna with a thin, fenestrated (with small pores) internal elastic lamina that disappears at the terminal end. The tunica media consists of one to two layers of smooth muscle cells having a circular orientation in the vessel wall.

Vascular (venous) sinus

Many veins, especially those in the limbs, also contain valves, thin folds of tunica interna that form flaplike cusps. The valve cusps project into the lumen, pointing toward the heart The low blood pressure in veins allows blood returning to the heart to slow and even back up; the valves aid in venous return by preventing the backflow of blood. A _________________ is a vein convey deoxygenated blood from the brain to the heart. Another example of a vascular sinus is the coronary sinus of the heart

muscular arteries

Medium-sized arteries are called ______________ because their tunica media contains more smooth muscle and fewer elastic fibers than elastic arteries. The large amount of smooth muscle, approximately three-quarters of the total mass, makes the walls of muscular arteries relatively thick. Thus, muscular arteries are capable of greater vasoconstriction and vasodilation to adjust the rate of blood flow.________________ have a well-defined internal elastic lamina but a thin external elastic lamina. These two elastic laminae form the inner and outer boundaries of the muscular tunica media. In large arteries, the thick tunica media can have as many as 40 layers of circumferentially arranged smooth muscle cells; in smaller arteries there are as few as three layers. (Medium diameter More smooth muscle, fewer elastic fibers Distribute blood to various parts of the body)

Arterioles

Medium-sized arteries then divide into small arteries, which in turn divide into still smaller arteries are called?

continuous capillaries

Most capillaries are ________________, in which the plasma membranes of endothelial cells form a continuous tube that is interrupted only by intercellular clefts, gaps between neighboring endothelial cells. Continuous capillaries are found in the central nervous system, lungs, muscle tissue, and the skin.

intercellular clefts

Most capillaries are continuous capillaries, in which the plasma membranes of endothelial cells form a continuous tube that is interrupted only by _______________, gaps between neighboring endothelial cells. Continuous capillaries are found in the central nervous system, lungs, muscle tissue, and the skin.

The foramen ovale

Most of the fetal blood does not pass from the right ventricle to the lungs, as it does in postnatal circulation, because an opening called ______________ exists in the septum between the right and left atria. Most of the blood that enters the right atrium passes through the foramen ovale into the left atrium and joins the systemic circulation.

Anastomosis

Most tissues of the body receive blood from more than one artery. The union of the branches of two or more arteries supplying the same body region is called an _______________.

Distributing Arteries

Muscular arteries span a range of sizes from the pencil-sized femoral and axillary arteries to string-sized arteries that enter organs, measuring as little as 0.5 mm (1∕4 inch) in diameter. Compared to elastic arteries, the vessel wall of muscular arteries comprises a larger percentage (25%) of the total vessel diameter. Because the muscular arteries continue to branch and ultimately distribute blood to each of the various organs, they are called _______________________. Examples include the brachial artery in the arm and radial artery in the forearm

interstitial fluid osmotic pressure (IFOP)

Opposing BCOP is __________, which "pulls" fluid out of capillaries into interstitial fluid. Normally, IFOP is very small—0.1-5 mmHg—because only tiny amounts of protein are present in interstitial fluid. The small amount of protein that leaks from blood plasma into interstitial fluid does not accumulate there because it passes into lymph in lymphatic capillaries and is eventually returned to the blood. For discussion, we can use a value of 1 mmHg for IFOP.

Fenestrated Capillaries

Other capillaries of the body are ____________. The plasma membranes of the endothelial cells in these capillaries have many fenestrations, small pores (holes) ranging from 70 to 100 nm in diameter. ________________ are found in the kidneys, villi of the small intestine, choroid plexuses of the ventricles in the brain, ciliary processes of the eyes, and most endocrine glands.

Fenestrations

Other capillaries of the body are fenestrated capillaries. The plasma membranes of the endothelial cells in these capillaries have many ________________, small pores (holes) ranging from 70 to 100 nm in diameter. Fenestrated capillaries are found in the kidneys, villi of the small intestine, choroid plexuses of the ventricles in the brain, ciliary processes of the eyes, and most endocrine glands.

3. Total blood vessel length.

Resistance to blood flow through a vessel is directly proportional to the length of the blood vessel. The longer a blood vessel, the greater the resistance. Obese people often have hypertension (elevated blood pressure) because the additional blood vessels in their adipose tissue increase their total blood vessel length. An estimated 650 km (about 400 miles) of additional blood vessels develop for each extra kilogram (2.2 lb) of fat.

interconnected negative feedback

Several _____________________________________ systems control blood pressure by adjusting heart rate, stroke volume, systemic vascular resistance, and blood volume. Some systems allow rapid adjustments to cope with sudden changes, such as the drop in blood pressure in the brain that occurs when you get out of bed; others act more slowly to provide long-term regulation of blood pressure. The body may also require adjustments to the distribution of blood flow. During exercise, for example, a greater percentage of the total blood flow is diverted to skeletal muscles.

2. Vasodilating and vasoconstricting chemicals.

Several types of cells—including white blood cells, platelets, smooth muscle fibers, macrophages, and endothelial cells—release a wide variety of chemicals that alter blood-vessel diameter. Vasodilating chemicals released by metabolically active tissue cells include K+, H+, lactic acid (lactate), and adenosine (from ATP). Another important vasodilator released by endothelial cells is nitric oxide (NO). Tissue trauma or inflammation causes release of vasodilating kinins and histamine. Vasoconstrictors include thromboxane A2, superoxide radicals, serotonin (from platelets), and endothelins (from endothelials cells).

The coronary (cardiac) circulation

Some of the subdivisions of the systemic circulation include ________________, which supplies the myocardium of the heart.

Angioblast and blood islands

Spaces soon appear in the islands and become the lumens of the blood vessels. Some of the angioblasts immediately around the spaces give rise to the endothelial lining of the blood vessels. Angioblasts around the endothelium form the tunics (interna, media, and externa) of the larger blood vessels. Growth and fusion of blood islands form an extensive network of blood vessels throughout the embryo. By continuous branching, blood vessels outside the embryo connect with those inside the embryo, linking the embryo with the placenta.

Diffusing

Substances in blood or interstitial fluid can cross the walls of a capillary by ___________ through the intercellular clefts or fenestrations or by diffusing through the endothelial cells. Water-soluble substances such as glucose and amino acids pass across capillary walls through intercellular clefts or fenestrations.Lipid-soluble materials, such as O2, CO2, and steroid hormones, may pass across capillary walls directly through the lipid bilayer of endothelial cell plasma membranes. Most plasma proteins and red blood cells cannot pass through capillary walls of continuous and fenestrated capillaries because they are too large to fit through the intercellular clefts and fenestrations.

Portal System

Such a circulation of blood is called a ___________ The name of the _______________ gives the name of the second capillary location. For example, there are _______________ associated with the liver (hepatic portal circulation) and the pituitary gland (hypophyseal portal system).

Vasoconstriction

Such a decrease in the diameter of the lumen of a blood vessel is called?

The marginal branch

Supplies the right ventricle.

aorta

The _____ is the largest artery of the body, with a diameter of 2-3 cm (about 1 in.). Its four principal divisions are the ascending _______, arch of the ________, thoracic _______, and abdominal ___________.

Splenic Vein

The ___________ drains blood from the stomach, pancreas, and portions of the large intestine through the short gastric, left gastro-omental, pancreatic, and inferior mesenteric veins. The inferior mesenteric vein, which passes into the splenic vein, drains portions of the large intestine through the superior rectal, sigmoidal, and left colic veins. The right and left gastric veins, which open directly into the hepatic portal vein, drain the stomach. The cystic vein, which also opens into the hepatic portal vein, drains the gallbladder.

hepatic portal

The ______________ circulation carries venous blood from the gastrointestinal organs and spleen to the liver. A vein that carries blood from one capillary network to another is called a portal vein.

carotid sinuses

The _______________ are small widenings of the right and left internal carotid arteries just above the point where they branch from the common carotid arteries. Blood pressure stretches the wall of the carotid sinus, which stimulates the baroreceptors. Nerve impulses propagate from the carotid sinus baroreceptors over sensory axons in the glossopharyngeal (IX) nerves to the cardiovascular center in the medulla oblongata.

cardiovascular (CV) center

The __________________ in the medulla oblongata helps regulate heart rate and stroke volume. The ________ also controls neural, hormonal, and local negative feedback systems that regulate blood pressure and blood flow to specific tissues. Groups of neurons scattered within the________ regulate heart rate, contractility (force of contraction) of the ventricles, and blood vessel diameter. Some neurons stimulate the heart (_____); others inhibit the heart (________). Still others control blood vessel diameter by causing constriction (vasoconstrictor center) or dilation (vasodilator center); these neurons are referred to collectively as the vasomotor center. Because the ________ center neurons communicate with one another, function together, and are not clearly separated anatomically, we discuss them here as a group. The ___________________ receives input both from higher brain regions and from sensory receptors. Nerve impulses descend from the cerebral cortex, limbic system, and hypothalamus to affect the cardiovascular center. For example, even before you start to run a race, your heart rate may increase due to nerve impulses conveyed from the limbic system to the __________. If your body temperature rises during a race, the hypothalamus sends nerve impulses to the __________. The resulting vasodilation of skin blood vessels allows heat to dissipate more rapidly from the surface of the skin.

1. Size of the lumen.

The __________________ of a blood vessel, the greater its resistance to blood flow. Resistance is inversely proportional to the fourth power of the diameter (d) of the blood vessel's lumen (R x 1/d4). The smaller the diameter of the blood vessel, the greater the resistance it offers to blood flow. For example, if the diameter of a blood vessel decreases by one-half, its resistance to blood flow increases 16 times. Vasoconstriction narrows the lumen, and vasodilation widens it. Normally, moment-to-moment fluctuations in blood flow through a given tissue are due to vasoconstriction and vasodilation of the tissue's arterioles. As arterioles dilate, resistance decreases, and blood pressure falls. As arterioles constrict, resistance increases, and blood pressure rises.

hepatic portal vein

The ___________________ receives blood from capillaries of gastrointestinal organs and the spleen and delivers it to the sinusoids of the liver.

pulmonary trunk, the right pulmonary artery, the left pulmonary artery

The ____________________ emerges from the right ventricle and passes superiorly, posteriorly, and to the left. It then divides into two branches: ___________________ to the right lung and the _______________ to the left lung.

Respiratory Pump

The ____________________ is also based on alternating compression and decompression of veins. During inhalation, the diaphragm moves downward, which causes a decrease in pressure in the thoracic cavity and an increase in pressure in the abdominal cavity. As a result, abdominal veins are compressed, and a greater volume of blood moves from the compressed abdominal veins into the decompressed thoracic veins and then into the right atrium. When the pressures reverse during exhalation, the valves in the veins prevent backflow of blood from the thoracic veins to the abdominal veins.

hepatic portal vein recieves

The _____________________ blood from capillaries of gastrointestinal organs and the spleen and delivers it to the sinusoids of the live.After a meal, hepatic portal blood is rich in nutrients absorbed from the gastrointestinal tract. The liver stores some of them and modifies others before they pass into the general circulation. For example, the liver converts glucose into glycogen for storage, reducing blood glucose level shortly after a meal. The liver also detoxifies harmful substances, such as alcohol, that have been absorbed from the gastrointestinal tract and destroys bacteria by phagocytosis.

Hepatic Portal Circulation

The _____________________ carries venous blood from the gastrointestinal organs and spleen to the liver. A vein that carries blood from one capillary network to another is called a portal vein.

pulmonary circulation

The ________________________ carries deoxygenated blood from the right ventricle to the air sacs (alveoli) within the lungs and returns oxygenated blood from the air sacs to the left atrium

Common Iliac arteries

The abdominal aorta descends to the level of the fourth lumbar vertebra where it divides into two _____________________, which carry blood to the pelvis and lower limbs. Each division of the aorta gives off arteries that branch into distributing arteries that lead to various organs. Within the organs, the arteries divide into arterioles and then into capillaries that service the systemic tissues (all tissues except the alveoli of the lungs).

Collateral Circulation

The alternative route of blood flow to a body part through an anastomosis is known as _________________.

Superficial Veins

The anastomotic veins cross the accompanying artery to form ladderlike rungs between the paired veins. The greatest number of paired veins occurs within the limbs. The subcutaneous layer deep to the skin is another source of veins. These veins, called _____________________, course through the subcutaneous layer unaccompanied by parallel arteries.

net filtration pressure

The balance of these pressures, called _______________, determines whether the volumes of blood and interstitial fluid remain steady or change. Overall, the volume of fluid and solutes reabsorbed normally is almost as large as the volume filtered. This near equilibrium is known as Starling's law of the capillaries. Let's see how these hydrostatic and osmotic pressures balance.

Starling's law of the capillaries

The balance of these pressures, called net filtration pressure, determines whether the volumes of blood and interstitial fluid remain steady or change. Overall, the volume of fluid and solutes reabsorbed normally is almost as large as the volume filtered. This near equilibrium is known as _________________ . Let's see how these hydrostatic and osmotic pressures balance. (Under normal conditions, the volume of fluid and solutes reabsorbed is almost as large as the volume filtered.)

The two most important baroreceptor reflexes are?

The carotid sinus reflex and the aortic reflex.

Glossopharyngeal (IX) nerves

The carotid sinuses are small widenings of the right and left internal carotid arteries just above the point where they branch from the common carotid arteries. Blood pressure stretches the wall of the carotid sinus, which stimulates the baroreceptors. Nerve impulses propagate from the carotid sinus baroreceptors over sensory axons in the ______________ to the cardiovascular center in the medulla oblongata.

fetal circulation

The circulatory system of a fetus, called the __________________, exists only in the fetus and contains special structures that allow the developing fetus to exchange materials with its mother. It differs from the postnatal (after birth) circulation because the lungs, kidneys, and gastrointestinal organs do not begin to function until birth. The fetus obtains O2 and nutrients from the maternal blood and eliminates CO2 and other wastes into it.

mesoderm

The development of blood cells and the formation of blood vessels begins outside the embryo as early as 15 to 16 days in the ________________ of the wall of the yolk sac, chorion, and connecting stalk. About 2 days later, blood vessels form within the embryo. The early formation of the cardiovascular system is linked to the small amount of yolk in the ovum and yolk sac. As the embryo develops rapidly during the third week, there is a greater need to develop a cardiovascular system to supply sufficient nutrients to the embryo and remove wastes from it

Sphygmomanometer (nstrument used to measure pressure)

The device used to measure blood pressure is a __________________. It consists of a rubber cuff connected to a rubber bulb that is used to inflate the cuff and a meter that registers the pressure in the cuff. With the arm resting on a table so that it is about the same level as the heart, the cuff of the sphygmomanometer is wrapped around a bared arm. The cuff is inflated by squeezing the bulb until the brachial artery is compressed and blood flow stops,

Blood colloid osmotic pressure (BCOP)

The difference in osmotic pressure across a capillary wall is due almost entirely to the presence in blood of plasma proteins, which are too large to pass through either fenestrations or gaps between endothelial cells. _______________ is a force caused by the colloidal suspension of these large proteins in plasma that averages 26 mmHg in most capillaries. The effect of ___________ is to "pull" fluid from interstitial spaces into capillaries.

Thoroughfare Channel

The distal end of the vessel has no smooth muscle; it resembles a capillary and is called a _________________. Such a channel provides a direct route for blood from an arteriole to a venule, thus bypassing capillaries.

placenta and umbilicus

The exchange of materials between fetal and maternal circulations occurs through the ____________, which forms inside the mother's uterus and attaches to the ___________ (navel) of the fetus by the umbilical cord. The placenta communicates with the mother's cardiovascular system through many small blood vessels that emerge from the uterine wall. The umbilical cord contains blood vessels that branch into capillaries in the placenta. Wastes from the fetal blood diffuse out of the capillaries, into spaces containing maternal blood (intervillous spaces) in the placenta, and finally into the mother's uterine veins. Nutrients travel the opposite route—from the maternal blood vessels to the intervillous spaces to the fetal capillaries. Normally, there is no direct mixing of maternal and fetal blood because all exchanges occur by diffusion through capillary walls.

The primary function of capillaries is?

The exchange of substances between the blood and interstitial fluid. Because of this, these thin-walled vessels are referred to as exchange vessels. (Capillaries are microscopic vessels that usually connect arterioles and venules. Capillary walls are composed of a single layer of cells and a basement membrane. Because their walls are so thin, capillaries permit the exchange of nutrients and wastes between blood and tissue cells)

brachiocephalic trunk

The first and largest branch from the arch of the aorta is the ____________. It extends superiorly, bending slightly to the right, and divides at the right sternoclavicular joint to form the right subclavian artery and right common carotid artery.

postcapillary venule

The flow of blood from a metarteriole through capillaries and into a ____________ (_________ that receives blood from a capillary) is called the microcirculation of the body

Microcirculation

The flow of blood from a metarteriole through capillaries and into a postcapillary venule is called the __________________ of the body.

Most blood draining from the head passes into three pairs of veins:

The internal jugular, external jugular, and vertebral veins.

Blood Reservoirs

The largest portion of your blood volume at rest—about 64%—is in systemic veins and venules. Systemic arteries and arterioles hold about 13% of the blood volume, systemic capillaries hold about 7%, pulmonary blood vessels hold about 9%, and the heart holds about 7%. Because systemic veins and venules contain a large percentage of the blood volume, they function as _______________ from which blood can be diverted quickly if the need arises.

Homeostasis response to shock

The major mechanisms of compensation in shock are negative feedback systems that work to return cardiac output and arterial blood pressure to norma. When shock is mild, compensation by homeostatic mechanisms prevents serious damage. In an otherwise healthy person, compensatory mechanisms can maintain adequate blood flow and blood pressure despite an acute blood loss of as much as 10% of total volume.

Capillary Exchange

The mission of the entire cardiovascular system is to keep blood flowing through capillaries to allow ____________________, the movement of substances between blood and interstitial fluid. The 7% of the blood in systemic capillaries at any given time is continually exchanging materials with interstitial fluid. Substances enter and leave capillaries by three basic mechanisms: diffusion, transcytosis, and bulk flow.

Simple Diffusion

The most important method of capillary exchange is _______________. Many substances, such as oxygen (O2), carbon dioxide (CO2), glucose, amino acids, and hormones, enter and leave capillaries by simple diffusion. Because O2 and nutrients normally are present in higher concentrations in blood, they diffuse down their concentration gradients into interstitial fluid and then into body cells. CO2 and other wastes released by body cells are present in higher concentrations in interstitial fluid, so they diffuse into blood.

Ascending Aorta

The portion of the aorta that emerges from the left ventricle posterior to the pulmonary trunk is_________ . The beginning of the aorta contains the aortic valve. __________ gives off two coronary arteries that supply the myocardium of the heart. (is about 5 cm (2 in.) in length and begins at the aortic valve. It is directed superiorly, slightly anteriorly, and to the right. It ends at the level of the sternal angle, where it becomes the arch of the aorta. The beginning of the ______________ is posterior to the pulmonary trunk and right auricle; the right pulmonary artery is posterior to it. At its origin, the ascending aorta contains three dilations called aortic sinuses. Two of these, the right and left sinuses, give rise to the right and left coronary arteries, respectively.)

70 to 80 beats

The pulse rate normally is the same as the heart rate, about ___________ per minute at rest

The average blood pressure in veins

The pumping action of the heart is a major factor in moving venous blood back to the heart. The contraction of skeletal muscles in the lower limbs also helps boost venous return to the heart. ______________________________ is considerably lower than in arteries. The difference in pressure can be noticed when blood flows from a cut vessel. Blood leaves a cut vein in an even, slow flow but spurts rapidly from a cut artery. Most of the structural differences between arteries and veins reflect this pressure difference. For example, the walls of veins are not as strong as those of arteries.

Vasodilation

The resulting increase in lumen diameter is called?

Systemic Circulation

The routes are parallel; that is, in most cases a portion of the cardiac output flows separately to each tissue of the body. Thus, each organ receives its own supply of freshly oxygenated blood. The two basic postnatal (after birth) routes for blood flow are the _________________ and the pulmonary circulation. The systemic circulation includes all arteries and arterioles that carry oxygenated blood from the left ventricle to systemic capillaries, plus the veins and venules that return deoxygenated blood to the right atrium after flowing through body organs. Blood leaving the aorta and flowing through the systemic arteries is a bright red color. As it moves through capillaries, it loses some of its oxygen and picks up carbon dioxide, so that blood in systemic veins is dark red.

Left Common Carotid Artery

The second branch from the arch of the aorta is ______________________, which divides into the same branches with the same names as the right common carotid artery.

Capillary walls

The structure of capillaries is well suited to their function as exchange vessels because they lack both a tunica media and a tunica externa. Because ___________________ are composed of only a single layer of endothelial cells and a basement membrane, a substance in the blood must pass through just one cell layer to reach the interstitial fluid and tissue cells. Exchange of materials occurs only through the walls of capillaries and the beginning of venules; the walls of arteries, arterioles, most venules, and veins present too thick a barrier. Capillaries form extensive branching networks that increase the surface area available for rapid exchange of materials.

mesenteric vein

The superior _________________ drains blood from the small intestine and portions of the large intestine, stomach, and pancreas through the jejunal, ileal, ileocolic, right colic, middle colic, pancreaticoduodenal, and right gastro-omental veins.

Metarteriole

The terminal end of the arteriole, the region called the _________________, tapers toward the capillary junction. At the _______________-capillary junction, the distalmost muscle cell forms the precapillary sphincter.

Venules

The thin walls of capillaries allow the exchange of substances between the blood and body tissues. Groups of capillaries within a tissue reunite to form small veins are called? These in turn merge to form progressively larger blood vessels called veins.

Left Subclavian Artery

The third branch from the arch of the aorta is the _____________________, which distributes blood to the left vertebral artery and vessels of the left upper limb. Arteries branching from the left subclavian artery are similar in distribution and name to those branching from the right subclavian artery.

proprioceptors, baroreceptors, and chemoreceptors

The three main types of sensory receptors that provide input to the cardiovascular center are __________________________.

sympathetic nerves

The tunica externa of the arteriole consists of areolar connective tissue containing abundant unmyelinated ________________. This _____________ supply, along with the actions of local chemical mediators, can alter the diameter of arterioles and thus vary the rate of blood flow and resistance through these vessels.

Arteries explained

The wall of an ______ has the three layers of a typical blood vessel, but has a thick muscular-toelastic tunica media. Due to their plentiful elastic fibers, arteries normally have high compliance, which means that their walls stretch easily or expand without tearing in response to a small increase in pressure.

2. Blood viscosity.

The_______________ depends mostly on the ratio of red blood cells to plasma (fluid) volume, and to a smaller extent on the concentration of proteins in plasma. The higher the blood's viscosity, the higher the resistance. Any condition that increases the viscosity of blood, such as dehydration or polycythemia (an unusually high number of red blood cells), thus increases blood pressure. A depletion of plasma proteins or red blood cells, due to anemia or hemorrhage, decreases viscosity and thus decreases blood pressure.

Vasa vVasorum

These small vessels that supply blood to the tissues of the vessel are called ______________ or vessels to the vessels. They are easily seen on large vessels such as the aorta. In addition to the important role of supplying the vessel wall with nerves and self-vessels, the tunica externa helps anchor the vessels to surrounding tissues.

Vasomotion

This intermittent contraction and relaxation, which may occur 5 to 10 times per minute, is called _______________.

Capillary Bed

Throughout the body, capillaries function as part of a capillary bed, a network of 10-100 capillaries that arises from a single metarteriole.

Venule

Unlike their thick-walled arterial counterparts, venules and veins have thin walls that do not readily maintain their shape. _________ drain the capillary blood and begin the return flow of blood back toward the heart and wastes and white blood cell emigration, and for this reason form part of the microcirculatory exchange unit along with the capillaries. (Venules are small vessels that are formed by the union of several capillaries. Venules drain blood from capillaries into veins.)

portal vein

Usually blood passes from the heart and then in sequence through arteries, arterioles, capillaries, venules, and veins and then back to the heart. In some parts of the body, however, blood passes from one capillary network into another through a vein called a ___________.

1. Physical changes.

Warming promotes vasodilation, and cooling causes vasoconstriction. In addition, smooth muscle in arteriole walls exhibits a myogenic response it contracts more forcefully when it is stretched and relaxes when stretching lessens. If, for example, blood flow through an arteriole decreases, stretching of the arteriole walls decreases. As a result, the smooth muscle relaxes and produces vasodilation, which increases blood flow.

MAP = CO x R

We have already seen that cardiac output equals heart rate multiplied by stroke volume. Another way to calculate cardiac output is to divide mean arterial pressure (MAP) by resistance (R): CO = MAP / R. By rearranging the terms of this equation, you can see that ___________. If cardiac output rises due to an increase in stroke volume or heart rate, then the mean arterial pressure rises as long as resistance remains steady. Likewise, a decrease in cardiac output causes a decrease in mean arterial pressure if resistance does not change.

Pulmonary Circulation

When blood returns to the heart from the systemic route, it is pumped out of the right ventricle through the _________________ to the lungs. In capillaries of the air sacs (alveoli) of the lungs, the blood loses some of its carbon dioxide and takes on oxygen. Bright red again, it returns to the left atrium of the heart and reenters the systemic circulation as it is pumped out by the left ventricle.

Renin-angiotensin-aldosterone (RAA) system.

When blood volume falls or blood flow to the kidneys decreases, juxtaglomerular cells in the kidneys secrete renin into the bloodstream. In sequence, renin and angiotensin-converting enzyme (ACE) act on their substrates to produce the active hormone angiotensin II, which raises blood pressure in two ways. First, angiotensin II is a potent vasoconstrictor; it raises blood pressure by increasing systemic vascular resistance. Second, it stimulates secretion of aldosterone, which increases reabsorption of sodium ions (Na) and water by the kidneys. The water reabsorption increases total blood volume, which increases blood pressure.

the abdominal aorta

When the thoracic aorta reaches the bottom of the thorax it passes through the aortic hiatus of the diaphragm to become ________________. The ______________ is the continuation of the thoracic aorta after it passes through the diaphragm.. It begins at the aortic hiatus in the diaphragm and ends at about the level of the fourth lumbar vertebra, where it divides into the right and left common iliac arteries. The abdominal aorta lies anterior to the vertebral column.

The Balance of Pressures.

Whether fluids leave or enter capillaries depends on the balance of pressures. If the pressures that push fluid out of capillaries exceed the pressures that pull fluid into capillaries, fluid will move from capillaries into interstitial spaces (filtration). If, however, the pressures that push fluid out of interstitial spaces into capillaries exceed the pressures that pull fluid out of capillaries, then fluid will move from interstitial spaces into capillaries (reabsorption).

Veins

While _________ do show structural changes as they increase in size from small to medium to large, the structural changes are not as distinct as they are in arteries. __________, in general, have very thin walls relative to their total diameter (average thickness is less than one-tenth of the vessel diameter). They range in size from 0.5 mm in diameter for small ______ to 3 cm in the large superior and interior venae cavae entering the heart.

anastomotic vein

While veins follow paths similar to those of their arterial counterparts, they differ from arteries in a number of ways, aside from the structures of their walls. First, veins are more numerous than arteries for several reasons. Some veins are paired and accompany medium- to small-sized muscular arteries. These double sets of veins escort the arteries and connect with one another via venous channels called ______________________/

The skeletal muscle pump operates as follows 1:

While you are standing at rest, both the venous valve closer to the heart (proximal valve) and the one farther from the heart (distal valve) in this part of the leg are open, and blood flows upward toward the heart.

Dural venous sinuses

Within the cranial cavity, all veins drain into dural venous sinuses and then into the internal jugular veins. ________________ are endothelial-lined venous channels between layers of the cranial dura mater.

The blood hydrostatic pressure (BHP)

Within vessels, the hydrostatic pressure is due to the pressure that water in blood plasma exerts against blood vessel walls. ___________________ is about 35 millimeters of mercury (mmHg) at the arterial end of a capillary, and about 16 mmHg at the capillary's venous end

Sinusoids

_________ are wider and more winding than other capillaries. Their endothelial cells may have unusually large fenestrations. In addition to having an incomplete or absent basement membrane, ___________ have very large intercellular clefts that allow proteins and in some cases even blood cells to pass from a tissue into the bloodstream. For example, newly formed blood cells enter the bloodstream through the ____________ of red bone marrow. In addition, ___________ contain specialized lining cells that are adapted to the function of the tissue. ______________ in the liver, for example, contain phagocytic cells that remove bacteria and other debris from the blood. The spleen, anterior pituitary, and parathyroid and adrenal glands also have ________________.

Blood flows

___________ is the volume of blood that flows through any tissue in a given time period (in mL/min). Total blood flow is cardiac output (CO), the volume of blood that circulates through systemic (or pulmonary) blood vessels each minute. In Chapter 20 we saw that cardiac output depends on heart rate and stroke volume: Cardiac output (CO) =. heart rate (HR) + stroke volume (SV). How the cardiac output becomes distributed into circulatory routes that serve various body tissues depends on two more factors: (1) the pressure difference that drives the blood flow through a tissue and (2) the resistance to blood flow in specific blood vessels. Blood flows from regions of higher pressure to regions of lower pressure; the greater the pressure difference, the greater the blood flow. But the higher the resistance, the smaller the _____________.

Baroreceptors

____________ monitor changes in pressure and stretch in the walls of blood vessels. ___________, pressure-sensitive sensory receptors, are located in the aorta, internal carotid arteries (arteries in the neck that supply blood to the brain), and other large arteries in the neck and chest. They send impulses to the cardiovascular center to help regulate blood pressure.

Capillaries 2

______________ are found near almost every cell in the body, but their number varies with the metabolic activity of the tissue they serve. Body tissues with high metabolic requirements, such as muscles, the brain, the liver, the kidneys, and the nervous system, use more O2 and nutrients and thus have extensive capillary networks. Tissues with lower metabolic requirements, such as tendons and ligaments, contain fewer _______________. ______________ are absent in a few tissues, such as all covering and lining epithelia, the cornea and lens of the eye, and cartilage. 2

Bulk flow

______________ is a passive process in which large numbers of ions, molecules, or particles in a fluid move together in the same direction. The substances move at rates far greater than can be accounted for by diffusion alone. Bulk flow occurs from an area of higher pressure to an area of lower pressure, and it continues as long as a pressure difference exists. (_____________ is a passive process in which large numbers of ions, molecules, or particles in a fluid move together in the same direction. ______________ occurs from an area of higher pressure to an area of lower pressure, and it continues as long as a pressure difference exists Bulk flow is more important for regulation of the relative volumes of blood and interstitial fluid.)

Circulation time

______________ is the time required for a drop of blood to pass from the right atrium, through the pulmonary circulation, back to the left atrium, through the systemic circulation down to the foot, and back again to the right atrium. In a resting person, circulation time normally is about 1 minute.

Tachycardia

_______________ is a rapid resting heart or pulse rate over 100 beats/min.

Antidiuretic hormone (ADH).

_______________ is produced by the hypothalamus and released from the posterior pituitary in response to dehydration or decreased blood volume. Among other actions, ADH causes vasoconstriction, which increases blood pressure. For this reason ADH is also called vasopressin. ADH also promotes movement of water from the lumen of kidney tubules into the bloodstream. This results in an increase in blood volume and a decrease in urine output.

Obstructive shock

_______________ occurs when blood flow through a portion of the circulation is blocked. The most common cause is pulmonary embolism, a blood clot lodged in a blood vessel of the lungs.

Venous return

_______________, the volume of blood flowing back to the heart through the systemic veins, occurs due to the pressure generated by contractions of the heart's left ventricle. The pressure difference from venules (averaging about 16 mmHg) to the right ventricle (0 mmHg), although small, normally is sufficient to cause ___________ to the heart. If pressure increases in the right atrium or ventricle, __________ will decrease. One cause of increased pressure in the right atrium is an incompetent (leaky) tricuspid valve, which lets blood regurgitate (flow backward) as the ventricles contract. The result is decreased ____________ and buildup of blood on the venous side of the systemic circulation. (Venous return, the volume of blood flowing back to the heart through the systemic veins, occurs due to the pressure generated by contractions of the heart's left ventricle. Venous return is assisted by: Valves, Respiratory pump, Skeletal muscle pump)

Capillaries defined

_________________, the smallest of blood vessels, and form the U-turns that connect the arterial outflow to the venous return. Since red blood cells have a diameter of 8 m, they must often fold on themselves in order to pass single file through the lumens of these vessels. _____________ form an extensive network, approximately 20 billion in number, of short (hundreds of micrometers in length), branched, interconnecting vessels that course among the individual cells of the body. This network forms an enormous surface area to make contact with the body's cells.

Anastomoses

__________________ between arteries provide alternative routes for blood to reach a tissue or organ. If blood flow stops for a short time when normal movements compress a vessel, or if a vessel is blocked by disease, injury, or surgery, then circulation to a part of the body is not necessarily stopped (An _____________ is the union of the branches of 2 or more arteries supplying the same region of the body. This provides an alternate route for blood flow. Arteries that do not form an anastomosis are called "end arteries" If an end artery is blocked, blood cannot get to that particular region of the body and necrosis can occur)

Systolic blood pressure (SBP)

__________________ is the highest pressure attained in arteries during systole,

Diastolic blood pressure (DBP)

__________________ is the lowest arterial pressure during diastole

Proprioceptors monitor

__________________ movements of joints and muscles and provide input to the cardiovascular center during physical activity. Their activity accounts for the rapid increase in heart rate at the beginning of exercise.

The anterior interventricular branch,

___________________ also known as the left anterior descending (LAD) branch, of the left coronary artery supplies both ventricles, and the circumflex branch supplies the left atrium and left ventricle.

Hepatic portal circulation

___________________, which extends from the gastrointestinal tract to the liver. The nutrient arteries to the lungs, such as the bronchial arteries, are also part of the systemic circulation.

The arch of the aorta

____________________ is 4-5 cm (almost 2 in.) in length and is the continuation of the ascending aorta. It emerges from the pericardium posterior to the sternum at the level of the sternal angle. The arch of the aorta is directed superiorly and posteriorly to the left and then inferiorly; it ends at the intervertebral disc between the fourth and fifth thoracic vertebrae, where it becomes the thoracic aorta. Three major arteries branch from the superior aspect of __________________: the brachiocephalic trunk, the left common carotid, and the left subclavian.

Chemoreceptors

____________________ monitor the concentration of various chemicals in the blood.

Mean arterial pressure (MAP)

_____________________, the average blood pressure in arteries, is roughly one-third of the way between the diastolic and systolic pressures.

The superior mesenteric vein

________________________ drains blood from the small intestine and portions of the large intestine, stomach, and pancreas through the jejunal, ileal, ileocolic, right colic, middle colic, pancreaticoduodenal, and right gastro-omental veins. The splenic vein drains blood from the stomach, pancreas, and portions of the large intestine through the short gastric, left gastro-omental, pancreatic, and inferior

The paired visceral branches arise

_____________________________ from the lateral surfaces of the aorta and include the suprarenal, renal, and gonadal arteries. The lone unpaired parietal branch is the median sacral artery. The paired parietal branches arise from the posterolateral surfaces of the aorta and include the inferior phrenic and lumbar arteries.

Both superficial and deep veins return blood from the upper limbs to the heart.

____________________________________. Superficial veins are located just deep to the skin and are often visible. They anastomose extensively with one another and with deep veins, and they do not accompany arteries. Superficial veins are larger than deep veins and return most of the blood from the upper limbs. Deep veins are located deep in the body. They usually accompany arteries and have the same names as the corresponding arteries. Both superficial and deep veins have valves, but valves are more numerous in the deep veins.

The abdominal aorta ends by dividing into the right and left common iliac arteries

_________________________________________. These, in turn, divide into the internal and external iliac arteries. In sequence, the external iliacs become the femoral arteries in the thighs, the popliteal arteries posterior to the knee, and the anterior and posterior tibial arteries in the legs.

The wall of a blood vessel consists of three layers or tunics, of different tissues:

an epithelial inner lining, a middle layer consisting of smooth muscle and elastic connective tissue, a connective tissue outer covering

Elastic arteries perform

an important function: They help propel blood onward while the ventricles are relaxing. As blood is ejected from the heart into elastic arteries, their walls stretch, easily accommodating the surge of blood.

The tunica interna is a

basement membrane deep to the endothelium. It provides a physical support base for the epithelial layer. Its framework of collagen fibers affords the basement membrane significant tensile strength, yet its properties also provide resilience for stretching and recoil. The basement membrane anchors the endothelium to the underlying connective tissue while also regulating molecular movement. It appears to play an important role in guiding cell movements during tissue repair of blood vessel walls.

The posterior interventricular

branch of the right coronary artery supplies both ventricles.

Arteries

carry blood away from the heart to other organs. Large, elastic arteries leave the heart and divide into medium-sized, muscular arteries that branch out into the various regions of the body

Tunica media

is a muscular and connective tissue layer that displays the greatest variation among the different vessel types (Figure 21.1a, b). In most vessels, it is a relatively thick layer comprising mainly smooth muscle cells and substantial amounts of elastic fibers. The primary role of the smooth muscle cells, which extend circularly around the lumen like a ring encircles your finger, is to regulate the diameter of the lumen. An increase in sympathetic stimulation typically stimulates the smooth muscle to contract, squeezing the vessel wall and narrowing the lumen. (Middle layer, smooth muscle and elastic fibers)

Internal elastic lamina

is a thin sheet of elastic fibers with a variable number of windowlike openings that give it the look of Swiss cheese. These openings facilitate diffusion of materials through the tunica interna to the thicker tunica media.

endothelium

is continuous with the endocardial lining of the heart. ___________ is a thin layer of flattened cells that lines the inner surface of the entire cardiovascular system (heart and blood vessels).

Vascular Spasm

n addition to regulating blood flow and blood pressure, smooth muscle contracts when a small artery or arteriole is damaged _______________ to help limit loss of blood through the injured vessel.

In contrast, when sympathetic stimulation decreases,

or in the presence of certain chemicals (such as nitric oxide, H+, and lactic acid) or in response to blood pressure, smooth muscle fibers relax.

Hemodynamics

the forces involved in circulating blood throughout the body; and on the blood vessels that constitute the major circulatory routes.

Elastic arteries

the largest arteries in the body, ranging from the garden hose-sized aorta and pulmonary trunk to the fingersized branches of the aorta. They have the largest diameter among arteries, but their vessel walls (approximately one-tenth of the vessel's total diameter) are relatively thin compared with the overall size of the vessel. These vessels are characterized by well defined internal and external elastic laminae, along with a thick tunica media that is dominated by elastic fibers, called the elastic lamellae. ____________ include the two major trunks that exit the heart (the aorta and the pulmonary trunk), along with the aorta's major initial branches, such as the brachiocephalic, subclavian, common carotid, and common iliac arterie. (Large diameter More elastic fibers, less smooth muscle Function as pressure reservoirs)

The three structural layers of a generalized blood vessel from innermost to outermost are

the tunica interna (intima), tunica media, tunica externa (adventitia)

The tunica externa is often thicker than

the tunica media in muscular arteries. This outer layer contains fibroblasts, collagen fibers, and elastic fibers all oriented longitudinally. The loose structure of this layer permits changes in the diameter of the vessel to take place but also prevents shortening or retraction of the vessel when it is cut

Endothelial cells

were regarded as little more than a passive barrier between the blood and the remainder of the vessel wall. It is now known that _____________ are active participants in a variety of vessel-related activities, including physical influences on blood flow, secretion of locally acting chemical mediators that influence the contractile state of the vessel's overlying smooth muscle, and assistance with capillary permeability. In addition, their smooth luminal surface facilitates efficient blood flow by reducing surface friction

The outermost part of the tunica interna

which forms the boundary between the tunica interna and tunica media, is the internal elastic lamina.

Cerebral Circulation

which supplies the brain

Sign and Symptoms of Shock

• Systolic blood pressure is lower than 90 mmHg. • Resting heart rate is rapid due to sympathetic stimulation and increased blood levels of epinephrine and norepinephrine. • Pulse is weak and rapid due to reduced cardiac output and fast heart rate. • Skin is cool, pale, and clammy due to sympathetic constriction of skin blood vessels and sympathetic stimulation of sweating. • Mental state is altered due to reduced oxygen supply to the brain. • Urine formation is reduced due to increased levels of aldosterone and antidiuretic hormone (ADH). • The person is thirsty due to loss of extracellular fluid. • The pH of blood is low (acidosis) due to buildup of lactic acid. • The person may have nausea because of impaired blood flow to the digestive organs from sympathetic vasoconstriction.